SOFIA-upGREAT imaging spectroscopy of the [C II] 158um fine structure line of the Sgr B region in the Galactic center

TL;DR

This study uses SOFIA-upGREAT imaging spectroscopy to map the [C II] 158um line in the Sgr B region of the Galactic center, revealing its structure, emission sources, and implications for star formation and galaxy comparisons.

Contribution

First detailed velocity-resolved [C II] imaging of Sgr B, linking emission to star formation regions and cloud interactions in the Galactic center.

Findings

Sgr B extends 34 pc along the Galactic plane.

[C II] emission correlates with UV surfaces of clouds.

Local cloud-cloud collision may trigger star formation.

Abstract

We report SOFIA-upGREAT spectroscopic imaging of the [C II] 158um spectral line, as well as a number of [O I] 63um spectra, across a 67x45 pc field toward the Sgr B region in our Galactic center. The fully-sampled and velocity-resolved [C II] images have 0.55 pc spatial and 1 km/s velocity resolutions. We find that Sgr B extends as a coherent structure spanning some 34 pc along the Galactic plane. Bright [C II] emission encompasses Sgr B1 (G0.5-0.0), the G0.6-0.0 HII region, and passes behind and beyond the luminous star forming cores toward Sgr B2 (G0.7-0.0). Sgr B is a major contributor to the entire Galactic center's [C II] luminosity, with surface brightness comparable to [C II] from the Arches region. [C II], 70um, and 20cm emission share nearly identical spatial distributions. Combined with the lack of [C II] self-absorption, this indicates that these probes trace UV on the near surfaces of more extended clouds visible in CO isotopologues and 160um continuum. Stars from regions of local star formation likely dominate the UV field. Photodissociation regions and HII regions contribute similar amounts of [C II] flux. The extreme star formation cores of Sgr B2 contribute negligible amounts to the total [C II] intensity from the Sgr B region. Velocity fields and association with a narrow dust lane indicate that they may have been produced in a local cloud-cloud collision. The cores are likely local analogs of the intense star formation regions where ideas to explain the "C+ deficit" in ultra-luminous galaxies can be tested.