Galaxy and Mass Assembly (GAMA): Extended Intra-Group Light in a group at $z=0.2$ from deep Hyper-Suprime Cam images

We present a pilot study to assess the potential of Hyper Suprime-Cam Public Data Release 2 (HSC-PDR2) images for the analysis of extended faint structures within groups of galaxies. We examine the intra-group light (IGL) of the group 400138 ($M_{\mathrm{d}\mathrm{y}\mathrm{n}}=1.3\pm 0.5\times {10}^{13}$M${}_{\odot }$, $z\sim 0.2$) from the Galaxy And Mass Assembly (GAMA) survey using Hyper-Suprime Cam Subaru Strategic Program Public Data Release 2 (HSC-PDR2) images in $g$, $r$, and $i$ bands. We present the most extended IGL measurement to date, reaching down to ${\mu }_g^{\mathrm{l}\mathrm{i}\mathrm{m}}=30.76$ mag arcsec${}^{-2}$ ($3\sigma$; $10\times 10$ arcsec${}^2$) at a semi-major axis of 275 kpc. The IGL shows mean colour values of $g-i=0.92$, $g-r=0.60$, and $r-i=0.32$ ($\pm$0.01). The IGL stellar populations are younger ($2-2.5$ Gyr) and less metal-rich ([Fe/H] $\sim -$0.4) than those of the host group galaxies. We find a range of IGL fractions as a function of total group luminosity of $\sim 2-36\mathrm{\%}$ depending on the definition of IGL, with larger fractions the bluer the observation wavelength. The early-type to late-type galaxy ratio suggests that 400138 is a more evolved group, dominated by ETGs, and the IGL fraction agrees with that of other similarly evolved groups. These results are consistent with tidal stripping of the outer parts of Milky Way-like galaxies as the main driver of the IGL build-up. This is supported by the detection of substructure in the IGL towards the galaxy member 1660615 suggesting a recent interaction ($<1$ Gyr ago) of that galaxy with the core of the group.