471 research outputs found
Comparing Dense Galaxy Cluster Redshift Surveys with Weak Lensing Maps
We use dense redshift surveys of nine galaxy clusters at to
compare the galaxy distribution in each system with the projected matter
distribution from weak lensing. By combining 2087 new MMT/Hectospec redshifts
and the data in the literature, we construct spectroscopic samples within the
region of weak-lensing maps of high (70--89%) and uniform completeness. With
these dense redshift surveys, we construct galaxy number density maps using
several galaxy subsamples. The shape of the main cluster concentration in the
weak-lensing maps is similar to the global morphology of the number density
maps based on cluster members alone, mainly dominated by red members. We cross
correlate the galaxy number density maps with the weak-lensing maps. The cross
correlation signal when we include foreground and background galaxies at
0.5 is % larger than for cluster members alone
at the cluster virial radius. The excess can be as high as 30% depending on the
cluster. Cross correlating the galaxy number density and weak-lensing maps
suggests that superimposed structures close to the cluster in redshift space
contribute more significantly to the excess cross correlation signal than
unrelated large-scale structure along the line of sight. Interestingly, the
weak-lensing mass profiles are not well constrained for the clusters with the
largest cross correlation signal excesses (20% for A383, A689 and A750). The
fractional excess in the cross correlation signal including foreground and
background structures could be a useful proxy for assessing the reliability of
weak-lensing cluster mass estimates.Comment: 22 pages, 19 figures, 2 tables. To appear in ApJ. Paper with high
resolution figures is available at
http://astro.kias.re.kr/~hshwang/ms_hwang20141014.pd
Quantifying Feedbacks Between Ice Flow, Grain Size, and Basal Meltwater on Annual and Decadal Time-Scales Using a 2-D Ice Sheet Model:
Thesis advisor: Mark D. BehnIce sheet flow is strongly controlled by the conditions at the ice-bed interface. While these processes are hard to observe directly, comparisons between numerical modeling and ice surface observations can be used to indirectly infer subglacial processes. Specifically, seasonal summer speed up near the margin of the Greenland Ice Sheet (GIS) has been linked to the presence of subglacial water. For decades, the Glen flow law has been the most widely-accepted constitutive relation for modeling ice flow. However, while the Glen law captures the temperature-dependent, nonlinear viscosity of ice, it does not explicitly incorporate ice grain size, which has been shown in laboratory experiments to influence ice rheology. To compensate for the lack of explicit grain size dependence, ice sheet models often utilize an “enhancement factor” that modifies the flow law to better match observations, but does not provide insight into the physical processes at play. Using a grain size sensitive rheology that incorporates grain size evolution due to dynamic recrystallization and grain growth, I model the effects of seasonal variations of subglacial hydrology in a 2-D vertical cross-section of ice flow on both annual and inter-annual timescales. The presence of subglacial water reduces the frictional coupling between the ice and the bed. Here I simulate the presence of water at the ice-bed interface during the melt season using patches of free-slip and explore a range of patch sizes and geometries to investigate their role in modulating ice surface velocities and grain size within the ice. I compare modeled winter and summer surface velocities to observations taken on the western margin of the GIS and find that realistic surface velocities are achievable using agrain size sensitive flow law without the introduction of an enhancement factor. Further, the grain size of the internal ice responds on an inter-annual timescale to these seasonal forcings at the bed, potentially leading to long-term changes in surface velocities.Thesis (MS) — Boston College, 2022.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Earth and Environmental Sciences
CAIRNS: The Cluster And Infall Region Nearby Survey III. Environmental Dependence of H-alpha Properties of Galaxies
We investigate the environmental dependence of star formation in cluster
virial regions and infall regions as part of CAIRNS (Cluster And Infall Region
Nearby Survey), a large spectroscopic survey of the infall regions surrounding
nine nearby rich clusters of galaxies. Our long-slit spectroscopy yields
estimates of star formation rates in environments from cluster cores to the
general large-scale structure. The fraction of galaxies with current star
formation in their inner disks as traced by H-alpha emission increases with
distance from the cluster and converges to the ``field'' value only at 2-3
virial radii, in agreement with other investigations. However, among galaxies
with significant current star formation (EW[Ha]geq2\AA), there is no difference
