Great Observatories Origins Deep Survey Research Articles

Lyman Continuum Leakers in the AstroSat Ultraviolet Deep Field: Extreme-ultraviolet Emitters at the Cosmic Noon

We report the direct detection of Lyman continuum (LyC) emission from nine galaxies and one active galactic nucleus at z ∼ 1.1–1.6 in the GOODS-North field using deep observations from the Ultraviolet Imaging Telescope (UVIT) on board AstroSat. The absolute escape fraction of the sources estimated from the far-ultraviolet and Hα-line luminosities using Monte Carlo analysis of two intergalactic medium models span a range ∼10%–55%. The rest-frame UV wavelength of the sources falls in the extreme-ultraviolet regime ∼550–700 Å, the shortest LyC wavelength range probed so far. This redshift range remains devoid of direct detections of LyC emission due to the instrumental limitations of previously available facilities. With UVIT having very low detector noise, each of these sources is detected with an individual signal-to-noise ratio (S/N) > 3, while for the stack of six sources, we achieve an S/N ∼ 7.4. The LyC emission is seen to be offset from the optical centroids and extended beyond the UVIT point-spread function of 1.″6 in most of the sources. This sample fills an important niche between GALEX and Cosmic Origins Spectrograph at low z and Hubble Space Telescope's Wide Field Camera 3 at high z and is crucial in understanding the evolution of LyC leakers.

The VLBA CANDELS GOODS-North Survey. II – Wide-field source catalogue comparison between the VLBA, EVN, e-MERLIN, and VLA

ABSTRACT Deep radio surveys of extragalactic legacy fields trace a large range of spatial and brightness temperature sensitivity scales, and therefore have differing biases to radio-emitting physical components within galaxies. This is particularly true of radio surveys performed at $\lesssim 1 \ \mathrm{arcsec}$ angular resolutions, and so robust comparisons are necessary to better understand the biases present in each survey. We present a multiresolution and multiwavelength analysis of the sources detected in a new Very Long Baseline Array (VLBA) survey of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey Great Observatories Origins Deep Survey-North field. For the 24 VLBA-selected sources described in Paper I, we augment the VLBA data with EVN data, and ∼0.1–1 arcsec angular resolution data provided by Very Large Array (VLA) and enhanced-Multi Element Remotely Linked Interferometry Network. This sample includes new active galactic nuclei (AGN) detected in this field, thanks to a new source extraction technique that adopts priors from ancillary multiwavelength data. The high brightness temperatures of these sources (TB ≳ 106 K) confirm AGN cores, that would often be missed or ambiguous in lower-resolution radio data of the same sources. Furthermore, only 15 sources are identified as ‘radiative’ AGN based on available X-ray and infrared constraints. By combining VLA and VLBA measurements, we find evidence that the majority of the extended radio emission is also AGN dominated, with only three sources with evidence for extended potentially star formation-dominated radio emission. We demonstrate the importance of wide-field multiresolution (arcsecond–milliarcsecond) coverage of the faint radio source population, for a complete picture of the multiscale processes within these galaxies.

The VLBA CANDELS GOODS-North Survey – I. survey design, processing, data products, and source counts

ABSTRACT The past decade has seen significant advances in wide-field cm-wave very long baseline interferometry (VLBI), which is timely given the wide-area, synoptic survey-driven strategy of major facilities across the electromagnetic spectrum. While wide-field VLBI poses significant post-processing challenges that can severely curtail its potential scientific yield, many developments in the km-scale connected-element interferometer sphere are directly applicable to addressing these. Here we present the design, processing, data products, and source counts from a deep (11 μJy beam−1), quasi-uniform sensitivity, contiguous wide-field (160 arcmin2) 1.6 GHz VLBI survey of the CANDELS GOODS-North field. This is one of the best-studied extragalactic fields at milli-arcsecond resolution and, therefore, is well-suited as a comparative study for our Tera-pixel VLBI image. The derived VLBI source counts show consistency with those measured in the COSMOS field, which broadly traces the AGN population detected in arcsecond-scale radio surveys. However, there is a distinctive flattening in the S1.4GHz ∼100–500 μJy flux density range, which suggests a transition in the population of compact faint radio sources, qualitatively consistent with the excess source counts at 15 GHz that is argued to be an unmodelled population of radio cores. This survey approach will assist in deriving robust VLBI source counts and broadening the discovery space for future wide-field VLBI surveys, including VLBI with the Square Kilometre Array, which will include new large field-of-view antennas on the African continent at ≳1000 km baselines. In addition, it may be useful in the design of both monitoring and/or rapidly triggered VLBI transient programmes.

