The host galaxies of micro-Jansky radio sources

Abstract

We combine a deep 0.5~deg${}^2$, 1.4~GHz deep radio survey in the Lockman Hole with infrared and optical data in the same field, including the SERVS and UKIDSS near-infrared surveys, to make the largest study to date of the host galaxies of radio sources with typical radio flux densities $\sim 50\mu$Jy. 87% (1274/1467) of radio sources have identifications in SERVS to $AB\approx 23.1$ at 3.6 or 4.5$\mu$m, and 9% are blended with bright objects (mostly stars), leaving only 4% (59 objects) which are too faint to confidently identify in the near-infrared. We are able to estimate photometric redshifts for 68% of the radio sources. We use mid-infrared diagnostics to show that the source population consists of a mixture of star forming galaxies, rapidly accreting (cold mode) AGN and low accretion rate, hot mode AGN, with neither AGN nor starforming galaxies clearly dominating. We see the breakdown in the $K-z$ relation in faint radio source samples, and show that it is due to radio source populations becoming dominated by sources with radio luminosities $\sim 10^{23}\mathrm{WH}{\mathrm{z}}^{-1}$. At these luminosities, both the star forming galaxies and the cold mode AGN have hosts with stellar luminosities about a factor of two lower than those of hot mode AGN, which continue to reside in only the most massive hosts. We show that out to at least $z\sim 2$, galaxies with stellar masses $>10^{11.5}{M}_{\odot }$ have a radio-loud fraction up to $\sim 30$%. This is consistent with there being a sufficient number of radio sources that radio-mode feedback could play a role in galaxy evolution.

13 pages, accepted by AJ

References in corpus (14)

• The UKIRT Infrared Deep Sky Survey (UKIDSS)
• The mass evolution of the first galaxies: stellar mass functions and star formation rates at $4<z<7$ in the CANDELS GOODS-South field
• An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: High resolution 870um source counts
• The Massive Hosts of Radio Galaxies Across Cosmic Time
• Optical spectroscopy and X-ray detections of a sample of quasars and AGN selected in the mid-infrared from two Spitzer wide-area surveys
• Radio imaging of the Subaru/XMM-Newton Deep Field - I. The 100-microJy catalogue, optical identifications, and the nature of the faint radio source population
• The Star Formation History of the Universe as Revealed by Deep Radio Observations
• Spitzer Reveals Hidden Quasar Nuclei in Some Powerful FR II Radio Galaxies
• A new method to separate star forming from AGN galaxies at intermediate redshift: The submillijansky radio population in the VLA-COSMOS survey
• Radio faint AGN: a tale of two populations
• Exploring the infrared/radio correlation at high redshift
• Mean and Extreme Radio Properties of Quasars and the Origin of Radio Emission
• The Deep SWIRE Field II. 90cm Continuum Observations and 20cm-90cm Spectra
• Multiwavelength characterization of faint Ultra Steep Spectrum radio sources : A search for high-redshift radio galaxies

Cited by in corpus (11)

• Is the Observable Universe Consistent with the Cosmological Principle?
• The MeerKAT Galaxy Cluster Legacy Survey I. Survey Overview and Highlights
• The Lockman Hole Project: new constraints on the sub-mJy source counts from a wide-area 1.4 GHz mosaic
• Deep 3 GHz Observations of the Lockman Hole North with the Very Large Array -2. Catalogue and μJy source properties
• A Spitzer survey of Deep Drilling Fields to be targeted by the Vera C. Rubin Observatory Legacy Survey of Space and Time
• Revolutionizing Our Understanding of AGN Feedback and its Importance to Galaxy Evolution in the Era of the Next Generation Very Large Array
• Active Galactic Nuclei as seen by the Spitzer Space Telescope
• 10C continued: a deeper radio survey at 15.7 GHz
• The Nature of the Faint Low-Frequency Radio Source Population
• Faint polarised sources in the Lockman Hole field at 1.4 GHz
• Solar system peculiar motion from the Hubble diagram of quasars and testing the Cosmological Principle