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SKA-MID surveys will be the first in the radio domain to achieve clearly sub-arcsecond resolution at high sensitivity over large areas, opening new science applications for galaxy evolution. To investigate the potential of these surveys, we create simulated SKA-MID images of a ∼0.04 deg2 region of GOODS-North, constructed using multi-band HST imaging of 1723 real galaxies containing significant substructure at 0 < z < 2.5. We create images at the proposed depths of the band 2 wide, deep, and ultradeep reference surveys (RMS = 1.0, 0.2, and 0.05 μJy over 1000, 10–30, and 1 deg2, respectively), using the telescope response of SKA-MID at 0.6 arcsec resolution. We quantify the star formation rate – stellar mass space the surveys will probe, and asses to which stellar masses the surveys will be complete. We measure galaxy flux density, half-light radius (R 50), concentration, Gini (distribution of flux), second-order moment of the brightest pixels (M 20), and asymmetry before and after simulation with the SKA response, to perform input-output tests as a function of depth, separating the effects of convolution and noise. We find that the recovery of Gini and asymmetry is more dependent on survey depth than for R 50, concentration and M 20. We also assess the relative ranking of parameters before and after observation with SKA-MID. R 50 best retains its ranking, while asymmetries are poorly recovered. We confirm that the wide tier will be suited to the study of highly star-forming galaxies across different environments, whilst the ultradeep tier will enable detailed morphological analysis to lower SFRs. [ABSTRACT FROM AUTHOR]

We present CEERS JWST/NIRCam imaging of a massive galaxy group at z = 1.85, to explore the early JWST view on massive group formation in the distant Universe. The group contains ≳16 members (including six spectroscopic confirmations) down to log10(M⋆/M⊙) = 8.5, including the brightest group galaxy (BGG) in the process of actively assembling at this redshift. The BGG is comprised of multiple merging components extending ∼3.6″ (30 kpc) across the sky. The BGG contributes 69% of the group's total galactic stellar mass, with one of the merging components containing 76% of the total mass of the BGG and a star formation rate > 1810 M⊙ yr−1. Most importantly, we detected intra-halo light (IHL) in several HST and JWST/NIRCam bands, allowing us to construct a state-of-the-art rest-frame UV-NIR spectral energy distribution of the IHL for the first time at this high redshift. This allows stellar population characterisation of both the IHL and member galaxies, as well as the morphology distribution of group galaxies versus their star formation activity when coupled with Herschel data. We created a stacked image of the IHL, giving us a sensitivity to extended emission of 28.5 mag arcsec−2 at rest-frame 1 μm. We find that the IHL is extremely dust poor (Av ∼ 0), containing an evolved stellar population of log10(t50/yr) = 8.8, corresponding to a formation epoch for 50% of the stellar material 0.63 Gyr before z = 1.85. There is no evidence of ongoing star formation in the IHL. The IHL in this group at z = 1.85 contributes ∼10% of the total stellar mass, comparable with what is observed in local clusters. This suggests that the evolution of the IHL fraction is more self-similar with redshift than predicted by some models, challenging our understanding of IHL formation during the assembly of high-redshift clusters. JWST is unveiling a new side of group formation at this redshift, which will evolve into Virgo-like structures in the local Universe. [ABSTRACT FROM AUTHOR]

We present NOEMA CO (2–1) line and ALMA 870 µm continuum observations of a main-sequence galaxy at z = 1.38. The galaxy was initially deemed a "gas giant" based on the gas mass derived from sub-mm continuum (log(Mgas/M⊙) = 11.20 ± 0.20), however, the gas mass derived from CO (2−1) luminosity brings the gas mass value down to a level that is consistent with typical values for star-forming galaxies at that redshift (log(Mgas/M⊙) = 10.84 ± 0.03). Meanwhile, the dust-to-stellar mass ratio remains elevated above the scaling relations by a factor of 5. In this work, we explore the potential physical picture and consider an underestimated stellar mass and optically thick dust as possible explanations. Based on the updated gas-to-stellar mass ratio, we can rule out the former; while the latter may indeed contribute to the overestimation of the dust mass, it is not sufficient enough to explain the observed physical picture overall. Instead, other plausible explanations include enhanced HI reservoirs, an unusually high metallicity, or the presence of an optically dark, dusty contaminant. Using the ALMA data at 870 µm coupled with HST/ACS imaging, we find an extended morphology in dust continuum and clumpy star-formation in rest-frame UV in this galaxy. In addition, a tentative ~10 kpc dusty arm is found to be bridging the galaxy center and a clump in F814W image. The galaxy shows levels of dust obscuration similar to the so-called HST-dark galaxies at higher redshifts, thus falling into the optically faint and dark JWST color-color selection at z > 2. It is therefore possible that our object may stand as a low-z analog of the HST-dark populations. This galaxy serves as a caveat to the gas masses based on the continuum alone, with a larger sample required to unveil the full picture. [ABSTRACT FROM AUTHOR]

