11 research outputs found
Clustering of Intermediate Luminosity X-ray selected AGN at z~3
We present the first clustering results of X-ray selected AGN at z~3. Using
Chandra X-ray imaging and UVR optical colors from MUSYC photometry in the
ECDF-S field, we selected a sample of 58 z~3 AGN candidates. From the optical
data we also selected 1385 LBG at 2.8<z< 3.8 with R<25.5. We performed
auto-correlation and cross-correlation analyses, and here we present results
for the clustering amplitudes and dark matter halo masses of each sample. For
the LBG we find a correlation length of r_0,LBG = 6.7 +/- 0.5 Mpc, implying a
bias value of 3.5 +/- 0.3 and dark matter (DM) halo masses of log(Mmin/Msun) =
11.8 +/- 0.1. The AGN-LBG cross-correlation yields r_0,AGN-LBG = 8.7 +/- 1.9
Mpc, implying for AGN at 2.8<z<3.8 a bias value of 5.5 +/- 2.0 and DM halo
masses of log(Mmin/Msun) = 12.6 +0.5/-0.8. Evolution of dark matter halos in
the Lambda CDM cosmology implies that today these z~3 AGN are found in high
mass galaxies with a typical luminosity of 7+4/-2 L*.Comment: Accepted for publication in ApJ Letters. 4 pages, 4 figures (1 in
color
Galaxy Zoo: Motivations of Citizen Scientists
Citizen science, in which volunteers work with professional scientists to
conduct research, is expanding due to large online datasets. To plan projects,
it is important to understand volunteers' motivations for participating. This
paper analyzes results from an online survey of nearly 11,000 volunteers in
Galaxy Zoo, an astronomy citizen science project. Results show that volunteers'
primary motivation is a desire to contribute to scientific research. We
encourage other citizen science projects to study the motivations of their
volunteers, to see whether and how these results may be generalized to inform
the field of citizen science.Comment: 41 pages, including 6 figures and one appendix. In press at Astronomy
Education Revie
Finding Rare AGN: X-ray Number Counts of Chandra Sources in Stripe 82
We present the first results of a wide area X-ray survey within the Sloan
Digital Sky Survey (SDSS) Stripe 82, a 300 deg region of the sky with a
substantial investment in multi-wavelength coverage. We analyzed archival {\it
Chandra} observations that cover 7.5 deg within Stripe 82 ("Stripe 82
ACX"), reaching 4.5 flux limits of 7.9,
3.4 and 1.8 erg s cm in the soft
(0.5-2 keV), hard (2-7 keV) and full (0.5-7 keV) bands, to find 774, 239 and
1118 X-ray sources, respectively. Three hundred twenty-one sources are detected
only in the full band and 9 sources are detected solely in the soft band.
Utilizing data products from the {\it Chandra} Source Catalog, we construct
independent Log-Log relationships, detailing the number density of X-ray
sources as a function of flux, which show general agreement with previous {\it
Chandra} surveys. We compare the luminosity distribution of Stripe 82 ACX with
the smaller, deeper CDF-S + E-CDFS surveys and with {\it Chandra}-COSMOS,
illustrating the benefit of wide-area surveys in locating high luminosity AGN.
