1,060 research outputs found
Optical Spectroscopy of the unusual galaxy J2310-43
We present and discuss new spectroscopic observations of the unusual galaxy
J2310-43. The observations cover a wide wavelength range, from 3700 A to 9800 A
allowing the study of both the regions where H alpha and the Ca II ``contrast''
are expected. No evidence for H alpha in emission is found and we thus confirm
the absence of emission lines in the spectrum of J2310-43, ruling out the
possibility that it may host a Seyfert nucleus. The CaII break is clearly
detected and the value of the contrast (38 +/-4 %) is intermediate between that
of a typical elliptical galaxy (about 50 %) and that of a BL Lac object (<25
%). This result imposes limits on the intensity of a possible non-stellar
continuum and, in the light of the radio and X-ray loudness of the source,
draws further attention to the problem of the recognition of a BL Lac object.
Objects like J2310-43 may be more common than previously recognized, and begin
to emerge in surveys of radio-emitting X-ray sources.Comment: 7 pages, 1 figure; to be published in The Astronomical Journa
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
Broad-band properties of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies
We report about recent updates of broad-band properties of radio-loud
narrow-line Seyfert 1 galaxies.Comment: 5 pages, no figures. Proceedings 28th Texas Symposium on Relativistic
Astrophysics, Geneva (Switzerland), 13-18 December 201
An orientation-based unification of young jetted AGN: the case of 3C 286
In recent years, the old paradigm according to which only high-mass black
holes can launch powerful relativistic jets in active galactic nuclei (AGN) has
begun to crumble. The discovery of -rays coming from narrow-line
Seyfert 1 galaxies (NLS1s), usually considered young and growing AGN harboring
a central black hole with mass typically lower than 10 M, indicated
that also these low-mass AGN can produce powerful relativistic jets. The search
for parent population of -ray emitting NLS1s revealed their connection
with compact steep-spectrum sources (CSS). In this proceeding we present a
review of the current knowledge of these sources, we present the new important
case of 3C 286, classified here for the fist time as NLS1, and we finally
provide a tentative orientation based unification of NLS1s and CSS sources.Comment: 12 pages, 3 figures. Proceeding of the conference "Quasars at all
cosmic epochs", held in Padova, April 2-7, 2017, published on Frontiers in
Astronomy and Space Science
X-ray observation of ULAS J1120+0641, the most distant quasar at z=7.08
We aim at probing the emission mechanism of the accreting super massive black
holes in the high redshift Universe. We study the X-ray spectrum of
ULAS1120+0641, the highest redshift quasar detected so far at z=7.085, which
has been deeply observed (340 ks) by XMM-Newton. Despite the long integration
time the spectral analysis is limited by the poor statistics, with only 150
source counts being detected. We measured the spectrum in the 2-80 keV
rest-frame (0.3-10 keV observed) energy band. Assuming a simple power law model
we find a photon index of 2.0+/-0.3 and a luminosity of 6.7+/-0.3 10^44 erg/s
in the 2-10 keV band, while the intrinsic absorbing column can be only loosely
constrained (NH< 1E23 cm^-2). Combining our data with published data we
calculate that the X-ray-to-optical spectral index alpha_OX is1.8+/-0.1, in
agreement with the alpha_OX-UV luminosity correlation valid for lower redshift
quasars. We expanded to high energies the coverage of the spectral energy
distribution of ULAS1120+0641. This is the second time that a z >6 quasar has
been investigated through a deep X-ray observation. In agreement with previous
studies of z~6 AGN samples, we do not find any hint of evolution in the
broadband energy distribution. Indeed from our dataset ULAS 1120+0641 is
indistinguishable from the population of optically bright quasar at lower
redshift.Comment: 5 pages, 4 figures, A&A in press; updated with the accepted versio
Suzaku and SWIFT-BAT observations of a newly discovered Compton-thick AGN
Obscured AGN are fundamental to understand the history of Super Massive Black
Hole growth and their influence on galaxy formation. However, the Compton-thick
AGN (NH>1e24 cm^-2) population is basically unconstrained, with less than few
dozen confirmed Compton-thick AGN found and studied so far. A way to select
heavily obscured AGN is to compare the X-ray emission below 10 keV (which is
strongly depressed) with the emission from other bands less affected by the
absorption, i.e. the IR band. To this end, we have cross-correlated the 2XMM
catalogue with the IRAS Point Source catalogue and, by using the X-ray to
infrared flux ratio and X-ray colors, we selected a well defined sample of
Compton-thick AGN candidates at z<0.1. The aim of this work is to confirm the
nature and to study one of these local Compton-thick AGN candidates, the nearby
