6,567 research outputs found
Classifications of the Host Galaxies of Supernovae, Set II
Classifications on the DDO system are given for an additional 231 host
galaxies of supernovae that have been discovered during the course of the Lick
Observatory Supernova Search with the Katzman Automatic Imaging Telescope
(KAIT). This brings the total number of hosts of supernovae discovered (or
independently rediscovered) by KAIT, which have so far been classified on a
homogeneous system, to 408. The probability that SNe Ia and SNe II have a
different distribution of host galaxy Hubble types is found to be 99.7%. A
significant difference is also found between the distributions of the host
galaxies of SNe Ia and of SNe Ibc (defined here to include SNe Ib, Ib/c, and
Ic). However, no significant difference is detected between the frequency
distributions of the host galaxies of SNe II and SNe IIn. This suggests that
SNe IIn are generally not SNe Ia embedded in circumstellar material that are
masquerading as SNe II. Furthermore, no significant difference is found between
the distribution of the Hubble types of the hosts of SNe Ibc and of SNe II.
Additionally, SNe II-P and SNe II-L are found to occur among similar stellar
populations. The ratio of the number of SNe Ia-pec to normal SNe Ia appears to
be higher in early-type galaxies than it is in galaxies of later morphological
types. This suggests that the ancestors of SNe Ia-pec may differ systematically
in age or composition from the progenitors of normal SNe Ia. Unexpectedly, five
SNe of Types Ib/c, II, and IIn (all of which are thought to have massive
progenitors) are found in host galaxies that are nominally classified as types
E and S0. However, in each case the galaxy classification is uncertain, or
newly inspected images show evidence suggesting a later classification
(abridged) ...Comment: Accepted for publishing in PAS
Classifications of the Host Galaxies of Supernovae
Classifications on the DDO system are given for the host galaxies of 177
supernovae (SNe) that have been discovered since 1997 during the course of the
Lick Observatory Supernova Search with the Katzman Automatic Imaging Telescope.
Whereas SNe Ia occur in all galaxy types, it is found, at a high level of
statistical confidence, that SNe Ib, Ic, and II are strongly concentrated in
late-type galaxies. However, attention is drawn to a possible exception
provided by SN 2001I. This SN IIn occurred in the E2 galaxy UGC 2836, which was
not expected to harbor a massive young supernova progenitor.Comment: Accepted to be published in PAS
The Mass of the Centaurus A Group of Galaxies
The mass M, and the radius R_h, of the Centaurus A group are estimated from
the positions and radial velocities of 30 probable cluster members. For an
assumed distance of 3.9 Mpc it is found that R_h \sim 640 kpc. The velocity
dispersion in the Cen A group is 114 \pm 21 km/s. From this value, and R_h =
640 kpc, the virial theorem yields a total mass of 1.4 \times 10^{13} M_{\sun}
for the Cen A group. The projected mass method gives a mass of 1.8 \times
10^{13} M_{\sun}. These values suggest that the Cen A group is about seven
times as massive as the Local Group. The Cen A mass-to-light ratio is found to
be M/L_B = 155-200 in solar units. The cluster has a zero-velocity radius R_0 =
2.3 Mpc.Comment: 8 pages, 1 figure, in LaTeX format; to appear in the Astronomical
Journal in January 200
Are the Luminosities of RR Lyrae Stars Affected by Second Parameter Effects?
There is a serious discrepancy between the distance to the LMC derived from
the Cepheid Period-Luminosity relation and that obtained by using the Galactic
calibration for the luminosity of RR Lyrae stars. It is suggested that this
problem might be due to the fact that second parameter effects make it
inappropriate to apply Galactic calibrations to RR Lyrae variables in the
Magellanic Clouds, i.e. Mv(RR) could depend on both [Fe/H] and on one or more
second parameters.Comment: 10 pages as uuencoded compressed Postscript. Also available at
http://www.dao.nrc.ca/DAO/SCIENCE/science.htm
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
The Luminosity Distribution of Local Group Galaxies
From a rediscussion of Local Group membership, and of distances to individual
galaxies, we obtain values for 35 probable and possible Local Group
members. The luminosity function of these objects is well fitted by a Schechter
function with faint end slope . The probability that the
luminosity distribution of the Local Group is a single Schechter function with
steeper than -1.3 is less than 1 per cent. However, more complicated
luminosity functions, such as multi-component Schechter functions with steep
faint-end slopes, cannot be ruled out. There is some evidence that the
luminosity distribution of dwarf spheroidal galaxies in the Local Group is
steeper than that of dwarf irregular galaxies.Comment: 13 pages, 2 figures, accepted for publication in The Astronomical
Journal. Figure 2 replaced, conclusion based on this figure change
Some Global Characteristics of the Galactic Globular Cluster System
The relations between the luminosities , the metallicities ,
the Galactocentric radii , and the central concentration indices of
Galactic globular clusters are discussed. It is found that the most luminous
clusters rarely have collapsed cores. The reason for this might be that the
core collapse time scales for such populous clusters are greater than the age
of the Galaxy. Among those clusters, for which the structure has not been
modified by core collapse, there is a correlation between central concentration
and integrated luminosity, in the sense that the most luminous clusters have
the strongest central concentration. The outermost region of the Galaxy with
kpc was apparently not able to form metal-rich globular
clusters, whereas such clusters (of which Ter 7 is the prototype) were able to
form in some nearby dwarf spheroidal galaxies. It is not yet clear how the
popular hypothesis that globular clusters were initially formed with a single
power law mass spectrum can be reconciled with the observation that both (1)
Galactic globular clusters with kpc, and (2) the globulars associated
with the Sagittarius dwarf, appear to have bi-modal luminosity functions.Comment: 15 pages, 1 figur
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
Spiral Structure and Galaxy Environment
Among 330 normal spirals of types Sa-Sc the fraction of objects exhibiting
``ring'', ``intermediate'' and ``spiral'' arm varieties does not correlated
with environment. A similar conclusion appears to apply to the arm varieties of
123 barred spirals of types SBa-SBc. It is concluded that, among the northern
Shapley-Ames galaxies, the distinction between the spiral and ring varieties of
spiral arms is, within the accuracy of presently available data, independent of
galaxy environment. This result suggests that the detailed morphology of spiral
arms depends primarily on parent galaxy characteristics, rather than on the
galactic environment.Comment: 8 pages. no figures. To be published in the August 2202 issue of A
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