Mon. Not. R. Astron. Soc., 476, 2446-2456 (2018/May-2)
Study of diffuse H II regions potentially forming part of the gas streams around Sgr A*.
ARMIJOS-ABENDANO J., LOPEZ E., MARTIN-PINTADO J., BAEZ-RUBIO A., ARAVENA M., REQUENA-TORRES M.A., MARTIN S., LLERENA M., ALDAS F., LOGAN C. and RODRIGUEZ-FRANCO A.
Abstract (from CDS):
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 Hnα and Hmβ radio recombination lines (RRLs). Henα and Hemβ 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 Hmβ to Hnα 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.
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
ISM: clouds - H II regions - Galaxy: centre
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