Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7986s&link_type=abstract
HST Proposal ID #7986
Astronomy and Astrophysics
Astrophysics
Hst Proposal Id #7986 Extragalactic Astrophysics
Scientific paper
About half of all spiral and S0 galaxies are barred: recent observations show that the main bar often harbors one, and sometimes two, smaller ``nuclear bars''. The inner bars appear to be dynamically distinct, rotating faster than the outer main bars. Fast-rotating bars form only in dynamically cold disks, so the presence of an inner bar indicates that disk material is present right into the center. The complex time-varying gravitational field of a multiply-barred galaxy sweeps gas in towards the center, or causes it to build up in a circumnuclear ring. The development of the central regions of a galaxy must depend on how much material accumulates there with ``no place to go''; nuclear bars must strongly influence the flow of gas in the innermost kiloparsec of disk galaxies, and merit detailed study to determine their physical and evolutionary characteristics. We propose to investigate central structures in nearby barred galaxies, including some of the best examples of double bars, using archival WFPC2 and NICMOS images. Since nuclear bars have physical sizes << 1 kpc, they can be detected from the ground but not properly resolved. We will measure bar amplitudes and isophotal shapes, map dust lanes which reveal gas flow, and make color maps for most of our galaxies. We will investigate the influence of central bars on the nuclear region, as revealed by the presence of circumnuclear rings, regions of intense star formation, nuclear star clusters, or bright compact nuclei.
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