Using a sample of four galaxy clusters at 1.35 < z < 1.65 and 10 galaxy clusters at 0.85 < z < 1.35, we measure the environmental quenching timescale, tQ, corresponding to the time required after a ...galaxy is accreted by a cluster for it to fully cease star formation. Cluster members are selected by a photometric-redshift criterion, and categorized as star-forming, quiescent, or intermediate according to their dust-corrected rest-frame colors and magnitudes. We employ a "delayed-then-rapid" quenching model that relates a simulated cluster mass accretion rate to the observed numbers of each type of galaxy in the cluster to constrain tQ. For galaxies of mass M* 1010.5 M , we find a quenching timescale of tQ = Gyr in the z ∼ 1.5 cluster sample, and Gyr at z ∼ 1. Using values drawn from the literature, we compare the redshift evolution of tQ to timescales predicted for different physical quenching mechanisms. We find tQ to depend on host halo mass such that quenching occurs over faster timescales in clusters relative to groups, suggesting that properties of the host halo are responsible for quenching high-mass galaxies. Between z = 0 and z = 1.5, we find that tQ evolves faster than the molecular gas depletion timescale and slower than an estimated star formation rate-outflow timescale, but is consistent with the evolution of the dynamical time. This suggests that environmental quenching in these galaxies is driven by the motion of satellites relative to the cluster environment, although due to uncertainties in the atomic gas budget at high redshift, we cannot rule out quenching due to simple gas depletion.
We present ALMA CO (2-1) detections in 11 gas-rich cluster galaxies at z ∼ 1.6, constituting the largest sample of molecular gas measurements in z > 1.5 clusters to date. The observations span three ...galaxy clusters, derived from the Spitzer Adaptation of the Red-sequence Cluster Survey. We augment the >5 detections of the CO (2-1) fluxes with multi-band photometry, yielding stellar masses and infrared-derived star formation rates, to place some of the first constraints on molecular gas properties in z ∼ 1.6 cluster environments. We measure sizable gas reservoirs of 0.5-2 × 1011 M☉ in these objects, with high gas fractions (fgas) and long depletion timescales (τ), averaging 62% and 1.4 Gyr, respectively. We compare our cluster galaxies to the scaling relations of the coeval field, in the context of how gas fractions and depletion timescales vary with respect to the star-forming main sequence. We find that our cluster galaxies lie systematically off the field scaling relations at z = 1.6 toward enhanced gas fractions, at a level of ∼4 , but have consistent depletion timescales. Exploiting CO detections in lower-redshift clusters from the literature, we investigate the evolution of the gas fraction in cluster galaxies, finding it to mimic the strong rise with redshift in the field. We emphasize the utility of detecting abundant gas-rich galaxies in high-redshift clusters, deeming them as crucial laboratories for future statistical studies.
Recent observations have revealed that starburst galaxies can drive molecular gas outflows through stellar radiation pressure. Molecular gas is the phase of the interstellar medium from which stars ...form, so these outflows curtail stellar mass growth in galaxies. Previously known outflows, however, involve small fractions of the total molecular gas content and have typical scales of less than a kiloparsec. In at least some cases, input from active galactic nuclei is dynamically important, so pure stellar feedback (the momentum return into the interstellar medium) has been considered incapable of rapidly terminating star formation on galactic scales. Molecular gas has been detected outside the galactic plane of the archetypal starburst galaxy M82 (refs 4 and 5), but so far there has been no evidence that starbursts can propel substantial quantities of cold molecular gas to the same galactocentric radius (about 10 kiloparsecs) as the warmer gas that has been traced by metal ion absorbers in the circumgalactic medium. Here we report observations of molecular gas in a compact (effective radius 100 parsecs) massive starburst galaxy at redshift 0.7, which is known to drive a fast outflow of ionized gas. We find that 35 per cent of the total molecular gas extends approximately 10 kiloparsecs, and one-third of this extended gas has a velocity of up to 1,000 kilometres per second. The kinetic energy associated with this high-velocity component is consistent with the momentum flux available from stellar radiation pressure. This demonstrates that nuclear bursts of star formation are capable of ejecting large amounts of cold gas from the central regions of galaxies, thereby strongly affecting their evolution by truncating star formation and redistributing matter.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
We investigate the resolved kinematics of the molecular gas, as traced by the Atacama Large Millimeter/submillimeter Array in CO (2−1), of 25 cluster member galaxies across three different ...clusters at a redshift of
z
∼ 1.6. This is the first large-scale analysis of the molecular gas kinematics of cluster galaxies at this redshift. By separately estimating the rotation curve of the approaching and receding sides of each galaxy via kinematic modeling, we quantify the difference in total circular velocity to characterize the overall kinematic asymmetry of each galaxy. 3/14 of the galaxies in our sample that we are able to model have similar degrees of asymmetry as that observed in galaxies in the field at similar redshift based on observations of mainly ionized gas. However, this leaves 11/14 galaxies in our sample with significantly higher asymmetry, and some of these galaxies have degrees of asymmetry of up to ∼50 times higher than field galaxies observed at similar redshift. Some of these extreme cases also have one-sided tail-like morphology seen in the molecular gas, supporting a scenario of tidal and/or ram pressure interaction. Such stark differences in the kinematic asymmetry in clusters versus the field suggest the evolutionary influence of dense environments, established as being a major driver of galaxy evolution at low redshift, is also active in the high-redshift universe.
