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Galaxy evolution is regulated by the continuous cycle of gas accretion, consumption and feedback. Crucial in this cycle is the availability of neutral atomic (HI) and molecular hydrogen. Our current inventory of HI, however, is very limited beyond the local Universe (z > 0.25), resulting in an incomplete picture. ORCHIDSS is designed to address this critical challenge, using the powerful combination of 4MOST spectroscopy and sensitive radio observations from the MeerKAT deep extragalactic surveys to trace the evolution of neutral gas and its lifecycle within galaxies across the bulk of cosmic history., Published in The Messenger vol. 190, pp. 25-27, March 2023.

MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual robotic positioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64-1.8 micron wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue., Comment: 8 pages, 5 Figures, Published on the ESO Messenger No. 180

We present spectroscopic observations of 466 galaxies in and around a superstructure at z ∼ 0.84 targeted by the VIMOS Spectroscopic Survey of a Supercluster in the COSMOS field (VIS³COS). We use [OII]λ3727, Hδ, and D_n4000 to trace recent, medium-, and long-term star formation histories and investigate the effect of stellar mass and local environment on them. By studying trends in individual and composite galaxy spectra, we find that stellar mass and environment play a role in the observed galactic properties. Galaxies with low stellar mass (10 < log₁₀ (M⋆/M⊙) < 10.5) in the field show the strongest Hδ absorption. Similarly, the massive population (log₁₀ (M⋆/M⊙) > 11) shows an increase in Hδ absorption strengths in intermediate-density environments (e.g. filaments). Galaxies with intermediate stellar mass (10.5 < log₁₀ (M⋆/M⊙) < 11) have similar Hδ absorption profiles in all environments, but show an indication of enhanced [OII] emission in intermediate-density environments. This indicates that field galaxies with low stellar mass and filament galaxies with high stellar mass are more likely to have experienced a recent burst of star formation, while galaxies of the intermediate stellar-mass show an increase of star formation at filament-like densities. We also find that the median [OII] equivalent width (|EW_([OII])|) decreases from 27 ± 2 Å to 2.0^(+0.5)_(−0.4) Å and D_n4000 increases from 1.09 ± 0.01 to 1.56 ± 0.03 with increasing stellar mass (from ∼10^(9.25) to ∼10^(11.35) M⊙). For the dependence on the environment, we find that at fixed stellar mass, |EW_([OII])| is tentatively lower in environments with higher density. We find for D_n4000 that the increase with stellar mass is sharper in denser environments, which indicates that these environments may accelerate galaxy evolution. Moreover, we find higher D_n4000 values in denser environments at fixed stellar mass, suggesting that galaxies are on average older and/or more metal rich in these dense environments. This set of tracers depicts a scenario where the most massive galaxies have, on average, the lowest specific star formation rates and the oldest stellar populations (age ≳ 1 Gyr, showing a mass-downsizing effect). We also hypothesize that the observed increase in star formation (higher EW_([OII]|), higher specific star formation rate) at intermediate densities may lead to quenching because we find that the quenched fraction increases sharply from the filament to cluster-like regions at similar stellar masses.

We present new results from near-infrared spectroscopy with Keck/MOSFIRE of [O III]-selected galaxies at z similar to 3.2. With our H and K band spectra, we investigate the interstellar medium (ISM) conditions, such as ionization states and gas metallicities. [O III] emitters at z similar to 3.2 show a typical gas metallicity of 12+ log(O/H)= 8.07 +/- 0.07 at log(M-*/M-circle dot) similar to 9.0-9.2 and 12+ log(O/H)= 8.31 +/- 0.04 at log(M-*/M-circle dot) similar to 9.7-10.2 when using the empirical calibration method. We compare the [O III] emitters at z similar to 3.2 with UV-selected galaxies and Lya emitters at the same epoch and find that the [O III]-based selection does not appear to show any systematic bias in the selection of star-forming galaxies. Moreover, comparing with star-forming galaxies at z similar to 2 from the literature, our samples show similar ionization parameters and gas metallicities as those obtained by the previous studies that used the same calibration method. We find no strong redshift evolution in the ISM conditions between z similar to 3.2 and z similar to 2. Considering that the star formation rates at a fixed stellar mass also do not significantly change between the two epochs, our results support the idea that the stellar mass is the primary quantity to describe the evolutionary stages of individual galaxies at z > 2.

