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Long GRB hosts at z<1 are usually low-mass, low metallicity star-forming galaxies. Here we present the until now most detailed, spatially resolved study of the host of GRB 171205A, a grand-design barred spiral galaxy at z=0.036. Our analysis includes MUSE integral field spectroscopy, complemented by high spatial resolution UV/VIS HST imaging and CO(1-0) and HI 21cm data. The GRB is located in a small star-forming region in a spiral arm of the galaxy at a deprojected distance of ~ 8 kpc from the center. The galaxy shows a smooth negative metallicity gradient and the metallicity at the GRB site is half solar, slightly below the mean metallicity at the corresponding distance from the center. Star formation in this galaxy is concentrated in a few HII regions between 5-7 kpc from the center and at the end of the bar, inwards of the GRB region, however, the HII region hosting the GRB is in the top 10% of regions with highest specific star-formation rate. The stellar population at the GRB site has a very young component (< 5 Myr) contributing a significant part of the light. Ionized and molecular gas show only minor deviations at the end of the bar. A parallel study found an asymmetric HI distribution and some additional gas near the position of the GRB, which might explain the star-forming region of the GRB site. Our study shows that long GRBs can occur in many types of star-forming galaxies, however, the actual GRB sites consistently have low metallicity, high star formation and a young population. Furthermore, gas inflow or interactions triggering the star formation producing the GRB progenitor might not be evident in ionized or even molecular gas but only in HI., Comment: 22 pages, 18 figures, Appendix with additional figures, A&A under revision

The advent of the JWST has revolutionised our understanding of high-redshift galaxies. In particular, the NIRCam instrument on-board JWST has revealed a population of Hubble Space Telescope (HST)-dark galaxies that had previously evaded optical detection, potentially due to significant dust obscuration, quiescence, or simply extreme redshift. Here, we present the first NIRSpec spectra of 23 HST-dark galaxies ($\mathrm{H-F444W>1.75}$), unveiling their nature and physical properties. This sample includes both dusty and quiescent galaxies with spectroscopic data from NIRSpec/PRISM, providing accurate spectroscopic redshifts with $\mathrm{\overline{z}_{spec} = 4.1 \pm 0.7}$. The spectral features demonstrate that, while the majority of HST-dark galaxies are dusty, a substantial fraction, $\mathrm{13^{+9}_{-6} \%}$, are quiescent. For the dusty galaxies, we have quantified the dust attenuation using the Balmer decrement ($\mathrm{H\alpha / H\beta}$), finding attenuations $\mathrm{A_{V} > 2\ mag}$. We find that HST-dark dusty galaxies are $\mathrm{H\alpha}$ emitters with equivalent widths spanning the range $\mathrm{ 68 A < EW_{H\alpha} < 550 A }$, indicative of a wide range of recent star-formation activity. Whether dusty or quiescent, we find that HST-dark galaxies are predominantly massive, with 85\% of the galaxies in the sample having masses $\mathrm{log(M_{*}/M_{\odot}) > 9.8}$. This pilot NIRSpec program reveals the diverse nature of HST-dark galaxies and highlights the effectiveness of NIRSpec/PRISM spectroscopic follow-up in distinguishing between dusty and quiescent galaxies and properly quantifying their physical properties. Upcoming research utilising higher-resolution NIRSpec data and combining JWST with ALMA observations will enhance our understanding of these enigmatic and challenging sources., Comment: 13 pages, 11 figures

We present a new determination of the star-forming main sequence (MS), obtained through stacking 100k K-band-selected galaxies in the far-IR Herschel and James Clerk Maxwell Telescope (JCMT) imaging. By fitting the dust emission curve to the stacked far-IR photometry, we derive the IR luminosities (LIR) and, hence, star formation rates (SFR) out to z~7. The functional form of the MS is found, with the linear SFR-M* relation that flattens at high stellar masses and the normalization that increases exponentially with redshift. We derive the corresponding redshift evolution of the specific star formation rate (sSFR) and compare our findings with the recent literature. We find our MS to be exhibiting slightly lower normalization at z<=2 and to flatten at larger stellar masses at high redshifts. By deriving the relationship between the peak dust temperature (Td) and redshift, where Td increases linearly from ~20K at z=0.5 to ~50 K at z=6, we conclude that the apparent inconsistencies in the shapes of the MS are most likely caused by the different dust temperatures assumed when deriving SFRs in the absence of far-IR data. Finally, we investigate the derived shape of the star-forming MS by simulating the time evolution of the observed galaxy stellar mass function (GSMF). While the simulated GSMF is in good agreement with the observed one, some inconsistencies persist. In particular, we find the simulated GSMF to be somewhat overpredicting the number density of low-mass galaxies at z>2., Comment: 16 pages, 11 figures, 2 tables, submitted to A&A

We present a comparison between the performance of a selection of source finders using a new software tool called Hydra. The companion paper, Paper~I, introduced the Hydra tool and demonstrated its performance using simulated data. Here we apply Hydra to assess the performance of different source finders by analysing real observational data taken from the Evolutionary Map of the Universe (EMU) Pilot Survey. EMU is a wide-field radio continuum survey whose primary goal is to make a deep ($20\mu$Jy/beam RMS noise), intermediate angular resolution ($15^{\prime\prime}$), 1\,GHz survey of the entire sky south of $+30^{\circ}$ declination, and expecting to detect and catalogue up to 40 million sources. With the main EMU survey expected to begin in 2022 it is highly desirable to understand the performance of radio image source finder software and to identify an approach that optimises source detection capabilities. Hydra has been developed to refine this process, as well as to deliver a range of metrics and source finding data products from multiple source finders. We present the performance of the five source finders tested here in terms of their completeness and reliability statistics, their flux density and source size measurements, and an exploration of case studies to highlight finder-specific limitations., Comment: Paper accepted for publication in PASA

The latest generation of radio surveys are now producing sky survey images containing many millions of radio sources. In this context it is highly desirable to understand the performance of radio image source finder (SF) software and to identify an approach that optimises source detection capabilities. We have created Hydra to be an extensible multi-SF and cataloguing tool that can be used to compare and evaluate different SFs. Hydra, which currently includes the SFs Aegean, Caesar, ProFound, PyBDSF, and Selavy, provides for the addition of new SFs through containerisation and configuration files. The SF input RMS noise and island parameters are optimised to a 90\% ''percentage real detections'' threshold (calculated from the difference between detections in the real and inverted images), to enable comparison between SFs. Hydra provides completeness and reliability diagnostics through observed-deep ($\mathcal{D}$) and generated-shallow ($\mathcal{S}$) images, as well as other statistics. In addition, it has a visual inspection tool for comparing residual images through various selection filters, such as S/N bins in completeness or reliability. The tool allows the user to easily compare and evaluate different SFs in order to choose their desired SF, or a combination thereof. This paper is part one of a two part series. In this paper we introduce the Hydra software suite and validate its $\mathcal{D/S}$ metrics using simulated data. The companion paper demonstrates the utility of Hydra by comparing the performance of SFs using both simulated and real images., Comment: Paper accepted for publication in PASA

We present 850um imaging of the XMM-LSS field observed for 170 hours as part of the James Clerk Maxwell Telescope SCUBA-2 Large eXtragalactic Survey (S2LXS). S2LXS XMM-LSS maps an area of 9 square degrees, reaching a moderate depth of 1-sigma ~ 4 mJy/beam. This is the largest contiguous area of extragalactic sky mapped by JCMT at 850um to date. The wide area of the S2LXS XMM-LSS survey allows us to probe the ultra-bright (S_850um > 15 mJy), yet rare submillimetre population. We present the S2LXS XMM-LSS catalogue, which comprises 40 sources detected at >5-sigma significance, with deboosted flux densities in the range of 7 mJy to 48 mJy. We robustly measure the bright-end of the 850um number counts at flux densities >7 mJy, reducing the Poisson errors compared to existing measurements. The S2LXS XMM-LSS observed number counts show the characteristic upturn at bright fluxes, expected to be motivated by local sources of submillimetre emission and high-redshift strongly lensed galaxies. We find that the observed 850um number counts are best reproduced by model predictions that include either strong lensing or source blending from a 15 arcsec beam, indicating that both may make an important contribution to the observed over-abundance of bright single dish 850um selected sources. We make the S2LXS XMM-LSS 850um map and >5-sigma catalogue presented here publicly available., Comment: Accepted for publication in MNRAS

