58 research outputs found
Was 49b: An Overmassive AGN in a Merging Dwarf Galaxy?
We present a combined morphological and X-ray analysis of Was 49, an
isolated, dual AGN system notable for the presence of a dominant AGN Was 49b in
the disk of the primary galaxy Was 49a, at a projected radial distance of 8 kpc
from the nucleus. Using X-ray data from Chandra, NuSTAR, and Swift, we find
that this AGN has a bolometric luminosity of L_bol ~ 2 x 10^45 erg/s, with a
black hole mass of M_BH=1.3^{+2.9}_{-0.9} x 10^8 M_Sol. Despite its large mass,
our analysis of optical data from the Discovery Channel Telescope shows that
the supermassive black hole is hosted by a stellar counterpart with a mass of
only 5.6^{+4.9}_{-2.6} x 10^9 M_Sol, making the SMBH potentially larger than
expected from SMBH-galaxy scaling relations, and the stellar counterpart
exhibits a morphology that is consistent with dwarf elliptical galaxies. Our
analysis of the system in the r and K bands indicates that Was 49 is a minor
merger, with a mass ratio of Was 49a to Was 49b between 1:7 and 1:15. This is
in contrast with findings that the most luminous merger-triggered AGNs are
found in major mergers, and that minor mergers predominantly enhance AGN
activity in the primary galaxy.Comment: 11 pages, 6 figures, accepted for publication in Ap
Radio-Optical Reference Catalog, version 1
The fundamental celestial reference frame (CRF) is based on two catalogs of
astrometric positions, the third realization of the International Celestial
Reference Frame (ICRF3), and the much larger Gaia~CRF, built from the third
data release (DR3). The objects in common between these two catalogs are mostly
distant AGNs and quasars that are both sufficiently optically bright for Gaia
and radio-loud for the VLBI. This limited collection of reference objects is
crucially important for the mutual alignment of the two CRFs and maintenance of
all the other frames and coordinate systems branching from the ICRF. In this
paper, we show that the three components of ICRF3 (S/X, K, and X/Ka band
catalogs) have significantly different sky-correlated vector fields of position
offsets with respect to Gaia~DR3. When iteratively expanded in the vector
spherical harmonics up to degree 4 on a carefully vetted set of common sources,
each of these components includes several statistically significant terms. The
median sky-correlated offsets from the Gaia positions are found to be 56
as for the S/X, 100 as for the K, and 324 as for the Ka
catalogs. The weighted mean vector field is subtracted from the Gaia reference
positions, while the deviations from that field are added to each of the ICRF3
components. The corrected positions from each of the four input catalogs are
combined into a single weighted mean catalog, which we propose to be the
current most accurate realization of an inertial radio-optical CRF.Comment: To be published in A
Buried AGNs in Advanced Mergers:Mid-infrared color selection as a dual AGN finder
A direct consequence of hierarchical galaxy formation is the existence of
dual supermassive black holes (SMBHs), which may be preferentially triggered as
active galactic nuclei (AGN) during galaxy mergers. Despite decades of
searching, however, dual AGNs are extremely rare, and most have been discovered
serendipitously. Using the all-sky WISE survey, we identified a population of
over 100 morphologically identified interacting galaxies or mergers that
display red mid-infrared colors often associated in extragalactic sources with
powerful AGNs. The vast majority of these advanced mergers are optically
classified as star-forming galaxies suggesting that they may represent an
obscured population of AGNs that cannot be found through optical studies. In
this work, we present Chandra/ACIS observations and near-infrared spectra with
the Large Binocular Telescope of six advanced mergers with projected pair
separations less than ~ 10 kpc. The combined X-ray, near-infrared, and
mid-infrared properties of these mergers provide confirmation that four out of
the six mergers host at least one AGN, with four of the mergers possibly
hosting dual AGNs with projected separations less than ~10 kpc, despite showing
no firm evidence for AGNs based on optical spectroscopic studies. Our results
demonstrate that 1) optical studies miss a significant fraction of single and
dual AGNs in advanced mergers, and 2) mid-infrared pre-selection is extremely
effective in identifying dual AGN candidates in late-stage mergers. Our
multi-wavelength observations suggest that the buried AGNs in these mergers are
