Astrophysics astro-ph new abstracts 7 Sep 2000
Astrophysics
astro-ph new abstracts, Thu, 7 Sep 00 04:00:11 GMT
0009078 — 0009101 received
astro-ph/0009078 [abs, src, ps, other] :
Title: High Spatial Resolution Imaging of NGC 1068 in the Mid Infrared
Authors:
J.J. Bock,
G. Neugebauer,
K. Matthews,
B.T. Soifer,
E.E. Becklin M. Ressler,
K. Marsh,
M.W. Werner,
E. Egami,
R.D. Blandford
Comments: 42 pages, 2 tables, 9 figures; Accepted for publication in AJ
Mid-infrared observations of the central source of NGC 1068 have been
obtained with a spatial resolution in the deconvolved image of 0.1″ (~ 7pc).
The central source is extended by ~1″ in the north-south direction but appears
unresolved in the east-west direction over most of its length. About two-thirds
of its flux can be ascribed to a core structure which is itself elongated
north-south and does not show a distinct unresolved compact source. The source
is strongly asymmetric, extending significantly further to the north than to
the south. The morphology of the mid-infrared emission appears similar to that
of the radio jet, and has features which correlate with the images in [O III].
Its 12.5-24.5 micron color temperature ranges from 215 to 260 K and does not
decrease smoothly with distance from the core. Silicate absorption is strongest
in the core and to the south and is small in the north.
The core, apparently containing two-thirds of the bolometric luminosity of
the inner 4″ diameter area, may be explained by a thick, dusty torus near the
central AGN viewed at an angle of ~65 deg to its plane. There are, however,
detailed difficulties with existing models, especially the narrow east-west
width of the thin extended mid-infrared “tongue” to the north of the core. We
interpret the tongue as re-processed visual and ultraviolet radiation that is
strongly beamed and that originates in the AGN.
(175kb)
astro-ph/0009079 [abs, src, ps, other] :
Title: Constraints on the Inner Mass Profiles of Lensing Galaxies from Missing
Odd Images
Authors:
D. Rusin,
Chung-Pei Ma (U. Penn.)
Comments: 13 pages, including 4 figures, ApJL submitted
Most gravitational lens systems consist of two or four observable images. The
absence of detectable odd images allows us to place a lower limit on the
power-law slope of the inner mass profile of lensing galaxies. Using a sample
of six two-image radio-loud lens systems and assuming a singular power-law
surface density [Sigma propto r^(-beta)] for the inner several kpc of the mass
distribution, we find a statistical bound of beta >= 0.94 at 68% and beta >=
0.84 at 95%. Furthermore, individual mass modeling using elliptical deflectors
yields beta >= 0.85 for B0739+366 and beta >= 0.91 for B1030+074. Modeling
central black holes as additional point masses changes the constraints in these
systems only slightly to beta >= 0.84 and beta >= 0.82, respectively. The inner
mass profiles of lensing galaxies are therefore not much shallower than
isothermal.
(531kb)
astro-ph/0009080 [abs, src, ps, other] :
Title: NVO and the LSB Universe
Authors:
James M. Schombert (UOregon)
Comments: NVO Workshop, Caltech, June 12-16, 2000, 6 pages, ASP Conf format
There is tremendous scientific potential in a National Virtual Observatory,
particularly for projects that need to mine large databases for rare or unusual
objects. However, the NVO will also make an impact on any project, large or
small, the requires a mixture of datasets to explore a wide range of
astrophysical phenomenon. In this article I discuss the influence of the NVO on
research into the formation and evolution of low surface brightness (LSB)
galaxies. In particular, I present the preliminary results from an NVO-style
project that combines the DPOSS and 2MASS datasets to search for giant disk
galaxies.
(277kb)
astro-ph/0009081 [abs, src, ps, other] :
Title: Ionized Gas in Damped Lyman Alpha Protogalaxies: I. Model-Independent
Inferences From Kinematic Data
Authors:
Arthur M. Wolfe (University of California, San Diego),
Jason X. Prochaska (The Observatories of the Carnegie Institute of Washington)
We investigate the kinematics of ionized and neutral gas in a sample of 35
damped Lyman alpha protogalaxies (DLAs) with HIRES on the Keck I 10 m
telescope. Velocity profiles with resolution of ~ 8 km/s are obtained for high
ions such as C IV and Si IV, and for intermediate ions such as Al III.
Combining these profiles with accurate low-ion (e.g., Fe II) profiles, we
investigate the kinematic state of DLAs in the redshift range 1.8 < z < 4.4 by
comparisons between data for various ion pairs.
We find the DLAs comprise distinct kinematic subsystems: a low ion subsystem
in which the low ions are physically associated with intermediate ions, and a
high subsystem containing neither low nor intermediate ions. The evidence for
two subsystems stems from (a) differences between the widths of the velocity
profiles, (b) misalignment in velocity space between the narrow components
comprising the profiles in each subsystem, and (c) significant dissimilarities
between the mean velocities of the high ion and low ion velocity profiles. In
every case we find that test statistics such as velocity width and various
asymmetry parameters distribute differently for low ions than for high ions.