JADES Initial Data Release for the Hubble Ultra Deep Field: Revealing the Faint Infrared Sky with Deep JWST NIRCam Imaging

JWST has revolutionized the field of extragalactic astronomy with its sensitive and high-resolution infrared view of the distant Universe. Adding to the new legacy of JWST observations, we present the first NIRCam imaging data release from the JWST Advanced Deep Extragalactic Survey (JADES), providing nine filters of infrared imaging of ∼25 arcmin2 covering the Hubble Ultra Deep Field and portions of Great Observatories Origins Deep Survey South. Utilizing 87 on-sky dual-filter hours of exposure time, these images reveal the deepest ever near-infrared view of this iconic field. We supply carefully constructed nine-band mosaics of the JADES bands, as well as matching reductions of five additional bands from the JWST Extragalactic Medium-band Survey. Combining with existing Hubble Space Telescope imaging, we provide 23-band space-based photometric catalogs and photometric redshifts for ≈47,500 sources. To promote broad engagement with JADES, we have created an interactive FitsMap website to provide an interface for professional researchers and the public to experience these JWST data sets. Combined with the first JADES NIRSpec data release, these public JADES imaging and spectroscopic data sets provide a new foundation for discoveries of the infrared Universe by the worldwide scientific community.

JADES NIRSpec Spectroscopy of GN-z11: Lyman-α emission and possible enhanced nitrogen abundance in a z = 10.60 luminous galaxy

We present JADES JWST/NIRSpec spectroscopy of GN-z11, the most luminous candidate z > 10 Lyman break galaxy in the GOODS-North field with MUV = −21.5. We derive a redshift of z = 10.603 (lower than previous determinations) based on multiple emission lines in our low and medium resolution spectra over 0.7 − 5.3 μm. We significantly detect the continuum and measure a blue rest-UV spectral slope of β = −2.4. Remarkably, we see spatially extended Lyman-α in emission (despite the highly neutral intergalactic medium expected at this early epoch), offset 555 km s−1 redwards of the systemic redshift. From our measurements of collisionally excited lines of both low and high ionisation (including [O II] λ3727, [Ne III] λ3869, and C III] λ1909), we infer a high ionisation parameter (log U ∼ −2). We detect the rarely seen N IV] λ1486 and N III] λ1748 lines in both our low and medium resolution spectra, with other high ionisation lines seen in the low resolution spectrum, such as He II (blended with O III]) and C IV (with a possible P-Cygni profile). Based on the observed rest-UV line ratios, we cannot conclusively rule out photoionisation from an active galactic nucleus (AGN), although the high C III]/He II and N III]/He II ratios are compatible with a star formation explanation. If the observed emission lines are powered by star formation, then the strong N III] λ1748 observed may imply an unusually high N/O abundance. Balmer emission lines (Hγ, Hδ) are also detected, and if powered by star formation rather than an AGN, we infer a star formation rate of ∼20 − 30 M⊙ yr−1 (depending on the initial mass function) and low dust attenuation. Our NIRSpec spectroscopy confirms that GN-z11 is a remarkable galaxy with extreme properties seen 430 Myr after the Big Bang.

The clustering properties of high-redshift passive galaxies

ABSTRACT We investigate the clustering properties of 3 < z < 5 candidate passive galaxies from the Merlin et al. (2019) sample residing in the GOODS-North (35 sources) and GOODS-South (33 sources) fields. Within the large uncertainties due to the paucity of sources we do not detect clustering signal in GOODS-North, while this is present in GOODS-South, highlighting the importance of the effects of cosmic variance. The estimated correlation length in GOODS-South is $r_0=12^{+4}_{-5}$ Mpc, while the estimated minimum mass for a halo capable to host one of such high-redshift quenched galaxies is log10(Mmin/M⊙) = 13.0 ± 0.3, once also the constraints from their space density are taken into account. Both values are compatible with the results from GOODS-North. Putting the above findings in a cosmological context, these suggest no evolution of the dark matter content of the hosts of passive galaxies during the past 12.5 Gyr, i.e. during more than 90 per cent of the age of the Universe. We discuss possible scenarios for the observed trend.

