ALBERT

Description: We investigate the evolution of the H β + [O iii ] and [O ii ] luminosity functions from z  ~ 0.8 to ~5 in four redshift slices per emission line using data from the High- z Emission Line Survey (HiZELS). This is the first time that the H β + [O iii ] and [O ii ] luminosity functions have been studied at these redshifts in a self-consistent analysis. This is also the largest sample of [O ii ] and H β + [O iii ] emitters (3475 and 3298 emitters, respectively) in this redshift range, with large comoving volumes ~1  x  10 6  Mpc –3 in two independent volumes (COSMOS and UDS), greatly reducing the effects of cosmic variance. The emitters were selected by a combination of photometric redshift and colour–colour selections, as well as spectroscopic follow-up, including recent spectroscopic observations using DEIMOS and MOSFIRE on the Keck Telescopes and FMOS on Subaru. We find a strong increase in L * and a decrease in * for both H β + [O iii ] and [O ii ] emitters. We derive the [O ii ] star formation history of the Universe since z  ~ 5 and find that the cosmic star formation rate density (SFRD) rises from z  ~ 5 to ~3 and then drops towards z  ~ 0. We also find that our star formation history is able to reproduce the evolution of the stellar mass density up to z  ~ 5 based only on a single tracer of star formation. When comparing the H β + [O iii ] SFRDs to the [O ii ] and H α SFRD measurements in the literature, we find that there is a remarkable agreement, suggesting that the H β + [O iii ] sample is dominated by star-forming galaxies at high- z rather than AGNs.

Description: A sample of 576 X-ray-selected LINERs was constructed by combining data from the 3XMM-DR4 and SDSS-DR7 catalogues. The sample was used to investigate the fraction of galaxies hosting a LINER, finding that the fraction is a strong function of both stellar mass and black hole mass (increasing as ${f_{\rm LINER} \propto M^{1.6 \pm 0.2}_{*}}$ and ${f_{\rm LINER} \propto M^{0.6 \pm 0.1}_{{\rm BH}}}$ , respectively) and that it rises close to unity at the highest black hole masses and lowest X-ray luminosities. After obtaining radio flux densities from the FIRST survey, the sample was also used to investigate the Fundamental Plane of black hole activity – a scale-invariant relationship between black hole mass, X-ray luminosity and radio luminosity that is believed to hold across at least nine orders of magnitude of mass. There are key advantages in using only LINERs for the derivation as these are the counterparts of the ‘low-hard’ X-ray binaries for which the relationship is tightest. The Fundamental Plane was found to be $\log (\frac{L_{\rm R}}{\mathrm{erg\,s}^{-1}}) = 0.65^{+0.07}_{-0.07}\log (\frac{L_{\rm X}}{10^{42}\,\mathrm{erg\,s}^{-1}}) + 0.69^{+0.10}_{-0.10}\log (\frac{M_{\rm BH}}{10^8\,\mathrm{M}_{{\odot }}}) + 38.35^{+0.10}_{-0.10}$ . The scatter around the plane was 0.73 ± 0.03 dex, too large to suggest that the Fundamental Plane can be used as a tool to estimate black hole mass from the observables of X-ray and radio luminosity. The black hole mass scaling is sensitive to the slope of the mass – velocity dispersion relation and, in order to achieve consistency with X-ray binaries, the analysis favours a steep gradient for this relationship, as found in recent research.

Description: We investigate the properties of z  = 2.23 Hα and [O iii ] 5007 emitters using the narrow-band-selected samples obtained from the High- z Emission Line Survey. We construct two samples of the Hα and [O iii ] emitters and compare their integrated physical properties. We find that the distribution of stellar masses, dust extinction, star formation rates (SFRs), and specific SFRs (sSFRs) is not statistically different between the two samples. When we separate the full galaxy sample into three subsamples according to the detections of the Hα and/or [O iii ] emission lines, most of the sources detected with both Hα and [O iii ] show log(sSFR UV ) –9.5. The comparison of the three subsamples suggests that sources with strong [O iii ] line emission tend to have the highest star-forming activity out all galaxies that we study. We argue that the [O iii ] emission line can be used as a tracer of star-forming galaxies at high redshift, and that it is especially useful to investigate star-forming galaxies at z  〉 3, for which Hα emission is no longer observable from the ground.