Despite misalignment in velocity space, the low and high ion kinematic
subsystems are interrelated. This is indicated by detection of a statistically
significant C IV versus low-ion cross correlation function, and by a systematic
effect where the C IV velocity widths are greater than or equal to the low ion
velocity widths in 29 out of 32 systems. These phenomena are consistent with
the location of the two subsystems in the same potential well.
(206kb)
astro-ph/0009082 [abs, src, ps, other] :
Title: Ionized Gas in Damped Lyman Alpha Protogalaxies: II. Comparison Between
Models and the Kinematic Data
Authors:
Arthur M. Wolfe (University of California, San Diego),
Jason X. Prochaska (The Observatories of the Carnegie Institute of Washington)
We test semi-analytic models for galaxy formation with accurate kinematic
data of damped Lyman alpha protogalaxies (DLAs) presented in the companion
paper I. The models envisage centrifugally supported exponential disks at the
centers of dark matter halos which are filled with ionized gas undergoing
radial infall to the disks. The halo masses are drawn from cross-section
weighted mass distributions predicted by CDM cosmogonies, or by the null
hypothesis (TF model) that the dark matter mass distribution has not evolved
since z ~ 3. In our models, C IV absorption lines detected in DLAs arise in
infalling ionized clouds while the low-ion absorption lines arise from neutral
gas in the disks. Using Monte Carlo methods we find: (a) The CDM models are
incompatible with the low-ion statistics at more than 99% confidence whereas
some TF models cannot be excluded at more than 88% confidence. (b) Both CDM and
TF models agree with the observed distribution of C IV velocity widths. (c) The
CDM models generate differences between the mean velocities of C IV and low ion
profiles in agreement with the data, while the TF model produces differences in
the means that are too large. (d) Both CDM and TF models produce ratios of C IV
to low-ion velocity widths that are too large. (e) Both CDM and TF models
generate C IV versus low-ion cross-correlation functions incompatible with the
data.
While it is possible to select model parameters resulting in consistency with
the data, the disk-halo configuration assumed in both cosmogonies still does
not produce significant overlap in velocity space between C IV low-ion velocity
profiles. We conjecture that including angular momentum of the infalling clouds
will increase the overlap between C IV and low-ion profiles.
(143kb)
astro-ph/0009083 [abs, src, ps, other] :
Title: Red Quasars and Quasar Evolution: the Case of BALQSO FIRST
J155633.8+351758
Authors:
Joan Najita,
Arjun Dey,
Michael Brotherton (NOAO)
Comments: 23 pages, 4 embedded postscript figures; Accepted for publication in
The Astronomical Journal, December 2000
We present the first near-IR spectroscopy of the z=1.5 radio-loud BALQSO
FIRST J155633.8+351758. Both the Balmer decrement and the slope of the
rest-frame UV-optical continuum independently suggest a modest amount of
extinction along the line of sight to the BLR (E(B-V)~0.5 for SMC-type screen
extinction at the QSO redshift). The implied gas column density along the line
of sight is much less than is implied by the weak X-ray flux of the object,
suggesting that either the BLR and BAL region have a low dust-to-gas ratio, or
that the rest-frame optical light encounters significantly lower mean column
density lines of sight than the X-ray emission. From the rest-frame UV-optical
spectrum, we are able to constrain the stellar mass content of the system.
Comparing the maximal stellar mass with the black hole mass estimated from the
bolometric luminosity of the QSO, we find that the ratio of the black hole to
stellar mass may be comparable to the Magorrian value, which would imply that
the Magorrian relation is already in place at z=1.5. However, multiple factors
favor a much larger black hole to stellar mass ratio. This would imply that if
the Magorrian relation characterizes the late history of QSOs, and the
situation observed for F1556+3517 is typical of the early evolutionary history
of QSOs, central black hole masses develop more rapidly than bulge masses.
[ABRIDGED]
(134kb)
astro-ph/0009084 [abs, src, ps, other] :
Title: A grid of composite models for the simulation of the emission-line
spectra from the NLR of active galaxies
Authors:
M. Contini (Tel-Aviv University),
S.M. Viegas (IAG,USP)
Comments: 14 pages Latex + 2 Postscript tables + 1 Postscript figures
A grid of composite models for the narrow line region of active galaxies,
which consistently account for both the effect of a photoionizing radiation
from the active center and of a shock front, is presented. Theoretical results,
calculated with the SUMA code, are given for different values of shock
velocities, preshock densities, geometrical thickness of the clouds, and,
particularly, for the ionizing radiation intensity in a large range. The input
parameters are chosen within the ranges indicated by previous fits of several
observed emission-line and continuum spectra from active galaxies. Shock
velocities from 100 kms ~to 1500 kms ~and preshock densities from 100 cm3 to
1000 cm3 are considered. The line intensities of the most important
ultraviolet, optical and infrared transitions are obtained and are listed in
several tables.
