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

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

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Title: ΛCDM Satellites and H I Companions—the Arecibo ALFA Survey of NGC 2903
Author: van Driel, W.; Putman, M. E.; Momjian, E.; Brinks, E.; de Blok, W. J. G.; Koribalski, B. S.; Davies, J.; Catinella, B.; Linder, S. M.; Hoffman, G. Lyle; Haynes, M. P.; Giovanelli, R.; Irwin, J. A.; Spekkens, K.
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.
URI: http://hdl.handle.net/10385/543
Date: 2009-02-20

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