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Is I Zw 18 a young galaxy? | Y. I. Izotov
; P. Papaderos
; T. X. Thuan
; K. J. Fricke
; C. B. Foltz
; N. G. Guseva
; | Date: |
7 Jul 1999 | Subject: | astro-ph | Affiliation: | Main Astronomical Observatory, Kiev, Ukraine, Universitat Sternwarte, Goettingen, University of Virginia, Charlottesville, USA, Multiple Mirror Telescope Observatory, Tucson, USA | Abstract: | 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. | Source: | arXiv, astro-ph/9907082 | Services: | Forum | Review | PDF | Favorites |
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