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We present the Large Area Radio Galaxy Evolution Spectroscopic Survey (LARGESS), a spectroscopic catalogue of radio sources designed to include the full range of radio AGN populations out to redshift z ~ 0.8. The catalogue covers ~800 deg² of sky, and provides optical identifications for 19 179 radio sources from the 1.4 GHz Faint Images of the Radio Sky at Twenty-cm (FIRST) survey down to an optical magnitude limit of imod < 20.5 in Sloan Digital Sky Survey (SDSS) images. Both galaxies and point-like objects are included, and no colour cuts are applied. In collaboration with the WiggleZ and Galaxy And Mass Assembly (GAMA) spectroscopic survey teams, we have obtained new spectra for over 5000 objects in the LARGESS sample. Combining these new spectra with data from earlier surveys provides spectroscopic data for 12 329 radio sources in the survey area, of which 10 856 have reliable redshifts. 85 per cent of the LARGESS spectroscopic sample are radio AGN (median redshift z = 0.44), and 15 per cent are nearby star-forming galaxies (median z = 0.08). Low-excitation radio galaxies (LERGs) comprise the majority (83 per cent) of LARGESS radio AGN at z < 0.8, with 12 per cent being high-excitation radio galaxies (HERGs) and 5 per cent radioloud QSOs. Unlike the more homogeneous LERG and QSO sub-populations, HERGs are a heterogeneous class of objects with relatively blue optical colours and a wide dispersion in mid-infrared colours. This is consistent with a picture in which most HERGs are hosted by galaxies with recent or ongoing star formation as well as a classical accretion disc. [ABSTRACT FROM AUTHOR]

The Lockman Hole is a well-studied extragalactic field with extensive multi-band ancillary data covering a wide range in frequency, essential for characterizing the physical and evolutionary properties of the various source populations detected in deep radio fields (mainly star-forming galaxies and AGNs). In this paper, we present new 150-MHz observations carried out with the LOw-Frequency ARray (LOFAR), allowing us to explore a new spectral window for the faint radio source population. This 150-MHz image covers an area of 34.7 square degrees with a resolution of 18.6×14.7 arcsec and reaches an rms of 160 μJy beam-1 at the centre of the field. As expected for a low-frequency selected sample, the vast majority of sources exhibit steep spectra, with a median spectral index of α1400 150 = -0.78 ± 0.015. The median spectral index becomes slightly flatter (increasing from α1400 150 = -0.84 to α1400 150 = -0.75) with decreasing flux density down to S150 ~10 mJy before flattening out and remaining constant below this flux level. For a bright subset of the 150-MHz selected sample, we can trace the spectral properties down to lower frequencies using 60-MHz LOFAR observations, finding tentative evidence for sources to become flatter in spectrum between 60 and 150 MHz. Using the deep, multi-frequency data available in the Lockman Hole, we identify a sample of 100 ultra-steepspectrum sources and 13 peaked-spectrum sources.We estimate that up to 21 per cent of these could have z > 4 and are candidate high-z radio galaxies, but further follow-up observations are required to confirm the physical nature of these objects. [ABSTRACT FROM AUTHOR]

ABSTRACT We present spectroscopic and 11-band photometric redshifts for galaxies in the 100- μJy Subaru/ XMM-Newton Deep Field radio source sample. We find good agreement between our redshift distribution and that predicted by the Square Kilometre Array (SKA) Simulated Skies project. We find no correlation between K-band magnitude and radio flux, but show that sources with 1.4-GHz flux densities below ∼1 mJy are fainter in the near-infrared than brighter radio sources at the same redshift, and we discuss the implications of this result for spectroscopically incomplete samples where the K- z relation has been used to estimate redshifts. We use the infrared-radio correlation to separate our sample into radio-loud and radio-quiet objects and show that only radio-loud hosts have spectral energy distributions consistent with predominantly old stellar populations, although the fraction of objects displaying such properties is a decreasing function of radio luminosity. We calculate the 1.4-GHz radio luminosity function (RLF) in redshift bins to z= 4 and find that the space density of radio sources increases with lookback time to z≈ 2, with a more rapid increase for more powerful sources. We demonstrate that radio-loud and radio-quiet sources of the same radio luminosity evolve very differently. Radio-quiet sources display strong evolution to z≈ 2 while radio-loud active galactic nuclei below the break in the RLF evolve more modestly and show hints of a decline in their space density at z > 1, with this decline occurring later for lower-luminosity objects. If the radio luminosities of these sources are a function of their black hole spins then slowly rotating black holes must have a plentiful fuel supply for longer, perhaps because they have yet to encounter the major merger that will spin them up and use the remaining gas in a major burst of star formation. [ABSTRACT FROM AUTHOR]

