211 research outputs found
Evidence of Environmental Quenching at Redshift z ~ 2
We report evidence of environmental quenching among galaxies at redshift ~ 2,
namely the probability that a galaxy quenches its star formation activity is
enhanced in the regions of space in proximity of other quenched, more massive
galaxies. The effect is observed as strong clustering of quiescent galaxies
around quiescent galaxies on angular scales \theta < 20 arcsec, corresponding
to a proper(comoving) scale of 168 (502) kpc at z = 2. The effect is observed
only for quiescent galaxies around other quiescent galaxies; the probability to
find star-forming galaxies around quiescent or around star-forming ones is
consistent with the clustering strength of galaxies of the same mass and at the
same redshift, as observed in dedicated studies of galaxy clustering. The
effect is mass dependent in the sense that the quenching probability is
stronger for galaxies of smaller mass () than for more
massive ones, i.e. it follows the opposite trend with mass relative to
gravitational galaxy clustering. The spatial scale where the effect is observed
suggests these environments are massive halos, in which case the observed
effect would likely be satellite quenching. The effect is also redshift
dependent in that the clustering strength of quiescent galaxies around other
quiescent galaxies at z = 1.6 is ~ 1.7 times larger than that of the galaxies
with the same stellar mass at z = 2.6. This redshift dependence allows for a
crude estimate of the time scale of environmental quenching of low-mass
galaxies, which is in the range 1.5 - 4 Gyr, in broad agreement with other
estimates and with our ideas on satellite quenching.Comment: 12 pages, 9 figures, Accepted for publication in Ap
Homogeneous Velocity-Distance Data for Peculiar Velocity Analysis. I. Calibration of Cluster Samples
We have combined five Tully-Fisher (TF) redshift-distance samples for
peculiar velocity analysis: the cluster data of Han, Mould and coworkers
(1991-93, HM) and Willick (1991, W91CL), and the field data of Aaronson et al.
(1992), Willick (1991), Courteau & Faber (1992), and Mathewson et al. (1992),
totaling over 3000 spiral galaxies. We treat the cluster data in this paper,
which is the first of a series; in Paper II we treat the field TF samples.
These data are to be combined with elliptical data (e.g., Faber et al. 1989) to
form the MARK III CATALOG OF GALAXY PECULIAR VELOCITIES, which we will present
in Paper III. The catalog will be used as input for POTENT reconstruction of
velocity and density fields, described in later papers, as well as for
alternative velocity analyses. Our main goal in Papers I & II is to place the
TF data onto a self-consistent system by (i) applying a uniform set of
corrections to the raw observables, (ii) determining the TF slopes and scatters
separately for each sample, and (iii) adjusting the TF zeropoints to ensure
mutually consistent distances. The global zeropoint is set by the HM sample,
chosen because of its depth and uniformity on the sky and its substantial
overlap with each of the other samples. In this paper, we calibrate the
``forward'' and ``inverse'' TF relations for HM and W91CL. We study the
selection criteria for these samples and correct for the resultant statistical
biases. The bias corrections are validated by comparing forward and inverse
cluster distances. We find that many sample clusters are better modeled as
``expanding'' than relaxed, which significantly affects the TF calibrations.
Proper corrections for internal extinction are derived self-consistently from
the data.Comment: 42 Pages, uuencoded PostScript. Submitted to ApJ. 22 Figures not
included, can be obtained via ftp, contact [email protected]
z~2: An Epoch of Disk Assembly
We explore the evolution of the internal gas kinematics of star-forming
galaxies from the peak of cosmic star-formation at to today.
Measurements of galaxy rotation velocity , which quantify ordered
motions, and gas velocity dispersion , which quantify disordered
motions, are adopted from the DEEP2 and SIGMA surveys. This sample covers a
continuous baseline in redshift from to , spanning 10 Gyrs. At
low redshift, nearly all sufficiently massive star-forming galaxies are
rotationally supported (). By , the percentage of
galaxies with rotational support has declined to 50 at low stellar mass
() and 70 at high stellar mass
(). For , the percentage
drops below 35 for all masses. From to now, galaxies exhibit
remarkably smooth kinematic evolution on average. All galaxies tend towards
rotational support with time, and it is reached earlier in higher mass systems.
This is mostly due to an average decline in by a factor of 3 since a
redshift of 2, which is independent of mass. Over the same time period,
increases by a factor of 1.5 for low mass systems, but does not
evolve for high mass systems. These trends in and with
time are at a fixed stellar mass and should not be interpreted as evolutionary
tracks for galaxy populations. When galaxy populations are linked in time with
abundance matching, not only does decline with time as before, but
strongly increases with time for all galaxy masses. This enhances the
evolution in . These results indicate that is a
period of disk assembly, during which the strong rotational support present in
today's massive disk galaxies is only just beginning to emerge.Comment: 12 pages, 8 figures, submitted to Ap
The Design of the Keck Observatory and Telescope
This report describes the design of the Ten Meter Telescope and Observatory.
Since 1977 the University of California has been actively designing a ten meter telescope
for visible and infrared ground-based astronomy. The University of California
and the California Institute of Technology have now joined in a collaboration to construct
and operate this telescope and observatory. A generous gift of seventy million
dollars to Caltech from the W. M. Keck Foundation, announced in January 1985, will
provide funds for the construction of the facility. In recognition the facility will be
named the W. M. Keck Telescope and Observatory. The University of California will
provide funds for its operation. We expect construction to be completed by 1990.
