IA/U.Lisboa Seminar - Characterisation of high-z dusty galaxies in Herschel cosmological survey - 6 junho 2017

The abundance of dusty galaxies at high-redshifts tests our theories about early galaxy formation. However, due to limited samples and limited sensitivities of instruments observing at shorter wavelengths, this observable remains very inaccurately measured and the contribution of dusty galaxies to the cosmic star formation rate density (SFRD) at z > 4 is still unknown. One of widely used methods to detect potentially z > 4 dusty galaxies is to select Herschel sources whose thermal SED peak shifts to wavelengths longer than 500 microns (so-called "FIR-risers"). The method was successful to identify most distant starburst galaxies. However,most of previous studies were limited to very few objects. Aiming to build statistically significant sample of “FIR-risers” and thus obtain the shape of differential number counts, we consider one of the largest Herschel surveys, the Herschel Virgo Cluster Survey (HeViCS). Since detection of "FIR-risers" is very challenging process due to the high source confusion, we implemented a new selection technique to find these sources, combining de-blending and SED fitting of sources detected in 250 micron maps, and modelling the spectral emission of each source as a modified blackbody (Donevski et al. 2017, in prep).

We made a final sample of 133 “FIR-riser” galaxies reaching a reasonable good agreement with evolutionary models. It challenges previous studies in other Herschel fields which conclude to a under-prediction of the number of “FIR-risers” by the models. However, it still remains unclear what mechanisms could drive a galaxy to such prodigious IR luminosities at early cosmic times.