Study of diffuse H II regions potentially forming part of the gas streams around Sgr A

J. Armijos-Abendaño, E. López, J. Martín-Pintado, A. Báez-Rubio, M. Aravena, M. A. Requena-Torres, S. Martín, M. Llerena, F. Aldás, C. Logan, A. Rodríguez-Franco. 2018. Study of diffuse H II regions potentially forming part of the gas streams around Sgr A. Monthly Notices of teh Royal Astronomical Society 476, 2, 2446-2456 DOI: 10.1093/mnras/sty391

We present a study of diffuse extended ionized gas towards three clouds located in the Galactic Centre (GC). One line of sight (LOS) is towards the 20 km s(-1) cloud (LOS-0.11) in the Sgr A region, another LOS is towards the 50 km s(-1) cloud (LOS-0.02), also in Sgr A, while the third is towards the Sgr B2 cloud (LOS+0.693). The emission from the ionized gas is detected from Hn alpha and Hm beta radio recombination lines (RRLs). Hen alpha and Hem beta RRL emission is detected with the same n and m as those from the hydrogen RRLs only towards LOS+0.693. RRLs probe gas with positive and negative velocities towards the two Sgr A sources. The Hm beta to Hn alpha ratios reveal that the ionized gas is emitted under local thermodynamic equilibrium conditions in these regions. We find a He to H mass fraction of 0.29 +/- 0.01 consistent with the typical GC value, supporting the idea that massive stars have increased the He abundance compared to its primordial value. Physical properties are derived for the studied sources. We propose that the negative velocity component of both Sgr A sources is part of gas streams considered previously to model the GC cloud kinematics. Associated massive stars with what are presumably the closest H II regions to LOS-0.11 (positive velocity gas), LOS-0.02, and LOS+0.693 could be the main sources of ultraviolet photons ionizing the gas. The negative velocity components of both Sgr A sources might be ionized by the same massive stars, but only if they are in the same gas stream.

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