Observed UV Continuum Slopes (β) of Galaxies at z = 0.40–0.75 in the GOODS-North Field

We estimate the UV continuum slope (β) of 465 galaxies (with luminosities of 0.028–3.3 ) in the Great Observatories Origins Survey Northern field in the redshift range z = 0.40–0.75. We use two AstroSat/UVIT (N242W, N245M) bands, two Hubble Space Telescope (F275W, F336W) bands, and a KPNO (U) band to sample the UV continuum slope of selected galaxies between 1215 and 2600 Å. The mean (median) and 1σ scatter in the observed β are found to be −1.33 ± 0.07 ( − 1.32) and 0.60 within the considered redshift range. We do not find any significant evolution in the mean β within our redshift window. Our measurements add new data points to the global β–z relation in the least-explored redshift regime, further reinforcing the gradual reddening of galaxy UV continuum with cosmic time. We notice no strong consistent trend between β and M 1500 for the entire luminosity range −21 <M 1500 < − 15 mag. However, the majority of the most-luminous galaxies (M 1500 < − 19 mag) are found to have relatively redder slopes. Using UVIT, we detect galaxies as faint as M 1500 = − 15.6 mag (i.e., 0.028 ). The faintest galaxies (M 1500 > − 16 mag) tend to be redder, which indicates they were less actively forming stars during this cosmic time interval. Our study highlights the unique capability of UVIT near-UV imaging to characterize the rest-frame far-UV properties of galaxies at redshift z ∼ 0.5.

Deep Large Binocular Camera r-band Observations of the GOODS-N Field

We obtained 838 Sloan r-band images (∼28 hr) of the GOODS-North field with the Large Binocular Camera (LBC) on the Large Binocular Telescope in order to study the presence of extended, low surface brightness features in galaxies and investigate the trade-off between image depth and resolution. The individual images were sorted by effective seeing, which allowed for optimal resolution and optimal depth mosaics to be created with all images with seeing FWHM < 0.″9 and FWHM < 2.″0, respectively. Examining bright galaxies and their substructure as well as accurately deblending overlapping objects requires the optimal resolution mosaic, while detecting the faintest objects possible (to a limiting magnitude of m AB ∼ 29.2 mag) requires the optimal depth mosaic. The better surface brightness sensitivity resulting from the larger LBC pixels, compared to those of extant WFC3/UVIS and ACS/WFC cameras aboard the Hubble Space Telescope allows for unambiguous detection of both diffuse flux and very faint tidal tails. Azimuthally-averaged radial surface brightness profiles were created for the 360 brightest galaxies in each of the two mosaics. On average, these profiles showed minimal difference between the optimal resolution and optimal depth surface brightness profiles. However, ≲15% of the profiles show excess flux in the galaxy outskirts down to surface brightness levels of ≃ 31 mag arcsec−2. This is relevant to Extragalactic Background Light (EBL) studies as diffuse light in the outer regions of galaxies are thought to be a major contribution to the EBL. While some additional diffuse light exists in the optimal depth profiles compared to the shallower, optimal resolution profiles, we find that diffuse light in galaxy outskirts is a minor contribution to the EBL overall in the r-band.

The Dwarf Galaxy Population at z ∼ 0.7: A Catalog of Emission Lines and Redshifts from Deep Keck Observations

