6.7 GHz CH3OH absorption towards the N3 Galactic Center point-source

TL;DR

This study detects 6.7 GHz methanol and 4.8 GHz formaldehyde absorption towards the N3 Galactic Center source, revealing molecular gas on the near side and indicating turbulence within the cloud.

Contribution

First detection of methanol and formaldehyde absorption towards N3, providing insights into the cloud's kinematics and turbulence at the Galactic Center.

Findings

Methanol absorption centered at ~10 km/s

Formaldehyde shows two velocity components (~-3 and +8 km/s)

Absorption indicates gas on the near side of the continuum source

Abstract

We present evidence of 6.7 GHz methanol (CH3OH)~and 4.8 GHz formaldehyde (H2CO) absorption towards the Galactic Center (GC) point-source `N3'. Both absorption features are unresolved and spatially aligned with N3. The 6.7 GHz CH3OH contains a single velocity component (centered at ~10 km/s) while the 4.8 GHz H2CO shows two velocity components (centered at ~-3 and +8 km/s). We find that the velocity of these absorption components are similar to that of emission lines from other molecules (e.g., SiO and H3CN) detected toward this compact-source (-13 to +25 km/s; `N3 cloud'). The detection of these absorption features is a firm indication that some of the molecular gas in the N3 molecular cloud is on the near-side of the continuum source. Analysis of the CH3OH absorption kinematics shows a relatively large velocity dispersion (3.8 km/s) for the size scale of this feature (<0.1'', <0.01 pc at the GC; Ludovici et al. 2016), when compared with other similar size GC clouds in the Larson linewidth-size relationship. Further, this linewidth is closer to velocity dispersion measurements for size scales of 1.3 pc, which is roughly the width of the N3 cloud (25''; 1.0 pc). We argue that this relatively broad linewidth, over a small cross-sectional area, is due to turbulence through the depth of the cloud, where the cloud has a presumed line-of-sight thickness of ~1 pc.