paper

The Abundance Gradient of NGC 1365: Evidence for a Recently Formed Bar in an Archetype Barred Spiral Galaxy?

arXiv:astro-ph/9705032 · doi:10.1093/mnras/288.3.715

Abstract

Emission-line optical spectrophotometry for 55 H II regions in the prominent southern barred spiral galaxy NGC 1365 is presented. Nebular diagnostic diagrams such as [N II]/[O II] and [S II]/[O II] versus [O II]/{O III] show that the H II regions of the barred galaxy have the same range of physical conditions as found in non-barred late-type galaxies. Extinction is moderately high across the disc and there is evidence for a slight trend of extinction with galactocentric distance; the logarithmic extinction at H-beta falls from about c = 1.2 in the centre to 0.6 -- 0.8 in the outer regions. The global O/H distribution has a moderate gradient of about -0.5 dex/rho0 (about -0.02 dex/kpc) consistent with the known trend between the slope of the abundance gradient and the strength of the bar. A break is seen in the O/H gradient just beyond the -4/1 resonance, the gradient being moderately steep at about -0.8 dex/rho0 (-0.05 dex/kpc) inside this resonance, and flat beyond rho/rho0 > 0.55. The abundance distribution is compared with another barred spiral galaxy, NGC 3359, and with that of two well-sampled normal spiral galaxies, NGC 2997 and M 101. The possibility that the bar formed recently in NGC 1365 is considered. The difficulties encountered in doing spectrophotometry with fibre optics are discussed and shown not to be insurmountable.

To appear in MNRAS. (Latex, 14 pages, 6 postscript figures)

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