1,818 research outputs found
Redshifts in the Southern Abell Redshift Survey Clusters. I. The Data
The Southern Abell Redshift Survey contains 39 clusters of galaxies with
redshifts in the range 0.0 < z < 0.31 and a median redshift depth of z =
0.0845. SARS covers the region 0 21h (while
avoiding the LMC and SMC) with b > 40. Cluster locations were chosen from the
Abell and Abell-Corwin-Olowin catalogs while galaxy positions were selected
from the Automatic Plate Measuring Facility galaxy catalog with
extinction-corrected magnitudes in the range 15 <= b_j < 19. SARS utilized the
Las Campanas 2.5 m duPont telescope, observing either 65 or 128 objects
concurrently over a 1.5 sq deg field. New redshifts for 3440 galaxies are
reported in the fields of these 39 clusters of galaxies.Comment: 20 pages, 5 figures, accepted for publication in the Astronomical
Journal, Table 2 can be downloaded in its entirety from
http://trotsky.arc.nasa.gov/~mway/SARS1/sars1-table2.cs
Star Formation, Metallicity and Dust Properties Derived from the SAPM Galaxy Survey Spectra
We have derived star formation rates (SFRs), gas-phase oxygen abundances and
effective dust absorption optical depths for a sample of galaxies drawn from
the Stromlo-APM redshift survey using the new Charlot and Longhetti (2001;
CL01) models, which provide a physically consistent description of the effects
of stars, gas and dust on the integrated spectra of galaxies. Our sample
consists of 705 galaxies with measurements of the fluxes and equivalent widths
of Halpha, [OII], and one or both of [NII] and [SII]. For a subset of the
galaxies, 60 and 100 micron IRAS fluxes are available. We compare the star
formation rates derived using the models with those derived using standard
estimators based on the Halpha, the [OII] and the far-infrared luminosities of
the galaxies. The CL01 SFR estimates agree well with those derived from the
IRAS fluxes, but are typically a factor of ~3 higher than those derived from
the Halpha or the [OII] fluxes, even after the usual mean attenuation
correction of A_Halpha=1 mag is applied to the data. We show that the reason
for this discrepancy is that the standard Halpha estimator neglects the
absorption of ionizing photons by dust in HII regions and the contamination of
Halpha emission by stellar absorption. We also use our sample to study
variations in star formation and metallicity as a function of galaxy absolute
bJ magnitude. For this sample, the star formation rate per unit bJ luminosity
is independent of magnitude. The gas-phase oxygen abundance does increase with
bJ luminosity, although the scatter in metallicity at fixed magnitude is large.Comment: 17 pages, 8 figures, accepted for publication in MNRA
Intrinsic Axis Ratio Distribution of Early-type Galaxies From Sloan Digital Sky Survey
Using Sloan Digital Sky Survey Data Release 5, we have investigated the
intrinsic axis ratio distribution (ARD) for early-type galaxies. We have
constructed a volume-limited sample of 3,922 visually-inspected early-type
galaxies at carefully considering sampling biases
caused by the galaxy isophotal size and luminosity. We attempt to de-project
the observed ARD into three-dimensional types (oblate, prolate, and triaxial),
which are classified in terms of triaxiality. We confirm that no linear
combination of -distributed axis ratios of the three types can
reproduce the observed ARD. However, using Gaussian intrinsic distributions, we
have found reasonable fits to the data with preferred mean axis ratios for
oblate, prolate, and triaxial (triaxials in two axis ratios), where the fractions of
oblate, prolate and triaxial types are
\textrm{O:P:T}=0.29^{\pm0.09}:0.26^{\pm0.11}:0.45^{\pm0.13}-23.3 < M_r \leq -21.2-21.2 < M_r <-19.3$) sample does. Oblate is
relatively more abundant among the less luminous galaxies. Interestingly, the
preferences of axis ratios for triaxial types in the two luminosity classes are
remarkably similar. We have not found any significant influence of the local
galaxy number density on ARD. We show that the results can be seriously
affected by the details in the data selection and type classification scheme.
Caveats and implications on galaxy formation are discussed.Comment: 9 pages, 11 figures, Accepted for publication in Ap
NGC1600 - Cluster or Field Elliptical?
A study of the galaxy distribution in the field of the elliptical galaxy
NGC1600 has been undertaken. Although this galaxy is often classified as a
member of a loose group, all the neighbouring galaxies are much fainter and
could be taken as satellites of NGC1600. The number density profile of galaxies
in the field of this galaxy shows a decline with radius, with evidence of a
background at approximately 1.3 Mpc. The density and number density profile are
consistent with that found for other isolated early-type galaxies. NGC1600
appears as an extended source in X-rays, and the center of the X-ray emission
seems not to coincide with the center of the galaxy. The velocity distribution
of neighbouring galaxies has been measured from optical spectroscopic
observations and shows that the mean radial velocity is approximately 85 km/s
less than that of NGC1600, indicating that the centre of mass could lie outside
the galaxy. The velocity dispersion of the `group' is estimated at 429 km/s.
The inferred mass of the system is therefore of the order of 10^14 solar
masses, a value that corresponds to a large group. NGC1600 therefore shares
some similarities, but is not identical to, the `fossil clusters' detected in
X-ray surveys. Implications of this result for studies of isolated early-type
galaxies are briefly discussed.Comment: 8 pages, 5 figures and 2 table, accepted for publication in the Ap
Neutrino-Lasing in The Early Universe
Recently, Madsen has argued that relativistic decays of massive neutrinos
into lighter fermions and bosons may lead, via thermalization, to the formation
of a Bose condensate. If correct, this could generate mixed hot and cold dark
matter, with important consequences for structure formation.