(z=0.029) Seyfert 2 galaxy IRAS 04507+0358, by constraining the amount of
intrinsic absorption (NH) and thus the intrinsic luminosity. To this end we
obtained deep (100 ks) Suzaku observations (AO4 call) and performed a joint fit
with SWIFT-BAT data. We analyzed XMM-Newton, Suzaku and SWIFT-BAT data and we
present here the results of this broad-band (0.4-100 keV) spectral analysis. We
found that the broad-band X-ray emission of IRAS 04507+0358 requires a large
amount of absorption (larger than 1e24 cm^-2) to be well reproduced, thus
confirming the Compton-thick nature of this source. In particular, the most
probable scenario is that of a mildly (NH (1.3-1.5)x1e24 cm^-2, L(2-10 keV)
(5-7)x1e43 erg s^-1) Compton-thick AGN.Comment: Accepted for publication in A&A; 8 pages, 7 figure
XMM-Newton spectroscopy of an X-ray selected sample of RL AGNs
This paper presents the X-ray spectroscopy of an X-ray selected sample of 25
radio-loud (RL) AGNs extracted from the XBSS sample. The main goal is to study
the origin of the X-ray spectral differences usually observed between
radio-loud and radio-quiet (RQ) AGNs. To this end, a comparison sample of 53 RQ
AGNs has been also extracted from the same XBSS sample and studied together
with the sample of RL AGNs. We have focused the analysis on the distribution of
the X-ray spectral indices of the power-law component that models the large
majority of the spectra in both samples. We find that the mean X-ray energy
spectral index is very similar in the 2 samples and close to alpha_X~1.
However, the intrinsic distribution of the spectral indices is significantly
broader in the sample of RL AGNs. In order to investigate the origin of this
difference, we have divided the RL AGNs into blazars and ``non-blazars'', on
the basis of the available optical and radio information. We find strong
evidence that the broad distribution observed in the RL AGN sample is mainly
due to the presence of the blazars. Furthermore, within the blazar class we
have found a link between the X-ray spectral index and the value of the
radio-to-X-ray spectral index suggesting that the observed X-ray emission is
directly connected to the emission of the relativistic jet. This trend is not
observed among the ``non-blazars'' RL AGNs. This favours the hypothesis that,
in these latter sources, the X-ray emission is not significantly influenced by
the jet emission and it has probably an origin similar to the RQ AGNs. Overall,
the results presented here indicate that the observed distribution of the X-ray
spectral indices in a given sample of RL AGNs is strongly dependent on the
amount of relativistic beaming present in the selected sources.Comment: 18 pages, 10 figures, accepted for publication in A&
Unveiling the parent population of beamed narrow-line Seyfert 1s
Narrow-line Seyfert 1 galaxies (NLS1s) are active galactic nuclei (AGN)
recently identified as a new class of -ray sources. The high energy
emission is explained by the presence of a relativistic jet observed at small
angles, just like in the case of blazars. When the latter are observed at
larger angles they appear as radio-galaxies, but an analogue parent population
for beamed NLS1s has not yet been determined. In this work we analyze this
problem by studying the physical properties of three different samples of
parent sources candidates: steep-spectrum radio-loud NLS1s, radio-quiet NLS1s,
and disk-hosted radio-galaxies, along with compact steep-spectrum sources. In
our approach, we first derived black hole mass and Eddington ratio from the
optical spectra, then we investigated the interaction between the jet and the
narrow-line region from the [O III] 4959,5007 lines. Finally,
the radio luminosity function allowed us to compare their jet luminosity and
hence determine the relations between the samples.Comment: 6 pages, no figures. Proceedings of the 28th Texas Symposium, Geneva,
December 13-18, 201
What is in a radio loud NLS1?
A fraction of Narrow Line Seyfert 1 galaxies (NLS1) are hosted by galaxies
that present a disturbed morphology, in some cases hinting for merger
processes, that are putative sources of gas replenishment. We have been
investigating the poorly studied population of radio loud NLS1 (RL-NLS1)
showing a flat radio spectrum, assumed to be the manifestation of the presence
of a radio jet. In some of the objects the infrared emission is well fitted by
a combination of an AGN component and an "active" host galaxy component like
M82, the estimate SFR being in the LIRG/ULIRG range (10-500 Msun/year). In
order to better characterize that component, we have been investigating the
sub-millimeter/millimeter emission of the sources using APEX. Here we present
the results concerning a pilot sample of 2 representative objects.Comment: 5 pages, published on Proceedings of Science - volume "Revisiting
narrow-line Seyfert 1 galaxies and their place in the Universe
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