16,831 research outputs found
The Black Hole Mass Scale of Classical and Pseudo Bulges in Active Galaxies
The mass estimator used to calculate black hole (BH) masses in broad-line
active galactic nuclei (AGNs) relies on a virial coefficient (the " factor")
that is determined by comparing reverberation-mapped (RM) AGNs with measured
bulge stellar velocity dispersions against the relation
of inactive galaxies. It has recently been recognized that only classical
bulges and ellipticals obey a tight relation;
pseudobulges have a different zero point and much larger scatter. Motivated by
these developments, we reevaluate the factor for RM AGNs with available
measurements, updated H RM lags, and new bulge
classifications based on detailed decomposition of high-resolution ground-based
and space-based images. Separate calibrations are provided for the two bulge
types, whose virial coefficients differ by a factor of :
for classical bulges and ellipticals and for pseudobulges. The
structure and kinematics of the broad-line region, at least as crudely encoded
in the factor, seems to related to the large-scale properties or formation
history of the bulge. Lastly, we investigate the bulge stellar masses of the RM
AGNs, show evidence for recent star formation in the AGN hosts that correlates
with Eddington ratio, and discuss the potential utility of the relation as a more promising alternative to the
conventionally used relation for future refinement of the
virial mass estimator for AGNs.Comment: 2014, ApJ, 789, 1
Magellan Spectroscopy of Low-Redshift Active Galactic Nuclei
We present an atlas of moderate-resolution (R ~ 1200-1600) optical spectra of
94 low-redshift (z < 0.5) active galactic nuclei taken with the Magellan 6.5 m
Clay Telescope. The spectra mostly cover the rest-frame region 3600-6000 Ang.
All the objects have preexisting Hubble Space Telescope imaging, and they were
chosen as part of an ongoing program to investigate the relationship between
black hole mass and their host galaxy properties. A significant fraction of the
sample has no previous quantitative spectroscopic measurements in the
literature. We perform spectral decomposition of the spectra and present
detailed fits and basic measurements of several commonly used broad and narrow
emission lines, including [O II] 3727, He II 4686, Hbeta, and [O III] 4959,
5007. Eight of the objects are narrow-line sources that were previously
misclassified as broad-line (type 1) Seyfert galaxies; of these, five appear
not to be accretion-powered.Comment: To appear in ApJS, 25 page
Correlation between Galaxy Mergers and Luminous AGN
It is not yet clear what triggers the activity of active galactic nuclei
(AGNs), but galaxy merging has been suspected to be one of the main mechanisms
fuelling the activity. Using deep optical images taken at various ground-based
telescopes, we investigate the fraction of galaxy mergers in 39 luminous AGNs
(M -22.6 mag) at 0.3 (a median redshift of 0.155), of
which the host galaxies are generally considered as early-type galaxies.
Through visual inspection of the images, we find that 17 of 39 AGN host
galaxies (43.6%) show the evidence for current or past mergers like tidal
tails, shells, and disturbed morphology. In order to see if this fraction is
abnormally high, we also examined the merging fraction of normal early-type
galaxies in the Sloan Digital Sky Survey (SDSS) Strip 82 data (a median
redshift of 0.04), of which the surface-brightness limit is comparable to our
imaging data. To correct for the effects related to the redshift difference of
the two samples, we performed an image simulation by putting a bright point
source as an artificial AGN in the images of SDSS early-type galaxies and
placing them onto the redshifts of AGNs. The merging fraction in this realistic
sample of simulated AGNs is only ( to of that of
real AGNs). Our result strongly suggests that luminous AGN activity is
associated with galaxy merging.Comment: 57 pages, 19 figures, published in Astrophysical Journa
Dipole-interacting Fermionic Dark Matter in positron, antiproton, and gamma-ray channels
Cosmic ray signals from dipole-interacting dark matter annihilation are
considered in the positron, antiproton and photon channels. The predicted
signals in the positron channel could nicely account for the excess of positron
fraction from Fermi LAT, PAMELA, HEAT and AMS-01 experiments for the dark
matter mass larger than 100 GeV with a boost (enhancement) factor of 30-80. No
excess of antiproton over proton ratio at the experiments also gives a severe
restriction for this scenario. With the boost factors, the predicted signals
from Galactic halo and signals as mono-energetic gamma-ray lines (monochromatic
photons) for the region close to the Galactic center are investigated. The
gamma-ray excess of recent tentative analyses based on Fermi LAT data and the
potential probe of the monochromatic lines at a planned experiment, AMS-02, are
also considered.Comment: Version to be published in PRD(2013), Title changed, text modifie
Stellar Photometric Structures of the Host Galaxies of Nearby Type 1 Active Galactic Nuclei
We present detailed image analysis of rest-frame optical images of 235
low-redshift ( 0.35) type 1 active galactic nuclei (AGNs) observed with
the Hubble Space Telescope. The high-resolution images enable us to perform
rigorous two-dimensional image modeling to decouple the luminous central point
source from the host galaxy, which, when warranted, is further decomposed into
its principal structural components (bulge, bar, and disk). In many cases, care
must be taken to account for structural complexities such as spiral arms, tidal
features, and overlapping or interacting companion galaxies. We employ Fourier
modes to characterize the degree of asymmetry of the light distribution of the
stars, as a quantitative measure of morphological distortion due to
interactions or mergers. We examine the dependence of the physical parameters
of the host galaxies on the properties of the AGNs, namely radio-loudness and
the width of the broad emission lines. In accordance with previous studies,
narrow-line (H FWHM km~s) type 1 AGNs, in contrast to
their broad-line (H FWHM km~s) counterparts, are
preferentially hosted in later type, lower luminosity galaxies, which have a
higher incidence of pseudo-bulges, are more frequently barred, and are less
morphologically disturbed. This suggests narrow-line type 1 AGNs experienced a
more quiescent evolutionary history driven primarily by internal secular
evolution instead of external dynamical perturbations. The fraction of AGN
hosts showing merger signatures is larger for more luminous sources. Radio-loud
AGNs generally preferentially live in earlier type (bulge-dominated), more
massive hosts, although a minority of them appears to contain a significant
disk component. We do not find convincing evidence for enhanced merger
signatures in the radio-loud population.Comment: Published in ApJ
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