We present the results from multi-wavelength observations of a transient discovered during the follow-up of S191213g, a gravitational wave (GW) event reported by the LIGO-Virgo Collaboration as a possible binary neutron star merger in a low latency search. This search yielded SN2019wxt, a young transient in a galaxy whose sky position (in the 80\% GW contour) and distance ($\sim$150\,Mpc) were plausibly compatible with the localisation uncertainty of the GW event. Initially, the transient's tightly constrained age, its relatively faint peak magnitude ($M_i \sim -16.7$\,mag) and the $r-$band decline rate of $\sim 1$\,mag per 5\,days appeared suggestive of a compact binary merger. However, SN2019wxt spectroscopically resembled a type Ib supernova, and analysis of the optical-near-infrared evolution rapidly led to the conclusion that while it could not be associated with S191213g, it nevertheless represented an extreme outcome of stellar evolution. By modelling the light curve, we estimated an ejecta mass of $\sim 0.1\,M_\odot$, with $^{56}$Ni comprising $\sim 20\%$ of this. We were broadly able to reproduce its spectral evolution with a composition dominated by helium and oxygen, with trace amounts of calcium. We considered various progenitors that could give rise to the observed properties of SN2019wxt, and concluded that an ultra-stripped origin in a binary system is the most likely explanation. Disentangling electromagnetic counterparts to GW events from transients such as SN2019wxt is challenging: in a bid to characterise the level of contamination, we estimated the rate of events with properties comparable to those of SN2019wxt and found that $\sim 1$ such event per week can occur within the typical GW localisation area of O4 alerts out to a luminosity distance of 500\,Mpc, beyond which it would become fainter than the typical depth of current electromagnetic follow-up campaigns., Comment: By the ENGRAVE collaboration (engrave-eso.org). 35 pages, 20 figures, final version accepted by A&A

We examine the far-IR properties of a sample of 5391 optically selected QSOs in the 0.544.7, using SPIRE data from Herschel-ATLAS. We split the sample in a grid of 74 luminosity-redshift bins and compute the average optical-infrared spectral energy distribution (SED) in each bin. By normalising an intrinsic AGN template to the AGN optical power (at 5100A) we decompose the total infrared emission (L_IR; 8-1000um) into an AGN (L_IR,AGN) and star-forming component (L_IR,SF). We find that the AGN contribution to L_IR increases as a function of AGN power which manifests as a reduction of the `far-IR bump' in the average QSO SEDs. We note that L_IR,SF does not correlate with AGN power; the mean star formation rates (SFRs) of AGN host galaxies are a function of redshift only and they range from ~6 Msun/yr at z~0 to a plateau of <200 Msun/yr at z~2.6. Our results indicate that the accuracy of far-IR emission as a proxy for SFR decreases with increasing AGN luminosity. We show that, at any given redshift, observed trends between infrared luminosity (whether monochromatic or total) and AGN power (in the optical or X-rays) can be explained by a simple model which is the sum of two components: (A) the infrared emission from star-formation, uncorrelated with AGN power and (B) the infrared emission from AGN, directly proportional to AGN power in the optical or X-rays., Comment: 20 pages, 10 figures, accepted for publication in MNRAS

Long ($>2$ s) gamma ray bursts (GRBs) are associated with explosions of massive stars, although in three instances, supernovae (SNe) have not been detected, despite deep observations. With new HI line and archival optical integral field spectroscopy data, we characterize the interstellar medium (ISM) of the host galaxy of one of these events, GRB 111005A, in order to shed light on the unclear nature of these peculiar objects. We found that the atomic gas, radio continuum, and rotational patterns are in general very smooth throughout the galaxy, which does not indicate a recent gas inflow or outflow. There is also no gas concentration around the GRB position. The ISM in this galaxy differs from that in hosts of other GRBs and SNe, which may suggest that the progenitor of GRB 111005A was not an explosion of a very massive star (e.g. a compact object merger). However, there are subtle irregularities of the GRB 111005A host (most at a $2\sigma$ level), which may point to a weak gas inflow or interaction. Since in the SE part of the host there is 15% more atomic gas and twice less molecular gas than in NW part, the molecular gas fraction is low. In the SE part there is also a region with very high H$\alpha$ equivalent width. There is more continuum 1.4 GHz emission to the SE and an S-shaped warp in the UV. Finally, there is also a low-metallicity region 3.5" (1 kpc) from the GRB position. Two galaxies within 300 kpc or a past merger can be responsible for these irregularities., Comment: Accepted for publication in ApJS, 18 pages, 10 figures

Short-GRB progenitors could come in various flavors, depending on the nature of the merging compact stellar objects (including a stellar-mass black hole or not) or depending on their ages (millions or billions of years). At a redshift of z=0.122, the nearly face-on spiral host of the short GRB 080905A is one of the closest short-GRB host galaxies identified so far. This made it a preferred target to explore spatially resolved star-formation and to investigate the afterglow position in the context of its star formation structures. We used VLT/MUSE integral-field unit observations, supplemented by ATCA 5.5/9.0 GHz radio-continuum measurements and publicly available HST data, to study the star-formation activity in the GRB 080905A host galaxy. The MUSE observations reveal that the entire host is characterized by strong line emission. Using the Halpha line flux, we measure for the entire galaxy an SFR of about 1.6 Msun/yr, consistent with its non-detection by ATCA. Several individual star-forming regions are scattered across the host. The most luminous region has a Halpha luminosity that is nearly four times as high as the luminosity of the Tarantula nebula in the Large Magellanic Cloud. Even though star-forming activity can be traced as close to about 3 kpc (in projection) distance to the GRB explosion site, stellar population synthesis calculations show that none of the Halpha-bright star-forming regions is a likely birthplace of the short-GRB progenitor., Comment: The Astrophysical Journal Supplement Series, in press

Fluorine is one of the most interesting elements for nuclear and stellar astrophysics. Fluorine abundance was first measured for stars other than the Sun in 1992, then for a handful metal-poor stars, which are likely to have formed in the early Universe. The main production sites of fluorine are under debate and include asymptotic giant branch (AGB) stars, $\nu$-process in core-collapse supernovae, and Wolf-Rayet (WR) stars. Due to the difference in the mass and lifetime of progenitor stars, high redshift observations of fluorine can help constrain the mechanism of fluorine production in massive galaxies. Here, we report the detection of HF (S/N = 8) in absorption in a gravitationally lensed dusty star-forming galaxy at redshift z=4.4 with $N_{\rm HF}$/$N_{\rm{H_2}}$ as high as $\sim2\times10^{-9}$, indicating a very quick ramp-up of the chemical enrichment in this high-z galaxy. At z=4.4, AGB stars of a few solar masses are very unlikely to dominate the enrichment. Instead, we show that WR stars are required to produce the observed fluorine abundance at this time, with other production mechanisms becoming important at later times. These observations therefore provide an insight into the underlying processes driving the `ramp-up' phase of chemical enrichment alongside rapid stellar mass assembly in a young massive galaxy., Comment: 21 pages, 4 figures, published in Nature Astronomy

We present LMT/AzTEC 1.1mm observations of $\sim100$ luminous high-redshift dusty star-forming galaxy candidates from the $\sim600\,$sq.deg $Herschel$-ATLAS survey, selected on the basis of their SPIRE red far-infrared colours and with $S_{500\mu\rm m}=35-80$ mJy. With an effective $\theta_{\rm FWHM}\approx9.5\,$ arcsec angular resolution, our observations reveal that at least 9 per cent of the targets break into multiple systems with SNR $\geq 4$ members. The fraction of multiple systems increases to $\sim23\,$ per cent (or more) if some non-detected targets are considered multiples, as suggested by the data. Combining the new AzTEC and deblended $Herschel$ photometry we derive photometric redshifts, IR luminosities, and star formation rates. While the median redshifts of the multiple and single systems are similar $(z_{\rm med}\approx3.6)$, the redshift distribution of the latter is skewed towards higher redshifts. Of the AzTEC sources $\sim85\,$ per cent lie at $z_{\rm phot}>3$ while $\sim33\,$ per cent are at $z_{\rm phot}>4$. This corresponds to a lower limit on the space density of ultra-red sources at $44$ galaxies., Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society. 23 pages, 18 figures

We present observations of a region of the Galactic plane taken during the Early Science Program of the Australian Square Kilometre Array Pathfinder (ASKAP). In this context, we observed the SCORPIO field at 912 MHz with an uncompleted array consisting of 15 commissioned antennas. The resulting map covers a square region of ~40 deg^2, centred on (l, b)=(343.5{\deg}, 0.75{\deg}), with a synthesized beam of 24"x21" and a background rms noise of 150-200 {\mu}Jy/beam, increasing to 500-600 {\mu}Jy/beam close to the Galactic plane. A total of 3963 radio sources were detected and characterized in the field using the CAESAR source finder. We obtained differential source counts in agreement with previously published data after correction for source extraction and characterization uncertainties, estimated from simulated data. The ASKAP positional and flux density scale accuracy were also investigated through comparison with previous surveys (MGPS, NVSS) and additional observations of the SCORPIO field, carried out with ATCA at 2.1 GHz and 10" spatial resolution. These allowed us to obtain a measurement of the spectral index for a subset of the catalogued sources and an estimated fraction of (at least) 8% of resolved sources in the reported catalogue. We cross-matched our catalogued sources with different astronomical databases to search for possible counterparts, finding ~150 associations to known Galactic objects. Finally, we explored a multiparametric approach for classifying previously unreported Galactic sources based on their radio-infrared colors., Comment: 31 pages, 15 figures, 15 tables