We study stellar population and structural properties of massive log (M ⋆/ M ⊙) > 11 galaxies at z ≈ 2.7 in the Magneticum and IllustrisTNG hydrodynamical simulations and GAEA semi-analytic model. We find stellar mass functions broadly consistent with observations, with no scarcity of massive, quiescent galaxies at z ≈ 2.7, but with a higher quiescent galaxy fraction at high masses in IllustrisTNG. Average ages of simulated quiescent galaxies are between ≈0.8 and |${1.0\, \textrm {Gyr}}$|⁠ , older by a factor ≈2 than observed in spectroscopically confirmed quiescent galaxies at similar redshift. Besides being potentially indicative of limitations of simulations in reproducing observed star formation histories, this discrepancy may also reflect limitations in the estimation of observed ages. We investigate the purity of simulated UVJ rest-frame colour-selected massive quiescent samples with photometric uncertainties typical of deep surveys (e.g. COSMOS). We find evidence for significant contamination (up to |${60\, \rm {per\, cent}}$|⁠) by dusty star-forming galaxies in the UVJ region that is typically populated by older quiescent sources. Furthermore, the completeness of UVJ-selected quiescent samples at this redshift may be reduced by |$\approx {30\, \rm {per\, cent}}$| due to a high fraction of young quiescent galaxies not entering the UVJ quiescent region. Massive, quiescent galaxies in simulations have on average lower angular momenta and higher projected axis ratios and concentrations than star-forming counterparts. Average sizes of simulated quiescent galaxies are broadly consistent with observations within the uncertainties. The average size ratio of quiescent and star-forming galaxies in the probed mass range is formally consistent with observations, although this result is partly affected by poor statistics. [ABSTRACT FROM AUTHOR]

The origin of the quenching in galaxies is still highly debated. Different scenarios and processes are proposed. We use multiband (400–1600 nm) bulge–disc decompositions of massive galaxies in the redshift range 0 < z < 2 to explore the distribution and the evolution of galaxies in the |$\log \, {\rm SFR-log}\: M_{*}$| plane as a function of the stellar mass weighted bulge-to-total ratio (⁠|$B/T_{M_{*}}$|⁠) and also for internal galaxy components (bulge/disc) separately. We find evidence of a clear link between the presence of a bulge and the flattening of the main sequence in the high-mass end. All bulgeless galaxies (⁠|$B/T_{M_{*}}$| < 0.2) lie on the main sequence, and there is little evidence of a quenching channel without bulge growth. Galaxies with a significant bulge component (⁠|$B/T_{M_{*}}$| > 0.2) are equally distributed in number between star forming and passive regions. The vast majority of bulges in the main-sequence galaxies are quiescent, while star formation is localized in the disc component. Our current findings underline a strong correlation between the presence of the bulge and the star formation state of the galaxy. A bulge, if present, is often quiescent, independently of the morphology or the star formation activity of the host galaxy. Additionally, if a galaxy is quiescent, with a large probability, is hosting a bulge. Conversely, if the galaxy has a discy shape is highly probable to be star forming. [ABSTRACT FROM AUTHOR]

We measure the relationship between stellar mass and stellar metallicity for 1336 star-forming galaxies at 1.6 ≤ z ≤ 3.0 using rest-frame far-ultraviolet spectra from the zCOSMOS-deep survey. High signal-to-noise ratio composite spectra containing stellar absorption features are fit with stellar population synthesis model spectra of a range of stellar metallicity. We find stellar metallicities, which mostly reflect instantaneous iron abundances, scaling as [ Fe / H ] = âˆ' (0.81 ± 0.01) + (0.32 + 0.03) log (M * / 10 10 M ⊙) across the stellar mass range of 109 ≲ M */ M ⊙ ≲ 1011. The instantaneous oxygen-to-iron ratio (α -enhancement) inferred using the gas-phase massâ€"metallicity relation is on average found to be O / Fe ≈ 0.47 , being higher than the local O / Fe ≈ 0. The observed changes in [O/Fe] and [Fe/H] are reproduced in simple gas-regulator models with steady star formation histories. Our models show that the [O/Fe] is determined almost entirely by the instantaneous specific star formation rate alone while being independent of the mass and the characteristic of the gas regulation. We also find that the locations of ∼ 1010 M ⊙ galaxies at z ∼ 2 in the [O/Fe]â€"metallicity planes are in remarkable agreement with the sequence of low-metallicity thick-disk stars in our own Galaxy. This manifests a beautiful concordance between the results of Galactic archeology and observations of high-redshift Milky Way progenitors. There remains, however, a question of how and when the old metal-rich, low α /Fe stars seen in the bulge had formed by z ∼ 2 because such a stellar population is not seen in our data and is difficult to explain in the context of our models. [ABSTRACT FROM AUTHOR]

We present a comparative study of X-ray and IR active galactic nuclei (AGNs) at z ≈ 2 to highlight the important AGN selection effects on the distributions of host-galaxy properties. Compared with non-AGN star-forming galaxies (SFGs) on the main sequence, X-ray AGNs have similar median star formation (SF) properties, but their incidence (q AGN) is higher among galaxies with either enhanced or suppressed SF, and among galaxies with a larger stellar-mass surface density, regardless if it is measured within the half-light radius (Σ e ) or central 1 kpc (Σ1kpc). Unlike X-ray AGNs, IR AGNs are less massive and have enhanced SF and similar distributions of colors, Σ e and Σ1kpc, relative to non-AGN SFGs. Given that Σ e and Σ1kpc strongly correlate with M *, we introduce the fractional mass within the central 1 kpc ( M 1 kpc / M ∗ ), which only weakly depends on M *, to quantify galaxy compactness. Both AGN populations have similar M 1 kpc / M ∗ distributions compared to non-AGN SFGs’. While q AGN increases with Σ e and Σ1kpc, it remains constant with M 1 kpc / M ∗ , indicating that the trend of increasing q AGN with Σ is driven by M * more than morphology. While our findings are not in conflict with the scenario of AGN quenching, they do not imply it either, because the incidence of AGNs hosted in transitional galaxies depends crucially on AGN selections. Additionally, despite the relatively large uncertainty of AGN bolometric luminosities, their very weak correlation, if any, with SF activities, regardless of AGN selections, also argues against a direct causal link between the presence of AGNs and the quenching of massive galaxies at z ∼ 2. [ABSTRACT FROM AUTHOR]

