The multiwavelength spectrum of NGC 3115: Hot accretion flow properties

TL;DR

This study models the multiwavelength spectrum of NGC 3115's nucleus using radiatively inefficient accretion flow models, revealing key properties of the hot accretion flow and its outflows.

Contribution

It provides the first comprehensive SED modeling of NGC 3115 with RIAF, constraining the density profile and explaining radio emission without jets.

Findings

RIAF models fit the SED well

Density profile constrained to ρ(r) ∝ r^{-0.73}

Radio emission explained by nonthermal electrons in RIAF

Abstract

NGC 3115 is the nearest galaxy hosting a billion solar mass black hole and is also a low-luminosity active galactic nucleus (LLAGN). X-ray observations of this LLAGN are able to spatially resolve the hot gas within the sphere of gravitational influence of the supermassive black hole. These observations make NGC 3115 an important testbed for black hole accretion theory in galactic nuclei since they constrain the outer boundary conditions of the hot accretion flow. We present a compilation of the multiwavelength spectral energy distribution (SED) of the nucleus of NGC 3115 from radio to X-rays. We report the results from modeling the observed SED with radiatively inefficient accretion flow (RIAF) models. The radio emission can be well-explained by synchrotron emission from the RIAF without the need for contribution from a relativistic jet. We obtain a tight constraint on the RIAF density profile, $\rho(r) \propto r^{-0.73_{-0.02} ^{+0.01}}$, implying that mass-loss through subrelativistic outflows from the RIAF is significant. The lower frequency radio observation requires the synchrotron emission from a nonthermal electron population in the RIAF, similarly to Sgr A*.