The RMS Survey: The Luminosity Functions and Timescales of Massive Young Stellar Objects and Compact H II Regions

• Published in: Astrophysical journal. Letters Vol. 730; no. 2; pp. L33 - jQuery1323918071489='48'
• Main Authors: Mottram, Joseph C, Hoare, Melvin G, Davies, Ben, Lumsden, Stuart L, Oudmaijer, Rene D, Urquhart, James S, Moore, Toby J. T, Cooper, Heather D. B, Stead, Joseph J
• Format: Journal Article
• Language: English
• Published: United States IOP Publishing 01.04.2011
• Subjects: ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EMISSION; FUNCTIONS; GALAXIES; LIFETIME; LUMINOSITY; MILKY WAY; OPTICAL PROPERTIES; PHYSICAL PROPERTIES; STARS
• ISSN: 2041-8205; 2041-8213
• DOI: 10.1088/2041-8205/730/2/L33

We present a determination of the luminosity functions of massive young stellar objects (MYSOs) and compact (C) H II regions within the Milky Way using the large, well-selected sample of these sources identified by the Red MSX Source survey. The MYSO luminosity function decreases monotonically such that there are few with L105 L , while the CH II regions are detected up to ~106 L . The lifetimes of these phases are also calculated as a function of luminosity by comparison with the luminosity function for local main-sequence OB stars. These indicate that the MYSO phase has a duration ranging from 4X105 yr for 104 L to ~7X104 yr at 105 L , while the CH II region phase lasts of order 3X105 yr or ~3%-10% of the exciting star's main-sequence lifetime. MYSOs between 104 L and ~105 L are massive but do not display the radio continuum or near-IR H I recombination line emission indicative of an H II region, consistent with being swollen due to high ongoing or recent accretion rates. Above ~105 L the MYSO phase lifetime becomes comparable to the main-sequence Kelvin-Helmholtz timescale, at which point the central star can rapidly contract onto the main sequence even if still accreting, and ionize a CH II region, thus explaining why few highly luminous MYSOs are observed.