We present a catalog of photometric redshifts and stellar masses for galaxies from imaging surveys serving the Dark Energy Spectroscopic Instrument project. The imaging footprints cover an area of ...over 14,000 deg2. This catalog contains about 0.17 billion morphologically classified galaxies with r < 23 mag. It covers the redshift range of z < 1 and the mass range of . A total of five photometric bands are used, including three optical filters (g, r, and z) and two infrared filters (Wide-field Infrared Survey Explorer W1 and W2). We use k-nearest neighbors and local linear regression algorithms to estimate photometric redshifts. Based on a spectroscopic sample of about 2.2 million galaxies, we achieve a redshift bias of = 2.4 × 10−4, accuracy of = 0.017, and outlier rate of about 5.1%. The stellar mass and other physical parameters are derived by stellar population synthesis model fitting based on our photometric redshifts. The differences in derived using spectroscopic and photometric redshifts present a 1 dispersion of 0.09 dex.
Previous findings show that the existence of dense cores or bulges is the prerequisite for quenching a galaxy, leading to a proposed two-step quenching scenario: compaction and quenching. In this ...scenario, galaxies first grow their cores to a stellar mass surface density threshold, and subsequently quenching occurs, suggesting that galaxies evolve from extended star-forming galaxies (eSFGs), through compact star-forming galaxies (cSFGs), to a quenched population. In this work, we aim at examining the possible evolutionary link between eSFGs and cSFGs by identifying the trends in star formation rate (SFR), gas-phase metallicity, and H I content, since one would naturally expect that galaxies evolve along the track of cold gas consumption and metal enhancement. We select a volume-limited sample of 15,933 galaxies with stellar mass above and redshift of from the NASA Sloan Atlas catalog within the ALFALFA footprint. The cSFGs on average exhibit similar or slightly higher SFRs of ∼0.06 dex and significantly higher gas-phase metallicity (up to 0.2 dex at low mass) with respect to the eSFGs, while the cSFGs dominate the galaxy population of the most intense star formation activities. More importantly, overall the median H i content and gas depletion time of cSFGs are about half of eSFGs. Our result supports the compaction and quenching scenario that galaxies evolve and grow their cores along the track of cold gas consumption and metal enhancement. The environments of eSFGs and cSFGs are indistinguishable, suggesting that the compaction process is independent of any environmental effects at least for the low-redshift universe.
Abstract
We use 789 disk-like, star-forming galaxies (with 596 H
i
detections) from H
i
follow-up observations for the SDSS-IV MaNGA survey to study the possible role of inner H
i
gas in causing ...secondary dependences in the mass–gas-phase metallicity relation. We use the gas-phase metallicity derived at the effective radii of the galaxies. We derive the inner H
i
mass within the optical radius, but also use the total H
i
mass and star formation rate (SFR) for a comparison. We confirm the anticorrelation between the total H
i
mass and gas-phase metallicity at fixed stellar mass, but the anticorrelation is significantly strengthened when the total H
i
mass is replaced by the inner H
i
mass. Introducing a secondary relation with the inner H
i
mass can produce a small but noticeable decrease (16%) in the scatter of the mass–gas-phase metallicity relation, in contrast to the negligible effect with the SFR. The correlation with the inner H
i
mass is robust when using different diagnostics of metallicity, but the correlation with SFR is not. The correlation with the inner H
i
mass becomes much weaker when the gas-phase metallicity is derived in the central region instead of at the effective radius. These results support the idea that the scatter in the mass–metallicity relation is regulated by gas accretion, and not directly by the SFR, and stress the importance of deriving the gas mass and the metallicity from roughly the same region. The new relation between inner H
i
mass and gas-phase metallicity will provide new constraints for chemical and galaxy evolution models.
We complement the parsec data base of stellar evolutionary tracks with new models of massive stars, from the pre-main-sequence phase to the central carbon ignition. We consider a broad range of ...metallicities, 0.0001 ≤ Z ≤ 0.04 and initial masses up to M
ini = 350 M⊙. The main difference with respect to our previous models of massive stars is the adoption of a recent formalizm accounting for the mass-loss enhancement when the ratio of the stellar to the Eddington luminosity, Γ
e
, approaches unity. With this new formalizm, the models are able to reproduce the Humphreys–Davidson limit observed in the Galactic and Large Magellanic Cloud colour–magnitude diagrams, without an ad hoc mass-loss enhancement. We also follow the predictions of recent wind models indicating that the metallicity dependence of the mass-loss rates becomes shallower when Γ
e
approaches unity. We thus find that the more massive stars may suffer from substantial mass-loss even at low metallicity. We also predict that the Humphreys–Davidson limit should become brighter at decreasing metallicity. We supplement the evolutionary tracks with new tables of theoretical bolometric corrections, useful to compare tracks and isochrones with the observations. For this purpose, we homogenize existing stellar atmosphere libraries of hot and cool stars (Potsdam Wolf–Rayet, atlas9 and phoenix) and we add, where needed, new atmosphere models computed with wm-basic. The mass, age and metallicity grids are fully adequate to perform detailed investigations of the properties of very young stellar systems, both in local and distant galaxies. The new tracks supersede the previous old padova models of massive stars.