in the distribution of EW[Ha] inside and outside the virial radius. This
surprising result, first seen by Carter et al., suggests that (1) star
formation is truncated on either very short timescales or only at moderate and
high redshifts or (2) that projection effects contaminate the measurement. The
number density profiles of star-forming and non-star-forming galaxies indicate
that, among galaxies projected inside the virial radius, at least half of the
former and 20% of the latter are ``infall interlopers,'' galaxies in the infall
region but outside the virial region. The kinematics of star-forming galaxies
in the infall region closely match those of absorption-dominated galaxies. This
result shows that the star forming galaxies in the infall regions are not
interlopers from the field and excludes one model of the backsplash scenario of
galaxy transformation. Finally, we quantify systematic uncertainties in
estimating the global star formation in galaxies from their inner disks.Comment: 25 pages, 21 figures, accepted for publication in A
CIRS: Cluster Infall Regions in the Sloan Digital Sky Survey I. Infall Patterns and Mass Profiles
We use the Fourth Data Release of the Sloan Digital Sky Survey to test the
ubiquity of infall patterns around galaxy clusters and measure cluster mass
profiles to large radii. We match X-ray cluster catalogs with SDSS, search for
infall patterns, and compute mass profiles for a complete sample of X-ray
selected clusters. Very clean infall patterns are apparent in most of the
clusters, with the fraction decreasing with increasing redshift due to
shallower sampling. All 72 clusters in a well-defined sample limited by
redshift (ensuring good sampling) and X-ray flux (excluding superpositions)
show infall patterns sufficient to apply the caustic technique. This sample is
by far the largest sample of cluster mass profiles extending to large radii to
date. Similar to CAIRNS, cluster infall patterns are better defined in
observations than in simulations. Further work is needed to determine the
source of this difference. We use the infall patterns to compute mass profiles
for 72 clusters and compare them to model profiles. Cluster scaling relations
using caustic masses agree well with those using X-ray or virial mass
estimates, confirming the reliability of the caustic technique. We confirm the
conclusion of CAIRNS that cluster infall regions are well fit by NFW and
Hernquist profiles and poorly fit by singular isothermal spheres. This much
larger sample enables new comparisons of cluster properties with those in
simulations. The shapes (specifically, NFW concentrations) of the mass profiles
agree well with the predictions of simulations. The mass inside the turnaround
radius is on average 2.190.18 times that within the virial radius. This
ratio agrees well with recent predictions from simulations of the final masses
of dark matter haloes.Comment: 34 pages, 24 figures, accepted for publication in AJ, full resolution
version available at http://www.astro.yale.edu/krines
XMM-Newton/SDSS: star formation efficiency in galaxy clusters and constraints on the matter density parameter
It is believed that the global baryon content of clusters of galaxies is
representative of the matter distribution of the universe, and can, therefore,
be used to reliably determine the matter density parameter Omega_m. This
assumption is challenged by the growing evidence from optical and X-ray
observations that the total baryon mass fraction increases towards rich
clusters. In this context, we investigate the dependence of stellar, and total
baryon mass fractions as a function of mass. To do so, we used a subsample of
nineteen clusters extracted from the X-ray flux limited sample HIFLUGCS that
have available DR-7 Sloan Digital Sky Survey (SDSS) data. From the optical
analysis we derived the stellar masses. Using XMM-Newton we derived the gas
masses. Then, adopting a scaling relation we estimate the total masses. Adding
the gas and the stellar mass fractions we obtain the total baryonic content
that we find to increase with cluster mass, reaching 7-year Wilkinson Microwave
Anisotropy Probe (WMAP-7) prediction for clusters with M_500 = 1.6 x 10^{15}
M_sun. We observe a decrease of the stellar mass fraction (from 4.5% to ~1.0%)
with increasing total mass where our findings for the stellar mass fraction
agree with previous studies. This result suggests a difference in the number of
stars formed per unit of halo mass, though with a large scatter for low-mass
systems. That is, the efficiency of star formation varies on cluster scale that
lower mass systems are likely to have higher star formation efficiencies. It
follows immediately that the dependence of the stellar mass fraction on total
mass results in an increase of the mass-to-light ratio from lower to higher
mass systems. We also discuss the consequences of these results in the context
of determining the cosmic matter density parameter Omega_m.Comment: Accepted for publication in ApJ, 11 pages, 5 figures.
