16 research outputs found
Chandra Detection of Intra-cluster X-ray sources in Virgo
We present a survey of X-ray point sources in the nearest and dynamically
young galaxy cluster, Virgo, using archival Chandra observations that sample
the vicinity of 80 early-type member galaxies. The X-ray source populations at
the outskirt of these galaxies are of particular interest. We detect a total of
1046 point sources (excluding galactic nuclei) out to a projected
galactocentric radius of 40 kpc and down to a limiting 0.5-8 keV
luminosity of . Based on the cumulative
spatial and flux distributions of these sources, we statistically identify
120 excess sources that are not associated with the main stellar content
of the individual galaxies, nor with the cosmic X-ray background. This excess
is significant at a 3.5 level, when Poisson error and cosmic variance
are taken into account. On the other hand, no significant excess sources are
found at the outskirt of a control sample of field galaxies, suggesting that at
least some fraction of the excess sources around the Virgo galaxies are truly
intra-cluster X-ray sources. Assisted with ground-based and HST optical imaging
of Virgo, we discuss the origins of these intra-cluster X-ray sources, in terms
of supernova-kicked low-mass X-ray binaries (LMXBs), globular clusters, LMXBs
associated with the diffuse intra-cluster light, stripped nucleated dwarf
galaxies and free-floating massive black holes.Comment: 29 pages, 8 figures. Accepted for publication in ApJ. Comments
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NOEMA Detection of Circumnuclear Molecular Gas in X-ray Weak Dual Active Galactic Nuclei: No Evidence for Heavy Obscuration
Dual active galactic nuclei (AGN), which are the manifestation of two
actively accreting supermassive black holes (SMBHs) hosted by a pair of merging
galaxies, are a unique laboratory for studying the physics of SMBH feeding and
feedback during an indispensable stage of galaxy evolution. In this work, we
present NOEMA CO(2-1) observations of seven kpc-scale dual-AGN candidates drawn
from a recent Chandra survey of low-redshift, optically classified AGN pairs.
These systems are selected because they show unexpectedly low 2-10 keV X-ray
luminosities for their small physical separations signifying an
intermediate-to-late stage of merger. Circumnuclear molecular gas traced by the
CO(2-1) emission is significantly detected in 6 of the 7 pairs and 10 of the 14
nuclei, with an estimated mass ranging between . The primary nuclei, i.e., the ones with the higher
stellar velocity dispersion, tend to have a higher molecular gas mass than the
secondary. Most CO-detected nuclei show a compact morphology, with a velocity
field consistent with a kpc-scale rotating structure. The inferred hydrogen
column densities range between ,
but mostly at a few times , in broad agreement with those
derived from X-ray spectral analysis. Together with the relatively weak
mid-infrared emission, the moderate column density argues against the
prevalence of heavily obscured, intrinsically luminous AGNs in these seven
systems, but favors a feedback scenario in which AGN activity triggered by a
recent pericentric passage of the galaxy pair can expel circumnuclear gas and
suppress further SMBH accretion.Comment: 12 pages, 3 figures, 2 tables. Accepted for publication in ApJ.
Comments welcom
X-Ray Constraints on the Hot Gaseous Corona of Edge-on Late-type Galaxies in Virgo
We present a systematic study of the putative hot gas corona around late-type
galaxies (LTGs) residing in the Virgo cluster, based on archival Chandra
observations. Our sample consists of 21 nearly edge-on galaxies representing a
star formation rate (SFR) range of () a stellar mass
() range of , the majority of which
have not been explored with high-sensitivity X-ray observations so far.
Significant extraplanar diffuse X-ray (0.5-2 keV) emission is detected in only
three LTGs, which are also the three galaxies with the highest SFR. A stacking
analysis is performed for the remaining galaxies without individual detection,
dividing the whole sample into two subsets based on SFR, stellar mass, or
specific SFR. Only the high-SFR bin yields a significant detection, which has a
value of per galaxy. The stacked
extraplanar X-ray signals of the Virgo LTGs are consistent with the empirical
and relations found among highly inclined disk
galaxies in the field, but appear to be systematically lower than that of a
comparison sample of simulated cluster star-formation galaxies identified from
the Illustris-TNG100 simulation. The apparent paucity of hot gas coronae in the
sampled Virgo LTGs might be understood as the net outcome of the long-lasting
effect of ram pressure stripping exerted by the hot intra-cluster medium and
in-disk star-forming activity acting on shorter timescales. A better
understanding of the roles of environmental effects in regulating the hot gas
content of cluster galaxies invites sensitive X-ray observations for a large
galaxy sample.Comment: 18 pages, 7 figures. Accepted for publication in ApJ. Comments
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An X-Ray Census of Active Galactic Nuclei in the Virgo and Fornax Clusters of Galaxies with SRG/eROSITA
We present a uniform and sensitive X-ray census of active galactic nuclei (AGNs) in the two nearest galaxy clusters, Virgo and Fornax, utilizing the newly released X-ray source catalogs from the first all-sky scan of Spectrum-Roentgen-Gamma/eROSITA. A total of 50 and 10 X-ray sources are found positionally coincident with the nuclei of member galaxies in Virgo and Fornax, respectively, down to a 0.2β2.3 keV luminosity of βΌ10 ^39 erg s ^β1 and reaching out to a projected distance well beyond the virial radius of both clusters. The majority of the nuclear X-ray sources are newly identified. There is weak evidence that the nuclear X-ray sources are preferentially found in late-type hosts. Several hosts are dwarf galaxies with a stellar mass below βΌ10 ^9 M _β . We find that contamination by nonnuclear X-ray emission can be neglected in most cases, indicating the dominance of a genuine AGN. In the meantime, no nuclear X-ray source exhibits a luminosity higher than a few times 10 ^41 erg s ^β1 , which might be owing to a steep intrinsic luminosity function. The X-ray AGN occupation rate is only βΌ3% in both clusters, apparently much lower than that in field galaxies inferred from previous X-ray studies. Both aspects suggest that the cluster environment effectively suppresses AGN activity. The findings of this census have important implications for the interplay between galaxies and their central massive black holes in cluster environments