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The Herschel Dwarf Galaxy Survey investigates the interplay of star formationactivity and the the metal-poor gas and dust of dwarf galaxies using FIR andsubmillimetre imaging spectroscopic and photometric observations in the 50 to550mu window of the Herschel Space Observatory. The dust SEDs are wellconstrained with the new Herschel and MIR Spitzer data. A submillimetre excessis often found in low metallicity galaxies, which,if tracing very cold dust,would highlight large dust masses not easily reconciled in some cases, giventhe low metallicities and expected gas-to-dust mass ratios. The galaxies arealso mapped in the FIR fine-structure lines (63 and 145mu OI, 158mu CII, 122and 205mu NII, 88mu OIII) probing the low density ionised gas, the HII regionsand photodissociation regions. While still early in the Herschel mission we canalready see, along with earlier studies, that line ratios in the metal-poor ISMdiffer remarkably from those in the metal-rich starburst environments. In dwarfgalaxies, L[CII]/L(CO) (>10^4) is at least an order of magnitude greater thanin the most metal-rich starburst galaxies. The enhanced [CII] arises from thelarger photodissociation region where H2, not traced by the CO, can exist. The88mu [OIII] line usually dominates the FIR line emission over galaxy-widescales in dwarf galaxies, not the 158mu [CII] line which is the dominant FIRcooling line in metal-rich galaxies. All of the FIR lines together cancontribute 1% to 2% of the L(TIR). The Herschel Dwarf Galaxy survey willprovide statistical information on the nature of the dust and gas in lowmetallicity galaxies, elucidating the origin of the submm excess in dwarfgalaxies, and help determine a ([CII] +CO) to H2 conversion factor, thusproviding observational constraints on chemical evolution models of galaxies.

The Elusive ISM of Dwarf Galaxies: Excess Submillimetre Emission and CO-Dark Molecular Gas