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Register a new userThe MOSDEF Survey: Environmental dependence of the gas-phase metallicity of galaxies at $1.4 leq z leq 2.6$
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Using the near-IR spectroscopy of the MOSFIRE Deep Evolution Field (MOSDEF) survey, we investigate the role of local environment in the gas-phase metallicity of galaxies. The local environment measurements are derived from accurate and uniformly calculated photometric redshifts with well-calibrated probability distributions. Based on rest-frame optical emission lines, [NII]$lambda6584$ and H$alpha$, we measure gas-phase oxygen abundance of 167 galaxies at $1.37leq zleq1.7$ and 303 galaxies at $2.09leq zleq2.61$, located in diverse environments. We find that at $zsim1.5$, the average metallicity of galaxies in overdensities with $M_*sim10^{9.8}M_odot, 10^{10.2}M_odot$ and $10^{10.8}M_odot$ is higher relative to their field counterparts by $0.094pm0.051$, $0.068pm0.028$ and $0.052pm0.043$ dex, respectively. However, this metallicity enhancement does not exist at higher redshift, $zsim2.3$, where, compared to the field galaxies, we find $0.056pm0.043$, $0.056pm0.028$ and $0.096pm 0.034$ dex lower metallicity for galaxies in overdense environments with $M_*sim10^{9.8}M_odot, 10^{10.2}M_odot$ and $10^{10.7}M_odot$, respectively. Our results suggest that, at $1.37leq zleq2.61$, the variation of mass-metallicity relation with local environment is small ($<0.1$dex), and reverses at $zsim2$. Our results support the hypothesis that, at the early stages of cluster formation, owing to efficient gas cooling, galaxies residing in overdensities host a higher fraction of pristine gas with prominent primordial gas accretion, which lowers their gas-phase metallicity compared to their coeval field galaxies. However, as the Universe evolves to lower redshifts ($zlesssim2$), shock-heated gas in overdensities cannot cool down efficiently, and galaxies become metal-rich rapidly due to the suppression of pristine gas inflow and re-accretion of metal-enriched outflows in overdensities.
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We present results on the dust attenuation curve of z~2 galaxies using early observations from the MOSFIRE Deep Evolution Field (MOSDEF) survey. Our sample consists of 224 star-forming galaxies with nebular spectroscopic redshifts in the range z= 1.36-2.59 and high S/N measurements of, or upper limits on, the H-alpha and H-beta emission lines obtained with Keck/MOSFIRE. We construct composite SEDs of galaxies in bins of specific SFR and Balmer optical depth in order to directly constrain the dust attenuation curve from the UV through near-IR for typical star-forming galaxies at high redshift. Our results imply an attenuation curve that is very similar to the SMC extinction curve at wavelengths redward of 2500 Angstroms. At shorter wavelengths, the shape of the curve is identical to that of the Calzetti relation, but with a lower normalization (R_V). Hence, the new attenuation curve results in SFRs that are ~20% lower, and log stellar masses that are 0.16 dex lower, than those obtained with the Calzetti attenuation curve. Moreover, we find that the difference in the reddening---and the total attenuation---of the ionized gas and stellar continuum correlates strongly with SFR, such that for dust-corrected SFRs larger than 20 Msun/yr assuming a Chabrier IMF, the nebular emission lines suffer an increasing degree of obscuration relative to the continuum. A simple model that can account for these trends is one in which the UV through optical stellar continuum is dominated by a population of less reddened stars, while the nebular line and bolometric luminosities become increasingly dominated by dustier stellar populations for galaxies with large SFRs, as a result of the increased dust enrichment that accompanies such galaxies. Consequently, UV- and SED-based SFRs may underestimate the total SFR at even modest levels of ~20 Msun/yr. [Abridged]
Using the CANDELS photometric catalogs for the HST/ACS and WFC3, we identified massive evolved galaxies at $3 < z < 4.5$, employing three different selection methods. We find the comoving number density of these objects to be $sim 2 times 10^{-5}$ and $8 times 10^{-6}Mpc^{-3}$ after correction for completeness for two redshift bins centered at $z=3.4, 4.7$. We quantify a measure of how much confidence we should have for each candidate galaxy from different selections and what are the conservative error estimates propagated into our selection. Then we compare the evolution of the corresponding number densities and their stellar mass density with numerical simulations, semi-analytical models, and previous observational estimates, which shows slight tension at higher redshifts as the models tend to underestimate the number and mass densities. By estimating the average halo masses of the candidates ($M_h approx 4.2, 1.9, 1.3 times 10^{12} M_odot$ for redshift bins centered at $z=3.4, 4.1, 4.7$), we find them to be consistent with halos that were efficient in turning baryons to stars and were relatively immune to the feedback effects and on the verge of transition into hot-mode accretion. This can suggest the relative cosmological starvation of the cold gas followed by an overconsumption phase in which the galaxy consumes the available cold gas rapidly as one of the possible drivers for the quenching of the massive evolved population at high redshift.
