Dark supernova remnant buried in the Galactic-Centre "Brick" G0.253+0.016 revealed by an expanding CO-line bubble

Abstract

We performed a 12CO and 13CO-line study of the "Brick" (G0.253+0.016) in the Galactic Centre (GC) by analyzing archival data obtained with the Nobeyama 45-m telescope. We present kinematics and molecular gas distributions in the longitude-velocity diagram, and suggest that the Brick is located along the GC Arm I in the central molecular zone (CMZ), which yields a distance from the Sun of 8 kpc and galacto-centric distance of 0.2 kpc. The major and minor-axis diameters of the Brick are $D_x\times D_y=8.4\mathrm{pc}\times 4.1\mathrm{epc}$ at position angle of $40°$ and $130°$, respectively, and the scale radius is $r_{\mathrm{brick}}=\sqrt{D_x{D}_y}=2.96$ pc. The molecular mass inferred from the 12CO-line integrated intensity is $M_{\mathrm{bri},\mathrm{xco}}\sim 5.1\times 10^4{M}_{\odot }$ for a conversion factor $X_{\mathrm{CO}}=1.0\times 10^{20}$ H${}_2$ cm${}^{-2}$ [K km/s]${}^{-1}$. On the other hand, the dynamical (Virial) mass for the measured velocity dispersion of ${\sigma }_v=10.0$ km/s is calculated to be $M_{\mathrm{bri},\mathrm{vir}}\sim 6.8\times 10^4{M}_{\odot }$, which yields a new conversion factor of $X_{\mathrm{CO}}=1.3\times 10^{20}$ H${}_2$ cm${}^{-2}$ [K km/s]$-1$. The Brick's center has a cavity surrounded by a spherical molecular bubble of radius $r_{\mathrm{bub}}=1.85$ pc and mass $\sim 1.7\times 10^4{M}_{\odot }$ expanding at $v_{\exp }\simeq 10$ km/s with kinetic energy of $E_0\sim 1.7\times 10^{49}$ erg. If the bubble is approximated by an adiabatic spherical shock wave, the age is estimated to be $t\sim 2/5r_{\mathrm{bub}}/v_{\exp }\sim 7.2\times 10^4$ y. Neither non-thermal radio structures nor thermal radio emission indicative of HII region are found in the archival data from the MeerKAT. We suggest that the molecular bubble will be a dark supernova remnant buried in the Brick, which, therefore, has experienced in the past ($\sim 0.1$ Myr ago) massive-star formation with a supernova explosion.

15 pages, 9 figures, 1 table, accepted for PASJ (submitted on Jan.7, 2024)