SIMBAD references

2021ApJ...923L..11C - Astrophys. J., 923, L11-L11 (2021/December-2)

Molecular gas within the Milky Way's nuclear wind.

CASHMAN F.H., FOX A.J., SAVAGE B.D., WAKKER B.P., KRISHNARAO D., BENJAMIN R.A., RICHTER P., ASHLEY T., JENKINS E.B., LOCKMAN F.J., BORDOLOI R. and KIM T.-S.

Abstract (from CDS):

We report the first direct detection of molecular hydrogen associated with the Galactic nuclear wind. The Far-Ultraviolet Spectroscopic Explorer spectrum of LS 4825, a B1 Ib-II star at l, b = 1.67°,-6.63° lying d = 9.9–0.8+1.4 kpc from the Sun, ∼1 kpc below the Galactic plane near the Galactic center, shows two high-velocity H2 components at vLSR = -79 and -108 km s–1. In contrast, the FUSE spectrum of the nearby (∼0.6° away) foreground star HD 167402 at d = 4.9–0.7+0.8 kpc reveals no H2 absorption at these velocities. Over 60 lines of H2 from rotational levels J = 0 to 5 are identified in the high-velocity clouds. For the vLSR = -79 km s–1 cloud we measure total log N(H2) >= 16.75 cm–2, molecular fraction fH2_ >= 0.8%, and T01 >= 97 and T25 <= 439 K for the ground- and excited-state rotational excitation temperatures. At vLSR = -108 km s–1, we measure log N(H2) = 16.13 ± 0.10 cm–2, fH2_ >= 0.5%, and T01 = 77–18+34 and T25 = 1092–117+149 K, for which the excited-state ortho- to para-H2 is 1.0–0.1+0.3, much less than the equilibrium value of 3 expected for gas at this temperature. This nonequilibrium ratio suggests that the -108 km s–1 cloud has been recently excited and has not yet had time to equilibrate. As the LS 4825 sight line passes close by a tilted section of the Galactic disk, we propose that we are probing a boundary region where the nuclear wind is removing gas from the disk.

Abstract Copyright: © 2021. The Author(s). Published by the American Astronomical Society.

Journal keyword(s): Galactic center - Galactic winds - Molecular gas - Ultraviolet astronomy

Simbad objects: 9

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