22,274 research outputs found
The Atacama Cosmology Telescope: Sunyaev-Zel'dovich Selected Galaxy Clusters at 148 GHz from Three Seasons of Data
[Abridged] We present a catalog of 68 galaxy clusters, of which 19 are new
discoveries, detected via the Sunyaev-Zel'dovich effect (SZ) at 148 GHz in the
Atacama Cosmology Telescope (ACT) survey of 504 square degrees on the celestial
equator. A subsample of 48 clusters within the 270 square degree region
overlapping SDSS Stripe 82 is estimated to be 90% complete for M_500c > 4.5e14
Msun and 0.15 < z < 0.8. While matched filters are used to detect the clusters,
the sample is studied further through a "Profile Based Amplitude Analysis"
using a single filter at a fixed \theta_500 = 5.9' angular scale. This new
approach takes advantage of the "Universal Pressure Profile" (UPP) to fix the
relationship between the cluster characteristic size (R_500) and the integrated
Compton parameter (Y_500). The UPP scalings are found to be nearly identical to
an adiabatic model, while a model incorporating non-thermal pressure better
matches dynamical mass measurements and masses from the South Pole Telescope. A
high signal to noise ratio subsample of 15 ACT clusters is used to obtain
cosmological constraints. We first confirm that constraints from SZ data are
limited by uncertainty in the scaling relation parameters rather than sample
size or measurement uncertainty. We next add in seven clusters from the ACT
Southern survey, including their dynamical mass measurements based on galaxy
velocity dispersions. In combination with WMAP7 these data simultaneously
constrain the scaling relation and cosmological parameters, yielding \sigma_8 =
0.829 \pm 0.024 and \Omega_m = 0.292 \pm 0.025. The results include
marginalization over a 15% bias in dynamical mass relative to the true halo
mass. In an extension to LCDM that incorporates non-zero neutrino mass density,
we combine our data with WMAP7+BAO+Hubble constant measurements to constrain
\Sigma m_\nu < 0.29 eV (95% C. L.).Comment: 32 pages, 21 figures To appear in J. Cosmology and Astroparticle
Physic
XMM-Newton and ESO observations of the two unidentified gamma-ray sources 3EG J0616-3310 and 3EG J1249-8330
The limited angular resolution of gamma-ray telescopes prevents a direct
identification of the majority of sources detected so far. This is particularly
true for the low latitude, probably galactic, ones only 10 % of which has been
identified. Most counterparts of the identified low-latitude gamma-ray sources
are Isolated Neutron Stars (INS), both radio-loud and radio-quiet
(Geminga-like) objects, which are characterised by an extremely high value of
the X-ray-to-optical flux ratio f_X/f_opt. Therefore, the systematic X-ray and
optical coverage of low-latitude unidentified gamma-ray sources aiming at high
f_X/f_opt sources seems one of the most promising ways to spot INS candidate
counterparts. Since low latitude sources are heavily affected by the
interstellar absorption at both X-ray and optical wavelengths, we have focussed
on two middle-latitude, probably galactic, GRO/EGRET sources: 3EG J0616-3310
and 3EG J1249-8330. These two sources, which could belong to a local galactic
population, have been selected owing to their relatively good positional
accuracy, spectral shape and lack of candidate extragalactic radio
counterparts. Here we report on X-ray observations of the two gamma-ray error
boxes performed with XMM-Newton and on their optical follow-up carried on with
the Wide Field Imager at the ESO/MPG 2.2m telescope. Less than half of the ~300
sources detected by the X-ray coverage have no optical counterparts. Among
those, we have selected few interesting sources with f_X/f_opt > 100, which we
consider promising INS candidates.Comment: 18 pages, 10 figures, 8 tables. Accepted for publication by Astronomy
& Astrophysic
Chandra survey in the AKARI North Ecliptic Pole Deep Field. I. X-ray data, point-like source catalog, sensitivity maps, and number counts
We present data products from the 300 ks Chandra survey in the AKARI North
Ecliptic Pole (NEP) deep field. This field has a unique set of 9-band infrared
photometry covering 2-24 micron from the AKARI Infrared Camera, including
mid-infrared (MIR) bands not covered by Spitzer. The survey is one of the
deepest ever achieved at ~15 micron, and is by far the widest among those with
similar depths in the MIR. This makes this field unique for the MIR-selection
of AGN at z~1. We design a source detection procedure, which performs joint
Maximum Likelihood PSF fits on all of our 15 mosaicked Chandra pointings
covering an area of 0.34 square degree. The procedure has been highly optimized
and tested by simulations. We provide a point source catalog with photometry
and Bayesian-based 90 per cent confidence upper limits in the 0.5-7, 0.5-2,
2-7, 2-4, and 4-7 keV bands. The catalog contains 457 X-ray sources and the