(92kb)
astro-ph/0009085 [abs, src, ps, other] :
Title: On the Gas Surrounding High Redshift Galaxy Clusters
Authors:
Paul J. Francis (1),
Greg M. Wilson (1),
Bruce E. Woodgate (2) ((1) The Australian National University, (2) NASA GSFC)
Comments: 19 pages, 5 figures. Accepted for publication in PASA
Francis & Hewett (1993) identified two 10-Mpc scale regions of the high
redshift universe that were seemingly very overdense in neutral hydrogen.
Subsequent observations showed that at least one of these gas-rich regions
enveloped a cluster of galaxies at redshift 2.38. We present improved
observations of the three background QSOs with sightlines passing within a few
Mpc of this cluster of galaxies. All three QSOs show strong neutral hydrogen
absorption at the cluster redshift, suggesting that this cluster (and perhaps
all high redshift clusters) may be surrounded by a ~5 Mpc scale region
containing ~ 10^12 solar masses of neutral gas.
If most high redshift clusters are surrounded by such regions, we show that
the gas must be in the form of many small (< 1 kpc), dense (> 0.03 cm^-3)
clouds, each of mass < 10^6 solar masses. These clouds are themselves probably
gathered into > 20 kpc sized clumps, which may be galaxy halos or
protogalaxies.
If this gas exists, it will be partially photoionised by the UV background.
We predict the diffuse Ly-alpha flux from this photoionisation, and place
observational limits on its intensity.
(67kb)
astro-ph/0009086 [abs, src, ps, other] :
Title: The Maximum Effect of Thermal Instability on Galactic Outflows
Authors:
Yutaka Fujita (NAOJ)
Comments: 19 pages, 6 figures; to appear in ApJ
We have investigated steady, radial gas outflows (or winds) from galaxies and
the development of thermal instability in the hot gas. In order to see the
maximum influence of the instability on the global structure of the galactic
outflows, we study inhomogeneous comoving flows and the non-linear fate of the
fluctuations in the flows. We compare the results with solutions for
homogeneous flows. In the case of supersonic flows, the global structure of
inhomogeneous flows is not much different from that of homogeneous flows.
However, detailed investigation shows that the average density of inhomogeneous
flows decreases faster than that of homogeneous flows, because local thermal
instability removes overdense regions in the inhomogeneous flows and reduces
the mass flux. We also find that when the gravity of a galaxy is strong, the
cold clouds formed from the removed gas are distributed in the galactic halo.
In the case of subsonic flows, the form of inhomogeneous flows is different
from that of homogeneous flows near the regions where the flows terminate. The
density rise appearing near the regions where the homogeneous flows terminate
is not seen in the inhomogeneous flows because the local thermal instability
decreases the mass flux. The cold clouds formed through thermal instability in
the inhomogeneous flow almost all coast to the same maximum radius.
(99kb)
astro-ph/0009087 [abs, src, ps, other] :
Title: Magnetospheric Accretion and Winds on the T Tauri Star SU Aurigae:
Multi-Spectral Line Variability and Cross-Correlation Analysis
Authors:
J.M. Oliveira (ESTEC/ESA, CAUP Portugal),
B.H. Foing (ESTEC/ESA),
J.Th. van Loon (IoA Cambridge UK),
Y.C. Unruh (University of Vienna)
Comments: Accepted for publication in A&A Main Journal; 13 pages, 6 eps figures
SU Aurigae is a T Tauri star that was well monitored during the MUSICOS 96
multi-site campaign. We present the results of the spectroscopic analysis of
the circumstellar environment of this star, particularly of the Halpha, Hbeta,
Na I D and He I D3 line profiles. The signatures of modulated outflows and mass
accretion events are analysed, as well as transient spectral features. We
compute the cross-correlation function (CCF) of several pairs of (velocity bins
in) spectral lines to better investigate the profiles’ temporal variability. We
found increasing time lags between the variability of He I D3, Na I D and
Hbeta. We propose this may be understood in terms of azimuthal distortion of
the magnetic field lines due to the different rotation rates of the star and
the disk. We find the slightly blueshifted absorption features in Halpha, Hbeta
and Na I D to be anti-correlated with the accretion flow signatures. We propose
that the transient absorption features in the blue wings of Halpha, Hbeta and
Na I D (signatures of mass outflows), and flare brightenings are related to the
disruption of distorted magnetospheric field lines.
(350kb)
astro-ph/0009088 [abs, src, ps, other] :
Title: Two-Dimensional MHD Numerical Simulations of Magnetic Reconnection
Triggered by A Supernova Shock in Interstellar Medium, Generation of X-Ray
Gas in Galaxy
Authors:
Syuniti Tanuma (STEL),
Takaaki Yokoyama,
Takahiro Kudoh (NAOJ),
Kazunari Shibata (Kyoto Univ)
Comments: 17 pages using emulateapj.sty, 24 figures (4colors), submitted to
ApJ, mpeg simulations and psfiles are available at
this http URL
We examine the magnetic reconnection triggered by a supernova (or a point
explosion) in interstellar medium, by performing two-dimensional resistive
magnetohydrodynamic (MHD) numerical simulations with high spatial resolution.
