Multistructured accretion flow of Sgr A* II: Signatures of a Cool Accretion Disk in Hydrodynamic Simulations of Stellar Winds

TL;DR

Hydrodynamic simulations reveal a cold accretion disk around Sgr A*, with current X-ray data unable to distinguish between models, but future high-resolution missions could clarify the accretion flow structure.

Contribution

This study demonstrates that a cold gas disk forms around Sgr A* in hydrodynamic simulations, consistent across numerical methods, and compares plasma scenarios to X-ray observations.

Findings

A cold gas disk forms around Sgr A* in simulations.

Current X-ray data cannot distinguish plasma kinematic signatures.

Future high-resolution X-ray missions could differentiate accretion models.

Abstract

Hydrodynamic simulations of the stellar winds from Wolf-Rayet stars within the Galactic Center can provide predictions for the X-ray spectrum of supermassive black hole Sgr A*. Herein, we present results from updated smooth particle hydrodynamics simulations, building on the architecture of Cuadra et al. (2015); Russell et al. (2017), finding that a cold gas disk forms around Sgr A* with a simulation runtime of 3500 years. This result is consistent with previous grid-based simulations, demonstrating that a cold disk can form regardless of numerical method. We examine the plasma scenarios arising from an environment with and without this cold disk, by generating synthetic spectra for comparison to the quiescent Fe K alpha Sgr A* spectrum from Chandra HETG-S, taken through the Chandra X-ray Visionary Program. We find that current and future X-ray missions are unlikely to distinguish between the kinematic signatures in the plasma in these two scenarios. Nonetheless, the stellar wind plasma model presents a good fit to the dispersed Chandra spectra within 1.5" of Sgr A*. We compare our results to the Radiatively Inefficient Accretion Flow (RIAF) model fit to the HETG-S spectrum presented in Paper I and find that the Bayesian model evidence does not strongly favor either model. With 9" angular resolution and high spectral resolution of the X-IFU, NewAthena will offer a clearer differentiation between the RIAF plasma model and hydrodynamic simulations, but only a future X-ray mission with arcsecond resolution will significantly advance our understanding of Sgr A*'s accretion flow in X-rays.