spurious fraction is estimated to be ~1.7 per cent. Sensitivity and 90 per cent
confidence upper flux limits maps in all bands are provided as well. We search
for optical MIR counterparts in the central 0.25 square degree, where deep
Subaru Suprime-Cam multiband images exist. Among the 377 X-ray sources detected
there, ~80 per cent have optical counterparts and ~60 per cent also have AKARI
mid-IR counterparts. We cross-match our X-ray sources with MIR-selected AGN
from Hanami et al. (2012). Around 30 per cent of all AGN that have MID-IR SEDs
purely explainable by AGN activity are strong Compton-thick AGN candidates.Comment: 23 pages, 20 figures; catalogs, sensitivity maps, and upper limit
flux maps are available from the VizieR Servic
XMM-Newton observation of the interacting galaxies NGC1512 and NGC1510
The galaxy NGC1512 is interacting with the smaller galaxy NGC1510 and shows a
peculiar morphology, characterised by two extended arms immersed in an HI disc
whose size is about four times larger than the optical diameter of NGC1512. For
the first time we performed a deep X-ray observation of the galaxies NGC1512
and NGC1510 with XMM-Newton to gain information on the population of X-ray
sources and diffuse emission in a system of interacting galaxies. We identified
and classified the sources detected in the XMM-Newton field of view by means of
spectral analysis, hardness-ratios calculated with a Bayesian method, X-ray
variability, and cross-correlations with catalogues in optical, infrared, and
radio wavelengths. We also made use of archival Swift (X-ray) and Australia
Telescope Compact Array (radio) data to better constrain the nature of the
sources detected with XMM-Newton. We detected 106 sources in the energy range
of 0.2-12 keV, out of which 15 are located within the D_25 regions of NGC1512
and NGC1510 and at least six sources coincide with the extended arms. We
identified and classified six background objects and six foreground stars. We
discussed the nature of a source within the D_25 ellipse of NGC1512, whose
properties indicate a quasi-stellar object or an intermediate ultra-luminous
X-ray source. Taking into account the contribution of low-mass X-ray binaries
and active galactic nuclei, the number of high-mass X-ray binaries detected
within the D_25 region of NGC1512 is consistent with the star formation rate
obtained in previous works based on radio, infrared optical, and UV
wavelengths. We detected diffuse X-ray emission from the interior region of
NGC1512 with a plasma temperature of kT=0.68(0.31-0.87) keV and a 0.3-10 keV
X-ray luminosity of 1.3E38 erg/s, after correcting for unresolved discrete
sources.Comment: Accepted for publication in Astronomy and Astrophysics. 20 pages.
Appendix B will be published electronically onl
The XMM-Newton serendipitous survey. VII. The third XMM-Newton serendipitous source catalogue
Thanks to the large collecting area (3 x ~1500 cm at 1.5 keV) and wide
field of view (30' across in full field mode) of the X-ray cameras on board the
European Space Agency X-ray observatory XMM-Newton, each individual pointing
can result in the detection of hundreds of X-ray sources, most of which are
newly discovered. Recently, many improvements in the XMM-Newton data reduction
algorithms have been made. These include enhanced source characterisation and
reduced spurious source detections, refined astrometric precision, greater net
sensitivity and the extraction of spectra and time series for fainter sources,
with better signal-to-noise. Further, almost 50\% more observations are in the
public domain compared to 2XMMi-DR3, allowing the XMM-Newton Survey Science
Centre (XMM-SSC) to produce a much larger and better quality X-ray source
catalogue. The XMM-SSC has developed a pipeline to reduce the XMM-Newton data
automatically and using improved calibration a new catalogue version has been
produced from XMM-Newton data made public by 2013 Dec. 31 (13 years of data).
Manual screening ensures the highest data quality. This catalogue is known as
3XMM. In the latest release, 3XMM-DR5, there are 565962 X-ray detections
comprising 396910 unique X-ray sources. For the 133000 brightest sources,
spectra and lightcurves are provided. For all detections, the positions on the
sky, a measure of the quality of the detection, and an evaluation of the X-ray
variability is provided, along with the fluxes and count rates in 7 X-ray
energy bands, the total 0.2-12 keV band counts, and four hardness ratios. To
identify the detections, a cross correlation with 228 catalogues is also
provided for each X-ray detection. 3XMM-DR5 is the largest X-ray source
catalogue ever produced. Thanks to the large array of data products, it is an
excellent resource in which to find new and extreme objects.Comment: 23 pages, version accepted for publication in A&
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