We found that the magnetic reconnection starts long after a supernova shock
(fast-mode MHD shock) passes a current sheet. The current sheet evolves as
follows: (i) Tearing-mode instability is excited by the supernova shock, and
the current sheet becomes thin in its nonlinear stage. (ii) The current-sheet
thinning is saturated when the current-sheet thickness becomes comparable to
that of Sweet-Parker current sheet. After that, Sweet-Parker type reconnection
starts, and the current-sheet length increases. (iii) “Secondary tearing-mode
instability” occurs in the thin Sweet-Parker current sheet. (iv) As a result,
further current-sheet thinning occurs and anomalous resistivity sets in,
because gas density decreases in the current sheet. Petschek type reconnection
starts and heats interstellar gas. Magnetic energy is released quickly while
magnetic islands are moving in the current sheet during Petschek type
reconnection. The released magnetic energy is determined by the interstellar
magnetic field strength, not energy of initial explosion nor distance to
explosion. We suggest that magnetic reconnection is a possible mechanism to
generate X-ray gas in Galaxy.
(488kb)
astro-ph/0009089 [abs, src, ps, other] :
Title: On the matter entrainment by stellar jets and the acceleration of
molecular outflows
Authors:
M. Micono (1 and 2),
G. Bodo (1),
S. Massaglia (2),
P. Rossi (1),
A. Ferrari (1 and 2) ((1) Universita` di Torino, (2) Osservatorio Astronomico di Torino)
Comments: 9 pages containing 10 postscript figures; uses A&A macros. To appear
in Astronomy and Astrophysics
We study, by numerical simulations, the entrainment process in a supersonic,
radiative jet flow, during the evolution of Kelvin-Helmholtz instabilities, in
the context of the the acceleration problem of molecular bipolar outflows,
observed in Giant Molecular Clouds. Our results show that a large fraction of
the initial jet momentum can be transferred to the ambient medium by this
process. We therefore analyze in detail the instability evolution and compare
some of the main observational properties of molecular outflows with those of
the entrained material that we observe in our simulations. In particular, we
find a good agreement for the mass vs. velocity distribution and for the
outflow collimation structure, especially when a light jet is moving into a
denser ambient medium. This is probably the case for (obscured) optical jets
driving powerful molecular outflows in the denser environment of the inner
regions of molecular clouds.
(109kb)
astro-ph/0009090 [abs, src, ps, other] :
Title: The `Second Parameter’: A Memory from the Globular Cluster Formation
Epoch
Author:
Noam Soker,
Ron Hadar (Univ. of Haifa)
Comments: 11 pages, 4 figures, submitted to MNRAS
We study the correlations between the distribution of stars on the horizontal
branch (HB), the HB morphology, with some other properties of globular clusters
(GCs) in a large sample of GCs. We strengthen previous results that a general
correlation exists only between HB morphology and metallicity. Correlations
with other properties, e.g., central density and core radius, exist only for
GCs within a narrow metallicity range. We conjecture that the lack of
correlations with present properties of GCs (besides metallicity), is because
the variation of the HB morphologies between GCs having similar metallicities
is caused by a process, or processes, whose effect was determined at the
formation time of GCs. This process (or processes) is historically termed the
`second parameter’, metallicity being the `first parameter’. We then argue that
the `planet second parameter’ model, where the presence of planets and to a
lesser degree brown dwarfs and low mass main sequence stars is the `second
parameter’, fits this conjecture.
(27kb)
astro-ph/0009091 [abs, src, ps, other] :
Title: Neutral and ionized gas distribution in and around the radio galaxy Coma
A
Authors:
R. Morganti (NFRA),
T. Oosterloo (NFRA),
C.N. Tadhunter (Sheffield Univ.),
K. A. Wills (Sheffield Univ.)
Comments: To appear in the proceedings of the conference “Gas and Galaxy
Evolution” (ASP Conference Series), eds. J. Hibbard, M. Rupen, and J. van
Gorkom, 2 pages, 1 PS figure
HI absorption has been detected with the WSRT against both lobes of the radio
galaxy Coma A. This radio galaxy could be expanding in a particularly gas rich
environment, perhaps the result from interactions/mergers between the dominant
giant galaxy (associated with the radio galaxy) and less massive galaxies in
the same group.
(83kb)
astro-ph/0009092 [abs, src, ps, other] :
Title: Evolution of the X-ray luminosity and metallicity of starburst blown
superbubbles
Authors:
Sergey A. Silich (Main Astronomical Observatory Kiev Ukraine and INAOE Puebla Mexico),
Guillermo Tenorio-Tagle (INAOE),
Roberto Terlevich (IoA Cambridge UK),
Elena Terlevich (INAOE),
Hagai Netzer (School of Physics and Astronomy, Tel Aviv, Israel)
Comments: latex, 10 pages, 7 figures. Submitted to MNRAS on February 2000
We calculate the time-dependent metal production expected from starbursts and
use them as boundary conditions in our 2D simulations of evolving superbubbles.
We assume that the produced metals (oxygen and iron) thoroughly mix with the
ejected stellar envelopes, and/or with the matter thermally evaporated from the
superbubble cold outer shell. The metal production process determines the
time-dependent metallicity in hot superbubble interiors, and leads to values of
Z greater or equal than solar, when oxygen is used as tracer, and under-solar
when the metallicity is measured with respect to iron. In either case, the
enhanced metallicity boosts the X-ray emissivity of superbubbles, bringing
theory and observations closer together.