We study the buildup of the bimodal galaxy population using the NEWFIRM Medium-Band Survey, which provides excellent redshifts and well-sampled spectral energy distributions of 2,000 galaxies with K ...< 22.8 at 0.4 < z < 2.2. We first show that star-forming galaxies and quiescent galaxies can be robustly separated with a two-color criterion over this entire redshift range. We then study the evolution of the number density and mass density of quiescent and star-forming galaxies, extending the results of the COMBO-17, DEEP2, and other surveys to z = 2.2. The mass density of quiescent galaxies with M 3 X 1010 M increases by a factor of ~10 from z ~ 2 to the present day, whereas the mass density in star-forming galaxies is flat or decreases over the same time period. Modest mass growth by a factor of ~2 of individual quiescent galaxies can explain roughly half of the strong density evolution at masses >1011 M , due to the steepness of the exponential tail of the mass function. The rest of the density evolution of massive, quiescent galaxies is likely due to transformation (e.g., quenching) of the massive star-forming population, a conclusion which is consistent with the density evolution we observe for the star-forming galaxies themselves, which is flat or decreasing with cosmic time. Modest mass growth does not explain the evolution of less massive quiescent galaxies (~1010.5 M ), which show a similarly steep increase in their number densities. The less massive quiescent galaxies are therefore continuously formed by transforming galaxies from the star-forming population.
We select 25,000 galaxies from the NEWFIRM Medium Band Survey (NMBS) to study the rest-frame U - V color distribution of galaxies at 0 < z approx< 2.5. The five unique NIR filters of the NMBS enable ...the precise measurement of photometric redshifts and rest-frame colors for 9900 galaxies at 1 < z < 2.5. The rest-frame U - V color distribution at all z approx< 2.5 is bimodal, with a red peak, a blue peak, and a population of galaxies in between (the green valley). Model fits to the optical-NIR spectral energy distributions and the distribution of MIPS-detected galaxies indicate that the colors of galaxies in the green valley are determined largely by the amount of reddening by dust. This result does not support the simplest interpretation of green valley objects as a transition from blue star forming to red quiescent galaxies. We show that correcting the rest-frame colors for dust reddening allows a remarkably clean separation between the red and blue sequences up to z approx 2.5. Our study confirms that dusty-starburst galaxies can contribute a significant fraction to red-sequence samples selected on the basis of a single rest-frame color (i.e., U - V), so extra care must be taken if samples of truly 'red and dead' galaxies are desired. Interestingly, of galaxies detected at 24 mum, 14% remain on the red sequence after applying the reddening correction.
It is now well established that galaxies have different morphologies, gas contents, and star formation rates (SFR) in dense environments like galaxy clusters. The impact of environmental density ...extends to several virial radii, and galaxies appear to be pre-processed in filaments and groups before falling into the cluster. Our goal is to quantify this pre-processing in terms of gas content and SFR, as a function of density in cosmic filaments. We have observed the two first CO transitions in 163 galaxies with the IRAM-30 m telescope, and added 82 more measurements from the literature, thus forming a sample of 245 galaxies in the filaments around the Virgo cluster. We gathered HI-21cm measurements from the literature and observed 69 galaxies with the Nançay telescope to complete our sample. We compare our filament galaxies with comparable samples from the Virgo cluster and with the isolated galaxies of the AMIGA sample. We find a clear progression from field galaxies to filament and cluster galaxies for decreasing SFR, increasing fraction of galaxies in the quenching phase, an increasing proportion of early-type galaxies, and decreasing gas content. Galaxies in the quenching phase, defined as having a SFR below one-third of that of the main sequence (MS), are only between 0% and 20% in the isolated sample, according to local galaxy density, while they are 20%–60% in the filaments and 30%–80% in the Virgo cluster. Processes that lead to star formation quenching are already at play in filaments; they depend mostly on the local galaxy density, while the distance to the filament spine is a secondary parameter. While the HI-to-stellar-mass ratio decreases with local density by an order of magnitude in the filaments, and two orders of magnitude in the Virgo cluster with respect to the field, the decrease is much less for the H2-to-stellar-mass ratio. As the environmental density increases, the gas depletion time decreases, because the gas content decreases faster than the SFR. This suggests that gas depletion precedes star formation quenching.