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations towards 27 low-redshift ($0.02< z<0.2$) star-forming galaxies taken from the Valpara\'iso ALMA/APEX Line Emission Survey (VALES). We perform stacking analyses of the $^{12}$CO($1-0$), $^{13}$CO($1-0$) and C$^{18}$O($1-0$) emission lines to explore the $L'$ ($^{12}$CO($1-0$))/$L'$($^{13}$CO($1-0$))) (hereafter $L'$($^{12}$CO)/$L'$($^{13}$CO)) and $L'$($^{13}$CO($1-0$))/$L'$(C$^{18}$O($1-0$)) (hereafter $L'$($^{13}$CO)/$L'$(C$^{18}$O) line luminosity ratio dependence as a function of different global galaxy parameters related to the star formation activity. The sample has far-IR luminosities $10^{10.1-11.9}$L$_{\odot}$ and stellar masses of $10^{9.8-10.9}$M$_{\odot}$ corresponding to typical star-forming and starburst galaxies at these redshifts. On average we find a $L'$($^{12}$CO)/$L'$($^{13}$CO) line luminosity ratio value of 16.1$\pm$2.5. Galaxies with evidences of possible merging activity tend to show higher $L'$($^{12}$CO)/$L'$($^{13}$CO) ratios by a factor of two, while variations of this order are also found in galaxy samples with higher star formation rates or star formation efficiencies. We also find an average $L'$($^{13}$CO)/$L'$(C$^{18}$O) line luminosity ratio of 2.5$\pm$0.6, which is in good agreement with those previously reported for starburst galaxies. We find that galaxy samples with high $L_{\text{IR}}$, SFR and SFE show low $L'$($^{13}$CO)/$L'$(C$^{18}$O) line luminosity ratios with high $L'$($^{12}$CO)/$L'$($^{13}$CO) line luminosity ratios, suggesting that these trends are produced by selective enrichment of massive stars in young starbursts., Comment: 16 pages, 10 figures to be published in MNRAS

Using the EMIR instrument on the IRAM 30m telescope, we conducted a spectroscopic redshift search of seven z$_{\rm phot}$ $\sim$ 4 sub-millimetre bright galaxies selected from the Herschel Bright Sources (HerBS) sample with fluxes at 500 $\mu$m greater than 80 mJy. For four sources, we obtained spectroscopic redshifts between 3.4 < z < 4.1 through the detection of multiple CO-spectral lines with J $\leq$ 3. Later, we detected low-J transitions for two of these sources with the GBT including the CO(1-0) transition. For the remaining three sources, more data are needed to determine the spectroscopic redshift unambiguously. The measured CO luminosities and line widths suggest that all these sources are gravitationally lensed. These observations demonstrate that the 2 mm window is indispensable to confirm robust spectroscopic redshifts for z < 4 sources. Finally, we present an efficient graphical method to correctly identify spectroscopic redshifts., Comment: 20 Pages, 8 Figures + 7 Appendix Figures + 1 animated figure. Resubmitted in order to reflect the version as printed in MNRAS

Scaling laws of dust, HI gas and metal mass with stellar mass, specific star formation rate and metallicity are crucial to our understanding of the buildup of galaxies through their enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass ($M_{\text{HI}}$/$M_{\star}$) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) - incluidng stellar dust production, grain growth, and dust destruction - within a Bayesian framework to enable a rigorous search of the multi-dimensional parameter space. We find that these scaling laws for galaxies with $-1.0\lesssim \log M_{\text{HI}}$/$M_{\star}\lesssim0$ can be reproduced using closed-box models with high fractions (37-89$\%$) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies ($\epsilon$=30-40), and long dus lifetimes (1-2\,Gyr). The models have present-day dust masses with similar contributions from stellar sources (50-80\,$\%$) and grain growth (20-50\,$\%$). Over the entire lifetime of these galaxies, the contribution from stardust ($>$90\,$\%$) outweighs the fraction of dust grown in the interstellar medium ($<$10$\%$). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth timescales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium., Comment: 56 pages, 30 figures, accepted for publication in MNRAS

We measure the 850-$\mu$m source densities of 46 candidate protoclusters selected from the Planck High-z catalogue (PHz) and the Planck Catalogue of Compact Sources (PCCS) that were followed up with Herschel-SPIRE and SCUBA-2. This paper aims to search for overdensities of 850-$\mu$m sources in order to select the fields that are most likely to be genuine protoclusters. Of the 46 candidate protoclusters, 25 have significant overdensities ($>$5 times the field counts), 11 have intermediate overdensities (3--5 times the field counts) and 10 have no overdensity ($<$3 times the field counts) of 850-$\mu$m sources. We find that the enhanced number densities are unlikely to be the result of sample variance. Compared with the number counts of another sample selected from Planck's compact source catalogues, this [PHz+PCCS]-selected sample has a higher fraction of candidate protoclusters with significant overdensities, though both samples show overdensities of 850-$\mu$m sources above intermediate level. Based on the estimated star-formation rate densities (SFRDs), we suggest that both samples can efficiently select protoclusters with starbursting galaxies near the redshift at which the global field SFRD peaks ($2 < z < 3$). Based on the confirmation of overdensities found here, future follow-up observations on other PHz targets may greatly increase the number of genuine DSFG-rich clusters/protoclusters., Comment: 8 pages, 1 figure, 1 table, accepted for publication in MNRAS

We investigate the evolution of the gas mass fraction for galaxies in the COSMOS field using submillimetre emission from dust at 850$\mu$m. We use stacking methodologies on the 850$\mu$m S2COSMOS map to derive the gas mass fraction of galaxies out to high redshifts, 0 <= $z$ <= 5, for galaxies with stellar masses of $10^{9.5} < M_* (\rm M_{\odot}) < 10^{11.75}$. In comparison to previous literature studies we extend to higher redshifts, include more normal star-forming galaxies (on the main sequence), and also investigate the evolution of the gas mass fraction split by star-forming and passive galaxy populations. We find our stacking results broadly agree with scaling relations in the literature. We find tentative evidence for a peak in the gas mass fraction of galaxies at around $z$ ~ 2.5-3, just before the peak of the star formation history of the Universe. We find that passive galaxies are particularly devoid of gas, compared to the star-forming population. We find that even at high redshifts, high stellar mass galaxies still contain significant amounts of gas., Comment: 17 pages (+ 9 pages of appendices), 8 figures (+ 7 figures in appendices), accepted for publication in MNRAS

Using data from ALMA and near-infrared (NIR) integral field spectrographs including both SINFONI and KMOS on the VLT, we investigate the two-dimensional distributions of H$\alpha$ and rest-frame far-infrared (FIR) continuum in six submillimeter galaxies at $z\sim2$. At a similar spatial resolution ($\sim$0.5" FWHM; $\sim$4.5 kpc at $z=2$), we find that the half-light radius of H$\alpha$ is significantly larger than that of the FIR continuum in half of the sample, and on average H$\alpha$ is a median factor of $2.0\pm0.4$ larger. Having explored various ways to correct for the attenuation, we find that the attenuation-corrected H$\alpha$-based SFRs are systematically lower than the IR-based SFRs by at least a median factor of $3\pm1$, which cannot be explained by the difference in half-light radius alone. In addition, we find that in 40% of cases the total $V$-band attenuation ($A_V$) derived from energy balance modeling of the full ultraviolet(UV)-to-FIR spectral energy distributions (SEDs) is significantly higher than that derived from SED modeling using only the UV-to-NIR part of the SEDs, and the discrepancy appears to increase with increasing total infrared luminosity. Finally, considering all our findings along with the studies in the literature, we postulate that the dust distributions in SMGs, and possibly also in less IR luminous $z\sim2$ massive star-forming galaxies, can be decomposed into three main components; the diffuse dust heated by older stellar populations, the more obscured and extended young star-forming HII regions, and the heavily obscured central regions that have a low filling factor but dominate the infrared luminosity in which the majority of attenuation cannot be probed via UV-to-NIR emissions., Comment: 15 pages, 8 figures, A&A in press

On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. Preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope (ENGRAVE) collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical/near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS and VINROUGE projects also carried out a search on this event. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN) possibly generated by this NS-BH merger, and for the strategy of future searches. Altogether, our observations allow us to exclude a KN with large ejecta mass $M\gtrsim 0.1\,\mathrm{M_\odot}$ to a high ($>90\%$) confidence, and we can exclude much smaller masses in a subsample of our observations. This disfavours the tidal disruption of the neutron star during the merger. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundreds Mpc will be detected only by large facilities with both high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event., Comment: 52 pages, revised version now accepted for publication in A&A. Abstract abridged to meet arXiv requirements

We analyse 870um Atacama Large Millimetre Array (ALMA) dust continuum detections of 41 canonically-selected z~3 Lyman-break galaxies (LBGs), as well as 209 ALMA-undetected LBGs, in follow-up of SCUBA-2 mapping of the UKIDSS Ultra Deep Survey (UDS) field. We find that our ALMA-bright LBGs lie significantly off the locally calibrated IRX-beta relation and tend to have relatively bluer rest-frame UV slopes (as parametrised by beta), given their high values of the 'infrared excess' (IRX=L_IR/L_UV), relative to the average 'local' IRX-beta relation. We attribute this finding in part to the young ages of the underlying stellar populations but we find that the main reason behind the unusually blue UV slopes are the relatively shallow slopes of the corresponding dust attenuation curves. We show that, when stellar masses are being established via SED fitting, it is absolutely crucial to allow the attenuation curves to vary (rather than fixing it on Calzetti-like law), where we find that the inappropriate curves may underestimate the resulting stellar masses by a factor of ~2-3x on average. In addition, we find these LBGs to have relatively high specific star-formation rates (sSFRs), dominated by the dust component, as quantified via the fraction of obscured star formation ( f_obs = SFR_IR/SFR_(UV+IR)). We conclude that the ALMA-bright LBGs are, by selection, massive galaxies undergoing a burst of a star formation (large sSFRs, driven, for example, by secular or merger processes), with a likely geometrical disconnection of the dust and stars, responsible for producing shallow dust attenuation curves., Comment: 17 pages, 12 figures. Resubmitted to MNRAS after referee report

