2009ApJ...692L..96F

We present spectroscopic evidence for the infall motion of gas in the natal cloud core harboring an extremely young low-mass protostar GF 9-2. We previously discussed that the ongoing collapse of the GF 9-2 core has agreement with the Larson-Penston-Hunter (LPH) theoretical solution for the gravitational collapse of a core. To discuss the gas infall on firmer ground, we have carried out on-the-fly mapping observations of the HCO⁺ (1-0) line using the Nobeyama 45 m telescope equipped with the 25 Beam Array Receiver System. Furthermore, we observed the HCN (1-0) line with the 45 m telescope, and the HCO⁺ (3-2) line with the Caltech Submillimeter Observatory 10.4 m telescope. The optically thick HCO⁺ and HCN lines show blueskewed profiles whose deepest absorptions are seen at the peak velocity of optically thin lines, i.e., the systemic velocity of the cloud, indicating the presence of gas infall toward the central protostar. We compared the observed HCO⁺ line profiles with model ones by solving the radiative transfer in the core under LTE assumption. We found that the core gas has a constant infall velocity of ∼0.5 km/s in the central region, leading to a mass accretion rate of 2.5x10^–5 M_☉/yr. Consequently, we confirm that the gas infall in the GF 9-2 core is consistent with the LPH solution.