Star formation in the inner few parsecs of the Galaxy is generally presumed to be suppressed by strong tidal forces in the vicinity of the 4 106 solar mass black hole, Sgr A*. This is caused by the Roche density 2 108 (r/pc)3 far exceeding the density of typical molecular clouds. However, the discovery of OB stars orbiting within 1000 (0.4 pc) of Sgr A* has made it apparent that star formation has occurred within the last few million years. This population of stars is thought to have formed via gravitational instability in a dense 0.5 pc disk of gas captured from an interstellar cloud . Recent observation of the gaseous ring within 2–5 pc Sgr A*, known as the Circumnuclear Ring (CNR), have determined clump densities that can become gravitationally unstable . Hsieh et al. (2021) identified a surprising population of high density ( > 6 106 cm3), potential gravitationally-unstable gas clumps in the molecular ring. In addition, multiple transitions of CH3OH and H2O masers, N2H+and SiO emission have been detected at a location 3 pc away from Sgr A*, where the radiation field and tidal effects are reduced substantially. These features have similar velocities within the range of 30–50 km s1, indicating association with each other . These characteristics, which are only seen in the NE region of the molecular ring, suggest signatures of ongoing star formation 3 pc away from Sgr A*. This presents us with an opportunity to explore this small region in more detail. The main objective of this proposal is to use ALMA archival data from projects 2011.0.00887.S and 2017.1.00040.S taken in 2012 and 2017-18 respectively to confirm these tantalizing measurements and establish the presence of young stars in the molecular ring by detecting key tracers of star formation activity. Project 2011.0.00887.S observed the CNR in cycle 1 using the most extended array. The observations for the 100 GHz channel had 40 km s1 spacing with 1.5” resolution. Project 2017.1.00040.S observed the whole CNR in 5 bands for CS from 2017 to 2018. The resolutions are for CS (2–1), CS (3–2), CS (4–3), CS (5–4), and CS (7–6) are 1.0”, 0.9”, 1.3”, 0.5”, and 0.8”, respectively, all with 2 km s1 channel spacing. Previous studies conducted using this data have not looked at column densities of N2H+( crit = 2:0 105 cm3) nor CH3OH ( crit = 7:9 105 cm3), nor given the characteristics of the gas that are not gravitationally unstable (n &lt; 6 106 cm3) . We want to look at and analyze different stabilities in the CNR, specifically in the F and G clouds  of the NE Arm. This region is promising because it is not close to Sgr A* and has signatures of active star formation. We will look at N2H+,CH3OH (8-7), CS, as well as maser and SiO emission from archival VLA observations (project codes: 14A-229 and 14A-247). We plan to use the data to better characterize the NE Arm and build a stronger case for active star formation in the region, as well as the CND as a whole. We will test how stars are formed in an environment where tidal effects by Sgr A* and external pressures (e.g., winds) are moderately strong by identifying sites of on-going star formation within the inner circumnuclear ring orbiting Sgr A*. In addition, a census of star formation in the circumnuclear molecular ring will provide a more accurate estimate of the ongoing star formation rate and the initial mass function near supermassive black holes in other galaxies.
|Effective start/end date||10/1/22 → 9/30/24|
- Associated Universities, Inc., National Radio Astronomy Observatory (SOSPADA-027//AST-1519126)
- National Science Foundation (SOSPADA-027//AST-1519126)
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