Description: We present a study of the prevalence and luminosity of active galactic nuclei (AGN; traced by optical spectra) as a function of both environment and galaxy interactions. For this study, we used a sample of more than 250 000 galaxies drawn from the Sloan Digital Sky Survey and, crucially, we controlled for the effect of both stellar mass and central star formation activity. Once these two factors are taken into account, the effect of the local density of galaxies and of one-on-one interactions is minimal in both the prevalence of AGN activity and AGN luminosity. This suggests that the level of nuclear activity depends primarily on the availability of cold gas in the nuclear regions of galaxies and that secular processes can drive the AGN activity in the majority of cases. Large-scale environment and galaxy interactions only affect AGN activity in an indirect manner, by influencing the central gas supply.

Description: We present results from the largest contiguous narrow-band survey in the near-infrared. We have used the wide-field infrared camera/Canada–France–Hawaii Telescope and the lowOH2 filter (1.187 ± 0.005 μm) to survey 10 deg 2 of contiguous extragalactic sky in the SA22 field. A total of ~6000 candidate emission-line galaxies are found. We use deep ugrizJK data to obtain robust photometric redshifts. We combine our data with the High-redshift(Z) Emission Line Survey (HiZELS), explore spectroscopic surveys (VVDS, VIPERS) and obtain our own spectroscopic follow-up with KMOS, FMOS and MOSFIRE to derive large samples of high-redshift emission-line selected galaxies: 3471 Hα emitters at z  = 0.8, 1343 [O iii ] + Hβ emitters at z  = 1.4 and 572 [O ii ] emitters at z  = 2.2. We probe comoving volumes of 〉10 6  Mpc 3 and find significant overdensities, including an 8.5 (spectroscopically confirmed) overdensity of Hα emitters at z  = 0.81. We derive Hα, [O iii ] + Hβ and [O ii ] luminosity functions at z  = 0.8, 1.4, 2.2, respectively, and present implications for future surveys such as Euclid . Our uniquely large volumes/areas allow us to subdivide the samples in thousands of randomized combinations of areas and provide a robust empirical measurement of sample/cosmic variance. We show that surveys for star-forming/emission-line galaxies at a depth similar to ours can only overcome cosmic-variance (errors 〈10 per cent) if they are based on volumes 〉5  x  10 5  Mpc 3 ; errors on L * and * due to sample (cosmic) variance on surveys probing ~10 4 and ~10 5  Mpc 3 are typically very high: ~300 and ~40–60 per cent, respectively.

Description: We present a study of the prevalence of optical and radio nuclear activity with respect to the environment and interactions in a sample of the Sloan Digital Sky Survey (SDSS) galaxies. The aim is to determine the independent effects of distinct aspects of source environment on the triggering of different types of nuclear activity. We defined a local density parameter and a tidal force estimator and used a cluster richness estimator from the literature to trace different aspects of environment and interaction. The possible correlations between the environmental parameters were removed using a principal component analysis. By far, the strongest trend found for the active galactic nuclei (AGN) fractions, of all AGN types, is with galaxy mass. We therefore applied a stratified statistical method that takes into account the effect of possible confounding factors like the galaxy mass. We found that (at fixed mass) the prevalence of optical AGN is a factor of 2–3 lower in the densest environments, but increases by a factor of ~2 in the presence of strong one-on-one interactions. These effects are even more pronounced for star-forming nuclei. The importance of galaxy interactions decreases from star-forming nuclei to Seyferts to low-ionization nuclear emission-line regions to passive galaxies, in accordance with previous suggestions of an evolutionary time-sequence. The fraction of radio AGN increases very strongly (by nearly an order of magnitude) towards denser environments, and is also enhanced by galaxy interactions. Overall, the results agree with a scenario in which the mechanisms of accretion into the black hole are determined by the presence and nature of a supply of gas, which in turn is controlled by the local density of galaxies and their interactions. A plentiful cold gas supply is required to trigger star formation, optical AGN and radiatively efficient radio AGN. This is less common in the cold-gas-poor environments of groups and clusters, but is enhanced by one-on-one interactions which result in the flow of gas into nuclear regions; these two factors compete against each other. In the denser environments where cold gas is rare, cooling hot gas can supply the nucleus at a sufficient rate to fuel low-luminosity radiatively inefficient radio AGN. However, the increased prevalence of these AGN in interacting galaxies suggests that this is not the only mechanism by which radiatively inefficient AGN can be triggered.

