Kavli Affiliate: Feng Yuan
| First 5 Authors: Fangzheng Shi, Bocheng Zhu, Zhiyuan Li, Feng Yuan,
| Summary:
Super-massive black holes (SMBHs) spend most of their lifetime accreting at a
rate well below the Eddington limit, manifesting themselves as low-luminosity
active galactic nuclei (LLAGNs). The prevalence of a hot wind from LLAGNs is a
generic prediction by theories and numerical simulations of black hole
accretion and is recently becoming a crucial ingredient of AGN kinetic feedback
in cosmological simulations of galaxy evolution. However, direct observational
evidence for this hot wind is still scarce. In this work, we identify
significant Fe XXVI Ly$alpha$ and Fe XXV K$alpha$ emission lines from
high-resolution Chandra grating spectra of the LLAGN in NGC,7213, a nearby Sa
galaxy hosting a $sim10^8rm~M_odot$ SMBH, confirming previous work. We find
that these lines exhibit a blueshifted line-of-sight velocity of
$sim1100rm~km s^{-1}$ and a high XXVI Ly$alpha$ to XXV K$alpha$ flux ratio
implying for a $sim16$ keV hot plasma. By confronting these spectral features
with synthetic X-ray spectra based on our custom magnetohydrodynamical
simulations, we find that the high-velocity, hot plasma is naturally explained
by the putative hot wind driven by the hot accretion flow powering this LLAGN.
Alternative plausible origins of this hot plasma, including stellar activities,
AGN photoionization and the hot accretion flow itself, are quantitatively
disfavored. The inferred kinetic energy and momentum carried by the wind can
serve as strong feedback to the environment. We compare NGC,7213 to M81*, in
which strong evidence for a hot wind was recently presented, and discuss
implications on the universality and detectability of hot winds from LLAGNs.
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