ABSTRACT
Using ∼5000 spectroscopically confirmed galaxies drawn from the Observations of Redshift Evolution in Large Scale Environments (ORELSE) survey we investigate the relationship between colour ...and galaxy density for galaxy populations of various stellar masses in the redshift range 0.55 ≤ z ≤ 1.4. The fraction of galaxies with colours consistent with no ongoing star formation (fq) is broadly observed to increase with increasing stellar mass, increasing galaxy density, and decreasing redshift, with clear differences observed in fq between field and group/cluster galaxies at the highest redshifts studied. We use a semi-empirical model to generate a suite of mock group/cluster galaxies unaffected by environmentally specific processes and compare these galaxies at fixed stellar mass and redshift to observed populations to constrain the efficiency of environmentally driven quenching (Ψconvert). High-density environments from 0.55 ≤ z ≤ 1.4 appear capable of efficiently quenching galaxies with $\log (\mathcal {M}_{\ast }/\mathcal {M}_{\odot })\gt 10.45$. Lower stellar mass galaxies also appear efficiently quenched at the lowest redshifts studied here, but this quenching efficiency is seen to drop precipitously with increasing redshift. Quenching efficiencies, combined with simulated group/cluster accretion histories and results on the star formation rate-density relation from a companion ORELSE study, are used to constrain the average time from group/cluster accretion to quiescence and the elapsed time between accretion and the inception of the quenching event. These time-scales were constrained to be 〈tconvert〉 = 2.4 ± 0.3 and 〈tdelay〉 = 1.3 ± 0.4 Gyr, respectively, for galaxies with $\log (\mathcal {M}_{\ast }/\mathcal {M}_{\odot })\gt 10.45$ and 〈tconvert〉 = 3.3 ± 0.3 and 〈tdelay〉 = 2.2 ± 0.4 Gyr for lower stellar mass galaxies. These quenching efficiencies and associated time-scales are used to rule out certain environmental mechanisms as being the primary processes responsible for transforming the star formation properties of galaxies over this 4 Gyr window in cosmic time.
Abstract
We present an exploration of ∼500 spectroscopically confirmed galaxies in and around two large-scale structures (LSSs) at z ∼ 1 drawn from the Observations of Redshift Evolution in Large ...Scale Environments survey, an ongoing, wide-field photometric and spectroscopic campaign targeting a large ensemble of LSSs at 0.6 < z < 1.3. A sub-sample of these galaxies (∼150) was targeted for the initial phase of a near-infrared MOSFIRE spectroscopic campaign investigating the differences in selections of galaxies that had recently ended a burst of star formation and/or had rapidly quenched (i.e. post-starburst/K+A galaxies). Selection with MOSFIRE utilizing the H α and N ii emission features resulted in a post-starburst sample more than double that selected by traditional z ∼ 1 (observed-frame optical) methods even after the removal of the relatively large fraction of dusty starburst galaxies selected through traditional methods. While the traditional post-starburst fraction increased with increasing global density, the MOSFIRE-selected post-starburst fraction was found to be constant across field, group, and cluster environments. However, this fraction computed relative to the number of star-forming galaxies was observed to elevate in the cluster environment. Post-starbursts selected with MOSFIRE exhibited moderately strong O ii emission originating from activity other than star formation. Such galaxies, termed K+A with ImposteR O ii-derived Star formation (KAIROS) galaxies, were found to be younger than and likely undergoing feedback absent or diminished in their optically selected counterparts. A comparison between the environments of the two types of post-starbursts suggested a picture in which the evolution of a post-starburst galaxy is considerably different in cluster environments than in the more rarefied environments of a group or the field.
Sulphur is one of the most abundant elements in the Universe (S/H
1.3
10
) and plays a crucial role in biological systems on Earth. The understanding of its chemistry is therefore of major ...importance.
Our goal is to complete the inventory of S-bearing molecules and their abundances in the prototypical photodissociation region (PDR) the Horsehead nebula to gain insight into sulphur chemistry in UV irradiated regions. Based on the WHISPER (Wide-band High-resolution Iram-30m Surveys at two positions with Emir Receivers) millimeter (mm) line survey, our goal is to provide an improved and more accurate description of sulphur species and their abundances towards the core and PDR positions in the Horsehead.
The Monte Carlo Markov Chain (MCMC) methodology and the molecular excitation and radiative transfer code RADEX were used to explore the parameter space and determine physical conditions and beam-averaged molecular abundances.
A total of 13 S-bearing species (CS, SO, SO
, OCS, H
CS - both ortho and para - HDCS, C
S, HCS
, SO
, H
S, S
H, NS and NS
) have been detected in the two targeted positions. This is the first detection of SO
in the Horsehead and the first detection of NS
in any PDR. We find a differentiated chemical behaviour between C-S and O-S bearing species within the nebula. The C-S bearing species C
S and o-H
CS present fractional abundances a factor of > two higher in the core than in the PDR. In contrast, the O-S bearing molecules SO, SO
, and OCS present similar abundances towards both positions. A few molecules, SO
, NS, and NS
, are more abundant towards the PDR than towards the core, and could be considered as PDR tracers.
