The ultraviolet luminosity function of star-forming galaxies between redshifts of 0.4 and 0.6

ABSTRACT We combine ultraviolet imaging of the $13^{H}$ survey field, taken with the XMM–Newton Optical Monitor telescope (XMM–OM) and the Neil Gehrels Swift Observatory Ultraviolet and Optical Telescope (UVOT) in the UVM2 band, to measure rest-frame ultraviolet 1500 Å luminosity functions of star-forming galaxies with redshifts z between 0.4 and 0.6. In total the UVM2 imaging covers a sky area of 641 arcmin$^{2}$, and we detect 273 galaxies in the UVM2 image with $0.4\lt z\lt 0.6$. The luminosity function is fit by a Schechter function with best-fitting values for the faint end slope $\alpha =-1.8^{+0.4}_{-0.3}$ and characteristic absolute magnitude $M^{*} = -19.1^{+0.3}_{-0.4}$. In common with XMM–OM based studies at higher redshifts, our best-fitting value for $M^{*}$ is fainter than previous measurements. We argue that the purging of active galactic nuclei from the sample, facilitated by the cospatial X-ray survey carried out with XMM–Newton is important for the determination of $M^{*}$. At the brightest absolute magnitudes ($M_{1500}\lt -18.5$), the average UV colour of our galaxies is consistent with that of minimal-extinction local analogues, but the average UV colour is redder for galaxies at fainter absolute magnitudes, suggesting that higher levels of dust attenuation enter the sample at absolute magnitudes somewhat fainter than $M^{*}$.