243 research outputs found
The Effelsberg-Bonn HI Survey (EBHIS)
The new L-band 7-feed-array at the 100-m telescope in Effelsberg will be used
to perform an unbiased fully sampled HI survey of the entire northern
hemisphere observing the galactic and extragalactic sky using simultaneously
two different backends.
The survey will be extremely valuable for a broad range of research topics:
study of the low-mass end of the HI mass function (HIMF) in the local volume,
environmental and evolutionary effects (as seen in the HIMF), the search for
galaxies near low-redshift Lyman-alpha absorbers, and analysis of multiphase
and extraplanar gas, HI shells, and ultra-compact high-velocity-clouds.Comment: 2 pages, 1 figure, to appear in proceeding of "Galaxies in the Local
Volume" Sydney 8-13 July 200
Large Scale Structure in CHILES
We demonstrate that the Discrete Persistent Source Extractor (DisPerSE) can
be used with spectroscopic redshifts to define the cosmic web and its distance
to galaxies in small area deepfields. Here we analyze the use of DisPerSE to
identify structure in observational data. We apply DisPerSE to the distribution
of galaxies in the COSMOS field and find the best parameters to identify
filaments. We compile a catalog of 11500 spectroscopic redshifts from the
Galaxy and Mass Assembly (GAMA) G10 data release. We analyze two-dimensional
slices, extract filaments and calculate the distance for each galaxy to its
nearest filament. We find that redder and more massive galaxies are closer to
filaments. To study the growth of galaxies across cosmic time, and environment,
we are carrying out an HI survey covering redshifts z = 0 - 0.45, the COSMOS HI
Large Extragalactic Survey (CHILES). In addition we present the predicted HI
mass fraction as a function of distance to filaments for the spectroscopically
known galaxies in CHILES. Lastly, we discuss the cold gas morphology of a few
individual galaxies and their positions with respect to the cosmic web. The
identification of the cosmic web, and the ability of CHILES to study the
resolved neutral hydrogen morphologies and kinematics of galaxies, will allow
future studies of the properties of neutral hydrogen in different cosmic web
environments across the redshift range z = 0.1 - 0.45.Comment: Accepted for publication in the Astronomical Journal; 11 pages ; 8
figure
The HI distribution in the outskirts of M33 with the ALFALFA survey
Spiral galaxies appear to be dynamical systems whose disks are still forming
at the current epoch and which continue to accrete mass. The presence of
extraplanar gas in spirals indicates that galactic halos can contain at least
part of the material needed to fuel the star formation activity in their disks.
Here we present the analysis of the ALFALFA survey data in the region of M33
aimed at searching high velocity clouds around this Local Group galaxy. We find
a varied population of HI clouds with masses ranging between 4 x 10^4 and few
times 10^6 M_sun. We also detect an extended HI complex at anomalous
velocities, whose extragalactic nature cannot be firmly established. We
estimate that the total amount of neutral hydrogen mass associated to these
clouds is around 10^7 M_sun.Comment: 3 pages, 2 figures, to appear in the Conference Proceedings "The
Evolution of Galaxies through the Neutral Hydrogen Window",eds. R. Minchin &
E. Momjia
A GBT Survey for HI 21 cm Absorption in the Disks and Halos of Low-Redshift Galaxies
We present an HI 21 cm absorption survey with the Green Bank Telescope (GBT)
of galaxy-quasar pairs selected by combining data from the Sloan Digital Sky
Survey (SDSS) and the Faint Images of the Radio Sky at Twenty-Centimeters
(FIRST) survey. Our sample consists of 23 sightlines through 15 low-redshift
foreground galaxy - background quasar pairs with impact parameters ranging from
1.7 kpc up to 86.7 kpc. We detected one absorber in the GBT survey from the
foreground dwarf galaxy, GQ1042+0747, at an impact parameter of 1.7 kpc and
another possible absorber in our follow-up Very Large Array (VLA) imaging of
the nearby foreground galaxy, UGC 7408. Both of the absorbers are narrow (FWHM
of 3.6 and 4.8 km/s), have sub Damped Lyman alpha column densities, and most
likely originate in the disk gas of the foreground galaxies. We also detected H
I emission from three foreground galaxies, including UGC 7408. Although our
sample contains both blue and red galaxies, the two H I absorbers as well as
the H I emissions are associated with blue galaxies. We discuss the physical
conditions in the 21 cm absorbers and some drawbacks of the large GBT beam for
this type of survey.Comment: 15 pages, 6 figures, 3 table
The Arecibo Galaxy Environments survey IV: the NGC7448 region and the HI mass function
In this paper we describe results from the Arecibo Galaxy Environments Survey
(AGES). The survey reaches column densities of ~3x10^18 cm^-2 and masses of
~10^7 M_O, over individual regions of order 10 sq deg in size, out to a maximum
velocity of 18,000 km s^-1. Each surveyed region is centred on a nearby galaxy,
group or cluster, in this instance the NGC7448 group. Galaxy interactions in
the NGC7448 group reveal themselves through the identification of tidal tails
and bridges. We find ~2.5 times more atomic gas in the inter-galactic medium
than in the group galaxies. We identify five new dwarf galaxies, two of which
appear to be members of the NGC7448 group. This is too few, by roughly an order
of magnitude, dwarf galaxies to reconcile observation with theoretical
predictions of galaxy formation models. If they had observed this region of sky
previous wide area blind HI surveys, HIPASS and ALFALFA, would have detected
only 5% and 43% respectively of the galaxies we detect, missing a large
fraction of the atomic gas in this volume. We combine the data from this paper
with that from our other AGES papers (370 galaxies) to derive a HI mass
function with the following Schechter function parameters alpha=-1.52+/-0.05,
M^*=5.1+/-0.3x10^9 h_72^-2 M_O, phi=8.6+/-1.1x10-3 h_72^3 Mpc^-3 dex-1.
Integrating the mass function leads to a cosmic mass density of atomic hydrogen
of Omega_HI=5.3+/-0.8x10^-4 h_72^-1. Our mass function is steeper than that
found by both HIPASS and ALFALFA (alpha=1.37 and 1.33 respectively), while our
cosmic mass density is consistent with ALFALFA, but 1.7 times larger than found
by HIPASS
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