64 research outputs found
X-ray observations of the Compton-thick Seyfert 2 galaxy, NGC 5643
We present results from a ~55 ks long XMM-Newton observation of the obscured
AGN, NGC 5643, performed in July 2009. A previous, shorter (about 10 ks)
XMM-Newton observation in February 2003 had left two major issues open, the
nature of the hard X-ray emission (Compton-thin vs Compton-thick) and of the
soft X-ray excess (photoionized vs collisionally ionized matter). The new
observation shows that the source is Compton-thick and that the dominant
contribution to the soft X-ray emission is by photoionized matter (even if it
is still unclear whether collisionally ionized matter may contribute as well).
We also studied three bright X-ray sources that are in the field of NGC 5643.
The ULX NGC 5643 X-1 was confirmed to be very luminous, even if more than a
factor 2 fainter than in 2003. We then provided the first high quality spectrum
of the cluster of galaxies Abell 3602. The last source, CXOJ143244.5-442020, is
likely an unobscured AGN, possibly belonging to Abell 3602.Comment: 6 pages. Accepted for publication in A&
XMM-Newton view of the double-peaked Fe K-alpha complex in E1821+643
We present the results of the analysis of the hard band XMM-Newton spectra of
the luminous, L(2-10keV)~3.4E+45 erg/s, radio-quiet quasar, E1821+643. Two
emission features were observed in the 6-7 keV rest frame band, confirming
previous Chandra detection of these structures. We interpret these features as
two single emission lines, one consistent with the neutral Fe K-alpha line at
6.4 keV and the other most likely due to FeXXVI. If related to the quasar, the
high-energy emission line should originate in highly ionised matter, i.e. the
accretion disc or the clouds of the emission line regions. Alternatively, it
may be related to the intergalactic medium of the rich galaxy cluster in which
E1821+643 is embedded. A composite broad emission line in combination with an
absorption line model, however, also fits the data well. We discuss the
possible physical interpretations of the origin of these features.Comment: Accepted for publication in A&A, 7 pages and 7 figure
The XMM-Newton view of PG quasars: II. Properties of the Fe K-alpha line
The properties of the fluorescence Fe K-alpha emission lines of a sample of
38 quasars (QSOs) observed with XMM-Newton are studied. These objects are
included in the optically selected sample from the Palomar-Green (PG) Bright
Quasar Survey with an X-ray luminosity 1.3E43<L(2-10 keV)<5.1E45 ergs/s and
z<1.72. For each object in the sample, we investigated the presence of both
narrow and broad iron lines in detail. A total of 20 out of the 38 QSOs show
evidence of an Fe K-alpha emission line with a narrow profile. The majority of
the lines are consistent with an origin in low ionization material, which is
likely to be located in the outer parts of the accretion disk, the molecular
torus, and/or the Broad Line Region. The average properties of the narrow Fe
K-alpha emission line observed in the sample are similar to those of Seyfert
type galaxies as inferred from recent XMM-Newton and Chandra studies. A broad
line has been significantly detected in only three objects. Furthermore, we
studied the relationship between the equivalent width (EW) of the iron line and
the hard band X-ray luminosity for radio quiet quasars. The analysis indicates
that no clear correlation between the strength of the line and the hard X-ray
luminosity is present, and our results do not show compelling evidence for an
anticorrelation between these two quantities, i.e. the so-called X-ray Baldwin
effect.Comment: 10 pages, 3 figures, accepted by A&
A long hard look at the minimum state of PG 2112+059 with XMM-Newton
XMM-Newton successfully detected the minimum state of PG 2112+059 during a
short snapshot observation and performed a long follow-up observation. The high
signal-to-noise spectra are modelled assuming different emission scenarios and
compared with archival spectra taken by XMM-Newton and Chandra.
The PG 2112+059 X-ray spectra acquired in May 2007 allowed the detection of a
weak iron fluorescent line, which is interpreted as being caused by reflection
from neutral material at some distance from the primary X-ray emitting source.
The X-ray spectra of PG 2112+059 taken at five different epochs during
different flux states can be interpreted within two different scenarios. The
first consists of two layers of ionised material with column densities of N_H
~5 x 10^22 cm^-2 and N_H ~3.5 x 10^23 cm^-2, respectively. The first layer is
moderately ionised and its ionisation levels follow the flux changes, while the
other layer is highly ionised and does not show any correlation with the flux
of the source. The spectra can also be interpreted assuming reflection by an
ionised accretion disk seen behind a warm absorber. The warm absorber
ionisation is consistent with being correlated with the flux of the source,
which provides an additional degree of self-consistency with the overall
reflection-based model. We explain the spectral variability with light bending
according to the models of Miniutti and Fabian and constrain the black hole
spin to be a/M > 0.86. Both scenarios also assume that a distant cold reflector
is responsible for the Fe K \alpha emission line.