We present sensitive 850$\mu$m imaging of the COSMOS field using 640hr of new and archival observations taken with SCUBA-2 at the East Asian Observatory's James Clerk Maxwell Telescope. The SCUBA-2 COSMOS survey (S2COSMOS) achieves a median noise level of $\sigma_{850\mu{\mathrm{m}}}$=1.2mJy/beam over an area of 1.6 sq. degree (MAIN; HST/ACS footprint), and $\sigma_{850\mu{\mathrm{m}}}$=1.7mJy/beam over an additional 1 sq. degree of supplementary (SUPP) coverage. We present a catalogue of 1020 and 127 sources detected at a significance level of >4$\sigma$ and >4.3$\sigma$ in the MAIN and SUPP regions, respectively, corresponding to a uniform 2% false-detection rate. We construct the single-dish 850$\mu$m number counts at $S_{850}$>2mJy and show that these S2COSMOS counts are in agreement with previous single-dish surveys, demonstrating that degree-scale fields are sufficient to overcome the effects of cosmic variance in the $S_{850}$=2-10mJy population. To investigate the properties of the galaxies identified by S2COSMOS sources we measure the surface density of near-infrared-selected galaxies around their positions and identify an average excess of 2.0$\pm$0.2 galaxies within a 13$''$ radius (~100kpc at $z$~2). The bulk of these galaxies represent near-infrared-selected SMGs and/or spatially-correlated sources and lie at a median photometric redshift of $z$=2.0$\pm$0.1. Finally, we perform a stacking analysis at sub-millimeter and far-infrared wavelengths of stellar-mass-selected galaxies ($M_{\star}$=10$^{10}$-10$^{12}{\rm M_{\odot}}$) from $z$=0-4, obtaining high-significance detections at 850um in all subsets (SNR=4-30), and investigate the relation between far-infrared luminosity, stellar mass, and the peak wavelength of the dust SED. The publication of this survey adds a new deep, uniform sub-millimeter layer to the wavelength coverage of this well-studied COSMOS field., Comment: Published in ApJ July 2019

We present radio and optical afterglow observations of the TeV-bright long Gamma Ray Burst (GRB) 190114C at a redshift of $z=0.425$, which was detected by the MAGIC telescope. Our observations with ALMA, ATCA, and uGMRT were obtained by our low frequency observing campaign and range from $\sim1$ to $\sim140$ days after the burst and the optical observations were done with three optical telescopes spanning up to $\sim25$ days after the burst. Long term radio/mm observations reveal the complex nature of the afterglow, which does not follow the spectral and temporal closure relations expected from the standard afterglow model. We find that the microphysical parameters of the external forward shock, representing the share of shock-created energy in the non-thermal electron population and magnetic field, are evolving with time. The inferred kinetic energy in the blast-wave depends strongly on the assumed ambient medium density profile, with a constant density medium demanding almost an order of magnitude higher energy than in the prompt emission, while a stellar wind-driven medium requires approximately the same amount energy as in prompt emission., Comment: MNRAS, in press, expanded after referee report, 19 pages, 15 figures, 6 tables

GRB 190114C is the first GRB for which the detection of very-high energy emission up to the TeV range has been reported. It is still unclear whether environmental properties might have contributed to the production of these very high-energy photons, or if it is solely related to the released GRB emission. The relatively low redshift of the GRB (z=0.425) allows us to study the host galaxy of this event in detail, and to potentially identify idiosyncrasies that could point to progenitor characteristics or environmental properties responsible for such a unique event. We use ultraviolet, optical, infrared and submillimetre imaging and spectroscopy obtained with HST, VLT and ALMA to obtain an extensive dataset on which the analysis of the host galaxy is based. The host system is composed of a close pair of interacting galaxies (Delta v = 50 km s^-1), both of which are well-detected by ALMA in CO(3-2). The GRB occurred within the nuclear region (~170 pc from the centre) of the less massive but more star-forming galaxy of the pair. The host is more massive (log(M/M_odot)=9.3) than average GRB hosts at that redshift and the location of the GRB is rather unique. The enhanced star-formation rate was probably triggered by tidal interactions between the two galaxies. Our ALMA observations indicate that both host galaxy and companion have a high molecular gas fraction, as has been observed before in interacting galaxy pairs. The location of the GRB within the core of an interacting galaxy with an extinguished line-of-sight is indicative of a denser environment than typically observed for GRBs and could have been crucial for the generation of the very-high-energy photons that were observed., Comment: A&A, in press, 11 pages

Dusty star-forming galaxies (DSFGs) detected at $z > 4$ provide important examples of the first generations of massive galaxies. However, few examples with spectroscopic confirmation are currently known, with Hershel struggling to detect significant numbers of $z > 6$ DSFGs. NGP6_D1 is a bright 850 $\mu m$ source (12.3 $\pm$ 2.5 mJy) with no counterparts at shorter wavelengths (a SPIRE dropout). Interferometric observations confirm it is a single source, with no evidence for any optical or NIR emission, or nearby likely foreground lensing sources. No $>3\sigma$ detected lines are seen in both LMT RSR and IRAM 30m EMIR spectra of NGP6_D1 across 32 $GHz$ of bandwidth despite reaching detection limits of $\sim 1 mJy/500 km~s^{-1}$, so the redshift remains unknown. Template fitting suggests that NGP6_D1 is most likely between $z = 5.8$ and 8.3. SED analysis finds that NGP6_D1 is a ULIRG, with a dust mass $\sim 10^8$ - $10^9$ $M_{\odot}$ and a SFR of $\sim$ 500 $M_{\odot}~yr^{-1}$. We place upper limits on the gas mass of NGP6_D1 of $M_{H2}$ $ < (1.1~\pm~3.5) \times 10^{11}$ $M_{\odot}$, consistent with a gas-to-dust ratio of $\sim$ 100 - 1000. We discuss the nature of NGP6_D1 in the context of the broader submm population, and find that comparable SPIRE dropouts account for $\sim$ 20% of all SCUBA-2 detected sources, but with a similar flux density distribution to the general population., Comment: Accepoted for publication in MNRAS

We present an analysis of the morphology and profiles of the dust continuum emission in 153 bright sub-millimetre galaxies (SMGs) detected with ALMA at S/N ratios of $>8$ in high-resolution $0.18''$ ($\sim1$kpc) 870$\mu$m maps. We measure sizes, shapes and light profiles for the rest-frame far-infrared emission from these luminous star-forming systems and derive a median effective radius ($R_e$) of $0.10''\pm0.04''$ for our sample with a median flux of $S_{870}=5.6\pm0.2$mJy. We find that the apparent axial ratio ($b/a$) distribution of the SMGs peaks at $b/a\sim0.63\pm0.24$ and is best described by triaxial morphologies, while their emission profiles are best fit by a Sersic model with $n\simeq1.0\pm0.1$, similar to exponential discs. This combination of triaxiality and $n\sim1$ Sersic index are characteristic of bars and we suggest that the bulk of the 870$\mu$m dust continuum emission in the central $\sim2$kpc of these galaxies arises from bar-like structures. By stacking our 870$\mu$m maps we recover faint extended dust continuum emission on $\sim4$kpc scales which contributes $13\pm1$% of the total 870$\mu$m emission. The scale of this extended emission is similar to that seen for the molecular gas and rest-frame optical light in these systems, suggesting that it represents an extended dust and gas disc at radii larger than the more active bar component. Including this component in our estimated size of the sources we derive a typical effective radius of $\simeq0.15''\pm0.05''$ or $1.2\pm0.4$kpc. Our results suggest that kpc-scale bars are ubiquitous features of high star-formation rate systems at $z\gg1$, while these systems also contain fainter and more extended gas and stellar envelopes. We suggest that these features, seen some $10-12$Gyrs ago, represent the formation phase of the earliest galactic-scale components: stellar bulges., Comment: 14 pages, 10 figures, accepted for publication in MNRAS

