arXiv subjects

Masaya Yamada

Publications and source records attributed to Masaya Yamada.

3 recordsLinked to original sources

arXiv2018

Magnetohydrodynamic Simulations of a Plunging Black Hole into a Molecular Cloud

Using two-dimensional magnetohydrodynamic simulations, we investigated the gas dynamics around a black hole plunging into a molecular cloud. In these calculations, we assumed a parallel-magnetic-field layer in the cloud. The size of the accelerated region is far larger than the Bondi-Hoyle-Lyttleton radius, being approximately inversely proportional to the Alfvén Mach number for the plunging black hole. Our results successfully reproduce the "Y" shape in position velocity maps of the "Bullet" in the W44 molecular cloud. The size of the Bullet is also reproduced within an order of magnitude using a reasonable parameter set. This consistency supports the shooting model of the Bullet, according to which an isolated black hole plunged into a molecular cloud to form a compact broad-velocity-width feature.

astro-ph.GA↗

arXiv2018

Detection of Another Molecular Bubble in the Galactic Center

The $l=-1.2^{\circ}$ region in the Galactic center has a high CO $J$=3-2/$J$=1-0 intensity ratio and extremely broad velocity width. This paper reports the detection of five expanding shells in the $l=-1.2^{\circ}$ region based on the CO $J$=1-0, $^{13}$CO $J$=1-0, CO $J$=3-2, and SiO $J$=8-7 line data sets obtained with the Nobeyama Radio Observatory 45 m telescope and James Clerk Maxwell Telescope. The kinetic energy and expansion time of the expanding shells are estimated to be $10^{48.3-50.8}$ erg and $10^{4.7-5.0}$ yr, respectively. The origin of these expanding shells is discussed. The total kinetic energy of $10^{51}$ erg and the typical expansion time of ${\sim}10^5$ yr correspond to multiple supernova explosions at a rate of $10^{-5}$-$10^{-4}$ yr$^{-1}$. This indicates that the $l=-1.2^{\circ}$ region may be a molecular bubble associated with an embedded massive star cluster, although the absence of an infrared counterpart makes this interpretation somewhat controversial. The expansion time of the shells increases as the Galactic longitude decreases, suggesting that the massive star cluster is moving from Galactic west to east with respect to the interacting molecular gas. We propose a model wherein the cluster is moving along the innermost x1 orbit and the interacting gas collides with it from the Galactic eastern side.

astro-ph.GA↗

arXiv2016

Kinematics of Ultra-High-Velocity Gas in the Expanding Molecular Shell adjacent to the W44 Supernova Remnant

We mapped the ultra-high-velocity feature (the "Bullet") detected in the expanding molecular shell associated with the W44 supernova remnant using the Nobeyama Radio Observatory 45-m telescope and the ASTE 10-m telescope. The Bullet clearly appears in the CO ${\it J}$=1-0, CO ${\it J}$=3-2, CO ${\it J}$=4-3, and HCO$^+$ ${\it J}$=1-0 maps with a compact appearance ($0.5\times 0.8$ pc$^2$) and an extremely broad velocity width ($ΔV\!\simeq\!100 \ \rm km \, s ^{-1}$). The line intensities indicate that the Bullet has a higher density and temperature than those in the expanding molecular shell. The kinetic energy of the Bullet amounts to $10^{48.0} \ {\rm erg}$ which is approximately 1.5 orders of magnitude greater than the kinetic energy shared to the small solid angle of it. Two possible formation scenarios with an inactive isolated black hole (BH) are presented.

astro-ph.GA↗