A Detailed Study of the Interstellar Protons toward the TeV γ-Ray SNR RX J0852.0-4622 (G266.2-1.2, Vela Jr.): The Third Case of the γ-Ray and ISM Spatial Correspondence

We present a new analysis of the interstellar protons toward the TeV γ-ray SNR RX J0852.0-4622 (G266.2-1.2, Vela Jr.). We used the NANTEN2 ¹²CO(J = 1-0) and Australia Telescope Compact Array and Parkes H i data sets in order to derive the molecular and atomic gas associated with the TeV γ-ray shell of the SNR. We find that atomic gas over a velocity range from V _LSR = -4 to 50 km s^-1 or 60 km s^-1 is associated with the entire SNR, while molecular gas is associated with a limited portion of the SNR. The large velocity dispersion of the H i is ascribed to the expanding motion of a few H i shells overlapping toward the SNR but is not due to the Galactic rotation. The total masses of the associated H i and molecular gases are estimated to be M _o and ∼10³ M _o, respectively. A comparison with the High Energy Stereoscopic System TeV γ-rays indicates that the interstellar protons have an average density around 100 cm^-3 and shows a good spatial correspondence with the TeV γ-rays. The total cosmic-ray proton energy is estimated to be ∼10⁴⁸ erg for the hadronic γ-ray production, which may still be an underestimate by a factor of a few due to a small filling factor of the SNR volume by the interstellar protons. This result presents a third case, after RX J1713.7-3946 and HESS J1731-347, of the good spatial correspondence between the TeV γ-rays and the interstellar protons, lending further support for a hadronic component in the γ-rays from young TeV γ-ray SNRs.