We present a study of photometric redshift performance for galaxies and active galactic nuclei detected in deep radio continuum surveys. Using two multi-wavelength datasets, over the NOAO Deep Wide Field Survey Bo\"otes and COSMOS fields, we assess photometric redshift (photo-z) performance for a sample of $\sim 4,500$ radio continuum sources with spectroscopic redshifts relative to those of $\sim 63,000$ non radio-detected sources in the same fields. We investigate the performance of three photometric redshift template sets as a function of redshift, radio luminosity and infrared/X-ray properties. We find that no single template library is able to provide the best performance across all subsets of the radio detected population, with variation in the optimum template set both between subsets and between fields. Through a hierarchical Bayesian combination of the photo-z estimates from all three template sets, we are able to produce a consensus photo-z estimate which equals or improves upon the performance of any individual template set., Comment: 20 pages, 17 figures. Accepted for publication in MNRAS

We present the CAlibrating LYMan-$\alpha$ with H$\alpha$ (CALYMHA) pilot survey and new results on Lyman-$\alpha$ (Lya) selected galaxies at z~2. We use a custom-built Lya narrow-band filter at the Isaac Newton Telescope, designed to provide a matched volume coverage to the z=2.23 Ha HiZELS survey. Here we present the first results for the COSMOS and UDS fields. Our survey currently reaches a 3$\sigma$ line flux limit of ~4x10$^{-17}$ erg/s/cm$^{2}$, and a Lya luminosity limit of ~10$^{42.3}$ erg/s. We find 188 Lya emitters over 7.3x10$^5$ Mpc$^{3}$, but also find significant numbers of other line emitting sources corresponding to HeII, CIII] and CIV emission lines. These sources are important contaminants, and we carefully remove them, unlike most previous studies. We find that the Lya luminosity function at z=2.23 is very well described by a Schechter function up to L~10$^{43}$ erg/s with L$^*=10^{42.59+-0.05}$ erg/s, $\phi^*=10^{-3.09+-0.08}$ Mpc$^{-3}$ and $\alpha$=-1.75+-0.15. Above L~10$^{43}$ erg/s the Lya luminosity function becomes power-law like, driven by X-ray AGN. We find that Lya-selected emitters have a high escape fraction of 37+-7%, anti-correlated with Lya luminosity and correlated with Lya equivalent width. Lya emitters have ubiquitous large (~40 kpc) Lya haloes, 2x larger than their Ha extents. By directly comparing our Lya and Ha luminosity functions we find that the global/overall escape fraction of Lya photons (within a 13 kpc radius) from the full population of star-forming galaxies is 5.1+-0.2% at the peak of the star formation history. An extra 3.3+-0.3% of Lya photons likely still escape, but at larger radii.

We present results from the largest contiguous narrow-band survey in the near-infrared. We have used WIRCam/CFHT and the lowOH2 filter (1.187$\pm$0.005 $\mu$m) 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 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 H$\alpha$ emitters at z=0.8, 1343 [OIII]+H$\beta$ emitters at z=1.4 and 572 [OII] emitters at z=2.2. We probe co-moving volumes of >10$^6$ Mpc$^3$ and find significant over-densities, including an 8.5$\sigma$ (spectroscopically confirmed) over-density of H$\alpha$ emitters at z=0.81. We derive H$\alpha$, [OIII]+H$\beta$ and [OII] 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 sub-divide the samples in thousands of randomised 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 5x10$^{5}$ Mpc$^{3}$; errors on $L^*$ and $\phi^*$ due to sample (cosmic) variance on surveys probing ~10$^4$ Mpc$^{3}$ and ~10$^5$ Mpc$^{3}$ are typically very high: ~300% and ~40-60%, respectively., Comment: 22 pages, 15 figures, accepted for publication in MNRAS. Full catalogue of line emitters available in FITS format with final MNRAS published paper

