292 research outputs found
Hard X-ray emitting Active Galactic Nuclei selected by the Chandra Multi-wavelength Project
We present X-ray and optical analysis of 188 AGN identified from 497 hard
X-ray (f (2.0-8.0 keV) > 2.7x10^-15 erg cm^-2 s^-1) sources in 20 Chandra
fields (1.5 deg^2) forming part of the Chandra Multi-wavelength Project. These
medium depth X-ray observations enable us to detect a representative subset of
those sources responsible for the bulk of the 2-8 keV Cosmic X-ray Background.
Brighter than our optical spectroscopic limit, we achieve a reasonable degree
of completeness (77% of X-ray sources with counter-parts r'< 22.5 have been
classified): broad emission line AGN (62%), narrow emission line galaxies
(24%), absorption line galaxies (7%), stars (5%) or clusters (2%). We find that
most X-ray unabsorbed AGN (NH<10^22 cm^-2) have optical properties
characterized by broad emission lines and blue colors, similiar to
optically-selected quasars from the Sloan Digital Sky Survey but with a slighly
broader color distribution. However, we also find a significant population of
redder (g'-i'>1.0) AGN with broad optical emission lines. Most of the X-ray
absorbed AGN (10^22<NH<10^24 cm^-2) are associated with narrow emission line
galaxies, with red optical colors characteristically dominated by luminous,
early type galaxy hosts rather than from dust reddening of an AGN. We also find
a number of atypical AGN; for instance, several luminous AGN show both strong
X-ray absorption (NH>10^22 cm^-2) and broad emission lines. Overall, we find
that 81% of X-ray selected AGN can be easily interpreted in the context of
current AGN unification models. Most of the deviations seem to be due to an
optical contribution from the host galaxies of the low luminosity AGN.Comment: 26 pages; 13 figures (7 color); accepted for publication in the
Astrophysical Journa
The Luminosity Function of X-ray Selected Active Galactic Nuclei: Evolution of Supermassive Black Holes at High Redshift
We present a measure of the hard (2-8 keV) X-ray luminosity function (XLF) of
Active Galactic Nuclei up to z~5. At high redshifts, the wide area coverage of
the Chandra Multiwavength Project is crucial to detect rare and luminous (Lx >
10^44 erg s^-1) AGN. The inclusion of samples from deeper published surveys,
such as the Chandra Deep Fields, allows us to span the lower Lx range of the
XLF. Our sample is selected from both the hard (z 6.3x10^-16
erg cm^-2 s^-1) and soft (z > 3; f(0.5-2.0 keV) > 1.0x10^-16 erg cm^-2 s^-1)
energy band detections. Within our optical magnitude limits (r',i' < 24), we
achieve an adequate level of completeness (>50%) regarding X-ray source
identification (i.e., redshift). We find that the luminosity function is
similar to that found in previous X-ray surveys up to z~3 with an evolution
dependent upon both luminosity and redshift. At z > 3, there is a significant
decline in the numbers of AGN with an evolution rate similar to that found by
studies of optically-selected QSOs. Based on our XLF, we assess the resolved
fraction of the Cosmic X-ray Background, the cumulative mass density of
Supermassive Black Holes (SMBHs), and the comparison of the mean accretion rate
onto SMBHs and the star formation history of galaxies as a function of
redshift. A coevolution scenario up to z~2 is plausible though at higher
redshifts the accretion rate onto SMBHs drops more rapidly. Finally, we
highlight the need for better statistics of high redshift AGN at z > 3, which
is achievable with the upcoming Chandra surveys.Comment: Accepted for publication in ApJ; 25 pages, 18 figure
The ChaMP Extended Stellar Survey (ChESS): Photometric and Spectroscopic Properties of Serendipitously Detected Stellar X-Ray Sources
We present 348 X-ray-emitting stars identified from correlating the Extended Chandra Multiwavelength Project (ChaMP), a wide-area serendipitous survey based on archival X-ray images, with the Sloan Digital Sky Survey (SDSS). We use morphological star/galaxy separation, matching to an SDSS quasar catalog, an optical color-magnitude cut, and X-ray data-quality tests to create our catalog, the ChaMP Extended Stellar Survey (ChESS), from a sample of 2121 matched ChaMP/SDSS sources. Our cuts retain 92% of the spectroscopically confirmed stars in the original sample while excluding 99.6% of the 684 spectroscopically confirmed extragalactic sources. Fewer than 3% of the sources in our final catalog are previously identified stellar X-ray emitters. For 42 catalog members, spectroscopic classifications are available in the literature. We present new spectral classifications and Hα measurements for an additional 79 stars. The catalog is dominated by main-sequence stars; we estimate the fraction of giants in ChESS is ~10%. We identify seven giant stars (including a possible Cepheid and an RR Lyrae star) as ChaMP sources, as well as three cataclysmic variables. We derive distances from ~10 to 2000 pc for the stars in our catalog using photometric parallax relations appropriate for dwarfs on the main sequence and calculate their X-ray and bolometric luminosities. These stars lie in a unique space in the L_X-distance plane, filling the gap between the nearby stars identified as counterparts to sources in the ROSAT All Sky Survey and the more distant stars detected in deep Chandra and XMM-Newton surveys. For 36 newly identified X-ray-emitting M stars we calculate LHα/Lbol. The quantities LHα/Lbol and L_X/L_bol are linearly related below L_X/L_bol ~ 3 Ă 10â»âŽ, while L_Hα/L_bol appears to turn over at larger L_X/L_bol values. Stars with reliable SDSS photometry have an ~0.1 mag blue excess in u â g, likely due to increased chromospheric continuum emission. Photometric metallicity estimates suggest that the sample is evenly split between the young and old disk populations of the Galaxy; the lowest activity sources belong to the old disk population, a clear signature of the decay of magnetic activity with age. Future papers will present analyses of source variability and comparisons of this catalog to models of stellar activity in the Galactic disk
The Red-Sequence Luminosity Function in Galaxy Clusters since z~1
We use a statistical sample of ~500 rich clusters taken from 72 square
degrees of the Red-Sequence Cluster Survey (RCS-1) to study the evolution of
~30,000 red-sequence galaxies in clusters over the redshift range 0.35<z<0.95.