(72kb)
astro-ph/0009093 [abs, src, ps, other] :
Title: Medium Effects in Neutrino Cooling of Neutron Stars
Authors:
D.N. Voskresensky
Comments: Invited talk at Intern. Workshop on Phys. of Neutron Star Interiors,
Trento, June 2000; 30 pages
This review demonstrates that neutrino emission from dense hadronic component
in neutron stars is subject of strong modifications due to collective effects
in the nuclear matter. With the most important in-medium processes incorporated
in the cooling code an overall agreement with available soft $X$ ray data can
be easily achieved. With these findings so called “standard” and “non-standard”
cooling scenarios are replaced by one general “nuclear medium cooling scenario”
which relates slow and rapid neutron star coolings to the star masses (interior
densities). In-medium effects take important part also at early hot stage of
neutron star evolution decreasing the neutrino opacity for less massive and
increasing for more massive neutron stars. A formalism for calculation of
neutrino radiation from nuclear matter is presented that treats on equal
footing one-nucleon and multiple-nucleon processes as well as reactions with
resonance bosons and condensates.
(184kb)
astro-ph/0009094 [abs, src, ps, other] :
Title: Shocks and Nonthermal Processes in Clusters
Authors:
Craig L. Sarazin (Univ. Virginia)
Comments: To appear in Constructing the Universe with Clusters of Galaxies,
edited by F. Durret & D. Gerbal. 8 pages, LaTeX, iap2000 style, 9 Postscript
figures, some in color. A higher resolution gzip Postscript file is available
via ftp at this http URL
Clusters of galaxies generally form by the gravitational merger of smaller
clusters and groups. Major cluster mergers are the most energetic events in the
Universe since the Big Bang. Mergers drive shocks into the intracluster gas,
and these shocks heat the intracluster gas, and should also accelerate
nonthermal relativistic particles. The X-ray signatures of the thermal effects
of merger shocks will be discussed. X-ray observations of shocks can be used to
determine the geometry and kinematics of the merger. As a result of particle
acceleration in shocks, clusters of galaxies should contain very large
populations of relativistic electrons and ions. Electrons with Lorentz factors
gamma~300 (energies E = gamma m_e c^2 ~ 150 MeV) are expected to be
particularly common. Observations and models for the radio, extreme
ultraviolet, hard X-ray, and gamma-ray emission from nonthermal particles
accelerated in these shocks will also be described. The predicted gamma-ray
fluxes of clusters should make them easily observable with GLAST.
(162kb)
astro-ph/0009095 [abs, src, ps, other] :
Title: The Formation of Supermassive Black Holes and the Evolution of
Supermassive Stars
Authors:
Kimberly C. B. New (LANL),
Stuart L. Shapiro (UIUC)
Comments: 6 pages, 1 figure; submitted to a Special Issue of Classical and
Quantum Gravity, Proceedings of the Third LISA Symposium
The existence of supermassive black holes is supported by a growing body of
observations. Supermassive black holes and their formation events are likely
candidates for detection by proposed long-wavelength, space-based gravitational
wave interferometers like LISA. However, the nature of the progenitors of
supermassive black holes is rather uncertain. Supermassive black hole formation
scenarios that involve either the stellar dynamical evolution of dense clusters
or the hydrodynamical evolution of supermassive stars have been proposed. Each
of these formation scenarios is reviewed and the evolution of supermassive
stars is then examined in some detail. Supermassive stars that rotate uniformly
during their secular cooling phase will spin up to the mass-shedding limit and
eventually contract to the point of relativistic collapse. Supermassive stars
that rotate differentially as they cool will likely encounter the dynamical bar
mode instability prior to the onset of relativistic collapse. A supermassive
star that undergoes this bar distortion, prior to or during collapse, may be a
strong source of quasiperiodic, long-wavelength gravitational radiation.
(256kb)
astro-ph/0009096 [abs, src, ps, other] :
Title: Damped Lyman-Alpha Galaxies
Authors:
D. Turnshek (1),
S. Rao (1),
W. Lane (1,2),
E. Monier (1,3),
D. Nestor (1),
J. Bergeron (4),
F. Briggs (2),
A. Smette (5) ((1) University of Pittsburgh, (2) Kapteyn Astronomical Institute, (3) Ohio State University, (4) ESO Garching, (5) NASA GSFC)
Comments: To appear in “Gas and Galaxy Evolution”, ASP Conference Series, eds.
Hibbard, Rupen, and van Gorkum. 2 pages, 1 postscript table, 1 color
postscript figure. newpasp.sty included
Some results from an imaging program to identify low-redshift (0.09<z<1.63)
damped Lyman-alpha (DLA) galaxies are presented. The standard paradigm that was
widely accepted a decade ago, that DLA galaxies are the progenitors of luminous
disk galaxies, is now being seriously challenged. The indisputable conclusion
from imaging studies at low redshift is that the morphological types of DLA
galaxies are mixed and that they span a range in luminosities and surface
brightnesses.