Candidate galaxies at redshifts of $z \sim 10$ are now being found in extremely deep surveys, probing very small areas. As a consequence, candidates are very faint, making spectroscopic confirmation practically impossible. In order to overcome such limitations, we have undertaken the CF-HiZELS survey, which is a large area, medium depth near infrared narrow-band survey targeted at $z=8.8$ Lyman-$\alpha$ (Ly$\alpha$) emitters (LAEs) and covering 10 deg$^2$ in part of the SSA22 field with the Canada-France-Hawaii Telescope. We surveyed a comoving volume of $4.7\times 10^6$ Mpc$^3$ to a Ly$\alpha$ luminosity limit of $6.3\times10^{43}$ erg s$^{-1}$. We look for Ly$\alpha$ candidates by applying the following criteria: i) clear emission line source, ii) no optical detections ($ugriz$ from CFHTLS), iii) no visible detection in the optical stack ($ugriz > 27$), iv) visually checked reliable NB$_J$ and $J$ detections and v) $J-K \leq 0$. We compute photometric redshifts and remove a significant amount of dusty lower redshift line-emitters at $z \sim 1.4 $ or $2.2$. A total of 13 Ly$\alpha$ candidates were found, of which two are marked as strong candidates, but the majority have very weak constraints on their SEDs. Using follow-up observations with SINFONI/VLT we are able to exclude the most robust candidates as Ly$\alpha$ emitters. We put a strong constraint on the Ly$\alpha$ luminosity function at $z \sim 9$ and make realistic predictions for ongoing and future surveys. Our results show that surveys for the highest redshift LAEs are susceptible of multiple contaminations and that spectroscopic follow-up is absolutely necessary., Comment: 15 pages, 9 figures, accepted for publication in MNRAS

We present adaptive optics assisted integral field spectroscopy of nine Halpha-selected galaxies at z=0.84--2.23 selected from the HiZELS narrow-band survey. Our observations map the star-formation and kinematics of these representative star-forming galaxies on ~kpc-scales. We demonstrate that within the ISM of these galaxies, the velocity dispersion of the star-forming gas (\sigma) follows a scaling relation \sigma\propto\Sigma_SFR^(1/n)+constant (where \Sigma_SFR is the star formation surface density and the constant includes the stellar surface density). Assuming the disks are marginally stable (Toomre Q=1), we show that this follows from the Kennicutt-Schmidt relation (\Sigma_SFR = A\Sigma_gas^n), and we use the data to derive best fit parameters of n=1.34+/-0.15 and A=3.4_(-1.6)^(+2.5)x10^(-4)Mo/yr/kpc^2, consistent with the local relation and implying cold molecular gas masses of M_gas=10^(9-10)Mo and molecular gas fractions M_gas/(M_gas+Mstars)=0.3+/-0.1, with a range of 10-75%. These values confirm the high gas fractions for high-redshift star-forming galaxies, independent of CO-H_2 conversion factor. We also identify eleven ~kpc-scale star-forming regions (clumps) within our sample and show that their sizes are comparable to the wavelength of the fastest growing unstable mode. The luminosities and velocity dispersions of these clumps follow the same scaling relations as local HII regions, although their star formation densities are a factor 15+/-5x higher than typically found locally. We discuss how the clump properties are related to the disk, and show that their high masses and luminosities are a consequence of the high disk surface density., Comment: ApJ in press. 11 pages, 6 figures, 2 tables

