H I and CO velocity dispersions in nearby galaxies

Journal Article · Fri Jan 01 04:00:00 EST 2016 · The Astronomical Journal (Online)

DOI:https://doi.org/10.3847/0004-6256/151/1/15· OSTI ID:22890167

Mogotsi, K. M.; Caldú-Primo, A.; Walter, F. ^[1]; Ianjamasimanana, R. ^[2]

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1. Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117, Heidelberg (Germany)
2. College of Graduate Studies, University of South Africa, P.O. Box 392, UNISA, 0003 (South Africa)

We analyze the velocity dispersions of individual H i and CO profiles in a number of nearby galaxies from the high-resolution HERACLES CO and THINGS H i surveys. Focusing on regions with bright CO emission, we find a CO dispersion value σ{sub CO} = 7.3 ± 1.7 km s{sup −1}. The corresponding H i dispersion σ{sub HI} = 11.7 ± 2.3 km s{sup −1}, yielding a mean dispersion ratio σ{sub HI}/σ{sub CO} = 1.4 ± 0.2, independent of radius. We find that the CO velocity dispersion increases toward lower peak fluxes. This is consistent with previous work where we showed that when using spectra averaged (“stacked”) over large areas, larger values for the CO dispersion are found, and a lower ratio σ{sub HI}/σ{sub CO} = 1.0 ± 0.2. The stacking method is more sensitive to low-level diffuse emission, whereas individual profiles trace narrow-line, GMC-dominated, bright emission. These results provide further evidence that disk galaxies contain not only a thin, low velocity dispersion, high density CO disk that is dominated by GMCs, but also a fainter, higher dispersion, diffuse disk component.

• OSTI ID: 22890167
• Journal Information: The Astronomical Journal (Online), Journal Name: The Astronomical Journal (Online) Journal Issue: 1 Vol. 151; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON MONOXIDE
DENSITY
DISPERSIONS
EMISSION
GALAXIES
H1 REGIONS
MOLECULES
RESOLUTION
SPECTRA
STARS