Radio free–free emission is considered to be one of the most reliable tracers of star formation in galaxies. However, as it constitutes the faintest part of the radio spectrum—being roughly an order of magnitude less luminous than radio synchrotron emission at the GHz frequencies typically targeted in radio surveys—the usage of free–free emission as a star formation rate tracer has mostly remained limited to the local universe. Here, we perform a multifrequency radio stacking analysis using deep Karl G. Jansky Very Large Array observations at 1.4, 3, 5, 10, and 34 GHz in the COSMOS and GOODS-North fields to probe free–free emission in typical galaxies at the peak of cosmic star formation. We find that z ∼ 0.5–3 star-forming galaxies exhibit radio emission at rest-frame frequencies of ∼65–90 GHz that is ∼1.5–2 times fainter than would be expected from a simple combination of free–free and synchrotron emission, as in the prototypical starburst galaxy M82. We interpret this as a deficit in high-frequency synchrotron emission, while the level of free–free emission is as expected from M82. We additionally provide the first constraints on the cosmic star formation history using free–free emission at 0.5 ≲ z ≲ 3, which are in good agreement with more established tracers at high redshift. In the future, deep multifrequency radio surveys will be crucial in order to accurately determine the shape of the radio spectrum of faint star-forming galaxies, and to further establish radio free–free emission as a tracer of high-redshift star formation. [ABSTRACT FROM AUTHOR]

In Dou et al., we introduced the fundamental formation relation (FFR), a tight relation between specific star formation rate (sSFR), H2 star formation efficiency (SFE), and the ratio of H2 to stellar mass. Here, we show that atomic gas H ɪ does not follow a similar FFR as H2. The relation between SFEHɪ and sSFR shows significant scatter and strong systematic dependence on all of the key galaxy properties that we have explored. The dramatic difference between H ɪ and H2 indicates that different processes (e.g., quenching by different mechanisms) may have very different effects on H ɪ in different galaxies and hence produce different SFEHɪ–sSFR relations, while the SFE –sSFR relation remains unaffected. The fact that the SFE –sSFR relation is independent of other key galaxy properties, and that sSFR is directly related to the cosmic time and acts as the cosmic clock, make it natural and very simple to study how different galaxy populations (with different properties and undergoing different processes) evolve on the same SFE –sSFR ∼ t relation. In the gas regulator model (GRM), the evolution of a galaxy on the SFE –sSFR(t) relation is uniquely set by a single mass-loading parameter. This simplicity allows us to accurately derive the H2 supply and removal rates of the local galaxy populations with different stellar masses, from star-forming galaxies to the galaxies in the process of being quenched. This combination of FFR and GRM, together with the stellar metallicity requirement, provide a new powerful tool to study galaxy formation and evolution. [ABSTRACT FROM AUTHOR]

Infrared quasi-stellar objects (IR QSOs) are a rare subpopulation selected from ultraluminous infrared galaxies (ULIRGs) and have been regarded as promising candidates of ULIRG-to-optical QSO transition objects. Here we present NOEMA observations of the CO (1−0) line and 3 mm continuum emission in IR QSO IRAS F07599+6508 at z = 0.1486, which has many properties in common with Mrk 231. The CO emission is found to be resolved with a major axis of ∼6.1 kpc that is larger than the size of ∼4.0 kpc derived for 3 mm continuum. We identify two faint CO features located at a projected distance of ∼11.4 and 19.1 kpc from the galaxy nucleus, both of which are found to have counterparts in the optical and radio bands and may have a merger origin. A systematic velocity gradient is found in the CO main component, suggesting that the bulk of molecular gas is likely rotationally supported. Based on the radio-to-millimeter spectral energy distribution and IR data, we estimate that about 30% of the flux at 3 mm arises from free–free emission and infer a free–free-derived star formation rate of 77 M⊙ yr−1, close to the IR estimate corrected for the AGN contribution. We find a high-velocity CO emission feature at the velocity range of about −1300 to −2000 km s−1. Additional deep CO observations are needed to confirm the presence of a possible very high velocity CO extension of the OH outflow in this IR QSO. [ABSTRACT FROM AUTHOR]

We report the detection of multiple faint radio sources, that we identify as active galactic nucleus (AGN) jets, within CLJ1449+0856 at z  = 2 using 3 GHz Very Large Array observations. We study the effects of radio-jet-based kinetic feedback at high redshifts, which has been found to be crucial in low-redshift clusters to explain the observed thermodynamic properties of their intracluster medium (ICM). We investigate this interaction at an epoch featuring high levels of AGN activity and a transitional phase of ICM in regards to the likelihood of residual cold gas accretion. We measure a total flux of |$\rm 30.6 \pm 3.3\, \mu Jy$| from the six detected jets. Their power contribution is estimated to be |$1.2 \, (\pm 0.6)\, \times 10^{44} \, \rm erg\, s^{-1}$|⁠ , although this value could be up to |$4.7 \, \times 10^{44} \, \rm erg\, s^{-1}$|⁠. This is a factor of ∼0.25–1.0 of the previously estimated instantaneous energy injection into the ICM of CLJ1449+0856 from AGN outflows and star formation that have already been found to be sufficient in globally offsetting the cooling flows in the cluster core. In line with the already detected abundance of star formation, this mode of feedback being distributed over multiple sites, contrary to a single central source observed at low redshifts, points to accretion of gas into the cluster centre. This also suggests a 'steady state' of the cluster featuring non-cool-core-like behaviour. Finally, we also examine the total infrared–radio luminosity ratio for the known sample of galaxies within the cluster core and find that dense environments do not have any serious consequence on the compliance of galaxies to the infrared–radio correlation. [ABSTRACT FROM AUTHOR]

