5,593 research outputs found
What are S0 (0) Galaxies?
Among early-type galaxies with almost circular isophotes E0 and E1 galaxies
are, at 99.3% significance, more luminous than face-on objects classified as S0
(0) and S(0) (1). This result supports the view that rotation and "diskiness"
are more important in the outer regions of faint-early type galaxies than they
are for more luminous galaxies of very early morphological type.Comment: 7 pages. 0 figures. Astrophysical Jounral Letters in pres
Caltech Faint Galaxy Redshift Survey XV: Classification of Galaxies with 0.2 < z < 1.1 in the Hubble Deep Field (North) and its Flanking Fields
To circumvent the spatial effects of resolution on galaxy classification, the
images of 233 objects of known redshift in the Hubble Deep Field (HDF) and its
Flanking Fields (FF) that have redshifts in the range 0.20 < z < 1.10 were
degraded to the resolution that they would have had if they were all located at
a redshift z= 1.00. As in paper XIV of the present series, the effects of
shifts in rest wavelength were mitigated by using R-band images for the
classification of galaxies with 0.2 < z < 0.6 and I-band images for objects
with redshifts 0.6 < z < 1.1. A special effort was made to search for bars in
distant galaxies. The present data strongly confirm the previous conclusion
that the Hubble tuning fork diagram only provides a satisfactory framework for
the classification of galaxies with z ~< 0.3. More distant disk galaxies are
often difficult to shoehorn into the Hubble classification scheme. The paucity
of barred spirals and of grand-design spirals at large redshifts is confirmed.
It is concluded that the morphology of disk galaxies observed at look-back
times smaller than 3--4 Gyr differs systematically from that of more distant
galaxies viewed at look-back times of 4--8 Gyr. The disks of late-type spirals
at z >0.5 are seen to be more chaotic than those of their nearer counterparts.
Furthermore the spiral structure in distant early-type spirals appears to be
less well-developed than it is in nearby early-galaxies.Comment: Accepted for publication in the A
Ten Billion Years of Galaxy Evolution
Observations in the Hubble Deep Fields have been used to study the evolution
of galaxy morphology over time. The majority of galaxies with z < 1 are seen to
be disk like, whereas most objects with z > 2 appear to be either chaotic or
centrally concentrated ``blobs''. Such blobs might be the ancestral objects of
ellipticals or of galaxy bulges. About 1/3 of objects with z > 2 appear to be
in the process of merging. The region with 1 < z < 2 marks an important
transition in the global history of star formation from a merger dominated
regime at z > 2, to one at z < 1 in which most star formation takes place in
galactic disks. It is speculated that the break in the Madau plot at z sim 1.5
might be related to the transition from merger-dominated star formation at z >
2 to disk-dominated star formation at at z < 1.Comment: 19 pages. 1 figure. To be published in the August 2002 issue of PAS
Killing spinor space-times and constant-eigenvalue Killing tensors
A class of Petrov type D Killing spinor space-times is presented, having the
peculiar property that their conformal representants can only admit Killing
tensors with constant eigenvalues.Comment: 11 pages, submitted to CQ
The Stellar Mass Spectrum in the Young Populous Cluster NGC 1866
The young populous cluster NGC 1866 in the Large Magellanic Cloud LMC), which
is probably one of the most massive object formed in the LMC during the last ~
3 Gyr, appears to have an unexpectedly high mass-to-light ratio. From its
velocity dispersion Fischer et al. (1992) find its mass to be (1.35 " 0.25) x
105 Mu. The luminosity of this cluster is MV = -8.93 " 0.13, corresponding to
LV = (3.2 " 0.4) x 105 LV (u). This yields M/LV = 0.42 " 0.09 in solar units.
For a cluster of age 0.1 Gyr such a relatively high mass-to-light ratio
requires a mass spectrum with an exponent x = 1.72 " 0.09; or x = 1.75 " 0.09
if mass loss by evolving stars is taken into account.Comment: To be published in the October 1999 issue of the Publications of the
Astronomical Society of the Pacifi
Severe acute maternal morbidity and associated deaths in conflict and post-conflict settings in Africa
Globular Clusters and Dwarf Spheroidal Galaxies
Traditionally globular clusters and dwarf spheroidal galaxies have been
distinguished by using one or more of the following criteria: (1) mass, (2)
luminosity, (3) size, (4) mass-to-light ratio and (5) spread in metallicity.
However, a few recently discovered objects show some overlap between the
domains in parameter space that are occupied by galaxies and clusters. In the
present note it is shown that ellipticity can, in some cases, be used to help
distinguish between globular clusters and dwarf spheroidal galaxies.Comment: MNRAS (Letters), in pres
General non-rotating perfect-fluid solution with an abelian spacelike C_3 including only one isometry
The general solution for non-rotating perfect-fluid spacetimes admitting one
Killing vector and two conformal (non-isometric) Killing vectors spanning an
abelian three-dimensional conformal algebra (C_3) acting on spacelike
hypersurfaces is presented. It is of Petrov type D; some properties of the
family such as matter contents are given. This family turns out to be an
extension of a solution recently given in \cite{SeS} using completely different
methods. The family contains Friedman-Lema\^{\i}tre-Robertson-Walker particular
cases and could be useful as a test for the different FLRW perturbation
schemes. There are two very interesting limiting cases, one with a non-abelian
G_2 and another with an abelian G_2 acting non-orthogonally transitively on
spacelike surfaces and with the fluid velocity non-orthogonal to the group
orbits. No examples are known to the authors in these classes.Comment: Submitted to GRG, Latex fil
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