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Chemical and Photometric Evolution of Extended Ultraviolet Disks: Optical Spectroscopy of M83 (NGC5236) and NGC4625

A. Gil de Paz·B. F. Madore·S. Boissier·D. Thilker·L. Bianchi·C. Sánchez Contreras·T. A. Barlow·T. Conrow·K. Forster·P. G. Friedman·D. C. Martin·P. Morrissey·S. G. Neff·R. M. Rich·D. Schiminovich·M. Seibert·T. Small·J. Donas·T. M. Heckman·Y. -W. Lee·B. Milliard·A. S. Szalay·T. K. Wyder·S. Yi
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Abstract

We present the results from the analysis of optical spectra of 31 Halpha-selected regions in the extended UV (XUV) disks of M83 (NGC5236) and NGC4625 recently discovered by GALEX. The spectra were obtained using IMACS at Las Campanas Observatory 6.5m Magellan I telescope and COSMIC at the Palomar 200-inch telescope, respectively for M83 and NGC4625. The line ratios measured indicate nebular oxygen abundances (derived from the R23 parameter) of the order of Zsun/5-Zsun/10. For most emission-line regions analyzed the line fluxes and ratios measured are best reproduced by models of photoionization by single stars with masses in the range 20-40 Msun and oxygen abundances comparable to those derived from the R23 parameter. We find indications for a relatively high N/O abundance ratio in the XUV disk of M83. Although the metallicities derived imply that these are not the first stars formed in the XUV disks, such a level of enrichment could be reached in young spiral disks only 1 Gyr after these first stars would have formed. The amount of gas in the XUV disks allow maintaining the current level of star formation for at least a few Gyr.

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A. Gil de Paz, B. F. Madore, S. Boissier, D. Thilker, L. Bianchi, C. Sánchez Contreras, T. A. Barlow, T. Conrow, K. Forster, P. G. Friedman, D. C. Martin, P. Morrissey, S. G. Neff, R. M. Rich, D. Schiminovich, M. Seibert, T. Small, J. Donas, T. M. Heckman, Y. -W. Lee, B. Milliard, A. S. Szalay, T. K. Wyder, S. Yi. 2007-02-12. Chemical and Photometric Evolution of Extended Ultraviolet Disks: Optical Spectroscopy of M83 (NGC5236) and NGC4625. https://doi.org/10.1086/513730

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