Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Arecibo Legacy Fast ALFA Survey: II. Results of Precursor
  Observations   In preparation for the full Arecibo Legacy Fast ALFA extragalactic HI survey,
precursor observations were carried out in Aug--Sep 2004 with the 7-beam
Arecibo L-band feed array (ALFA) receiver system and the WAPP spectral
processors. While these observations were geared mainly at testing and
debugging survey strategy, hardware and software, approximately 36 hours of
telescope time yielded science--quality data. From those observations, an
initial list of 730 tentative detections of varying degree of reliability was
extracted. Ninety--eight high signal-to-noise candidates were deemed to be bona
fide HI line detections. To test our ability to discriminate cosmic signals
from RFI and noise, 165 candidates ranging in reliability likelihood were
re--observed with the single beam L--band wide system at Arecibo in Jan--Feb
2005. Of those, 41% were confirmed as real. We present the results of both the
ALFA and single beam observations for the sample of 166 confirmed HI sources,
as well as our assessment of their optical counterparts. Of the 166 sources, 62
coincide with previously known HI sources, while optical redshifts were
available for an additional 18 galaxies; thus, 52% of the redshifts reported
here were previously unknown. Of the 166 HI detections, 115 are identified with
previously cataloged galaxies, of either known or unknown redshift, leaving 51
objects identified for the first time. Because of the higher sensitivity of the
Arecibo system, fewer than 10% of the 166 HI sources would have been detected
by a HIPASS--like survey of the same region. Three of the objects have HI
masses less than 10^7 solar masses. The full ALFALFA survey which commenced in
February 2005 should detect more than 100 times as many objects of similarly
low HI mass over the next 5 years.

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The categories of this paper are: q-alg
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The categories of this paper are: comp-gas
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The categories of this paper are: solv-int
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The categories of this paper are: cs
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The categories of this paper are: nucl-th
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The categories of this paper are: econ
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The categories of this paper are: acc-phys
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The categories of this paper are: stat
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The categories of this paper are: physics
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The categories of this paper are: quant-ph
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The categories of this paper are: adap-org
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The categories of this paper are: math
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The categories of this paper are: nucl-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: q-bio
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The categories of this paper are: alg-geom