We present SCUBA-2 850-$\mu$m observations of 13 candidate starbursting protoclusters selected using Planck and Herschel data. The cumulative number counts of the 850-$\mu$m sources in 9/13 of these candidate protoclusters show significant overdensities compared to the field, with the probability $<$10$^{-2}$ assuming the sources are randomly distributed in the sky. Using the 250-, 350-, 500- and 850-$\mu$m flux densities, we estimate the photometric redshifts of individual SCUBA-2 sources by fitting spectral energy distribution (SED) templates with an MCMC method. The photometric redshift distribution, peaking at $22$ protoclusters and the peak of the cosmic star-formation rate density (SFRD). We find that the 850-$\mu$m sources in our candidate protoclusters have infrared luminosities of $L_{\mathrm{IR}}\gtrsim$10$^{12}L_{\odot}$ and star-formation rates of SFR=(500-1,500)$M_{\odot}$yr$^{-1}$. By comparing with results in the literature considering only Herschel photometry, we conclude that our 13 candidate protoclusters can be categorised into four groups: six of them being high-redshift starbursting protoclusters, one being a lower-redshift cluster/protocluster, three being protoclusters that contain lensed DSFG(s) or are rich in 850-$\mu$m sources, and three regions without significant Herschel or SCUBA-2 source overdensities. The total SFRs of the candidate protoclusters are found to be comparable or higher than those of known protoclusters, suggesting our sample contains some of the most extreme protocluster population. We infer that cross-matching Planck and Herschel data is a robust method for selecting candidate protoclusters with overdensities of 850-$\mu$m sources., Comment: 30 pages, 8 figures, 5 tables, accepted for publication in MNRAS

We combine high-resolution ALMA and HST/CANDELS observations of 20 submillimeter galaxies (SMGs) predominantly from the AS2UDS survey at z~2 with bright rest-frame optical counterparts (Ks < 22.9) to investigate the resolved structural properties of their dust and stellar components. We derive two-dimensional stellar-mass distributions that are inferred from spatial mass-to-light ratio (M/L) corrections based on rest-frame optical colors. Due to the high central column densities of dust in our SMGs, our mass distributions likely represent a lower limit to the true central mass density. The centroid positions between the inferred stellar-mass and the dust distributions agree within 1.1 kpc, indicating an overall good spatial agreement between the two components. The majority of our sources exhibit compact dust configurations relative to the stellar component (with a median ratio of effective radii Re,dust/Re,Mstar = 0.6). This ratio does not change with specific star-formation rate (sSFR) over the factor of 30 spanned by our targets, sampling the locus of "normal" main sequence galaxies up to the starburst regime, log(sSFR/sSFRMS) > 0.5. Our results imply that massive SMGs are experiencing centrally enhanced star formation unlike typical spiral galaxies in the local Universe. The sizes and stellar densities of our SMGs are in agreement with those of the passive population at z=1.5, consistent with these systems being the descendants of z~2 SMGs., Comment: 26 pages, 11 figures, accepted for publication in ApJ

The mechanism of dust formation in galaxies at high redshift is still unknown. Asymptotic giant branch (AGB) stars and explosions of supernovae (SNe) are possible dust producers, and non-stellar processes may substantially contribute to dust production, for example grain growth in the interstellar medium (ISM). Our aim is to determine the contribution to dust production of AGB stars and SNe in nine galaxies at z ~ 6-8.3, for which observations of dust have been recently attempted. In order to determine the origin of the observed dust we have determined dust yields per AGB star and SN required to explain the total amounts of dust in these galaxies. We find that AGB stars were not able to produce the amounts of dust observed in the galaxies in our sample. In order to explain these dust masses, SNe would have to have maximum efficiency and not destroy the dust which they formed. Therefore, the observed amounts of dust in the galaxies in the early universe were formed either by efficient supernovae or by a non-stellar mechanism, for instance the grain growth in the interstellar medium., Comment: Accepted for publication in A&A, 5 pages, 1 figure

We analyse the multi-frequency radio spectral properties of $41$ 6GHz-detected ALMA-identified, submillimetre galaxies (SMGs), observed at 610MHz, 1.4GHz, 6GHz with GMRT and the VLA. Combining high-resolution ($\sim0.5''$) 6GHz radio and ALMA $870\,\mu$m imaging (tracing rest-frame $\sim20$GHz, and $\sim250\,\mu$m dust continuum), we study the far-infrared/radio correlation via the logarithmic flux ratio $q_{\rm IR}$, measuring $\langle q_{\rm IR}\rangle=2.20\pm 0.06$ for our sample. We show that the high-frequency radio sizes of SMGs are $\sim1.9\pm 0.4\times$ ($\sim2$-$3$kpc) larger than those of the cool dust emission, and find evidence for a subset of our sources being extended on $\sim 10$kpc scales at 1.4GHz. By combining radio flux densities measured at three frequencies, we can move beyond simple linear fits to the radio spectra of high-redshift star-forming galaxies, and search for spectral curvature, which has been observed in local starburst galaxies. At least a quarter (10/41) of our sample show evidence of a spectral break, with a median $\langle\alpha^{1.4\,{\rm GHz}}_{610\,{\rm GHz}}\rangle=-0.60\pm 0.06$, but $\langle\alpha^{6\,{\rm GHz}}_{1.4\,{\rm GHz}}\rangle=-1.06\pm 0.04$ -- a high-frequency flux deficit relative to simple extrapolations from the low-frequency data. We explore this result within this subset of sources in the context of age-related synchrotron losses, showing that a combination of weak magnetic fields ($B\sim35\,\mu$G) and young ages ($t_{\rm SB}\sim40$--$80\,$Myr) for the central starburst can reproduce the observed spectral break. Assuming these represent evolved (but ongoing) starbursts and we are observing these systems roughly half-way through their current episode of star formation, this implies starburst durations of $\lesssim100$Myr, in reasonable agreement with estimates derived via gas depletion timescales., Comment: 25 pages, 10 colour figures, 2 tables; accepted for publication in ApJ

We present the catalogue and properties of sources in AS2UDS, an 870-$\mu$m continuum survey with the Atacama Large Millimetre/sub-millimetre Array (ALMA) of 716 single-dish sub-millimetre sources detected in the UKIDSS/UDS field by the SCUBA-2 Cosmology Legacy Survey. In our sensitive ALMA follow-up observations we detect 708 sub-millimetre galaxies (SMGs) at $>$\,4.3$\sigma$ significance across the $\sim$\,1-degree diameter field. We combine our precise ALMA positions with the extensive multi-wavelength coverage in the UDS field to fit the spectral energy distributions of our SMGs to derive a median redshift of $z_{\rm phot}=$\,2.61$\pm$0.09. This large sample reveals a statistically significant trend of increasing sub-millimetre flux with redshift suggestive of galaxy downsizing. 101 ALMA maps do not show a $>$\,4.3$\sigma$ SMG, but we demonstrate from stacking {\it Herschel} SPIRE observations at these positions, that the vast majority of these blank maps correspond to real single-dish sub-millimetre sources. We further show that these blank maps contain an excess of galaxies at $z_{\rm phot}=$\,1.5--4 compared to random fields, similar to the redshift range of the ALMA-detected SMGs. In addition, we combine X-ray and mid-infrared active galaxy nuclei activity (AGN) indicators to yield a likely range for the AGN fraction of 8--28\,\% in our sample. Finally, we compare the redshifts of this population of high-redshift, strongly star-forming galaxies with the inferred formation redshifts of massive, passive galaxies being found out to $z\sim$\,2, finding reasonable agreement -- in support of an evolutionary connection between these two classes of massive galaxy., Comment: Submitted to MNRAS; Comments welcome. Full catalogue will be made publicly available on acceptance of paper

Using ALMA, we report high angular-resolution observations of the redshift z=3.63 galaxy, G09v1.97, one of the most luminous strongly lensed galaxies discovered by the H-ATLAS survey. We present 0"2-0"4 resolution images of the rest-frame 188 and 419$\mu$m dust continuum and the CO(6-5), H2O(211-202) and J=2 H2O+ line emission. We also report the detection of H$_2^{18}$O in this source. The dust continuum and molecular gas emission are resolved into a nearly complete ~1"5 diameter Einstein ring plus a weaker image in the center, which is caused by a special dual deflector lensing configuration. The observed line profiles of the CO, H2O and H2O+ lines are strikingly similar. In the source plane, we reconstruct the dust continuum images and the spectral cubes of the line emission at sub-kpc scales. The reconstructed dust emission in the source plane is dominated by a compact disk with an effective radius of 0.7kpc plus an overlapping extended disk with a radius twice as large. While the average magnification for the dust continuum is $\mu$~10-11, the magnification of the line emission varies 5 to 22 across different velocity components. The emission lines have similar spatial and kinematic distributions. The molecular gas and dust content reveal that G09v1.97 is a gas-rich major merger in its pre-coalescence phase. Both of the merging companions are intrinsically ULIRGs with LIR reaching $\gtrsim 4\times10^{12}L_\odot$, and the total LIR of G09v1.97 is $1.4\times10^{13}L_\odot$. The approaching southern galaxy shows no obvious kinematic structure with a semi-major half-light radius a_s=0.4kpc, while the receding galaxy resembles an a_s=1.2kpc rotating disk. The two galaxies are separated by a projected distance of 1.3kpc, bridged by weak line emission that is co-spatially located with the cold-dust-emission peak, suggesting a large amount of cold ISM in the interacting region. (abridged), Comment: 19 pages, 12 figures, and 4-page appendix, A&A in press. Minor changes to match language editing