Star formation and quenching are two of the most important processes in galaxy formation and evolution. We explore in the local universe the interrelationships among key integrated galaxy properties, including stellar mass M*, star formation rate (SFR), specific SFR (sSFR), molecular gas mass , star formation efficiency (SFE) of the molecular gas, and the molecular gas to stellar mass ratio μ. We aim to identify the most fundamental scaling relations among these key galaxy properties and their interrelationships. We show that the integrated –SFR, SFR–M*, and –M* relations can be simply transformed from the μ–sSFR, SFE–μ, and SFE–sSFR relations, respectively. The transformation, in principle, can increase or decrease the scatter of each relation. Interestingly, we find that the latter three relations all have significantly smaller scatter than the corresponding former three. We show that the probability to achieve the observed small scatter by accident is extremely close to zero. This suggests that the smaller scatters of the latter three relations are driven by a more universal physical connection among these quantities. We then show that the large scatters in the former relations are due to their systematic dependence on other galaxy properties, and on the star formation and quenching process. We propose the sSFR–μ–SFE relation as the fundamental formation relation (FFR), which governs the star formation and quenching process and provides a simple framework to study galaxy evolution. Other scaling relations, including the integrated Kennicutt–Schmidt law, star-forming main sequence, and molecular gas main sequence, can all be derived from the FFR. [ABSTRACT FROM AUTHOR]

We make use of sensitive (9.3 μJy beam−1 rms) 1.2 mm continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra-Deep Field (ASPECS) large program to probe dust-enshrouded star formation from 1362 Lyman-break galaxies spanning the redshift range z = 1.5–10 (to ∼7–28 M⊙ yr−1 at 4σ over the entire range). We find that the fraction of ALMA-detected galaxies in our z = 1.5–10 samples increases steeply with stellar mass, with the detection fraction rising from 0% at 109.0M⊙ to % at >1010M⊙. Moreover, on stacking all 1253 low-mass (<109.25M⊙) galaxies over the ASPECS footprint, we find a mean continuum flux of −0.1 ± 0.4 μJy beam−1, implying a hard upper limit on the obscured star formation rate of <0.6 M⊙ yr−1 (4σ) in a typical low-mass galaxy. The correlation between the infrared excess (IRX) of UV-selected galaxies (LIR/LUV) and the UV-continuum slope is also seen in our ASPECS data and shows consistency with a Calzetti-like relation at > and an SMC-like relation at lower masses. Using stellar mass and β measurements for z ∼ 2 galaxies over the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we derive a new empirical relation between β and stellar mass and then use this correlation to show that our IRX–β and IRX–stellar mass relations are consistent with each other. We then use these constraints to express the IRX as a bivariate function of β and stellar mass. Finally, we present updated estimates of star formation rate density determinations at z > 3, leveraging present improvements in the measured IRX and recent probes of ultraluminous far-IR galaxies at z > 2. [ABSTRACT FROM AUTHOR]

We present a CO and atomic fine-structure line-luminosity function analysis using the ALMA Spectroscopic Survey (ASPECS) in the Hubble Ultra Deep Field. ASPECS consists of two spatially overlapping mosaics that cover the entire ALMA 3 mm and 1.2 mm bands. We combine the results of a line-candidate search of the 1.2 mm data cube with those previously obtained from the 3 mm cube. Our analysis shows that ∼80% of the line flux observed at 3 mm arises from CO(2–1) or CO(3–2) emitters at z = 1–3 ("cosmic noon"). At 1.2 mm, more than half of the line flux arises from intermediate-J CO transitions (Jup = 3–6); ∼12% from neutral carbon lines; and <1% from singly ionized carbon, [C ii ]. This implies that future [C ii ] intensity mapping surveys in the epoch of reionization will need to account for a highly significant CO foreground. The CO luminosity functions probed at 1.2 mm show a decrease in the number density at a given line luminosity (in units of L′) at increasing Jup and redshift. Comparisons between the CO luminosity functions for different CO transitions at a fixed redshift reveal subthermal conditions on average in galaxies up to z ∼ 4. In addition, the comparison of the CO luminosity functions for the same transition at different redshifts reveals that the evolution is not driven by excitation. The cosmic density of molecular gas in galaxies, ρH2, shows a redshift evolution with an increase from high redshift up to z ∼ 1.5 followed by a factor ∼6 drop down to the present day. This is in qualitative agreement with the evolution of the cosmic star formation rate density, suggesting that the molecular gas depletion time is approximately constant with redshift, after averaging over the star-forming galaxy population. [ABSTRACT FROM AUTHOR]

