2022PASJ...74..318S

This paper reports detections of Hα emission and stellar continuum out to approximately 30 physical kiloparsecs, and Hα directionality in the outskirts of Hα-emitting galaxies (Hα emitters) at z = 0.4. This research adopts narrow-band selected Hα emitters at z = 0.4 from the emission-line object catalog by Hayashi et al. (2020, PASJ, 72, 86), which is based on data in the Deep and Ultradeep layers of the Hyper Suprime-Cam Subaru Strategic Program. Deep narrow- and broad-band images of 8625 Hα emitters across 16.8 deg² enable us to construct deep composite emission-line and continuum images. The stacked images show diffuse Hα emission (down to ∼5 x 10^–20 erg s^–1 cm^–2 arcsec^–2) and stellar continuum (down to ∼5 x 10^–22 erg s^–1 cm^–2 Å^–1 arcsec^–2), extending beyond 10 kpc at stellar masses >10⁹ M_☉, parts of which may originate from stellar halos. Those radial profiles are broadly consistent with each other. In addition, we obtain a dependence of the Hα emission on the position angle because relatively higher Hα equivalent width has been detected along the minor-axis towards galaxy disks. While the Hα directionality could be attributed to biconical outflows, further research with hydrodynamic simulations is highly demanded to pin down the exact cause.