869 research outputs found
Detection of Faint BLR Components in the Starburst/Seyfert Galaxy NGC 6221 and Measure of the Central BH Mass
In the last decade, using single epoch virial based techniques in the optical
band, it has been possible to measure the central black hole mass on large AGN1
samples. However these measurements use the width of the broad line region as a
proxy of the virial velocities and are therefore difficult to be carried out on
those obscured (type 2) or low luminosity AGN where the nuclear component does
not dominate in the optical. Here we present the optical and near infrared
spectrum of the starburst/Seyfert galaxy NGC 6221, observed with X-shooter/VLT.
Previous observations of NGC 6221 in the X-ray band show an absorbed (N_H=8.5
+/- 0.4 x 10^21 cm^-2) spectrum typical of a type 2 AGN with luminosity
log(L_14-195 keV) = 42.05 erg/s, while in the optical band its spectrum is
typical of a reddened (A_V=3) starburst. Our deep X-shooter/VLT observations
have allowed us to detect faint broad emission in the H_alpha, HeI and Pa_beta
lines (FWHM ~1400-2300 km/s) confirming previous studies indicating that NGC
6221 is a reddened starburst galaxy which hosts an AGN. We use the measure of
the broad components to provide a first estimate of its central black hole mass
(M_BH = 10^(6.6 +/- 0.3) Msol, lambda_Edd=0.01-0.03), obtained using recently
calibrated virial relations suitable for moderately obscured (N_H<10^24 cm^-2)
AGN.Comment: 13 pages, 3 figures, 1 table. Published in Frontiers in Astronomy and
Space Science
Compton thick AGN in the NuSTAR era
We present the 2-100 keV spectral analysis of 30 candidate Compton thick
(CT-) active galactic nuclei (AGN) selected in the Swift-BAT 100-month survey.
The average redshift of these objects is 0.03 and they
all lie within 500 Mpc. We used the MyTorus (Murphy et al. 2009) model to
perform X-ray spectral fitting both without and with the contribution of the
NuSTAR data in the 3-50 keV energy range. When the NuSTAR data are added to the
fit, 14 out of 30 of these objects (47% of the whole sample) have intrinsic
absorption N3 confidence level,
i.e., they are re-classified from Compton thick to Compton thin. Consequently,
we infer an overall observed fraction of CT-AGN with respect to the whole AGN
population lower than the one reported in previous works, and as low as
4%. We find evidence that this over-estimation of N is likely
due to the low quality of a subsample of spectra, either in the 2-10 keV band
or in the Swift-BAT one.Comment: 19 pages, 10 figures, accepted for publication on the Astrophysical
Journa
Extending Virial Black Hole Mass Estimates to Low-Luminosity or Obscured AGN: the cases of NGC 4395 and MCG -01-24-012
In the last decade, using single epoch (SE) virial based spectroscopic
optical observations, it has been possible to measure the black hole (BH) mass
on large type 1 Active Galactic Nuclei (AGN) samples. However this kind of
measurements can not be applied on those obscured type 2 and/or low luminosity
AGN where the nuclear component does not dominate in the optical. We have
derived new SE relationships, based on the FWHM and luminosity of the broad
line region component of the Pabeta emission line and/or the hard X-ray
luminosity in the 14-195 keV band, which have the prospect of better working
with low luminosity or obscured AGN. The SE relationships have been calibrated
in the 10^5-10^9 M_sol mass range, using a sample of AGN whose BH masses have
been previously measured using reverberation mapping techniques. Our tightest
relationship between the reverberation-based BH mass and the SE virial product
has an intrinsic spread of 0.20 dex. Thanks to these SE relations, in agreement
with previous estimates, we have measured a BH mass of M_BH =1.7^+1.3_-0.7 X
10^5 M_sol for the low luminosity, type 1, AGN NGC 4395 (one of the smallest
active galactic BH known). We also measured, for the first time, a BH mass of
M_BH = 1.5^+1.1_-0.6 X 10^7 M_sol for the Seyfert 2 galaxy MCG -01-24-012.Comment: 10 pages, 7 figures. Accepted by MNRA
Compton-thick AGN in the NuSTAR era III: A systematic study of the torus covering factor
We present the analysis of a sample of 35 candidate Compton thick (CT-)
active galactic nuclei (AGNs) selected in the nearby Universe (average redshift
~0.03) with the Swift-BAT 100-month survey. All sources have available
NuSTAR data, thus allowing us to constrain with unprecedented quality important
spectral parameters such as the obscuring torus line-of-sight column density
(N_{H, z}), the average torus column density (N_{H, tor}) and the torus
covering factor (f_c). We compare the best-fit results obtained with the widely
used MyTorus (Murphy et al. 2009) model with those of the recently published
borus02 model (Balokovic et al. 2018) used in the same geometrical
configuration of MyTorus (i.e., with f_c=0.5). We find a remarkable agreement
between the two, although with increasing dispersion in N_{H, z} moving towards
higher column densities. We then use borus02 to measure f_c. High-f_c sources
have, on average, smaller offset between N_{H, z} and N_{H, tor} than low-f_c
ones. Therefore, low f_c values can be linked to a "patchy torus" scenario,
where the AGN is seen through an over-dense region in the torus, while high-f_c
objects are more likely to be obscured by a more uniform gas distribution.