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 present the clustering analysis of photometric luminous red galaxies (LRGs) at a redshift range of $0.1leq z leq 1.05$ using $615,317$ photometric LRGs selected from the Hyper Suprime-Cam Subaru Strategic Program covering $sim124$ deg$^{2}$. Our sample covers a broad range of stellar masses and photometric redshifts and enables a halo occupation distribution analysis to study the redshift and stellar-mass dependence of dark halo properties of LRGs. We find a tight correlation between the characteristic dark halo mass to host central LRGs, $M_{min}$, and the number density of LRGs independently of redshifts, indicating that the formation of LRGs is associated with the global environment. The $M_{min}$ of LRGs depends only weakly on the stellar mass $M_{star}$ at $M_{star} lesssim 10^{10.75}h^{-2} M_{odot}$ at $0.3<z<1.05$, in contrast to the case for all photometrically selected galaxies for which $M_{min}$ shows significant dependence on $M_{star}$ even at low $M_{star}$. The weak stellar mass dependence is indicative of the dark halo mass being the key parameter for the formation of LRGs rather than the stellar mass. Our result suggests that the halo mass of $sim 10^{12.5 pm 0.2}h^{-1} M_{odot}$ is the critical mass for an efficient halo quenching due to the halo environment. We compare our result with the result of the hydrodynamical simulation to find that low-mass LRGs at $z sim 1$ will increase their stellar masses by an order magnitude from $z=1$ to $0$ through mergers and satellite accretions, and a large fraction of massive LRGs at $z<0.9$ consist of LRGs that are recently migrated from massive green valley galaxies or those evolved from less massive LRGs through mergers and satellite accretions.
The ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Band 6 scan (212-272 GHz) covers potential [CII] emission in galaxies at $6leq z leq8$ throughout a 2.9 arcmin$^2$ area. By selecting on known Lyman-$alpha$ emitters (LAEs) and photometric dropout galaxies in the field, we perform targeted searches down to a 5$sigma$ [CII] luminosity depth $L_{mathrm{[CII]}}sim2.0times10^8$ L$_{odot}$, corresponding roughly to star formation rates (SFRs) of $10$-$20$ M$_{odot}$ yr$^{-1}$ when applying a locally calibrated conversion for star-forming galaxies, yielding zero detections. While the majority of galaxies in this sample are characterized by lower SFRs, the resulting upper limits on [CII] luminosity in these sources are consistent with the current literature sample of targeted ALMA observations of $z=6$-$7$ LAEs and Lyman-break galaxies (LBGs), as well as the locally calibrated relations between $L_{mathrm{[CII]}}$ and SFR -- with the exception of a single [CII]-deficient, UV luminous LBG. We also perform a blind search for [CII]-bright galaxies that may have been missed by optical selections, resulting in an upper limit on the cumulative number density of [CII] sources with $L_{mathrm{[CII]}}>2.0times10^8$ L$_{odot}$ ($5sigma $) to be less than $1.8times10^{-4}$ Mpc$^{-3}$ (90% confidence level). At this luminosity depth and volume coverage, we present an observed evolution of the [CII] luminosity function from $z=6$-$8$ to $zsim0$ by comparing the ASPECS measurement to literature results at lower redshift.
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