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Asad Ukani

Publications and source records attributed to Asad Ukani.

2 recordsLinked to original sources

Stellar-wind Fueled Accretion onto Sagittarius A* in the Presence of a Nuclear Star Cluster

The Milky Way's Galactic Center hosts the black hole Sagittarius A* (Sgr A*), which provides us with a close-up view into supermassive black hole accretion and feedback. Recent works have shown that the winds from $\sim 30$ Wolf-Rayet (WR) stars orbiting Sgr A* at about 4 arcsec are important contributors to feeding the supermassive black hole. A nuclear star cluster (NSC) with a mass of several $10^6 \, \text{M}_\odot$, of which $10^6 \, \text{M}_\odot$ is within 1 pc, also surrounds Sgr A*. The NSC contributes to the gravitational potential in the Galactic Center, affecting the orbits of the WR stars and their stellar winds. In this work, we examine the effects that the NSC has on the accretion of these stellar winds onto Sgr A* which have previously been neglected. We find that, on the parsec scale, the effect from the gravitational potential of the NSC is negligible on the wind-fed accretion flow, validating the existing simulations used in the literature.

astro-ph.HE

Modeling the Milky Way Circumnuclear Disk: Rosettes and Rings

The Milky Way Galactic Center hosts a $\sim4\times10^{6}\,M_\odot$ supermassive black hole (SMBH), Sagittarius A* (Sgr A*). The dominant structures in its immediate vicinity are the nuclear star cluster (NSC), whose enclosed mass at 2 pc is approximately half that of the SMBH, and the circumnuclear disk (CND)/ring, which extends between $\sim0.5$ pc and $\sim3$ pc from Sgr A* and is the largest reservoir of molecular gas in this region. Existing models of the CND commonly use one circular orbit to describe the motion of its gas. Here, we explore a much broader range of models. In the combined potential of Sgr A* and the NSC, we consider non-Keplerian rosette orbits as well as a circular disk, which is formed using a finely spaced set of concentric rings. For both systems, we test various inner/outer radii, inclinations, and position angles, sampling a total of $\sim3.3 \times 10^{5}$ models. We then conduct mock observations of all models to construct velocity maps, which we compare with HCN ($J=1{-}0$) observations of the CND. We find that the best-fitting model is a circular disk with inner and outer radii of 1.0 pc and 2.9 pc, an inclination of $i=60^{\circ}$, and a position angle of $\text{PA} = 35^{\circ}.$

astro-ph.GA