MAMMOTH-Subaru III. Ly$α$ Halo Extended to $\sim200$ kpc Identified by Stacking $\sim 3300$ Ly$α$ Emitters at $z=2.2-2.3$

Abstract: In this paper, we present a Ly$\alpha$ halo extended to $\sim200$ kpc identified by stacking $\sim 3300$ Ly$\alpha$ emitters at $z=2.2-2.3$. We carry out imaging observations and data reduction with Subaru/Hyper Suprime-Cam (HSC). Our total survey area is $\sim12$ deg$^2$ and imaging depths are $25.5-27.0$ mag. Using the imaging data, we select 1,240 and 2,101 LAE candidates at $z=2.2$ and 2.3, respectively. We carry out spectroscopic observations of our LAE candidates and data reduction with Magellan/IMACS to estimate the contamination rate of our LAE candidates. We find that the contamination rate of our sample is low (8%). We stack our LAE candidates with a median stacking method to identify the Ly$\alpha$ halo at $z=2$. We show that the Ly$\alpha$ halo is extended to $\sim200$ kpc at a surface brightness level of $10^{-20}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Comparing to previous studies, our Ly$\alpha$ halo is more extended at radii of $\sim25-100$ kpc, which is not likely caused by the contamination in our sample but by different redshifts and fields instead. To investigate how central galaxies affect surrounding LAHs, we divide our LAEs into subsamples based on the Ly$\alpha$ luminosity ($L_{\rm Ly\alpha}$), rest-frame Ly$\alpha$ equivalent width (EW$0$), and UV magnitude (M${\rm uv}$). We stack the subsamples and find that higher $L_{\rm Ly\alpha}$, lower EW$0$, and brighter M${\rm uv}$ cause more extended halos. Our results suggest that more massive LAEs generally have more extended Ly$\alpha$ halos.