# The Mid-Infrared Emission of M87

## TL;DR

This study uses mid-infrared observations from Subaru and Spitzer telescopes to analyze M87's core, revealing thermal dust emission and challenging the presence of a classical IR-bright torus in low-luminosity AGNs.

## Contribution

First mid-infrared spectral analysis of M87's nucleus showing dust emission and its implications for AGN unification models.

## Key findings

- Detected thermal dust emission at 55 K in M87's nucleus.
- Found jet emission consistent with synchrotron radiation.
- No evidence of a classical IR torus in M87.

## Abstract

We discuss Subaru and Spitzer Space Telescope imaging and spectroscopy of M87 in the mid-infrared from 5-35 um. These observations allow us to investigate mid-IR emission mechanisms in the core of M87 and to establish that the flaring, variable jet component HST-1 is not a major contributor to the mid-IR flux. The Spitzer data include a high signal-to-noise 15-35 $\mu$m spectrum of the knot A/B complex in the jet, which is consistent with synchrotron emission. However, a synchrotron model cannot account for the observed {\it nuclear} spectrum, even when contributions from the jet, necessary due to the degrading of resolution with wavelength, are included. The Spitzer data show a clear excess in the spectrum of the nucleus at wavelengths longer than 25 um, which we model as thermal emission from cool dust at a characteristic temperature of 55 \pm 10 K, with an IR luminosity \sim 10^{39} {\rm ~erg ~s^{-1}}. Given Spitzer's few-arcsecond angular resolution, the dust seen in the nuclear spectrum could be located anywhere within ~5'' (390 pc) of the nucleus. In any case, the ratio of AGN thermal to bolometric luminosity indicates that M87 does not contain the IR-bright torus that classical unified AGN schemes invoke. However, this result is consistent with theoretical predictions for low-luminosity AGNs