ALBERT

Description: The KMOS Redshift One Spectroscopic Survey (KROSS) is an ESO-guaranteed time survey of 795 typical star-forming galaxies in the redshift range z = 0.8–1.0 with the KMOS instrument on the Very Large Telescope. In this paper, we present resolved kinematics and star formation rates for 584 z ~ 1 galaxies. This constitutes the largest near-infrared Integral Field Unit survey of galaxies at z ~ 1 to date. We demonstrate the success of our selection criteria with 90 per cent of our targets found to be H α emitters, of which 81 per cent are spatially resolved. The fraction of the resolved KROSS sample with dynamics dominated by ordered rotation is found to be 83 ± 5 per cent. However, when compared with local samples these are turbulent discs with high gas to baryonic mass fractions, ~35 per cent, and the majority are consistent with being marginally unstable (Toomre Q ~ 1). There is no strong correlation between galaxy averaged velocity dispersion and the total star formation rate, suggesting that feedback from star formation is not the origin of the elevated turbulence. We postulate that it is the ubiquity of high (likely molecular) gas fractions and the associated gravitational instabilities that drive the elevated star formation rates in these typical z ~ 1 galaxies, leading to the 10-fold enhanced star formation rate density. Finally, by comparing the gas masses obtained from inverting the star formation law with the dynamical and stellar masses, we infer an average dark matter to total mass fraction within 2.2 r e (9.5 kpc) of 65 ± 12 per cent, in agreement with the results from hydrodynamic simulations of galaxy formation.

Description: We present first results from the KMOS ( K -band Multi-Object Spectrograph) Redshift One Spectroscopic Survey, an ongoing large kinematical survey of a thousand, z ~ 1 star-forming galaxies, with VLT KMOS. Out of the targeted galaxies (~500 so far), we detect and spatially resolve Hα emission in ~90 and 77 per cent of the sample, respectively. Based on the integrated Hα flux measurements and the spatially resolved maps, we derive a median star formation rate (SFR) of ~7.0 M  yr –1 and a median physical size of 〈 $r^{\prime }_{\rm 1/2}$ 〉 = 5.1 kpc. We combine the inferred SFRs and effective radii measurements to derive the star formation surface densities ( SFR ) and present a ‘resolved’ version of the star formation main sequence (MS) that appears to hold at subgalactic scales, with similar slope and scatter as the one inferred from galaxy-integrated properties. Our data also yield a trend between SFR and (sSFR) (distance from the MS) suggesting that galaxies with higher sSFR are characterized by denser star formation activity. Similarly, we find evidence for an anticorrelation between the gas phase metallicity ( Z ) and the (sSFR), suggesting a 0.2 dex variation in the metal content of galaxies within the MS and significantly lower metallicities for galaxies above it. The origin of the observed trends between SFR –(sSFR) and Z –(sSFR) could be driven by an interplay between variations of the gas fraction or the star formation efficiency of the galaxies along and off the MS. To address this, follow-up observations of our sample that will allow gas mass estimates are necessary.

Description: We have observed a sample of typical z  ~ 1 star-forming galaxies, selected from the HiZELS survey, with the new K -band Multi-Object Spectrograph (KMOS) near-infrared, multi-integral field unit instrument on the Very Large Telescope (VLT), in order to obtain their dynamics and metallicity gradients. The majority of our galaxies have a metallicity gradient consistent with being flat or negative (i.e. higher metallicity cores than outskirts). Intriguingly, we find a trend between metallicity gradient and specific star formation rate (sSFR), such that galaxies with a high sSFR tend to have relatively metal poor centres, a result which is strengthened when combined with data sets from the literature. This result appears to explain the discrepancies reported between different high-redshift studies and varying claims for evolution. From a galaxy evolution perspective, the trend we see would mean that a galaxy's sSFR is governed by the amount of metal-poor gas that can be funnelled into its core, triggered either by merging or through efficient accretion. In fact, merging may play a significant role as it is the starburst galaxies at all epochs, which have the more positive metallicity gradients. Our results may help to explain the origin of the fundamental metallicity relation, in which galaxies at a fixed mass are observed to have lower metallicities at higher star formation rates, especially if the metallicity is measured in an aperture encompassing only the central regions of the galaxy. Finally, we note that this study demonstrates the power of KMOS as an efficient instrument for large-scale resolved galaxy surveys.

