69,571 research outputs found
Similarity solutions of Reaction-Diffusion equation with space- and time-dependent diffusion and reaction terms
We consider solvability of the generalized reaction-diffusion equation with
both space- and time-dependent diffusion and reaction terms by means of the
similarity method. By introducing the similarity variable, the
reaction-diffusion equation is reduced to an ordinary differential equation.
Matching the resulting ordinary differential equation with known exactly
solvable equations, one can obtain corresponding exactly solvable
reaction-diffusion systems. Several representative examples of exactly solvable
reaction-diffusion equations are presented.Comment: 11 pages, 4 figure
The CO Tully-Fisher Relation and Implications for the Host Galaxies of High-Redshift Quasars
The integrated line width derived from CO spectroscopy provides a powerful
tool to study the internal kinematics of extragalactic objects, including
quasars at high redshift, provided that the observed line width can be properly
translated to more conventionally used kinematical parameters of galaxies. We
show, through construction of a K-band CO Tully-Fisher relation for nearby
galaxies spanning a wide range in infrared luminosity, that the CO line width
measured at 20% of the peak intensity, when corrected for inclination and other
effects, successfully recovers the maximum rotation velocity of the disk. The
line width at 50% of the peak intensity performs much more poorly, in large
part because CO lines have a wide range of profiles, which are shown to vary
systematically with infrared luminosity. We present a practical prescription
for converting observed CO line widths into the stellar velocity dispersion of
the bulge (sigma), and then apply it to a sample of low-redshift (z < 0.2) and
high-redshift (1.4 < z < 6.4) quasars to study their host galaxies. Nearby
quasars roughly fall on the correlation between black hole mass and bulge
stellar velocity dispersion established for inactive galaxies, but the host
galaxies of the high-z quasars systematically deviate from the local M_BH-sigma
relation. At a given sigma, high-z quasars have black hole masses larger by a
factor of 4 relative to local galaxies, suggesting that early in the life-cycle
of galaxies the development of the bulge lags behind the growth of the central
black hole. An alternative explanation for these observations, which currently
cannot be ruled out rigorously, is that high-redshift quasars are
preferentially viewed at face-on orientations.Comment: To appear in ApJ; 10 page
Young Star Clusters in Starburst Environments
Recent high-resolution observations with the Hubble Space Telescope (HST)
reveal that young star clusters of extraordinary luminosity and compactness
("super star clusters") are commonly found in starburst systems. Cluster
formation appears to be a dominant mode of star formation in starbursts. The
principal properties of the young clusters are summarized. A new ultraviolet
HST imaging survey of the central regions of nearby galaxies indicates that
young clusters form in a wide range of environments. Circumnuclear star-forming
rings, in particular, are richly populated with clusters, and several examples
from recent imaging studies are discussed. There has been much speculation that
super star clusters represent present-day analogs of young globular clusters. I
will present evidence suggesting that at least some super star clusters indeed
have masses and mass densities comparable to those of evolved globular clusters
in the Milky Way.Comment: Invited paper to appear in Rev. Mex. Astr. Astrofis. (1996),
proceedings of Starburst Activity in Galaxies, ed. J. Franco, R. Terlevich,
and G. Tenorio-Tagle. LaTex, 9 pages, including 1 postcript figure.
rmaaconf.sty macros included. 3 greyscale figures (Fig. 1-3) here as jpegs,
or in compressed PostScript at ftp://cfa0.harvard.edu/outgoing/lho/clusters/
(mget fig*ps.Z
On the Relationship Between Radio Emission and Black Hole Mass in Galactic Nuclei
We use a comprehensive database of black hole masses and nuclear luminosities
to investigate the relationship between radio emission and black hole mass. Our
sample covers a wide range of nuclear activity, from nearby inactive nuclei to
classical Seyfert 1 nuclei and luminous quasars. Contrary to some previous
studies, we find that the radio continuum power, either integrated for the
entire galaxy or isolated for the core, correlates poorly with black hole mass.
The degree of nuclear radio loudness, parameterized by the radio-to-optical
luminosity ratio R, also shows no clear dependence on black hole mass.
Radio-loud nuclei exist in galaxies with a wide range of black hole mass, from
\~ 10^6 to a few X 10^9 solar masses, and in a variety of hosts, from
disk-dominated spirals to giant ellipticals. We demonstrate that R is strongly
inversely correlated with L/L_E, the ratio of nuclear luminosity to the
Eddington luminosity, and hence with mass accretion rate. Most or all of the
weakly active nuclei in nearby galaxies are radio-loud, highly sub-Eddington
systems that are plausibly experiencing advection-dominated accretion.Comment: To appear in ApJ. 14 page
Optical Spectroscopy of LINERs and Low-Luminosity Seyfert Nuclei
An unprecedentedly large number of LINERs has been discovered in a recently
completed optical spectroscopic survey of nearby galaxies, allowing several
statistical properties of the host galaxies and of the line-emitting regions to
be examined reliably for the first time. As a consequence of the many
detections and some revised classifications, the detailed demographics of
emission-line nuclei have been updated from those given in older surveys.
Consistent with previous studies, it is found that LINERs are extremely common
in the present epoch, comprising approximately 1/3 of all galaxies with B <=
12.5 mag. If all LINERs are nonstellar in origin, then they are the dominant
constituents of the active galactic nucleus population. Many fundamental
characteristics of LINERs closely resemble those of low-luminosity Seyfert
nuclei, although several aspects of their narrow-line regions appear to differ
in a systematic manner. These differences could hold important clues to the key
parameters controlling the ionization level in active nuclei. Lastly, a
substantial fraction of LINERs has been found to contain a broad-line region,
yielding direct evidence, at least in these objects, of a physical link between
LINERs and classical Seyfert 1 nuclei and QSOs.Comment: Invited review paper to appear in The Physics of LINERs in View of
Recent Observations, ed. M. Eracleous, A. P. Koratkar, L. C. Ho, and C.
