HALOGAS Observations of NGC 4559: Anomalous and Extraplanar H i and its Relation to Star Formation
- Department of Astronomy, New Mexico State University, Las Cruces, NM 88001 (United States)
- CSIRO Astronomy and Space Science, 26 Dick Perry Ave, Kensington, WA 6151 (Australia)
- Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen (Netherlands)
- Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States)
- Department of Physics and Astronomy, University of New Mexico, 1919 Lomas Blvd. NE, Albuquerque, NM 87131 (United States)
- SKA South Africa Radio Astronomy Research Group, 3rd Floor, The Park, Park Rd., Pinelands 7405 (South Africa)
- Department of Physics and Astrophysics, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels (Belgium)
- INAF-Osservatorio Astronomico di Cagliari, Via della Scienza 5, I-09047 Selargius (Italy)
We use new deep 21 cm H i observations of the moderately inclined galaxy NGC 4559 in the HALOGAS survey to investigate the properties of extraplanar gas. We use TiRiFiC to construct simulated data cubes to match the H i observations. We find that a thick-disk component of scale height ∼2 kpc, characterized by a negative vertical gradient in its rotation velocity (lag) of ∼13 ± 5 km s{sup −1} kpc{sup −1} is an adequate fit to extraplanar gas features. The tilted ring models also present evidence for a decrease in the magnitude of the lag outside R {sub 25}, and a radial inflow of ∼10 km s{sup −1}. We extracted lagging extraplanar gas through Gaussian velocity profile fitting. From both the 3D models and extraction analyses we conclude that ∼10%–20% of the total H i mass is extraplanar. Most of the extraplanar gas is spatially coincident with regions of star formation in spiral arms, as traced by H α and GALEX FUV images, so it is likely due to star formation processes driving a galactic fountain. We also find the signature of a filament of a kinematically “forbidden” H i feature, containing ∼1.4 × 10{sup 6} M {sub ⊙} of H i, and discuss its potential relationship to a nearby H i hole. We discover a previously undetected dwarf galaxy in H i located ∼0.°4 (∼58 kpc) from the center of NGC 4559, containing ∼4 × 10{sup 5} M {sub ⊙}. This dwarf has counterpart sources in SDSS with spectra typical of H ii regions, and we conclude that it is two merging blue compact dwarf galaxies.
- OSTI ID:
- 22663680
- Journal Information:
- Astrophysical Journal, Vol. 839, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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