Journal
ASTRONOMICAL JOURNAL
Volume 140, Issue 1, Pages 157-166Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-6256/140/1/157
Keywords
catalogs; Galaxy: general; H II regions; ISM: supernova remnants; radio continuum: ISM; surveys
Categories
Funding
- National Science Foundation [AST-05-07598, AST-02-6-55]
- US Department of Energy by Lawrence Livermore National Laboratory [W-7405-ENG-48]
- NASA [NAG5-13062]
- Space Telescope Science Institute [NAS5-26555]
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Using three epochs of Very Large Array observations of the Galactic plane in the first quadrant taken similar to 15 years apart, we have conducted a search for a population of variable Galactic radio emitters in the flux density range 1-100 mJy at 6 cm. We find 39 variable sources in a total survey area of 23.2 deg(2). Correcting for various selection effects and for the extragalactic variable population of active galactic nuclei, we conclude there are similar to 1.6 deg(-2) Galactic sources which vary by more than 50% on a time scale of years (or shorter). We show that these sources are much more highly variable than extragalactic objects; more than 50% show variability by a factor >2 compared to <10% for extragalactic objects in the same flux density range. We also show that the fraction of variable sources increases toward the Galactic center (another indication that this is a Galactic population), and that the spectral indices of many of these sources are flat or inverted. A small number of the variables are coincident with mid-IR sources and two are coincident with X-ray emitters, but most have no known counterparts at other wavelengths. Intriguingly, one lies at the center of a supernova remnant, while another appears to be a very compact planetary nebula; several are likely to represent activity associated with star formation regions. We discuss the possible source classes which could contribute to the variable cohort and follow-up observations which could clarify the nature of these sources.
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