Abstract
ABSTRACT By fitting stellar populations to the fourth generation of the Sloan Digital Sky Survey (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey observations of ∼7000 suitably weighted individual galaxies, we reconstruct the star formation history of the Universe, which we find to be in reasonable agreement with previous studies. Dividing the galaxies by their present-day stellar mass, we demonstrate the downsizing phenomenon, whereby the more massive galaxies hosted the most star formation at earlier times. Further dividing the galaxy sample by colour and morphology, we find that a galaxy’s present-day colour tells us more about its historical contribution to the cosmic star formation history than its current morphology. We show that downsizing effects are greatest among galaxies currently in the blue cloud, but that the level of downsizing in galaxies of different morphologies depends quite sensitively on the morphological classification used, due largely to the difficulty in classifying the smaller low-mass galaxies from their ground-based images. Nevertheless, we find agreement that among galaxies with stellar masses $M_{\star } \gt 6\times 10^{9}\, \mathrm{ M}_{\odot }$, downsizing is most significant in spirals. However, there are complicating factors. For example, for more massive galaxies, we find that colour and morphology are predictors of the past star formation over a longer time-scale than in less massive systems. Presumably this effect is reflecting the longer period of evolution required to alter these larger galaxies’ physical properties, but shows that conclusions based on any single property do not tell the full story.
Highlights
The question of when and where the stars residing in today’s galaxies formed is essential to understanding the present-day Universe
By fitting stellar populations to the fourth generation of the Sloan Digital Sky Survey (SDSS-IV) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey observations of ∼7000 suitably weighted individual galaxies, we reconstruct the star formation history of the Universe, which we find to be in reasonable agreement with previous studies
We find that the agreement between the star formation histories measured using each MaNGA sample is only seen when the galaxy redshifts are taken into account, and that the above close agreement is smaller than the difference in median lookback times for each sample’s galaxy populations
Summary
See analyses by Hopkins & Beacom (2006), Behroozi, Wechsler & Conroy (2013), Madau & Dickinson (2014), and references therein Within this picture, studies of galaxy populations at different redshifts have demonstrated the link between the star formation history of the Universe and the evolution of its constituent galaxies. It would be possible to understand which property transition – morphology or colour; ‘shape’ or ‘shade’ – is more fundamental, and whether the associated time-scales vary according to galaxy properties such as stellar mass By their nature, studies of galaxy populations at different redshifts are limited to studying the average statistical behaviour of a galaxy population’s star formation at different snapshots in the Universe’s history, and are unable to trace how individual galaxies have evolved. The calibrated spectra are reduced and combined into threedimensional data cubes by a custom data reduction pipeline (DRP; Law et al 2016; Law et al 2021), and a data analysis pipeline (DAP; Cherinka et al 2019; Westfall et al 2019) provides data analysis products such as spectral index maps, stellar and gas kinematics, and emission line fluxes (Belfiore et al 2019)
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