We present a characterization of the physical properties of a sample of 35 securely detected, dusty galaxies in the deep ALMA 1.2 mm image obtained as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Large Program. This sample is complemented by 26 additional sources identified via an optical/infrared source positional prior. Using their well-characterized spectral energy distributions, we derive median stellar masses and star formation rates (SFR) of and 30 M☉ yr−1, respectively, and interquartile ranges of (2.4–11.7) × 1010 M☉ and 20–50 M☉ yr−1. We derive a median spectroscopic redshift of 1.8 with an interquartile range 1.1–2.6, significantly lower than submillimeter galaxies detected in shallower, wide-field surveys. We find that 59% ± 13%, 6% ± 4%, and 34% ± 9% of our sources are within, above, and below±0.4 dex from the SFR–stellar-mass relation or main sequence (MS), respectively. The ASPECS galaxies closely follow the SFR–molecular gas mass relation and other previously established scaling relations, confirming a factor of five increase of the gas-to-stellar-mass ratio from z = 0.5 to 2.5 and a mild evolution of the gas depletion timescales with a typical value of 0.7 Gyr at z = 1–3. ASPECS galaxies located significantly below the MS, a poorly exploited parameter space, have low gas-to-stellar-mass ratios of ∼0.1–0.2 and long depletion timescales >1 Gyr. Galaxies along the MS dominate the cosmic density of molecular gas at all redshifts. Systems above the MS have an increasing contribution to the total gas reservoirs from z < 1 to z = 2.5, while the opposite is found for galaxies below the MS. [ABSTRACT FROM AUTHOR]

We present the hitherto largest sample of gas-phase metallicity radial gradients measured at sub-kpc resolution in star-forming galaxies in the redshift range of z ∈ [1.2, 2.3]. These measurements are enabled by the synergy of slitless spectroscopy from the Hubble Space Telescope near-infrared channels and the lensing magnification from foreground galaxy clusters. Our sample consists of 76 galaxies with stellar mass ranging from 107 to 1010 , an instantaneous star formation rate in the range of [1, 100] yr−1, and global metallicity of solar. At a 2σ confidence level, 15/76 galaxies in our sample show negative radial gradients, whereas 7/76 show inverted gradients. Combining ours and all other metallicity gradients obtained at a similar resolution currently available in the literature, we measure a negative mass dependence of Δlog(O/H)/ = (−0.020 ± 0.007) + (−0.016 ± 0.008) , with the intrinsic scatter being σ = 0.060 ± 0.006 over 4 orders of magnitude in stellar mass. Our result is consistent with strong feedback, not secular processes, being the primary governor of the chemostructural evolution of star-forming galaxies during the disk mass assembly at cosmic noon. We also find that the intrinsic scatter of metallicity gradients increases with decreasing stellar mass and increasing specific star formation rate. This increase in the intrinsic scatter is likely caused by the combined effect of cold-mode gas accretion and merger-induced starbursts, with the latter more predominant in the dwarf mass regime of. [ABSTRACT FROM AUTHOR]

We report the detection of CO(J = 2 → 1) emission from three massive dusty starburst galaxies at z > 5 through molecular line scans in the NSF's Karl G. Jansky Very Large Array (VLA) CO Luminosity Density at High Redshift (COLDz) survey. Redshifts for two of the sources, HDF 850.1 (z = 5.183) and AzTEC-3 (z = 5.298), were previously known. We revise a previous redshift estimate for the third source GN10 (z = 5.303), which we have independently confirmed through detections of CO J = 1 → 0, 5 → 4, 6 → 5, and [C ii ] 158 μm emission with the VLA and the NOrthern Extended Milllimeter Array. We find that two currently independently confirmed CO sources in COLDz are "optically dark", and that three of them are dust-obscured galaxies at z > 5. Given our survey area of ∼60 arcmin2, our results appear to imply a ∼6–55 times higher space density of such distant dusty systems within the first billion years after the Big Bang than previously thought. At least two of these z > 5 galaxies show star formation rate surface densities consistent with so-called "maximum" starbursts, but we find significant differences in CO excitation between them. This result may suggest that different fractions of the massive gas reservoirs are located in the dense, star-forming nuclear regions—consistent with the more extended sizes of the [C ii ] emission compared to the dust continuum and higher [C ii ]-to-far-infrared luminosity ratios in those galaxies with lower gas excitation. We thus find substantial variations in the conditions for star formation between z > 5 dusty starbursts, which typically have dust temperatures that are ∼57% ± 25% warmer than starbursts at z = 2–3 due to their enhanced star formation activity. [ABSTRACT FROM AUTHOR]

We study the rest-frame optical mass–size relation of bulges and discs from z ∼ 2 to z ∼ 0 for a complete sample of massive galaxies in the CANDELS fields using two-component Sérsic models. Discs and star-forming galaxies follow similar mass–size relations. The mass–size relation of bulges is less steep than the one of quiescent galaxies (best-fitting slope of 0.7 for quiescent galaxies against 0.4 for bulges). We find little dependence of the structural properties of massive bulges and discs with the global morphology of galaxies (disc versus bulge dominated) and the star formation activity (star-forming versus quiescent). This result suggests similar bulge formation mechanisms for most massive galaxies and also that the formation of the bulge component does not significantly affect the disc structure. Our results pose a challenge to current cosmological models that predict distinct structural properties for stellar bulges arising from mergers and disc instabilities. [ABSTRACT FROM AUTHOR]