We present a catalog of spectroscopically measured redshifts over 0 < z < 2 and emission-line fluxes for 1440 galaxies. The majority (∼65%) of the galaxies come from the HALO7D survey, with the remainder from the DEEPwinds program. This catalog includes redshifts for 646 dwarf galaxies with . Eight-hundred and ten catalog galaxies did not have previously published spectroscopic redshifts, including 454 dwarf galaxies. HALO7D used the DEIMOS spectrograph on the Keck II telescope to take very deep (up to 32 hr exposure, with a median of ∼7 hr) optical spectroscopy in the COSMOS, EGS, GOODS-North, and GOODS-South CANDELS fields, and in some areas outside CANDELS. We compare our redshift results to existing spectroscopic and photometric redshifts in these fields, finding only a 1% rate of discrepancy with other spectroscopic redshifts. We measure a small increase in median photometric redshift error (from 1.0% to 1.3%) and catastrophic outlier rate (from 3.5% to 8%) with decreasing stellar mass. We obtained successful redshift fits for 75% of massive galaxies, and demonstrate a similar 70%–75% successful redshift measurement rate in galaxies, suggesting similar survey sensitivity in this low-mass range. We describe the redshift, mass, and color–magnitude distributions of the catalog galaxies, finding HALO7D galaxies representative of CANDELS galaxies up to i-band magnitudes of 25. The catalogs presented will enable studies of star formation, the mass–metallicity relation, star formation–morphology relations, and other properties of the z ∼ 0.7 dwarf galaxy population.

COLDz: Probing Cosmic Star Formation With Radio Free–Free Emission

Abstract 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.

The Spitzer/IRAC Legacy over the GOODS Fields: Full-depth 3.6, 4.5, 5.8, and 8.0 μm Mosaics and Photometry for &gt;9000 Galaxies at z ∼ 3.5–10 from the GOODS Reionization Era Wide-area Treasury from Spitzer (GREATS)

Abstract We present the deepest Spitzer/InfraRed Array Camera (IRAC) 3.6, 4.5, 5.8, and 8.0 μm wide-area mosaics yet over the Great Observatories Origins Deep Survey (GOODS)-N and GOODS-S fields as part of the GOODS Reionization Era wide-Area Treasury from Spitzer (GREATS) project. We reduced and mosaicked in a self-consistent way observations taken by the 11 different Spitzer/IRAC programs over the two GOODS fields from 12 yr of Spitzer cryogenic and warm-mission data. The cumulative depth in the 3.6 μm and 4.5 μm bands amounts to ∼4260 hr, ∼1220 hr of which are new very deep observations from the GREATS program itself. In the deepest area, the full-depth mosaics reach ≳200 hr over an area of ∼100 arcmin2, corresponding to a sensitivity of ∼29 AB magnitude at 3.6 μm (1σ for point sources). Archival cryogenic 5.8 μm and 8.0 μm band data (a cumulative 976 hr) are also included in the release. The mosaics are projected onto the tangential plane of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey/GOODS at a 0.″3 pixel−1 scale. This paper describes the methodology enabling, and the characteristics of, the public release of the mosaic science images, the corresponding coverage maps in the four IRAC bands, and the empirical point-spread functions (PSFs). These PSFs enable mitigation of the source blending effects by taking into account the complex position-dependent variation in the IRAC images. The GREATS data products are in the Infrared Science Archive. We also release the deblended 3.6–8.0 μm photometry 9192 Lyman-break galaxies at z ∼ 3.5–10. GREATS will be the deepest mid-infrared imaging until the James Webb Space Telescope and, as such, constitutes a major resource for characterizing early galaxy assembly.

On the Impact of Inclination-dependent Attenuation on Derived Star Formation Histories: Results from Disk Galaxies in the Great Observatories Origins Deep Survey Fields

Abstract We develop and implement an inclination-dependent attenuation prescription for spectral energy distribution (SED) fitting and study its impact on derived star formation histories. We apply our prescription within the SED fitting code Lightning to a clean sample of 82, z = 0.21–1.35 disk-dominated galaxies in the Great Observatories Origins Deep Survey North and South fields. To compare our inclination-dependent attenuation prescription with more traditional fitting prescriptions, we also fit the SEDs with the inclination-independent Calzetti et al. (2000) attenuation curve. From this comparison, we find that fits to a subset of 58, z &lt; 0.7 galaxies in our sample, utilizing the Calzetti et al. (2000) prescription, recover similar trends with inclination as the inclination-dependent fits for the far-UV-band attenuation and recent star formation rates. However, we find a difference between prescriptions in the optical attenuation (A V ) that is strongly correlated with inclination (p‐value &lt; 10−11). For more face-on galaxies, with i ≲ 50°, (edge-on, i ≈ 90°), the average derived A V is 0.31 ± 0.11 magnitudes lower (0.56 ± 0.16 magnitudes higher) for the inclination-dependent model compared to traditional methods. Further, the ratio of stellar masses between prescriptions also has a significant (p‐value &lt; 10−2) trend with inclination. For i = 0°–65°, stellar masses are systematically consistent between fits, with log 10 ( M ⋆ inc / M ⋆ Calzetti ) = − 0.05 ± 0.03 dex and scatter of 0.11 dex. However, for i ≈ 80°–90°, the derived stellar masses are lower for the Calzetti et al. (2000) fits by an average factor of 0.17 ± 0.03 dex and scatter of 0.13 dex. Therefore, these results suggest that SED fitting assuming the Calzetti et al. (2000) attenuation law potentially underestimates stellar masses in highly inclined disk-dominated galaxies.

