152 research outputs found
The Phase Space and Stellar Populations of Cluster Galaxies at z ~ 1: Simultaneous Constraints on the Location and Timescale of Satellite Quenching
We investigate the velocity vs. position phase space of z ~ 1 cluster
galaxies using a set of 424 spectroscopic redshifts in 9 clusters drawn from
the GCLASS survey. Dividing the galaxy population into three categories:
quiescent, star-forming, and poststarburst, we find that these populations have
distinct distributions in phase space. Most striking are the poststarburst
galaxies, which are commonly found at small clustercentric radii with high
clustercentric velocities, and appear to trace a coherent ``ring" in phase
space. Using several zoom simulations of clusters we show that the coherent
distribution of the poststarbursts can be reasonably well-reproduced using a
simple quenching scenario. Specifically, the phase space is best reproduced if
satellite quenching occurs on a rapid timescale (0.1 < tau_{Q} < 0.5 Gyr) after
galaxies make their first passage of R ~ 0.5R_{200}, a process that takes a
total time of ~ 1 Gyr after first infall. We compare this quenching timescale
to the timescale implied by the stellar populations of the poststarburst
galaxies and find that the poststarburst spectra are well-fit by a rapid
quenching (tau_{Q} = 0.4^{+0.3}_{-0.4} Gyr) of a typical star-forming galaxy.
The similarity between the quenching timescales derived from these independent
indicators is a strong consistency check of the quenching model. Given that the
model implies satellite quenching is rapid, and occurs well within R_{200},
this would suggest that ram-pressure stripping of either the hot or cold gas
component of galaxies are the most plausible candidates for the physical
mechanism. The high cold gas consumption rates at z ~ 1 make it difficult to
determine if hot or cold gas stripping is dominant; however, measurements of
the redshift evolution of the satellite quenching timescale and location may be
capable of distinguishing between the two.Comment: 10 pages, 4 figures, submitted to the Ap
Interannual Variability of Winds in the Antarctic Mesosphere and Lower Thermosphere Over Rothera (67°S, 68°W) During 2005â2021 in Meteor Radar Observations and WACCMâX
The mesosphere and lower thermosphere (MLT) plays a critical role in linking the middle and upper atmosphere. However, many General Circulation Models do not model the MLT and those that do remain poorly constrained. We use long-term meteor radar observations (2005â2021) from Rothera (67°S, 68°W) on the Antarctic Peninsula to evaluate the Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X) and investigate interannual variability. We find some significant differences between WACCM-X and observations. In particular, at upper heights, observations reveal eastwards wintertime (AprilâSeptember) winds, whereas the model predicts westwards winds. In summer (OctoberâMarch), the observed winds are northwards but predictions are southwards. Both the model and observations reveal significant interannual variability. We characterize the trend and the correlation between the winds and key phenomena: (a) the 11-year solar cycle, (b) El Niño Southern Oscillation, (c) Quasi-Biennial Oscillation and (d) Southern Annular Mode using a linear regression method. Observations of the zonal wind show significant changes with time. The summertime westwards wind near 80 km is weakening by up to 4â5 msâ1 per decade, whilst the eastward wintertime winds around 85â95 km are strengthening at by around 7 msâ1 per decade. We find that at some times of year there are significant correlations between the phenomena and the observed/modeled winds. The significance of this work lies in quantifying the biases in a leading General Circulation Model and demonstrating notable interannual variability in both modeled and observed winds
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The Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS): The Role of Environment and Self-Regulation in Galaxy Evolution at z ~ 1
We evaluate the effects of environment and stellar mass on galaxy properties
at 0.85 < z < 1.20 using a 3.6um-selected spectroscopic sample of 797 cluster
and field galaxies drawn from the GCLASS survey. We confirm that for galaxies
with LogM* > 9.3 the well-known correlations between environment and properties
such as star-forming fraction (f_SF), SFR, SSFR, D(4000), and color are already
in place at z ~ 1. We separate the effects of environment and stellar mass on
galaxies by comparing the properties of star-forming and quiescent galaxies at
fixed environment, and fixed stellar mass. The SSFR of star-forming galaxies at
fixed environment is correlated with stellar mass; however, at fixed stellar
mass it is independent of environment. The same trend exists for the D(4000)
measures of both the star-forming and quiescent galaxies and shows that their
properties are determined primarily by their stellar mass, not by their
environment. Instead, it appears that environment's primary role is to control
the fraction of star-forming galaxies. Using the spectra we identify candidate
poststarburst galaxies and find that those with 9.3 < LogM* < 10.7 are 3.1 +/-
1.1 times more common in high-density regions compared to low-density regions.
The clear association of poststarbursts with high-density regions as well as
the lack of a correlation between the SSFRs and D(4000)s of star-forming
galaxies with their environment suggests that at z ~ 1 the
environmental-quenching timescale must be rapid. Lastly, we construct a simple
quenching model which demonstrates that the lack of a correlation between the
D(4000) of quiescent galaxies and their environment results naturally if self
quenching dominates over environmental quenching at z > 1, or if the evolution
of the self-quenching rate mirrors the evolution of the environmental-quenching
rate at z > 1, regardless of which dominates.Comment: 26 pages, 15 figures, accepted for publication in Ap
Characteristics of men responding to an invitation to undergo testing for prostate cancer as part of a randomised trial
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