Nothing to Hide - Mid-infrared and X-ray Surveys of Star Formation Activity in the Pipe Nebula

Forbrich, Jan; Lada, C. J.; Muench, A.; Alves, J.; Lombardi, M.; Posselt, B.; Covey, K.
American Astronomical Society, AAS Meeting #215, #414.22; Bulletin of the American Astronomical Society, Vol. 42, p.257


The Pipe Nebula, a large nearby molecular cloud, lacks obvious signposts of star formation in all but one of more than 130 dust extinction cores that have been identified within it. In order to quantitatively determine the current level of star formation activity in the Pipe Nebula, we analyzed 13 square degrees of sensitive mid-infrared maps of the entire cloud, obtained with the Multiband Imaging Photometer for Spitzer at wavelengths of 24 micron and 70 micron, to search for candidate young stellar objects (YSOs) in the high-extinction regions. We argue that our search is complete for class I and typical class II YSOs with bolometric luminosities of about 0.2 solar luminosities and greater. We find only 18 candidate YSOs in the high-extinction regions of the entire Pipe cloud. Twelve of these sources are previously known members of a small cluster associated with Barnard 59, the largest and most massive dense core in the cloud. With only six candidate class I and class II YSOs detected toward extinction cores outside of this cluster, our findings emphatically confirm the notion of an extremely low level of star formation activity in the Pipe Nebula. The resulting star formation efficiency for the entire cloud mass is only 0.06%. X-ray observations allow us to extend our survey to constrain any population of classical and weak-line T Tauri stars. In a first step, we use the ROSAT All-Sky Survey to constrain any overall T Tauri star population of the Pipe Nebula. Subsequently, we use XMM-Newton observations pointed at three high-extinction regions within the Pipe Nebula to analyze these regions at higher sensitivity. The X-ray data contain no indications of an additional YSO population and corroborate our previous Spitzer result that the star formation efficiency of the Pipe Nebula is extremely low.