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Register a new userA Census of Sub-kiloparsec Resolution Metallicity Gradients in Star-forming Galaxies at Cosmic Noon from HST Slitless Spectroscopy
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We present hitherto the largest sample of gas-phase metallicity radial gradients measured at sub-kiloparsec resolution in star-forming galaxies in the redshift range of $zin[1.2, 2.3]$. These measurements are enabled by the synergy of slitless spectroscopy from the Hubble Space Telescope near-infrared channels and the lensing magnification from foreground galaxy clusters. Our sample consists of 76 galaxies with stellar mass ranging from 10$^7$ to 10$^{10}$ $M_odot$, instantaneous star-formation rate in the range of [1, 100] $M_odot$/yr, and global metallicity [$frac{1}{12}$, 2] solar. At 2-$sigma$ confidence level, 15/76 galaxies in our sample show negative radial gradients, whereas 7/76 show inverted gradients. Combining ours and all other metallicity gradients obtained at similar resolution currently available in the literature, we measure a negative mass dependence of $Deltalog({rm O/H})/Delta r~ [mathrm{dex~kpc^{-1}}] = left(-0.020pm0.007right) + left(-0.016pm0.008right) log(M_ast/10^{9.4} M_odot)$ with the intrinsic scatter being $sigma=0.060pm0.006$ over four orders of magnitude in stellar mass. Our result is consistent with strong feedback, not secular processes, being the primary governor of the chemo-structural evolution of star-forming galaxies during the disk mass assembly at cosmic noon. We also find that the intrinsic scatter of metallicity gradients increases with decreasing stellar mass and increasing specific star-formation rate. This increase in the intrinsic scatter is likely caused by the combined effect of cold-mode gas accretion and merger-induced starbursts, with the latter more predominant in the dwarf mass regime of $M_astlesssim10^9 M_odot$.
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The MAMMOTH-Grism slitless spectroscopic survey is a Hubble Space Telescope (HST) cycle-28 medium program, which is obtaining 45 orbits of WFC3/IR grism spectroscopy in the density peak regions of three massive galaxy protoclusters at $z=2-3$ discovered using the MAMMOTH technique. We introduce this survey by presenting the first measurement of mass-metallicity relation (MZR) at high redshift in overdense environments via grism spectroscopy. From the completed MAMMOTH-Grism observation in the field of the BOSS1244 protocluster at $z=2.24pm0.02$, We secure a sample of 36 protocluster member galaxies at $zsim2.24$, showing strong nebular emission lines ([O III], H$beta$ and [O II]) in their G141 spectra. Using the multi-wavelength broad-band deep imaging from HST and ground-based telescopes, we measure their stellar masses in the range of $[10^{9},10^{10.4}]M_odot$, instantaneous star formation rates (SFR) from 10 to 240$M_odot yr^{-1}$, and global gas-phase metallicities [1/3,1] of solar. Compared with similarly selected field galaxy sample at the same redshift, our galaxies show on average increased SFRs by ~0.06dex and ~0.18dex at ~10$^{10.1}M_odot$ and ~10$^{9.8}M_odot$, respectively. Using the stacked spectra of our sample galaxies, we derive the MZR in the BOSS1244 protocluster core as $12+log({rm O/H})=(0.136pm0.018)timeslog(M_ast/M_odot)+(7.082pm0.175)$, showing significantly shallower slope than that in the field. This shallow MZR slope is likely caused by the combined effects of efficient recycling of feedback-driven winds and cold-mode gas accretion in protocluster environments. The former effect helps low-mass galaxies residing in overdensities retain their metal production, whereas the latter effect dilutes the metal content of high-mass galaxies, making them more metal poor than their coeval field counterparts.
The existence of a spatially resolved Star-Forming Main Sequence (rSFMS) and a spatially resolved Mass-Metallicity Relation (rMZR) is now well established for local galaxies. Moreover, gradients with metallicity decreasing with radius seem to be common in local disc galaxies. These observations suggest that galaxy formation is a self-regulating process, and provide constraints for galaxy evolution models. Studying the evolution of these relations at higher redshifts is still however very challenging. In this paper, we analyse three gravitationally lensed galaxies at z = 0.6, 0.7 and 1, observed with MUSE and SINFONI. These galaxies are highly magnified by galaxy clusters, which allow us to observe resolved scaling relations and metallicity gradients on physical scales of a couple of hundred parsecs, comparable to studies of local galaxies. We confirm that the rSFMS is already in place at these redshifts on sub-kpc scales, and establish, for the first time, the existence of the rMZR at higher redshifts. We develop a forward-modelling approach to fit 2D metallicity gradients of multiply imaged lensed galaxies in the image plane, and derive gradients of -0.027+/-0.003, -0.019+/-0.003 and -0.039+/-0.060 dex/kpc. Despite the fact that these are clumpy galaxies, typical of high redshift discs, the metallicity variations in the galaxies are well described by global linear gradients, and we do not see any difference in metallicity associated with the star-forming clumps.