The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) Survey Design, Reductions, and Detections*

Abstract We describe the survey design, calibration, commissioning, and emission-line detection algorithms for the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX). The goal of HETDEX is to measure the redshifts of over a million Lyα emitting galaxies between 1.88 &lt; z &lt; 3.52, in a 540 deg2 area encompassing a comoving volume of 10.9 Gpc3. No preselection of targets is involved; instead the HETDEX measurements are accomplished via a spectroscopic survey using a suite of wide-field integral field units distributed over the focal plane of the telescope. This survey measures the Hubble expansion parameter and angular diameter distance, with a final expected accuracy of better than 1%. We detail the project’s observational strategy, reduction pipeline, source detection, and catalog generation, and present initial results for science verification in the Cosmological Evolution Survey, Extended Groth Strip, and Great Observatories Origins Deep Survey North fields. We demonstrate that our data reach the required specifications in throughput, astrometric accuracy, flux limit, and object detection, with the end products being a catalog of emission-line sources, their object classifications, and flux-calibrated spectra.

Galaxy Stellar Mass Functions from z ∼ 10 to z ∼ 6 using the Deepest Spitzer/Infrared Array Camera Data: No Significant Evolution in the Stellar-to-halo Mass Ratio of Galaxies in the First Gigayear of Cosmic Time

Abstract We present new stellar mass functions at z ∼ 6, z ∼ 7, z ∼ 8, z ∼ 9 and, for the first time, z ∼ 10, constructed from ∼800 Lyman-break galaxies previously identified over the eXtreme Deep Field and Hubble Ultra-Deep Field parallel fields and the five Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey fields. Our study is distinctive due to (1) the much deeper (∼200 hr) wide-area Spitzer/Infrared Array Camera (IRAC) imaging at 3.6 μm and 4.5 μm from the Great Observatories Origins Deep Survey Re-ionization Era Wide-area Treasury from Spitzer program (GREATS) and (2) consideration of z ∼ 6–10 sources over a 3× larger area than those of previous Hubble Space Telescope+Spitzer studies. The Spitzer/IRAC data enable ≥2σ rest-frame optical detections for an unprecedented 50% of galaxies down to a stellar mass limit of ∼ 10 8  ⊙ across all redshifts. Schechter fits to our volume densities suggest a combined evolution in the characteristic mass  * and normalization factor ϕ * between z ∼ 6 and z ∼ 8. The stellar mass density (SMD) increases by ∼1000× in the ∼500 Myr between z ∼ 10 and z ∼ 6, with indications of a steeper evolution between z ∼ 10 and z ∼ 8, similar to the previously reported trend of the star formation rate density. Strikingly, abundance matching to the Bolshoi–Planck simulation indicates halo mass densities evolving at approximately the same rate as the SMD between z ∼ 10 and z ∼ 4. Our results show that the stellar-to-halo mass ratios, a proxy for the star formation efficiency, do not change significantly over the huge stellar mass buildup occurred from z ∼ 10 to z ∼ 6, indicating that the assembly of stellar mass closely mirrors the buildup in halo mass in the first ∼1 Gyr of cosmic history. The James Webb Space Telescope is poised to extend these results into the “first galaxy” epoch at z ≳ 10.