Description: We use new near-infrared spectroscopic observations to investigate the nature and evolution of the most luminous Hα emitters at z ~ 0.8–2.23, which evolve strongly in number density over this period, and compare them to more typical Hα emitters. We study 59 luminous Hα emitters with L Hα 〉  $L_{\rm H\alpha }^{\ast }$ , roughly equally split per redshift slice at z ~ 0.8, 1.47 and 2.23 from the HiZELS and CF-HiZELS surveys. We find that, overall, 30 ± 8 per cent are active galactic nuclei [AGNs; 80 ± 30 per cent of these AGNs are broad-line AGNs, BL-AGNs], and we find little to no evolution in the AGN fraction with redshift, within the errors. However, the AGN fraction increases strongly with Hα luminosity and correlates best with L Hα / $L_{\rm H\alpha }^{\ast }(z)$ . While L Hα  ≤  $L_{\rm H\alpha }^{\ast }(z)$ Hα emitters are largely dominated by star-forming galaxies (〉80 per cent), the most luminous Hα emitters ( $L_{\rm H\alpha } 〉 10L_{\rm H\alpha }^{\ast }(z)$ ) at any cosmic time are essentially all BL-AGN. Using our AGN-decontaminated sample of luminous star-forming galaxies, and integrating down to a fixed Hα luminosity, we find a factor of ~1300 evolution in the star formation rate density from z  = 0 to 2.23. This is much stronger than the evolution from typical Hα star-forming galaxies and in line with the evolution seen for constant luminosity cuts used to select ‘ultraluminous’ infrared galaxies and/or sub-millimetre galaxies. By taking into account the evolution in the typical Hα luminosity, we show that the most strongly star-forming Hα-selected galaxies at any epoch ( $L_{\rm H\alpha } 〉 L^{\ast }_{\rm H\alpha }(z)$ ) contribute the same fractional amount of 15 per cent to the total star formation rate density, at least up to z  = 2.23.

Description: This paper presents the first measurement of the radio luminosity function of ‘jet-mode’ (radiatively inefficient) radio-AGN out to z  = 1, in order to investigate the cosmic evolution of radio-AGN feedback. Eight radio source samples are combined to produce a catalogue of 211 radio-loud AGN with 0.5 〈  z  〈 1.0, which are spectroscopically classified into jet-mode and radiative-mode (radiatively efficient) AGN classes. Comparing with large samples of local radio-AGN from the Sloan Digital Sky Survey, the cosmic evolution of the radio luminosity function of each radio-AGN class is independently derived. Radiative-mode radio-AGN show an order of magnitude increase in space density out to z   1 at all luminosities, consistent with these AGN being fuelled by cold gas. In contrast, the space density of jet-mode radio-AGN decreases with increasing redshift at low radio luminosities ( L 1.4 GHz   10 24  W Hz –1 ) but increases at higher radio luminosities. Simple models are developed to explain the observed evolution. In the best-fitting models, the characteristic space density of jet-mode AGN declines with redshift in accordance with the declining space density of massive quiescent galaxies, which fuel them via cooling of gas in their hot haloes. A time delay of 1.5–2 Gyr may be present between the quenching of star formation and the onset of jet-mode radio-AGN activity. The behaviour at higher radio luminosities can be explained either by an increasing characteristic luminosity of jet-mode radio-AGN activity with redshift (roughly as (1 +  z ) 3 ) or if the jet-mode radio-AGN population also includes some contribution of cold-gas-fuelled sources seen at a time when their accretion rate was low. Higher redshifts measurements would distinguish between these possibilities.