To exploit synergies between the Herschel Space Observatory and next generation radio facilities, we have extended the semi-empirical extragalactic radio continuum simulation of Wilman et al. to the mid- and far-infrared. Here, we describe the assignment of infrared spectral energy distributions (SEDs) to the star-forming galaxies and active galactic nuclei, using Spitzer 24, 70 and 160 μm and SCUBA 850 μm survey results as the main constraints. Star-forming galaxies dominate the source counts, and a model in which their far-infrared–radio correlation and infrared SED assignment procedure are invariant with redshift underpredicts the observed 24 and 70 μm source counts. The 70 μm deficit can be eliminated if the star-forming galaxies undergo stronger luminosity evolution than originally assumed for the radio simulation, a requirement which may be partially ascribed to known non-linearity in the far-infrared–radio correlation at low luminosity if it evolves with redshift. At 24 μm, the shortfall is reduced if the star-forming galaxies develop SEDs with cooler dust and correspondingly stronger polycyclic aromatic hydrocarbon emission features with increasing redshift at a given far-infrared luminosity, but this trend may reverse at in order not to overproduce the submillimetre source counts. The resulting model compares favourably with recent Balloon-borne Large Aperture Submillimetre Telescope ( BLAST) results, and we have extended the simulation data base to aid the interpretation of Herschel surveys. Such comparisons may also facilitate further model refinement and revised predictions for the Square Kilometre Array and its precursors. [ABSTRACT FROM AUTHOR]

Gigahertz-peaked spectrum (GPS) radio sources are thought to be young objects which later evolve into Fanaro–Riley type I (FR I) and FR II radio galaxies. We have used the Australia Telescope 20 GHz (AT20G) survey catalogue to select a uniform sample of GPS sources with spectral peaks above 5 GHz, which should represent the youngest members of this class. In this paper, we present e-VLBI observations of 10 such objects which are associated with nearby galaxies and so represent a new population of local, low-power GPS sources. Our e-VLBI observations were carried out at 4.8 GHz with the Australia Telescope Long Baseline Array (LBA) using a real-time software correlator. All 10 sources were detected, and were unresolved on scales of ∼100 mas, implying that they are typically less than 100 pc in linear size. [ABSTRACT FROM AUTHOR]

We have used the Australia Telescope Compact Array (ATCA) at 95 GHz to carry out continuum observations of 130 extragalactic radio sources selected from the Australia Telescope 20 GHz (AT20G) survey. We use a triple-correlation method to measure simultaneous 20- and 95-GHz flux densities for these objects, and over 90 per cent of our target sources are detected at 95 GHz. We demonstrate that the ATCA can robustly measure 95-GHz flux densities with an accuracy of ∼10 per cent in a few minutes for sources stronger than about 50 mJy. We measure the distribution of radio spectral indices in a flux-limited sample of extragalactic sources, and show that the median 20–95 GHz spectral index does not vary significantly with flux density for . This finding allows us to estimate the extragalactic radio source counts at 95 GHz by combining our observed 20–95 GHz spectral-index distribution with the accurate 20-GHz source counts measured in the AT20G survey. Our derived 95-GHz source counts at flux densities above 80 mJy are significantly lower than those found by several previous studies. The main reason is that most radio sources with flat or rising spectra in the frequency range 5–20 GHz show a spectral turnover between 20 and 95 GHz. As a result, there are fewer 95-GHz sources (by almost a factor of 2 at 0.1 Jy) than would be predicted on the basis of extrapolation from the source populations seen in lower-frequency surveys. We also derive the predicted confusion noise in cosmic microwave background surveys at 95 GHz and find a value 20–30 per cent lower than previous estimates. The 95-GHz source population at the flux levels probed by this study is dominated by quasi-stellar objects with a median redshift . We find a correlation between optical magnitude and 95-GHz flux density which suggests that many of the brightest 95-GHz sources may be relativistically beamed, with both the optical and millimetre continuum significantly brightened by Doppler boosting. [ABSTRACT FROM AUTHOR]

We present results on spectral index distributions, number counts, redshift distribution and other general statistical properties of extragalactic point sources in the New Extragalactic WMAP Point Source5σ (NEWPS) sample. The flux calibrations at all the Wilkinson Microwave Anisotropy Probe channels have been reassessed both by comparison with ground-based observations and through estimates of the effective beam areas. The two methods yield consistent statistical correction factors. A search of the NASA Extragalactic Data base (NED) has yielded optical identifications for ∼89 per cent of sources in the complete subsample of 252 sources with signal-to-noise ratio (S/N) ≥ 5 and S≥ 1.1 Jy at 23 GHz; five sources turned out to be Galactic and were removed. The NED also yielded redshifts for ≃92 per cent of the extragalactic sources at | b| > 10°. Their distribution was compared with model predictions; the agreement is generally good but a possible discrepancy is noted. Using the 5 GHz fluxes from the GB6 or PMN surveys, we find that ∼76 per cent of the 191 extragalactic sources with Jy can be classified as flat-spectrum sources between 5 and 23 GHz. A spectral steepening is observed at higher frequencies: only 59 per cent of our sources are still flat-spectrum sources between 23 and 61 GHz, and the average spectral indexes steepen from to . We think, however, that the difference may be due to a selection effect. The source number counts have a close to Euclidean slope and are in good agreement with the predictions of the cosmological evolution model by De Zotti et al. The observed spectral index distributions were exploited to get model-independent extrapolations of counts to higher frequencies. The risks of such operations are discussed and reasons of discrepancies with other recent estimates are clarified. [ABSTRACT FROM AUTHOR]

