# H-ATLAS/GAMA: The nature and characteristics of optically red galaxies detected at submillimetre wavelengths

Dariush, A, Dib, S, Hony, S, Smith, DJB, Zhukovska, S, Dunne, L, Eales, S, Andrae, E, Baes, M, Baldry, IK, Bauer, A, Bland-Hawthorn, J, Brough, S, Bourne, N, Cava, A, Clements, D, Cluver, M, Cooray, A, Zotti, GD, Driver, S , Grootes, MW, Hopkins, AM, Hopwood, R, Kaviraj, S, Kelvin, L, Lara-Lopez, MA, Liske, J, Loveday, J, Maddox, S, Madore, B, Michalowski, MJ, Pearson, C, Popescu, C, Robotham, A, Rowlands, K, Seibert, M, Shabani, F, Smith, MWL, Taylor, EN, Tuffs, R, Valiante, E and Virdee, JS (2016) H-ATLAS/GAMA: The nature and characteristics of optically red galaxies detected at submillimetre wavelengths. Monthly Notices of the Royal Astronomical Society, 456 (2). pp. 2221-2259. ISSN 0035-8711

We combine Herschel/SPIRE sub-millimeter (submm) observations with existing multi-wavelength data to investigate the characteristics of low redshift, optically red galaxies detected in submm bands. We select a sample of galaxies in the redshift range 0.01$\leq$z$\leq$0.2, having >5$\sigma$ detections in the SPIRE 250 micron submm waveband. Sources are then divided into two sub-samples of $red$ and $blue$ galaxies, based on their UV-optical colours. Galaxies in the $red$ sample account for $\approx$4.2 per cent of the total number of sources with stellar masses M$_{*}\gtrsim$10$^{10}$ Solar-mass. Following visual classification of the $red$ galaxies, we find that $\gtrsim$30 per cent of them are early-type galaxies and $\gtrsim$40 per cent are spirals. The colour of the $red$-spiral galaxies could be the result of their highly inclined orientation and/or a strong contribution of the old stellar population. It is found that irrespective of their morphological types, $red$ and $blue$ sources occupy environments with more or less similar densities (i.e., the $\Sigma_5$ parameter). From the analysis of the spectral energy distributions (SEDs) of galaxies in our samples based on MAGPHYS, we find that galaxies in the $red$ sample (of any morphological type) have dust masses similar to those in the $blue$ sample (i.e. normal spiral/star-forming systems). However, in comparison to the $red$-spirals and in particular $blue$ systems, $red$-ellipticals have lower mean dust-to-stellar mass ratios. Besides galaxies in the $red$-elliptical sample have much lower mean star-formation/specific-star-formation rates in contrast to their counterparts in the $blue$ sample. Our results support a scenario where dust in early-type systems is likely to be of an external origin.