Description: We present a novel method to estimate accurate redshifts of star-forming galaxies by measuring the flux ratio of the same emission line observed through two adjacent narrow-band filters. We apply this method to our NB 912 and new NB 921 data taken with Suprime-Cam on the Subaru Telescope of a galaxy cluster, XMMXCS J2215.9–1738, at z  = 1.46 and its surrounding structures. We obtain redshifts for 170 [O ii ] emission line galaxies at z ~ 1.46, among which 41 galaxies are spectroscopically confirmed with Multi-Object Infrared Camera and Spectrograph and Fibre Multi Object Spectrograph on the Subaru mainly, showing an accuracy of (( z  –  z spec )/(1 +  z spec )) = 0.002. This allows us to reveal filamentary structures that penetrate towards the centre of the galaxy cluster and intersect with other structures, consistent with the picture of hierarchical cluster formation. We also find that the projected celestial distribution does not precisely trace the real distribution of galaxies, indicating the importance of the three-dimensional view of structures to properly identify and quantify galaxy environments. We investigate the environmental dependence of galaxy properties with local density, confirming that the median colour of galaxies becomes redder in higher density region, while the star formation rate of star-forming galaxies does not depend strongly on local environment in this structure. This implies that the star-forming activity in galaxies is truncated on a relatively short time-scale in the cluster centre.

Description: We describe the far-infrared (far-IR; rest-frame 8–1000-μm) properties of a sample of 443 Hα-selected star-forming galaxies in the Cosmic Evolution Survey (COSMOS) and Ultra Deep Survey (UDS) fields detected by the High-redshift Emission Line Survey (HiZELS) imaging survey. Sources are identified using narrow-band filters in combination with broad-band photometry to uniformly select Hα (and [O ii ] if available) emitters in a narrow redshift slice at z  = 1.47 ± 0.02. We use a stacking approach in Spitzer -MIPS mid-IR, Herschel -PACS/SPIRE far-IR [from the PACS Evolutionary Prove (PEP) and Herschel Multi-tiered Extragalactic Survey (HerMES)] and AzTEC mm-wave images to describe their typical far-IR properties. We find that HiZELS galaxies with observed Hα luminosities of L (Hα) obs 10 8.1-9.1  L ( 10 41.7-42.7  erg s –1 ) have bolometric far-IR luminosities of typical luminous IR galaxies, $L(8{\rm -}1000\,\mu {\rm m})\approx 10^{11.41^{+0.04}_{-0.06}} $  L . Combining the Hα and far-IR luminosities, we derive median star formation rates (SFRs) of SFR Hα, FIR  = 32 ± 5 M  yr –1 and Hα extinctions of A Hα  = 1.0 ± 0.2 mag. Perhaps surprisingly, little difference is seen in typical HiZELS extinction levels compared to local star-forming galaxies. We confirm previous empirical stellar mass ( M * ) to A Hα relations and the little or no evolution up to z  = 1.47. For HiZELS galaxies (or similar samples) we provide an empirical parametrization of the SFR as a function of rest-frame ( u  –  z ) colours and 3.6-μm photometry – a useful proxy to aid in the absence of far-IR detections in high- z galaxies. We find that the observed Hα luminosity is a dominant SFR tracer when rest-frame ( u  –  z ) colours are 0.9 mag or when Spitzer -3.6-μm photometry is fainter than 22 mag (Vega) or when stellar masses are lower than 10 9.7 M . We do not find any correlation between the [O ii ]/Hα and far-IR luminosity, suggesting that this emission line ratio does not trace the extinction of the most obscured star-forming regions, especially in massive galaxies where these dominate. The luminosity-limited HiZELS sample tends to lie above of the so-called main sequence for star-forming galaxies, especially at low stellar masses, indicating high star formation efficiencies in these galaxies. This work has implications for SFR indicators and suggests that obscured star formation is linked to the assembly of stellar mass, with deeper potential wells in massive galaxies providing dense, heavily obscured environments in which stars can form rapidly.