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A first core is a first hydrostatic object formed in the course of dynamicalcontraction of a molecular cloud core. Since the inflow pattern changesdrastically before and after the first core formation, it is regarded as amilestone in the star formation process. In order to identify the first corefrom a mapping observation, the features expected for the first core arestudied for CS rotation transitions at radio wavelengths. The non-LTE radiationtransfer is calculated for the results of radiation magnetohydrodynamicalsimulations of the contraction of the magnetized molecular cloud core inrotation (Tomida et al. 2010a). We use the Monte-Carlo method to solve thenon-LTE radiation transfer in a nested grid hierarchy. In the first core phase,an outflow arises from the vicinity of the first core due to the twistedmagnetic field amplified by the rotation motion of the contracting gas disk.The disk and outflow system has several characteristic observational features:(i) in the pole-on view, relatively opaque lines indicate asymmetry in theemission lines in which the blue side is stronger than the red side (an infallsignature of the envelope); (ii) in the edge-on view, the disk has a signatureof simultaneous rotation and infall, i.e., the integrated intensity of thereaching side is brighter than that of the receding side and the gradient inthe intensity-weighted velocity is larger in the reaching side; (iii) theobserved outflow indicates rotation around the rotation axis. The size of theoutflow gives the approximate age after the first core is formed, since theoutflow is not expected for the earlier runaway isothermal collapse phase.

Observational Identification of First Cores: Non-LTE Radiative Transfer Simulation