From a detailed study of such decays, we arrive at substantially different
conclusions; for a wide range of masses and decay times, we find that
stimulated emission of bosons dominates the decay. This phenomenon can best be
described as a neutrino laser, pumped by the QCD phase transition. We discuss
the implications for structure formation and the dark-matter problem.Comment: 7 pages, 3 figures included as uuencoded file, CITA/93/
An Observational Limit on the Dwarf Galaxy Population of the Local Group
We present the results of an all-sky, deep optical survey for faint Local
Group dwarf galaxies. Candidate objects were selected from the second Palomar
survey (POSS-II) and ESO/SRC survey plates and follow-up observations performed
to determine whether they were indeed overlooked members of the Local Group.
Only two galaxies (Antlia and Cetus) were discovered this way out of 206
candidates. Based on internal and external comparisons, we estimate that our
visual survey is more than 77% complete for objects larger than one arc minute
in size and with a surface brightness greater than an extremely faint limit
over the 72% of the sky not obstructed by the Milky Way. Our limit of
sensitivity cannot be calculated exactly, but is certainly fainter than 25
magnitudes per square arc second in R, probably 25.5 and possibly approaching
26. We conclude that there are at most one or two Local Group dwarf galaxies
fitting our observational criteria still undiscovered in the clear part of the
sky, and a roughly a dozen hidden behind the Milky Way. Our work places the
"missing satellite problem" on a firm quantitative observational basis. We
present detailed data on all our candidates, including surface brightness
measurements.Comment: 58 pages in AJ manuscript format; some figures at slightly reduced
quality; accepted by the Astronomical Journa
Impediments to mixing classical and quantum dynamics
The dynamics of systems composed of a classical sector plus a quantum sector
is studied. We show that, even in the simplest cases, (i) the existence of a
consistent canonical description for such mixed systems is incompatible with
very basic requirements related to the time evolution of the two sectors when
they are decoupled. (ii) The classical sector cannot inherit quantum
fluctuations from the quantum sector. And, (iii) a coupling among the two
sectors is incompatible with the requirement of physical positivity of the
theory, i.e., there would be positive observables with a non positive
expectation value.Comment: RevTex, 21 pages. Title slightly modified and summary section adde
Unavoidable Selection Effects in the Analysis of Faint Galaxies in the Hubble Deep Field: Probing the Cosmology and Merger History of Galaxies
(Abridged) We present a detailed analysis of the number count and photometric
redshift distribution of faint galaxies in the Hubble Deep Field (HDF), paying
a special attention to the selection effects including the cosmological dimming
of surface brightness of galaxies. We find a considerably different result from
previous studies ignoring the selection effects, and these effects should
therefore be taken into account in the analysis. We find that the model of pure
luminosity evolution (PLE) of galaxies in the Einstein-de Sitter (EdS) universe
predicts much smaller counts than those observed at faint magnitude limits by a
factor of more than 10, so that a very strong number evolution of galaxies with
\eta > 3-4 must be invoked to reproduce the I_{814} counts, when parametrized
as \phi^* \propto (1+z)^\eta. However we show that such a strong number
evolution under realistic merging processes of galaxies can not explain the
steep slope of the B_{450} and V_{606} counts, and it is seriously inconsistent
with their photometric redshift distribution. We find that these difficulties
still persist in an open universe with \Omega_0 > 0.2, but are resolved only
when we invoke a -dominated flat universe, after examining various
systematic uncertainties in modeling the formation and evolution of galaxies.
The present analysis revitalizes the practice of using faint number counts as
an important cosmological test, giving one of the arguments against the EdS
universe and suggests acceleration of the cosmic expansion by vacuum energy
density. While a modest number evolution of galaxies with \eta ~ 1 is still
necessary even in a Lambda-dominated universe, a stronger number evolution with
\eta > 1 is rejected from the HDF data, giving a strong constraint on the
merger history of galaxies.Comment: 24 pages, 15 figures, final version matching publication in ApJ. Some
references added. The complete ps file of Table 3 is available at
http://th.nao.ac.jp/~totani/images/paper/ty2000-table3.p
A Quantitative Evaluation of the Galaxy Component of COSMOS and APM Catalogs
We have carried out an independent quantitative evaluation of the galaxy
component of the "COSMOS/UKST Southern Sky Object Catalogue" (SSC) and the
"APM/UKST J Catalogue" (APM). Using CCD observations our results corroborate
the accuracy of the photometry of both catalogs, which have an overall
dispersion of about 0.2 mag in the range 17 <= b_J <= 21.5. The SSC presents
externally calibrated galaxy magnitudes that follow a linear relation, while
the APM instrumental magnitudes of galaxies, only internally calibrated by the
use of stellar profiles, require second-order corrections. The completeness of
both catalogs in a general field falls rapidly fainter than b_J = 20.0, being
slightly better for APM. The 90% completeness level of the SSC is reached
between b_J = 19.5 and 20.0, while for APM this happens between b_J = 20.5 and
21.0. Both SSC and APM are found to be less complete in a galaxy cluster field.
Galaxies misclassified as stars in the SSC receive an incorrect magnitude
because the stellar ones take saturation into account besides using a different
calibration curve. In both cases, the misclassified galaxies show a large
diversity of colors that range from typical colors of early-types to those of
blue star-forming galaxies. A possible explanation for this effect is that it
results from the combination of low sampling resolutions with properties of the
image classifier for objects with characteristic sizes close to the
instrumental resolution. We find that the overall contamination by stars
misclassified as galaxies is < 5% to b_J = 20.5, as originally estimated for
both catalogs. Although our results come from small areas of the sky, they are
extracted from two different plates and are based on the comparison with two
independent datasets.Comment: 14 pages of text and tables, 8 figures; to be published in the
Astronomical Journal; for a single postscript version file see
ftp://danw.on.br/outgoing/caretta/caretta.p
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