ΛCDM Satellites and H I Companions—the Arecibo ALFA Survey of NGC 2903

Putman, M. E.; Haynes, M. P.; Davies, J.; de Blok, W. J. G.; Brinks, E.; Giovanelli, R.; van Driel, W.; Momjian, E.; Irwin, J. A.; Catinella, B.; Hoffman, G. Lyle; Linder, S. M.; Koribalski, B. S.; Spekkens, K.

ΛCDM Satellites and H I Companions—the Arecibo ALFA Survey of NGC 2903

Abstract

We have conducted a deep, complete H i survey, using Arecibo/Arecibo L-band Feed Array (ALFA), of a field
centered on the nearby, isolated galaxy, NGC 2903, which is similar to the MilkyWay in its properties. The field size
was 150 kpc × 260 kpc and the final velocity range spanned from 100 to 1133 km s−1. The ALFA beams have been
mapped as a function of azimuth and cleaned from each azimuth-specific cube prior to forming final cubes. The final
H i data are sensitive down to an H i mass of 2×105M and column density of 2 × 1017 cm−2 at the 3 σ 2δ V level,
where σ is the rms noise level and δ V is the velocity resolution. NGC 2903 is found to have an H i envelope that
is larger than previously known, extending to at least three times the optical diameter of the galaxy. Our search for
companions yields one newdiscovery with anHi mass of 2.6×106M . The companion is 64 kpc fromNGC2903 in
projection, is likely associated with a small optical galaxy of similar total stellarmass, and is darkmatter dominated,
with a total mass >108 M . In the region surveyed, there are now two known companions: our new discovery and
a previously known system that is likely a dwarf spheroidal, lacking H i content. If H i constitutes 1% of the total
mass in all possible companions, then we should have detected 230 companions, according to Λ cold dark matter
(ΛCDM) predictions. Consequently, if this number of dark-matter clumps are indeed present, then they contain less
than 1% H i content, possibly existing as very faint dwarf spheroidals or as starless, gasless dark-matter clumps.

Title	ΛCDM Satellites and H I Companions—the Arecibo ALFA Survey of NGC 2903
Creator	Putman, M. E.
	Haynes, M. P.
	Davies, J.
	de Blok, W. J. G.
	Brinks, E.
	Giovanelli, R.
	van Driel, W.
	Momjian, E.
	Irwin, J. A.
	Catinella, B.
	Hoffman, G. Lyle
	Linder, S. M.
	Koribalski, B. S.
	Spekkens, K.
Publisher	Astrophysical Journal
Academic Department	Physics
Division	Natural Sciences
Organization	Lafayette College
Date Issued	February 20, 2009
Date Available	2010-01-08T15:09:50Z
Type	Article
Language	English
Keyword	galaxies: spiral
	galaxies: individual (NGC 2903)
	radio lines: ISM
	dark matter
	galaxies: formation
Bibliographic Citation	Irwin, J. A., G. L. Hoffman, et al. (2009). "ΛCDM Satellites and H I Companions—the Arecibo ALFA Survey of NGC 2903." Astrophysical Journal 692: 1447-1463.
Standard Identifier	DOI 10.1088/0004-637X/692/2/1447
Standard Identifier	Handle 10385/543
Permalink	http://hdl.handle.net/10385/543
Rights Statement	In Copyright
Rights Holders	American Astronomical Society