(66kb)
astro-ph/0009097 [abs, src, ps, other] :
Title: The effects of seeing on Sersic profiles
Authors:
I. Trujillo,
J. A. L. Aguerri,
J. Cepa,
C. M. Gutierrez
Comments: 7 pages, 5 figure. Accepted for publication in MNRAS
The effects of seeing on the parameters of the S`ersic profile are studied
in an analytical form using a Gaussian point spread function. The surface
brightness of S`ersic profiles is proportional (in magnitudes) to $r^{1/n}$.
The parameter $n$ serves to classify the type of profile and is related to the
central luminosity concentration. It is the parameter most affected by seeing;
furthermore, the value of $n$ that can be measured is always smaller than the
real one. It is shown that the luminosity density of the S`ersic profile with
$n$ less than 0.5 has a central depression, which is physically unlikely. Also,
the intrinsic ellipticity of the sources has been taken into account and we
show that the parameters are dependent when the effects of seeing are
non-negligible. Finally, a prescription for correcting raw effective radii,
central intensities and $n$ parameters is given.
(43kb)
astro-ph/0009098 [abs, src, ps, other] :
Title: The Cosmological Evolution of Quasar Damped Lyman-Alpha Systems
Authors:
Sandhya Rao (University of Pittsburgh)
Comments: To appear in “Gas and Galaxy Evolution”, ASP Conference Series, eds.
Hibbard, Rupen, and van Gorkum. 4 pages, 5 encapsulated postscript figures.
newpasp.sty included
We present results from an efficient, non-traditional survey to discover
damped Lyman-alpha (DLA) absorption-line systems with neutral hydrogen column
densities N(HI)>2×10^{20} atoms cm^{-2} and redshifts z<1.65. Contrary to
previous studies at higher redshift that showed a decrease in the cosmological
mass density of neutral gas in DLA absorbers, Omega_{DLA}, with time, our
results indicate that Omega_{DLA} is consistent with remaining constant from
redshifts z approx 4 to z approx 0.5. There is no evidence that Omega_{DLA}
is approaching the value at z=0. Other interesting results from the survey are
also presented.
(34kb)
astro-ph/0009099 [abs, src, ps, other] :
Title: Do mergers make (normal) ellipticals?
Authors:
Chris Mihos (Case Western Reserve University)
Comments: 4 pages, 1 Postscript figure, uses newpasp.sty. To apear in the
conference proceedings of “Gas and Galaxy Evolution”
Under the merger hypothesis, elliptical galaxies are built through mergers of
gas-rich spirals. However, the relative paucity of HI in most normal
ellipticals demands significant processing of atomic gas into other forms if
this process is to be viable. Here I present a few qualitative remarks on how
the properties of merger-spawned ellipticals might depend on the (evolving) gas
content of the progenitor disks, then turn to a more quantitative study of the
constraints provided by the nuclear properties of ellipticals and merger
remnants.
(22kb)
astro-ph/0009100 [abs, src, ps, other] :
Title: The Impact of External Tidal Fields on the ISM of Dwarf Spheroidals
Authors:
Sergey Mashchenko,
Claude Carignan
Comments: 2 pages, 2 figures; to appear in the proceedings of the conference
“Gas and Galaxy Evolution” (ASP Conference Series), eds. J. E. Hibbard, M. P.
Rupen, and J. H. van Gorkom
It was found that for three dwarf spheroidal galaxies – Sculptor, Tucana, and
Cetus – there is a correspondence between the distribution of associated HI gas
and the projected tidal axis direction. Numerical hydrodynamical simulations
confirmed the following scenario: SN Ia explosions remove most of the
interstellar medium beyond the tidal radius of the dwarf galaxy, with most of
the mass being in clouds moving along the principal tidal axis.
(144kb)
astro-ph/0009101 [abs, src, ps, other] :
Title: MACS: A quest for the most massive galaxy clusters in the universe
Authors:
H. Ebeling (IfA, Hawaii),
A.C. Edge (Univ. of Durham, UK),
J.P. Henry (IfA, Hawaii)
Comments: Submitted to ApJ. 11 figures, many of them in colour. A
high-resolution colour postscript version of the full paper is available at
this http URL
We describe the design and current status of a new X-ray cluster survey aimed
at the compilation of a statistically complete sample of very X-ray luminous
(and thus, by inference, massive), distant clusters of galaxies. The primary
goal of the MAssive Cluster Survey (MACS) is to increase the number of known
massive clusters at z>0.3 from a handful to hundreds. Upon completion of the
survey, the MACS cluster sample will greatly improve our ability to study
quantitatively the physical and cosmological parameters driving cluster
evolution at redshifts and luminosities poorly sampled by all existing surveys.
To achieve these goals we apply an X-ray flux and X-ray hardness-ratio cut to
select distant cluster candidates from the ROSAT Bright Source Catalogue.
Starting from a list of more than 5,000 X-ray sources within the survey area of
22,735 square degrees we use positional cross-correlations with public
catalogues of Galactic and extragalactic objects, reference to APM colours,
visual inspection of Digitized Sky Survey images, extensive CCD imaging, and
finally spectroscopic observations with the University of Hawaii’s 2.2m and the
Keck 10m telescopes to compile the final cluster sample.
