554 research outputs found
Secular Evolution in Disk Galaxies: Pseudobulge Growth and the Formation of Spheroidal Galaxies
Updating Kormendy & Kennicutt (2004, ARAA, 42, 603), we review internal
secular evolution of galaxy disks. One consequence is the growth of
pseudobulges that often are mistaken for true (merger-built) bulges. Many
pseudobulges are recognizable as cold, rapidly rotating, disky structures.
Bulges have Sersic function brightness profiles with index n > 2; most
pseudobulges have n <= 2. Recognition of pseudobulges makes the biggest problem
with cold dark matter galaxy formation more acute: How can hierarchical
clustering make so many pure disk galaxies with no evidence for merger-built
bulges? E. g., the giant Scd galaxies M101 and NGC 6946 have rotation
velocities of V ~ 200 km/s but nuclear star clusters with velocity dispersions
of 25 to 40 km/s. Within 8 Mpc of us, 11 of 19 galaxies with V > 150 km/s show
no evidence for a classical bulge, while only 7 are ellipticals or have
classical bulges. It is hard to understand how bulgeless galaxies could form as
the quiescent tail of a distribution of merger histories. Our second theme is
environmental secular evolution. We confirm that spheroidal galaxies have
fundamental plane (FP) correlations that are almost perpendicular to those for
bulges and ellipticals. Spheroidals are not dwarf ellipticals. Rather, their
structural parameters are similar to those of late-type galaxies. We suggest
that spheroidals are defunct late-type galaxies transformed by internal
processes such as supernova-driven gas ejection and environmental processes
such as secular harassment and ram-pressure stripping. Minus spheroidals, the
FP of ellipticals and bulges has small scatter. With respect to these,
pseudobulges are larger and less dense.Comment: 11 pages, 6 Postscript figures; requires asp2006.sty; as published,
except with updated references; for a version with full resolution figures,
see http://chandra.as.utexas.edu/~kormendy/kormendy-rome.pd
The structure of the central disk of NGC 1068: a clumpy disk model
NGC 1068 is one of the best studied Seyfert II galaxies, for which the
blackhole mass has been determined from the Doppler velocities of water maser.
We show that the standard -disk model of NGC 1068 gives disk mass
between the radii of 0.65 pc and 1.1 pc (the region from which water maser
emission is detected) to be about 7x10 M (for ), more
than four times the blackhole mass, and a Toomre Q-parameter for the disk is
0.001. This disk is therefore highly self-gravitating and is subject to
large-amplitude density fluctuations. We conclude that the standard
-viscosity description for the structure of the accretion disk is
invalid for NGC 1068.
In this paper we develop a new model for the accretion disk. The disk is
considered to be composed of gravitationally bound clumps; accretion in this
clumped disk model arises because of gravitational interaction of clumps with
each other and the dynamical frictional drag exerted on clumps from the stars
in the central region of the galaxy. The clumped disk model provides a
self-consistent description of the observations of NGC 1068. The computed
temperature and density are within the allowed parameter range for water maser
emission, and the rotational velocity in the disk falls off as .Comment: To appear in Ap
The Accuracy of Morphological Decomposition of Active Galactic Nucleus Host Galaxies
In order to assess the accuracy with which we can determine the morphologies
of AGN host galaxies, we have simulated more than 50,000 ACS images of galaxies
with z < 1.25, using image and noise properties appropriate for the GOODS
survey. We test the effect of central point-source brightness on host galaxy
parameter recovery with a set of simulated AGN host galaxies made by adding
point sources to the centers of normal galaxies. We extend this analysis and
also quantify the recovery of intrinsic morphological parameters of AGN host
galaxies with a set of fully simulated inactive and AGN host galaxies.
