Dust In I Zw 18 From Hubble Space Telescope Narrow Band Imaging

Details Dust In I Zw 18 From Hubble Space Telescope Narrow Band Imaging Dust In I Zw 18 From Hubble Space Telescope Narrow Band Imaging

2001-09-28

arxiv.org/abs/astro-ph/0109558v1

Astronomy and Astrophysics

Astrophysics

26 pages, 3 figures. Accepted for publication in the Astrophysical Journal, Volume 565

Scientific paper

10.1086/324691

We present new WFPC2 narrow band imaging of the blue compact dwarf galaxy I Zw 18, which is host to the lowest-metallicity HII regions known. Images at H-alpha and H-beta are combined with archival broad band images to allow the study of the ionized gas distribution and morphology. Analysis of the H-alpha/H-beta flux ratio reveals significant enhancements in some areas of both the ``Northwest'' and ``Southeast'' regions of the galaxy, with ratios elevated to levels as high as 3.4. The H-alpha/H-beta ratio varies considerably with position throughout the galaxy. Comparing this distribution with the stellar distribution indicates that the regions of enhanced H-alpha/H-beta ratio are not due to the effects of either collisional excitation or underlying stellar absorption, and therefore are most likely interpreted as the presence of dust. This dust has an estimated mass of (2-5)x10^3 solar masses, which is consistent with the IRAS far-IR non-detection. Under the assumption that dust traces the presence of molecular gas, these results suggest that the molecular component of the ISM of I Zw 18, which is needed to fuel its active star formation, is also very clumpy. Such a distribution would be consistent with the recent FUSE non-detections of diffuse H_2.

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