2011A&A...536L...7I

We present the results of a search for Sloan Digital Sky Survey (SDSS) emission-line galaxies with very red 3.4µm-4.6µm (W1-W2) colours in the Wide-field Infrared Survey Explorer (WISE) Preliminary Release Source Catalogue (PRSC) aiming to find objects with hot dust emission. For this purpose we considered a sample of ∼16000 galaxies with strong emission lines selected out of a total of ∼900000 SDSS spectra and identified them with the PRSC sources. We find that ∼5000 sources out of the ∼16000 SDSS galaxies are present in the PRSC, including ∼1000 galaxies with sufficiently strong [OIII] λ4363 emission lines to permit reliable determinations of the oxygen abundance. No correlation of W1-W2 with metallicity is found. On the other hand, there is clear evidence for a redder W1-W2 index in galaxies with higher Hβ luminosity and higher Hβ equivalent width, implying that strong UV radiation from young starbursts efficiently heats interstellar dust to high temperatures. However, galaxies with very red colours W1-W2>2mag, similar to that in the local extreme star-forming galaxy SBS 0335-052E, are very rare. In addition to three previously known sources, which are not present in our sample, we found only four such galaxies.