We discuss in detail the X-ray selection procedure and the resulting
selection function, and present model predictions for the number of distant
clusters expected to emerge from MACS. At the time of this writing the MACS
cluster sample comprises 88 spectroscopically confirmed clusters at 0.3<z<0.6;
more than two thirds of these are new discoveries. Our preliminary sample is
already 15 times larger than that of the EMSS in the same redshift and X-ray
luminosity range.
(347kb)
Cross-listings
gr-qc/0009005 [abs, src, ps, other] :
Title: Back Reaction Problem in the Inflationary Universe
Authors:
Yasusada Nambu
Comments: 17 pages, some small corrections
We investigate the back reaction of cosmological perturbations on an
inflationary universe using the renormalization-group method. The second-order
zero mode solution which appears by the nonlinearity of the Einstein equation
is regarded as a secular term of a perturbative expansion, we renormalized a
constant of integration contained in the background solution and absorbed the
secular term to this constant in a gauge-invariant manner. The resultant
renormalization-group equation describes the back reaction effect of
inhomogeneity on the background universe. For scalar type classical
perturbation, by solving the renormalization-group equation, we find that the
back reaction of the long wavelength fluctuation works as a positive spatial
curvature, and the short wavelength fluctuation works as a radiation fluid. For
the long wavelength quantum fluctuation, the effect of back reaction is
equivalent to a negative spatial curvature.
(10kb)
hep-ph/0008297 [abs, src, ps, other] :
Title: Ultra High Energy Cosmic Rays and Gamma Ray Bursts from Axion Stars
Authors:
Aiichi Iwazaki
Comments: 16 pages, Revtex
We propose a model in which ultra high energy cosmic rays and gamma ray
bursts are produced by collisions between neutron stars and axion stars. The
acceleration of such a cosmic ray is made by the electric field, $sim 10^{15}
(B/10^{12} {G}) {eV} {cm}^{-1}$, which is induced in an axion star by
relatively strong magnetic field $B>10^{12}$ G of a neutron star. On the other
hand, similar collisions generate gamma ray bursts when magnetic field is
relatively small, e.g. $leq 10^{10}$ G. Assuming that the axion mass is $sim
10^{-9}$ eV, we can explain huge energies of the gamma ray bursts $sim
10^{54}$ erg as well as the ultra high energies of the cosmic rays $sim
10^{20}$ eV. We estimate rate of energy release in the collisions and we find
that the rate roughly agrees with observations. In addition, we show that these
axion stars are plausible candidates for MACHOs. Since the axion star induces
oscillating electric current under the magnetic field, observable monochromatic
radiations are emitted.
(18kb)
hep-ph/0009044 [abs, src, ps, other] :
Title: Astrophysical neutrinos: 20th Century and Beyond
Authors:
John N. Bahcall
Comments: IUPAP Centennial Lecture, Neutrino 2000; related information:
this http URL
Subj-class: High Energy Physics – Phenomenology; History of Physics
I summarize the first four decades of solar neutrino research and suggest
what may be possible to learn with extragalactic neutrinos and with solar
neutrinos in the next decade.
(148kb)
hep-ph/0009058 [abs, src, ps, other] :
Title: The Phases of QCD in Heavy Ion Collisions and Compact Stars
Author:
Krishna Rajagopal (MIT)
Comments: 29 pages. 4 figures. latex with aipproc. one version of this review
is to appear in the Comments of Nuclear and Particle Physics section of
Comments on Modern Physics. two other versions were contributed to the
proceedings of the Conference on Intersections of Nuclear and Particle
Physics, Quebec, May 2000 and to the proceedings of the 40th Zakopane School
of Theoretical Physics, June 2000
I review arguments for the existence of a critical point in the QCD phase
diagram as a function of temperature and baryon chemical potential. I describe
how heavy ion collision experiments at the SPS and RHIC can discover the
tell-tale signatures of such a critical point, thus mapping this region of the
QCD phase diagram. I then review the phenomena expected in cold dense quark
matter: color superconductivity and color-flavor locking. I close with a
snapshot of ongoing explorations of the implications of recent developments in
our understanding of cold dense quark matter for the physics of compact stars.
(163kb)
nucl-th/0009012 [abs, src, ps, other] :
Title: Neutrino Reactions on Deuteron
Authors:
S. Nakamura (1),
T. Sato (1 and 2),
V. Gudkov (2),
K. Kubodera (2) ((1)Osaka University, (2) University of South Carolina)
Comments: 46 pages, REVTeX, 21 figures, to be submitted to Phys. Rev. C
The cross sections for the
u-d and ar{
u}-d reactions are calculated for
the incident energy up to E_
u = 170 MeV, with the use of a phenomenological
Lagrangian approach. We assess and improve the reliability of the employed
calculational method by examining the dependence of the results on various
input and approximations that go into the calculation. The main points of
improvements over the existing work are: (1) use of the “modern” NN potentials;
(2) use of the more accurate nucleon weak-interaction form factors; (3)
monitoring the strength of a vertex that governs the exchange-current
contribution, with the use of data on the related process, n+p o d+gamma. In
addition to the total cross sections, we present various differential cross
sections that are expected to be useful for the SNO and other experiments. In
the low energy regime relevant to the solar neutrinos, the newly calculated
total cross sections agree with the existing literature values. The origins of
slight differences found for higher energies are discussed.