Directed evolution based on saturation mutagenesis at sites lining the binding pocket is a commonly practiced strategy for enhancing or inverting the stereoselectivity of enzymes for use in organic ...chemistry or biotechnology. However, as the number of residues in a randomization site increases to five or more, the screening effort for 95 % library coverage increases astronomically until it is no longer feasible. We propose the use of a single amino acid for saturation mutagenesis at superlarge randomization sites comprising 10 or more residues. When used to reshape the binding pocket of limonene epoxide hydrolase, this strategy, which drastically reduces the search space and thus the screening effort, resulted in R,R‐ and S,S‐selective mutants for the hydrolytic desymmetrization of cyclohexene oxide and other epoxides. X‐ray crystal structures and docking studies of the mutants unveiled the source of stereoselectivity and shed light on the mechanistic intricacies of this enzyme.
Emil Fischer’s lock‐and‐key hypothesis has been revisited in experiments to reshape the binding pocket of limonene epoxide hydrolase (see picture) by using a single amino acid building block in the saturation mutagenesis of a 10‐residue site. Catalytic variants selective for the formation of both (R,R)‐ and (S,S)‐1,2‐cyclohexanediol in the hydrolytic desymmetrization of cyclohexene oxide were identified in one and the same mutant library.
Matrix metalloproteinases (MMPs) are zinc‐dependent endopeptidases at the intersection of health and disease due to their involvement in processes such as tissue repair and immunity as well as cancer ...and inflammation. Because of the high structural conservation in the catalytic domains and shallow substrate binding sites, selective, small‐molecule inhibitors of MMPs have remained elusive. In a tour‐de‐force peptide engineering approach combining phage‐display selections, rational design of enhanced zinc chelation, and d‐amino acid screening, we succeeded in developing a first synthetic MMP‐2 inhibitor that combines high potency (Ki=1.9±0.5 nm), high target selectivity, and proteolytic stability, and thus fulfills all the required qualities for in cell culture and in vivo application. Our work suggests that selective MMP inhibition is achievable with peptide macrocycles and paves the way for developing specific inhibitors for application as chemical probes and potentially therapeutics.
The selective inhibition of individual matrix metalloproteinase has been a great challenge due to high structural conservation in the catalytic domains and shallow substrate binding sites. Herein, we show that inhibitors with high selectivity for specific MMPs can be developed based on peptide macrocycles.
We present the first results from the ongoing Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) project, which is the largest narrowband survey for z ∼ 7 galaxies to date. Using a specially ...built narrowband filter NB964 for the superb large-area Dark Energy Camera (DECam) on the NOAO/CTIO 4 m Blanco telescope, LAGER has collected 34 hr NB964 narrowband imaging data in the 3 deg2 COSMOS field. We have identified 23 Ly Emitter candidates at z = 6.9 in the central 2-deg2 region, where DECam and public COSMOS multi-band images exist. The resulting luminosity function (LF) can be described as a Schechter function modified by a significant excess at the bright end (four galaxies with LLy ∼ 1043.4 0.2 erg s−1). The number density at LLy ∼ 1043.4 0.2 erg s−1 is little changed from z = 6.6, while at fainter LLy it is substantially reduced. Overall, we see a fourfold reduction in Ly luminosity density from z = 5.7 to z = 6.9. Combined with a more modest evolution of the continuum UV luminosity density, this suggests a factor of ∼3 suppression of Ly by radiative transfer through the z ∼ 7 intergalactic medium (IGM). It indicates an IGM neutral fraction of xH i ∼ 0.4-0.6 (assuming Ly velocity offsets of 100-200 km s−1). The changing shape of the Ly LF between z 6.6 and z = 6.9 supports the hypothesis of ionized bubbles in a patchy reionization at z ∼ 7.
Abstract
By applying our previously developed two-step scheme for galaxy morphology classification, we present a catalog of galaxy morphology for
H
-band-selected massive galaxies in the COSMOS-DASH ...field, which includes 17,292 galaxies with stellar mass
M
⋆
> 10
10
M
⊙
at 0.5 <
z
< 2.5. The classification scheme is designed to provide a complete morphology classification for galaxies via a combination of two machine-learning steps. We first use an unsupervised machine-learning method (i.e., bagging-based multiclustering) to cluster galaxies into five categories: spherical (SPH), early-type disk, late-type disk, irregular (IRR), and unclassified. About 48% of the galaxies (8258/17,292) are successfully clustered during this step. For the remaining sample, we adopt a supervised machine-learning method (i.e., GoogLeNet) to classify them, during which galaxies that are well classified in the previous step are taken as our training set. Consequently, we obtain a morphology classification result for the full sample. The t-SNE test shows that galaxies in our sample can be well aggregated. We also measure the parametric and nonparametric morphologies of these galaxies. We find that the Sérsic index increases from IRR to SPH and the effective radius decreases from IRR to SPH, consistent with the corresponding definitions. Galaxies from different categories are separately distributed in the
G
–
M
20
space. Such consistencies with other characteristic descriptions of galaxy morphology demonstrate the reliability of our classification result, ensuring that it can be used as a basic catalog for further galaxy studies.
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