Leitherer (San Francisco: ASP), in press. LaTex, 29 pages. ASP Conference
Series macros include
A criterion for finite rank -Toeplitz operators
Let be a complex number in the closed unit disc , and be a separable Hilbert space with the orthonormal basis, say,
. A bounded operator on is called
a -Toeplitz operator if (where
is the inner product on ). The subject
arises naturally from a special case of the operator equation S^*AS=\lambda
A+B,\ \mbox{where $S$ is a shift on $\cal H$}, which plays an essential role
in finding bounded matrix on that solves the system of
equations for all ,
where , , , are bounded matrices on
and . It is also clear that the well-known
Toeplitz operators are precisely the solutions of , when is the
unilateral shift. In this paper we verify some basic issues, such as
boundedness and compactness, for -Toeplitz operators and, our main
result is to give necessary and sufficient conditions for finite rank
-Toeplitz operators
The Central Engines of Low-Luminosity AGNs
I summarize the main characteristics of AGNs in nearby galaxies and present a
physical picture of their central engines.Comment: To appear in Active Galactic Nuclei: from Central Engine to Host
Galaxy, ed. S. Collin, F. Combes, & I. Shlosman (San Francisco: ASP), in
pres
The Carnegie Observatories Astrophysics Series
On the occasion of the Centennial of the Carnegie Institution of Washington,
Carnegie Observatories held a series of four astrophysics symposia in Pasadena
from October 2002 to February 2003. The topics of the symposia were:
(1) Coevolution of Black Holes and Galaxies [Ed. L. C. Ho]
(2) Measuring and Modeling the Universe [Ed. W. L. Freedman]
(3) Clusters of Galaxies: Probes of Cosmological Structure and Galaxy
Evolution [Ed. J. S. Mulchaey, A. Dressler, and A. Oemler]
(4) Origin and Evolution of the Elements [Ed. A. McWilliam and M. Rauch]
The invited papers of the symposia, which have been peer-reviewed and
carefully edited, will be published in 2004 by Cambridge University Press, as
the first four volumes of the Carnegie Observatories Astrophysics Series. The
papers from the contributed talks and posters, along with the full set of the
invited papers, are available electronically at
http://www.ociw.edu/ociw/symposia/series/. The purpose of this note is to alert
the community of the availability of this resource.Comment: The Carnegie Observatories Astrophysics Series is available online at
http://www.ociw.edu/ociw/symposia/series
Origin and Dynamical Support of Ionized Gas in Galaxy Bulges
We combine ionized gas ([N II] 6583) and stellar central velocity dispersions
for a sample of 345 galaxies, with and without active galactic nuclei (AGNs),
to study the dynamical state of the nuclear gas and its physical origin. The
gas dispersions strongly correlate with the stellar dispersions over the
velocity range of 30-350 km/s such that sigma_g/sigma_* ~ 0.6-1.4, with an
average value of 0.80. These results are independent of Hubble type (for
galaxies from E to Sbc), presence or absence of a bar, or local galaxy
environment. For galaxies of type Sc and later and that have sigma_* < 40 km/s,
the gas seems to have a minimum threshold of sigma_g ~ 30 km/s, such that
sigma_g/sigma_* always exceeds 1. Within the sample of AGNs, sigma_g/sigma_*
increases with nuclear luminosity or Eddington ratio, a possible manifestation
of AGN feedback associated with accretion disk winds or outflows. This extra
source of nongravitational line broadening should be removed when trying to use
sigma_g to estimate sigma_*. We show that the mass budget of the narrow-line
region can be accounted for by mass loss from evolved stars. The kinematics of
the gas, dominated by random motions, largely reflect the velocity field of the
hot gas in the bulge. Lastly, we offer a simple explanation for the correlation
between line width and line luminosity observed in the narrow-line region of
AGNs.Comment: To appear in ApJ, 11 pages, 6 figure
Bulge and Halo Kinematics Across the Hubble Sequence
The correlation between the maximum rotational velocity of the disk (v_m) and
the central stellar velocity dispersion of the bulge (sigma) offers insights
into the relationship between the halo and the bulge. We have assembled
integrated H I line widths and central stellar velocity dispersions to study
the v_m-sigma relation for 792 galaxies spanning a broad range of Hubble types.
Contrary to earlier studies based on much smaller samples, we find that the
v_m-sigma relation exhibits significant intrinsic scatter and that its
zeropoint varies systematically with galaxy morphology, bulge-to-disk ratio,
and light concentration, as expected from basic dynamical considerations.
Nucleated but bulgeless late-type spiral galaxies depart significantly from the
v_m-sigma relation. While these results render questionable any attempt to
supplant the bulge with the halo as the fundamental determinant of the central
black hole mass in galaxies, the observed distribution of v_m/sigma, which
depends on both the density profile and kinematic structure of the galaxy,
offers a useful constraint on galaxy formation models. With the aid of a
near-infrared Tully-Fisher relation, we identify a population of otherwise
normal, luminous galaxies that have exceptionally low values of v_m/sigma. We
argue that a significant fraction of the H I gas in these kinematically
anomalous objects is dynamically unrelaxed, having been acquired externally
either through capture from tidal interactions or through cold accretion from
the intergalactic medium.Comment: 17 pages. To appear in Ap
- âŠ