We aim to study the statistical properties of dusty star-forming galaxies, such as their number counts, luminosity functions (LF) and dust-obscured star-formation rate density (SFRD). We use state-of-the-art de-blended Herschel catalogue in the COSMOS field, generated by combining the Bayesian source extraction tool XID+ and informative prior on the spectral energy distributions, to measure the number counts and LFs at far-infrared (FIR) and sub-millimetre (sub-mm) wavelengths. Thanks to our de-confusion technique and deep multi-wavelength photometry, we are able to achieve more accurate measurements while probing ten times below the confusion limit. Our number counts at 250 microns agree well with previous Herschel studies. However, our counts at 350 and 500 microns are considerably below previous Herschel results. This is due to previous studies suffering from source confusion which worsens towards longer wavelength. Our number counts at 450 and 870 microns show excellent agreement with previous determinations derived from single dish and interferometric observations. Our measurements of the monochromatic LF and the total IR LF agree well with previous results. The increased dynamic range of our measurements allows us to better measure the faint-end slope of the LF and measure the dust-obscured SFRD out to z~6. We find that the fraction of dust obscured star-formation activity is at its highest around z~1 which then decreases towards both low and high redshift. We do not find a shift of balance between z~3 and z~4 in the cosmic star-formation history from being dominated by unobscured star formation at higher redshift to obscured star formation at lower redshift. However, we do find 3

Long gamma-ray bursts mark the death of massive stars, as revealed by their association with energetic broad-lined stripped-envelope supernovae. The scarcity of nearby events and the brightness of the GRB afterglow, dominating the first days of emission, have so far prevented the study of the very early stages of the GRB-SN evolution. Here we present detailed, multi-epoch spectroscopic observations of SN 2017iuk, associated with GRB 171205A which display features at extremely high expansion velocities of $\sim$ 100,000 km s$^{-1}$ within the first day after the burst. These high-velocity components are characterized by chemical abundances different from those observed in the ejecta of SN 2017iuk at later times. Using spectral synthesis models developed for the SN 2017iuk, we explain these early features as originating not from the supernova ejecta, but from a hot cocoon generated by the energy injection of a mildly-relativistic GRB jet expanding into the medium surrounding the progenitor star. This cocoon becomes rapidly transparent and is outshone by the supernova emission which starts dominating three days after the burst. These results proves that the jet plays an important role not only in powering the GRB event but also its associated supernova., Comment: 30 pages, 11 figures, 4 tables. Original author manuscript version of a Letter published in Nature journal. Full article available at https://goo.gl/7y9ZeM

We present measurements of the angular correlation function of sub-millimeter (sub-mm) galaxies (SMGs) identified in four out of the five fields of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) - GAMA-9h, GAMA-12h, GAMA-15h and NGP - with flux densities $S_{250\mu m}$>30 mJy at 250 {\mu}m. We show that galaxies selected at this wavelength trace the underlying matter distribution differently at low and high redshifts. We study the evolution of the clustering finding that at low redshifts sub-mm galaxies exhibit clustering strengths of $r_0$ $\sim$ 2 - 3 $h^{-1}$ Mpc, below z < 0.3. At high redshifts, on the other hand, we find that sub-mm galaxies are more strongly clustered with correlation lengths $r_0$ = 8.1 $\pm$ 0.5, 8.8 $\pm$ 0.8 and 13.9 $\pm$ 3.9 $h^{-1}$Mpc at z = 1 - 2, 2 - 3 and 3 - 5, respectively. We show that sub-mm galaxies across the redshift range 1 < z < 5, typically reside in dark-matter halos of mass of the order of ~ $10^{12.5}$ - $10^{13.0}$ $h^{-1} \, M_{\odot}$ and are consistent with being the progenitors of local massive elliptical galaxies that we see in the local Universe., Comment: 17 pages, 11 figures, 3 tables. Accepted for publication in MNRAS

We present Atacama Large Millimeter/submillimeter Array (ALMA) resolved observations of molecular gas in galaxies up to $z=0.35$ to characterise the role of global galactic dynamics on the global interstellar medium (ISM) properties. These observations consist of a sub-sample of 39 galaxies taken from the Valpara\'iso ALMA Line Emission Survey (VALES). From the CO($J=1-0)$ emission line, we quantify the kinematic parameters by modelling the velocity fields. We find that the IR luminosity increases with the rotational to dispersion velocity ratio ($V_{\rm rot}/\sigma_v$, corrected for inclination). We find a dependence between $V_{\rm rot}/\sigma_v$ and the [CII]/IR ratio, suggesting that the so-called `[CII] deficit' is related to the dynamical state of the galaxies. We find that global pressure support is needed to reconcile the dynamical mass estimates with the stellar masses in our systems with low $V_{\rm rot}/\sigma_v$ values. The star formation rate (SFR) is weakly correlated with the molecular gas fraction ($f_{\rm H_2}$) in our sample, suggesting that the release of gravitational energy from cold gas may not be the main energy source of the turbulent motions seen in the VALES galaxies. By defining a proxy of the `star formation efficiency' parameter as the SFR divided by the CO luminosity (SFE$'\equiv$ SFR/L$'_{\rm CO}$), we find a constant SFE$'$ per crossing time ($t_{\rm cross}$). We suggest that $t_{\rm cross}$ may be the controlling timescale in which the star formation occurs in dusty $z\sim0.03-0.35$ galaxies., Comment: Accepted for publication in MNRAS. 28 pages, 15 figures, 2 Tables

Long gamma-ray bursts are produced during the dramatic deaths of massive stars with very short lifetimes, meaning that they explode close to the birth place of their progenitors. During a short period they become the most luminous objects observable in the Universe, being perfect beacons to study high-redshift star-forming regions. To use the afterglow of GRB 161023A at a redshift $z=2.710$ as a background source to study the environment of the explosion and the intervening systems along its line-of-sight. r the first time, we complement UV/Optical/NIR spectroscopy with millimetre spectroscopy using ALMA, which allows us to probe the molecular content of the host galaxy. The X-shooter spectrum shows a plethora of absorption features including fine-structure and metastable transitions of Fe, Ni, Si, C and O. We present photometry ranging from 43 s to over 500 days after the burst. We infer a host-galaxy metallicity of [Zn/H] $=-1.11\pm0.07$, which corrected for dust depletion results in [X/H] $=-0.94\pm0.08$. We do not detect molecular features in the ALMA data, but we derive limits on the molecular content of $log(N_{CO}/cm^{-2})<15.7$ and $log(N_{HCO+}/cm^{-2})<13.2$, which are consistent with those that we obtain from the optical spectra, $log(N_{H_2}/cm^{-2})<15.2$ and $log(N_{CO}/cm^{-2})<14.5$. Within the host galaxy we detect three velocity systems through UV/Optical/NIR absorption spectroscopy, all with levels that were excited by the GRB afterglow. We determine the distance from these systems to the GRB to be in the range between 0.7 and 1.0 kpc. The sight-line to GRB 161023A shows 9 independent intervening systems, most of them with multiple components. (Abridged), Comment: 28 pages, 19 pages main text, 9 pages appendix; accepted for publication in A&A

We describe the application of the supervised machine-learning algorithms to identify the likely multi-wavelength counterparts to submillimeter sources detected in panoramic, single-dish submillimeter surveys. As a training set, we employ a sample of 695 ($S_{\rm 870\mu m}$ >1 mJy) submillimeter galaxies (SMGs) with precise identifications from the ALMA follow-up of the SCUBA-2 Cosmology Legacy Survey's UKIDSS-UDS field (AS2UDS). We show that radio emission, near-/mid-infrared colors, photometric redshift, and absolute $H$-band magnitude are effective predictors that can distinguish SMGs from submillimeter-faint field galaxies. Our combined radio+machine-learning method is able to successfully recover $\sim$85 percent of ALMA-identified SMGs which are detected in at least three bands from the ultraviolet to radio. We confirm the robustness of our method by dividing our training set into independent subsets and using these for training and testing respectively, as well as applying our method to an independent sample of $\sim$100 ALMA-identified SMGs from the ALMA/LABOCA ECDF-South Survey (ALESS). To further test our methodology, we stack the 870$\mu$m ALMA maps at the positions of those $K$-band galaxies that are classified as SMG counterparts by the machine-learning but do not have a $>$4.3$ \sigma$ ALMA detection. The median peak flux density of these galaxies is $S_{\rm 870\mu m}=(0.61\pm0.03)$ mJy, demonstrating that our method can recover faint and/or diffuse SMGs even when they are below the detection threshold of our ALMA observations. In future, we will apply this method to samples drawn from panoramic single-dish submillimeter surveys which currently lack interferometric follow-up observations, to address science questions which can only be tackled with large, statistical samples of SMGs., Comment: 25 pages, 10 figures, three tables, accepted for publication in ApJ

