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We present an analysis of the luminosities and equivalent widths of the 284 z < 0.56 [O ii]-emitting galaxies found in the 169 arcmin2 pilot survey for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). By combining emission-line fluxes obtained from the Mitchell spectrograph on the McDonald 2.7 m telescope with deep broadband photometry from archival data, we derive each galaxy’s dereddened [O ii] λ3727 luminosity and calculate its total star formation rate. We show that over the last ∼5Gyr of cosmic time, there has been substantial evolution in the [O ii] emission-line luminosity function, with L ∗ decreasing by ∼0.6 ± 0.2 dex in the observed function, and by ∼0.9 ± 0.2 dex in the dereddened relation. Accompanying this decline is a significant shift in the distribution of [Oii] equivalent widths, with the fraction of high equivalent-width emitters declining dramatically with time. Overall, the data imply that the relative intensity of star formation within galaxies has decreased over the past ∼5Gyr, and that the star formation rate density of the universe has declined by a factor of ∼2.5 between z ∼ 0.5 and z ∼ 0. These observations represent the first [O ii]-based star formation rate density measurements in this redshift range, and foreshadow the advancements which will be generated by the main HETDEX survey. [ABSTRACT FROM AUTHOR]

This paper presents an environment and stellar mass study of a large sample of star-forming Hα emitters at from the High- z Emission Line Survey (HiZELS), over 1.3 deg split over two fields (COSMOS and UKIDSS UDS). By taking advantage of a truly panoramic coverage of a wide range of environments, from the field to a rich cluster, it is shown that both stellar mass and environment play crucial roles in determining the properties of star-forming galaxies. Specific star formation rates (sSFRs) decline with stellar mass in all environments, and the fraction of Hα star-forming galaxies declines sharply from per cent for galaxies with masses around 10 M to effectively zero above , confirming that mass-downsizing is generally in place by . The fraction of star-forming galaxies is also found to fall sharply as a function of local environmental density from per cent in the field to approaching zero at rich group/cluster densities. When star formation does occur in such high density regions, it is found to be mostly dominated by potential mergers and, indeed, if only non-merging star-forming galaxies are considered, then the environment and mass trends are even stronger and are qualitatively similar at all masses and environments, respectively, as in the local Universe. The median SFR of Hα emitters at is found to increase with density for both field and intermediate (group or cluster outskirts) densities; this is clearly seen as a change in the faint-end slope of the Hα luminosity function from steep , in poor fields, to shallow in groups and clusters. Interestingly, the relation between median SFR and environment is only found for low- to moderate-mass galaxies (with stellar masses below about M, and is not seen for the most massive star-forming galaxies. Overall, these observations provide a detailed view over a sufficiently large range of mass and environment to reconcile previous observational claims: stellar mass is the primary predictor of star formation activity at , but the environment, while initially enhancing the median SFR of (lower mass) star-forming galaxies, is ultimately responsible for suppressing star formation activity in all galaxies above surface densities of 10-30 Mpc (group and cluster environments). [ABSTRACT FROM AUTHOR]

The clustering properties of a well-defined sample of 734 Hα emitters at , obtained as part of the Hi- z Emission Line Survey, are investigated. The spatial correlation function of these Hα emitters is very well described by the power-law , with a real-space correlation, r0, of . The correlation length r0 increases strongly with Hα luminosity , from for the most quiescent galaxies [star formation rates (SFRs) of ] up to for the brightest galaxies in Hα. The correlation length also increases with increasing rest-frame K-band luminosity, but the correlation maintains its full statistical significance at fixed . At , star-forming galaxies classified as irregulars or mergers are much more clustered than discs and non-mergers, respectively; however, once the samples are matched in and , the differences vanish, implying that the clustering is independent of morphological type at just as in the local Universe. The typical Hα emitters found at reside in dark matter haloes of , but those with the highest SFRs reside in more massive haloes of . The results are compared with those of Hα surveys at different redshifts: although the break of the Hα luminosity function evolves by a factor of ∼30 from to 2.23, if the Hα luminosities at each redshift are scaled by then the correlation lengths indicate that, independently of cosmic time, galaxies with the same are found in dark matter haloes of similar masses. This not only confirms that the star formation efficiency in high redshift haloes is higher than locally but also suggests a fundamental connection between the strong negative evolution of since and the quenching of star formation in galaxies residing within dark matter haloes significantly more massive than at any given epoch. [ABSTRACT FROM AUTHOR]

