The Luminosity Functions and Timescales of MYSOs and Compact HII regions

Abstract

We present a determination of the luminosity functions of massive young stellar objects (MYSOs) and compact (C)HII regions within the Milky Way Galaxy using the large, well-selected sample of these sources identified by the Red MSX Source (RMS) survey. The MYSO luminosity function decreases monotonically such that there are few with $L\gtrsim 10^5$Lsol, whilst the CHII regions are detected up to ~10${}^{6}Lsol.Thelifetimesofthesephasesarealsocalculatedasafunctionofluminositybycomparisonwiththeluminosityfunctionforlocalmain-sequenceOBstars.TheseindicatethattheMYSOphasehasadurationrangingfrom4x10$^{5}$yrsfor10$^{4}$Lsolto7x10$^{4}$yrsat10$^{5}$Lsol,whilsttheCHIIregionphaselastsoforder3x10$^{5}$yrsor3-10$^{4} Lsol and ~10${}^5$ Lsol are massive but do not display the radio continuum or near-IR \HI{} recombination line emission indicative of an HII region, consistent with being swollen due to high ongoing or recent accretion rates. Above ~10${}^5$ Lsol 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 ionise a CHII region, thus explaining why few highly luminous MYSOs are observed.

16 pages in pre-print format, 4 figures, 1 table, accepted to ApJL

References in corpus (4)

• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• The RMS Survey: Radio observations of candidate massive YSOs in the southern hemisphere
• The RMS Survey: Mid-Infrared Observations of Candidate Massive YSOs in the Southern Hemisphere
• The RMS Survey: ${}^{13}$CO observations of candidate massive YSOs in the northern Galactic plane

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• [Fe II] 1.64 um Imaging Observations of the Outflow Features around Ultracompact H II Regions in the 1st Galactic Quadrant
• Herschel Hi-GAL imaging of massive young stellar objects