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We present a comparison of the nitrogen-to-oxygen ratio (N/O) in 37 high-redshift galaxies at z ∼ 2 taken from the KMOS Lensed Emission Lines and VElocity Review (KLEVER) Survey with a comparison sample of local galaxies, taken from the Sloan Digital Sky Survey (SDSS). The KLEVER sample shows only a mild enrichment in N/O of +0.1 dex when compared to local galaxies at a given gas-phase metallicity (O/H), but shows a depletion in N/O of −0.35 dex when compared at a fixed stellar mass (M *). We find a strong anticorrelation in local galaxies between N/O and SFR in the M *–N/O plane, similar to the anticorrelation between O/H and SFR found in the mass–metallicity relation (MZR). We use this anticorrelation to construct a fundamental nitrogen relation (FNR), analogous to the fundamental metallicity relation (FMR). We find that KLEVER galaxies are consistent with both the FMR and the FNR. This suggests that the depletion of N/O in high- z galaxies when considered at a fixed M * is driven by the redshift evolution of the mass–metallicity relation in combination with a near redshift-invariant N/O–O/H relation. Furthermore, the existence of an fundamental nitrogen relation suggests that the mechanisms governing the fundamental metallicity relation must be probed by not only O/H, but also N/O, suggesting pure-pristine gas inflows are not the primary driver of the FMR, and other properties such as variations in galaxy age and star formation efficiency must be important. [ABSTRACT FROM AUTHOR]

We present near-infrared observations of 42 gravitationally lensed galaxies obtained in the framework of the KMOS Lensed Emission Lines and VElocity Review (KLEVER) Survey, a programme aimed at investigating the spatially resolved properties of the ionized gas in 1.2 < z < 2.5 galaxies by means of a full coverage of the YJ, H , and K near-infrared bands. Detailed metallicity maps and gradients are derived for a subsample of 28 galaxies from reconstructed source-plane emission-line maps, exploiting the variety of different emission-line diagnostics provided by the broad wavelength coverage of the survey. About |$85 {{\, per\ cent}}$| of these galaxies are characterized by metallicity gradients shallower than |$0.05\ \rm dex\, kpc^{-1}$| and |$89{{\ \rm per\ cent}}$| are consistent with a flat slope within 3σ (⁠|$67{{\ \rm per\ cent}}$| within 1σ), suggesting a mild evolution with cosmic time. In the context of cosmological simulations and chemical evolution models, the presence of efficient feedback mechanisms and/or extended star formation profiles on top of the classical 'inside-out' scenario of mass assembly is generally required to reproduce the observed flatness of the metallicity gradients beyond z  ∼ 1. Three galaxies with significantly (>3σ) 'inverted' gradients are also found, showing an anticorrelation between metallicity and star formation rate density on local scales, possibly suggesting recent episodes of pristine gas accretion or strong radial flows in place. Nevertheless, the individual metallicity maps are characterized by a variety of different morphologies, with flat radial gradients sometimes hiding non-axisymmetric variations on kpc scales, which are washed out by azimuthal averages, especially in interacting systems or in those undergoing local episodes of recent star formation. [ABSTRACT FROM AUTHOR]

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 2.2re (9.5 kpc) of 65 ± 12 per cent, in agreement with the results from hydrodynamic simulations of galaxy formation. [ABSTRACT FROM AUTHOR]

This paper presents new deep and wide narrow-band surveys undertaken with United Kingdom Infrared Telescope (UKIRT), Subaru and the Very Large Telescope (VLT), a unique combined effort to select large, robust samples of Hα star-forming galaxies at z = 0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyr) in a uniform manner over ∼2 deg2 in the Cosmological Evolution Survey and Ultra Deep Survey fields. The deep multi-epoch Hα surveys reach a matched 3σ flux limit of ≈3 M⊙ yr−1 out to z = 2.2 for the first time, while the wide area and the coverage over two independent fields allow us to greatly overcome cosmic variance and assemble by far the largest samples of Hα emitters. Catalogues are presented for a total of 1742, 637, 515 and 807 Hα emitters, robustly selected at z = 0.40, 0.84, 1.47 and 2.23, respectively, and used to determine the Hα luminosity function and its evolution. The faint-end slope of the Hα luminosity function is found to be α = −1.60 ± 0.08 over z = 0–2.23, showing no significant evolution. The characteristic luminosity of star-forming galaxies, L*Hα, evolves significantly as log L*Hα(z) = 0.45z + log L*z = 0. This is the first time Hα has been used to trace star formation activity with a single homogeneous survey at z = 0.4–2.23. Overall, the evolution seen with Hα is in good agreement with the evolution seen using inhomogeneous compilations of other tracers of star formation, such as far-infrared and ultraviolet, jointly pointing towards the bulk of the evolution in the last 11 Gyr being driven by a statistically similar star-forming population across cosmic time, but with a strong luminosity increase from z ∼ 0 to ∼2.2. Our uniform analysis allows us to derive the Hα star formation history (SFRH) of the Universe, showing a clear rise up to z ∼ 2.2, for which the simple parametrization log10ρSFR = −2.1(1 + z)−1 is valid over 80 per cent of the age of the Universe. The results reveal that both the shape and normalization of the Hα SFRH are consistent with the measurements of the stellar mass density growth, confirming that our Hα SFRH is tracing the bulk of the formation of stars in the Universe for z < 2.23. The star formation activity over the last ∼11 Gyr is responsible for producing ∼95 per cent of the total stellar mass density observed locally, with half of that being assembled in 2 Gyr between z = 1.2 and 2.2, and the other half in 8 Gyr (since z < 1.2). If the star formation rate density continues to decline with time in the same way as seen in the past ∼11 Gyr, then the stellar mass density of the Universe will reach a maximum which is only 5 per cent higher than the present-day value. [ABSTRACT FROM PUBLISHER]

