Is I Zw 18 a young galaxy?
| Autor: | Izotov, Y. I., Papaderos, P., Thuan, T. X., Fricke, K. J., Foltz, C. B., Guseva, N. G. |
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| Rok vydání: | 1999 |
| Předmět: | |
| DOI: | 10.48550/arxiv.astro-ph/9907082 |
| Popis: | Hubble Space Telescope (HST) colour - magnitude diagrams in B, V and R along with long-slit Multiple Mirror Telescope (MMT) spectrophotometric data are used to investigate the evolutionary status of the nearby blue compact dwarf (BCD) galaxy I Zw 18. We find that the distance to I Zw 18 should be as high as 20 Mpc, twice the previously accepted distance, to be consistent with existing observational data on the galaxy: colour-magnitude diagrams, the high ionization state of the gas and presence of WR stars in the main body, and the ionization state of the C component. The spectral energy distribution (SED) of the main body of I Zw 18 is consistent with that of a stellar population with age < 5 Myr. However, the presence of large-scale shells observed around the main body suggests that star formation began ~ 20 Myr at the NW end and propagated in the SE direction. Our analysis of colour-magnitude diagrams and of the spectral energy distribution of the C component implies that star formation in this component started < 100 Myr ago at the NW end, propagated to the SE and stopped ~ 15 Myr ago. Thus, I Zw 18 is likely to be one of the youngest nearby extragalactic objects. 14 pages, 9 Postscript figures |
| Databáze: | OpenAIRE |
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