EPoS Contribution
EPoS Contribution
Star Formation Rate and Efficiency in the Orion A Giant Molecular Cloud

Josefa Grossschedl
U Vienna, Vienna, AT
We construct resolved maps of SFR and SFE across the entire archetypical GMC Orion A (using a Planck/Herschel dust column-density map), after updating existing YSO catalogs in this region. To refine previously existing catalogues of YSOs we used a deep NIR ESO-VISTA survey allowing us to rule out false positives from previous samples (e.g. galaxies, cloud edges), and to add new candidates (about 200) to get a complete census of the spatial distribution of YSOs in this cloud beyond the Spitzer coverage. We find that the spatial distribution of flat spectrum sources shows a stronger connection to regions of high dust column-density compared to Class IIs. This suggests that flats may not be an observational artefact, as often suggested in the literature (disk inclination effects), and should be considered as a younger evolutionary phase, likely closer to the protostellar phase (Class I). From the resolved SFR and SFE maps of the cloud we find that the SFR varies by about a factor of 10 across the cloud (highest at ONC) while the instantaneous SFE is about constant (within a factor of two). We present the SFR and SFE profiles along the Orion A main filament in the Figure below. The increased SFR at the head of the cloud, including the ONC region, could be explained by cloud compression by external feedback mechanisms (e.g. SNe feedback, feedback from the local massive stars). Remarkably, the efficiency of conversion of dense gas into stars seems to be largely independent of external processes and might be an intrinsic property of the star forming gas.
Caption: Bottom: Planck-Herschel dust column-density map (Lombardi et al. 2014) including contours at AK=0.8 mag (red). This is a suggested star formation threshold (Lada et al. 2010), which is used to calculated the star formation efficiency. The vertical colored lines indicate the bins over which the gas mass and YSO stellar mass is sampled (YSOs not shown here). Top: Star formation rate (SFR, dark blue) and instantaneous star formation efficiency (SFE, orange) along the cloud (i.e. along galactic longitude) with the same x-axis as the map below. The SFR is calculated using all known YSOs (with IR-excess), while the SFE is calculated using only protostars and flat-spectrum sources, since these sources are at a younger evolutionary stage and therefore are more likely still directly connected to the denser parts of the cloud. The two black vertical dashed lines give the cloud boundaries, to exclude regions without significant gas mass, i.e. the grey shaded areas in the top plot should be ignored.
Collaborators:
J. Alves, U Vienna, AT
S. Meingast, U Vienna, AT
A. Hacar, Leiden, NL
C. Lada, CfA, US
Suggested Session: Star formation "laws" and IMF