We can reliably separate good from poor fit results using a combination of
reasonable error cuts, in the regime where L_{host}:L_{PS} > 1:4. We give
quantitative estimates of parameter errors as a function of
host-to-point-source ratio. In general, we separate host and point-source
magnitudes reliably at all redshifts; point sources are well recovered more
than 90% of the time, although spurious detection of central point sources can
be as high as 25% for bulge-dominated sources. We find a general correlation
between Sersic index and intrinsic bulge-to-total ratio, such that a host
galaxy with Sersic n < 1.5 generally has at least 80% of its light from a disk
component. Likewise, "bulge-dominated" galaxies with n > 4 typically derive at
least 70% of their total host galaxy light from a bulge, but this number can be
as low as 55%. Single-component Sersic fits to an AGN host galaxy are
statistically very reliable to z < 1.25 (for ACS survey data like ours). In
contrast, two-component fits involving separate bulge and disk components tend
to over-estimate the bulge fraction by ~10%, with uncertainty of order 50%.Comment: 45 pages, 20 figures, submitted to ApJ ; Accepted Version --
additions to introduction and conclusions; title changed, was "Simulations of
AGN Host Galaxy Morphologies
Orbit-Based Dynamical Models of the Sombrero Galaxy (NGC 4594)
We present axisymmetric, orbit-based models to study the central black hole,
stellar mass-to-light ratio, and dark matter halo of NGC 4594 (M104, the
Sombrero Galaxy). For stellar kinematics, we use published high-resolution
kinematics of the central region taken with the Hubble Space Telescope, newly
obtained Gemini long-slit spectra of the major axis, and integral field
kinematics from the SAURON instrument. At large radii, we use globular cluster
kinematics to trace the mass profile and apply extra leverage to recovering the
dark matter halo parameters. We find a black hole of mass M_{\bullet}=(6.6 +/-
0.4) x 10^8 M_{\odot}, and determine the stellar M/L_I=3.4 +/- 0.05
(uncertainties are the 68% confidence band marginalized over the other
parameters). Our best fit dark matter halo is a cored logarithmic model with
asymptotic circular speed V_c=376 +/- 12 km/s and core radius r_c= 4.7 +/- 0.6
kpc. The fraction of dark to total mass contained within the half-light radius
is 0.52. Taking the bulge and disk components into account in our calculation
of \sigma_e puts NGC 4594 squarely on the M-\sigma relation. We also determine
that NGC 4594 lies directly on the M-L relation.Comment: 13 pages, 10 figures, accepted for publication in Ap
Keplerian Motion of Broad-Line Region Gas as Evidence for Supermassive Black Holes in Active Galactic Nuclei
Emission-line variability data on NGC 5548 argue strongly for the existence
of a mass of order 7 x 10^7 solar masses within the inner few light days of the
nucleus in the Seyfert 1 galaxy NGC 5548. The time-delayed response of the
emission lines to continuum variations is used to infer the size of the
line-emitting region, and these determinations are combined with measurements
of the Doppler widths of the variable line components to estimate a virial
mass. The data for several different emission lines spanning an order of
magnitude in distance from the central source show the expected V proportional
to r^{-1/2} correlation and are consistent with a single value for the mass.Comment: 9 pages, 2 Figures. accepted by ApJ Letter
Thermal evolution of the primordial clouds in warm dark matter models with keV sterile neutrinos
We analyze the processes relevant for star formation in a model with dark
matter in the form of sterile neutrinos. Sterile neutrino decays produce an
X-ray background radiation that has a two-fold effect on the collapsing clouds
of hydrogen. First, the X-rays ionize the gas and cause an increase in the
fraction of molecular hydrogen, which makes it easier for the gas to cool and
to form stars. Second, the same X-rays deposit a certain amount of heat, which
could, in principle, thwart the cooling of gas. We find that, in all the cases
we have examined, the overall effect of sterile dark matter is to facilitate
the cooling of gas. Hence, we conclude that dark matter in the form of sterile
neutrinos can help the early collapse of gas clouds and the subsequent star
formation.Comment: aastex, 31 pages, 4 figures; one figure and some references added,
minor changes in the text; to appear in Astrophysical Journa
Virial Masses of Black Holes from Single Epoch Spectra of AGN
We describe the general problem of estimating black hole masses of AGN by
calculating the conditional probability distribution of M_BH given some set of
observables. Special attention is given to the case where one uses the AGN
continuum luminosity and emission line widths to estimate M_BH, and we outline
how to set up the conditional probability distribution of M_BH given the
observed luminosity, line width, and redshift. We show how to combine the broad
line estimates of M_BH with information from an intrinsic correlation between
M_BH and L, and from the intrinsic distribution of M_BH, in a manner that
improves the estimates of M_BH. Simulation was used to assess how the
distribution of M_BH inferred from the broad line mass estimates differs from
the intrinsic distribution, and we find that this can lead to an inferred
distribution that is too broad. We use these results and a sample of 25 sources
that have recent reverberation mapping estimates of AGN black hole masses to
investigate the effectiveness of using the C IV emission line to estimate M_BH
and to indirectly probe the C IV region size--luminosity (R--L) relationship.