We construct red-sequence luminosity functions (RSLFs) for a well-defined,
homogeneously selected, richness limited sample. The RSLF at higher redshifts
shows a deficit of faint red galaxies (to M_V=> -19.7) with their numbers
increasing towards the present epoch. This is consistent with the `down-sizing`
picture in which star-formation ended at earlier times for the most massive
(luminous) galaxies and more recently for less massive (fainter) galaxies. We
observe a richness dependence to the down-sizing effect in the sense that, at a
given redshift, the drop-off of faint red galaxies is greater for poorer (less
massive) clusters, suggesting that star-formation ended earlier for galaxies in
more massive clusters. The decrease in faint red-sequence galaxies is
accompanied by an increase in faint blue galaxies, implying that the process
responsible for this evolution of faint galaxies is the termination of
star-formation, possibly with little or no need for merging. At the bright end,
we also see an increase in the number of blue galaxies with increasing
redshift, suggesting that termination of star-formation in higher mass galaxies
may also be an important formation mechanism for higher mass ellipticals. By
comparing with a low-redshift Abell Cluster sample, we find that the
down-sizing trend seen within RCS-1 has continued to the local universe.Comment: ApJ accepted. 11 pages, 5 figure
Cyber-infrastructure to Support Science and Data Management for the Dark Energy Survey
The Dark Energy Survey (DES; operations 2009-2015) will address the nature of
dark energy using four independent and complementary techniques: (1) a galaxy
cluster survey over 4000 deg2 in collaboration with the South Pole Telescope
Sunyaev-Zel'dovich effect mapping experiment, (2) a cosmic shear measurement
over 5000 deg2, (3) a galaxy angular clustering measurement within redshift
shells to redshift=1.35, and (4) distance measurements to 1900 supernovae Ia.
The DES will produce 200 TB of raw data in four bands, These data will be
processed into science ready images and catalogs and co-added into deeper,
higher quality images and catalogs. In total, the DES dataset will exceed 1 PB,
including a 100 TB catalog database that will serve as a key science analysis
tool for the astronomy/cosmology community. The data rate, volume, and duration
of the survey require a new type of data management (DM) system that (1) offers
a high degree of automation and robustness and (2) leverages the existing high
performance computing infrastructure to meet the project's DM targets. The DES
DM system consists of (1) a grid-enabled, flexible and scalable middleware
developed at NCSA for the broader scientific community, (2) astronomy modules
that build upon community software, and (3) a DES archive to support automated
processing and to serve DES catalogs and images to the collaboration and the
public. In the recent DES Data Challenge 1 we deployed and tested the first
version of the DES DM system, successfully reducing 700 GB of raw simulated
images into 5 TB of reduced data products and cataloguing 50 million objects
with calibrated astrometry and photometry.Comment: 12 pages, 3 color figures, 1 table. Published in SPIE vol. 627
A Multiband Study of the Galaxy Populations of the First Four Sunyaev--Zeldovich Effect selected Galaxy Clusters
We present first results of an examination of the optical properties of the
galaxy populations in SZE selected galaxy clusters. Using clusters selected by
the South Pole Telescope survey and deep multiband optical data from the Blanco
Cosmology Survey, we measure the radial profile, the luminosity function, the
blue fraction and the halo occupation number of the galaxy populations of these
four clusters with redshifts ranging from 0.3 to 1. Our goal is to understand
whether there are differences among the galaxy populations of these SZE
selected clusters and previously studied clusters selected in the optical and
the X-ray. The radial distributions of galaxies in the four systems are
consistent with NFW profiles with a galaxy concentration of 3 to 6. We show
that the characteristic luminosities in bands are consistent with
passively evolving populations emerging from a single burst at redshift .
