6 research outputs found
HI content in galaxies in loose groups
Gas deficiency in cluster spirals is well known and ram-pressure stripping is
considered the main gas removal mechanism. In some compact groups too gas
deficiency is reported. However, gas deficiency in loose groups is not yet well
established. Lower dispersion of the member velocities and the lower density of
the intra-group medium in small loose groups favour tidal stripping as the main
gas removal process in them. Recent releases of data from HI Parkes all sky
survey (HIPASS) and catalogues of nearby loose groups with associated diffuse
X-ray emission have allowed us to test this notion. In this paper, we address
the following questions: (a) do galaxies in groups with diffuse X-ray emission
statistically have lower gas content compared to the ones in groups without
diffuse X-ray emission? (b) does HI deficiency vary with the X-ray luminosity
of the loose group in a systematic way? We find that (a) galaxies in groups
with diffuse X-ray emission, on average, are HI deficient, and have lost more
gas compared to those in groups without X-ray emission; the later are found not
to have significant HI deficiency; (b) no systematic dependence of the HI
deficiency with X-ray luminosity is found. Ram pressure assisted tidal
stripping and evaporation by thermal conduction are the two possible mechanisms
to account for this excess gas loss.Comment: 9 pages, 4 figures, accepted in MNRA
Intracluster Planetary Nebulae in the Virgo Cluster I. Initial Results
We report the initial results of a survey for intracluster planetary nebulae
in the Virgo Cluster. In two 16' x 16' fields, we identify 69 and 16
intracluster planetary nebula candidates, respectively. In a third 16' x 16'
field near the central elliptical galaxy M87, we detect 75 planetary nebula
candidates, of which a substantial fraction are intracluster in nature. By
examining the number of the planetaries detected in each field and the shape of
the planetary nebula luminosity function, we show that 1) the intracluster
starlight of Virgo is distributed non-uniformly, and varies between subclumps A
and B, 2) the Virgo Cluster core extends ~3 Mpc in front of M87, and thus is
elongated along the line-of-sight, and 3) a minimum of 22% of Virgo's stellar
luminosity resides between the galaxies in our fields, and that the true number
may be considerably larger. We also use our planetary nebula data to argue that
the intracluster stars in Virgo are likely derived from a population that is of
moderate age and metallicity.Comment: 20 pages, 3 figures, accepted for publication in the Astrophysical
Journal. Paper is also available at
http://www.astro.psu.edu/users/johnf/Text/research.htm
The JCMT Nearby Galaxies Legacy Survey - VIII : CO data and the L -L correlation in the SINGS sample
The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an Hi-selected sample of 155 galaxies spanning all morphological types with distances less than 25Mpc. We describe the scientific goals of the survey, the sample selection and the observing strategy. We also present an atlas and analysis of the CO J=3 - 2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey. We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift, which have also been observed in the CO J=3 - 2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of magnitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the L /L ratio with the atomic-to-molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase.Peer reviewe