H-ATLAS/GAMA: Quantifying the Morphological Evolution of the Galaxy
  Population Using Cosmic Calorimetry
  Using results from the Herschel Astrophysical Terrahertz Large-Area Survey
and the Galaxy and Mass Assembly project, we show that, for galaxy masses above
approximately 1.0e8 solar masses, 51% of the stellar mass-density in the local
Universe is in early-type galaxies (ETGs: Sersic n > 2.5) while 89% of the rate
of production of stellar mass-density is occurring in late-type galaxies (LTGs:
Sersic n < 2.5). From this zero-redshift benchmark, we have used a calorimetric
technique to quantify the importance of the morphological transformation of
galaxies over the history of the Universe. The extragalactic background
radiation contains all the energy generated by nuclear fusion in stars since
the Big Bang. By resolving this background radiation into individual galaxies
using the deepest far-infrared survey with the Herschel Space Observatory and a
deep near-infrared/optical survey with the Hubble Space Telescope (HST), and
using measurements of the Sersic index of these galaxies derived from the HST
images, we estimate that approximately 83% of the stellar mass-density formed
over the history of the Universe occurred in LTGs. The difference between this
and the fraction of the stellar mass-density that is in LTGs today implies
there must have been a major transformation of LTGs into ETGs after the
formation of most of the stars.
