738 research outputs found
HIPASS Detection of an Intergalactic Gas Cloud in the NGC 2442 Group
We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of a gas
cloud associated with the asymmetric spiral galaxy NGC 2442. This object,
designated HIPASS J0731-69, contains ~10^9 M_sun of HI, or nearly one-third as
much atomic gas as NGC 2442 itself. No optical counterpart to any part of
HIPASS J0731-69 has yet been identified, consistent with the gas being diffuse,
and with its stream-like kinematics. If the gas in HIPASS J0731-69 was once
part of NGC 2442, then it was most likely a fairly recent tidal encounter with
a moderately massive companion which tore it loose, although the possibility of
ram-pressure stripping cannot be ruled out. This discovery highlights the
potential of the HIPASS data for yielding new clues to the nature of some of
the best-known galaxies in the local universe.Comment: 8 pages, 4 figures, uses "emulateapj5.sty". Accepted for publication
in ApJ, Vol. 555, 1 July 2001. Figs 1 and 2 included as JPE
The 1000 Brightest HIPASS Galaxies: HI Mass Function and Omega_HI
We present a new accurate measurement of the HI mass function of galaxies
from the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the
highest HI peak flux densities in the southern hemisphere (Koribalski et al.
2003). This sample spans nearly four orders of magnitude in HI mass (from log
M_HI/M_sun=6.8 to 10.6, H0=75) and is the largest sample of HI selected
galaxies to date. We develop a bivariate maximum likelihood technique to
measure the space density of galaxies, and show that this is a robust method,
insensitive to the effects of large scale structure. The resulting HI mass
function can be fitted satisfactorily with a Schechter function with faint-end
slope alpha=-1.30. This slope is found to be dependent on morphological type,
with later type galaxies giving steeper slopes. We extensively test various
effects that potentially bias the determination of the HI mass function,
including peculiar motions of galaxies, large scale structure, selection bias,
and inclination effects, and quantify these biases. The large sample of
galaxies enables an accurate measurement of the cosmological mass density of
neutral gas: Omega_HI=(3.8 +/- 0.6) x 10^{-4}. Low surface brightness galaxies
contribute only 15% to this value, consistent with previous findings.Comment: accepted for publication in Astronomical Journal, 16 pages, including
17 figures. Corrected typos and reference
The Large Scale Distribution of Neutral Hydrogen in the Fornax Region
Using HIPASS data, we have searched for HI in a ~25x25 sq.deg. region centred
on the Fornax cluster. Within a velocity search range of 300 - 3700 km/s and a
lower flux limit of ~40 mJy, 110 galaxies with HI emission were detected, one
of which is previously uncatalogued. None of the detections has early-type
morphology. Previously unknown velocities for 14 galaxies have been determined,
with a further 4 velocity measurements being significantly dissimilar to
published values. Identification of an optical counterpart is relatively
unambiguous for more than ~90% of our HI galaxies. The galaxies appear to be
embedded in a sheet at the cluster velocity which extends for more than 30 deg
across the search area. At the nominal cluster distance of ~20 Mpc, this
corresponds to an elongated structure more than 10 Mpc in extent. A velocity
gradient across the structure is detected, with radial velocities increasing by
\~500 km/s from SE to NW. The clustering of galaxies evident in optical surveys
is only weakly suggested in the spatial distribution of our HI detections. Our
results suggest a considerable deficit of HI-rich galaxies in the centre of the
cluster. However, relative to the field, there is a 3(+/-1)-fold excess of
HI-rich galaxies in the outer parts of the cluster where galaxies may be
infalling towards the cluster for the first time.Comment: 16 pages, 14 figures, 110 HI spectra. To be published in MNRA
An Extragalactic HI Cloud with No Optical Counterpart?
