664 research outputs found
X-ray Photons in the CO 2-1 'Lacuna' of NGC 2110
A recent ALMA study of the Seyfert 2 Active Galactic Nucleus (AGN) NGC 2110
by Rosario et al. (2019) has reported a remarkable lack of CO 2-1 emission from
the circumnuclear region, where optical lines and H2 emission are observed,
leading to the suggestion of excitation of the molecular clouds by the AGN.
Since interaction with X-ray photons could be the cause of this excitation, we
have searched the archival Chandra data for corroborating evidence. We report
an extra-nuclear ~1'' (~170 pc) feature found in the soft (<1.0 keV) Chandra
data of the Seyfert 2 Active Galactic Nucleus (AGN) NGC 2110. This feature is
elongated to the north of the nucleus and its shape matches well that of the
optical lines and H2 emission observed in this region, which is devoid of CO
2-1 emission. The Chandra image completes the emerging picture of a multi-phase
circumnuclear medium excited by the X-rays from the AGN, with dense warm
molecular clouds emitting in H2 but depleted of CO 2-1 emission.Comment: ApJ Letters - in pres
Multiphase gas flows in the nearby Seyfert galaxy ESO428-G14
We present ALMA rest-frame 230 GHz continuum and CO(2-1) line observations of
the nearby Compton-thick Seyfert galaxy ESO428-G14, with angular resolution 0.7
arcsec (78 pc). We detect CO(2-1) emission from spiral arms and a
circum-nuclear ring with 200 pc radius, and from a transverse gas lane with
size of pc, which crosses the nucleus and connects the two portions
the circumnuclear ring. The molecular gas in the host galaxy is distributed in
a rotating disk with intrinsic circular velocity km/s,
inclination deg, and dynamical mass within a radius of kpc. In the inner 100 pc region CO is
distributed in a equatorial bar, whose kinematics is highly perturbed and
consistent with an inflow of gas towards the AGN. This inner CO bar overlaps
with the most obscured, Compton-thick region seen in X-rays. We derive a column
density of in this region,
suggesting that molecular gas may contribute significantly to the AGN
obscuration. We detect a molecular outflow with a total outflow rate , distributed along a bi-conical structure with
size of pc on both sides of the AGN. The bi-conical outflow is also
detected in the emission line at 2.12 m, which traces a warmer
nuclear outflow located within 170 pc from the AGN. This suggests that the
outflow cools with increasing distance from the AGN. We find that the hard
X-ray emitting nuclear region mapped with Chandra is CO-deprived, but filled
with warm molecular gas traced by - thus confirming that the hard
(3-6 keV) continuum and Fe K emission are due to scattering from dense
neutral clouds in the ISM.Comment: Submitted to Ap
New flaring of an ultraluminous X-ray source in NGC 1365
We have studied a highly variable ultraluminous X-ray source (ULX) in the
Fornax galaxy NGC 1365, with a series of 12 Chandra and XMM-Newton observations
between 2002 and 2006. In 2006 April, the source peaked at a luminosity ~ 3 x
10^{40} erg/s in the 0.3-10 keV band (similar to the maximum luminosity found
by ASCA in 1995), and declined on an e-folding timescale ~ 3 days. The X-ray
spectrum is always dominated by a broad power-law-like component. When the
source is seen at X-ray luminosities ~ 10^{40} erg/s, an additional soft
thermal component (which we interpret as emission from the accretion disk)
contributes ~ 1/4 of the X-ray flux; when the luminosity is higher, ~ 3 x
10^{40} erg/s, the thermal component is not detected and must contribute < 10%
of the flux. At the beginning of the decline, ionized absorption is detected
around 0.5-2 keV; it is a possible signature of a massive outflow. The
power-law is always hard, with a photon index Gamma ~ 1.7 (and even flatter at
times), as is generally the case with bright ULXs. We speculate that this
source and perhaps most other bright ULXs are in a high/hard state: as the
accretion rate increases well above the Eddington limit, more and more power is
extracted from the inner region of the inflow through non-radiative channels,
and is used to power a Comptonizing corona, jet or wind. The observed thermal
component comes from the standard outer disk; the transition radius between
outer standard disk and Comptonizing inner region moves further out and to
lower disk temperatures as the accretion rate increases. This produces the
observed appearance of a large, cool disk. Based on X-ray luminosity and
spectral arguments, we suggest that this accreting black hole has a likely mass
~ 50-150 Msun (even without accounting for possible beaming).Comment: 14 pages, to appear in MNRA
Hidden AGNs in Early-Type Galaxies
We present a stacking analysis of the complete sample of Early Type Galaxies
(ETGs) in the \textit{Chandra} COSMOS (C-COSMOS) survey, to explore the nature
of the X-ray luminosity in the redshift and stellar luminosity ranges
and {10}^{9}. Using established
scaling relations, we subtract the contribution of X-ray binary populations, to
estimate the combined emission of hot ISM and AGN. To discriminate between the
relative importance of these two components, we (1) compare our results with
the relation observed in the local universe for
hot gaseous halos emission in ETGs, and (2) evaluate the spectral signature of
each stacked bin. We find two regimes where the non-stellar X-ray emission is
hard, consisten t with AGN emission. First, there is evidence of hard, absorbed
X-ray emission in stacked bins including relatively high z () ETGs
with average high X-ray luminosity (L_{X-LMXB}\gtrsim 6\times{10}^{42}\mbox{
erg}/\mbox{s}). These luminosities are consistent with the presence ofhighly
absorbed "hidden" AGNs in these ETGs, which are not visible in their optical-IR
spectra and spectral energy distributions. Second, confirming the early
indication from our C-COSMOS study of X-ray detected ETGs, we find
significantly enhanced X-ray luminoaity in lower stellar mass ETGs
(L_K\lesssim{10}^{11}L_{\astrosun}), relative to the local
relation. The stacked spectra of these ETGs also
suggest X-ray emission harder than expected from gaseous hot halos. This
emission is consistent with inefficient accretion
onto M_{BH}\sim
{10}^{6}-{10}^{8}\,M_{\astrosun}.Comment: 22 pages, 7 figures, 2 tables. Accepted for publications on Ap
A sample of X-ray emitting normal galaxies from the BMW -- HRI Catalogue
We have obtained a sample of 143 normal galaxies with X-ray luminosity in the
range erg s from the cross-correlation of the ROSAT
HRI Brera Multi-scale Wavelet (BMW -- HRI) Catalogue with the Lyon-Meudon
Extragalactic Database (LEDA). We find that the average X-ray properties of
this sample are in good agreement with those of other samples of galaxies in
the literature. We have selected a complete flux limited serendipitous sample
of 32 galaxies from which we have derived the logN-logS distribution of normal
galaxies in the flux range erg cm s.
The resulting distribution is consistent with the euclidean -1.5 slope.
Comparisons with other samples, such as the Extended Medium Sensitivity Survey,
the ROSAT All Sky Survey, the XMM - Newton/2dF survey and the Chandra Deep
Field Survey indicate that the logN-logS distribution of normal galaxies is
consistent with an euclidean slope over a flux range of about 6 decades.Comment: Accepted for publication in A&A. 19 pages, 7 figures. Full resolution
version of Figure 2 is available at http://www.brera.mi.astro.it/~tajer
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