Finally, we find potential evidence of an inverse trend between f_c and the AGN
2-10 keV luminosity, i.e., sources with higher f_c values have on average lower
luminosities.Comment: 35 Pages, 23 Figures. Accepted for publication in Ap
Multiple AGN in the crowded field of the compact group SDSSJ0959+1259
We present a multi-wavelength study of a newly discovered compact group (CG),
SDSS J0959+1259, based data from XMM-Newton, SDSS and the Calar Alto optical
imager BUSCA. With a maximum velocity offset of 500 km s, a mean
redshift of 0.035, and a mean spatial extension of 480 kpc, this CG is
exceptional in having the highest concentration of nuclear activity in the
local Universe, established with a sensitivity limit L10
erg s in 2--10 keV band and R-band magnitude . The group is
composed of two type-2 Seyferts, one type-1 Seyfert, two LINERs and three star
forming galaxies. Given the high X-ray luminosity of LINERs which reaches erg s, it is likely that they are also accretion driven,
bringing the number of active nuclei in this group to to 5 out of 8 (AGN
fraction of 60\%). The distorted shape of one member of the CG suggests that
strong interactions are taking place among its galaxies through tidal forces.
Therefore, this system represents a case study for physical mechanisms that
trigger nuclear activity and star formation in CGs.Comment: 8 pages, 4 figures and 4 tables. Accepted for publication in MNRA
Investigating the complex X-ray spectrum of a broad-line 2MASS red quasar: XMM-Newton observation of FTM 0830+3759
We report results from a 50 ks XMM-Newton observation of the dust-reddened
broad-line quasar FTM 0830+3759 (z=0.413) selected from the FIRST/2MASS Red
Quasar survey. For this AGN, a very short 9 ks Chandra exposure had suggested a
feature-rich X-ray spectrum and HST images revealed a very disturbed host
galaxy morphology. Contrary to classical, optically-selected quasars, the X-ray
properties of red (i.e. with J-Ks> 1.7 and R-Ks> 4) broad line quasars are
still quite unexplored, although there is a growing consensus that, due to
moderate obscuration, these objects can offer a unique view of spectral
components typically swamped by the AGN light in normal, blue quasars. The
XMM-Newton observation discussed here has definitely confirmed the complexity
of the X-ray spectrum revealing the presence of a cold (or mildly-ionized)
absorber with Nh ~10^{22} cm^-2 along the line of sight to the nucleus and a
Compton reflection component accompanied by an intense Fe K emission line in
this quasar with a Lum(2-10) ~5 x 10^{44} erg/s. A soft-excess component is
also required by the data. The match between the column density derived by our
spectral analysis and that expected on the basis of reddening due to the dust
suggests the possibility that both absorptions occur in the same medium. FTM
0830+3759 is characterized by an extinction/absorption-corrected
X-ray-to-optical flux ratio alphaox = -2.3, that is steeper than expected on
the basis of its UV luminosity. These findings indicate that the X-ray
properties of FTM 0830+3759 differs from those typically observed for
optically-selected broad line quasars with comparable hard X-ray luminosity.Comment: Accepted for publication in Ap
NGC 1275: An Outlier of the Black Hole-Host Scaling Relations
The active galaxy NGC 1275 lies at the center of the Perseus cluster of
galaxies, being an archetypal BH-galaxy system that is supposed to fit
well with the M-BH-host scaling relations obtained for quiescent
galaxies. Since it harbors an obscured AGN, only recently our group has
been able to estimate its black hole mass. Here our aim is to pinpoint
NGC 1275 on the less dispersed scaling relations, namely the
M-BH-sigma(*) and M-BH - L-bul planes. Starting from our previous work
(Ricci et al., 2017a), we estimate that NGC 1275 falls well outside the
intrinsic dispersion of the M-BH-sigma(*) plane being 1.2 dex (in
black hole mass) displaced with respect to the scaling relations. We
then perform a 2D morphological decomposition analysis on Spitzer/IRAC