We investigate the nature of star-forming galaxies with reduced specific star formation rate (sSFR) and high stellar masses, those 'green valley' objects that seemingly cause a reported bending, or flattening, of the star-forming main sequence. The fact that such objects host large bulges recently led some to suggest that the internal formation of bulges was a late event that induced the sSFRs of massive galaxies to drop in a slow downfall, and thus the main sequence to bend. We have studied in detail a sample of 10 galaxies at 0.45 < z < 1 with secure SFR from Herschel, deep Keck optical spectroscopy, and HST imaging from CANDELS allowing us to perform multiwavelength bulge to disc decomposition, and to derive star formation histories for the separated bulge and disc components. We find that the bulges hosted in these systems below main sequence are virtually all maximally old, with ages approaching the age of the Universe at the time of observation, while discs are young (〈 T 50〉 ∼ 1.5 Gyr). We conclude that, at least based on our sample, the bending of the main sequence is, for a major part, due to rejuvenation, and we disfavour mechanisms that postulate the internal formation of bulges at late times. The very old stellar ages of our bulges suggest a number density of early-type galaxies at z  = 1–3 higher than actually observed. If confirmed, this might represent one of the first direct validations of hierarchical assembly of bulges at high redshifts. [ABSTRACT FROM AUTHOR]

Follow-up observations at high-angular resolution of bright submillimeter galaxies selected from deep extragalactic surveys have shown that the single-dish sources are comprised of a blend of several galaxies. Consequently, number counts derived from low- and high-angular-resolution observations are in tension. This demonstrates the importance of resolution effects at these wavelengths and the need for realistic simulations to explore them. We built a new 2 deg2 simulation of the extragalactic sky from the far-infrared to the submillimeter. It is based on an updated version of the 2SFM (two star-formation modes) galaxy evolution model. Using global galaxy properties generated by this model, we used an abundance-matching technique to populate a dark-matter lightcone and thus simulate the clustering. We produced maps from this simulation and extracted the sources, and we show that the limited angular resolution of single-dish instruments has a strong impact on (sub)millimeter continuum observations. Taking into account these resolution effects, we are reproducing a large set of observables, as number counts and their evolution with redshift and cosmic infrared background power spectra. Our simulation consistently describes the number counts from single-dish telescopes and interferometers. In particular, at 350 and 500 μm, we find that the number counts measured by Herschel between 5 and 50 mJy are biased towards high values by a factor ~2, and that the redshift distributions are biased towards low redshifts. We also show that the clustering has an important impact on the Herschel pixel histogram used to derive number counts from P(D) analysis. We find that the brightest galaxy in the beam of a 500 μm Herschel source contributes on average to only ~60% of the Herschel flux density, but that this number will rise to ~95% for future millimeter surveys on 30 m-class telescopes (e.g., NIKA2 at IRAM). Finally, we show that the large number density of red Herschel sources found in observations but not in models might be an observational artifact caused by the combination of noise, resolution effects, and the steepness of color- and flux density distributions. Our simulation, called Simulated Infrared Dusty Extragalactic Sky (SIDES), is publicly available. [ABSTRACT FROM AUTHOR]

We report the detection of 6.2 μm polycyclic aromatic hydrocarbon (PAH) and rest-frame 4-7 μm continuum emission in the z = 4.055 submillimeter galaxy GN20, using the Infrared Spectrograph on board the Spitzer Space Telescope. This represents the first detection of PAH emission at z > 4. The strength of the PAH emission feature is consistent with a very high star formation rate of ∼1600 M☼ yr–1. We find that this intense starburst powers at least ∼1/3 of the faint underlying 6 μm continuum emission, with an additional, significant (and perhaps dominant) contribution due to a power-law-like hot dust source, which we interpret to likely be a faint, dust-obscured active galactic nucleus (AGN). The inferred 6 μm AGN continuum luminosity is consistent with a sensitive upper limit on the hard X-ray emission as measured by the Chandra X-Ray Observatory if the previously undetected AGN is Compton-thick. This is in agreement with the finding at optical/infrared wavelengths that the galaxy and its nucleus are heavily dust-obscured. Despite the strong power-law component enhancing the mid-infrared continuum emission, the intense starburst associated with the photon-dominated regions that give rise to the PAH emission appears to dominate the total energy output in the infrared. GN20 is one of the most luminous starburst galaxies known at any redshift, embedded in a rich protocluster of star-forming galaxies. This investigation provides an improved understanding of the energy sources that power such exceptional systems, which represent the extreme end of massive galaxy formation at early cosmic times. [ABSTRACT FROM AUTHOR]

Recent studies have revealed a strong correlation between the star formation rate (SFR) and stellar mass of the majority of star-forming galaxies, the so-called star-forming main sequence. An empirical modeling approach (the 2-SFM framework) that distinguishes between the main sequence and rarer starburst galaxies is capable of reproducing most statistical properties of infrared galaxies, such as number counts, luminosity functions, and redshift distributions. In this paper, we extend this approach by establishing a connection between stellar mass and halo mass with the technique of abundance matching. Based on a few simple assumptions and a physically motivated formalism, our model successfully predicts the (cross-)power spectra of the cosmic infrared background (CIB), the crosscorrelation between CIB and cosmic microwave background (CMB) lensing, and the correlation functions of bright, resolved infrared galaxies measured by Herschel, Planck, ACT, and SPT. We use this model to infer the redshift distribution of CIB-anisotropies and of the CIB × CMB lensing signal, as well as the level of correlation between CIB-anisotropies at different wavelengths. We study the link between dark matter halos and star-forming galaxies in the framework of our model. We predict that more than 90% of cosmic star formation activity occurs in halos with masses between 1011.5 and 1013.5 M☉. If taking subsequent mass growth of halos into account, this implies that the majority of stars were initially (at z > 3) formed in the progenitors of clusters (Mh(z = 0) > 1013.5 M☉), then in groups (1012.5 < Mh(z = 0) < 1013.5 M☉) at 0.5 < z < 3, and finally in Milky-Way-like halos (1011.5 < Mh(z = 0) < 1012.5 M☉) at z < 0.5. At all redshifts, the dominant contribution to the SFR density stems from halos of mass ~1012 M☉, in which the instantaneous star formation efficiency - defined here as the ratio between SFR and baryonic accretion rate - is maximal (~70%). The strong redshift-evolution of SFR in the galaxies that dominate the CIB is thus plausibly driven by increased accretion from the cosmic web onto halos of this characteristic mass scale. Material (effective spectral energy distributions, differential emissivities of halos, relations between Mh and SFR) associated to this model is available at http://irfu.cea.fr/Sap/Phocea/Page/index.php?id=537. [ABSTRACT FROM AUTHOR]

