Relationships between the Stellar, Gaseous, and Star Formation Disks in LITTLE THINGS Dwarf Irregular Galaxies: Indirect Evidence for Substantial Fractions of Dark Molecular Gas

Journal Article · Mon Feb 01 04:00:00 EST 2021 · The Astronomical Journal (Online)

DOI:https://doi.org/10.3847/1538-3881/ABD089· OSTI ID:23159105

Hunter, Deidre A.; Goldberger, Esther; Taylor, Hannah; Ermakov, Anton I.; Malko, Bradley; Barandi, Brian; Jundt, Ryan ^[1]; Elmegreen, Bruce G. ^[2]; Herrmann, Kimberly A. ^[3]; Oh, Se-Heon ^[4]

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1. Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)
2. IBM T. J. Watson Research Center, PO Box 218, Yorktown Heights, NY (United States)
3. Department of Physics, Pennsylvania State University Mont Alto, 1 Campus Drive, Mont Alto, PA 17237 (United States)
4. Department of Physics and Astronomy, Sejong University, 209 Neungdong-ro, Gwangjin-gu, Seoul (Korea, Republic of)

The stellar, gaseous and young stellar disks in the LITTLE THINGS sample of nearby dwarf irregular galaxies are fitted with functions to search for correlations between the parameters. We find that the H i radial profiles are generally flatter in the center and fall faster in the outer regions than the V-band profiles, while young stars are more centrally concentrated, especially if the H i is more centrally flat. This pattern suggests that the H i is turning into molecules in the center, and the molecular clouds are forming stars and FUV. A model that assumes the molecular surface density is proportional to the total gas surface density to a power of 1.5 or 2, in analogy with the Kennicutt–Schmidt relation, reproduces the relationship between the ratio of the visible to the H i scale length and the H i Sérsic index. The molecular fraction is estimated as a function of radius for each galaxy by converting the FUV to a molecular surface density using conventional calibrations. The average molecular fraction inside 3R {sub D} is 23% ± 17%. However, the break in the stellar surface brightness profile has no unified tracer related to star formation.

• OSTI ID: 23159105
• Journal Information: The Astronomical Journal (Online), Journal Name: The Astronomical Journal (Online) Journal Issue: 2 Vol. 161; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
79 ASTRONOMY AND ASTROPHYSICS
BRIGHTNESS
CALIBRATION
CLOUDS
DENSITY
GALAXIES
MOLECULES
STARS
SURFACES