images at 3.6 mu m and find that, beyond the bright compact nucleus that
dominates the central emission, NGC 1275 follows a de Vaucouleurs
profile with no sign of significant star formation nor clear merger
remnants. Nonetheless, its displacement on the M-BH - L-3.6,L-bul plane
with respect to the scaling relation is as high as observed in the
M-BH-sigma(*). We explore various scenarios to interpret such
behaviors, of which the most realistic one is the evolutionary pattern
followed by NGC 1275 to approach the scaling relation. We indeed
speculate that NGC 1275 might be a specimen for those galaxies in which
the black holes adjusted to its host
X-ray redshifts for obscured AGN: a case study in the J1030 deep field
We present a procedure to constrain the redshifts of obscured ( cm) Active Galactic Nuclei (AGN) based on low-count statistics
X-ray spectra, which can be adopted when photometric and/or spectroscopic
redshifts are unavailable or difficult to obtain. We selected a sample of 54
obscured AGN candidates on the basis of their X-ray hardness ratio, ,
in the Chandra deep field (479 ks, 335 arcmin) around the QSO
SDSS J1030+0524. The sample has a median value of net counts in the
0.5-7 keV energy band. We estimate reliable X-ray redshift solutions taking
advantage of the main features in obscured AGN spectra, like the Fe 6.4 keV
K emission line, the 7.1 keV Fe absorption edge and the
photoelectric absorption cut-off. The significance of such features is
investigated through spectral simulations, and the derived X-ray redshift
solutions are then compared with photometric redshifts. Both photometric and
X-ray redshifts are derived for 33 sources. When multiple solutions are derived
by any method, we find that combining the redshift solutions of the two
techniques improves the rms by a factor of two. Using our redshift estimates
(), we derived absorbing column densities in the
range cm and absorption-corrected, 2-10 keV
rest-frame luminosities between and erg s, with
median values of cm and erg s, respectively. Our results suggest that
the adopted procedure can be applied to current and future X-ray surveys, for
sources detected only in the X-rays or that have uncertain photometric or
single-line spectroscopic redshifts.Comment: 22 pages, 18 figure
X-ray properties and obscured fraction of AGN in the J1030 Chandra field
The 500ks Chandra ACIS-I observation of the field around the quasar
SDSS J1030+0524 is currently the 5th deepest extragalactic X-ray survey. The
rich multi-band coverage of the field allowed for an effective identification
and redshift determination of the X-ray source counterparts: to date a catalog
of 243 extragalactic X-ray sources with either a spectroscopic or photometric
redshift estimate in the range is available over a 355 arcmin
area. Given its depth and the multi-band information, this catalog is an
excellent resource to investigate X-ray spectral properties of distant Active
Galactic Nuclei (AGN) and derive the redshift evolution of their obscuration.
We performed a thorough X-ray spectral analysis for each object in the sample,
measuring its nuclear column density and intrinsic (de-absorbed)
2-10 keV rest-frame luminosity, . Whenever possible, we also used the
presence of the Fe K emission line to improve the photometric redshift
estimates. We measured the fractions of AGN hidden by column densities in
excess of and cm ( and ,
respectively) as a function of and redshift, and corrected for
selection effects to recover the intrinsic obscured fractions. At ,
we found and , respectively, in broad
agreement with the results from other X-ray surveys. No significant variations
with X-ray luminosity were found within the limited luminosity range probed by
our sample (log). When focusing on luminous AGN with
log to maximize the sample completeness up to large
cosmological distances, we did not observe any significant change in
or over the redshift range . Nonetheless, the obscured
fractions we measure are significantly higher than ...Comment: A&A, in pres
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