We report the first results of AS2UDS: an 870 $\mu$m continuum survey with the Atacama Large Millimeter/Submillimeter Array (ALMA) of a total area of $\sim$ 50 arcmin$^2$ comprising a complete sample of 716 submillimeter sources drawn from the SCUBA-2 Cosmology Legacy Survey (S2CLS) map of the UKIDSS/UDS field. The S2CLS parent sample covers a 0.96 degree$^2$ field at $\sigma_{850}=0.90\pm0.05$ mJy beam$^{-1}$. Our deep, high-resolution ALMA observations with $\sigma_{\rm 870}\sim$ 0.25 mJy and a 0.15"--0.30" FWHM synthesized beam, provide precise locations for 695 submillimetre galaxies (SMGs) responsible for the submillimeter emission corresponding to 606 sources in the low resolution, single-dish map. We measure the number counts of SMGs brighter than $S_{\rm 870}\geq$ 4 mJy, free from the effects of blending and show that the normalisation of the counts falls by 28 $\pm$ 2% in comparison to the SCUBA-2 parent sample, but that the shape remains unchanged. We determine that 44$^{+16}_{-14}$% of the brighter single-dish sources with $S_{850}\geq$ 9 mJy consist of a blend of two or more ALMA-detectable SMGs brighter than $S_{870}\sim$ 1 mJy (corresponding to a galaxy with a total-infrared luminosity of $L_{IR}\geq$ 10$^{12}$ L$_\odot$), in comparison to 28 $\pm$ 2% for the single-dish sources at $S_{\rm 850}\geq$ 5 mJy. Using the 46 single-dish submillimeter sources that contain two or more ALMA-detected SMGs with photometric redshifts, we show that there is a significant statistical excess of pairs of SMGs with similar redshifts ($<$1% probability of occurring by chance), suggesting that at least 30% of these blends arise from physically associated pairs of SMGs., Comment: 11 pages, 4 figures, fixed typo (sorry Rob)

We report the results of a search for serendipitous [CII] 157.74$\mu$m emitters at $z\sim4.4$-$4.7$ using the Atacama Large Millimeter/submillimeter Array (ALMA). The search exploits the AS2UDS continuum survey, which covers ~50 arcmin$^2$ of the sky towards 695 luminous ($S_{870}\gtrsim1$mJy) submillimeter galaxies (SMGs), selected from the SCUBA-2 Cosmology Legacy Survey (S2CLS) 0.96deg$^2$ Ultra Deep Survey (UDS) field. We detect ten candidate line emitters, with an expected false detection rate of ten percent. All of these line emitters correspond to 870$\mu$m continuum-detected sources in AS2UDS. The emission lines in two emitters appear to be high-J CO, but the remainder have multi-wavelength properties consistent with [CII] from $z\simeq4.5$ galaxies. Using our sample, we place a lower limit of $>5\times10^{-6}$Mpc$^{-3}$ on the space density of luminous ($L_{\rm IR} \simeq 10^{13}$Lsun) SMGs at $z=4.40$-$4.66$, suggesting $\ge7$percent of SMGs with $S_{870\mu{\rm m}}\gtrsim1$mJy lie at $4

Dust-enshrouded, starbursting, submillimeter galaxies (SMGs) at $z \geq 3$ have been proposed as progenitors of $z \geq 2$ compact quiescent galaxies (cQGs). To test this connection, we present a detailed spatially resolved study of the stars, dust and stellar mass in a sample of six submillimeter-bright starburst galaxies at $z \sim 4.5$. The stellar UV emission probed by HST is extended, irregular and shows evidence of multiple components. Informed by HST, we deblend Spitzer/IRAC data at rest-frame optical finding that the systems are undergoing minor mergers, with a typical stellar mass ratio of 1:6.5. The FIR dust continuum emission traced by ALMA locates the bulk of star formation in extremely compact regions (median $r_{\rm{e}} = 0.70 \pm 0.29$ kpc) and it is in all cases associated with the most massive component of the mergers (median $\log (M_{*}/M_{\odot}) = 10.49 \pm 0.32$). We compare spatially resolved UV slope ($\beta$) maps with the FIR dust continuum to study the infrared excess ($\rm{IRX} = L_{\rm{IR}}/L_{\rm{UV}}$)-$\beta$ relation. The SMGs display systematically higher $\rm{IRX}$ values than expected from the nominal trend, demonstrating that the FIR and UV emissions are spatially disconnected. Finally, we show that the SMGs fall on the mass-size plane at smaller stellar masses and sizes than cQGs at $z = 2$. Taking into account the expected evolution in stellar mass and size between $z = 4.5$ and $z = 2$ due to the ongoing starburst and mergers with minor companions, this is in agreement with a direct evolutionary connection between the two populations., Comment: Accepted by ApJ. 25 pages, 6 figures

We present a multi-wavelength analysis of galaxies selected at 450 and 850um from the deepest SCUBA-2 observations in the Extended Groth Strip (EGS) field, which have an average depth of sigma_450=1.9 and sigma_850=0.46 mJy/beam over ~70 sq. arcmin. The final sample comprises 95 sources: 56 (59%) are detected at both wavelengths, 31 (33%) are detected only at 850um, and 8 (8%) are detected only at 450um. We identify counterparts for 75% of the whole sample. The redshift distributions of the 450 and 850um samples peak at different redshifts with median values of z=1.66 +/- 0.18 and z=2.30 +/- 0.20, respectively. However, the two populations have similar IR luminosities, SFRs, and stellar masses, with mean values of (1.5 +/- 0.2) x 10^12 L_sun, (150 +/- 20) M_sun/yr, and (9.0 +/- 0.6) x 10^10 M_sun, respectively. This places most of our sources (>85%) on the high-mass end of the `main-sequence' of star-forming galaxies. Exploring the IR excess vs UV-slope (IRX-beta) relation we find that the most luminous galaxies are consistent with the Meurer law, while the less luminous galaxies lie below this relation. Using the results of a two-dimensional modelling of the HST H_160-band imaging, we derive a median Sersic index of n=1.4 +0.3 -0.1 and a median half-light radius of R_1/2 = 4.8 +/ 0.4 kpc. Based on a visual-like classification in the same band, we find that the dominant component for most of the galaxies at all redshifts is a disk-like structure, although there is a transition from irregular disks to disks with a spheroidal component at z~1.4, which morphologically supports the scenario of SMGs as progenitors of massive elliptical galaxies., Comment: Accepted for publication in MNRAS

With the advent of wide-area submillimeter surveys, a large number of high-redshift gravitationally lensed dusty star-forming galaxies (DSFGs) has been revealed. Due to the simplicity of the selection criteria for candidate lensed sources in such surveys, identified as those with $S_{500\mu m} > 100$ mJy, uncertainties associated with the modelling of the selection function are expunged. The combination of these attributes makes submillimeter surveys ideal for the study of strong lens statistics. We carried out a pilot study of the lensing statistics of submillimetre-selected sources by making observations with the Atacama Large Millimetre Array (ALMA) of a sample of strongly-lensed sources selected from surveys carried out with the Herschel Space Observatory. We attempted to reproduce the distribution of image separations for the lensed sources using a halo mass function taken from a numerical simulation which contains both dark matter and baryons. We used three different density distributions, one based on analytical fits to the halos formed in the EAGLE simulation and two density distributions (Singular Isothermal Sphere (SIS) and SISSA) that have been used before in lensing studies. We found that we could reproduce the observed distribution with all three density distributions, as long as we imposed an upper mass transition of $\sim$$10^{13} M_{\odot}$ for the SIS and SISSA models, above which we assumed that the density distribution could be represented by an NFW profile. We show that we would need a sample of $\sim$500 lensed sources to distinguish between the density distributions, which is practical given the predicted number of lensed sources in the Herschel surveys., Comment: 14 pages, 7 figures, accepted for publication in MNRAS

We perform lens modelling and source reconstruction of Submillimeter Array (SMA) data for a sample of 12 strongly lensed galaxies selected at 500$\mu$m in the Herschel Astrophysical Terahertz Large Area Survey H-ATLAS. A previous analysis of the same dataset used a single S\`ersic profile to model the light distribution of each background galaxy. Here we model the source brightness distribution with an adaptive pixel scale scheme, extended to work in the Fourier visibility space of interferometry. We also present new SMA observations for seven other candidate lensed galaxies from the H-ATLAS sample. Our derived lens model parameters are in general consistent with previous findings. However, our estimated magnification factors, ranging from 3 to 10, are lower. The discrepancies are observed in particular where the reconstructed source hints at the presence of multiple knots of emission. We define an effective radius of the reconstructed sources based on the area in the source plane where emission is detected above 5$\sigma$. We also fit the reconstructed source surface brightness with an elliptical Gaussian model. We derive a median value $r_{eff}\,\sim 1.77\,$kpc and a median Gaussian full width at half maximum $\sim1.47\,$kpc. After correction for magnification, our sources have intrinsic star formation rates SFR$\,\sim900-3500\,M_{\odot}yr^{-1}$, resulting in a median star formation rate surface density $\Sigma_{SFR}\sim132\,M_{\odot}$ yr$^{-1}$ kpc$^{-2}$ (or $\sim 218\,M_{\odot}$ yr$^{-1}$ kpc$^{-2}$ for the Gaussian fit). This is consistent with what observed for other star forming galaxies at similar redshifts, and is significantly below the Eddington limit for a radiation pressure regulated starburst., Comment: 19 pages, 8 figures, accepted for publication in MNRAS