We explore the relationship between gas, dust, and star formation in a sample of 12 ultraluminous infrared galaxies (ULIRGs) at high-redshift compared to a similar sample of local galaxies.We present new CO observations and/or Spitzer mid-IR spectroscopy for six 70 μm selected galaxies at z ~ 1 in order to quantify the properties of the molecular gas reservoir, the contribution of an active galactic nucleus (AGN) to the mid-IR luminosity, and the star formation efficiency (SFE = LIR/L'CO). The mid-IR spectra show strong polycyclic aromatic hydrocarbon (PAH) emission, and our spectral decomposition suggests that the AGN makes a minimal contribution (<25%) to the mid-IR luminosity. The 70 μm selected ULIRGs, which we find to be spectroscopic close pairs, are observed to have high SFE, similar to local ULIRGs and high-redshift submillimeter galaxies, consistent with enhanced IR luminosity due to an ongoing major merger. Combined with existing observations of local and high-redshift ULIRGs, we further compare the PAH, IR, and CO luminosities. We show that the ratio LPAH,6.2/LIR decreases with increasing IR luminosity for both local and high-redshift galaxies, but the trend for high-redshift galaxies is shifted to higher IR luminosities; the average LPAH,6.2/LIR ratio at a given LIR is ~3 times higher at high-redshift. When we normalize by the molecular gas, we find this trend to be uniform for galaxies at all redshifts and that the molecular gas is correlated with the PAH dust emission. The similar trends seen in the [C II] to molecular gas ratios in other studies suggests that PAH emission, like [C II], continues to be a good tracer of photodissociation regions even at high-redshift. Together the CO, PAH, and far-IR fine structure lines should be useful for constraining the interstellar medium conditions in high-redshift galaxies. [ABSTRACT FROM AUTHOR]

We compare multi-wavelength star formation rate (SFR) indicators out to z ~ 3 in the GOODS-South field. Our analysis uniquely combines U to 8 µm photometry from FIREWORKS, MIPS 24 µm and PACS 70, 100, and 160 µm photometry from the PEP, and Hα spectroscopy from the SINS survey. We describe a set of conversions that lead to a continuity across SFR indicators. A luminosity-independent conversion from 24/um to total infrared luminosity yields estimates of LIR that are in the median consistent with the LIR derived from PACS photometry, albeit with significant scatter. Dust correction methods perform well at low-to-intermediate levels of star formation. They fail to recover the total amount of star formation in systems with large SFRIR/SFRUV ratios, typically occuring at the highest SFRs (SFRUV+IR ≳ 100 M⊙ yr-1) and redshifts (z ≳ 2.5) probed. Finally, we confirm that Hα-based SFRs at 1.5 < z < 2.6 are consistent with SFRSED and SFRUV+IR provided extra attenuation toward H II regions is taken into account (AV,neb = AV,continuum/0.44). With the cross-calibrated SFR indicators in hand, we perform a consistency check on the star formation histories inferred from spectral energy distribution (SED) modeling. We compare the observed SFR-M relations and mass functions at a range of redshifts to equivalents that are computed by evolving lower redshift galaxies backward in time. We find evidence for underestimated stellar ages when no stringent constraints on formation epoch are applied in SED modeling. We demonstrate how resolved SED modeling, or alternatively deep UV data, may help to overcome this bias. The age bias is most severe for galaxies with young stellar populations and reduces toward older systems. Finally, our analysis suggests that SFHs typically vary on timescales that are long (at least several 100 Myr) compared to the galaxies' dynamical time. [ABSTRACT FROM AUTHOR]

Fitting synthetic spectral energy distributions (SEDs) to the multiband photometry of galaxies to derive their star formation rates (SFRs), stellar masses, ages, etc. requires making a priori assumptions about their star formation histories (SFHs). A widely adopted parametrization of the SFH, the so-called τ models where SFR is shown to lead to unrealistically low ages when applied to a sample of actively star-forming galaxies at , a problem shared by other SFHs when the age is left as a free parameter in the fitting procedure. This happens because the SED of such galaxies, at all wavelengths, is dominated by their youngest stellar populations, which outshine the older ones. Thus, the SED of such galaxies conveys little information on the beginning of star formation (SF), i.e. on the age of their oldest stellar populations. To cope with this problem, besides τ models (hereafter called direct-τ models), we explore a variety of SFHs, such as constant SFR and inverted-τ models (with SFR ), along with various priors on age, including assuming that SF started at high redshift in all the galaxies in the test sample. We find that inverted-τ models with such latter assumption give SFRs and extinctions in excellent agreement with the values derived using only the UV part of the SED, which is the one most sensitive to ongoing SF and reddening. These models are also shown to accurately recover the SFRs and masses of mock galaxies at constructed from semi-analytic models, which we use as a further test. All other explored SFH templates do not fulfil these two tests as well as inverted-τ models do. In particular, direct-τ models with unconstrained age in the fitting procedure overestimate SFRs and underestimate stellar mass, and would exacerbate an apparent mismatch between the cosmic evolution of the volume densities of SFR and stellar mass. We conclude that for high-redshift star-forming galaxies an exponentially increasing SFR with a high formation redshift is preferable to other forms of the SFH so far adopted in the literature. [ABSTRACT FROM AUTHOR]

