459 research outputs found
GALEX measurements of the Big Blue Bump as a tool to study bolometric corrections in AGNs
Active Galactic Nuclei emit over the entire electromagnetic spectrum with the
peak of the accretion disk emission in the far-UV, a wavelength range
historically difficult to investigate. We use here the GALEX (Galaxy Evolution
Explorer) Near-UV and Far-UV measurements (complemented with optical data from
Sloan Digital Sky Survey (SDSS) and XMM-Newton X-ray spectra) of a sample of 83
X-ray selected type 1 AGN extracted from the XMM-Newton Bright Serendipitous
Survey to study their spectral energy distribution (SED) in the optical, Near
and Far-UV and X-ray energy bands. We have constrained the luminosity of the
accretion disk emission component and calculated the hard X-ray bolometric
corrections for a significant sample of AGN spanning a large range in
properties (z, L(x)).Comment: 2 pages, 2 figures, To appear in refereed Proceedings of "X-ray
Astronomy 2009: Present Status, Multi-Wavelength Approach and Future
Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri,
M. Cappi, and L. Angelin
Heavily obscured AGN with SIMBOL-X
By comparing an optically selected sample of narrow lines AGN with an X-ray
selected sample of AGN we have recently derived an estimate of the intrinsic
(i.e. before absorption) 2-10 keV luminosity function (XLF) of Compton Thick
AGNs. We will use this XLF to derive the number of Compton Thick AGN that will
be found in the SIMBOL-X survey(s).Comment: Talk at the Simbol-X symposium held in Paris, 2-5 December, 2008. 6
pages, 1 figure with three panel
The relationship between [OIII]5007A equivalent width and obscuration in AGN
In this paper we study the relationship between the equivalent width (EW) of
the [OIII]5007A narrow emission line in AGN and the level of obscuration. To
this end, we combine the results of a systematic spectral analysis, both in the
optical and in the X-rays, on a statistically complete sample of ~170 X-ray
selected AGN from the XMM-Newton Bright Serendipitous Source sample (XBS). We
find that the observed large range of [OIII]5007A equivalent widths observed in
the sample (from a few A up to 500A) is well explained as a combination of an
intrinsic spread, probably due to the large range of covering factors of the
Narrow Line Region, and the effect of absorption. The intrinsic spread is
dominant for EW below 40-50A while absorption brings the values of EW up to
~100-150A, for moderate levels of absorption (AV~0.5-2 mag) or up to ~500A for
AV>2 mag. In this picture, the absorption has a significant impact on the
observed EW also in type~1 AGN. Using numerical simulations we find that this
model is able to reproduce the [OIII]5007A EW distribution observed in the XBS
sample and correctly predicts the shape of the EW distribution observed in the
optically selected sample of QSO taken from the SDSS survey.Comment: 7 pages, 5 figures. Accepted for publication in MNRA
The Kormendy relation of massive elliptical galaxies at z~1.5. Evidence for size evolution ?
We present the morphological analysis based on HST-NIC2 (0.075 arcsec/pixel)
images in the F160W filter of a sample of 9 massive field (> 10^{11} M_\odot)
galaxies spectroscopically classified as early-types at 1.2<z<1.7. Our analysis
shows that all of them are bulge dominated systems. In particular, 6 of them
are well fitted by a de Vaucouleurs profile (n=4) suggesting that they can be
considered pure elliptical galaxies. The remaining 3 galaxies are better fitted
by a Sersic profile with index 1.9<n<2.3 suggesting that a disk-like component
could contribute up to 30% to the total light of these galaxies. We derived the
effective radius R_e and the mean surface brightness within R_e of our
galaxies and we compared them with those of early-types at lower redshifts. We
find that the surface brightness of our galaxies should get fainter by
2.5 mag from z~1.5 to z~0 to match the surface brightness of the local
ellipticals with comparable R_e, i.e. the local Kormendy relation. Luminosity
evolution without morphological changes can only explain half of this effect,
as the maximum dimming expected for an elliptical galaxy is ~1.6 mag in this
redshift range. Thus, other parameters, possibly structural, may undergo
evolution and play an important role in reconciling models and observations.
Hypothesizing an evolution of the effective radius of galaxies we find that R_e
should increase by a factor 1.5 from z~1.5 to z~0.Comment: Accepted for publication in MNRAS, 15 pages, 8 figure
X-ray Line Emitting Objects in XMM-Newton Observations: the Tip of the Iceberg
We present preliminary results from a novel search for X-ray Line Emitting
Objects (XLEOs) in XMM-Newton images. Three sources have been detected in a
test-run analysis of 13 XMM-Newton observations. The three objects found are
most likely extremely absorbed AGN characterized by a column density
NH~10^24cm^-2. Their redshift has been directly determined from the X-ray data,
by interpreting the detected emission line as the 6.4 keV Fe line. The measured
equivalent width of the X-ray line is, in all three cases, several keV. This
pilot study demonstrates the success of our search method and implies that a
large sample of XLEOs can be obtained from the public XMM-Newton data archive.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter
The structure of the X-ray absorber in Mrk 915 revealed by Swift
In this paper we present the results obtained with a monitoring programme (23
days long) performed with Swift-XRT on the local Seyfert galaxy Mrk 915. The
light-curve analysis shows a significant count rate variation (about a factor
of 2-3) on a time-scale of a few days, while the X-ray colours show a change in
the spectral curvature below 2 keV and the presence of two main spectral
states. From the spectral analysis we find that the observed variations can be
explained by the change of the intrinsic nuclear power (about a factor of 1.5)
coupled with a change of the properties of an ionized absorber. The quality of
the data prevents us from firmly establishing if the spectral variation is due
to a change in the ionization state and/or in the covering factor of the
absorbing medium. The latter scenario would imply a clumpy structure of the
ionized medium. By combining the information provided by the light curve and
the spectral analyses, we can derive some constraints on the location of the
absorber under the hypotheses of either homogeneous or clumpy medium. In both
cases, we find that the absorber should be located inside the outer edge of an
extended torus and, in particular, under the clumpy hypothesis, it should be
located near, or just outside, to the broad emission line region.Comment: 8 pages, 6 figures, 1 table. Accepted for publication on MNRA
Heavily obscured AGN in the local Universe
We present here a new powerful diagnostic plot to select heavily obscured AGN
in the local universe by combining infrared (Spitzer, IRAS) and X-ray (XMM)
information. On the basis of this plot, we selected a sample of X-ray obscured
sources in the 2XMM catalogue and found seven newly discovered Compton-thick
AGN candidates.Comment: 2 pages, 2 figures, To appear in refereed Proceedings of "X-ray
Astronomy 2009: Present Status, Multi-Wavelength Approach and Future
Perspectives", Bologna, Italy, September 7-11, 2009, AIP, eds. A. Comastri,
M. Cappi, and L. Angelin
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