Search

We present the first spectroscopic ALMA follow-up for a pilot sample of nine radio-selected near-IR-dark galaxies in the COSMOS field. These sources were initially selected as radio-detected sources (S3 GHz > 12.65 μJy) without an optical or near-IR (NIR) counterpart in the COSMOS2015 catalog (Ks ≳ 24.7 mag), and just three of them were subsequently detected in the deeper COSMOS2020. Several studies highlighted that this selection could provide a population of highly dust-obscured, massive, and star-bursting galaxies. With these new ALMA observations, we assess the spectroscopic redshifts of this pilot sample of sources and improve the quality of the physical properties estimated through SED-fitting. Moreover, we measure the quantity of molecular gas inside these galaxies and forecast their potential evolutionary path, finding that the radio-selected NIR-dark galaxies might likely represent a population of high-z progenitors of the massive and passive galaxies that were discovered at z ∼ 3. Finally, we present some initial constraints on the kinematics of the interstellar medium within the analyzed galaxies, reporting a high fraction (∼55%) of double-peaked lines that can be interpreted as the signature of a rotating structure in our targets or as the presence of major mergers in our sample. The results we present here show the scientific potential of (sub)mm observations for this elusive population of galaxies and highlight the potential contribution of these sources to the evolution of the massive and passive galaxies at high z. [ABSTRACT FROM AUTHOR]

We present photometric redshifts for ∼4 million galaxies detected in the Spitzer 3.6 or 4.5 |$\mu$| m bands of the Spitzer Extragalactic Representative Volume Survey (SERVS). The 18 deg2 area of SERVS covers five extragalactic fields with a variety of ancillary, optical, and near-infrared (IR) photometry. We evaluate the accuracy of our photometric redshifts with ∼90.000 publicly available, spectroscopic redshifts. Overall, we find an average of ∼0.038 for the normalized median absolute deviation (σNMAD), a measure similar to the standard deviation yet more robust against outliers, and outlier fraction η of 3.7 per cent for the sources with the widest wavelength coverage. On the example of the XMM field, we quantify the quality and reliability of photometric redshifts as a function of (1) the number of photometric bands available in the fitting, (2) i AB magnitude, (3) Infrared Array Camera (IRAC) 3.6 |$\, \mu$| m magnitude, (4) spectroscopic redshift, and (5) the survey origin of the spectroscopic redshift. The best results are achieved when the photometry available for the fitting covers rest-frame optical and near-IR wavelengths. σNMAD and η are smallest for the brightest objects. Similarly, we find σNMAD and η to be smaller on average at z < 1.5 than at z > 1.5. Photometric redshifts derived without the two IRAC filter bands, but detections in all other bands are slightly underestimated. Approximately 76 per cent of SERVS sources with at least five available filter bands lie between redshift 0 and ∼1.5. We find a tail of high-redshift galaxies, i.e. |${\sim }7\,$|  per cent of all objects with at least five available filter bands for the fitting lie at z > 3. We discuss ways to improve upon the photometric redshifts for SERVS galaxies in the future. [ABSTRACT FROM AUTHOR]

Upcoming surveys with new radio observatories such as the Square Kilometre Array will generate a wealth of imaging data containing large numbers of radio galaxies. Different classes of radio galaxies can be used as tracers of the cosmic environment, including the dark matter density field, to address key cosmological questions. Classifying these galaxies based on morphology is thus an important step towards achieving the science goals of next generation radio surveys. Radio galaxies have been traditionally classified as Fanaroff–Riley (FR) I and II, although some exhibit more complex 'bent' morphologies arising from environmental factors or intrinsic properties. In this work, we present the FIRST Classifier, an online system for automated classification of Compact and Extended radio sources. We developed the FIRST Classifier based on a trained deep Convolutional Neural Network model to automate the morphological classification of compact and extended radio sources observed in the FIRST radio survey. Our model achieved an overall accuracy of $$97{{\ \rm per\ cent}}$$ and a recall of $$98{{\ \rm per\ cent}}$$, $$100{{\ \rm per\ cent}}$$, $$98{{\ \rm per\ cent}}$$, and $$93{{\ \rm per\ cent}}$$ for Compact, BENT, FRI, and FRII galaxies, respectively. The current version of the FIRST classifier is able to predict the morphological class for a single source or for a list of sources as Compact or Extended (FRI, FRII, and BENT). [ABSTRACT FROM AUTHOR]

We investigate the relationship between environment and star formation main sequence (the relationship between stellar mass and star formation rate) to shed new light on the effects of the environments on star-forming galaxies. We use the large VLA-COSMOS 3 GHz catalogue that consist of star-forming galaxies (SFGs) and active galactic nuclei (AGN) in three different environments (field, filament, cluster) and for different galaxy types. We examine for the first time a comparative analysis for the distribution of SFGs with respect to the star formation main sequence (MS) consensus region from the literature, taking into account galaxy environment and using radio selected sample at 0.1 ≤ z ≤ 1.2 drawn from one of the deepest COSMOS radio surveys. We find that, as observed previously, SFRs increase with redshift independent on the environments. Furthermore, we observe that SFRs versus M* relation is flat in all cases, irrespective of the redshift and environments. [ABSTRACT FROM AUTHOR]

