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Extended HI Structures in the Irregular Galaxy NGC 4449

Published online by Cambridge University Press:  14 August 2015

Hugo van Woerden
Affiliation:
Kapteyn Institute, Postbus 800, 9700 AV Groningen, The Netherlands
Deidre A. Hunter
Affiliation:
Lowell Observatory, 1400 W Mars Hill Road, Flagstaff AZ 86001, USA
Eric M. Wilcots
Affiliation:
Washburn Observatory, 475 N. Charter Street, Madison WI 53706, USA
Jay S. Gallagher
Affiliation:
Washburn Observatory, 475 N. Charter Street, Madison WI 53706, USA

Extract

NGC 4449 is a bright (B = 9.5), nearby (4 Mpc) irregular galaxy with a high surface brightness and strong star-formation activity; for photos see Hunter and Gallagher (1989). Using the Effelsberg 100-meter dish, van Woerden et al. (1975) - and later also Bajają et al. (1994) - found its HI distribution to extend, at the level 2 × 1019 atoms cm-2 over a full degree, or ten times the D25 diameter. Van Woerden et al. also mentioned that the HI velocity gradient in this outer disk was opposite to that measured at Westerbork over the innermost 4 arcminutes.

With the VLA D-array, we have used a mosaic of 3 × 3 pointings to map the HI at resolutions of 1.0’ and 10 kms-1 over a field (FWHM) of 1° diameter (Hunter et al. 1998). The HI distribution (Fig. 1) shows the following features: 1) a bright inner body, centred on the optical galaxy and dominated by an annulus of 5 kpc diameter; 2) a symmetric elliptical - probably highly inclined - disk of 35 × 15 kpc diameter, with strong condensations at its NE and SW ends; 3) a set of narrow streamers, consisting of straight segments making abrupt angles, and containing several bright clouds. The HI mass in the inner body and elliptical disk together is 12 × 10s Mʘ the streamers (about 7 × 108 Mʘ of HI) are surrounded by a diffuse HI distribution, missed by the VLA interferometers but detected by the Effelsberg single-dish.

Type
II. Joint Discussions
Copyright
Copyright © Kluwer 1998

References

Bajaja, E., Huchtmeier, W.K., & Klein, U. 1994, A&A, 285, 388 Google Scholar
Hunter, D.A., & Gallagher, J.S. 1989, Science, 243, 1557 CrossRefGoogle Scholar
Hunter, D.A., Wilcots, E.M., van Woerden, H., Gallagher, J.S., & Kohle, S. 1998, ApJ, in preparationGoogle Scholar
Toomre, A., & Toomre, J. 1972, ApJ, 178, 623 CrossRefGoogle Scholar
van der Hulst, J.M. 1979, A&A, 75, 97 Google Scholar
van Woerden, H., Mebold, U., & Bosma, A. 1975, in La Dynamique des Galaxies Spirales, ed. Weliaehcw, L., Paris: CNRS, p. 483 Google Scholar
Yun, M.S., Ho, P.T.P., & Lo, K.Y. 1994, Nature, 372, 530 CrossRefGoogle Scholar

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