Issue |
A&A
Volume 695, March 2025
|
|
---|---|---|
Article Number | A60 | |
Number of page(s) | 7 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361/202452875 | |
Published online | 07 March 2025 |
Cold molecular gas in the hot nuclear wind of the Milky Way
1
Department of Astronomy, University of Massachusetts,
Amherst,
MA
01003,
USA
2
Dipartimento di Fisica e Astronomia, Universitá degli Studi di Firenze,
via G. Sansone 1,
50019
Sesto Fiorentino, Firenze,
Italy
3
Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autonóma de México,
Apartado Postal 3-72,
Morelia
58090,
Michoacán,
Mexico
4
Black Hole Initiative at Harvard University,
20 Garden Street,
Cambridge,
MA
02138,
USA
5
David Rockefeller Center for Latin American Studies, Harvard University,
1730 Cambridge Street,
Cambridge,
MA
02138,
USA
6
National Radio Astronomy Observatory,
Green Bank,
WV
24944,
USA
7
Research School of Astronomy and Astrophysics, Australian National University,
ACT 2611,
Australia
★ Corresponding author; heyer@umass.edu
Received:
4
November
2024
Accepted:
6
February
2025
Using the Large Millimeter Telescope and the SEQUOIA 3 mm focal plane array, we have searched for molecular line emission from two atomic clouds associated with the Fermi Bubble of the Milky Way. Neither 12CO nor 13CO J=1–0 emission is detected from the H I cloud, MW-C20. 12CO J=1–0 emission is detected from MW-C21 that is distributed within 11 clumps with most of the CO luminosity coming from a single clump. However, we find no 13CO emission to a 3σ brightness temperature limit of 0.3 K. Using this limit and RADEX non-local thermodynamic equilibrium (non-LTE) excitation models, we derive H2 column density upper limits of (0.4–3)×1021 cm−2 for a set of physical conditions and a H2 to 12CO abundance ratio of 104. Model CO-to-H2 conversion factors are derived for each set of physical conditions. We find the maximum value is 1.6×1020 cm−2/(K km s−1). Increasing [H2/12CO] to 105 to account for photodissociation and cosmic ray ionization increases the column density and X(CO) upper limits by a factor of 10. Applying these X(CO) limits to the CO luminosities, the upper limit on the total molecular mass in MW-C21 is 132±2 M⊙, corresponding to <27% of the neutral gas mass. For the three clumps that are fully resolved, lower limits to the virial ratios are 288±32, 68±28, and 157±39, which suggest that these structures are bound by external pressure to remain dynamically stable over the entrainment time of 2×106 years or are being disrupted by shear and expansion over the clump crossing times of 3–8×105 years. The observations presented in this study add to the growing census of cold gas entrained within the Galactic Center wind.
Key words: ISM: clouds / ISM: molecules / ISM: structure / Galaxy: center / Galaxy: kinematics and dynamics
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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