A detailed study of the interstellar protons toward the TeV gamma-ray SNR RX J0852.0-4622 (G266.2-1.2, Vela Jr.) : the third case of the gamma-Ray and ISM spatial correspondence

We present a new analysis of the interstellar protons toward the TeV gamma-ray SNR RX J0852.0-4622 (G266.2-1.2, Vela Jr.). We used the NANTEN2 (CO)-C-12(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 gamma-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 similar to 2.5 x 10(4) M-circle dot and similar to 10(3) M-circle dot), respectively. A comparison with the High Energy Stereoscopic System TeV gamma-rays indicates that the interstellar protons have an average density around 100 cm(-3) and shows a good spatial correspondence with the TeV gamma-rays. The total cosmic-ray proton energy is estimated to be 1048 erg for the hadronic gamma-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 gamma-rays and the interstellar protons, lending further support for a hadronic component in the gamma-rays from young TeV gamma-ray SNRs.