We investigate the process of rapid star formation quenching in a sample of 12 massive galaxies at intermediate redshift (z ∼ 0.6) that host high-velocity ionized gas outflows (v > 1000 km s−1). We ...conclude that these fast outflows are most likely driven by feedback from star formation rather than active galactic nuclei (AGNs). We use multiwavelength survey and targeted observations of the galaxies to assess their star formation, AGN activity, and morphology. Common attributes include diffuse tidal features indicative of recent mergers accompanied by bright, unresolved cores with effective radii less than a few hundred parsecs. The galaxies are extraordinarily compact for their stellar mass, even when compared with galaxies at z ∼ 2–3. For 9/12 galaxies, we rule out an AGN contribution to the nuclear light and hypothesize that the unresolved core comes from a compact central starburst triggered by the dissipative collapse of very gas-rich progenitor merging discs. We find evidence of AGN activity in half the sample but we argue that it accounts for only a small fraction (≲10 per cent) of the total bolometric luminosity. We find no correlation between AGN activity and outflow velocity and we conclude that the fast outflows in our galaxies are not powered by ongoing AGN activity, but rather by recent, extremely compact starbursts.
Context.
The study of galaxy cluster mass profiles (
M
(
r
)) provides constraints on the nature of dark matter and on physical processes affecting the mass distribution. The study of galaxy cluster ...velocity anisotropy profiles (
β
(
r
)) informs the orbits of galaxies in clusters, which are related to their evolution. The combination of mass profiles and velocity anisotropy profiles allows us to determine the pseudo phase-space density profiles (
Q
(
r
)); numerical simulations predict that these profiles follow a simple power law in cluster-centric distance.
Aims.
We determine the mass, velocity anisotropy, and pseudo phase-space density profiles of clusters of galaxies at the highest redshifts investigated in detail to date.
Methods.
We exploited the combination of the GOGREEN and GCLASS spectroscopic data-sets for 14 clusters with mass
M
200
≥ 10
14
M
⊙
at redshifts 0.9 ≤
z
≤ 1.4. We constructed an
ensemble
cluster by stacking 581 spectroscopically identified cluster members with stellar mass
M
⋆
≥ 10
9.5
M
⊙
. We used the MAMPOSSt method to constrain several
M
(
r
) and
β
(
r
) models, and we then inverted the Jeans equation to determine the
ensemble
cluster
β
(
r
) in a non-parametric way. Finally, we combined the results of the
M
(
r
) and
β
(
r
) analysis to determine
Q
(
r
) for the
ensemble
cluster.
Results.
The concentration
c
200
of the
ensemble
cluster mass profile is in excellent agreement with predictions from Λ cold dark matter (ΛCDM) cosmological numerical simulations, and with previous determinations for clusters of similar mass and at similar redshifts, obtained from gravitational lensing and X-ray data. We see no significant difference between the total mass density and either the galaxy number density distributions or the stellar mass distribution. Star-forming galaxies are spatially significantly less concentrated than quiescent galaxies. The orbits of cluster galaxies are isotropic near the center and more radial outside. Star-forming galaxies and galaxies of low stellar mass tend to move on more radially elongated orbits than quiescent galaxies and galaxies of high stellar mass. The profile
Q
(
r
), determined using either the total mass or the number density profile, is very close to the power-law behavior predicted by numerical simulations.
Conclusions.
The internal dynamics of clusters at the highest redshift probed in detail to date are very similar to those of lower-redshift clusters, and in excellent agreement with predictions of numerical simulations. The clusters in our sample have already reached a high degree of dynamical relaxation.
We report the discovery of a galaxy cluster at z = 1.62 located in the Spitzer Wide-Area Infrared Extragalactic survey XMM-LSS field. This structure was selected solely as an overdensity of galaxies ...with red Spitzer/Infrared Array Camera colors, satisfying (3.6 - 4.5){sub AB}> - 0.1 mag. Photometric redshifts derived from the Subaru XMM Deep Survey (BViz bands), the UKIRT Infrared Deep Survey-Ultra-Deep Survey (UKIDSS-UDS, JK bands), and from the Spitzer Public UDS survey (3.6-8.0 {mu}m) show that this cluster corresponds to a surface density of galaxies at z {approx} 1.6 that is >20{sigma} above the mean at this redshift. We obtained optical spectroscopic observations of galaxies in the cluster region using IMACS on the Magellan telescope. We measured redshifts for seven galaxies in the range z = 1.62-1.63 within 2.8 arcmin (<1.4 Mpc) of the astrometric center of the cluster. A posteriori analysis of the XMM data in this field reveal a weak (4{sigma}) detection in the 0.5-2 keV band compatible with the expected thermal emission from such a cluster. The color-magnitude diagram of the galaxies in this cluster shows a prominent red sequence, dominated by a population of red galaxies with (z - J)>1.7 mag. The photometric-redshift probability distributions for the red galaxies are strongly peaked at z = 1.62, coincident with the spectroscopically confirmed galaxies. The rest-frame (U - B) color and scatter of galaxies on the red sequence are consistent with a mean luminosity-weighted age of 1.2 {+-} 0.1 Gyr, yielding a formation redshift z-bar{sub f}=2.35{+-}0.10, and corresponding to the last significant star formation period in these galaxies.
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