472 research outputs found
HI observations of nearby galaxies I. The first list of the Karachentsev catalog
We present HI observations of the galaxies in the first list of the
Karachentsev catalog of previously unknown nearby dwarf galaxies (Karachentseva
& Karachentsev 1998). This survey covers all known nearby galaxy groups within
the Local Volume (i.e. within 10 Mpc) and their environment, that is about 25%
of the total sky. A total of 257 galaxies have been observed with a detection
rate of 60%. We searched a frequency band corresponding to heliocentric radial
velocities from -470 km/s to about +4000 km/s. Non-detections are either due to
limited coverage in radial velocity, confusion with Local HI (mainly in the
velocity range -140 km/s to +20 km/s, or lack of sensitivity for very weak
emission. 25% of the detected galaxies are located within the Local Volume.
Those galaxies are dwarf galaxies judged by their optical linear diameter (1.4
+/- 0.2 kpc on the average), their mean total HI mass (4.6 E7 solar masses),
and their observed linewidths (39 km/s).Comment: 22 pages, 9 ps figures, A&AS, in pres
Detection of CO emission in Hydra 1 cluster galaxies
A survey of bright Hydra cluster spiral galaxies for the CO(1-0) transition at 115 GHz was performed with the 15m Swedish-ESO submillimeter telescope (SEST). Five out of 15 galaxies observed have been detected in the CO(1-0) line. The largest spiral galaxy in the cluster, NGC 3312, got more CO than any spiral of the Virgo cluster. This Sa-type galaxy is optically largely distorted and disrupted on one side. It is a good candidate for ram pressure stripping while passing through the cluster's central region. A comparison with global CO properties of Virgo cluster spirals shows a relatively good agreement with the detected Hydra cluster galaxies
Free-Floating HI Clouds in the M 81 Group
Recent VLA observations pointed at dwarf spheroidal (dSph) galaxies in the M
81 group reveal a hitherto hidden population of extremely low mass (~1e5 Msol)
HI clouds with no obvious optical counterparts. We have searched 10 fields in
the M81 group totalling 2.2 square degree, both targeting known dwarf
spheroidal galaxies and blank fields around the central triplet. Our
observations show that the new population of low-mass HI clouds appears to be
confined to a region toward the South-East of the central triplet (at distances
of ~100 kpc from M 81). Possible explanations for these free-floating HI clouds
are that they are related to the dSphs found to the South-East of M 81, that
they belong to the galaxies of the M 81 triplet (equivalent to HVCs), that they
are of primordial nature and provide fresh, unenriched material falling into
the M 81 group, or that they are tidal debris from the 3-body interaction
involving M 81-M 82-NGC 3077. Based on circumstantial evidence, we currently
favour the latter explanation.Comment: To appear in the Proceedings of IAU Symp. 244 on "Dark Galaxies and
Lost Baryons", eds. J. I. Davies & M. J. Disne
Molecular gas content of galaxies in the Hydra-Centaurus supercluster
A survey of bright spiral galaxies in the Hydra-Centaurus supercluster for the CO(1-0) transition at 115 GHz was performed with the 15m Swedish-ESO submillimeter telescope (SEST). A total of 30 galaxies have been detected in the CO(1-0) transition out of 47 observed, which is a detection rate over 60%. Global physical parameters of these galaxies derived from optical, CO, HI, and IR measurements compare very well with properties of galaxies in the Virgo cluster
HI properties of nearby galaxies from a volume-limited sample
We consider global HI and optical properties of about three hundred nearby
galaxies with V km/s. The majority of them have individual
photometric distance estimates. The galaxy sample parameters, e.g. their linear
diameters, their HI mass-to-luminosity ratio, their total mass-to-luminosity
ratio, their mean optical surface brightness show some known and some new
correlations implying a meaningful dynamic explanation. For the LV galaxies
their HI mass and angular momentum follow a nearly linear relation expected for
rotating gaseous disks being near the threashold of gravitational instability,
favourable for active star formation.Comment: 5 pages, 9 figures, uses laa.sty accepted by A&A Suppl. Serie
HI studies of the Sculptor group galaxies. VIII. The background galaxies: NGC 24 and NGC 45
In order to complete our HI survey of galaxies in the Sculptor group area,
VLA observations of NGC 24 and NGC 45 are presented. These two galaxies of
similar magnitude M_B ~ -17.4 lie in the background of the Sculptor group and
are low surface brightness galaxies, especially NGC 45. The HI distribution and
kinematics are regular for NGC 24 while NGC 45 exhibits a kinematical twist of
its major axis. A tilted-ring model shows that the position angle of the major
axis changes by ~25 degrees. A best-fit model of their mass distribution gives
mass-to-light ratios for the stellar disk of 2.5 and 5.2 for NGC 24 and NGC 45
respectively. These values are higher than the ones expected from stellar
population synthesis models. Despite the large dark matter contribution, the
galaxy mass is still dominated by the stellar component in their very inner
regions. These high mass-to-light ratios are typical of what is seen in low
surface brightness galaxies and may indicate that, in those galaxies, disks are
far from the maximum disk case. The halo parameters derived from the best-fit
models are thus lower limits.Comment: 23 pages, 10 figures, accepted for publication in The Astronomical
Journa
Tidally Compressed Gas in Centers of Early Type and Ultraluminous Galaxies
In this paper we propose that the compressive tidal field in the centers of
flat-core early type galaxies and ultraluminous galaxies compresses molecular
clouds producing dense gas obseved in the centers of these galaxies. The effect
of galactic tidal fields is usually considered disruptive in the literature.
However, for some galaxies, the mass profile flattens towards the center and
the resulting galactic tidal field is not disruptive but instead it is
compressive within the flat-core region. We have used the virial theorem to
determine the minimum density of a molecular cloud to be stable and
gravitationally bound within the tidally compressive region of a galaxy. We
have applied the mechanism to determine the mean molecular cloud densities in
the centers of a sample of flat-core, early-type galaxies and ultraluminous
galaxies.Comment: 18 latex pages and uses aaspp4.sty, accepted for publication in
Astrophysical Journa
Cold gas in elliptical galaxies
We explore the evolution of the cold gas (molecular and neutral hydrogen) of
elliptical galaxies and merger remnants ordered into a time sequence on the
basis of spectroscopic age estimates. We find that the fraction of cold gas in
early merger remnants decreases significantly for ~1-2 Gyr, but subsequent
evolution toward evolved elliptical systems sees very little change. This trend
can be attributed to an initial gas depletion by strong star-formation which
subsequently declines to quiescent rates. This explanation is consistent with
the merger picture for the formation of elliptical galaxies. We also explore
the relation between HI-to-H2 mass ratio and spectroscopic galaxy age, but find
no evidence for a statistically significant trend. This suggests little net HI
to H2 conversion for the systems in the present sample.Comment: 11 pages, 6 figures, accepted for publication by MNRA
The HI Content of Compact Groups of Galaxies
The HI content of Hickson Compact Groups in the southern hemisphere is
measured using data from the HI Parkes All Sky Survey (HIPASS), and dedicated
observations using the narrowband filter on the Multibeam instrument on the
Parkes telescope. The expected HI mass of these groups was estimated using the
luminosity, diameter and morphological types of the member galaxies, calibrated
from published data. Taking careful account of non-detection limits, the
results show that the compact group population that has been detected by these
observations has an HI content similar to that of galaxies in the reference
field sample. The upper limits for the undetected groups lie within the normal
range; improvement of these limits will require a large increase in
sensitivity.Comment: 27 pages, 5 figures. Accepted for publication in PAS
- …