ABSTRACT This paper presents the results from the first wide and deep dual narrow-band survey to select Hα and [O ii] line emitters at z= 1.47 ± 0.02, exploiting synergies between the United Kingdom Infrared Telescope and the Subaru telescope by using matched narrow-band filters in the H and z′ bands. The Hα survey at z= 1.47 reaches a 3σ flux limit of FHα≈ 7 × 10−17 erg s−1 cm−2 (corresponding to a limiting star formation rate (SFR) in Hα of ≈7 M⊙ yr−1) and detects ≈200 Hα emitters over 0.7 deg2, while the much deeper [O ii] survey reaches an effective flux of ≈7 × 10−18 erg s−1 cm−2 (SFR in [O ii] of ∼1 M⊙ yr−1), detecting ≈1400 z= 1.47 [O ii] emitters in a matched comoving volume of ∼2.5 × 105 Mpc3. The combined survey results in the identification of 190 simultaneous Hα and [O ii] emitters at z= 1.47. Hα and [O ii] luminosity functions are derived and both are shown to evolve significantly from z∼ 0 in a consistent way. The SFR density of the Universe at z= 1.47 is evaluated, with the Hα analysis yielding ρSFR= 0.16 ± 0.05 M⊙ yr−1 Mpc−3 and the [O ii] analysis ρSFR= 0.17 ± 0.04 M⊙ yr−1 Mpc−3. The measurements are combined with other studies, providing a self-consistent measurement of the star formation history of the Universe over the last ∼11 Gyr. By using a large comparison sample at z∼ 0.1, derived from the Sloan Digital Sky Survey (SDSS), [O ii]/Hα line ratios are calibrated as probes of dust extinction. Hα emitters at z∼ 1.47 show on average AHα≈ 1 mag, the same as found by SDSS in the local Universe. It is shown that although dust extinction correlates with SFR, the relation evolves by about ∼0.5 mag from z∼ 1.5 to ∼0, with local relations overpredicting the dust extinction corrections at high z by that amount. Stellar mass is found to be a much more fundamental extinction predictor, with the same relation between mass and dust extinction being valid at both z∼ 0 and ∼1.5, at least for low and moderate stellar masses. The evolution in the extinction-SFR relation is therefore interpreted as being due to the evolution in median specific SFRs over cosmic time. Dust extinction corrections as a function of optical colours are also derived and shown to be broadly valid at both z∼ 0 and ∼1.5, offering simpler mechanisms for estimating extinction in moderately star-forming systems over the last ∼9 Gyr. [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]

ABSTRACT This paper presents the results from the first wide and deep dual narrow-band survey to select Hα and [O ii] line emitters at z= 1.47 ± 0.02, exploiting synergies between the United Kingdom Infrared Telescope and the Subaru telescope by using matched narrow-band filters in the H and z′ bands. The Hα survey at z= 1.47 reaches a 3σ flux limit of FHα≈ 7 × 10−17 erg s−1 cm−2 (corresponding to a limiting star formation rate (SFR) in Hα of ≈7 M⊙ yr−1) and detects ≈200 Hα emitters over 0.7 deg2, while the much deeper [O ii] survey reaches an effective flux of ≈7 × 10−18 erg s−1 cm−2 (SFR in [O ii] of ∼1 M⊙ yr−1), detecting ≈1400 z= 1.47 [O ii] emitters in a matched comoving volume of ∼2.5 × 105 Mpc3. The combined survey results in the identification of 190 simultaneous Hα and [O ii] emitters at z= 1.47. Hα and [O ii] luminosity functions are derived and both are shown to evolve significantly from z∼ 0 in a consistent way. The SFR density of the Universe at z= 1.47 is evaluated, with the Hα analysis yielding ρSFR= 0.16 ± 0.05 M⊙ yr−1 Mpc−3 and the [O ii] analysis ρSFR= 0.17 ± 0.04 M⊙ yr−1 Mpc−3. The measurements are combined with other studies, providing a self-consistent measurement of the star formation history of the Universe over the last ∼11 Gyr. By using a large comparison sample at z∼ 0.1, derived from the Sloan Digital Sky Survey (SDSS), [O ii]/Hα line ratios are calibrated as probes of dust extinction. Hα emitters at z∼ 1.47 show on average AHα≈ 1 mag, the same as found by SDSS in the local Universe. It is shown that although dust extinction correlates with SFR, the relation evolves by about ∼0.5 mag from z∼ 1.5 to ∼0, with local relations overpredicting the dust extinction corrections at high z by that amount. Stellar mass is found to be a much more fundamental extinction predictor, with the same relation between mass and dust extinction being valid at both z∼ 0 and ∼1.5, at least for low and moderate stellar masses. The evolution in the extinction-SFR relation is therefore interpreted as being due to the evolution in median specific SFRs over cosmic time. Dust extinction corrections as a function of optical colours are also derived and shown to be broadly valid at both z∼ 0 and ∼1.5, offering simpler mechanisms for estimating extinction in moderately star-forming systems over the last ∼9 Gyr. [ABSTRACT FROM AUTHOR]