We report on the gas-phase metallicity gradients of a sample of 264 star-forming galaxies at 0.6 < z < 2.6, measured through deep near-infrared Hubble Space Telescope slitless spectroscopy. The observations include 12-orbit depth Hubble/WFC3 G102 grism spectra taken as a part of the CANDELS Lya Emission at Reionization (CLEAR) survey, and archival WFC3 G102+G141 grism spectra overlapping the CLEAR footprint. The majority of galaxies (84%) in this sample are consistent with a zero or slightly positive metallicity gradient across the full mass range probed (8.5 < log M_*/M_sun < 10.5). We measure the intrinsic population scatter of the metallicity gradients, and show that it increases with decreasing stellar mass---consistent with previous reports in the literature, but confirmed here with a much larger sample. To understand the physical mechanisms governing this scatter, we search for correlations between the observed gradient and various stellar population properties at fixed mass. However, we find no evidence for a correlation with the galaxy properties we consider---including star-formation rates, sizes, star-formation rate surface densities, and star-formation rates per gravitational potential energy. We use the observed weakness of these correlations to provide material constraints for predicted intrinsic correlations from theoretical models.
We study the relationship between stellar mass, star formation rate (SFR),ionization state, and gas-phase metallicity for a sample of 41 normal star-forming galaxies at $3 lesssim z lesssim 3.7$. The gas-phase oxygen abundance, ionization parameter, and electron density of ionized gas are derived from rest-frame optical strong emission lines measured on near-infrared spectra obtained with Keck/MOSFIRE. We remove the effect of these strong emission lines in the broad-band fluxes to compute stellar masses via spectral energy distribution fitting, while the SFR is derived from the dust-corrected ultraviolet luminosity. The ionization parameter is weakly correlated with the specific SFR, but otherwise the ionization parameter and electron density do not correlate with other global galaxy properties such as stellar mass, SFR, and metallicity. The mass-metallicity relation (MZR) at $zsimeq3.3$ shows lower metallicity by $simeq 0.7$ dex than that at $z=0$ at the same stellar mass. Our sample shows an offset by $simeq 0.3$ dex from the locally defined mass-metallicity-SFR relation, indicating that simply extrapolating such relation to higher redshift may predict an incorrect evolution of MZR. Furthermore, within the uncertainties we find no SFR-metallicity correlation, suggesting a less important role of SFR in controlling the metallicity at high redshift. We finally investigate the redshift evolution of the MZR by using the model by Lilly et al. (2013), finding that the observed evolution from $z=0$ to $zsimeq3.3$ can be accounted for by the model assuming a weak redshift evolution of the star formation efficiency.
We present the high-mass end of the galaxy stellar mass function using the largest sample to date (5,352) of star-forming galaxies with $M_{star} > 10^{11} M_{odot}$ at cosmic noon, $1.5 < z < 3.5$. This sample is uniformly selected across 17.2 deg$^2$ ($sim$0.44 Gpc$^3$ comoving volume from $1.5 < z < 3.5$), mitigating the effects of cosmic variance and encompassing a wide range of environments. This area, a factor of 10 larger than previous studies, provides robust statistics at the high-mass end. Using multi-wavelength data in the Spitzer/HETDEX Exploratory Large Area (SHELA) footprint we find that the SHELA footprint star-forming galaxy stellar mass function is steeply declining at the high-mass end probing values as high as $sim$$10^{-4}$ Mpc$^3$/dex and as low as $sim$5$times$$10^{-8}$ Mpc$^3$/dex across a stellar mass range of log($M_star$/$M_odot$) $sim$ 11 - 12. We compare our empirical star-forming galaxy stellar mass function at the high mass end to three types of numerical models: hydrodynamical models from IllustrisTNG, abundance matching from the UniverseMachine, and three different semi-analytic models (SAMs; SAG, SAGE, GALACTICUS). At redshifts $1.5 < z < 3.5$ we find that results from IllustrisTNG and abundance matching models agree within a factor of $sim$2 to 10, however the three SAMs strongly underestimate (up to a factor of 1,000) the number density of massive galaxies. We discuss the implications of these results for our understanding of galaxy evolution.
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