http://stacks.iop.org/0004-637X/743/1
CAIRNS: The Cluster And Infall Region Nearby Survey I. Redshifts and Mass Profiles
The CAIRNS (Cluster And Infall Region Nearby Survey) project is a
spectroscopic survey of the infall regions surrounding eight nearby, rich,
X-ray luminous clusters of galaxies. We collect 15665 redshifts (3471 new or
remeasured) within \sim 5-10 Mpc of the centers of the clusters, making it the
largest study of the infall regions of clusters. We determine cluster
membership and the mass profiles of the clusters based on the phase space
distribution of the galaxies. All of the clusters display decreasing velocity
dispersion profiles. The mass profiles are fit well by functional forms based
on numerical simulations but exclude an isothermal sphere. Specifically, NFW
and Hernquist models provide good descriptions of cluster mass profiles to
their turnaround radii. Our sample shows that the predicted infall pattern is
ubiquitous in rich, X-ray luminous clusters over a large mass range. The
caustic mass estimates are in excellent agreement with independent X-ray
estimates at small radii and with virial estimates at intermediate radii. The
mean ratio of the caustic mass to the X-ray mass is 1.03\pm0.11 and the mean
ratio of the caustic mass to the virial mass (when corrected for the surface
pressure term) is 0.93\pm0.07. We further demonstrate that the caustic
technique provides reasonable mass estimates even in merging clusters.Comment: 54 pages, 18 figures, to appear in The Astronomical Journa
The Velocity Dispersion Function of Very Massive Galaxy Clusters: Abell 2029 and Coma
Based on an extensive redshift survey for galaxy clusters Abell 2029 and Coma, we measure the luminosity functions (LFs) and stellar mass functions (SMFs) for the entire cluster member galaxies. Most importantly, we measure the velocity dispersion functions (VDFs) for quiescent members. The MMT/Hectospec redshift survey for galaxies in A2029 identifies 982 spectroscopic members; for 838 members, we derive the central velocity dispersion from the spectroscopy. Coma is the only other cluster surveyed as densely. The LFs, SMFs, and VDFs for A2029 and Coma are essentially identical. The SMFs of the clusters are consistent with simulations. The A2029 and Coma VDFs for quiescent galaxies have a significantly steeper slope than those of field galaxies for velocity dispersion ≲ 100 {km} {{{s}}}-1. The cluster VDFs also exceed the field at velocity dispersion ≳ 250 {km} {{{s}}}-1. The differences between cluster and field VDFs are potentially important tests of simulations and of the formation of structure in the universe
TEMPORAL ASSESSMENT OF PHYSICAL CHARACTERISTICS AND REPRODUCTIVE STATUS OF MOOSE IN NEW HAMPSHIRE
Biological data collected from harvested moose (Alces alces) were analyzed to assess whether temporal change has occurred in the physical and reproductive condition of moose from 1988–2009 in New Hampshire. Measurements included age and field-dressed body weight of both sexes, number of corpora lutea (CL) and ovulation rate of females, and antler beam diameter (ABD) and antler spread of males. Similar data were obtained from Maine and Vermont for comparative analysis. The only significant changes (P <0.05) occurred in the yearling age class: mean body weight of both sexes, number of CL, and ABD all declined in New Hampshire. The current ovulation rate (~20%) and mean body weight (<200 kg) of yearling females in New Hampshire and Vermont were considered low. The declines measured in yearlings, yet relative stability in adults, are consistent with the presumption that winter ticks (Dermacentor albipictus) impact the productivity of moose populations through reduced calf survival and growth and fecundity of yearlings. Density-dependent factors related to habitat change are also discussed given the recent, rapid expansion of moose in the 3 states. Continued monitoring of physical parameters and productivity of harvested moose, particularly the yearling cohort, is warranted to better assess the relationships among winter ticks, habitat quality, and moose populations
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