We report the discovery, from the HI Parkes All-Sky Survey (HIPASS), of an
isolated cloud of neutral hydrogen which we believe to be extragalactic. The HI
mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10^7 Msun, using an
estimated distance of ~3.2 Mpc. Most significantly, we have found no optical
companion to this object to very faint limits (mu(B)~ 27 mag arcsec^-2). HIPASS
J1712-64 appears to be a binary system similar to, but much less massive than,
HI 1225+01 (the Virgo HI Cloud) and has a size of at least 15 kpc. The mean
velocity dispersion, measured with the Australia Telescope Compact Array
(ATCA), is only 4 km/s for the main component and because of the weak or
non-existent star-formation, possibly reflects the thermal linewidth (T<2000 K)
rather than bulk motion or turbulence. The peak column density for HIPASS
J1712-64, from the combined Parkes and ATCA data, is only 3.5 x 10^19 cm^-2,
which is estimated to be a factor of two below the critical threshold for star
formation. Apart from its significantly higher velocity, the properties of
HIPASS J1712-64 are similar to the recently recognised class of Compact High
Velocity Clouds. We therefore consider the evidence for a Local Group or
Galactic origin, although a more plausible alternative is that HIPASS J1712-64
was ejected from the interacting Magellanic Cloud/Galaxy system at
perigalacticon ~ 2 x 10^8 yr ago.Comment: 23 pages, 7 figures, AJ accepte
New Galaxies Discovered in the First Blind HI Survey of the Centaurus A Group
We have commenced a 21-cm survey of the entire southern sky (\delta < 0
degrees, -1200 km/s < v < 12700 km/s) which is ''blind'', i.e. unbiased by
previous optical information. In the present paper we report on the results of
a pilot project which is based on data from this all-sky survey. The project
was carried out on an area of 600 square degrees centred on the nearby
Centaurus A (Cen A) group of galaxies at a mean velocity of v ~ 500 km/s. This
was recently the subject of a separate and thorough optical survey.
We found 10 new group members to add to the 21 galaxies already known in the
Cen A group: five of these are previously uncatalogued galaxies, while five
were previously catalogued but not known to be associated with the group.
We found optical counterparts for all the HI detections, most of them
intrinsically very faint low surface brightness dwarfs. The new group members
add approximately 6% to the HI mass of the group and 4% to its light. The HI
mass function, derived from all the known group galaxies in the interval 10^7
\Msun of HI to 10^9 \Msun of HI, has a faint-end slope of 1.30 +/- 0.15,
allowing us to rule out a slope of 1.7 at 95% confidence. Even if the number in
the lowest mass bin is increased by 50%, the slope only increases to 1.45 +/-
0.15.Comment: 19 pages Latex, 6 figures (Fig. 2 in four parts, Fig.5 in two parts).
To appear in The Astrophysical Journal (Vol. 524, October 1999
HIPASS High-Velocity Clouds: Properties of the Compact and Extended Populations
A catalog of Southern anomalous-velocity HI clouds at Decl. < +2 deg is
presented, based on data from the HI Parkes All-Sky Survey (HIPASS). The
improved sensitivity (5sigma: T_B = 0.04 K) and resolution (15.5') of the
HIPASS data results in a substantial increase in the number of individual
clouds (1956, as well as 41 galaxies) compared to previous surveys. Most
high-velocity emission features, HVCs, have a filamentary morphology and are
loosely organized into large complexes extending over tens of degrees. In
addition, 179 compact and isolated anomalous-velocity objects, CHVCs, are
identified based on their size and degree of isolation. 25% of the CHVCs
originally classified by Braun & Burton (1999) are reclassified. Both the
entire population of high-velocity emission features and the CHVCs alone have
typical HI masses of ~ 4.5 D(kpc)^2 solar masses and have similar slopes for
their column density and flux distributions. On the other hand, the CHVCs
appear to be clustered and the population can be broken up into three spatially
distinct groups, while the entire population of clouds is more uniformly
distributed with a significant percentage aligned with the Magellanic Stream.
