205 research outputs found
Spectrodirectional investigation of a geometric-optical canopy reflectance model by laboratory simulation
Canopy reflectance models (CRMs) can accurately estimate vegetation canopy
biophysical-structural information such as Leaf Area Index (LAI) inexpensively using
satellite imagery. The strict physical basis which geometric-optical CRMs employ to
mathematically link canopy bidirectional reflectance and structure allows for the tangible
replication of a CRM's geometric abstraction of a canopy in the laboratory, enabling
robust CRM validation studies. To this end, the ULGS-2 goniometer was used to obtain
multiangle, hyperspectral (Spectrodirectional) measurements of a specially-designed
tangible physical model forest, developed based upon the Geometric-Optical Mutual
Shadowing (GOMS) CRM, at three different canopy cover densities. GOMS forwardmodelled
reflectance values had high levels of agreement with ULGS-2 measurements,
with obtained reflectance RMSE values ranging from 0.03% to 0.1%. Canopy structure
modelled via GOMS Multiple-Forward-Mode (MFM) inversion had varying levels of
success. The methods developed in this thesis can potentially be extended to more
complex CRMs through the implementation of 3D printing
The XMM Cluster Survey: The Dynamical State of XMMXCS J2215.9-1738 at z=1.457
We present new spectroscopic observations of the most distant X-ray selected
galaxy cluster currently known, XMMXCS J2215.9-1738 at z=1.457, obtained with
the DEIMOS instrument at the W. M. Keck Observatory, and the FORS2 instrument
on the ESO Very Large Telescope. Within the cluster virial radius, as estimated
from the cluster X-ray properties, we increase the number of known
spectroscopic cluster members to 17 objects, and calculate the line of sight
velocity dispersion of the cluster to be 580+/-140 km/s. We find mild evidence
that the velocity distribution of galaxies within the virial radius deviates
from a single Gaussian. We show that the properties of J2215.9-1738 are
inconsistent with self-similar evolution of local X-ray scaling relations,
finding that the cluster is underluminous given its X-ray temperature, and that
the intracluster medium contains ~2-3 times the kinetic energy per unit mass of
the cluster galaxies. These results can perhaps be explained if the cluster is
observed in the aftermath of an off-axis merger. Alternatively, heating of the
intracluster medium through supernovae and/or Active Galactic Nuclei activity,
as is required to explain the observed slope of the local X-ray
luminosity-temperature relation, may be responsible.Comment: 13 pages, 6 figures, accepted for publication in Ap
The XMM Cluster Survey: Active Galactic Nuclei and Starburst Galaxies in XMMXCS J2215.9-1738 at z=1.46
We use Chandra X-ray and Spitzer infrared observations to explore the AGN and
starburst populations of XMMXCS J2215.9-1738 at z=1.46, one of the most distant
spectroscopically confirmed galaxy clusters known. The high resolution X-ray
imaging reveals that the cluster emission is contaminated by point sources that
were not resolved in XMM observations of the system, and have the effect of
hardening the spectrum, leading to the previously reported temperature for this
system being overestimated. From a joint spectroscopic analysis of the Chandra
and XMM data, the cluster is found to have temperature T=4.1_-0.9^+0.6 keV and
luminosity L_X=(2.92_-0.35^+0.24)x10^44 erg/s extrapolated to a radius of 2
Mpc. As a result of this revised analysis, the cluster is found to lie on the
sigma_v-T relation, but the cluster remains less luminous than would be
expected from self-similar evolution of the local L_X-T relation. Two of the
newly discovered X-ray AGN are cluster members, while a third object, which is
also a prominent 24 micron source, is found to have properties consistent with
it being a high redshift, highly obscured object in the background. We find a
total of eight >5 sigma 24 micron sources associated with cluster members (four
spectroscopically confirmed, and four selected using photometric redshifts),
and one additional 24 micron source with two possible optical/near-IR
counterparts that may be associated with the cluster. Examining the IRAC colors
of these sources, we find one object is likely to be an AGN. Assuming that the
other 24 micron sources are powered by star formation, their infrared
luminosities imply star formation rates ~100 M_sun/yr. We find that three of
these sources are located at projected distances of <250 kpc from the cluster
center, suggesting that a large amount of star formation may be taking place in
the cluster core, in contrast to clusters at low redshift.Comment: Accepted for publication in ApJ, 16 pages, 10 figure
The XMM Cluster Survey: The Stellar Mass Assembly of Fossil Galaxies
This paper presents both the result of a search for fossil systems (FSs)
within the XMM Cluster Survey and the Sloan Digital Sky Survey and the results
of a study of the stellar mass assembly and stellar populations of their fossil
galaxies. In total, 17 groups and clusters are identified at z < 0.25 with
large magnitude gaps between the first and fourth brightest galaxies. All the
information necessary to classify these systems as fossils is provided. For
both groups and clusters, the total and fractional luminosity of the brightest
galaxy is positively correlated with the magnitude gap. The brightest galaxies
in FSs (called fossil galaxies) have stellar populations and star formation
histories which are similar to normal brightest cluster galaxies (BCGs).
