368 research outputs found
Chandra X-ray Observations of Galaxies in an Off-Center Region of the Coma Cluster
We have performed a pilot Chandra survey of an off-center region of the Coma
cluster to explore the X-ray properties and Luminosity Function of normal
galaxies. We present results on 13 Chandra-detected galaxies with optical
photometric matches, including four spectroscopically-confirmed Coma-member
galaxies. All seven spectroscopically confirmed giant Coma galaxies in this
field have detections or limits consistent with low X-ray to optical flux
ratios (fX/fR < 10^-3). We do not have sufficient numbers of X-ray detected
galaxies to directly measure the galaxy X-ray Luminosity Function (XLF).
However, since we have a well-measured optical LF, we take this low X-ray to
optical flux ratio for the 7 spectroscopically confirmed galaxies to translate
the optical LF to an XLF. We find good agreement with Finoguenov et al. (2004),
indicating that the X-ray emission per unit optical flux per galaxy is
suppressed in clusters of galaxies, but extends this work to a specific
off-center environment in the Coma cluster. Finally, we report the discovery of
a region of diffuse X-ray flux which might correspond to a small group
interacting with the Coma Intra-Cluster Medium (ICM).Comment: Accepted for publication in the Astrophysical Journa
The Spectra and Variability of X-ray Sources in a Deep Chandra Observation of the Galactic Center
We examine the X-ray spectra and variability of the sample of X-ray sources
with L_X = 10^{31}-10^{33} erg s^{-1} identified within the inner 9' of the
Galaxy. Very few of the sources exhibit intra-day or inter-month variations. We
find that the spectra of the point sources near the Galactic center are very
hard between 2--8 keV, even after accounting for absorption. When modeled as
power laws the median photon index is Gamma=0.7, while when modeled as thermal
plasma we can only obtain lower limits to the temperature of kT>8 keV. The
combined spectra of the point sources is similarly hard, with a photon index of
Gamma=0.8. Strong line emission is observed from low-ionization, He-like, and
H-like Fe, both in the average spectra and in the brightest individual sources.
The line ratios of the highly-ionized Fe in the average spectra are consistent
with emission from a plasma in thermal equilibrium. This line emission is
observed whether average spectra are examined as a function of the count rate
from the source, or as a function of the hardness ratios of individual sources.
This suggests that the hardness of the spectra may in fact to due local
absorption that partially-covers the X-ray emitting regions in the Galactic
center systems. We suggest that most of these sources are intermediate polars,
which (1) often exhibit hard spectra with prominent Fe lines, (2) rarely
exhibit either flares on short time scales or changes in their mean X-ray flux
on long time scales, and (3) are the most numerous hard X-ray sources with
comparable luminosities in the Galaxy.Comment: 27 pages, including 13 figures. To appear in ApJ, 1 October 2004,
v613 issue. An electronic version of table 2 is on
http://astro.ucla.edu/~mmuno/sgra/table2_electronic.txt and reduced data
files for each source are available on
http://www.astro.psu.edu/users/niel/galcen-xray-data/galcen-xray-data.htm
Chandra Observations of Galaxy Cluster Abell 2218
We present results from two observations (combined exposure of ~17 ks) of
galaxy cluster A2218 using the Advanced CCD Imaging Spectrometer on board the
Chandra X-ray Observatory that were taken on October 19, 1999. Using a
Raymond-Smith single temperature plasma model corrected for galactic absorption
we find a mean cluster temperature of kT = 6.9+/-0.5 keV, metallicity of
0.20+/-0.13 (errors are 90 % CL) and rest-frame luminosity in the 2-10 keV
energy band of 6.2x10^{44} erg/s in a LambdaCDM cosmology with H_0=65 km/s/Mpc.
The brightness distribution within 4'.2 of the cluster center is well fit by a
simple spherical beta model with core radius 66".4 and beta = 0.705 . High
resolution Chandra data of the inner 2' of the cluster show the x-ray
brightness centroid displaced ~22" from the dominant cD galaxy and the presence
of azimuthally asymmetric temperature variations along the direction of the
cluster mass elongation. X-ray and weak lensing mass estimates are in good
agreement for the outer parts (r > 200h^{-1}) of the cluster; however, in the
core the observed temperature distribution cannot reconcile the x-ray and
strong lensing mass estimates in any model in which the intracluster gas is in
thermal hydrostatic equilibrium. Our x-ray data are consistent with a scenario
in which recent merger activity in A2218 has produced both significant
non-thermal pressure in the core and substructure along the line of sight; each
of these phenomena probably contributes to the difference between lensing and
x-ray core mass estimates.Comment: 33 pages, 6 figures, uses AASTeX 5.02, ApJ submitte
Detecting high redshift evolved galaxies as the hosts of optically faint hard X-ray sources
We combine deep Subaru near-infrared images of the massive lensing clusters
A2390 and A370 with Keck optical data to map the spectral energy distributions
(SEDs) of Chandra X-ray sources lying behind the clusters. The three sources
behind A2390 are found to have extremely red colors with SEDs consistent with
evolved galaxies at redshifts z>1.4. One source has extremely anomalous colors,
which we interpret as evidence for a type Sa SED at a redshift around 2.5. The
photometric redshift of another source has been confirmed at z=1.467 from
near-infrared spectroscopy using the CISCO spectrograph on Subaru. Mapping of
optically faint hard X-ray sources may prove to be an extremely efficient way
to locate luminous evolved galaxies at high redshifts.Comment: 5 pages, ApJ Letters, in pres
Detection of X-ray Emission from Gravitationally Lensed Submillimeter Sources in the Field of Abell 370
We report the detection by Chandra of SMM J02399-0134 and SMM J02399-0136,
