Galaxy Zoo: the dependence of morphology and colour on environment

Abstract

Does the environment of a galaxy directly influence the quenching history of a galaxy? Here we investigate the detailed morphological structures and star formation histories of a sample of SDSS group galaxies with both classifications from Galaxy Zoo 2 and NUV detections in GALEX. We use the optical and NUV colours to infer the quenching time and rate describing a simple exponentially declining SFH for each galaxy, along with a control sample of field galaxies. We find that the time since quenching and the rate of quenching do not correlate with the relative velocity of a satellite but are correlated with the group potential. This quenching occurs within an average quenching timescale of ∼ 2.5 Gyr from star forming to complete quiescence, during an average infall time (from ∼ 10R 200 to 0.01R 200) of ∼ 2.6 Gyr. Our results suggest that the environment does play a direct role in galaxy quenching through quenching mechanisms which are correlated with the group potential, such as harassment, interactions or starvation. Environmental quenching mechanisms which are correlated with satellite velocity, such as ram pressure stripping, are not the main cause of quenching in the group environment. We find that no single mechanism dominates over another, except in the most extreme environments or masses. Instead an interplay of mergers , mass & morphological quenching and environment driven quenching mechanisms dependent on the group potential drive galaxy evolution in groups.

Rotation-invariant convolutional neural networks for galaxy morphology prediction

“…Data from the Galaxy Zoo projects have already been used in a wide variety of studies on galaxy structure, formation, and evolution (Skibba et al 2009;Bamford et al 2009;Schawinski et al 2009;Darg et al 2010;Masters et al 2010Masters et al , 2011Simmons et al 2013;Melvin et al 2014;Willett et al 2015). Comparisons of Galaxy Zoo morphologies to smaller samples from both experts and automated classifications show high levels of agreement, testifying to the accuracy of the crowdsourced annotations .…”

J1649+2635: a grand-design spiral with a large double-lobed radio source

“…Schawinski et al (2014) suggest that the starformation of red spirals has been quenched by the cool gas flow being cut-off by some mechanism such as a merger. Red spirals are preferentially found in intermediate density regimes (Bamford et al 2009;Masters et al 2010). Using the criterion (g-r) > 0.63− 0.02(Mr + 20) (Masters et al 2010), J1649+2635 is clearly a red spiral (Mr = −22.73, g-r = 1.02).…”

“…de Vaucouleurs 1961). The Galaxy Zoo project discovered the "red spiral" class of objects (Bamford et al 2009) and Masters et al (2010) find that just 6 per cent of face-on spiral galaxies are red in colour. Red spirals are found to have similar star-formation histories to blue spirals until 500 Myr ago, after which red spirals have up to 3× less star formation (Tojeiro et al 2013).…”

Evidence of pre-processing and a dependence on dynamical state for low-mass satellite galaxies

“…Therefore, in order to probe the environmentally driven aspects of galaxy evolution it is crucial to account for both the dependence on the host halo environment as well as the radial position within the group or cluster. The aforementioned environmental dependences are strongest for low-mass galaxies and it appears that properties of high-mass galaxies are less dependent on environment (Haines et al 2006;Bamford et al 2009). For high-mass galaxies, quenching is thought to be driven by internal, secular processes such as feedback from AGN (e.g.…”