The Galactic Center: Not an Active Galactic Nucleus

TL;DR

This study uses Spitzer spectra to analyze the interstellar medium in the Galactic Center's Central Molecular Zone, revealing that its emission line ratios resemble those of star-forming galaxies rather than active galactic nuclei.

Contribution

It provides extensive spectral maps of the CMZ and compares diagnostic line ratios to classify the region's activity, challenging previous assumptions about its nature.

Findings

Line ratios match star-forming galaxies

Most H2 emission is along the line-of-sight

The GC does not show AGN-like activity

Abstract

We present 10um-35um Spitzer spectra of the interstellar medium in the Central Molecular Zone (CMZ), the central 210 pc x 60 pc of the Galactic center (GC). We present maps of the CMZ in ionic and H2 emission, covering a more extensive area than earlier spectroscopic surveys in this region. The radial velocities and intensities of ionic lines and H2 suggest that most of the H2 0-0 S(0) emission comes from gas along the line-of-sight, as found by previous work. We compare diagnostic line ratios measured in the Spitzer Infrared Nearby Galaxies Survey (SINGS) to our data. Previous work shows that forbidden line ratios can distinguish star-forming galaxies from LINERs and AGNs. Our GC line ratios agree with star-forming galaxies and not with LINERs or AGNs.