We estimated M_BH from both C IV and H-Beta for a sample of 100 sources,
including new spectra of 29 quasars. We find that the two emission lines give
consistent estimates if one assumes R \propto L^{1/2}_{UV} for both lines.Comment: 38 pages, 6 figures, accepted by Ap
A Log-Quadratic Relation Between the Nuclear Black-Hole Masses and Velocity Dispersions of Galaxies
We demonstrate that a log-linear relation does not provide an adequate
description of the correlation between the masses of Super-Massive Black-Holes
(SMBH, M_bh) and the velocity dispersions of their host spheroid (sigma). An
unknown relation between log(M_bh) and log(sigma) may be expanded to second
order to obtain a log-quadratic relation of the form log(M_bh)=alpha+beta
log(sigma/200) + beta_2[log(sigma/200)]^2. We perform a Bayesian analysis using
the Nuker sample, and solve for beta, beta_2 and alpha, in addition to the
intrinsic scatter (delta). We find unbiased parameter estimates of
beta=4.2+/-0.37, beta_2=1.6+/-1.3 and delta=0.275+/-0.05. At the 80% level the
M_bh-sigma relation does not follow a uniform power-law. Indeed, over the
velocity range 70km/s<sigma<380km/s the logarithmic slope of the best fit
relation varies between 2.7 and 5.1, which should be compared with a power-law
estimate of 4.02+/-0.33. Assuming no systematic offset, single epoch virial
SMBH masses estimated for AGN follow the same log-quadratic M_bh-sigma relation
as the Nuker sample, but extend it downward in mass by an order of magnitude.
The log-quadratic term in the M_bh-sigma relation has a significant effect on
estimates of the local SMBH mass function at M_bh>10^9 solar masses, leading to
densities of SMBHs with M_bh>10^10 solar masses that are several orders of
magnitude larger than inferred from a log-linear relation. We also estimate
unbiased parameters for the SMBH-bulge mass relation. With a parameterisation
log(M_bh)=alpha_b + beta_b log(M_b/10^{11}) + beta_2b[log(M_b/10^{11})]^2, we
find beta_b=1.15+/-0.18 and beta_2b=0.12+/-0.14. We determined an intrinsic
scatter delta_b=0.41+/-0.07 which is ~50% larger than the scatter in the
M_bh-sigma relation.Comment: 21 pages, 14 figures. Replaced to correct errors in published versio
On the unification of dwarf and giant elliptical galaxies
The near orthogonal distributions of dwarf elliptical (dE) and giant
elliptical (E) galaxies in the mu_e-Mag and mu_e-log(R_e) diagrams have been
interpreted as evidence for two distinct galaxy formation processes. However,
continuous, linear relationships across the alleged dE/E boundary at M_B = -18
mag - such as those between central surface brightness (mu_0) and (i) galaxy
magnitude and (ii) light-profile shape (n) - suggest a similar, governing
formation mechanism. Here we explain how these latter two linear trends
necessitate a different behavior for dE and E galaxies, exactly as observed, in
diagrams involving mu_e (and also _e). A natural consequence is that the
distribution of dEs and Es in Fundamental Plane type analyses that use the
associated intensity I_e, or _e, are expected to appear different. Together
with other linear trends across the alleged dE/E boundary, such as those
between luminosity and color, metallicity, and velocity dispersion, it appears
that the dEs form a continuous extension to the E galaxies. The presence of
partially depleted cores in luminous (M_B < -20.5 mag) Es does however signify
the action of a different physical process at the centers (< ~300 pc) of these
galaxies.Comment: 5 pages from the proceedings of the 2004 conference "Penetrating bars
through masks of cosmic dust: the Hubble tuning fork strikes a new note".
Edited by D. L. Block, I. Puerari, K. C. Freeman, R. Groess, and E. K. Bloc
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