Oral Presentation
The relation between CMF and IMF in Orion A
Presenter: Hideaki Takemura (SOKENDAI / NAOJ)
Stars are formed in dense cores in molecular clouds. Therefore, it is important to understand how dense cores form from parental molecular clouds. In this study, we investigated core mass functions (CMFs) in Orion A using ALMA N2H+ data of OMC-1 (~4.5”) and wide-field CARMA-NRO combined C18O data (~8”). Applying Dendrogram to the N2H+ and C18O data cube, we identified 263 and 2033 starless cores, respectively. With these finest maps, we successfully resolved progenitors of stars in Orion A for the first time. In this presentation, we focus on the Orion Nebular Cluster region and directly compare between CMF and stellar mass function in the range of ~0.1 Msolar to ~10 Msolar. One of the interesting features is that the peak mass almost coincides with each other at a mass of ~0.1 Msolar. Taking into account the fact that stellar feedback blows out most of the core mass (~70%), the coincidence of the peak mass implies that accretion of the surrounding gas and/or core merging may be important to determine the final stellar masses. Another interesting feature is that CMF has a slope similar to the stellar MF at the high mass part (1~10 Msolar). The similar slope indicates that to reproduce the Salpeter IMF from our CMF, the timescales of core evolution and star formation are more or less independent of the core mass. Finally, if time permits, we present CMFs in three subregions of Orion A (OMC-1/2/3, OMC-4/5, L1641N/V380Ori ). We found low-mass parts of CMFs varies from region to region. For example, the low-mass core population (~0.1 Msolar) is significantly deficient in the southern region. Thus, our CMFs predict that the fraction of brown dwarfs is significantly lower in the southern part than that in the northern part. For high-mass parts, the most massive core in Orion A was found in OMC-1/2/3 region, having a mass of ~ 20 Msolar. On the other hand, we did not find massive cores with masses greater than 3 Msolar. This suggests that in the southern region, at most intermediate-mass stars such as late B and A stars can form. Our results may indicate that the core formation significantly depend on cloud environments.
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