The design of the telescope and observatory continues to be improved as the
detailed design progresses. The description given here is current as of January 1985.
Although many design details will change before construction, this description is accurate
in the general concept and in many particulars. The details of the design are
described in an ongoing series of Reports and Technical Notes. An index to this series
is given in the Reference Section of this report
Evolution of the Gas Mass Fraction of Progenitors to Today's Massive Galaxies: ALMA Observations in the CANDELS GOODS-S Field
We present an ALMA survey of dust continuum emission in a sample of 70
galaxies in the redshift range z=2-5 selected from the CANDELS GOODS-S field.
Multi-Epoch Abundance Matching (MEAM) is used to define potential progenitors
of a z = 0 galaxy of stellar mass 1.5 10^11 M_sun. Gas masses are derived from
the 850um luminosity. Ancillary data from the CANDELS GOODS-S survey are used
to derive the gas mass fractions. The results at z<=3 are mostly in accord with
expectations: The detection rates are 75% for the z=2 redshift bin, 50% for the
z=3 bin and 0% for z>=4. The average gas mass fraction for the detected z=2
galaxies is f_gas = 0.55+/-0.12 and f_gas = 0.62+/-0.15 for the z=3 sample.
This agrees with expectations for galaxies on the star-forming main sequence,
and shows that gas fractions have decreased at a roughly constant rate from z=3
to z=0. Stacked images of the galaxies not detected with ALMA give upper limits
to f_gas of <0.08 and <0.15, for the z=2 and z=3 redshift bins. None of our
galaxies in the z=4 and z=5 sample are detected and the upper limit from
stacked images, corrected for low metallicity, is f_gas<0.66. We do not think
that lower gas-phase metallicities can entirely explain the lower dust
luminosities. We briefly consider the possibility of accretion of very
low-metallicity gas to explain the absence of detectable dust emission in our
galaxies at z>4.Comment: Accepted for publication in the Astrophysical Journal. 33 pages; 11
figure
Evidence for a correlation between the sizes of quiescent galaxies and local environment to z ~ 2
We present evidence for a strong relationship between galaxy size and
environment for the quiescent population in the redshift range 1 < z < 2.
Environments were measured using projected galaxy overdensities on a scale of
400 kpc, as determined from ~ 96,000 K-band selected galaxies from the UKIDSS
Ultra Deep Survey (UDS). Sizes were determined from ground-based K-band
imaging, calibrated using space-based CANDELS HST observations in the centre of
the UDS field, with photometric redshifts and stellar masses derived from
11-band photometric fitting. From the resulting size-mass relation, we confirm
that quiescent galaxies at a given stellar mass were typically ~ 50 % smaller
at z ~ 1.4 compared to the present day. At a given epoch, however, we find that
passive galaxies in denser environments are on average significantly larger at
a given stellar mass. The most massive quiescent galaxies (M_stellar > 2 x
10^11 M_sun) at z > 1 are typically 50 % larger in the highest density
environments compared to those in the lowest density environments. Using Monte
Carlo simulations, we reject the null hypothesis that the size-mass relation is
independent of environment at a significance > 4.8 sigma for the redshift range
1 < z < 2. In contrast, the evidence for a relationship between size and
environment is much weaker for star-forming galaxies.Comment: Accepted for publication in MNRAS. 16 pages, 11 figures, 6 table
Compaction and Quenching of High-z Galaxies in Cosmological Simulations: Blue and Red Nuggets
We use cosmological simulations to study a characteristic evolution pattern
of high redshift galaxies. Early, stream-fed, highly perturbed, gas-rich discs
undergo phases of dissipative contraction into compact, star-forming systems
(blue nuggets) at z~4-2. The peak of gas compaction marks the onset of central
gas depletion and inside-out quenching into compact ellipticals (red nuggets)
by z~2. These are sometimes surrounded by gas rings or grow extended dry
stellar envelopes. The compaction occurs at a roughly constant specific
star-formation rate (SFR), and the quenching occurs at a constant stellar
surface density within the inner kpc (). Massive galaxies quench
earlier, faster, and at a higher than lower-mass galaxies, which
compactify and attempt to quench more than once. This evolution pattern is
consistent with the way galaxies populate the SFR-radius-mass space, and with
gradients and scatter across the main sequence. The compaction is triggered by
an intense inflow episode, involving (mostly minor) mergers, counter-rotating
streams or recycled gas, and is commonly associated with violent disc
instability. The contraction is dissipative, with the inflow rate >SFR, and the
maximum anti-correlated with the initial spin parameter, as
predicted by Dekel & Burkert (2014). The central quenching is triggered by the
high SFR and stellar/supernova feedback (possibly also AGN feedback) due to the
high central gas density, while the central inflow weakens as the disc
vanishes. Suppression of fresh gas supply by a hot halo allows the long-term
maintenance of quenching once above a threshold halo mass, inducing the
quenching downsizing.Comment: Resubmitted to MNRAS after responding to referee's comments; Updated
and added two figure
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