Unusual Galactic HII Regions at the Intersection of the Central Molecular Zone and the Far Dust Lane

Abstract

Sgr E is a massive star formation complex found toward the Galactic center that consists of numerous discrete, compact HII regions. It is located at the intersection between the Central Molecular Zone (CMZ) and the far dust lane of the Galactic bar, similar to "hot spots" seen in external galaxies. Compared with other Galactic star formation complexes, the Sgr E complex is unusual because its HII regions all have similar radio luminosities and angular extents, and they are deficient in ~10micron emission from their photodissociation regions (PDRs). Our Green Bank Telescope (GBT) radio recombination line observations increase the known membership of Sgr E to 19 HII regions. There are 43 additional HII region candidates in the direction of Sgr E, 26 of which are detected for the first time here using MeerKAT 1.28GHz data. Therefore, the true HII region population of Sgr E may number >60. Using APEX SEDIGISM 13CO 2-1 data we discover a 3.0x10^5 Solar mass molecular cloud associated with Sgr E, but find few molecular or far-infrared concentrations at the locations of the Sgr E HII regions. Comparison with simulations and an analysis of its radio continuum properties indicate that Sgr E formed upstream in the far dust lane of the Galactic bar a few Myr ago and will overshoot the CMZ, crashing into the near dust lane. We propose that the unusual infrared properties of the Sgr E HII regions are caused by their orbit about the Galactic center, which have possibly stripped their PDRs.

Accepted to ApJ

References in corpus (14)

• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• Physical properties of molecular clouds for the entire Milky Way disk
• An optimized algorithm for multi-scale wideband deconvolution of radio astronomical images
• An Ammonia Spectral Atlas of Dense Cores in Perseus
• Resolution of the Distance Ambiguity for Galactic HII Regions
• Tracing the young massive high-eccentricity binary system Theta 1 Orionis C through periastron passage
• The Survey of Water and Ammonia in the Galactic Center (SWAG): Molecular Cloud Evolution in the Central Molecular Zone
• Mass inflow rate into the Central Molecular Zone: observational determination and evidence of episodic accretion
• The Chemical Evolution of Helium
• The Molecular Properties of Galactic HII Regions
• The Infrared and Radio Fluxes Densities of Galactic HII Regions
• Ionized gas at the edge of the Central Molecular Zone
• Near-infrared spectroscopy of the massive stellar population of W51: evidence for multi-seeded star formation
• ALMA hints at the existence of an unseen reservoir of diffuse molecular gas in the Galactic bulge

Cited by in corpus (4)

• Three-Dimensional Structure of the Central Molecular Zone
• The Population of the Galactic Center Filaments: Position Angle Distribution Reveal a Degree-scale Collimated Outflow from Sgr A* along the Galactic Plane
• Measuring the Orbits of the Arches and Quintuplet Clusters using HST and Gaia: Exploring Scenarios for Star Formation Near the Galactic Center
• ALMA uncovers highly filamentary structure towards the Sgr E region