A New Approach to Identifying Massive Young Stellar Objects (MYSOs)

University Of Wisconsin-Madison, Madison WI

Investigators

Abstract

Recent Spitzer Space Telescope Infrared Array Camera (IRAC) surveys of the Galactic Plane have revealed a new class of objects that are characterized by bright extended emission in the IRAC 4.5 micron band. Over 300 of these objects (designated EGOs=extended green objects, for the common coding of the 4.5 micron band as green in 3-color IRAC images) have been catalogued by Dr. Edward Churchwell (University of Wisconsin - Madison) and his team. Analysis of the mid-infrared spectral energy distributions (SEDs) of EGOs indicates that they are massive young stellar objects (MYSOs). The mechanism for exciting the 4.5 micron emission, thought to be shocked H2 or CO gas in supersonic outflows, suggests that EGOs are MYSOs in a state of active accretion. The investigators will carry out a comprehensive set of multiwavelength studies designed to characterize the properties of the newly discovered EGOs and to place constraints on theories of massive star formation; in particular how accretion, outflows and clustering operate simultaneously. Very little is currently known about EGOs other than the mid-Infrared properties derived from Spitzer data. The studies that will be carried out under this project will characterize the outflow properties, luminosities, masses, and clustering properties of a well-chosen sample of 30 EGOs, via high angular resolution studies at near-Infrared through centimeter wavelengths. These include an Extended-Very Large Array (EVLA) search for 44 GHz Class I CH3OH masers, known to be associated with molecular outflows, which will be used in conjunction with lower-resolution molecular line surveys (HCO+ and SiO) to test the hypothesis of an outflow origin for the IRAC 4.5 micron emission and measure outflow properties. An EVLA search for 6.7 GHz Class II CH3OH masers, known to be associated with MYSOs, will be used along with simultaneously obtained high-resolution 3.6 cm and 7 mm continuum data to establish the mass range of EGOs. Kinematic distances will be determined for all the sources in the sample, permitting the luminosity, stellar mass, and envelope accretion rate to be extracted from their SEDs using a grid of protostar models. These follow-up observations on this new class of objects will add much needed information on this heretofore hidden stage of high-mass protostellar evolution. In addition to the primary research goals of better understanding the nature of MYSOs, this project will support the training of one full time graduate student and several undergraduate students over its duration as well as contributing to public outreach through several local organizations, including the University of Wisconsin Space Place, the off-campus outreach center of the Department of Astronomy, and a weekly astronomy radio program.