Universidad Complutense de Madrid
I will discuss our results about the Star Formation Histories (SFHs) of massive (M>10^10 M_sun) quiescent galaxies (MQGs) at z>1. These SFHs have been inferred from the analysis of rest-frame ultraviolet/optical spectro-photometric data from the SHARDS and Hubble Space Telescope Wide Field Camera 3 (HST/WFC3) G102 and G141 surveys of the GOODS-N field. Taking advantage of the SHARDS data resolution, we are able to break the typical degeneracies inherent to most stellar population studies by measuring UV and optical absorption indices. The population of MQGs at z>1 shows a duality in their properties. Dead galaxy samples at these redshifts are dominated (at the 80-85% level) by systems with relatively young mass-weighted ages, t_M < 2 Gyr, and short star formation timescales, 60-200 Myr. The evolution of these so-called mature galaxies from z < 1 to z=0 is consistent with being passive, but accompanied with a stellar mass increase not affecting the mean ages. There is also an older population of 'senior galaxies' (15% of the sample) with t_M=2-4 Gyr, longer star formation timescales, around 400 Myr, and larger masses, log(M/M_sun)~10.8 (0.3 dex larger than the mature population). The number density of this sub-population of senior galaxies is consistent with that found for massive quiescent galaxies at z~2, implying that those galaxies did not restart their star formation activity once they were quenched. We find that the derived SFHs for our MQGs are consistent with the slope and the location of the Main Sequence (MS) of star-forming galaxies at z>1.0, when our galaxies were 0.5-1.0 Gyr old. According to the derived SFHs, all of the MQGs experienced a Luminous Infrared Galaxy (LIRG) phase during typically 500 Myr and roughly half of them went through an Ultra Luminous Infrared Galaxy (ULIRG) phase for 100 Myr. Based on average mass-weighted ages for massive galaxies at z < 1 we find that that the build-up of the red sequence is continuous down to z~1, and only below that redshift (in the last 6 Gyr), the evolution of massive galaxies is dominated by quiescence.
2016 April 22, 12:00
Observatório Astronómico de Lisboa (Seminar room)
Tapada da Ajuda, 1349-018 Lisboa