On the interdependence of galaxy morphology, star formation and environment in massive galaxies in the nearby Universe

Abstract

Using multi-wavelength data, from UV-optical-near-mid IR, for ∼6000 galaxies in the local Universe, we study the dependence of star formation on the morphological Ttypes for massive galaxies (log M * /M ≥ 10). We find that, early-type spirals (Sa-Sbc) and S0s predominate in the green valley, which is a transition zone between the star forming and quenched regions. Within the early-type spirals, as we move from Sa to Sbc spirals the fraction of green valley and quenched galaxies decreases, indicating the important role of the bulge in the quenching of galaxies. The fraction of early-type spirals decreases as we enter the green valley from the blue cloud, which coincides with the increase in the fraction of S0s. This points towards the morphological transformation of early-type spiral galaxies into S0s which can happen due to environmental effects such as ram-pressure stripping, galaxy harassment, or tidal interactions. We also find a second population of S0s which are actively star-forming and are present in all environments. Since morphological T-type, specific star formation rate (sSFR), and environmental density are all correlated with each other, we compute the partial correlation coefficient for each pair of parameters while keeping the third parameter as a control variable. We find that morphology most strongly correlates with sSFR, independent of the environment, while the other two correlations (morphology-density and sSFR-environment) are weaker. Thus, we conclude that, for massive galaxies in the local Universe, the physical processes that shape their morphology are also the ones that determine their star-forming state.

Classification and evolution of galaxies according to the dynamical state of host clusters and galaxy luminosities

“…This suggests evolution through the GV, and that S0 type is crucial for understanding the transition from late to early type objects, in agreement with recent works (e.g. Bait et al 2017;Bremer et al 2018). At the same time, the fraction of Sab decreases from SF to PAS.…”

Galaxy and Mass Assembly (GAMA): Morphological transformation of galaxies across the green valley

“…Most of these also have significant disk components and, for this redshift and mass range, there are essentially no bulgeless objects (Sd or Irr). We note that Bait, Barway, & Wadadekar (2017) come to a similar conclusion from a study of de Vaucouleurs T-types as a function of colour in the Nair & Abraham (2010) sample drawn from SDSS. The significant difference in the E/S0/Sa fractions between blue and green subsamples again implies that if the green subsample is dominated by objects transitioning from the blue cloud, this transition takes place, and the galaxy turns green, only after a significant bulge component has been formed.…”

“…This confirms that, at the 50th percentile of each distribution, the green galaxies live in regions of 0.2 dex higher density than blue galaxies, but 0.1 dex lower density than red galaxies, generally avoiding both density extremes (cf. Bait, Barway, & Wadadekar 2017). This may suggest that (blue) galaxies in the lowest density environments have not (yet) had the opportunity to turn green, whilst most (red) galaxies in the highest density regions have already passed through any green phase at higher redshifts.…”

Are galactic star formation and quenching governed by local, global, or environmental phenomena?

“…We construct a new statistic to quantify the dependence of quenching (or star formation) on two parameters simultaneously. We begin with the partial correlation coefficient (PCC), which quantifies the strength of correlation between two variables at a fixed third variable (see Bluck et al 2019, Bait et al 2017. Specifically, the PCC is defined as:…”