However, at fixed group/cluster mass, the stellar masses of the fossil galaxies
are larger compared to normal BCGs, a fact that holds true over a wide range of
group/cluster masses. Moreover, the fossil galaxies are found to contain a
significant fraction of the total optical luminosity of the group/cluster
within 0.5R200, as much as 85%, compared to the non-fossils, which can have as
little as 10%. Our results suggest that FSs formed early and in the highest
density regions of the universe and that fossil galaxies represent the end
products of galaxy mergers in groups and clusters. The online FS catalog can be
found at http://www.astro.ljmu.ac.uk/~xcs/Harrison2012/XCSFSCat.html.Comment: 30 pages, 50 figures. ApJ published version, online FS catalog added:
http://www.astro.ljmu.ac.uk/~xcs/Harrison2012/XCSFSCat.htm
The Massive and Distant Clusters of WISE Survey: MOO J1142+1527, a 10^(15) M_â Galaxy Cluster at z = 1.19
We present confirmation of the cluster MOO J1142+1527, a massive galaxy cluster discovered as part of the Massive and Distant Clusters of WISE Survey. The cluster is confirmed to lie at z = 1.19, and using the Combined Array for Research in Millimeter-wave Astronomy we robustly detect the SunyaevâZel'dovich (SZ) decrement at 13.2Ï. The SZ data imply a mass of M_(200m) = (1.1 ± 0.2) Ă 10^(15)M_â, making MOO J1142+1527 the most massive galaxy cluster known at z > 1.15 and the second most massive cluster known at z > 1. For a standard ÎCDM cosmology it is further expected to be one of the ~5 most massive clusters expected to exist at z â„ 1.19 over the entire sky. Our ongoing Spitzer program targeting ~1750 additional candidate clusters will identify comparably rich galaxy clusters over the full extragalactic sky
The Chandra Deep Wide-field Survey: A New Chandra Legacy Survey in the Boötes Field. I. X-Ray Point Source Catalog, Number Counts, and Multiwavelength Counterparts
We present a new, ambitious survey performed with the Chandra X-ray Observatory of the 9.3 deg2 Boötes field of the NOAO Deep Wide-Field Survey. The wide field probes a statistically representative volume of the universe at high redshift. The Chandra Deep Wide-field Survey exploits the excellent sensitivity and angular resolution of Chandra over a wide area, combining 281 observations spanning 15 yr, for a total exposure time of 3.4 Ms, and detects 6891 X-ray point sources down to limiting fluxes of 4.7 Ă 10â16, 1.5 Ă 10â16, and 9 Ă10â16 erg cmâ2 sâ1 in the 0.5â7, 0.5â2, and 2â7 keV bands, respectively. The robustness and reliability of the detection strategy are validated through extensive, state-of-the-art simulations of the whole field. Accurate number counts, in good agreement with previous X-ray surveys, are derived thanks to the uniquely large number of point sources detected, which resolve 65.0% ± 12.8% of the cosmic X-ray background between 0.5 and 2 keV and 81.0% ± 11.5% between 2 and 7 keV. Exploiting the wealth of multiwavelength data available on the field, we assign redshifts to ~94% of the X-ray sources, estimate their obscuration, and derive absorption-corrected luminosities. We provide an electronic catalog containing all of the relevant quantities needed for future investigations
The XMM Cluster Survey: Forecasting cosmological and cluster scaling-relation parameter constraints
We forecast the constraints on the values of sigma_8, Omega_m, and cluster
scaling relation parameters which we expect to obtain from the XMM Cluster
Survey (XCS). We assume a flat Lambda-CDM Universe and perform a Monte Carlo
Markov Chain analysis of the evolution of the number density of galaxy clusters
that takes into account a detailed simulated selection function. Comparing our
current observed number of clusters shows good agreement with predictions. We
determine the expected degradation of the constraints as a result of
self-calibrating the luminosity-temperature relation (with scatter), including
temperature measurement errors, and relying on photometric methods for the
estimation of galaxy cluster redshifts. We examine the effects of systematic
errors in scaling relation and measurement error assumptions. Using only (T,z)
self-calibration, we expect to measure Omega_m to +-0.03 (and Omega_Lambda to
the same accuracy assuming flatness), and sigma_8 to +-0.05, also constraining
the normalization and slope of the luminosity-temperature relation to +-6 and
+-13 per cent (at 1sigma) respectively in the process. Self-calibration fails
to jointly constrain the scatter and redshift evolution of the
luminosity-temperature relation significantly. Additional archival and/or
follow-up data will improve on this. We do not expect measurement errors or
imperfect knowledge of their distribution to degrade constraints significantly.
Scaling-relation systematics can easily lead to cosmological constraints 2sigma
or more away from the fiducial model. Our treatment is the first exact
treatment to this level of detail, and introduces a new `smoothed ML' estimate
of expected constraints.Comment: 28 pages, 17 figures. Revised version, as accepted for publication in
MNRAS. High-resolution figures available at http://xcs-home.org (under
"Publications"
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