The VLA Frontier Field Survey: A Comparison of the Radio and UV/Optical Size of 0.3 ≲ z ≲ 3 Star-forming Galaxies

o investigate the growth history of galaxies, we measure the rest-frame radio, ultraviolet (UV), and optical sizes of 98 radio-selected, star-forming galaxies (SFGs) distributed over 0.3 ≲ z ≲ 3 with a median stellar mass of $\mathrm{log}({M}_{\star }/{M}_{\odot })\approx 10.4$. We compare the size of galaxy stellar disks, traced by rest-frame optical emission, relative to the overall extent of star formation activity that is traced by radio continuum emission. Galaxies in our sample are identified in three Hubble Frontier Fields: MACS J0416.1−2403, MACS J0717.5+3745, and MACS J1149.5+2223. Radio continuum sizes are derived from 3 and 6 GHz radio images (≲0farcs6 resolution, ≈0.9 μJy beam−1 noise level) from the Karl G. Jansky Very Large Array. Rest-frame UV and optical sizes are derived using observations from the Hubble Space Telescope and the Advanced Camera for Surveys and Wide Field Camera 3 instruments. We find no clear dependence between the 3 GHz radio size and stellar mass of SFGs, which contrasts with the positive correlation between the UV/optical size and stellar mass of galaxies. Focusing on SFGs with $\mathrm{log}({M}_{\star }/{M}_{\odot })\gt 10$, we find that the radio/UV/optical emission tends to be more compact in galaxies with high star formation rates (≳100 M⊙ yr−1), suggesting that a central, compact starburst (and/or an active galactic nucleus) resides in the most luminous galaxies of our sample. We also find that the physical radio/UV/optical size of radio-selected SFGs with log(M⋆/M⊙) > 10 increases by a factor of 1.5–2 from z ≈ 3 to z ≈ 0.3, yet the radio emission remains two to three times more compact than that from the UV/optical. These findings indicate that these massive, radio-selected SFGs at 0.3 ≲ z ≲ 3 tend to harbor centrally enhanced star formation activity relative to their outer disks

COLDz:: probing cosmic star formation with radio free-free emission

Galaxie

The Hawaii SCUBA-2 Lensing Cluster Survey: Radio-detected Submillimeter Galaxies in the HST Frontier Fields

In this second paper of the Hawaii SCUBA-2 Lensing Cluster Survey series, we cross-match SCUBA-2 maps with 3 and 6 GHz images from the Janksy-VLA Frontier Fields Legacy Survey for three cluster fields, MACS J0416.1--2403, MACS J0717.5+3745, and MACS J1149.5+2223. Within the HST coverage, 14 out of 44 850 μm sources have 3 GHz counterparts, five of which are also detected at 6 GHz. The 850 μm flux densities of these detected sources span from 0.7 to 4.4 mJy after correcting for lensing amplification. The median redshift of the sample is z=1.28+0.07−0.09, much lower than the typical redshifts (z=2−3) of brighter submillimeter galaxies in the literature. In addition, we find that our sources have lower dust temperatures than those of the brighter submillimeter galaxies. This is also confirmed by an analysis of the ratio between infrared star formation rate and 850 μm flux density. However, these 14 sources may not represent the general submillimeter population at the same flux range, given that the SCUBA-2 sources without radio counterparts are likely at higher redshifts. Detection of these sources would require deeper radio images or submillimeter interferometry

The VLA Frontier Fields Survey: Deep, High-resolution Radio Imaging of the MACS Lensing Clusters at 3 and 6 GHz

