Astron. Astrophys. 348, 394-404 (1999)

Stars, H II regions, and shocked gas in the bar of NGC 1530

A. Greve, D. Reynaud and D. Downes

Institut de Radio Astronomie Millimétrique, F-38406 St. Martin d`Hères, France

Received 26 October 1998 / Accepted 4 June 1999

Abstract

We analyse long slit spectra taken along and perpendicular to the bar of the galaxy NGC 1530. Our data show that the H II regions, around young massive stars that form in the shock-compressed gas, share the same kinematics as the molecular gas in the orbits at the center of the galaxy. Along the bar, the H II regions are in the post-shock zone, downstream of the dust lanes that contain molecular gas. Outside of the H II regions in the bar is faint, diffuse, ionized gas with a low H / [NII] and H / [SII] line ratio, which confirms the presence of shocks in the bar and supports a shock origin of the dust lanes. The measured spatial variation of the H and [NII] line intensity is consistent with the distribution of molecular gas along the dust lanes and its high concentration near the first inner Lindblad resonance. From an image, we derive the surface brightness along the bar which we interpret as the stellar distribution. We use these data to estimate the mass in the various structural components of the bar. The mass of the stars and gas in the bar is , or 12% of the total mass of the galaxy.

Key words: galaxies: individual: NGC 1530 galaxies: ISM galaxies: kinematics and dynamics galaxies: structure

Send offprint requests to: A. Greve

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Contents

• 1. Introduction
  • 1.1. Bar shocks and dust lanes in model simulations
  • 1.2. Observational evidence for bar shocks
  • 1.3. Bar shocks in NGC 1530
• 2. Observations
• 3. Results for the gas
  • 3.1. The ionized gas of the bar
  • 3.2. Kinematics of the central H II regions ( kpc)
  • 3.3. The inner Lindblad resonance ( kpc)
  • 3.4. The H II regions along the bar ( kpc)
  • 3.5. Shock-excited, diffuse, ionized gas
• 4. Results on the stellar distribution
  • 4.1. The nuclear bulge ( kpc)
  • 4.2. The orbit stars ( kpc)
  • 4.3. The orbit stars (2 kpc kpc)
• 5. Estimates of the mass of stars
  • 5.1. Dynamical mass estimated from rotation velocities
  • 5.2. Stellar mass ratios derived from brightness distributions
  • 5.3. Mass distribution of gas and stars
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999
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