We use 3035 Herschel-SPIRE 500 μmsources from 20.3 deg² of sky in the HerMES Lockman, ES1 and XMM-LSS areas to estimate the star formation rate density at z = 0-6. 500 μm sources are associated first with 350 and 250 μm sources, and then with Spitzer 24 μm sources from the SWIRE photometric redshift catalogue. The infrared and submillimetre data are fitted with a set of radiative-transfer templates corresponding to cirrus (quiescent) and starburst galaxies. Lensing candidates are removed via a set of colour-colour and colour- redshift constraints. Star formation rates are found to extend from <1 to 20 000 M⊙ yr-1. Such high values were also seen in the all-sky IRAS Faint Source Survey. Star formation rate functions are derived in a series of redshift bins from 0 to 6, combined with earlier far-infrared estimates, where available, and fitted with a Saunders et al (1990) functional form. The star formation rate density as a function of redshift is derived and compared with other estimates. There is reasonable agreement with both infrared and ultraviolet estimates for z < 3, but we find higher star formation rate densities than ultraviolet estimates at z = 3-6. Given the considerable uncertainties in the submillimetre estimates, we cannot rule out the possibility that the ultraviolet estimates are correct. But the possibility that the ultraviolet estimates have seriously underestimated the contribution of dust-shrouded star formation can also not be excluded. [ABSTRACT FROM AUTHOR]

We investigate the star formation rate (SFR) and stellar mass, M*, relation of a star-forming (SF) galaxy (SFG) sample in the XMM-LSS field to z ~ 3.0 using the near-infrared data from the VISTA Deep Extragalactic Observations (VIDEO) survey. Combining VIDEO with broad-band photometry, we use the SED fitting algorithm cigale to derive SFRs and M* and have adapted it to account for the full photometric redshift probability-distribution-function uncertainty. Applying an SF selection using the D4000 index, we find evidence for strong evolution in the normalization of the SFR-M* relation out to z ~ 3 and a roughly constant slope of (SFR $\propto M_*{\alpha }$) a = 0.69 ± 0.02 to z ~ 1.7. We find this increases close to unity towards z ~ 2.65. Alternatively, if we apply a colour selection, we find a distinct turnover in the SFR-M* relation between 0.7 ≲ z ≲ 2.0 at the high-mass end, and suggest that this is due to an increased contamination from passive galaxies. We find evolution of the specific SFR (1 + z)2.60 at log10(M*/M) ~ 10.5, out to z ≲ 2.4 with an observed flattening beyond z ~ 2 with increased stellar mass. Comparing to a range of simulations we find the analytical scaling relation approaches, that invoke an equilibrium model, a good fit to our data, suggesting that a continual smooth accretion regulated by continual outflows may be a key driver in the overall growth of SFGs. [ABSTRACT FROM AUTHOR]

We have studied in detail a sample of 967 SPIRE sources with 5σ detections at 350 and 500 μm and associations with Spitzer-SWIRE 24 μm galaxies in the HerMES-Lockman survey area, fitting their mid- and far-infrared, and submillimetre, spectral energy distributions (SEDs) in an automatic search with a set of six infrared templates. For almost 300 galaxies, we have modelled their SEDs individually to ensure the physicality of the fits. We confirm the need for the new cool and cold cirrus templates, and also of the young starburst template, introduced in earlier work. We also identify 109 lensing candidates via their anomalous SEDs and provide a set of colour–redshift constraints which allow lensing candidates to be identified from combined Herschel and Spitzer data. The picture that emerges of the submillimetre galaxy population is complex, comprising ultraluminous and hyperluminous starbursts, lower luminosity galaxies dominated by interstellar dust emission, lensed galaxies and galaxies with surprisingly cold (10–13 K) dust. 11 per cent of 500 μm selected sources are lensing candidates. 70 per cent of the unlensed sources are ultraluminous infrared galaxies and 26 per cent are hyperluminous. 34 per cent are dominated by optically thin interstellar dust (‘cirrus’) emission, but most of these are due to cooler dust than is characteristic of our Galaxy. At the highest infrared luminosities we see SEDs dominated by M82, Arp 220 and young starburst types, in roughly equal proportions. [ABSTRACT FROM AUTHOR]

