The promise of multi-wavelength astronomy has been tempered by the large disparity in sensitivity and resolution between different wavelength regimes. Here we present a statistical approach which attempts to overcome this by fitting parametric models
directly to image data. Specifically, we fit a model for the radio luminosity function (LF) of star-forming galaxies to pixel intensity distributions at 1.4 GHz coincident with near-IR selected sources in COSMOS. Taking a mass-limited sample in redshift bins across the range $0<z<4$ we are able to fit the radio LF with ~0.2 dex precision in the key parameters (e.g. Phi*,L*). Good agreement is seen between our results and those using standard methods at radio and other wavelengths. Integrating our luminosity functions to get the star formation rate density we find that galaxies with a stellar mass greater than $10^{9.5},$M$_{odot}$ contribute at least 50 per cent of cosmic star formation at since $z=4$. The scalability of our approach is empirically estimated, with the precision in LF parameter estimates found to scale with the number of sources in the stack as $sqrt{N}$. This type of approach will be invaluable in the multi-wavelength analysis of upcoming surveys with the SKA pathfinder facilities; LOFAR, ASKAP and MeerKAT.
We investigate the multi-wavelength properties of a sample of 450-mu m selected sources from the SCUBA-2 Cosmology Legacy Survey (S2CLS). A total of 69 sources were identified above 4sigma in deep SCUBA-2 450-mu m observations overlapping the UDS and
COSMOS fields and covering 210 sq. arcmin to a typical depth of sigma 450=1.5 mJy. Reliable cross identification are found for 58 sources (84 per cent) in Spitzer and Hubble Space Telescope WFC3/IR data. The photometric redshift distribution (dN/dz) of 450mu m-selected sources is presented, showing a broad peak in the redshift range 1<z<3, and a median of z=1.4. Combining the SCUBA-2 photometry with Herschel SPIRE data from HerMES, the submm spectral energy distribution (SED) is examined via the use of modified blackbody fits, yielding aggregate values for the IR luminosity, dust temperature and emissivity of <LIR>=10^12 +/- 0.8 L_sol, <T_D>=42 +/- 11 K and <beta_D>=1.6 +/- 0.5, respectively. The relationship between these SED parameters and the physical properties of galaxies is investigated, revealing correlations between T_D and LIR and between beta_D and both stellar mass and effective radius. The connection between star formation rate and stellar mass is explored, with 24 per cent of 450 mu m sources found to be ``star-bursts, i.e. displaying anomalously high specific SFRs. However, both the number density and observed properties of these ``star-burst galaxies are found consistent with the population of normal star-forming galaxies.
We investigate the properties (e.g. star formation rate, dust attentuation, stellar mass and metallicity) of a sample of infrared luminous galaxies at z sim 1 via near-IR spectroscopy with Subaru-FMOS. Our sample consists of Herschel SPIRE and Spitze
r MIPS selected sources in the COSMOS field with photometric redshifts in the range 0.7 < z-phot < 1.8, which have been targeted in 2 pointings (0.5 sq. deg.) with FMOS. We find a modest success rate for emission line detections, with candidate H{alpha} emission lines detected for 57 of 168 SPIRE sources (34 per cent). By stacking the near-IR spectra we directly measure the mean Balmer decrement for the H{alpha} and H{beta} lines, finding a value of <E(B-V)> = 0.51pm0.27 for <LIR> = 10^12 Lsol sources at <z> = 1.36. By comparing star formation rates estimated from the IR and from the dust uncorrected H{alpha} line we find a strong relationship between dust attenuation and star formation rate. This relation is broadly consistent with that previously seen in star-forming galaxies at z ~ 0.1. Finally, we investigate the metallicity via the N2 ratio, finding that z ~ 1 IR-selected sources are indistinguishable from the local mass-metallicity relation. We also find a strong correlation between dust attentuation and metallicity, with the most metal-rich IR-sources experiencing the largest levels of dust attenuation.
We investigate the potential of submm-mm and submm-mm-radio photometric redshifts using a sample of mm-selected sources as seen at 250, 350 and 500 {mu}m by the SPIRE instrument on Herschel. From a sample of 63 previously identified mm-sources with r
eliable radio identifications in the GOODS-N and Lockman Hole North fields 46 (73 per cent) are found to have detections in at least one SPIRE band. We explore the observed submm/mm colour evolution with redshift, finding that the colours of mm-sources are adequately described by a modified blackbody with constant optical depth {tau} = ({ u}/{ u}0)^{beta} where {beta} = +1.8 and { u}0 = c/100 {mu}m. We find a tight correlation between dust temperature and IR luminosity. Using a single model of the dust temperature and IR luminosity relation we derive photometric redshift estimates for the 46 SPIRE detected mm-sources. Testing against the 22 sources with known spectroscopic, or good quality optical/near-IR photometric, redshifts we find submm/mm photometric redshifts offer a redshift accuracy of |z|/(1+z) = 0.16 (< |z| >= 0.51). Including constraints from the radio-far IR correlation the accuracy is improved to |z|/(1 + z) = 0.15 (< |z| >= 0.45). We estimate the redshift distribution of mm-selected sources finding a significant excess at z > 3 when compared to ~ 850 {mu}m selected samples.