The median velocities are V_GSR = -38 km/s for the CHVCs and -30 km/s for all
of the anomalous-velocity clouds. Based on the catalog sizes, high-velocity
features cover 19% of the southern sky and CHVCs cover 1%. (abridged)Comment: 32 pages, 26 figures in gif format, 2 ascii tables, to appear in the
Jan 2002 issue of The Astronomical Journal, high resolution version available
at http://origins.Colorado.EDU/~mputman/pubs.htm
The cosmological significance of Low Surface Brightness galaxies found in a deep blind neutral-hydrogen survey
We have placed limits on the cosmological significance of gas-rich low
surface-brightness (LSB) galaxies as a proportion of the total population of
gas-rich galaxies by carrying out a very deep survey (HIDEEP) for neutral
hydrogen (HI) with the Parkes multibeam system. Such a survey avoids the
surface-brightness selection effects that limit the usefulness of optical
surveys for finding LSB galaxies. To complement the HIDEEP survey we have
digitally stacked eight 1-hour R-band Tech Pan films from the UK Schmidt
Telescope covering 36 square degrees of the survey area to reach a very deep
isophotal limit of 26.5 R mag/sq. arcsec. At this level, we find that all of
the 129 HI sources within this area have optical counterparts and that 107 of
them can be identified with individual galaxies. We have used the properties of
the galaxies identified as the optical counterparts of the HI sources to
estimate the significance of LSB galaxies (defined to be those at least 1.5
magnitudes dimmer in effective surface-brightness than the peak in the observed
distribution seen in optical surveys). We calculate the contribution of LSB
galaxies to the total number, neutral hydrogen density, luminosity density,
baryonic mass density, dynamical mass density and cross-sectional area of
gas-rich galaxies. We do not find any `Crouching Giant' LSB galaxies such as
Malin 1, nor do we find a population of extremely low surface-brightness
galaxies not previously found by optical surveys. Such objects must either be
rare, gas-poor or outside the survey detection limits.Comment: 13 pages, 14 figures. Accepted for publication in MNRA
Utilisation of an operative difficulty grading scale for laparoscopic cholecystectomy
Background
A reliable system for grading operative difficulty of laparoscopic cholecystectomy would standardise description of findings and reporting of outcomes. The aim of this study was to validate a difficulty grading system (Nassar scale), testing its applicability and consistency in two large prospective datasets.
Methods
Patient and disease-related variables and 30-day outcomes were identified in two prospective cholecystectomy databases: the multi-centre prospective cohort of 8820 patients from the recent CholeS Study and the single-surgeon series containing 4089 patients. Operative data and patient outcomes were correlated with Nassar operative difficultly scale, using Kendallâs tau for dichotomous variables, or JonckheereâTerpstra tests for continuous variables. A ROC curve analysis was performed, to quantify the predictive accuracy of the scale for each outcome, with continuous outcomes dichotomised, prior to analysis.
Results
A higher operative difficulty grade was consistently associated with worse outcomes for the patients in both the reference and CholeS cohorts. The median length of stay increased from 0 to 4 days, and the 30-day complication rate from 7.6 to 24.4% as the difficulty grade increased from 1 to 4/5 (both pâ<â0.001). In the CholeS cohort, a higher difficulty grade was found to be most strongly associated with conversion to open and 30-day mortality (AUROCâ=â0.903, 0.822, respectively). On multivariable analysis, the Nassar operative difficultly scale was found to be a significant independent predictor of operative duration, conversion to open surgery, 30-day complications and 30-day reintervention (all pâ<â0.001).
Conclusion
We have shown that an operative difficulty scale can standardise the description of operative findings by multiple grades of surgeons to facilitate audit, training assessment and research. It provides a tool for reporting operative findings, disease severity and technical difficulty and can be utilised in future research to reliably compare outcomes according to case mix and intra-operative difficulty
Heterogeneity and Common Pool Resources: Collective Management of Forests in Himachal Pradesh, India
A catalog of HI-selected galaxies from the south celestial cap region of sky
The first deep catalog of the H I Parkes All Sky Survey (HIPASS) is presented, covering the south celestial cap (SCC) region. The SCC area is similar to2400 deg(2) and covers delta < -62&DEG;. The average rms noise for the survey is 13 mJy beam(-1). Five hundred thirty-six galaxies have been cataloged according to their neutral hydrogen content, including 114 galaxies that have no previous cataloged optical counterpart. This is the largest sample of galaxies from a blind H I survey to date. Most galaxies in optically unobscured regions of sky have a visible optical counterpart; however, there is a small population of low-velocity H I clouds without visible optical counterparts whose origins and significance are unclear. The rms accuracy of the HIPASS positions is found to be 1.'9. The H I mass range of galaxies detected is from &SIM;10(6) to &SIM;10(11) M-.. There are a large number of late-type spiral galaxies in the SCC sample (66%), compared with 30% for optically selected galaxies from the same region in the NASA Extragalactic Database. The average ratio of H I mass to B luminosity of the sample increases according to optical type, from 1.8 M-./L-. for early types to 3.2 M-./L-. for late-type galaxies. The H I-detected galaxies tend to follow the large-scale structure traced by galaxies found in optical surveys. From the number of galaxies detected in this region of sky, we predict the full HIPASS catalog will contain &SIM;5000 galaxies, to a peak flux density limit of &SIM;39 mJy (3 Ï), although this may be a conservative estimate as two large voids are present in the region. The H I mass function for this catalog is presented in a subsequent paper
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