Mid Infrared View of the High Mass Star Formation Region W51A

Abstract

In this paper we present the results of a mid infrared study of G49.5-0.4, or W51A, part of the massive starbirth complex W51. Combining public data from the $Spitzer$ IRAC camera, and Gemini mid infrared camera T-ReCS at 7.73, 9.69, 12.33 and 24.56 \micron, with spatial resolution of $\sim$0.5\arcsec, we have identified the mid infrared counterparts of 8 ultracompact HII regions, showing that two radio sources are deeply embedded in molecular clouds and another is a cloud of ionized gas. From the T-ReCS data we have unveiled the central core of W51 region, revealing massive young stellar candidates. We modeled the spectral energy distribution of the detected sources suggesting the embedded objects are sources with spectral types ranging from B3 to O5, but the majority of the fits indicate stellar objects with B1 spectral types. We also present an extinction map of IRS~2, showing that a region with lower extinction corresponds to the region where a proposed jet of gas has impacted the foreground cloud. From this map, we also derived the total extinction towards the enigmatic source IRS~2E, which amounts to $\sim$60 magnitudes in the $V$ band. We calculated the color temperature due to thermal emission of the circumstellar dust of the detected sources; the temperatures are in the interval of $\sim$100 -- 150 K, which corresponds to the emission of dust located at 0.1 pc from the central source. Finally, we show a possible mid infrared counterpart of a detected source at mm wavelengths that was found by \cite{zap08,zap09} to be a massive young stellar object undergoing a high accretion rate.

42 pag, 9 fig. accepted by ApJ

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Cited by in corpus (7)

• Thermal Feedback in the high-mass star and cluster forming region W51
• Surveying the Giant HII Regions of the Milky Way with SOFIA: I. W51A
• Surveying the Giant HII Regions of the Milky Way with SOFIA: IV. Sgr D, W42, and a Reassessment of the Giant HII Region Census
• Surveying the Giant HII Regions of the Milky Way with SOFIA: III. W49A
• Revisiting the formaldehyde masers
• Near-Infrared Spectroscopy of Ultracompact \ion{H}{2} regions in W51A with NIFS/ALTAIR
• GTC/CanariCam Mid-IR Polarimetry of Magnetic Fields in Star-Forming Region W51 IRS2