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Evidence for BlowOut in the Low-Mass Dwarf Galaxy Holmberg I

Ott, Jürgen and Walter, Fabian and Brinks, Elias and Van Dyk, Schuyler D. and Dirsch, Boris and Klein, Ulrich (2001) Evidence for BlowOut in the Low-Mass Dwarf Galaxy Holmberg I. Astronomical Journal, 122 (6). pp. 3070-3091. ISSN 0004-6256.

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We present radio and optical observations of Holmberg I (Ho I), a member of the M81 group of galaxies (distance ~3.6 Mpc). Ho I is a low-mass, low surface brightness dwarf galaxy. High-resolution, multiarray, Very Large Array observations in the line of neutral hydrogen (H I) reveal a supergiant shell (diameter 1.7 kpc) that covers about half the optical extent of Ho I and that comprises 75% of the total H I content (total H I mass: 1.1 × 10^8 M_⊙). We estimate the scale height of the H I layer to be 250 pc ≲ h ≲ 550 pc. We set a tentative upper limit to the dark matter content of ≲ 3.1 × 10^8 M_⊙. The H I data are complemented by deep, optical UBV(RI)C observations and narrowband Hα imaging obtained at the Calar Alto 2.2 m telescope. We find M_(H I) /L_B = 1.1 M_⊙/L. The total visible (stars plus gas) mass of Ho I adds up to 2.4 × 10^8 M_⊙. This leads to a total mass of ≲ 5.5 × 10^8 M_⊙ and an inclination for Ho I of 10° ≲ i ≲ 14°. The origin of Ho I's peculiar H I morphology is discussed in terms of a supergiant shell created by strong stellar winds and supernova explosions. We estimate that the energy deposited falls in the range of 1.2 × 10^(53) ergs ≲ E ≲ 2.6 × 10^(53) ergs (equivalent to 120–260 Type II SNe explosions). From a comparison with isochrones, as well as from dynamical modeling based on the H I data, we derive an age for the supergiant H I shell of ~80 ± 20 Myr. The morphological center of Ho I (i.e., the center of the ring) is offset by 0.75 kpc with respect to the dynamical center. Within the interior of the shell, the light distribution is exponential with a rather shallow gradient and blue optical colors. Beyond a radius corresponding to an H I column density of ~10^(21) cm^(-2), the putative star formation threshold, the disk becomes considerably redder and the slope for the exponential light distributions steepens. We attribute this to a uniform star formation activity in the recent past within the central 2 kpc of Ho I. Color-magnitude diagrams based on our CCD data show that young stars, with ages of 15–30 Myr, are situated along the inside of the rim of the giant H I shell. On the rim itself, we find even younger stars and some faint H II regions. It is speculated that these stars are the result of secondary star formation on the rim of the shell. Based on the global morphology and velocity dispersion, as well as the location of the H II regions, we find evidence for ram pressure within the M81 group. Finally, we discuss the likelihood of Ho I having lost some of its interstellar material to the intergalactic medium ("blow-out" scenario).

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ott, Jürgen0000-0001-8224-1956
Walter, Fabian0000-0003-4793-7880
Brinks, Elias0000-0002-7758-9699
Van Dyk, Schuyler D.0000-0001-9038-9950
Additional Information:© 2001. The American Astronomical Society. Received 2001 February 27; accepted 2001 August 20. J. O. would like to thank Thomas Fritz, Ulrich Mebold, and Axel Weiss for fruitful discussions. Without the funding of the Deutsche Forschungsgemeinschaft and the associated Graduiertenkolleg "Magellanic clouds and other dwarf galaxies," this work would not have been possible. The authors also thank the anonymous referee for valuable comments that have helped to improve the presentation of this paper. F. W. acknowledges NSF grant AST 96-13717. E. B. acknowledges support by CONACyT (grant 27606-E). B. D. acknowledges the award of a Feodor Lynen grant by the Alexander von Humboldt-Stiftung. Furthermore, we thank the staff of the Calar Alto Observatory for their kind support during the observations. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA). The authors also acknowledge the use of NASA's Astrophysical Data System Abstract Service (ADS) and NASA's SkyView.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Deutsche Forschungsgemeinschaft (DFG)UNSPECIFIED
NSFAST 96-13717
Consejo Nacional de Ciencia y Tecnología (CONACYT)27606-E
Alexander von Humboldt FoundationUNSPECIFIED
Subject Keywords:galaxies: dwarf; galaxies: individual (Holmberg I=UGC 5139=DDO 63) ; galaxies: irregular; galaxies: photometry; ISM: bubbles; ISM: H I
Issue or Number:6
Record Number:CaltechAUTHORS:20170408-161702618
Persistent URL:
Official Citation:Jürgen Ott et al 2001 AJ 122 3070
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76162
Deposited By: 1Science Import
Deposited On:14 Jul 2017 22:23
Last Modified:09 Mar 2020 13:18

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