SPITZER-IRAC SURVEY OF MOLECULAR JETS IN VELA-D

We present a survey of H2 jets from young protostars in the Vela-D molecular cloud (VMR-D), based on Spitzer-IRAC data between 3.6 ?m and 8.0 ?m. Our search has led to the identification of 15 jets (two new discoveries) and about 70 well-aligned knots within 1.2?deg2. We compare the Infrared Array Camera (IRAC) maps with observations of the H2 1-0 S(1) line at 2.12 ?m, with a Spitzer-MIPS map at 24 ?m and 70 ?m, and with a map of the dust continuum emission at 1.2?mm. From such a comparison, we find a tight association between molecular jets and dust peaks. The jet candidate exciting sources have been searched for in the published catalog of the young stellar objects of VMR-D. In particular, we searched for all the sources of Class II or (preferentially) earlier which are located close to the jet center and aligned with it. Furthermore, the association between jet and exciting source was validated by estimating the differential extinction between the jet opposite lobes. We are able to find a best-candidate exciting source in all but two jets, for which two alternative candidates are given. Four exciting sources are not (or very barely) observed at wavelengths shorter than 24 ?m, suggesting that they are very young protostars. Three of them are also associated with the most compact jets (projected length 0.1?pc). The exciting source spectral energy distributions (SEDs) have been constructed and modeled by means of all the available photometric data between 1.2 ?m and 1.2?mm. From SEDs fits, we derive the main source parameters, which indicate that most of them are low-mass protostars. A significant correlation is found between the projected jet length and the [24]?[70] color, which is consistent with an evolutionary scenario according to which shorter jets are associated with younger sources. A rough correlation is found between IRAC line cooling and exciting source bolometric luminosity, in agreement with the previous literature. The emerging trend suggests that mass loss and mass accretion are tightly related phenomena and that both decrease with time.