Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.137c&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Astronomy and Astrophysics
Astronomy
Scientific paper
Dwarf galaxies are of great importance in understanding the formation and evolution of galaxies. They are often metal-poor and can show extreme star formation activity, while they are known to be deficient in CO, the usual molecular gas tracer (Leroy et al. 2009). Under low-metallicity conditions, the [CII] line, coming from a warmer phase, might be a better tracer of the molecular gas content. Observations show that the [CII]/CO(1-0) ratio can be an order of magnitude higher than in normal galaxies (Madden 2000). The [CII]/LFIR ratio is also high, as observed previously in dwarfs (Poglitsch et al. 1995, Madden et al. 1997, Hunter et al. 2001). As part of the Herschel Dwarf Galaxy Survey (PI: S.C. Madden), we present observations of the dominant FIR fine-structure lines ([OIII] 88um, [CII] 158μm, [OI] 63μm ...) in a sample of about 30 local dwarf galaxies with the Herschel/PACS spectrometer. These lines probe the gas in different phases of the ISM, and ratios of [OIII]/[CII] and [OI]/[CII] are indicators of the density and radiation field in these environments. While we have no detection for the faintest objects, [CII] is detected in about 2/3 of the sample. More specifically, we find that the [CII] is the most extended line and brighter than the [OI] 63μm, dominating the cooling in the warm neutral medium. The [OIII] 88μm line traces the highly ionized medium and is the brightest of all, indicating young active star formation. All the FIR lines together can contribute to up to 1% of LFIR. We explore the correlation between the observed line intensities and ratios with global galaxy parameters, in particular metallicity, star formation activity and star formation history. This analysis shows that the structure of the ISM and star formation activity in these metal-poor environments are notably different than in more metal-rich galaxies.
Cormier Daniel
Galliano Frederic
Hony Sacha
Lebouteiller Vianney
Madden Suzanne
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