Astron. Astrophys. 326, 449-464 (1997)

Star formation in bar environments

I. Morphology, star formation rates and general properties

P. Martin ¹ and D. Friedli <sup>2, 3

1</sup> European Southern Observatory, Casilla 19001, Santiago 19, Chile (e-mail: pmartin@sc.eso.org)
² Département de physique and OMM, Université Laval, Ste-Foy, Québec, G1K 7P4, Canada (e-mail: dfriedli@phy.ulaval.ca)
³ Geneva Observatory, CH-1290 Sauverny, Switzerland

Received 19 March 1997 / Accepted 5 May 1997

Abstract

A study of the morphological properties and star formation rates (SFRs) of H II regions located along the bars of a sample of eleven late-type barred systems is presented and compared with numerical simulations. According to the relative intensity of star formation along the bar with respect to that of the nuclear region, three types of distributions are observed. They may be related to the age of the bar. Other important characteristics include angular misalignments (up to 15^o) between the stellar bar and the "H bar", a correlation between the location of the H II regions and dust lanes in certain bars (mostly early-type spirals), and a difference in axial ratio and length between stellar and H bars. A wide range of SFRs (from 0.03 to ) is observed, and star formation is generally highly asymmetric with respect to the bar minor axis. All these features can be reproduced in numerical models provided that the global mechanical energy release remains low (but non-zero). In NGC 7479, the total gas-to-star transformation efficiency inside the bar is estimated at about 0.26, meaning that, at present, maybe as nearly as 75% of the gas flowing into the bar region is not transformed into stars.

Key words: galaxies: evolution galaxies: ism galaxies: kinematics and dynamics galaxies: spiral galaxies: structure

Send offprint requests to: P. Martin

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Contents

• 1. Introduction
• 2. Database
  • 2.1. The sample of galaxies
  • 2.2. Observations
  • 2.3. Image analysis
• 3. Morphology
  • 3.1. General distributions
  • 3.2. Quantitative properties
  • 3.3. Notes on individual objects
• 4. Star formation rates
  • 4.1. Procedure
  • 4.2. SFR distributions
  • 4.3. Application: the gas-to-star transformation efficiency in NGC 7479
• 5. Numerical simulations
  • 5.1. Time-dependent systems: a word of caution!
  • 5.2. Stellar - H bar misalignments
  • 5.3. Stellar - H bar axis ratios
  • 5.4. Stellar - H bar lengths
  • 5.5. SFR distributions
  • 5.6. ILRs
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: October 15, 1997
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