The faint end power law slope of the luminosity function is found to be on
average in griz. Halo occupation numbers (to ) for
these systems appear to be consistent with those based on X-ray selected
clusters. The blue fraction estimated to , for the three lower
redshift systems, suggests an increase with redshift, although with the current
sample the uncertainties are still large. Overall, this pilot study of the
first four clusters provides no evidence that the galaxy populations in these
systems differ significantly from those in previously studied cluster
populations selected in the X-ray or the optical.Comment: 12 pages, 12 figures and 3 tables. Accepted for publication in Ap
The Chandra Multi-Wavelength Project: Optical Spectroscopy and the Broadband Spectral Energy Distributions of X-ray Selected AGN
From optical spectroscopy of X-ray sources observed as part of ChaMP, we
present redshifts and classifications for a total of 1569 Chandra sources from
our targeted spectroscopic follow up using the FLWO, SAAO, WIYN, CTIO, KPNO,
Magellan, MMT and Gemini telescopes, and from archival SDSS spectroscopy. We
classify the optical counterparts as 50% BLAGN, 16% NELG, 14% ALG, and 20%
stars. We detect QSOs out to z~5.5 and galaxies out to z~3. We have compiled
extensive photometry from X-ray to radio bands. Together with our spectroscopic
information, this enables us to derive detailed SEDs for our extragalactic
sources. We fit a variety of templates to determine bolometric luminosities,
and to constrain AGN and starburst components where both are present. While
~58% of X-ray Seyferts require a starburst event to fit observed photometry
only 26% of the X-ray QSO population appear to have some kind of star formation
contribution. This is significantly lower than for the Seyferts, especially if
we take into account torus contamination at z>1 where the majority of our X-ray
QSOs lie. In addition, we observe a rapid drop of the percentage of starburst
contribution as X-ray luminosity increases. This is consistent with the
quenching of star formation by powerful QSOs, as predicted by the merger model,
or with a time lag between the peak of star formation and QSO activity. We have
tested the hypothesis that there should be a strong connection between X-ray
obscuration and star-formation but we do not find any association between X-ray
column density and star formation rate both in the general population or the
star-forming X-ray Seyferts. Our large compilation also allows us to report
here the identification of 81 XBONG, 78 z>3 X-ray sources and 8 Type-2 QSO
candidates. Also we have identified the highest redshift (z=5.4135) X-ray
selected QSO with optical spectroscopy.Comment: 17 pages, 16 figures, accepted for publication in ApJS. Full data
table and README file can be found online at
http://hea-www.harvard.edu/~pgreen/Papers.htm
An extension of the SHARC survey
We report on our search for distant clusters of galaxies based on optical and
X-ray follow up observations of X-ray candidates from the SHARC survey. Based
on the assumption that the absence of bright optical or radio counterparts to
possibly extended X-ray sources could be distant clusters. We have obtained
deep optical images and redshifts for several of these objects and analyzed
archive XMM-Newton or Chandra data where applicable. In our list of candidate
clusters, two are probably galaxy structures at redshifts of z0.51 and
0.28. Seven other structures are possibly galaxy clusters between z0.3
and 1. Three sources are identified with QSOs and are thus likely to be X-ray
point sources, and six more also probably fall in this category. One X-ray
source is spurious or variable. For 17 other sources, the data are too sparse
at this time to put forward any hypothesis on their nature. We also
serendipitously detected a cluster at z=0.53 and another galaxy concentration
which is probably a structure with a redshift in the [0.15-0.6] range. We
discuss these results within the context of future space missions to
demonstrate the necessity of a wide field of view telescope optimized for the
0.5-2 keV range.Comment: Accepted in A&
The Blanco Cosmology Survey: Data Acquisition, Processing, Calibration, Quality Diagnostics and Data Release
The Blanco Cosmology Survey (BCS) is a 60 night imaging survey of 80
deg of the southern sky located in two fields: (,)= (5 hr,
) and (23 hr, ). The survey was carried out between
2005 and 2008 in bands with the Mosaic2 imager on the Blanco 4m
telescope. The primary aim of the BCS survey is to provide the data required to
optically confirm and measure photometric redshifts for Sunyaev-Zel'dovich
effect selected galaxy clusters from the South Pole Telescope and the Atacama
Cosmology Telescope. We process and calibrate the BCS data, carrying out PSF
corrected model fitting photometry for all detected objects. The median
10 galaxy (point source) depths over the survey in are
approximately 23.3 (23.9), 23.4 (24.0), 23.0 (23.6) and 21.3 (22.1),
respectively. The astrometric accuracy relative to the USNO-B survey is
milli-arcsec. We calibrate our absolute photometry using the stellar
locus in bands, and thus our absolute photometric scale derives from
2MASS which has % accuracy. The scatter of stars about the stellar locus
indicates a systematics floor in the relative stellar photometric scatter in
that is 1.9%, 2.2%, 2.7% and2.7%, respectively.
A simple cut in the AstrOmatic star-galaxy classifier {\tt spread\_model}
produces a star sample with good spatial uniformity. We use the resulting
photometric catalogs to calibrate photometric redshifts for the survey and
demonstrate scatter with an outlier fraction %
to . We highlight some selected science results to date and provide a
full description of the released data products.Comment: 23 pages, 23 figures . Response to referee comments. Paper accepted
for publication. BCS catalogs and images available for download from
http://www.usm.uni-muenchen.de/BC
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