5,068 research outputs found
M/L and Color Evolution for A Deep Sample of M* Cluster Galaxies at z~1: The Formation Epoch and the Tilt of the Fundamental Plane
We have measured velocity dispersions for a sample of 36 galaxies with J <
21.2 or Mr < -20.6 mag in MS1054-03, a massive cluster of galaxies at z = 0.83.
Our data are of uniformly high quality down to our selection limit, our 16-hour
exposures typically yielding errors of only \delta(dispersion)~10% for L* and
fainter galaxies. By combining our measurements with data from the literature,
we have 53 cluster galaxies with measured dispersions, and HST/ACS-derived
sizes, colors and surface brightnesses. This sample is complete for the typical
L* galaxy at z~1, unlike most previous z~1 cluster samples which are complete
only for the massive cluster members (>1e11 M_sun). We find no evidence for a
change in the tilt of the fundamental plane (FP). Nor do we find evidence for
evolution in the slope of the color-dispersion relation and M/L_B-dispersion
relations; measuring evolution at a fixed dispersion should minimize the impact
of size evolution found in other work. The M/L_B at fixed dispersion evolves by
\Delta log10 M/L_B=-0.50 +/- 0.03 between z=0.83 and z=0.02 or d(log10
M/L_B)=-0.60 +/- 0.04 dz, and we find \Delta (U-V)_z=-0.24 +/- 0.02 mag at
fixed dispersion in the rest-frame, matching the expected evolution in M/L_B
within 2.25 standard deviations. The implied formation redshift from both the
color and M/L_B evolution is z*=2.0 +/- 0.2 +/- 0.3 (sys), during the epoch in
which the cosmic star-formation activity peaked, with the systematic
uncertainty showing the dependence of z* on the assumptions we make about the
stellar populations. The lack of evolution in either the tilt of the FP or in
the M/L- and color-dispersion relations imply that the formation epoch depends
weakly on mass, ranging from z*=2.3 +1.3 -0.3 at 300 km/s to z*=1.7 +0.3 -0.2
at 160 km/s and implies that the IMF similarly varies slowly with galaxy mass.Comment: revised; typos corrected, references updated, and other cosmetic
changes to meet ApJ format ApJ accepted, 22 pages in emulate ApJ format, 8
color figures, 1 b/w figur
On the overconsumption of food portions : is the problem in the size or the number?
While larger food portions lead to greater consumption, the effect appears to be greater when the larger food portions are created by increasing the size of food units than when created by increasing the number of food units making up the portion. Study 1 shows consumer estimates of food quantities are more sensitive to unit-number information (i.e., the number of units) and less sensitive to unit-size information (i.e., the size of food units). Estimates of the food quantity presented in a portion size are larger when the portion is presented as many, smaller units than when presented as few, larger units. Study 2 demonstrates that participants tend to consume less when a portion is presented as more, smaller units vs. few, larger units. This result along with that of Study 1 suggest the portion-size effect on consumption is inversely related to the portion-size effect on quantity perceptions. When consumers are induced to focus on unit-size rather than unit-number (Study 3), quantity estimates can be made more sensitive to unit-size manipulations. Study 4 extends this finding to show that the portion-size effect on consumption is greatest when quantity estimation is insensitive to portion size change, and mitigated when information focus encourages processing of the relevant information
A constant limiting mass scale for flat early-type galaxies from z=1 to z=0: density evolves but shapes do not
We measure the evolution in the intrinsic shape distribution of early-type
galaxies from z~1 to z~0 by analyzing their projected axis-ratio distributions.