We use a sample of 4178 Lyman break galaxies (LBGs) at z = 3, 4 and 5 in the UKIRT Infrared Deep Sky Survey (UKIDSS) Ultra Deep Survey (UDS) field to investigate the relationship between the observed slope of the stellar continuum emission in the ultraviolet, {\beta}, and the thermal dust emission, as quantified via the so-called 'infrared excess' (IRX = LIR/LUV). Through a stacking analysis we directly measure the 850-{\mu}m flux density of LBGs in our deep (0.9mJy) James Clerk Maxwell Telescope (JCMT) SCUBA-2 850-{\mu}m map, as well as deep public Herschel/SPIRE 250-, 350- and 500-{\mu}m imaging. We establish functional forms for the IRX-{\beta} relation to z ~ 5, confirming that there is no significant redshift evolution of the relation and that the resulting average IRX-{\beta} curve is consistent with a Calzetti-like attenuation law. We compare our results with recent work in the literature, finding that discrepancies in the slope of the IRX-{\beta} relation are driven by biases in the methodology used to determine the ultraviolet slopes. Consistent results are found when IRX-{\beta} is evaluated by stacking in bins of stellar mass, M, and we argue that the near-linear IRX-M relationship is a better proxy for correcting observed UV luminosities to total star formation rates, provided an accurate handle on M can be had, and also gives clues as to the physical driver of the role of dust-obscured star formation in high-redshift galaxies., Comment: 12 pages, 10 figures, submitted to MNRAS

By determining the nature of all the Planck compact sources within 808.4 deg^2 of large Herschel surveys, we have identified 27 candidate proto-clusters of dusty star forming galaxies (DSFGs) that are at least 3{\sigma} overdense in either 250, 350 or 500 $\mu$mm sources. We find roughly half of all the Planck compact sources are resolved by Herschel into multiple discrete objects, with the other half remaining unresolved by Herschel. We find a significant difference between versions of the Planck catalogues, with earlier releases hosting a larger fraction of candidate proto-clusters and Galactic Cirrus than later releases, which we ascribe to a difference in the filters used in the creation of the three catalogues. We find a surface density of DSFG candidate proto-clusters of (3.3 $\pm$ 0.7) x 10^(-2) sources deg^(-2), in good agreement with previous similar studies. We find that a Planck colour selection of S_{857}/S_{545} < 2 works well to select candidate proto-clusters, but can miss proto-clusters at z < 2. The Herschel colours of individual candidate proto-cluster members indicate our candidate proto-clusters all likely all lie at z > 1. Our candidate proto-clusters are a factor of 5 times brighter at 353 GHz than expected from simulations, even in the most conservative estimates. Further observations are needed to confirm whether these candidate proto-clusters are physical clusters, multiple proto-clusters along the line of sight, or chance alignments of unassociated sources., Comment: Resubmitted to MNRAS after request for minor revision

Ultra-faint galaxies are hosted by small dark matter halos with shallow gravitational potential wells, hence their star formation activity is more sensitive to feedback effects. The shape of the faint-end of the high-$z$ galaxy luminosity function (LF) contains important information on star formation and its interaction with the reionization process during the Epoch of Reionization (EoR). High-$z$ galaxies with $M_{\rm UV}\gtrsim-17$ have only recently become accessible thanks to the Frontier Fields (FFs) survey combining deep {\it HST} imaging and the gravitational lensing effect. In this paper we investigate the faint-end of the LF at redshift $>$5 using the data of FFs clusters Abell 2744 (A2744), MACSJ0416.1-2403 (M0416), MACSJ0717.5+3745 (M0717) and MACSJ1149.5+2223 (M1149). We analyze both an empirical and a physically-motivated LF model to obtain constraints on a possible turn-over of LF at faint magnitudes. In the empirical model the LF drops fast when the absolute UV magnitude $M_{\rm UV}$ is much larger than a turn-over absolute UV magnitude $M_{\rm UV}^{\rm T}$. We obtain $M_{\rm UV}^{\rm T}\gtrsim-14.6 $ (15.2) at 1 (2) $\sigma$ confidence level (C.L.) for $z\sim6$. In the physically-motivated analytical model, star formation in halos with circular velocity below $v_c^*$ is fully quenched if these halos are located in ionized regions. Using updated lensing models and new additional FFs data, we re-analyze previous constraints on $v_c^*$ and $f_{\rm esc}$ presented by Castellano et al. 2016a (C16a) using a smaller dataset. We obtain new constraints on $v_c^*\lesssim 59$ km s$^{-1}$ and $f_{\rm esc}\lesssim 56\%$ (both at 2$\sigma$ C.L.) and conclude that there is no turn-over detected so far from the analyzed FFs data. Forthcoming {\it JWST} observations will be key to tight these constraints further., Comment: 16 pages, 7 figures, 3 tables; accepted for publication by ApJ

We studied the molecular gas properties of AzTEC/C159, a star-forming disk galaxy at $z=4.567$. We secured $^{12}$CO molecular line detections for the $J=2\to1$ and $J=5\to4$ transitions using the Karl G. Jansky VLA and the NOEMA interferometer. The broad (FWHM$\sim750\,{\rm km\,s}^{-1}$) and tentative double-peaked profiles of both $^{12}$CO lines are consistent with an extended molecular gas reservoir, which is distributed in a rotating disk as previously revealed from [CII] 158$\mu$m line observations. Based on the $^{12}$CO(2$\to$1) emission line we derived $L'_{\rm{CO}}=(3.4\pm0.6)\times10^{10}{\rm \,K\,km\,s}^{-1}{\rm \,pc}^{2}$, that yields a molecular gas mass of $M_{\rm H_2 }(\alpha_{\rm CO}/4.3)=(1.5\pm0.3)\times 10^{11}{\rm M}_\odot$ and unveils a gas-rich system with $\mu_{\rm gas}(\alpha_{\rm CO}/4.3)\equiv M_{\rm H_2}/M_\star=3.3\pm0.7$. The extreme star formation efficiency (SFE) of AzTEC/C159, parametrized by the ratio $L_{\rm{IR}}/L'_{\rm{CO}}=(216\pm80)\, {\rm L}_{\odot}{\rm \,(K\,km\,s}^{-1}{\rm \,pc}^{2})^{-1}$, is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies (ULIRGs) and SMGs. Likewise, the $^{12}$CO(5$\to$4)/CO(2$\to$1) line brightness temperature ratio of $r_{52}= 0.55\pm 0.15$ is consistent with high excitation conditions, similar to that observed in SMGs. We constrained the value for the $L'_{\text{CO}}-{\rm H}_2$ mass conversion factor in AzTEC/C159, i.e. $\alpha_{\text{CO}}=3.9^{+2.7}_{-1.3}{\rm \,M}_{\odot}{\rm \,K}^{-1}{\rm \,km}^{-1}{\rm \,s\,pc}^{-2}$, that is consistent with a self-gravitating molecular gas distribution as observed in local star-forming disk galaxies. Cold gas streams from cosmological filaments might be fueling a gravitationally unstable gas-rich disk in AzTEC/C159, which breaks into giant clumps forming stars as efficiently as in merger-driven systems and generate high gas excitation., Comment: 10 pages, 4 figures, Accepted for publication in A&A

We present the results of a new study of the relationship between infrared excess (IRX), UV spectral slope (beta) and stellar mass at redshifts 2= 9.75, both the IRX-beta and IRX-mass relations are well described by a Calzetti-like attenuation law., Comment: 17 pages, 7 figures, accepted version to be published in MNRAS

(abridged) We present the IRAM-30m observations of multiple-J CO and CI line emission in a sample of redshift ~2-4 Herschel-ATLAS SMGs. A non-negligible effect of differential lensing is found for the CO emission lines, which could have caused significant underestimations of the linewidths, hence of the dynamical masses. The CO SLEDs are found to be similar to those of the local starburst-dominated ULIRGs and of the previously studied SMGs. After correcting for lensing amplification, we derived the global properties of the bulk of molecular gas in the SMGs using non-LTE radiative transfer modelling. The gas thermal pressure is found to be correlated with star formation efficiency. Further decomposing the CO SLEDs into two excitation components, we find a low-excitation component, which is less correlated with star formation, and a high-excitation one which is tightly related to the on-going star-forming activity. Additionally, tight linear correlations between the FIR and CO line luminosities have been confirmed for the $J \ge 5$ CO lines, implying that these CO lines are good tracers of star formation. The [CI](2-1) lines follow the tight linear correlation between the luminosities of the [CI](2-1) and the CO(1-0) line found in local starbursts, indicating that CI lines could serve as good total molecular gas mass tracers for high-redshift SMGs. The total mass of the molecular gas reservoir, $(1-30) \times 10^{10} M_\odot$, suggests a typical molecular gas depletion time ~20-100 Myr and a gas to dust mass ratio ${\delta}_{\rm GDR}$~30-100. The ratio between CO line luminosity and the dust mass appears to be slowly increasing with redshift for the SMGs, which need to be further confirmed. Finally, through comparing the linewidth of CO and H2O lines, we find that they agree well in almost all our SMGs, confirming that the emitting regions are co-spatially located., Comment: A&A in press, 22 pages plus 20 pages of appendix (1 long table plus figures), 13 figures and 7 tables in main text; minor edits