Dr Imogen Whittam

Abstract:

Published by Oxford University Press on behalf of the Royal Astronomical Society. We have combined spectroscopic and photometric data from the Sloan Digital Sky Survey with 1.4 GHz radio observations, conducted as part of the Stripe 82 1-2 GHz Snapshot Survey using the Karl G. Jansky Very Large Array, which covers ~100 sq deg, to a flux limit of 88 μJy rms. Cross-matching the 11 768 radio source components with optical data via visual inspection results in a final sample of 4794 cross-matched objects, of which 1996 have spectroscopic redshifts and 2798 objects have photometric redshifts. Three previously undiscovered giant radio galaxies were found during the cross-matching process, which would have been missed using automated techniques. For the objects with spectroscopy, we separate radio-loud active galactic nuclei (AGN) and star-forming galaxies (SFGs) using three diagnostics and then further divide our radio-loud AGN into the high and low excitation radio galaxy (HERG and LERG) populations. A control-matched sample of HERGs and LERGs, matched on stellar mass, redshift, and radio luminosity, reveals that the host galaxies of LERGs are redder and more concentrated than HERGs. By combining with near-infrared data, we demonstrate that LERGs also follow a tight K - z relationship. These results imply the LERG populations are hosted by population ofmassive, passively evolving early-type galaxies. We go on to show that HERGs, LERGs, quasars, and SFGs in our sample all reside in different regions of aWide-field Infrared Survey Explorer colour-colour diagram. This cross-matched sample bridges the gap between previous 'wide but shallow' and 'deep but narrow' samples and will be useful for a number of future investigations.

Abstract:

We present 610-MHz Giant Metrewave Radio Telescope observations of 0.84 deg2 of the AMI001 field (centred on 00h23m10s, +31°53΄) with an rms noise of 18 μJy beam−1 in the centre of the field. A total of 955 sources are detected, and 814 are included in the source count analysis. The source counts from these observations are consistent with previous work. We have used these data to study the spectral index distribution of a sample of sources selected at 15.7 GHz from the recent deep extension to the Tenth Cambridge (10C) survey. The median spectral index, α, (where S ∝ ν−α) between 0.08

Abstract:

A complete sample of 96 faint ($S > 0.5$ mJy) radio galaxies is selected from the Tenth Cambridge (10C) survey at 15.7~GHz. Optical spectra are used to classify 17 of the sources as high-excitation or low-excitation radio galaxies (HERGs and LERGs respectively), for the remaining sources three other methods are used; these are optical compactness, X-ray observations and mid-infrared colour--colour diagrams. 32 sources are HERGs and 35 are LERGs while the remaining 29 sources could not be classified. We find that the 10C HERGs tend to have higher 15.7-GHz flux densities, flatter spectra, smaller linear sizes and be found at higher redshifts than the LERGs. This suggests that the 10C HERGs are more core dominated than the LERGs. Lower-frequency radio images, linear sizes and spectral indices are used to classify the sources according to their radio morphology; 18 are Fanaroff and Riley type I or II sources, a further 13 show some extended emission, and the remaining 65 sources are compact and are referred to as FR0 sources. The FR0 sources are sub-divided into compact, steep-spectrum (CSS) sources (13 sources) or GHz-peaked spectrum (GPS) sources (10 sources) with the remaining 42 in an unclassified class. FR0 sources are more dominant in the subset of sources with 15.7-GHz flux densities $<$1 mJy, consistent with the previous result that the fainter 10C sources have flatter radio spectra. The properties of the 10C sources are compared to the higher-flux density Australia Telescope 20 GHz (AT20G) survey. The 10C sources are found at similar redshifts to the AT20G sources but have lower luminosities. The nature of the high-frequency selected objects change as flux density decreases; at high flux densities the objects are primarily quasars, while at low flux densities radio galaxies dominate.