Light bending provides an attractive explanation of the different states of
PG 2112+059 and may also describe the physical cause of the observed properties
of other X-ray weak quasars.Comment: 15 pages, 12 figures, A&A latex, accepted for publication in
Astronomy & Astrophysic
Multiwavelength analysis of the Lyman alpha emitting galaxy Haro 2: relation between the diffuse Lyman alpha and soft X-ray emissions
In order to use Lyman alpha (Lya) emission as star formation tracer in
cosmological studies, we must understand how the resonant scattering affects
the escape fraction of the Lya photons. Thus, high spatial resolution
multiwavelength studies of nearby Lya emitters, like Haro 2, are highly needed.
For that purpose, we have used Chandra X-ray and HST (UV, optical and NIR)
images of Haro 2, and STIS and ground-based spectral images along its major and
minor axes, to characterize the Lya emission and the properties of the stellar
population. The UV, Ha (Halpha) and FIR luminosities of the Haro 2 nuclear
starburst are reproduced using evolutionary synthesis models assuming a young
stellar population with ages ~3.5-5.0 Myr, affected by differential
interstellar extinctions. The observed X-ray emission is attributed to gas
heated by the mechanical energy released by the starburst (soft component) and
a Ultra-Luminous X-ray source candidate (hard). Both compact and diffuse Lya
components are observed. Whereas Lya is spatially decoupled from Balmer lines
emission, Balmer decrement and UV continuum, the diffuse Lya component is
spatially correlated with the diffuse soft X-ray emission. Moreover, unlike the
compact one, diffuse Lya shows luminosities larger than predicted from Ha,
assuming case B recombination and dust extinction as derived from Ha/Hbeta. We
propose that, whereas the compact Lya emission is associated to the massive
stellar clusters and is affected by outflows and dust extinction, the diffuse
Lya originates in gas ionized by the hot plasma responsible for the soft X-ray
radiation, as suggested by their spatial correlation and by the measured
L(Ha)/LsoftX ratios. Calibration of Lya as star formation rate tracer should
therefore include both effects (destruction vs. enhancement) to avoid biases in
the study of galaxies at cosmological distances.Comment: Accepted for publication in A&A, 18 pages, 8 figures, 9 tables. If
problems with quality of images, see
http://www.cab.inta-csic.es/users/otih/haro2-v63.clean.pd
Physical properties and evolutionary state of the Lyman alpha emitting starburst galaxy IRAS 08339+6517
Though Lyman alpha emission (Lya) is one of the most used tracers of massive
star formation at high redshift, a correct understanding of radiation transfer
effects by neutral gas is required to properly quantify the star formation rate
along the history of the Universe. We are embarked in a program to study the
properties of the Lya emission (spectral profile, spatial distribution,
relation to Balmer lines intensity,...) in several local starburst galaxies. We
present here the results obtained for IRAS 08339+6517.
Using evolutionary population synthesis models, we have characterized the
properties of the starburst (UV continuum, Halpha, total infrared and X-ray
emissions, etc.), which transformed 1.4e+8 Mo of gas into stars around 5-6 Myr
ago. In addition to the central compact emission blob, we have identified a
diffuse Lya emission component smoothly distributed over the whole central area
of IRAS 08339+6517. This diffuse emission is spatially decoupled from the UV
continuum, the Halpha emission or the Halpha/Hbeta ratio. Both locally and
globally, the Lya/Halpha ratio is lower than the Case B predictions, even after
reddening correction, with an overall Lya escape fraction of only 4%.
We conclude that in IRAS 08339+6517 the resonant scattering of Lya photons by
an outflowing shell of neutral gas causes their highly-efficient destruction by
dust, which explains the low Lya escape fraction measured. These results stress
again the importance of a proper correction of scattering and transfer effects
when using Lya to derive the star formation rate in high-redshift galaxies.Comment: Accepted for publication in A&A, 17 pages, 13 figures, 8 tables. If
problems with quality of images, see
https://cloud.cab.inta-csic.es/public.php?service=files&file=%2Fotih%2Ffiles%2Foti_mas%2Firas%2Firas-v53.ack_referee.pd
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