* Astronomy

Title: A Candidate for the Most Luminous OB Association in the Galaxy
Authors: Mubdi Rahman, Christopher Matzner, Dae-Sik Moon

The Milky Way harbours giant H II regions which may be powered by star complexes more luminous than any Galactic OB association known. Being across the disk of the Galaxy, however, these brightest associations are severely extinguished and confused. We present a search for one such association toward the most luminous H II region in the recent catalogue by Murray and Rahman, which, at ~9.7 kpc, has recombination rate of ~7x10^{51} sec^{-1}. Prior searches have identified only small scale clustering around the rim of this shell-like region, but the primary association has not previously been identified. We apply a near-infrared colour selection and find an overdensity of point sources toward its southern central part. The colours and magnitudes of these excess sources are consistent with O- and early B-type stars at extinctions 0.96 < A_{K} < 1.2, and they are sufficiently numerous (406 ±102 after subtraction of field sources) to ionise the surrounding H II region, making this a candidate for the most luminous OB association in the Galaxy. We reject an alternate theory, in which the apparent excess is caused by localized extinction, as inconsistent with source demographics.

Read more (4742kb, PDF)