Parabolic-like Trend in SiO Ratios throughout the Central Molecular Zone: Possible Signature of a Past Nuclear Activity in the Galactic Center

Abstract

We report the discovery of a characteristic trend in the intensity ratios of SiO emissions across the Central Molecular Zone (CMZ) of our Galaxy. Using the Nobeyama Radio Observatory 45-m telescope, we conducted large-scale, high-sensitivity imaging observations in molecular lines including SiO $J$=2$-$1 and CS $J$=2$-$1. By identifying SiO-emitting clouds and examining their intensity ratios relative to the other molecular lines, we unveiled a parabolic-like trend showing lower ratios near the Galactic nucleus, Sgr A${}^{\ast }$, with gradual increases toward the edges of the CMZ. This pattern suggests a possible outburst of the nucleus within the last $\sim 10^5$ yr, which may have propagated through the entire CMZ with strong shocks. Alternatively, the observed trend may also be attributed to the destruction of small dust grains by high-energy photons. Our results can potentially lead to a new perspective on the history of nuclear activity and its impact on the surrounding molecular environment.

9 pages, 4 figures, accepted for publication in the Astrophysical Journal Letters

References in corpus (23)

• Array Programming with NumPy
• The NumPy array: a structure for efficient numerical computation
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• First Sagittarius A* Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole in the Center of the Milky Way
• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Structural Analysis of Molecular Clouds: Dendrograms
• The Galactic Centre Chimney
• Fermi and eRosita bubbles as relics of the past activity of the Galactic black hole
• The Galactic center chimneys: The base of the multiphase outflow of the Milky Way
• Cloud-cloud collisions in the common foot point of molecular loops 1 and 2 in the Galactic Center
• Indication of Another Intermediate-mass Black Hole in the Galactic Center
• ALMA Observations of Massive Clouds in the Central Molecular Zone: Ubiquitous Protostellar Outflows
• X-ray polarization evidence for a 200 years-old flare of Sgr A${}^{\ast }$
• The Fifth Candidate for an Intermediate-mass Black Hole in the Galactic Center
• Structure and kinematics of shocked gas in Sgr B2: further evidence of a cloud-cloud collision from SiO emission maps
• Three-Dimensional Structure of the Central Molecular Zone
• The chemical footprint of AGN feedback in the outflowing circumnuclear disk of NGC 1068
• The Central 300 pc of the Galaxy probed by infrared spectra of H3+ and CO: II. Expansion and morphology of the warm diffuse gas
• Localized SiO emission triggered by the passage of the W51C SNR shock
• Living on the edge of the Central Molecular Zone: G1.3 is the more likely candidate for gas accretion into the CMZ
• New Look at the Molecular Superbubble Candidate in the Galactic Center
• A Multiwavelength Study of the Sgr B Region: Contiguous Cloud-Cloud Collisions Triggering Widespread Star Formation Events?
• Discovery of the Tadpole Molecular Cloud near the Galactic Nucleus

Cited by in corpus (1)

• Gas Transfer Between the Inner 3-kpc Disk and the Galactic Central Molecular Zone