Description: We present the stellar mass ( M * ), and K-corrected K -band absolute magnitude ( M K ) Tully–Fisher relations (TFRs) for subsamples of the 584 galaxies spatially resolved in H α emission by the KMOS Redshift One Spectroscopic Survey (KROSS). We model the velocity field of each of the KROSS galaxies and extract a rotation velocity, V 80 at a radius equal to the major axis of an ellipse containing 80 per cent of the total integrated H α flux. The large sample size of KROSS allowed us to select 210 galaxies with well-measured rotation speeds. We extract from this sample a further 56 galaxies that are rotationally supported, using the stringent criterion V 80 / 〉 3, where is the flux weighted average velocity dispersion. We find the M K and M * TFRs for this subsample to be $M_{K} / \rm {mag}= (-7.3 \pm 0.9) \times [(\log (V_{80}/\rm {km\ s^{-1}})-2.25]- 23.4 \pm 0.2$ , and $\log (M_{{\ast }} / \mathrm{M}_{{\odot }})= (4.7 \pm 0.4) \times [(\log (V_{80}/\rm {km\ s^{-1}}) - 2.25] + 10.0 \pm 0.3$ , respectively. We find an evolution of the M * TFR zero-point of –0.41 ± 0.08 dex over the last ~8 billion years. However, we measure no evolution in the M K TFR zero-point over the same period. We conclude that rotationally supported galaxies of a given dynamical mass had less stellar mass at z ~ 1 than the present day, yet emitted the same amounts of K -band light. The ability of KROSS to differentiate, using integral field spectroscopy with KMOS, between those galaxies that are rotationally supported and those that are not explains why our findings are at odds with previous studies without the same capabilities.

Description: We measure the evolution of the velocity dispersion–temperature ( v – T X ) relation up to z  = 1 using a sample of 38 galaxy clusters drawn from the XMM Cluster Survey. This work improves upon previous studies by the use of a homogeneous cluster sample and in terms of the number of high-redshift clusters included. We present here new redshift and velocity dispersion measurements for 12 z  〉 0.5 clusters observed with the Gemini Multi Object Spectographs instruments on the Gemini telescopes. Using an orthogonal regression method, we find that the slope of the relation is steeper than that expected if clusters were self-similar, and that the evolution of the normalization is slightly negative, but not significantly different from zero ( v T 0.86±0.14 E ( z ) –0.37±0.33 ). We verify our results by applying our methods to cosmological hydrodynamical simulations. The lack of evolution seen in our data is consistent with simulations that include both feedback and radiative cooling.

Description: We obtained Subaru FMOS observations of Hα emitting galaxies selected from the HiZELS, to investigate the relationship between stellar mass, metallicity and star formation rate (SFR) at z  = 0.84–1.47, for comparison with the fundamental metallicity relation seen at low redshift. Our findings demonstrate, for the first time with a homogeneously selected sample, that a relationship exists for typical star-forming galaxies at z  ~ 1–1.5 and that it is surprisingly similar to that seen locally. Therefore, star-forming galaxies at z  ~ 1–1.5 are no less metal abundant than galaxies of similar mass and SFR at z  ~ 0.1, contrary to claims from some earlier studies. We conclude that the bulk of the metal enrichment for this star-forming galaxy population takes place in the 4 Gyr before z  ~ 1.5. We fit a new mass–metallicity–SFR plane to our data which is consistent with other high-redshift studies. However, there is some evidence that the mass–metallicity component of this high-redshift plane is flattened, at all SFR, compared with z  ~ 0.1, suggesting that processes such as star formation-driven winds, thought to remove enriched gas from low-mass haloes, are yet to have as large an impact at this early epoch. The negative slope of the SFR–metallicity relation from this new plane is consistent with the picture that the elevation in the SFR of typical galaxies at z 1 is fuelled by the inflow of metal-poor gas and not major merging.

Description: We use the HiZELS narrow-band Hα survey in combination with CANDELS, UKIDSS and WIRDS near-infrared imaging, to investigate the morphologies, merger rates and sizes of a sample of Hα emitting galaxies in the redshift range z  = 0.40–2.23, an epoch encompassing the rise to the peak of the star formation rate density. Merger rates are estimated from space- and ground-based imaging using the M 20 coefficient. To account for the increase in the specific star formation rate (sSFR) of the star forming ‘main sequence’ with redshift, we normalize the star formation rates of galaxies at each epoch to the typical value derived from the Hα luminosity function. Once this trend in sSFR is removed we see no evidence for an increase in the number density of star-forming galaxies or the merger rate with redshift. We thus conclude that neither is the main driver of the enhanced star-formation rate density at z  ~ 1–2, with secular processes such as instabilities within efficiently fuelled, gas-rich discs or multiple minor mergers the most likely alternatives. However, we find that ~40–50 per cent of starburst galaxies, those with enhanced specific star formation at their epoch, are major mergers and this fraction is redshift independent. Finally, we find the surprising result that the typical size of a star-forming galaxy of a given mass does not evolve across the redshift range considered, suggesting a universal size–mass relation. Taken in combination, these results indicate a star-forming galaxy population that is statistically similar in physical size, merger rate and mass over the ~6 Gyr covered in this study, despite the increase in typical sSFR.