We extract a low-redshift sample (0.04 < z < 0.08) of early-type galaxies with
very low star-formation rates from the SDSS, based on a color-color selection
scheme and verified through the absence of emission lines in the spectra. The
inferred intrinsic shape distribution of these early-type galaxies is strongly
mass dependent: the typical short-to-long intrinsic axis-ratio of high-mass
early-type galaxies (>1e11 M_sun) is 2:3, where as at masses below 1e11 M_sun
this ratio narrows to 1:3, or more flattened galaxies. In an entirely analogous
manner we select a high-redshift sample (0.6 < z < 0.8) from two deep-field
surveys: GEMS and COSMOS. We find a seemingly universal mass of ~1e11 M_sun for
highly flatted early-type systems at all redshifts. This implies that the
process that grows an early-type galaxy above this ceiling mass involves
forming round systems. Using both parametric and non-parametric tests, we find
no evolution in the projected axis-ratio distribution for galaxies with masses
>3e10 M_sun with redshift. At the same time, our samples imply an increase of
2-3x in co-moving number density for early-type galaxies at masses >3e10 M_sun,
in agreement with previous studies. Given the direct connection between the
axis-ratio distribution and the underlying bulge-to-disk ratio distribution,
our findings imply that the number density evolution of early-type galaxies is
not exclusively driven by the emergence of either bulge- or disk-dominated
galaxies, but rather by a balanced mix that depends only on the stellar mass of
the galaxy. The challenge for galaxy formation models is to reproduce this
overall non-evolving ratio of flattened to round early-type galaxies in the
context of a continually growing population.Comment: 14 pages in emulate ApJ format, 8 color figures, submitted to ApJ,
comments welcome, fixed missing reference
Lenticular Galaxies and Their Environments
It is widely believed that lenticular (S0) galaxies were initially spirals
from which the gas has been removed by interactions with hot cluster gas, or by
ram-pressure stripping of cool gas from spirals that are orbiting within rich
clusters of galaxies. However, problems with this interpretation are that: (1)
Some lenticulars, such as NGC 3115, are isolated field galaxies rather than
cluster members. (2) The distribution of flattening values of S0 galaxies in
clusters, in groups and in the field are statistically indistinguishable. This
is surprising because one might have expected most of the progenitors of field
S0 galaxies to have been flattened late-type galaxies, whereas lenticulars in
clusters are thought to have mostly been derived from bulge-dominated
early-type galaxies. (3) It should be hardest for ram-pressure to strip massive
luminous galaxies with deep potential wells. However, no statistically
significant differences are seen between the luminosity distributions of
early-type Shapley-Ames galaxies in clusters, groups and in the field. (4)
Finally, both ram-pressure stripping and evaporation by hot intra-cluster gas
would be most efficient in rich clusters. However, the small number of
available data in the Shapley-Ames sample appears to show no statistically
significant differences between the relative frequencies of dust-poor S0_1 and
dust-rich S0_3 galaxies in clusters, groups and in the field. It is tentatively
concluded that ram-pressure stripping, and heating by intra-cluster gas, may
not be the only evolutionary channels that lead to the formation of lenticular
galaxies. It is speculated that gas starvation, or gas ejection by active
nuclei, may have play a major role in the formation of a significant fraction
of all S0 galaxies.Comment: Astrophysical Journal, in pres
An exactly conservative particle method for one dimensional scalar conservation laws
A particle scheme for scalar conservation laws in one space dimension is
presented. Particles representing the solution are moved according to their
characteristic velocities. Particle interaction is resolved locally, satisfying
exact conservation of area. Shocks stay sharp and propagate at correct speeds,
while rarefaction waves are created where appropriate. The method is variation
diminishing, entropy decreasing, exactly conservative, and has no numerical
dissipation away from shocks. Solutions, including the location of shocks, are
approximated with second order accuracy. Source terms can be included. The
method is compared to CLAWPACK in various examples, and found to yield a
comparable or better accuracy for similar resolutions.Comment: 29 pages, 21 figure
Confirmation of Enhanced Dwarf-sensitive Absorption Features in the Spectra of Massive Elliptical Galaxies: Further Evidence for a Non-universal Initial Mass Function
We recently found that massive cluster elliptical galaxies have strong Na I
8183,8195 and FeH 9916 Wing-Ford band absorption, indicating the presence of a
very large population of stars with masses <~ 0.3 M_sun. Here we test this
result by comparing the elliptical galaxy spectra to those of luminous globular
clusters associated with M31. These globular clusters have similar
metallicities, abundance ratios and ages as massive elliptical galaxies but
their low dynamical mass-to-light ratios rule out steep stellar initial mass
functions (IMFs). From high quality Keck spectra we find that the
dwarf-sensitive absorption lines in globular clusters are significantly weaker
than in elliptical galaxies, and consistent with normal IMFs. The differences
in the Na I and Wing-Ford indices are 0.027 +- 0.007 mag and 0.017 +- 0.006 mag
respectively. We directly compare the two classes of objects by subtracting the
averaged globular cluster spectrum from the averaged elliptical galaxy