The Frontier Fields project is an observational campaign targeting six galaxy clusters, with the intention of using the magnification provided by gravitational lensing to study galaxies that are extremely faint or distant. We used the Karl G. Jansky Very Large Array (VLA) at 3 and 6 GHz to observe three Frontier Fields: MACS J0416.1 −2403 (z = 0.396), MACS J0717.5+3745 (z = 0.545), and MACS J1149.5+2223 (z = 0.543). The images reach noise levels of ∼1 μJy beam−1 with subarcsecond resolution (∼2.5 kpc at z = 3), providing a high-resolution view of high-z star-forming galaxies that is unbiased by dust obscuration. We generate dual-frequency continuum images at two different resolutions per band, per cluster, and derive catalogs totaling 1966 compact radio sources. Components within the areas of Hubble Space Telescope and Subaru observations are cross-matched, providing host galaxy identifications for 1296 of them. We detect 13 moderately lensed (2.1 < μ < 6.5) sources, one of which has a demagnified peak brightness of 0.9 μJy beam−1 , making it a candidate for the faintest radio source ever detected. There are 66 radio sources exhibiting complex morphologies, and 58 of these have host galaxy identifications. We reveal that MACS J1149.5+2223 is not a cluster with a double relic, as the western candidate relic is resolved as a double-lobed radio galaxy associated with a foreground elliptical at z = 0.24. The VLA Frontier Fields project is a public legacy survey. The image and catalog products from this work are freely available

The evolution of galaxy clustering since z = 3 using the UKIDSS Ultra Deep Survey: the divergence of passive and star-forming galaxies

We use the UKIDSS Ultra-Deep Survey to trace the evolution of galaxy clustering to z = 3. Using photometric redshifts derived from data covering the wavelength range 0.3 - 4.5 um we examine this clustering as a function of absolute K-band luminosity, colour and star-formation rate. Comparing the deprojected clustering amplitudes, we find that red galaxies are more strongly clustered than blue galaxies out to at least z = 1.5, irrespective of rest-frame K-band luminosity. We then construct passive and star-forming samples based on stellar age, colour and star-formation histories calculated from the best fitting templates. The clustering strength of star-forming galaxies declines steadily from r_0 ~ 7 h^-1 Mpc at z ~ 2 to r_0 ~ 3 h^-1 Mpc at z ~ 0, while passive galaxies have clustering strengths up to a factor of two higher. Within the passive and star-forming subsamples, however, we find very little dependence of galaxy clustering on K-band luminosity. Galaxy `passivity' appears to be the strongest indicator of clustering strength. We compare these clustering measurements with those predicted for dark matter halos and conclude that passive galaxies typically reside in halos of mass M > 10^13 M_sun while luminous star-forming galaxies occupy halos an order of magnitude less massive over the range 0.5 < z < 1.5. The decline in the clustering strength of star-forming galaxies with decreasing redshift indicates a decline in the hosting halo mass for galaxies of a given luminosity. We find evidence for convergence of clustering in star-forming and passive galaxies around z ~ 2, which is consistent with this being the epoch at which the red sequence of galaxies becomes distinct.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society. 11 pages containing 8 Figures and 1 table. The source contains additional results table

An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: radio properties and the far-infrared/radio correlation

We present a study of the radio properties of 870 μm-selected submillimetre galaxies (SMGs), observed at high resolution with Atacama Large Millimeter Array (ALMA) in the Extended Chandra Deep Field South. From our initial sample of 76 ALMA SMGs, we detect 52 SMGs at >3σ significance in Karl G. Jansky Very Large Array 1400 MHz imaging, of which 35 are also detected at >3σ in new 610 MHz Giant Metre-Wave Radio Telescope imaging. Within this sample of radio-detected SMGs, we measure a median radio spectral index α1400610=−0.79±0.06, (with inter-quartile range α = [−1.16, −0.56]) and investigate the far-infrared/radio correlation via the parameter qIR, the logarithmic ratio of the rest-frame 8–1000 μm flux and monochromatic radio flux. Our median qIR = 2.56 ± 0.05 (inter-quartile range qIR = [2.42, 2.78]) is higher than that typically seen in single-dish 870 μm-selected sources (qIR ∼ 2.4), which may reflect the fact that our ALMA-based study is not biased to radio-bright counterparts, as previous samples were. Finally, we search for evidence that qIR and α evolve with age in a codependent manner, as predicted by starburst models: the data populate the predicted region of parameter space, with the stellar mass tending to increase along tracks of qIR versus α in the direction expected, providing the first observational evidence in support of these models

Radio Spectra and Sizes of Atacama Large Millimeter/submillimeter Array-identified Submillimeter Galaxies: Evidence of Age-related Spectral Curvature and Cosmic-Ray Diffusion?

