178 research outputs found
Wide Area X-ray Surveys for AGN and Starburst Galaxies
While often the point sources in X-ray surveys are dominated by AGN, with the
high sensitivity of modern X-ray telescopes such as Chandra and XMM-Newton
normal/starburst galaxies are also being detected in large numbers. We have
made use of Bayesian statistics for both the selection of galaxies from deep
X-ray surveys and in the analysis of the luminosity functions for galaxies.
These techniques can be used to similarly select galaxies from wide-area X-ray
surveys and to analyze their luminosity function. The prospects for detecting
galaxies and AGN from a proposed ``wide-deep'' XMM-Newton survey and from
future wide-area X-ray survey missions (such as WFXT and eRosita) are also
discussed.Comment: 7 pages, 5 figures. Conference proceedings in "Classification and
Discovery in Large Astronomical Surveys", 2008, C.A.L. Bailer-Jones (ed.
Observing Evolution in Star-Forming Galaxies in X-Rays
The Chandra Deep Fields (CDFs) have reached flux limits where normal/starburst galaxies are significant contributors to the X-ray number counts (approximately 40% at F _{0.5-2.0} = 1 x 10(^)-17). Based on these results and current theoretical models of X-ray binary evolution we will discuss expectations for observing galaxy evolution in X-rays in IXO deep surveys. With the high sensitivity of IXO (particularly approximately 5" resolution constant across the WFI FOV and high effective area) IXO surveys should detect large numbers of galaxies which will allow evolution to be studied in multiple redshift bins. High spatial resolution will also drive the need to minimize source confusion below F _{0.5-2.0 keV} = 10^{-17} ergs/s/cm^2. In addition to detecting starburst galaxies individually, stacking will be used to constrain their properties on average, particularly Lyman-break galaxies at z greater than 2. We will also discuss challenges in segregating galaxies from obscured AGN in IXO deep fields and expectations proposed survey X-ray missions
Obscured AGN
Many obscured AGN show evidence of significant starburst emission dominating below 2 keV. Therefore wide-field X-ray surveys sensitive enough to luminosities below approximately 10^42 ergs per second will result in detections of galaxies with contributions of both obscured AGN and starburst emission. We will discuss Bayesian approaches to assessing the relative contribution of each component, minimizing survey biases and using the resultant posterior probabilities for the AGN and starburst components to determine their evolution
Hard X-ray Emission and the Ionizing Source in LINERs
We report X-ray fluxes in the 2--10 keV band from LINERs (low-ionization
nuclear emission-line regions) and low-luminosity Seyfert galaxies obtained
with the ASCA satellite. Observed X-ray luminosities are in the range between
4e39 and 5e41 ergs/s, which are significantly smaller than that of the
``classical'' low-luminosity Seyfert 1 galaxy NGC 4051. We found that X-ray
luminosities in 2--10 keV of LINERs with broad Halpha emission in their optical
spectra (LINER 1s) are proportional to their Halpha luminosities. This
correlation strongly supports the hypothesis that the dominant ionizing source
in LINER 1s is photoionization by hard photons from low-luminosity AGNs. On the
other hand, the X-ray luminosities of most LINERs without broad Halpha emission
(LINER 2s) in our sample are lower than LINER 1s at a given Halpha luminosity.