We also investigate the differences and similarities of X-ray and optical
selection to uncover obscured AGN in the local Universe. Finally, we estimate
the population of AGN we expect to find with increased coverage of 100 deg
or 300 deg, which will provide unprecedented insight into the high
redshift, high luminosity regime of black hole growth currently
under-represented in X-ray surveys.Comment: Accepted for publication in MNRAS, 15 pages, 6 Figures, 2 Table
The 31 Deg Release of the Stripe 82 X-ray Survey: The Point Source Catalog
We release the next installment of the Stripe 82 X-ray survey point-source
catalog, which currently covers 31.3 deg of the Sloan Digital Sky Survey
(SDSS) Stripe 82 Legacy field. In total, 6181 unique X-ray sources are
significantly detected with {\it XMM-Newton} () and {\it Chandra}
(). This catalog release includes data from {\it XMM-Newton} cycle
AO 13, which approximately doubled the Stripe 82X survey area. The flux limits
of the Stripe 82X survey are erg s cm,
erg s cm, and erg
s cm in the soft (0.5-2 keV), hard (2-10 keV), and full bands
(0.5-10 keV), respectively, with approximate half-area survey flux limits of
erg s cm, erg s
cm, and erg s cm. We matched the X-ray
source lists to available multi-wavelength catalogs, including updated matches
to the previous release of the Stripe 82X survey; 88\% of the sample is matched
to a multi-wavelength counterpart. Due to the wide area of Stripe 82X and rich
ancillary multi-wavelength data, including coadded SDSS photometry,
mid-infrared {\it WISE} coverage, near-infrared coverage from UKIDSS and VHS,
ultraviolet coverage from {\it GALEX}, radio coverage from FIRST, and
far-infrared coverage from {\it Herschel}, as well as existing 30\%
optical spectroscopic completeness, we are beginning to uncover rare objects,
such as obscured high-luminosity AGN at high-redshift. The Stripe 82X point
source catalog is a valuable dataset for constraining how this population grows
and evolves, as well as for studying how they interact with the galaxies in
which they live.Comment: accepted for publication in ApJ; 23 pages (emulateapj
The 31 Deg^2 Release of the Stripe 82 X-Ray Survey: The Point Source Catalog
We release the next installment of the Stripe 82 X-ray survey point-source catalog, which currently covers 31.3 deg^2 of the Sloan Digital Sky Survey (SDSS) Stripe 82 Legacy field. In total, 6181 unique X-ray sources are significantly detected with XMM-Newton (>5σ) and Chandra (>4.5σ). This catalog release includes data from XMM-Newton cycle AO 13, which approximately doubled the Stripe 82X survey area. The flux limits of the Stripe 82X survey are 8.7 × 10^(−16) erg s^(−1) cm^(−2), 4.7 × 10^(−15) erg s^(−1) cm^(−2), and 2.1 × 10^(−15) erg s^(−1) cm^(−2) in the soft (0.5–2 keV), hard (2–10 keV), and full bands (0.5–10 keV), respectively, with approximate half-area survey flux limits of 5.4 × 10^(−15) erg s^(−1) cm^(−2), 2.9 × 10^(−14) erg s^(−1) cm^(−2), and 1.7 × 10^(−14) erg s^(−1) cm^(−2). We matched the X-ray source lists to available multi-wavelength catalogs, including updated matches to the previous release of the Stripe 82X survey; 88% of the sample is matched to a multi-wavelength counterpart. Due to the wide area of Stripe 82X and rich ancillary multi-wavelength data, including coadded SDSS photometry, mid-infrared WISE coverage, near-infrared coverage from UKIDSS and VISTA Hemisphere Survey, ultraviolet coverage from GALEX, radio coverage from FIRST, and far-infrared coverage from Herschel, as well as existing ~30% optical spectroscopic completeness, we are beginning to uncover rare objects, such as obscured high-luminosity active galactic nuclei at high-redshift. The Stripe 82X point source catalog is a valuable data set for constraining how this population grows and evolves, as well as for studying how they interact with the galaxies in which they live
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Erratum: Finding rare AGN: XMM–Newton and Chandra observations of SDSS Stripe 82
Finding rare AGN: XMM–Newton and Chandra observations of SDSS Stripe 82
We have analyzed the {\it XMM-Newton} and {\it Chandra} data overlapping
16.5 deg of Sloan Digital Sky Survey Stripe 82, including 4.6
deg of proprietary {\it XMM-Newton} data that we present here. In total,
3362 unique X-ray sources are detected at high significance. We derive the {\it
XMM-Newton} number counts and compare them with our previously reported {\it
Chandra} Log-Log relations and other X-ray surveys. The Stripe 82 X-ray
source lists have been matched to multi-wavelength catalogs using a maximum
likelihood estimator algorithm. We discovered the highest redshift ()
quasar yet identified in an X-ray survey. We find 2.5 times more high
luminosity (L erg s) AGN than the smaller area {\it
Chandra} and {\it XMM-Newton} survey of COSMOS and 1.3 times as many identified
by XBo\"otes. Comparing the high luminosity AGN we have identified with those
predicted by population synthesis models, our results suggest that this AGN
population is a more important component of cosmic black hole growth than
previously appreciated. Approximately a third of the X-ray sources not detected
in the optical are identified in the infrared, making them candidates for the
elusive population of obscured high luminosity AGN in the early universe.Comment: 25 pages, 18 figures, 5 tables. accepted for publication in MNRAS.
Catalogs can be downloaded at http://www.astro.yale.edu/lamassa/s82x.htm