Following an episode of star formation, Type Ia supernova events occur over an extended period of time, following a distribution of delay times (DDT). We critically discuss some empirically based DDT functions that have been proposed in recent years, some favouring very early (prompt) events, other very late (tardy) ones, and therefore being mutually exclusive. We point out that in both the cases the derived DDT functions are affected by dubious assumptions, and therefore there is currently no ground for claiming either a DDT strongly peaked at early times, or at late ones. Theoretical DDT functions are known to accommodate both prompt as well as late SN Ia events, and can account for all available observational constraints. Recent observational evidence exist that both single and double degenerate precursors may be able of producing SN Ia events. We then explore on the basis of plausible theoretical models the possible variation with cosmic time of the mix between the events produced by the two different channels, which, in principle, could lead to systematic effects on the SN Ia properties with redshift. [ABSTRACT FROM AUTHOR]

The article offers information on the formation and evolution of the first generation of galaxy clusters. Topics include providing an opportunity to investigate key physical processes in both galaxy formation and cosmology; and discusses the first generation of clusters which are key to test structure growth theories, hence our cosmological framework, and study the formation sites of the most massive galaxies, such as the local ellipticals whose origin remain controversial.

Emission line diagnostic diagrams probing the ionization sources in galaxies, such as the Baldwin-Phillips-Terlevich (BPT) diagram, have been used extensively to distinguish active galactic nuclei (AGN) from purely star-forming galaxies. However, they remain poorly understood at higher redshifts. We shed light on this issue with an empirical approach based on a z ∼ 0 reference sample built from ∼300,000 Sloan Digital Sky Survey galaxies, from which we mimic selection effects due to typical emission line detection limits at higher redshift. We combine this low-redshift reference sample with a simple prescription for luminosity evolution of the global galaxy population to predict the loci of high-redshift galaxies on the BPT and Mass-Excitation (MEx) diagnostic diagrams. The predicted bivariate distributions agree remarkably well with direct observations of galaxies out to z ∼ 1.5, including the observed stellar mass-metallicity (MZ) relation evolution. As a result, we infer that high-redshift star-forming galaxies are consistent with having normal interstellar medium (ISM) properties out to z ∼ 1.5, after accounting for selection effects and line luminosity evolution. Namely, their optical line ratios and gas-phase metallicities are comparable to that of low-redshift galaxies with equivalent emission-line luminosities. In contrast, AGN narrow-line regions may show a shift toward lower metallicities at higher redshift. While a physical evolution of the ISM conditions is not ruled out for purely star-forming galaxies and may be more important starting at z ≳ 2, we find that reliably quantifying this evolution is hindered by selections effects. The recipes provided here may serve as a basis for future studies toward this goal. Code to predict the loci of galaxies on the BPT and MEx diagnostic diagrams and the MZ relation as a function of emission line luminosity limits is made publicly available. [ABSTRACT FROM AUTHOR]

We provide evidence for a correlation between the presence of giant clumps and the occurrence of active galactic nuclei (AGNs) in disk galaxies. Giant clumps of 108-109M☼ arise from violent gravitational instability in gas-rich galaxies, and it has been proposed that this instability could feed supermassive black holes (BHs). We use emission line diagnostics to compare a sample of 14 clumpy (unstable) disks and a sample of 13 smoother (stable) disks at redshift z ∼ 0.7. The majority of clumpy disks in our sample have a high probability of containing AGNs. Their [O III] λ5007 emission line is strongly excited, inconsistent with low-metallicity star formation (SF) alone. [Ne III] λ3869 excitation is also higher. Stable disks rarely have such properties. Stacking ultra sensitive Chandra observations (4 Ms) reveals an X-ray excess in clumpy galaxies, which confirms the presence of AGNs. The clumpy galaxies in our intermediate-redshift sample have properties typical of gas-rich disk galaxies rather than mergers, being in particular on the main sequence of SF. This suggests that our findings apply to the physically similar and numerous gas-rich unstable disks at z > 1. Using the observed [O III] and X-ray luminosities, we conservatively estimate that AGNs hosted by clumpy disks have typical bolometric luminosities of the order of a few 1043 erg s–1, BH growth rates yr–1, and that these AGNs are substantially obscured in X-rays. This moderate-luminosity mode could provide a large fraction of today's BH mass with a high duty cycle (>10%), accretion bursts with higher luminosities being possible over shorter phases. Violent instabilities at high redshift (giant clumps) are a much more efficient driver of BH growth than the weak instabilities in nearby spirals (bars), and the evolution of disk instabilities with mass and redshift could explain the simultaneous downsizing of SF and of BH growth. [ABSTRACT FROM AUTHOR]