917 research outputs found

    Testing 24 micron and Infrared Luminosity as Star Formation Tracers for Galactic Star Forming Regions

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    We have tested some relations for star formation rates used in extra-galactic studies for regions within the Galaxy. In nearby molecular clouds, where the IMF is not fully-sampled, the dust emission at 24 micron greatly underestimates star formation rates (by a factor of 100 on average) when compared to star formation rates determined from counting YSOs. The total infrared emission does no better. In contrast, the total far-infrared method agrees within a factor of 2 on average with star formation rates based on radio continuum emission for massive, dense clumps that are forming enough massive stars to have the total infrared luminosity exceed 10^4.5 Lsun. The total infrared and 24 micron also agree well with each other for both nearby, low-mass star forming regions and the massive, dense clumps regions

    The Gould Belt 'MISFITS' Survey: The Real Solar Neighborhood Protostars

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    We present an HCO+^{+} J=3-2 survey of Class 0+I and Flat SED young stellar objects (YSOs) found in the Gould Belt clouds by surveys with Spitzer. Our goal is to provide a uniform Stage 0+I source indicator for these embedded protostar candidates. We made single point HCO+^{+} J = 3-2 measurements toward the source positions at the CSO and APEX of 546 YSOs (89% of the Class 0+I + Flat SED sample). Using the criteria from van Kempen et al. (2009), we classify sources as Stage 0+I or bona fide protostars and find that 84% of detected sources meet the criteria. We recommend a timescale for the evolution of Stage 0+I (embedded protostars) of 0.54 Myr. We find significant correlations of HCO+^{+} integrated intensity with α{\alpha} and TbolT_{bol} but not with LbolL_{bol}. The detection fraction increases smoothly as a function of α{\alpha} and LbolL_{bol}, while decreasing smoothly with TbolT_{bol}. Using the Stage 0+I sources tightens the relation between protostars and high extinction regions of the cloud; 89% of Stage I sources lie in regions with AVA_{V} >8 mag. Class 0+I and Flat SED YSOs that are not detected in HCO+^{+} have, on average, a factor of ~2 higher TbolT_{bol} and a factor of ~5 lower LbolL_{bol} than YSOs with HCO+^{+} detections. We find less YSO contamination, defined as the number of undetected YSOs divided by the total number surveyed, for sources with TbolT_{bol}\lesssim 600 K and LbolL_{bol} \gtrsim 1 LL_{\odot}. The contamination percentage is >90% at AVA_{V}< 4 mag and decreases as AVA_{V} increases.Comment: 28 pages, 11 figures, 5 tables. Accepted for publication to the Astrophysical Journa