Shield: comparing gas and star formation in low-mass galaxies

Journal Article · Sun Nov 20 00:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/832/1/85· OSTI ID:22868440

Teich, Yaron G.; McNichols, Andrew T.; Nims, Elise; Cannon, John M.; Cave, Ian; Hagen, Cedric ^[1]; Adams, Elizabeth A. K. ^[2]; Giovanelli, Riccardo; Haynes, Martha P. ^[3]; McQuinn, Kristen B. W.; Skillman, Evan D. ^[4]; Salzer, John J.; Bernstein-Cooper, Elijah Z. ^[5]; Dolphin, Andrew ^[6]; Elson, E. C. ^[7]; Haurberg, Nathalie ^[8]; Józsa, Gyula I. G. ^[9]; Ott, Jürgen ^[10]; Saintonge, Amelie ^[11]; others, and

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1. Department of Physics and Astronomy, Macalester College, 1600 Grand Avenue, Saint Paul, MN 55105 (United States)
2. ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, 7990 AA, Dwingeloo (Netherlands)
3. Center for Astrophysics and Planetary Science, Space Sciences Building, 122 Sciences Drive, Cornell University, Ithaca NY 14853 (United States)
4. Minnesota Institute for Astrophysics, School of Physics and Astronomy, 116 Church Street, S.E., University of Minnesota, Minneapolis, MN 55455 (United States)
5. Department of Astronomy, Indiana University, 727 East Third Street, Bloomington, IN 47405 (United States)
6. Raytheon Company, 1151 E. Hermans Road, Tucson, AZ 85756 (United States)
7. Astrophysics, Cosmology and Gravity Centre (ACGC), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa)
8. Physics Department, Knox College, 2 East South Street, Galesburg, IL 61401 (United States)
9. SKA South Africa, Radio Astronomy Research Group, 3rd Floor, The Park, Park Road, Pinelands, 7405 (South Africa)
10. National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States)
11. Department of Physics and Astronomy, University College London, Gower Place, London WC1E 6BT (United Kingdom)

We analyze the relationships between atomic, neutral hydrogen (H i) and star formation (SF) in the 12 low-mass SHIELD galaxies. We compare high spectral (∼0.82 km s{sup −1} ch{sup −1}) and spatial resolution (physical resolutions of 160–640 pc) H i imaging from the VLA with Hα and far-ultraviolet imaging. We quantify the degree of co-spatiality between star-forming regions and regions of high H i column densities. We calculate the global star formation efficiencies (SFE; Σ{sub SFR} / Σ{sub HI}) and examine the relationships among the SFE and H i mass, H i column density, and star formation rate (SFR). The systems are consuming their cold neutral gas on timescales of order a few gigayears. While we derive an index for the Kennicutt–Schmidt relation of N ≈ 0.68 ± 0.04 for the SHIELD sample as a whole, the values of N vary considerably from system to system. By supplementing SHIELD results with those from other surveys, we find that H i mass and UV-based SFR are strongly correlated over five orders of magnitude. Identification of patterns within the SHIELD sample allows us to bin the galaxies into three general categories: (1) mainly co-spatial H i and SF regions, found in systems with the highest peak H i column densities and highest total H i masses; (2) moderately correlated H i and SF regions, found in systems with moderate H i column densities; and (3) obvious offsets between H i and SF peaks, found in systems with the lowest total H i masses. SF in these galaxies is dominated by stochasticity and random fluctuations in their ISM.

• OSTI ID: 22868440
• Journal Information: Astrophysical Journal, Vol. 832, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COMPARATIVE EVALUATIONS
DENSITY
FAR ULTRAVIOLET RADIATION
FLUCTUATIONS
GALAXIES
HYDROGEN
MASS
SPATIAL RESOLUTION
STAR EVOLUTION