Subaru Hyper Suprime-Cam revisits the large-scale environmental dependence on galaxy morphology over 360 deg$^2$ at z=0.3-0.6

TL;DR

This study uses deep learning on wide-field Subaru data to examine how large-scale environments influence galaxy morphology, revealing moderate density relations and spiral deficits near clusters at redshifts 0.3-0.6.

Contribution

It introduces a transfer learning approach with deep learning for galaxy morphology classification over a large area, enabling new insights into environmental effects on galaxy types.

Findings

Moderate morphology-density relation on 10 Mpc scales.

Spiral galaxy deficits near red sequence clusters.

No significant color-environment dependence observed.

Abstract

This study investigates the role of large-scale environments on the fraction of spiral galaxies at $z=$ 0.3-0.6 sliced to three redshift bins of $\Delta z=0.1$. Here, we sample 276220 massive galaxies in a limited stellar mass of $5\times10^{10}$ solar mass ($\sim M^\ast$) over 360 deg$^2$, as obtained from the Second Public Data Release of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). By combining projected two-dimensional density information (Shimakawa et al. 2021) and the CAMIRA cluster catalog (Oguri et al. 2018), we investigate the spiral fraction across large-scale overdensities and in the vicinity of red sequence clusters. We adopt transfer learning to significantly reduce the cost of labeling spiral galaxies and then perform stacking analysis across the entire field to overcome the limitations of sample size. Here we employ a morphological classification catalog by the Galaxy Zoo Hubble (Willet et al. 2017) to train the deep learning model. Based on 74103 sources classified as spirals, we find moderate morphology-density relations on ten comoving Mpc scale, thanks to the wide-field coverage of HSC-SSP. Clear deficits of spiral galaxies have also been confirmed, in and around 1136 red sequence clusters. Furthermore, we verify whether there is a large-scale environmental dependence on rest-frame $u-r$ colors of spiral galaxies; however, such a tendency was not observed in our sample.