(65kb)
Replacements
astro-ph/0005262 [abs, src, ps, other] :
Title: Reionization by Hard Photons: I. X-rays from the First Star Clusters
Authors:
S. Peng Oh (Princeton)
Comments: 29 pages, 3 figures, revised version submitted to ApJ
Note: replaced with revised version Wed, 6 Sep 2000 08:54:24 GMT (44kb)
astro-ph/0006119 [abs, src, ps, other] :
Title: On the Integrated Spectrum of the X-ray Binaries and the Origin of Soft
X-ray Emission from the Bulge of M31
Authors:
Konstantin N. Borozdin,
William C. Priedhorsky (NIS Division, Los Alamos National Laboratory, Los Alamos, NM)
Comments: 11 pages incl. 2 figures, 2 tables, accepted to ApJL
Note: replaced with revised version Wed, 6 Sep 2000 01:42:29 GMT (196kb)
astro-ph/0007076 [abs, src, ps, other] :
Title: A Possible X-ray and Radio Counterpart of the High-Energy Gamma-ray
Source 3EG J2227+6122
Authors:
J. P. Halpern,
E. V. Gotthelf,
K. M. Leighly,
D. J. Helfand
Comments: 26 pages, accepted by The Astrophysical Journal, new radio results
added
Note: replaced with revised version Wed, 6 Sep 2000 22:50:10 GMT (606kb)
astro-ph/0007212 [abs, src, ps, other] :
Title: Asymmetric Beams in Cosmic Microwave Background Anisotropy Experiments
Authors:
J. H. P. Wu,
A. Balbi,
J. Borrill,
P. G. Ferreira,
S. Hanany,
A. H. Jaffe,
A. T. Lee,
S. Oh,
B. Rabii,
P. L. Richards,
G. F. Smoot,
R. Stompor,
C. D. Winant
Comments: 41 pages, 13 figures; ApJS in press
Note: replaced with revised version Wed, 6 Sep 2000 21:33:21 GMT (257kb)
astro-ph/0007294 [abs, src, ps, other] :
Title: Accretion column disruption in GX 1+4
Authors:
D.K. Galloway
Comments: 10 pages, 2 figures, minor abstract typo and wording of final
paragraph corrected
Note: replaced with revised version Wed, 6 Sep 2000 18:22:29 GMT (51kb)
astro-ph/0008523 [abs, src, ps, other] :
Title: Pulsar Astronomy: the HST Contribution
Authors:
P.A. Caraveo (1),
R. P. Mignani (2),
G.G.Pavlov (3),
G.F. Bignami (4) ((1) IFC-CNR, Milan, Italy, (2) STECF-ESO, Garching, Germany, (3) Pennsylvania State Univ., USA, (4) ASI, Rome, Italy)
Comments: 4 pages, 1 figure, uses psfig.sty. To appear in the proceedings of A
Decade of HST Science (Baltimore, USA, April 2000)
Note: replaced with revised version Wed, 6 Sep 2000 16:38:11 GMT (28kb)
astro-ph/0009003 [abs, src, ps, other] :
Title: Non-Thermal Production of WIMPs and the Sub-Galactic Structure of the
Universe
Authors:
W.B. Lin,
D.H. Huang,
X. Zhang,
R. Brandenberger
Comments: 6 pages, 2 figures
Note: replaced with revised version Wed, 6 Sep 2000 03:31:11 GMT (34kb)
astro-ph/0009039 [abs, src, ps, other] :
Title: Southern Hemisphere Observations of a $10^{18}$eV Cosmic Ray Source Near
the Direction of the Galactic Centre
Authors:
J. A. Bellido,
R. W. Clay,
B. R. Dawson,
M. Johnston-Hollitt (The University of Adelaide)
Comments: 14 pages including 5 postscript figures, corrected the title
(replaced “Cosmic Ray Source” instead of “Cosmic Ray”)
Note: replaced with revised version Wed, 6 Sep 2000 05:11:19 GMT (126kb)
astro-ph/0009046 [abs, src, ps, other] :
Title: Using Perturbative Least Action to Reconstruct the Local Group
Authors:
David M. Goldberg (Yale University; Princeton University Observatory)
Comments: 18 Pages LaTeX, including 5 postscript figures. Submitted to
Astrophysical Journal
Note: replaced with revised version Wed, 6 Sep 2000 14:45:08 GMT (29kb)
astro-ph/0009076 [abs, src, ps, other] :
Title: Black Hole Demographics from the M(BH)-sigma Relation
Authors:
David Merritt,
Laura Ferrarese (Rutgers University)
Comments: 12 Latex pages, 4 postscript figures
Note: replaced with revised version Wed, 6 Sep 2000 20:07:36 GMT (24kb)
astro-ph/0009077 [abs, src, ps,