Seeing-sorted Visible Multi-Object Spectrograph U-band Imaging of the GOODS-south Field*

Abstract We present the optimal resolution and optimal depth U-filter mosaics using the seeing-sorted method of Ashcraft et al. on deep, ground-based U-bandimaging of the Great Observatories Origins Deep Survey South field as part of the near-UV imaging program UVCANDELS. We use the U-bandimages obtained with the VIsible Multi-Object Spectrograph on the European Southern Observatory Very Large Telescope by Nonino et al. Our best resolution mosaic includes images with a seeing full-width half maximum (FWHM) ≤ 0.″8, and encompasses 50% of the data. Our best depth mosaic includes images with FWHM ≤ 1.″5, corresponding to 100% of the data. Prior to being combined, the source fluxes in each individual background-subtracted image are corrected to match a 3D-HST photometric catalog of the same field to correct variations in the U-band zero-points. These mosaics provide deep U-banddata complementary to the UVCANDELS HST WFC3 F275W and ACS F435W images. We assess the depth of both U-bandmosaics.

COLDz: Deep 34 GHz Continuum Observations and Free–Free Emission in High-redshift Star-forming Galaxies

Abstract The high-frequency radio sky has historically remained largely unexplored due to the typical faintness of sources in this regime, and the modest survey speed compared to observations at lower frequencies. However, high-frequency radio surveys offer an invaluable tracer of high-redshift star formation, as they directly target the faint radio free–free emission. We present deep continuum observations at 34 GHz in the COSMOS and GOODS-North fields from the Karl G. Jansky Very Large Array (VLA), as part of the COLDz survey. The deep COSMOS mosaic spans down to σ = 1.3 μJy beam−1, while the wider GOODS-N observations cover to σ = 5.3 μJy beam−1. We detect a total of 18 galaxies at 34 GHz, of which nine show radio emission consistent with being powered by star formation; although for two sources, this is likely due to thermal emission from dust. Utilizing deep ancillary radio data at 1.4, 3, 5, and 10 GHz, we decompose the spectra of the remaining seven star-forming galaxies into their synchrotron and thermal free–free components, and find typical thermal fractions and synchrotron spectral indices comparable to those observed in local star-forming galaxies. We further determine free–free star formation rates (SFRs), and show that these are in agreement with SFRs from spectral energy distribution-fitting and the far-infrared/radio correlation. Our observations place strong constraints on the high-frequency radio emission in typical galaxies at high redshift, and provide some of the first insights into what is set to become a key area of study with future radio facilities, such as the Square Kilometer Array Phase 1 and next-generation VLA.

The MOSDEF Survey: calibrating the relationship between H α star formation rate and radio continuum luminosity at 1.4 &amp;lt; z &amp;lt; 2.6

ABSTRACT The observed empirical relation between the star formation rates (SFR) of low-redshift galaxies and their radio continuum luminosity offers a potential means of measuring SFR in high-redshift galaxies that is unaffected by dust obscuration. In this study, we make the first test for redshift evolution in the SFR-radio continuum relation at high redshift using dust-corrected H α SFR. Our sample consists of 178 galaxies from the MOSFIRE Deep Evolution Field (MOSDEF) Survey at 1.4 &amp;lt; z &amp;lt; 2.6 with rest-frame optical spectroscopy and deep 1.5 GHz radio continuum observations from the Karl G. Jansky Very Large Array (VLA) GOODS North field. Using a stacking analysis, we compare the observed radio continuum luminosities with those predicted from the dust-corrected H α SFR assuming a range of z ∼ 0 relations. We find no evidence for a systematic evolution with redshift, when stacking the radio continuum as a function of dust-corrected H α SFR and when stacking both optical spectroscopy and radio continuum as a function of stellar mass. We conclude that locally calibrated relations between SFR and radio continuum luminosity remain valid out to z ∼ 2.