Description: We present a photometric investigation into recent star formation in galaxy clusters at z  ~ 0.1. We use spectral energy distribution templates to quantify recent star formation in large X-ray-selected clusters from the LARCS survey using matched GALEX near-ultraviolet (NUV) photometry. These clusters all have signs of red sequence galaxy recent star formation (as indicated by the blue NUV –  R colour), regardless of the cluster morphology and size. A trend in environment is found for these galaxies, such that they prefer to occupy low-density, high-cluster-radius environments. The morphology of these UV-bright galaxies suggests that they are in fact red spirals, which we confirm with light profiles and Galaxy Zoo voting percentages as morphological proxies. These UV-bright galaxies are therefore seen to be either truncated spiral galaxies, caught by ram pressure infalling into the cluster, or high-mass spirals, with the photometry dominated by the older stellar population.

Description: We have investigated the effect of group environment on residual star formation in galaxies, using Galaxy Evolution Explorer near-ultraviolet (NUV) galaxy photometry with the Sloan Digital Sky Survey group catalogue of Yang et al. We compared the (NUV – r ) colours of grouped and non-grouped galaxies, and find a significant increase in the fraction of red sequence galaxies with blue (NUV – r ) colours outside of groups. When comparing galaxies in mass-matched samples of satellite (non-central), and non-grouped galaxies, we found a 〉4 difference in the distribution of (NUV – r ) colours, and an (NUV – r ) blue fraction 〉3 higher outside groups. A comparison of satellite and non-grouped samples has found the NUV fraction is a factor of ~2 lower for satellite galaxies between 10 10.5 and $10^{10.7}\,\text{M}_{\odot }$ , showing that higher mass galaxies are more likely to have residual star formation when not influenced by a group potential. There was a higher (NUV – r ) blue fraction of galaxies with lower Sérsic indices ( n 〈 3) outside of groups, not seen in the satellite sample. We have used stellar population models of Bruzual & Charlot with multiple burst, or exponentially declining star formation histories to find that many of the (NUV – r ) blue non-grouped galaxies can be explained by a slow (~2 Gyr) decay of star formation, compared to the satellite galaxies. We suggest that taken together, the difference in (NUV – r ) colours between samples can be explained by a population of secularly evolving, non-grouped galaxies, where star formation declines slowly. This slow channel is less prevalent in group environments where more rapid quenching can occur.

Description: We investigate the properties of ~7000 narrow-band selected galaxies with strong Hβ+[O iii ] and [O ii ] nebular emission lines from the High- z Emission-Line Survey between z ~ 0.8 and 5.0. Our sample covers a wide range in stellar mass ( M stellar ~ 10 7.5–12.0 M ), rest-frame equivalent widths (EW rest ~10–10 5 Å), and line luminosities ( L line ~ 10 40.5–43.2  erg s –1 ). We measure the Hβ+[O iii ]-selected stellar mass functions out to z ~ 3.5 and find that both M * and * increases with cosmic time. The [O ii ]-selected stellar mass functions show a constant M * 10 11.6 M and a strong, increasing evolution with cosmic time in * in line with Hα studies. We also investigate the evolution of the EW rest as a function of redshift with a fixed mass range (10 9.5–10.0 M ) and find an increasing trend best represented by (1 + z ) 3.81 ± 0.14 and (1 + z ) 2.72 ± 0.19 up to z ~ 2 and ~3 for Hβ+[O iii ] and [O ii ] emitters, respectively. This is the first time that the EW rest evolution has been directly measured for Hβ+[O iii ] and [O ii ] emitters up to these redshifts. There is evidence for a slower evolution for z 〉 2 in the Hβ+[O iii ] EW rest and a decreasing trend for z 〉 3 in the [O ii ] EW rest evolution, which would imply low [O ii ] EW at the highest redshifts and higher [O iii ]/[O ii ] line ratios. This suggests that the ionization parameter at higher redshift may be significantly higher than the local Universe. Our results set the stage for future near-IR space-based spectroscopic surveys to test our extrapolated predictions and also produce z 〉 5 measurements to constrain the high- z end of the EW rest and [O iii ]/[O ii ] evolution.