We present the SWIRE Photometric Redshift Catalogue 1 025 119 redshifts of unprecedented reliability and of accuracy comparable with or better than previous work. Our methodology is based on fixed galaxy and quasi-stellar object templates applied to data at 0.36–4.5 μm, and on a set of four infrared emission templates fitted to infrared excess data at 3.6–170 μm. The galaxy templates are initially empirical, but are given greater physical validity by fitting star formation histories to them, which also allows us to estimate stellar masses. The code involves two passes through the data, to try to optimize recognition of active galactic nucleus (AGN) dust tori. A few carefully justified priors are used and are the key to supression of outliers. Extinction, , is allowed as a free parameter. The full reduced distribution is given for each source, so the full error distribution can be used, and aliases investigated. We use a set of 5982 spectroscopic redshifts, taken from the literature and from our own spectroscopic surveys, to analyse the performance of our method as a function of the number of photometric bands used in the solution and the reduced . For seven photometric bands (5 optical + 3.6, 4.5 μm), the rms value of is 3.5 per cent, and the percentage of catastrophic outliers [defined as >15 per cent error in (1 + z)], is ∼1 per cent. These rms values are comparable with the best achieved in other studies, and the outlier fraction is significantly better. The inclusion of the 3.6- and 4.5-μm IRAC bands is crucial in supression of outliers. We discuss the redshift distributions at 3.6 and 24 μm. In individual fields, structure in the redshift distribution corresponds to clusters which can be seen in the spectroscopic redshift distribution, so the photometric redshifts are a powerful tool for large-scale structure studies. 10 per cent of sources in the SWIRE photometric redshift catalogue have z > 2, and 4 per cent have z > 3, so this catalogue is a huge resource for high-redshift galaxies. A key parameter for understanding the evolutionary status of infrared galaxies is . For cirrus galaxies this is a measure of the mean extinction in the interstellar medium of the galaxy. There is a population of ultraluminous galaxies with cool dust and we have shown SEDs for some of the reliable examples. For starbursts, we estimate the specific star formation rate, . Although the very highest values of this ratio tend to be associated with Arp220 starbursts, by no means all ultraluminous galaxies are. We discuss an interesting population of galaxies with elliptical-like spectral energy distributions in the optical and luminous starbursts in the infrared. For dust tori around type 1 AGN, is a measure of the torus covering factor and we deduce a mean covering factor of 40 per cent. Our infrared templates also allow us to estimate dust masses for all galaxies with an infrared excess. [ABSTRACT FROM AUTHOR]

We exploit deep combined observations with Spitzer and Chandra of the Spitzer Wide-Area Infrared Extragalactic Survey (SWIRE) in the ELAIS N1 region to investigate the nature of the faint X-ray and IR sources in common, to identify active galactic nucleus (AGN)/starburst diagnostics, and to study the sources of the X-ray and IR cosmic backgrounds (XRB and CIRB). In the 17' × 17' area of the Chandra ACIS-I image there are approximately 3400 SWIRE near-IR sources with 4 σ detections in at least two Infrared Array Camera (IRAC) bands and 988 sources detected at 24 μm with the Multiband Imaging Photometer (MIPS) brighter than S24 sime 0.1 mJy. Of these, 102 IRAC and 59 MIPS sources have Chandra counterparts, out of a total of 122 X-ray sources present in the area with S0.5–8 keV > 10-15 ergs cm-2 s-1. We have constructed spectral energy distributions (SEDs) for each source using data from the four IRAC wavebands, Chandra fluxes in the hard (2–8 keV) and soft (0.5–2 keV) X-rays, and optical follow-up data in the wavebands U, g', r', i', Z, and H. We fit a number of spectral templates to the SEDs at optical and IR wavelengths to determine photometric redshifts and spectral categories and also make use of diagnostics based on the X-ray luminosities, hardness ratios, X-ray to IR spectral slopes, and optical morphologies. Although we have spectroscopic redshifts for only a minority of the Chandra sources (10 type 1 QSOs or Seyfert sources and three galaxies), the available SEDs constrain the redshifts for most of the sample sources, which turn out to be typically at 0.5 < z < 2. We find that 39% of the Chandra sources are dominated by type 1 AGN emission (QSOs or Seyfert 1), 23% display optical/IR spectra typical of type 2 AGNs, while the remaining 38% show starburst-like or even normal galaxy spectra (including five passively evolving early-type galaxies). Since we prove that all these galaxies are dominated by AGN emission in X-rays (considering their large 0.5–8 keV rest-frame X-ray luminosities and their high X-ray to IR flux ratios), this brings the fraction of type 1 AGNs to 80% of the type 2 AGNs; even assuming that all the Chandra sources undetected by Spitzer are type 2 AGNs, the type 1 fraction would exceed 1/3 of the total population. Our analysis of the mid-IR MIPS 24 μm–selected sources, making up ~50% of the CIRB, shows that the fraction of those dominated by an AGN (either type 1 or type 2) is relatively constant with the IR flux and around 10%–15%. Our combined IR and hard X-ray observations allow us to verify that the dust covering fraction in type 1 AGNs is widely distributed between ~10% and 100%. A significant fraction, from 15% to 30% or more, of the sources of the XRB are hosted in galaxies whose optical/IR spectra are dominated by starburst (or normal galaxy) emission and for which only the hard X-ray spectra reveal the presence of a moderately luminous hidden AGN., Astronomy