UV and NIR size of the low-mass field galaxies: the UV compact galaxies

Context. Most of the massive star-forming galaxies are found to have “inside-out” stellar mass growth modes, which means the inner parts of the galaxies mainly consist of the older stellar population, while the star forming in the outskirt of the galaxy is still ongoing. Aims. The high-resolution HST images from Hubble Deep UV Legacy Survey and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey projects with the unprecedented depth in both F275W and F160W bands are the perfect data sets to study the forming and formed stellar distribution directly. Methods. We selected the low redshift (0.05 &lt; zspec &lt; 0.3) galaxy sample from the GOODS-North field where the HST F275W and F160W images are available. Then we measured the half light radius in F275W and F160W bands, which are the indicators of the star formation and stellar mass. Results. By comparing the F275W and F160W half light radius, we find the massive galaxies are mainly follow the “inside-out” growth mode, which is consistent with the previous results. Moreover, the HST F275W and F160W images reveal that some of the low-mass galaxies (&lt; 108 M⊙) have the “outside-in” growth mode: their images show a compact UV morphology, implying an ongoing star formation in the galaxy centre, while the stars in the outskirts of the galaxies are already formed. The two modes transit smoothly at stellar mass range about 108 − 9 M⊙ with a large scatter. We also try to identify the possible neighbour massive galaxies from the SDSS data, which represent the massive galaxy sample. We find that all of the spec-z selected galaxies have no massive galaxy nearby. Thus the “outside-in” mode we find in the low-mass galaxies are not likely originated from the environment.

The stellar host in star-forming low-mass galaxies: Evidence for two classes

Context.The morphological evolution of star-forming galaxies provides important clues to understand their physical properties, as well as the triggering and quenching mechanisms of star formation.Aims.We analyze the morphology of galaxies hosting star-forming events at low redshift (z &lt; 0.36). We aim at connecting morphology and star-formation properties of low-mass galaxies (median stellar mass ∼108.5 M⊙) beyond the local Universe.Methods.We use a sample of mediumband selected star-forming galaxies from the GOODS-North field. Hαimages for the sample are created combining both spectral energy distribution fits and HST data. Using them, we mask the star forming regions to obtain an unbiased two-dimensional model of the light distribution of the host galaxies. For this purpose we usePHI, a new Bayesian photometric decomposition code. We applied it independently to 7 HST bands, from the ultraviolet to the near-infrared, assuming a Sérsic surface brightness model.Results.Star-forming galaxy hosts show low Sérsic index (with mediann ∼ 0.9), as well as small sizes (medianRe ∼ 1.6 kpc), and negligible change of the parameters with wavelength (except for the axis ratio, which grows with wavelength in 46% of the sample). Using a clustering algorithm, we find two different classes of star-forming galaxies: A more compact, redder, and high-n(class A) and a more extended, bluer and lower-none (class B). This separation holds across all seven bands analyzed. In addition, we find evidence that the first class is more spheroidal-like (according to the distribution of observed axis ratios). We compute the color gradients of the host galaxies finding that 48% of the objects where the analysis could be performed show negative gradients, and only in 5% they are positive.Conclusions.The host component of low-mass star-forming galaxies atz &lt; 0.36 separates into two different classes, similar to what has been found for their higher mass counterparts. The results are consistent with an evolution from class B to class A. Several mechanisms from the literature, like minor and major mergers, and violent disk instability, can explain the physical process behind the likely transition between the classes.

A machine-learning approach for identifying the counterparts of submillimetre galaxies and applications to the GOODS-North field

ABSTRACT Identifying the counterparts of submillimetre (submm) galaxies (SMGs) in multiwavelength images is a critical step towards building accurate models of the evolution of strongly star-forming galaxies in the early Universe. However, obtaining a statistically significant sample of robust associations is very challenging due to the poor angular resolution of single-dish submm facilities. Recently, a large sample of single-dish-detected SMGs in the UKIDSS UDS field, a subset of the SCUBA-2 Cosmology Legacy Survey (S2CLS), was followed up with the Atacama Large Millimeter/submillimeter Array (ALMA), which has provided the resolution necessary for identification in optical and near-infrared images. We use this ALMA sample to develop a training set suitable for machine-learning (ML) algorithms to determine how to identify SMG counterparts in multiwavelength images, using a combination of magnitudes and other derived features. We test several ML algorithms and find that a deep neural network performs the best, accurately identifying 85 per cent of the ALMA-detected optical SMG counterparts in our cross-validation tests. When we carefully tune traditional colour-cut methods, we find that the improvement in using machine learning is modest (about 5 per cent), but importantly it comes at little additional computational cost. We apply our trained neural network to the GOODS-North field, which also has single-dish submm observations from the S2CLS and deep multiwavelength data but little high-resolution interferometric submm imaging, and we find that we are able to classify SMG counterparts for 36/67 of the single-dish submm sources. We discuss future improvements to our ML approach, including combining ML with spectral energy distribution fitting techniques and using longer wavelength data as additional features.