Issue |
A&A
Volume 417, Number 2, April II 2004
|
|
---|---|---|
Page(s) | 421 - 435 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20034423 | |
Published online | 19 March 2004 |
The WSRT wide-field H I survey*
II. Local Group features
1
ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands
2
Department of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore MD 21218-2695, USA
Corresponding author: R. Braun, rbraun@astron.nl
Received:
30
September
2003
Accepted:
10
October
2003
We have used the Westerbork array to carry out an unbiased
wide-field survey of H i emission features, achieving an rms sensitivity
of about 18 mJy/Beam at a velocity resolution of 17 km s-1 over 1800 deg2
and between km s-1. The primary data consists of
auto-correlation spectra with an effective angular resolution of 49′
FWHM. The survey region is centered approximately on the position of
Messier 31 and is Nyquist-sampled over
° in
. In this paper we present our H i detections at negative
velocities which could be distinguished from the Galactic foreground. Fully
29% of the entire survey area has high velocity H i emission at a column
density exceeding our 3σ limit of about
cm-2
over 30 km s-1. We tabulate the properties of 95 discrete HVC components in the
field, corresponding to more than an order of magnitude increase in number
over that known previously. The distribution of discrete object number with
flux density has an inflection point near 12 Jy-km s-1 which may correspond to
a characteristic mass and distance for this population. A faint population of
discrete HVCs is detected in the immediate vicinity of M 31 which spans a large
fraction of the M 31 rotation velocity. This class of features is confined to
about 12° (160 kpc) projected radius of M 31 and appears to be
physically associated. Independent confirmation of the features within 35
(47 kpc) of M 31 has been obtained in our Green Bank Telescope survey (Thilker
et al. [CITE]). We detect a diffuse northern extension of the
Magellanic Stream (MS) from at least
, which
subsequently loops back toward the south. Recent numerical simulations had
predicted just such an MS extension corresponding to the apo-galacticon
portion of the LMC/SMC orbit at a distance of 125 kpc. A faint bridge of H i
emission appears to join the systemic velocities of M 31 with that of M 33 and
continues beyond M 31 to the north-west. This may be the first detection
of H i associated with the warm-hot intergalactic medium (WHIM). The
distribution of peculiar velocity H i associated with M 31 can be described by
a projected exponential of 25 kpc scale-length and
cm-2
peak column density. We present the distribution function of NHI in the
extended M 31 environment, which agrees well with the low red-shift QSO
absorption line data over the range log(
to
. Our data extend this comparison about two orders of
magnitude lower than previously possible and provide the first image of the
Lyman limit absorption system associated with an L
Galaxy.
Key words: galaxies: Local Group / galaxies: evolution / galaxies: formation / galaxies: Magellanic Clouds / galaxies: intergalactic medium / quasars: absorption lines
© ESO, 2004
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