spectrum. The difference spectrum is well fit by the difference between a
stellar population synthesis model with a bottom-heavy IMF and one with a
bottom-light IMF. We speculate that the slope of the IMF may vary with velocity
dispersion, although it is not yet clear what physical mechanism would be
responsible for such a relation.Comment: Published in ApJ Letter
The Dependence of Star Formation Rates on Stellar Mass and Environment at z~0.8
We examine the star formation rates (SFRs) of galaxies in a redshift slice
encompassing the z=0.834 cluster RX J0152.7-1357. We used a low-dispersion
prism in the Inamori Magellan Areal Camera and Spectrograph (IMACS) to identify
galaxies with z<23.3 AB mag in diverse environments around the cluster out to
projected distances of ~8 Mpc from the cluster center. We utilize a
mass-limited sample (M>2x10^{10} M_sun) of 330 galaxies that were imaged by
Spitzer MIPS at 24 micron to derive SFRs and study the dependence of specific
SFR (SSFR) on stellar mass and environment. We find that the SFR and SSFR show
a strong decrease with increasing local density, similar to the relation at
z~0. Our result contrasts with other work at z~1 that find the SFR-density
trend to reverse for luminosity-limited samples. These other results appear to
be driven by star-formation in lower mass systems (M~10^{10} M_sun). Our
results imply that the processes that shut down star-formation are present in
groups and other dense regions in the field. Our data also suggest that the
lower SFRs of galaxies in higher density environments may reflect a change in
the ratio of star-forming to non-star-forming galaxies, rather than a change in
SFRs. As a consequence, the SFRs of star-forming galaxies, in environments
ranging from small groups to clusters, appear to be similar and largely
unaffected by the local processes that truncate star-formation at z~0.8.Comment: 5 pages, 3 figures, accepted for publication in ApJ
Microarray-based screening of differentially expressed genes of E. coli O157:H7 Sakai during preharvest survival on butterhead lettuce
Numerous outbreaks of Escherichia coli O157:H7 have been linked to the consumption of leafy vegetables. However, up to the present, little has been known about E. coli O157:H7's adaptive responses to survival on actively growing (and thus responsive) plants. In this study, whole genome transcriptional profiles were generated from E. coli O157:H7 cells (isolate Sakai, stx-) one hour and two days after inoculation on the leaves of growing butterhead lettuce, and compared with an inoculum control. A total of 273 genes of E. coli O157:H7 Sakai (5.04% of the whole genome) were significantly induced or repressed by at least two-fold (p < 0.01) in at least one of the analyzed time points in comparison with the control. Several E. coli O157:H7 genes associated with oxidative stress and antimicrobial resistance were upregulated, including the iron-sulfur cluster and the multiple antibiotic resistance (mar) operon, whereas the Shiga toxin virulence genes were downregulated. Nearly 40% of the genes with significantly different expression were poorly characterized genes or genes with unknown functions. These genes are of special interest for future research as they may play an important role in the pathogens' adaptation to a lifestyle on plants. In conclusion, these findings suggest that the pathogen actively interacts with the plant environment by adapting its metabolism and responding to oxidative stress
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Um, Err, Ahh Careers Practitioners Perceptions of Weight: A Thematic Analysis
A Wide-Field Study of the z~0.8 Cluster RX J0152.7-1357: the Role of Environment in the Formation of the Red-Sequence
[ABRIDGED] We present the first results from the largest spectroscopic survey
to date of an intermediate redshift galaxy cluster, the z=0.834 cluster RX
J0152.7-1357. We use the colors of galaxies, assembled from a D~12 Mpc region
centered on the cluster, to investigate the properties of the red-sequence as a
function of density and clustercentric radius. Our wide-field multi-slit survey
with a low-dispersion prism in the IMACS spectrograph at Magellan allowed us to
identify 475 new members of the cluster and its surrounding large scale
structure with a redshift accuracy of dz/(1+z)~1% and a contamination rate of
~2% for galaxies with i<23.75 mag. We combine these new members with the 279
previously known spectroscopic members to give a total of 754 galaxies from
which we obtain a mass-limited sample of 300 galaxies with stellar masses
M>4x10^{10} M_sun. We find that the red galaxy fraction is 93+/-3% in the two
merging cores of the cluster and declines to a level of 64+/-3% at projected
clustercentric radii R>~3 Mpc. At these large projected distances, the
correlation between clustercentric radius and local density is nonexistent.
This allows an assessment of the influence of the local environment on galaxy
evolution, as opposed to mechanisms that operate on cluster scales. Even beyond
R>3 Mpc we find an increasing fraction of red galaxies with increasing local
density. The red fraction at the highest local densities in two groups at R>3
Mpc matches the red fraction found in the two cores. Strikingly, galaxies at
intermediate densities at R>3 Mpc, that are not group members, also show signs
of an enhanced red fraction. Our results point to such intermediate density
regions and the groups in the outskirts of the cluster, as sites where the
local environment influences the transition of galaxies onto the red-sequence.Comment: 15 pages, 10 figures, 1 table, accepted for publication in ApJ,
expanded introduction and additional references adde
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