A Near-Infrared Search for Molecular Gas in the Fermi Bubbles

TL;DR

This study used near-infrared spectroscopy to search for molecular gas in the Fermi Bubbles but found no extended H2 emission, suggesting alternative methods are needed for future detection.

Contribution

First near-infrared integral field spectroscopy search for molecular gas in the Fermi Bubbles' nuclear wind, providing upper limits on H2 emission.

Findings

No extended H2 emission detected in the observed fields.

Surface brightness limits established for H2 lines.

Recommends UV absorption and emission-line studies for future research.

Abstract

We present Gemini/NIFS near-IR integral field spectroscopy of the fields-of-view around two AGNs behind the Fermi Bubbles (PDS 456 and 1H1613-097) to search for molecular gas in the Milky Way's nuclear wind. These two AGN sightlines were selected by the presence of high-velocity neutral and ionized gas seen in UV absorption. We do not detect any extended emission from the H2 ro-vibrational S(0) and S(1) lines at 2.224 and 2.122 microns in either direction. For the S(1) line, the 3-sigma surface brightness limits derived from spectra extracted across the full 3x3 arcsecond NIFS field-of-view are 2.4e-17 erg/cm2/s/A/arcsec2 for PDS 456 and and 4.9e-18 erg/cm2/s/A/arcsec2 for 1H1613-097. Given these non-detections, we conclude that CO emission-line studies and H2 UV absorption-line studies are more promising approaches for characterizing the molecular gas in the Fermi Bubbles.