We compare Hα, ultraviolet (UV) and infrared (IR) indicators of star formation rate (SFR) for a well-defined sample of emission-line galaxies from the High- z Emission Line Survey (HiZELS). Using emission-line, optical, IR, radio and X-ray diagnostics, we estimate that 5–11 per cent of Hα emitters at this redshift are active galactic nuclei. We detect 35 per cent of the Hα emitters individually at 24 μm, and stack the locations of star-forming emitters on deep 24-μm Spitzer Space Telescope images in order to calculate the typical SFRs of our Hα-emitting galaxies. These are compared to the observed Hα line fluxes in order to estimate the extinction at , and we find a significant increase in dust extinction for galaxies with higher SFRs. We demonstrate that the relationship between SFR and extinction found in the local Universe is also suitable for our high-redshift galaxies, and attribute the overall increase in the typical dust extinction for galaxies to an increase in the average SFR, rather than to a change in dust properties at higher redshift. We calculate the UV extinction, and find a similar dependence on SFR to the Hα results, but no evidence for a 2175 Å UV bump in the dust attenuation law for high-redshift star-forming galaxies. By comparing Hα and UV indicators, we calculate the conversion between the dust attenuation of nebular and stellar radiation, γ, and show that . The extinction/SFR relationship is shown to be applicable to galaxies with a range of morphologies and bulge-to-disc ratios, to both merging and non-merging galaxies, and to galaxies within high- and low-density environments, implying that it is a fundamental property of star-forming regions. In order to allow future studies to easily correct for a SFR-dependent amount of dust extinction, we present an equation to predict the extinction of a galaxy, based solely on its observed Hα luminosity, and use this to recalculate the Hα luminosity function and SFR density at . [ABSTRACT FROM AUTHOR]

The ROSAT-European Southern Observatory (ESO) flux-limited X-ray (REFLEX) galaxy cluster survey and the Two-degree Field Galaxy Redshift Survey (2dFGRS), respectively, comprise the largest, homogeneous X-ray selected cluster catalogue and completed galaxy redshift survey. In this work, we combine these two outstanding data sets in order to study the effect of the large-scale cluster environment, as traced by X-ray luminosity, on the properties of the cluster member galaxies. We measure the relation from the correlated data set and find it to be consistent with recent results found in the literature. Using a sample of 19 clusters with in the 0.1–2.4 keV band, and 49 clusters with lower X-ray luminosity, we find that the fraction of early spectral type , passively evolving galaxies is significantly higher in the high- LX sample within R200. We extend the investigation to include composite bJ cluster luminosity functions, and find that the characteristic magnitude of the Schechter-function fit to the early-type luminosity function is fainter for the high- LX sample compared to the low- LX sample . This seems to be driven by a deficit of such galaxies with M bJ∼−21. In contrast, we find no significant differences between the luminosity functions of star-forming, late-type galaxies. We believe these results are consistent with a scenario in which the high- LX clusters are more dynamically evolved systems than the low- LX clusters. [ABSTRACT FROM AUTHOR]

ABSTRACTWe estimate the cluster–galaxy cross-correlation function (ξcg), from the APM galaxy and galaxy cluster surveys. We obtain estimates both in real space from the inversion of projected statistics and in redshift space using the galaxy and cluster redshift samples. The amplitude of ξcg is found to be almost independent of cluster richness. At large separations, r ≥ 5 h-1Mpc (h=H0/100 km s-1 Mpc-1, where H0 is the Hubble constant), ξcg has a similar shape to the galaxy–galaxy and cluster–cluster autocorrelation functions. ξcg in redshift space can be related to the real-space ξcg by convolution with an appropriate velocity field model. Here we apply a spherical collapse model, which we have tested against N-body simulations, finding that it provides an accurate description of the averaged infall velocity of matter into galaxy clusters. We use this model to estimate β (β =Ο0.6/b, where b is the linear bias parameter), and find that it tends to overestimate the true result in simulations by only ∼ 10–30 per cent. Application to the APM results yields β =0.46 with β < 0.73 at 95 per cent confidence. This measure is complementary to the estimates made of the density parameter from larger scale bulk flows and from the virialized regions of clusters on smaller scales. We also compare the APM ξcg and galaxy autocorrelations directly with the mass correlation and cluster-mass correlations in COBE-normalized simulations of popular cosmological models, and derive two independent estimates of the galaxy biasing expected as a function of scale. This analysis reveals that both low-density and critical-density COBE-normalized cold dark matter (CDM) models require anti-biasing by a factor ∼ 2 on scales r ≤ 2 h-1 Mpc, and that the mixed dark matter (MDM) model is consistent with a constant biasing factor on all scales. The critical-density CDM model also suffers from the usual deficit of power on large scales (r ≥ 20 h-1 Mpc). We use the velocity fields predicted from the different models to distort the APM real-space cross-correlation function. Comparison with the APM redshift-space ξcg yields an estimate of the value of Ο0.6 needed in each model. We find that only the low-Ο model is fully consistent with observations, with MDM marginally excluded at the ∼ 2 σ level. [ABSTRACT FROM AUTHOR]