highly absorbed, with intrinsic column densities in excess of N_H >10^24cm^-2,
consistent with hydrodynamic simulations.Comment: 23 pages, 11 figures, accepted for publication to Ap
No Small Scale Radio Jets Here: Multi-Epoch Observations of Radio Continuum Structures in NGC 1068 with the VLBA
We present recent Very Long Baseline Array (VLBA) 5 GHz radio observations of
the nearby, luminous Seyfert 2 galaxy NGC 1068 for comparison to similar VLBA
observations made on 1997 April 26. By cross-correlating the positions of
emitting regions across both epochs, we find that spatially-resolved
extra-nuclear radio knots in this system have sub-relativistic transverse
speeds (v < 0.1c). We discuss sources of the observed knots and how the radio
emission relates to additional phases of gas in the central ~150 pcs of this
system. We suggest that the most likely explanation for the observed emission
is synchrotron radiation formed by shocked host media via interactions between
AGN winds and the host environment.Comment: 13 pages, 4 figures, accepted for publication in Ap
Buried Black Hole Growth in IR-selected Mergers: New Results from Chandra
Observations and theoretical simulations suggest that a significant fraction
of merger-triggered accretion onto supermassive black holes is highly obscured,
particularly in late-stage galaxy mergers, when the black hole is expected to
grow most rapidly. Starting with the Wide-Field Infrared Survey Explorer
all-sky survey, we identified a population of galaxies whose morphologies
suggest ongoing interaction and which exhibit red mid-infrared colors often
associated with powerful active galactic nuclei (AGNs). In a follow-up to our
pilot study, we now present Chandra/ACIS and XMM-Newton X-ray observations for
the full sample of the brightest 15 IR-preselected mergers. All mergers reveal
at least one nuclear X-ray source, with 8 out of 15 systems exhibiting dual
nuclear X-ray sources, highly suggestive of single and dual AGNs. Combining
these X-ray results with optical line ratios and with near-IR coronal emission
line diagnostics, obtained with the near-IR spectrographs on the Large
Binocular Telescope, we confirm that 13 out of the 15 mergers host AGNs, two of
which host dual AGNs. Several of these AGNs are not detected in the optical.
All X-ray sources appear X-ray weak relative to their mid-infrared continuum,
and of the nine X-ray sources with sufficient counts for spectral analysis,
eight reveal strong evidence of high absorption with column densities of
~cm. These observations demonstrate that a
significant population of single and dual AGNs are missed by optical studies,
due to high absorption, adding to the growing body of evidence that the epoch
of peak black hole growth in mergers occurs in a highly obscured phase.Comment: 29 pages, 22 figures; (Main text: 17 pages, 4 figures
CLASS Survey Description: Coronal Line Needles in the SDSS Haystack
Coronal lines are a powerful, yet poorly understood, tool to identify and
characterize Active Galactic Nuclei (AGNs). There have been few large scale
surveys of coronal lines in the general galaxy population in the literature so
far. Using a novel pre-selection technique with a flux-to-RMS ratio ,
followed by Markov-Chain Monte Carlo (MCMC) fitting, we searched for the full
suite of 20 coronal lines in the optical spectra of almost 1 million galaxies
from the Sloan Digital Sky Survey (SDSS) Data Release 8. We present a catalog
of the emission line parameters for the resulting 258 galaxies with detections.
The Coronal Line Activity Spectroscopic Survey (CLASS) includes line
properties, host galaxy properties, and selection criteria for all galaxies in
which at least one line is detected. This comprehensive study reveals that a
significant fraction of coronal line activity is missed in past surveys based
on a more limited set of coronal lines; 60% of our sample do not display
the more widely surveyed [Fe X] 6374. In addition, we discover a
strong correlation between coronal line and WISE W2 luminosities, suggesting
that the mid-infrared flux can be used to predict coronal line fluxes. For each
line we also provide a confidence level that the line is present, generated by
a novel neural network, trained on fully simulated data. We find that after
training the network to detect individual lines using 100,000 simulated
spectra, we achieve an overall true positive rate of 75.49% and a false
positive rate of only 3.96%.Comment: 27 pages, 16 figures, 4 table
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