Spitzer MIPS Survey of the Young Stellar Content in the Vela Molecular Ridge-D

A new, unbiased Spitzer MIPS imaging survey (~1.8 deg2) of the young stellar content of the Vela Molecular Ridge-D (VMR-D) is presented. The survey is complete down to 5 and 250 mJy at 24 and 70 μm, respectively. A total of 849 sources are detected at 24 μm, and 52 of them also have a 70 μm counterpart. The VMR-D region is one that we have already partially mapped in dust and gas millimeter emission, and we discuss the correlation between the Spitzer compact sources and the millimeter contours. About half of the 24 μm sources are located inside the region delimited by the 12CO(1-0) contours, corresponding to only one-third of the full area mapped with MIPS. Therefore, the 24 μm source density increases by about 100% moving from outside to inside the CO contours. For the 70 μm sources, the corresponding density increase is a factor of 4. About 400 sources of these have a 2MASS counterpart, and we have used this to construct a Ks versus Ks - [24] diagram and to identify the protostellar population inside the cloud. We find an excess of Class I sources in VMR-D in comparison with other star-forming regions. This result could be reasonably biased by the sensitivity limits at 2.2 and 24 μm or, alternatively, may reflect a very short lifetime (≲106 yr) for the protostellar content in this molecular cloud. The MIPS images have identified embedded cool objects in most of the previously identified starless cores in the region; in addition, there are six very young, possibly Class 0 objects identified. Finally, we report finding the driving sources for a set of five out of six very compact protostellar jets that had been previously discovered in near-IR images of VMR-D.