We analyze the multifrequency radio spectral properties of 41 6 GHz-detected Atacama Large Millimeter/submillimeter Array (ALMA)-identified, submillimeter galaxies (SMGs), observed at 610 MHz, 1.4 GHz, and 6 GHz with the Giant Metrewave Radio Telescope and the Very Large Array. Combining high-resolution (~0farcs5) 6 GHz radio and ALMA 870 μm imaging (tracing rest frame ~20 GHz, and ~250 μm dust continuum), we study the far-infrared/radio correlation via the logarithmic flux ratio q IR, measuring $\langle {q}_{\mathrm{IR}}\rangle =2.20\pm 0.06$ for our sample. We show that the high-frequency radio sizes of SMGs are ~1.9 ± 0.4× (~2–3 kpc) larger than those of the cool dust emission, and find evidence for a subset of our sources being extended on ~10 kpc scales at 1.4 GHz. By combining radio flux densities measured at three frequencies, we can move beyond simple linear fits to the radio spectra of high-redshift star-forming galaxies, and search for spectral curvature, which has been observed in local starburst galaxies. At least a quarter (10/41) of our sample shows evidence of a spectral break, with a median $\langle {\alpha }_{610\,\mathrm{GHz}}^{1.4\,\mathrm{GHz}}\rangle =-0.60\pm 0.06$, but $\langle {\alpha }_{1.4\,\mathrm{GHz}}^{6\,\mathrm{GHz}}\rangle =-1.06\pm 0.04$—a high-frequency flux deficit relative to simple extrapolations from the low-frequency data. We explore this result within this subset of sources in the context of age-related synchrotron losses, showing that a combination of weak magnetic fields (B ~ 35 μG) and young ages (t SB ~ 40–80 Myr) for the central starburst can reproduce the observed spectral break. Assuming these represent evolved (but ongoing) starbursts, and we are observing these systems roughly halfway through their current episode of star formation, this implies starburst durations of lesssim100 Myr, in reasonable agreement with estimates derived via gas depletion timescales

The e-MERGE Survey (e-MERLIN Galaxy Evolution Survey): overview and survey description

We present an overview and description of the e-MERGE Survey (e-MERLIN Galaxy Evolution Survey) Data Release 1 (DR1), a large program of high-resolution 1.5-GHz radio observations of the GOODS-N field comprising ∼140 h of observations with enhanced-Multi-Element Remotely Linked Interferometer Network (e-MERLIN) and ∼40 h with the Very Large Array (VLA). We combine the long baselines of e-MERLIN (providing high angular resolution) with the relatively closely packed antennas of the VLA (providing excellent surface brightness sensitivity) to produce a deep 1.5-GHz radio survey with the sensitivity (⁠∼1.5μ Jy beam−1), angular resolution (0.2–0.7 arcsec) and field-of-view (∼15 × 15 arcmin2) to detect and spatially resolve star-forming galaxies and active galactic nucleus (AGN) at z ≳ 1. The goal of e-MERGE is to provide new constraints on the deep, sub-arcsecond radio sky which will be surveyed by SKA1-mid. In this initial publication, we discuss our data analysis techniques, including steps taken to model in-beam source variability over an ∼20-yr baseline and the development of new point spread function/primary beam models to seamlessly merge e-MERLIN and VLA data in the uv plane. We present early science results, including measurements of the luminosities and/or linear sizes of ∼500 galaxies selected at 1.5 GHz. In combination with deep Hubble Space Telescope observations, we measure a mean radio-to-optical size ratio of re-MERGE/rHST ∼ 1.02 ± 0.03, suggesting that in most high-redshift galaxies, the ∼GHz continuum emission traces the stellar light seen in optical imaging. This is the first in a series of papers that will explore the ∼kpc-scale radio properties of star-forming galaxies and AGN in the GOODS-N field observed by e-MERGE DR1