This paper presents the results from the first wide and deep dual narrow-band survey to select H-alpha (Ha) and [OII] line emitters at z=1.47+-0.02 (using matched narrow-band filters in the H and z' bands), exploiting synergies between the UKIRT and Subaru telescopes. The Ha survey at z=1.47 reaches a flux limit of ~7x10^-17 erg/s/cm^2 and detects ~200 Ha emitters over 0.7deg^2, while the much deeper [OII] survey reaches an effective flux of ~7x10^-18 erg/s/cm^2, detecting ~1400 z=1.47 [OII] emitters in a matched co-moving volume of ~2.5x10^5 Mpc^3. The combined survey results in the identification of 190 simultaneous Ha and [OII] emitters at z=1.47. Ha and [OII] luminosity functions are derived and both are shown to evolve significantly from z~0 in a consistent way. The star formation rate density of the Universe at z=1.47 is evaluated, with the Ha analysis yielding 0.16+-0.05 M_sun/yr/Mpc^3 and the [OII] analysis 0.17+-0.04 M_sun/yr/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 ~11Gyrs. By using a large comparison sample at z~0.1 (from the SDSS), [OII]/Ha line ratios are calibrated as probes of dust-extinction. Ha emitters at z~1.47 show on average 1 mag of extinction at Ha, similar to the SDSS sources at z~0. Although we find that dust extinction correlates with SFR, the relation evolves by about ~0.5 mag from z~1.5 to z~0, with z~0 relations over-predicting the dust extinction corrections at high-z by that amount. Stellar mass is found to be a much more fundamental extinction predictor, with the relation between mass and extinction being valid at both z~0 and z~1.5. Dust extinction corrections as a function of optical colours are also derived, offering simpler mechanisms for estimating extinction in moderately star-forming systems over the last ~9Gyrs [Abridged]., Comment: Accepted for publication in MNRAS. Revised version following the reviewer's report. 21 pages, 23 figures

At z=0, clusters are primarily populated by red, elliptical and massive galaxies, while blue, spiral and lower-mass galaxies are common in low-density environments. Understanding how and when these differences were established is of absolute importance for our understanding of galaxy formation and evolution, but results at high-z remain contradictory. By taking advantage of the widest and deepest H-alpha narrow-band survey at z=0.84 over the COSMOS and UKIDSS UDS fields, probing a wide range of densities (from poor fields to rich groups and clusters, including a confirmed super-cluster with a striking filamentary structure), we show that the fraction of star-forming galaxies falls continuously from ~40% in fields to approaching 0% in rich groups/clusters. We also find that the median SFR increases with environmental density, at least up to group densities - but only for low and medium mass galaxies, and thus such enhancement is mass-dependent at z~1. The environment also plays a role in setting the faint-end slope (alpha) of the H-alpha luminosity function. Our findings provide a sharper view on galaxy formation and evolution and reconcile previously contradictory results at z~1: stellar mass is the primary predictor of star formation activity, but the environment also plays a major role., 5 pages, 4 figures, to appear in the proceedings of JENAM 2010 S2: `Environment and the Formation of Galaxies: 30 years later', ASSP, Springer

(Abridged) This paper presents an environment and stellar mass study of a large sample of star-forming (SF) galaxies at z=0.84 from the HiZELS survey, over 1.3 deg^2 in the COSMOS and UKIDSS UDS fields. By taking advantage of a truly panoramic coverage, from the field to a rich cluster, it is shown that both mass and environment play crucial roles in determining the properties of SF galaxies. The median specific SFR declines with mass in all environments, and the fraction of galaxies forming stars declines from ~40%, for M~10^10M_sun to effectively zero at M>10^11.5M_sun, confirming that mass-downsizing is generally in place by z~1. The fraction of SF galaxies also falls as a function of local environmental density from ~40% in the field to approaching zero at rich group/cluster densities. When SF does occur in high density regions, it is merger-dominated and, if only non-merging SF galaxies are considered, then the environment and mass trends are even stronger and largely independent, as in the local Universe. The median SFR of SF galaxies is found to increase with density up to intermediate (group or cluster outskirts) densities; this is clearly seen as a change in the faint-end slope of the H-alpha LF from steep (-1.9), in poor fields, to shallow (-1.1) in groups and clusters. Interestingly, the relation between median SFR and environment is only found for low to moderate-mass galaxies (below ~10^10.6M_sun), and is not seen for massive SF galaxies. Overall, these observations provide a detailed view over a sufficiently large range of mass and environment to reconcile previous observational claims: mass is the primary predictor of SF activity at z~1, but the environment, while enhancing the median SFR of (lower-mass) SF galaxies, is ultimately responsible for suppressing SF activity in all galaxies above surface densities of 10-30 Mpc^-2 (groups and clusters)., Accepted for publication in MNRAS, 18 pages, 16 figures, revised version following the reviewer's report