La Freccia Rossa: An IR-dark cloud hosting the Milky Way intermediate-mass black hole candidate

TL;DR

This study investigates the nature of the IR-dark cloud Freccia Rossa and its potential hosting of an intermediate-mass black hole, combining radio and infrared data to explore its properties and origins.

Contribution

It provides a multi-wavelength analysis of the Freccia Rossa cloud, challenging the IMBH interpretation and proposing a high-velocity cloud origin.

Findings

Radio and infrared data are inconsistent with an Sgr A*-like IMBH model.

A protostellar-disk scenario remains plausible.

The cloud may be a high-velocity cloud remnant from the Galactic halo.

Abstract

The dynamics of the high-velocity compact molecular cloud CO-0.40-0.22 have been interpreted as evidence for a $\sim10^{5}M_{\odot}$ black hole within 60 pc of Sgr A*. Recently, Oka et al. have identified a compact millimetre-continuum source, CO-0.40-0.22*, with this candidate black hole. Here we present a collation of radio and infrared data at this location. ATCA constraints on the radio spectrum, and the detection of a mid-infrared counterpart, are in tension with an Sgr A*-like model for CO-0.40-0.22* despite the comparable bolometric to Eddington luminosity ratios under the IMBH interpretation. A protostellar-disk scenario is, however, tenable. CO-0.40-0.22(*) is associated with an arrowhead-shaped infrared-dark cloud (which we call the Freccia Rossa). Radio-continuum observations reveal a candidate HII region associated with the system. If the $V_{\rm LSR}\approx70$ km s$^{-1}$ systemic velocity of CO-0.40-0.22 is common to the entire Freccia Rossa system, we hypothesise that it is the remnant of a high-velocity cloud that has plunged into the Milky Way from the Galactic halo.