Rotating Ionized Gas Ring around the Galactic Center IRS13E3

Abstract

We detected a compact ionized gas associated physically with IRS13E3, an Intermediate Mass Black Hole (IMBH) candidate in the Galactic Center, in the continuum emission at 232 GHz and H30$\alpha$ recombination line using ALMA Cy.5 observation (2017.1.00503.S, P.I. M.Tsuboi). The continuum emission image shows that IRS13E3 is surrounded by an oval-like structure. The angular size is $0".093\pm 0".006\times 0".061\pm 0".004$ ( $1.14\times 10^{16}$ cm $\times 0.74\times 10^{16}$ cm). The structure is also identified in the H30$\alpha$ recombination line. This is seen as an inclined linear feature in the position-velocity diagram, which is usually a defining characteristic of a rotating gas ring around a large mass. The gas ring has a rotating velocity of $V_{\mathrm{rot}}\simeq 230$ km s${}^{-1}$ and an orbit radius of $r\simeq 6\times 10^{15}$ cm. From these orbit parameters, the enclosed mass is estimated to be $M_{\mathrm{IMBH}}\simeq 2.4\times 10^4$ $M_{\odot }$. The mass is within the astrometric upper limit mass of the object adjacent to Sgr A${}^{\ast }$. Considering IRS13E3 has an X-ray counterpart, the large enclosed mass would be supporting evidence that IRS13E3 is an IMBH. Even if a dense cluster corresponds to IRS13E3, the cluster would collapse into an IMBH within $\tau <10^7$ years due to the very high mass density of $\rho \gtrsim 8\times 10^{11}{M}_{\odot }p{c}^{-3}$. Because the orbital period is estimated to be as short as $T=2\pi r/V_{\mathrm{rot}}\sim 50-100$ yr, the morphology of the observed ionized gas ring is expected to be changed in the next several decades. The mean electron temperature and density of the ionized gas are ${\bar{T}}_{\mathrm{e}}=6800\pm 700$ K and ${\bar{n}}_{\mathrm{e}}=6\times 10^5$ cm${}^{-3}$, respectively. Then the mass of the ionized gas is estimated to be $M_{\mathrm{gas}}=4\times 10^{-4}{M}_{\odot }$.

arXiv commentaccepted for publication in PASJ. 13 pages, 4 figures

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• X3: a high-mass Young Stellar Object close to the supermassive black hole Sgr~A*
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• Identification of Intermediate-mass Black Hole Candidates Among a Sample of Sd Galaxies
• Discovery of the Tadpole Molecular Cloud near the Galactic Nucleus
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