two distant (z=1.06 and z=2.81, respectively) submillimeter sources
gravitationally magnified by the galaxy cluster Abell 370. These are
high-significance (> 7-sigma) X-ray detections of the high-redshift
submillimeter source population. The X-ray positions are coincident with the
optical positions to within one arcsecond. The X-ray spectra, while of low
signal-to-noise ratio, are quite hard. Absorbed power law models with fixed
photon indices of imply local absorbing columns cm and unabsorbed luminosities erg s in both
sources. These results imply that nuclear activity is responsible for the bulk
of the luminosity in SMM J02399-0134, and for at least 20% of the luminosity of
SMM J02399-0136, consistent with previous optical observations. We also place
an upper limit on the X-ray flux of a third submillimeter source, SMM
J02400-0134. Considered together with previously published Chandra upper limits
on X-ray flux from submillimeter sources, our results imply that
% of submillimeter sources exhibit X-ray emission from AGN
(90% confidence), consistent with expectations of their contribution to the
diffuse X-ray background.Comment: Corrected typos in Figure 1 labels; Accepted for publication in ApJ
Letters, 6 pages, 2 figures, latex requires emulateapj5.st
The Chandra Deep Field North Survey. IX. Extended X-ray Sources
The ~1 Ms Chandra Deep Field North observation is used to study the extended
X-ray sources in the region surrounding the Hubble Deep Field North (HDF-N),
yielding the most sensitive probe of extended X-ray emission at cosmological
distances to date. A total of six such sources are detected, the majority of
which align with small numbers of optically bright galaxies. Their angular
sizes, band ratios, and X-ray luminosities -- assuming they lie at the same
distances as the galaxies coincident with the X-ray emission -- are generally
consistent with the properties found for nearby groups of galaxies. One source
is notably different and is likely to be a poor-to-moderate X-ray cluster at
high redshift (i.e., z > 0.7). We are also able to place strong constraints on
the optically detected cluster of galaxies ClG 1236+6215 at z=0.85 and the
wide-angle-tail radio galaxy VLA J123725.7+621128 at z~1-2. With rest-frame
0.5--2.0 keV X-ray luminosities of <(3-15)e42 ergs s^{-1}, the environments of
both sources are either likely to have a significant deficit of hot
intra-cluster gas compared to local clusters of galaxies, or they are X-ray
groups. We find the surface density of extended X-ray sources in this
observation to be 167 (+97,-67) deg^{-2} at a limiting soft-band flux of
approximately 3e-16 ergs s^{-1} cm^{-2}. No evolution in the X-ray luminosity
function of clusters is needed to explain this value. (Abridged)Comment: 16 pages, 14 figures (8 color), LaTeX emulateapj5.sty, accepted for
publication by the Astronomical Journal. Manuscript with full resolution
embedded images available at
http://www.astro.psu.edu/users/niel/hdf/hdf-chandra.htm
Oscillatory Microrheology, Creep Compliance and Stress Relaxation of Biological Cells Reveal Strong Correlations as Probed by Atomic Force Microscopy
The mechanical properties of cells are important for many biological processes, including wound healing, cancers, and embryogenesis. Currently, our understanding of cell mechanical properties remains incomplete. Different techniques have been used to probe different aspects of the mechanical properties of cells, among them microplate rheology, optical tweezers, micropipette aspiration, and magnetic twisting cytometry. These techniques have given rise to different theoretical descriptions, reaching from simple Kelvin-Voigt or Maxwell models to fractional such as power law models, and their combinations. Atomic force microscopy (AFM) is a flexible technique that enables global and local probing of adherent cells. Here, using an AFM, we indented single retinal pigmented epithelium cells adhering to the bottom of a culture dish. The indentation was performed at two locations: above the nucleus, and towards the periphery of the cell. We applied creep compliance, stress relaxation, and oscillatory rheological tests to wild type and drug modified cells. Considering known fractional and semi-fractional descriptions, we found the extracted parameters to correlate. Moreover, the Young’s modulus as obtained from the initial indentation strongly correlated with all of the parameters from the applied power-law descriptions. Our study shows that the results from different rheological tests are directly comparable. This can be used in the future, for example, to reduce the number of measurements in planned experiments. Apparently, under these experimental conditions, the cells possess a limited number of degrees of freedom as their rheological properties change
Supermassive Black Hole Accretion History Inferred from a Large Sample of Chandra Hard X-ray Sources
We describe the optical, near-infrared, and radio properties of a sample of
hard (2-7 keV) X-ray sources detected in a deep Chandra observation of the
field surrounding the Abell 370 cluster. We combine these data with similar
observations of the Chandra Deep Field-North and the Hawaii Survey Field SSA13
to obtain a sample of 69 hard X-ray sources (45 are spectroscopically
identified) with extremely deep 20 cm observations. We find that about 4% of
the >Lstar galaxy population is X-ray luminous at any time and hence that black
hole accretion has a duration of about half a Gyr. We find that about 30% of
the summed 2-7 keV flux from our total sample is from sources at z<1. We
estimate the bolometric luminosities of accretion onto supermassive black holes
and the mass inflow rates. The time history of the accretion rate density is
evaluated, and its integrated value is reasonably consistent with the value
inferred from the local black hole mass to bulge mass ratio.Comment: 17 pages, submitted to The Astronomical Journa
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