Abstract
The Herschel Dwarf Galaxy Survey investigates the interplay of star formation
activity and the the metal-poor gas and dust of dwarf galaxies using FIR and
submillimetre imaging spectroscopic and photometric observations in the 50 to
550mu window of the Herschel Space Observatory. The dust SEDs are well
constrained with the new Herschel and MIR Spitzer data. A submillimetre excess
is often found in low metallicity galaxies, which,if tracing very cold dust,
would highlight large dust masses not easily reconciled in some cases, given
the low metallicities and expected gas-to-dust mass ratios. The galaxies are
also mapped in the FIR fine-structure lines (63 and 145mu OI, 158mu CII, 122
and 205mu NII, 88mu OIII) probing the low density ionised gas, the HII regions
and photodissociation regions. While still early in the Herschel mission we can
already see, along with earlier studies, that line ratios in the metal-poor ISM
differ remarkably from those in the metal-rich starburst environments. In dwarf
galaxies, LCII/L(CO) (>10^4) is at least an order of magnitude greater than
in the most metal-rich starburst galaxies. The enhanced CII arises from the
larger photodissociation region where H2, not traced by the CO, can exist. The
88mu OIII line usually dominates the FIR line emission over galaxy-wide
scales in dwarf galaxies, not the 158mu CII line which is the dominant FIR
cooling line in metal-rich galaxies. All of the FIR lines together can
contribute 1% to 2% of the L(TIR). The Herschel Dwarf Galaxy survey will
provide statistical information on the nature of the dust and gas in low
metallicity galaxies, elucidating the origin of the submm excess in dwarf
galaxies, and help determine a (CII +CO) to H2 conversion factor, thus
providing observational constraints on chemical evolution models of galaxies.
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