Evidence for A Hot Wind from High-resolution X-ray Spectroscopic Observation of the Low-luminosity Active Galactic Nucleus in NGC 7213

Abstract

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 $\sim 10^8{\mathrm{M}}_{\odot }$ SMBH, confirming previous work. We find that these lines exhibit a blueshifted line-of-sight velocity of $\sim 1100\mathrm{km}{\mathrm{s}}^{-1}$ and a high XXVI Ly$\alpha$ to XXV K$\alpha$ flux ratio implying for a $\sim 16$ 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.

20 pages, 12 figures, Accepted for publication on ApJ

References in corpus (6)

• Simulating galaxy formation with black hole driven thermal and kinetic feedback
• Numerical Simulation of Hot Accretion Flows (III): Revisiting wind properties using trajectory approach
• A BLR origin for the iron K$\alpha$ line in NGC7213
• A luminous hot accretion flow in the low-luminosity active galactic nucleus NGC 7213
• A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213
• The molecular gas in the central region of NGC 7213

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• Heating or Cooling: Study of Advective Heat Transport in the Inflow and the Outflow of Optically Thin Advection-dominated Accretion Flows
• A Hydrodynamical Thermal Irradiated Wind from the Outer Thin Accretion Disk in Low-luminosity Active Galactic Nuclei