The observed X-ray luminosities in these objects are insufficient to power
their Halpha luminosities, suggesting that their primary ionizing source is
other than an AGN, or that an AGN, if present, is obscured even at energies
above 2 keV.Comment: 11 pages, 3 figures, To appear in the Astrophyscal Jouna
XMM-Newton Observations of a Complete Sample of Optically Selected Type 2 Seyfert Galaxies
(abridged)The majority of Active Galactic Nuclei (AGN) suffer from
significant obscuration by surrounding dust and gas. X-ray surveys in the 2-10
keV band will miss the most heavily-obscured AGN in which the absorbing column
density exceeds cm (the Compton-thick AGN). It is therefore
vital to know the fraction of AGN that are missed in such X-rays surveys and to
determine if these AGN represent some distinct population in terms of the
fundamental properties of AGN and/or their host galaxies. In this paper we
present the analysis of \textit{XMM-Newton} X-ray data for a complete sample of
17 low-redshift Type 2 Seyfert galaxies chosen from the Sloan Digital Sky
Survey based solely on the high observed flux of the [OIII]5007
emission-line. This line is formed in the Narrow Line Region hundreds of
parsecs away from the central engine. Thus, unlike the X-ray emission, it is
not affected by obscuration due to the torus surrounding the black hole. It
therefore provides a useful isotropic indicator of the AGN luminosity. As
additional indicators of the intrinsic AGN luminosity, we use the Spitzer Space
Telescope to measure the luminosities of the mid-infrared continuum and the
[OIV]25.89m narrow emission-line. We then use the ratio of the 2-10 keV
X-ray luminosity to the [OIII], [OIV], and mid-infrared luminosities to assess
the amount of X-ray obscuration and to distinguish between Compton-thick and
Compton-thin objects. We find that the majority of the sources suffer
significant amounts of obscuration: the observed 2-10 keV emission is depressed
by more than an order-of-magnitude in 11 of the 17 cases (as expected for
Compton-thick sources).Comment: accepted for publication to ApJ; 48 pages, 15 figure
A Chandra observation of the ultraluminous infrared galaxy IRAS 19254--7245 (the Superantennae): X-ray emission from the Compton-thick AGN and the diffuse starburst
We present a {\it Chandra} observation of IRAS 19254--7245, a nearby ULIRG
also known as {\it the Superantennae}. The high spatial resolution of {\it
Chandra} allows us to disentangle for the first time the diffuse starburst
emission from the embedded Compton-thick AGN. The 2-10 keV spectrum of the AGN
emission is fitted by a flat power-law ) and a He-like Fe K
line with EW1.5 keV, consistent with previous observations. The Fe
K line profile could be resolved as a blend of a neutral 6.4 keV line
and an ionized 6.7 keV (He-like) or 6.9 keV (H-like) line. Variability is
detected compared with the previous {\it XMM-Newton} and {\it suzaku}
observations, demonstrating the compact size of the iron line emission. We fit
the spectrum of the galaxy-scale extended emission excluding the AGN and other
bright point sources with a soft thermal component with kT~0.8 keV. The
luminosity of the extended emission is about one order of magnitude lower than
that of the AGN. The basic physical and structural properties of the extended
emission are fully consistent with a galactic wind being driven by the
starburst (no contribution to the feedback by the AGN is required). A candidate
ultra-luminous X-ray source is detected 8\arcsec\ south of the southern
nucleus. The 0.3-10 keV luminosity of this off-nuclear point source is
~ erg s if the emission is isotropic and the source is
associated with the Superantennae.Comment: 31 pages, 10 figures, submitted to Ap
NuSTAR Hard X-ray View of Low-luminosity Active Galactic Nuclei: High-energy Cutoff and Truncated Thin Disk
We report the analysis of simultaneous XMM-Newton+NuSTAR observations of two
low-luminosity Active Galactic Nuclei (LLAGN), NGC 3998 and NGC 4579. We do not
detect any significant variability in either source over the ~3 day length of
the NuSTAR observations. The broad-band 0.5-60 keV spectrum of NGC 3998 is best
fit with a cutoff power-law, while the one for NGC 4579 is best fit with a
combination of a hot thermal plasma model, a power-law, and a blend of
Gaussians to fit an Fe complex observed between 6 and 7 keV. Our main spectral
results are the following: (1) neither source shows any reflection hump with a
reflection fraction upper-limits and for NGC 3998
and NGC 4579, respectively; (2) the 6-7 keV line complex in NGC 4579 could
either be fit with a narrow Fe K line at 6.4 keV and a moderately broad Fe XXV
line, or 3 relatively narrow lines, which includes contribution from Fe XXVI;
(3) NGC 4579 flux is 60% brighter than previously detected with XMM-Newton,
accompanied by a hardening in the spectrum; (4) we measure a cutoff energy
keV in NGC 3998, which represents the lowest and
best constrained high-energy cutoff ever measured for an LLAGN; (5) NGC 3998
spectrum is consistent with a Comptonization model with either a sphere
() or slab () geometry, corresponding
to plasma temperatures between 20 and 150 keV. We discuss these results in the
context of hard X-ray emission from bright AGN, other LLAGN, and hot accretion
flow models.Comment: 14 pages, 11 figures, 4 tables, accepted for publication in Ap
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