This is the third in a series of papers that present observations and results for a sample of 76 ultrasteep-spectrum radio sources designed to find galaxies at high redshift. Here we present multifrequency radio observations, from the Australia Telescope Compact Array, for a subset of 37 galaxies from the sample. Matched resolution observations at 2.3, 4.8 and 6.2 GHz are presented for all galaxies, with the galaxies additionally observed at 8.6 and 18 GHz. New angular size constraints are reported for 19 sources based on high-resolution 4.8- and 6.2-GHz observations. Functional forms for the rest-frame spectral energy distributions are derived: 89 per cent of the sample is well characterized by a single power law, whilst the remaining 11 per cent show some flattening towards higher frequencies: not one source shows any evidence for high-frequency steepening. We discuss the implications of this result in light of the empirical correlation between redshift and spectral index seen in flux-limited samples of radio galaxies. Finally, a new physical mechanism to explain the redshift – spectral index correlation is posited: extremely steep-spectrum radio galaxies in the local universe usually reside at the centres of rich galaxy clusters. We argue that if a higher fractions of radio galaxies, as a function of redshift, are located in environments with densities similar to nearby rich clusters, then this could be a natural interpretation for the correlation. We briefly outline our plans to pursue this line of investigation. [ABSTRACT FROM AUTHOR]

We discuss the panchromatic properties of 99 088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 ‘main’ spectroscopic sample (a flux-limited sample for 1360 deg2). These galaxies are positionally matched to sources detected by ROSAT, Galaxy Evolution Explorer (GALEX), two-Micron All-Sky Survey (2MASS), Infrared Astronomical Satellite ( IRAS), Green Bank GB6 survey (GB6), Faint Images of the Radio Sky at Twenty-centimetres (FIRST), NRAO VLA Sky Survey (NVSS) and Westerbork Northern Sky Survey (WENSS). The matching fraction varies from <1 per cent for ROSAT and GB6 to ∼40 per cent for GALEX and 2MASS. In addition to its size, the advantages of this sample are well-controlled selection effects, faint flux limits and the wealth of measured parameters, including accurate X-ray to radio photometry, angular sizes and optical spectra. We find strong correlations between the detection fraction at other wavelengths and optical properties such as flux, colours and emission-line strengths. For example, ∼2/3 of SDSS ‘main’ galaxies classified as active galactic nucleus (AGN) using emission-line strengths are detected by 2MASS, while the corresponding fraction for star-forming galaxies (SFs) is only ∼1/10. Similarly, over 90 per cent of galaxies detected by IRAS display strong emission lines in their optical spectra, compared to ∼50 per cent for the whole SDSS sample. Using GALEX, SDSS and 2MASS data, we construct the ultraviolet–infrared (UV–IR) broad-band spectral energy distributions for various types of galaxies, and find that they form a nearly one-parameter family. For example, the SDSS u- and r-band data, supplemented with redshift, can be used to ‘predict’ K-band magnitudes measured by 2MASS with an rms scatter of only 0.2 mag. When a dust content estimate determined from SDSS spectra with the aid of models is also utilized, this scatter decreases to 0.1 mag and can be fully accounted for by measurement uncertainties. We demonstrate that this interstellar dust content, inferred from optical SDSS spectra by Kauffmann et al., is indeed higher for galaxies detected by IRAS and that it can be used to ‘predict’ measured IRAS 60 μm flux density within a factor of 2 using only SDSS data. We also show that the position of a galaxy in the emission-line-based Baldwin–Phillips–Terlevich diagram is correlated with the optical light concentration index and u− r colour determined from the SDSS broad-band imaging data, and discuss changes in the morphology of this diagram induced by requiring detections at other wavelengths. Notably, we find that SDSS ‘main’ galaxies detected by GALEX include a non-negligible fraction (10–30 per cent) of AGNs, and hence do not represent a clean sample of starburst galaxies. We study the IR–radio correlation and find evidence that its slope may be different for AGN and SFs and related to the Hα/Hβ line-strength ratio. [ABSTRACT FROM AUTHOR]

We present initial results from a follow-up of the 9C survey, complete to 25 mJy at 15 GHz, designed to assemble and investigate a sample of young radio sources. We have made radio continuum maps of 111 sources at frequencies spanning 1.4–43 GHz, and classified them according to their radio size and spectral index between 1.4 and 4.8 GHz. We find that selection at 15 GHz is twice as efficient at picking Gigahertz Peaked Spectrum (GPS) sources as selection at ∼5 GHz. Optical follow-up has now begun; imaging of GPS and compact steep spectrum sources suggests that a significant fraction of the host galaxies have close companions or disturbed morphologies. [Copyright &y& Elsevier]