EDP Sciences
Free access
Volume 485, Number 1, July I 2008
Page(s) 5 - 20
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20079129
Published online 16 April 2008

A&A 485, 5-20 (2008)
DOI: 10.1051/0004-6361:20079129

Where are the stars of the bar of NGC 1530 forming?

A. Zurita1, 2 and I. Pérez1, 2, 3

1  Departamento. de Física Teórica y del Cosmos, Campus de Fuentenueva, Universidad de Granada, 18071-Granada, Spain
    e-mail: azurita@ugr.es
2  Instituto Carlos I de Física Teórica y Computación, Spain
3  Kapteyn Astronomical Institute, University of Groningen, Postbus 800, Groningen 9700 AV, The Netherlands
    e-mail: isa@astro.rug.nl

Received 23 November 2007 / Accepted 21 February 2008

Aims. NGC 1530 has one of the strongest bars ever observed and recent star formation sites are distributed across its bar. Our aim is to study the photometric properties of the bar and its H II regions, to elucidate the conditions under which H II regions form and their spatial relation to the principal dynamical features of the bar.
Methods. We obtained $BVRK{\rm s}$ and H$\alpha$ photometry of the H II regions of the bar in NGC 1530. Broad-band integrated colours and H$\alpha$ equivalent widths were carefully measured and analysed as a function of position with respect to the main dust-lanes of the bar.
Results. We measured differences in the H$\alpha$ equivalent widths of the H II regions that are located in the trailing and leading sides of the bar dust-lane. The possible factors that could produce this difference, such as [N II] contamination, Lyman-continuum-photon dust-extinction, escape of ionizing radiation, metallicity, IMF and age, were carefully analysed. Age differences were confirmed to be the most plausible explanation. This implies that H II regions that are located further away from the bar dust-lane in its leading side, downstream from the main bar dust-lane, are older than the rest by ~1.5-2.5 Myr. In addition, a clear spatial correlation has been found between: location of H II regions, dust spurs on the trailing side of the bar dust-lane, and the loci of maximum velocity gradients parallel to the bar major axis (possibly tracing gas flow towards the main bar dust-lane).These results support the hypothesis that massive stars are forming on the trailing side of the bar dust-lane, and age as they cross the bar, on a timescale that is compatible with the bar dynamics timescale.

Key words: galaxies: structure -- galaxies: individual: NGC 1530 -- galaxies: ISM -- galaxies: spiral -- ISM: HII regions -- galaxies: kinematics and dynamics

© ESO 2008