This is the first complete study of S-bearing species towards a PDR. Our study shows that CS, SO, and H
S are the most abundant S-bearing molecules in the PDR with abundances of ∼ a few 10
. We recall that SH, SH
, S, and S
are not observable at the wavelengths covered by the WHISPER survey. At the spatial scale of our observations, the total abundance of S atoms locked in the detected species is < 10
, only ∼0.1% of the cosmic sulphur abundance.
Generative Adversarial Networks (GANs) have established themselves as a prevalent approach to image synthesis. Of these, StyleGAN offers a fascinating case study, owing to its remarkable visual ...quality and an ability to support a large array of downstream tasks. This state‐of‐the‐art report covers the StyleGAN architecture, and the ways it has been employed since its conception, while also analyzing its severe limitations. It aims to be of use for both newcomers, who wish to get a grasp of the field, and for more experienced readers that might benefit from seeing current research trends and existing tools laid out. Among StyleGAN's most interesting aspects is its learned latent space. Despite being learned with no supervision, it is surprisingly well‐behaved and remarkably disentangled. Combined with StyleGAN's visual quality, these properties gave rise to unparalleled editing capabilities. However, the control offered by StyleGAN is inherently limited to the generator's learned distribution, and can only be applied to images generated by StyleGAN itself. Seeking to bring StyleGAN's latent control to real‐world scenarios, the study of GAN inversion and latent space embedding has quickly gained in popularity. Meanwhile, this same study has helped shed light on the inner workings and limitations of StyleGAN. We map out StyleGAN's impressive story through these investigations, and discuss the details that have made StyleGAN the go‐to generator. We further elaborate on the visual priors StyleGAN constructs, and discuss their use in downstream discriminative tasks. Looking forward, we point out StyleGAN's limitations and speculate on current trends and promising directions for future research, such as task and target specific fine‐tuning.
Ortho-to-para (o/p) ratios of species like water, ammonia, and formaldehyde ( ) are believed to encode information about the formation history of the molecule. Measurements of o/p ratios in ...protoplanetary disks could thus be used to constrain their physical and chemical histories. We present the first measurement of the o/p ratio in a protoplanetary disk, using three ortho and two para lines observed with the Submillimeter Array (SMA) combined with one highly resolved measurement of a single line with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the disk around Herbig Ae star HD 163296. We find a disk-averaged o/p ratio of 1.8-2.8 (depending on the assumed disk structure), corresponding to a spin temperature of 11-22 K. We also derive a rotational temperature of 24 K from the flux ratio of the three ortho lines. The observed spatial distribution, as seen by ALMA, as well as the rotational temperature and the o/p ratio, at the large scales the SMA is most sensitive to, are consistent with a low-temperature formation pathway, most likely grain surface chemistry, of in this disk.
Utilizing spectroscopic observations taken for the VIMOS Ultra-Deep Survey (VUDS), new observations from Keck/DEIMOS, and publicly available observations of large samples of star-forming galaxies, we ...report here on the relationship between the star-formation rate (SFR) and the local environment (
δ
gal
) of galaxies in the early universe (2 <
z
< 5). Unlike what is observed at lower redshifts (
z
≲ 2), we observe a definite, nearly monotonic increase in the average SFR with increasing galaxy overdensity over more than an order of magnitude in
δ
gal
. The robustness of this trend is quantified by accounting for both uncertainties in our measurements and galaxy populations that are either underrepresented or not present in our sample (e.g., extremely dusty star-forming and quiescent galaxies), and we find that the trend remains significant under all circumstances. This trend appears to be primarily driven by the fractional increase of galaxies in high-density environments that are more massive in their stellar content and are forming stars at a higher rate than their less massive counterparts. We find that, even after stellar mass effects are accounted for, there remains a weak but significant SFR–
δ
gal
trend in our sample implying that additional environmentally related processes are helping to drive this trend. We also find clear evidence that the average SFR of galaxies in the densest environments increases with increasing redshift. These results lend themselves to a picture in which massive gas-rich galaxies coalesce into proto-cluster environments at
z
≳ 3, interact with other galaxies or with a forming large-scale medium, subsequently using or losing most of their gas in the process, and begin to seed the nascent red sequence that is present in clusters at slightly lower redshifts.
