THE NEUTRAL HYDROGEN BRIDGE BETWEEN M31 AND M33
- National Radio Astronomy Observatory, Green Bank, WV 24944 (United States)
The Green Bank Telescope has been used to search for 21 cm H I emission over a large area between the galaxies M31 and M33 in an attempt to confirm at 9.'1 angular resolution the detection by Braun and Thilker of a very extensive neutral gas 'bridge' between the two systems at the level N{sub HI} Almost-Equal-To 10{sup 17} cm{sup -2}. We detect H I emission at several locations up to 120 kpc in projected distance from M31, at least half the distance to M33, with velocities similar to that of the galaxies, confirming the essence of the Braun and Thilker discovery. The H I does not appear to be associated with the extraplanar high-velocity clouds of either galaxy. In two places we measure N{sub HI} > 3 Multiplication-Sign 10{sup 18} cm{sup -2}, indicative of concentrations of H I with {approx}10{sup 5} M{sub Sun} on scales {approx}< 2 kpc, but over most of the field we have only 5{sigma} upper limits of N{sub HI} {<=} 1.4 Multiplication-Sign 10{sup 18} cm{sup -2}. In very deep measurements in two directions H I lines were detected at a few 10{sup 17} cm{sup -2}. The absence of emission at another location to a 5{sigma} limit N{sub HI} {<=} 1.5 Multiplication-Sign 10{sup 17} cm{sup -2} suggests that the H I bridge is either patchy or confined to within {approx}125 kpc of M31. The measurements also cover two of M31's dwarf galaxies, And II and And XV, but in neither case is there evidence for associated H I at the 5{sigma} level of 1.4 Multiplication-Sign 10{sup 4} M{sub Sun} for And II and 9.3 Multiplication-Sign 10{sup 3} M{sub Sun} for And XV.
- OSTI ID:
- 22034388
- Journal Information:
- Astronomical Journal (New York, N.Y. Online), Vol. 144, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-3881
- Country of Publication:
- United States
- Language:
- English
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