The WIRCam Deep Survey II: Mass Selected Clustering

We present an analysis of the clustering of galaxies from z ~ 2 to the present day using the WIRCam Deep Survey (WIRDS). WIRDS combines deep near-infrared data with the deep optical data from the CFHTLS Deep fields, providing a photometric data-set over an effective area of 2.4 sq. deg., from which accurate photometric redshifts and stellar masses can be estimated. We use the data to calculate the angular correlation function for galaxy samples split by star-formation activity, stellar mass and redshift. We estimate the real-space clustering for each sample, determining clustering lengths and power-law slopes. For galaxies selected by constant mass, we find that the clustering scale shows no evolution up to z ~ 2. Splitting the galaxy sample by mass, we see that higher mass galaxies have larger clustering scales at all redshifts. We use our results to test the GALFORM semi-analytical galaxy formation model and find the two are consistent. We split the galaxy population into passive and star-forming populations and find that the passive galaxy population shows a significantly larger clustering scale at all redshifts than the star-forming population below masses of ~$10^{11}M_odot/h$, showing that even at z ~ 2 passive galaxies exist in denser environments than the bulk of the star-forming galaxy population. For star-forming galaxies with stellar masses $>10^{11}M_odot/h$, we find a clustering strength of ~8Mpc/h across all redshifts, comparable to the measurements for the passive population. Also, for star-forming galaxies we see that clustering strength increases for higher stellar mass systems, however there is little sign of a mass dependence in passive galaxies. Finally, we investigate the connection between galaxy stellar mass and dark matter halo mass, showing a clear correlation between the two in both the WIRDS data and the GALFORM predictions.

The VLT LBG Redshift Survey - III. The clustering and dynamics of Lyman-break galaxies at z ~ 3

We present a catalogue of 2135 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z ~ 3 galaxies in wide fields centred on background quasi-stellar objects. We have used deep optical imaging to select galaxies via the Lyman-break technique. Spectroscopy of the Lyman-break galaxies (LBGs) was then made using the Visible Multi-Object Spectrograph (VIMOS), giving a mean redshift of z=2.79. We analyse the clustering properties of the VLRS sample and also of the VLRS sample combined with the smaller area Keck-based survey of Steidel et al. From the semiprojected correlation function, wp({sigma}) we find that the results are well fit with a single power-law model, with clustering scale lengths of r0=3.46+-0.41 and 3.83+-0.24 Mpc/h, respectively. We note that the corresponding combined {xi}(r) slope is flatter than for local galaxies at {gamma} = 1.5-1.6 rather than {gamma}=1.8. This flat slope is confirmed by the z-space correlation function, {xi}(s), and in the range 10<s<100 Mpc/h the VLRS shows ~2.5{sigma} excess over the {Lambda} cold dark matter. This excess may be consistent with recent evidence for non-Gaussianity in clustering results at z~1. We then analyse the LBG z-space distortions using the 2D correlation function, {xi}({sigma}, {pi}), finding for the combined sample a large-scale infall parameter of $beta$ = 0.38+-0.19 and a velocity dispersion of 420km/s. Based on our measured {beta}, we are able to determine the gravitational growth rate, finding a value of f(z = 3)=0.99+-0.50 (or f{sigma}8 = 0.26+-0.13), which is the highest redshift measurement of the growth rate via galaxy clustering and is consistent with {Lambda}CDM. Finally, we constrain the mean halo mass for the LBG population, finding that the VLRS and combined sample suggest mean halo masses of log(MDM/Msun) = 11.57+-0.15 and 11.73+-0.07, respectively.

The WIRCam Deep Survey I: Counts, colours and mass-functions derived from near-infrared imaging in the CFHTLS deep fields

We present a new near-infrared imaging survey in the four CFHTLS deep fields: the WIRCam Deep Survey (WIRDS). WIRDS comprises extremely deep, high quality (FWHM ~0.6) J, H and K imaging covering a total effective area of 2.1 deg^2 and reaching AB 50% completeness limits of ~24.5. We combine our images with the CFHTLS to create a unique eight-band ugrizJHK photometric catalogues in the CFHTLS deep fields; these four separate fields allow us to make a robust estimate of the effect of cosmic variance for all our measurements. We use these catalogues to estimate precise photometric redshifts, galaxy types and stellar masses for a unique sample of ~1.8 million galaxies. Our JHK number counts are consistent with previous studies. We apply the BzK selection to our gzK filter set and find that the star forming BzK selection successfully selects 76% of star-forming galaxies in the redshift range 1.4<z<2.5 in our photometric catalogue. The passive BzK selection returns 52% of the passive 1.4<z<2.5 population identified in the photometric catalogue. We present the galaxy stellar mass function as a function of redshift up to z=2 and present fits using double Schechter functions. A mass-dependent evolution of the mass function is seen with the numbers of galaxies with masses of log(M)<10.75 still evolving at z<1, but galaxies of higher mass reaching their present day numbers by z~0.8-1. This is consistent with the present picture of downsizing in galaxy evolution. We compare our results with the predictions of the GALFORM semi-analytical galaxy formation model and find that the simulations provide a relatively successful fit to the observed mass functions at intermediate masses (i.e. 10<log(M)<11). However, the GALFORM results under-predict the mass function at low masses, whilst the fit as a whole degrades beyond redshifts of z~1.2.

Submillimetre observations of X-ray active galactic nuclei in the William Herschel Deep Field

We investigate the contribution made by active galactic nuclei (AGN) to the high-redshift, luminous, submillimetre (submm) source population using deep (< 2 mJy/beam) Large Apex Bolometer Camera (LABOCA) 870 um observations within the William Herschel Deep Field (WHDF). This submm data complements previously obtained Chandra X-ray data of the field, from which AGN have been identified with the aid of follow-up optical spectra. From the LABOCA data, we detect 11 submm sources (based on a detection threshold of 3.2 sigma) with estimated fluxes of > 3 mJy/beam. Of the 11 identified submm sources, we find that 2 coincide with observed AGN and that, based on their hardness ratios, both of these AGN appear to be heavily obscured. We perform a stacking of the submm data around the AGN, which we group by estimated column density, and find that only the obscured (N_H > 10^22 cm^2) AGN show significant associated submm emission. These observations support the previous findings of Page et al and Hill et al that obscured AGN preferentially show submm emission. Hill et al have argued that, in this case, the contribution to the observed submm emission (and thus the submm background) from AGN heating of the dust in these sources may be higher than previously thought.