We present the first results from a near-IR spectroscopic campaign of the Cl1604 supercluster at z {approx} 0.9 and the cluster RX J1821.6+6827 at z {approx} 0.82 to investigate the nature of O II ...{lambda}3727 emission in cluster galaxies at high redshift. Of the 401 members in Cl1604 and RX J1821+6827 confirmed using the Keck II/DEIMOS spectrograph, 131 galaxies have detectable O II emission with no other signs of current star formation activity, as well as strong absorption features indicative of a well-established older stellar population. The combination of these features suggests that the primary source of O II emission in these galaxies is not a result of star formation processes, but rather due to the presence of a low-ionization nuclear emission-line region (LINER) or Seyfert component. Using the NIRSPEC spectrograph on the Keck II 10 m telescope, 19 such galaxies were targeted, as well as 6 additional O II-emitting cluster members that exhibited signs of ongoing star formation activity. Nearly half ({approx}47%) of the 19 O II-emitting, absorption-line-dominated galaxies exhibit O II to H{alpha} equivalent width (EW) ratios higher than unity, the typical observed value for star-forming galaxies, with an EW distribution similar to that observed for LINERs at low redshift. A majority ({approx}68%) of these 19 galaxies are classified as LINER/Seyfert based primarily on the emission-line ratio of N II {lambda}6584 and H{alpha}. The fraction of LINER/Seyferts increases to {approx}85% for red O II-emitting, absorption-line-dominated galaxies. The LINER/Seyfert galaxies in our Cl1604 sample exhibit average L(O II)/L(H{alpha}) ratios that are significantly higher than that observed in populations of star-forming galaxies, suggesting that O II is a poor indicator of star formation in a significant fraction of high-redshift cluster members. From the prevalence of O II-emitting, absorption-line-dominated galaxies in both systems and the fraction of such galaxies that are classified as LINER/Seyfert, we estimate that at least {approx}20% of galaxies in high-redshift clusters with M{sub *}>10{sup 10}-10{sup 10.5} M{sub sun} contain a LINER/Seyfert component that can be revealed with line ratios. We also investigate the effect such a population has on the global star formation rate of cluster galaxies and the post-starburst fraction, concluding that LINER/Seyferts must be accounted for if these quantities are to be physically meaningful.
Sulphur chemistry in the L1544 pre-stellar core Vastel, Charlotte; Quénard, D; Le Gal, R ...
Monthly notices of the Royal Astronomical Society,
08/2018, Volume:
478, Issue:
4
Journal Article
Peer reviewed
Open access
ABSTRACT
The L1544 pre-stellar core has been observed as part of the ASAI IRAM 30 m Large Program as well as follow-up programs. These observations have revealed the chemical richness of the earliest ...phases of low-mass star-forming regions. In this paper, we focus on the 21 sulphur bearing species (ions, isotopomers, and deuteration) that have been detected in this spectral-survey through 51 transitions: CS, CCS, C3S, SO, SO2, H2CS, OCS, HSCN, NS, HCS+, NS+, and H2S. We also report the tentative detection (4σ level) for methyl mercaptan (CH3SH). LTE and non-LTE radiative transfer modelling have been performed and we used the nautilus chemical code updated with the most recent chemical network for sulphur to explain our observations. From the chemical modelling, we expect a strong radial variation for the abundances of these species, which mostly are emitted in the external layer where non-thermal desorption of other species has previously been observed. We show that the chemical study cannot be compared to what has been done for the TMC-1 dark cloud, where the abundance is supposed constant along the line of sight, and conclude that a strong sulphur depletion is necessary to fully reproduce our observations of the prototypical pre-stellar core L1544.
Abstract
We investigate the impact of local environment on the galaxy stellar mass function (SMF) spanning a wide range of galaxy densities from the field up to dense cores of massive galaxy ...clusters. Data are drawn from a sample of eight fields from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. Deep photometry allow us to select mass-complete samples of galaxies down to 109 M⊙. Taking advantage of >4000 secure spectroscopic redshifts from ORELSE and precise photometric redshifts, we construct three-dimensional density maps between 0.55 < z < 1.3 using a Voronoi tessellation approach. We find that the shape of the SMF depends strongly on local environment exhibited by a smooth, continual increase in the relative numbers of high- to low-mass galaxies towards denser environments. A straightforward implication is that local environment proportionally increases the efficiency of (a) destroying lower mass galaxies and/or (b) growth of higher mass galaxies. We also find a presence of this environmental dependence in the SMFs of star-forming and quiescent galaxies, although not quite as strongly for the quiescent subsample. To characterize the connection between the SMF of field galaxies and that of denser environments, we devise a simple semi-empirical model. The model begins with a sample of ≈106 galaxies at z
start = 5 with stellar masses distributed according to the field. Simulated galaxies then evolve down to z
final = 0.8 following empirical prescriptions for star-formation, quenching and galaxy–galaxy merging. We run the simulation multiple times, testing a variety of scenarios with differing overall amounts of merging. Our model suggests that a large number of mergers are required to reproduce the SMF in dense environments. Additionally, a large majority of these mergers would have to occur in intermediate density environments (e.g. galaxy groups).
PDF
