Imaging of z=3.1 HI absorbers in the SSA22 proto-cluster region

Ken Mawatari

Using galaxies as background light sources to map the Lya absorption lines is a novel approach to study the interplay between galaxies and the intergalactic medium (IGM). We utilize the wide narrow-band NB497 imaging data to characterize the strength of the Lya absorptions caused by z = 3.1 HI gas in the SSA22 prominent porto-cluster region (Steidel et al. 1998; Hayashino et al. 2004; Yamada et al. 2012a) and the control fields (SXDS and GOODS-N). For the background galaxies at z = 3.3 - 3.5 in these fields, we conducted the SED fitting using the Subaru/Suprime-Cam B, R, i', and z' bands photometry. The NB497 decrement is defined using the NB497 magnitudes observed and estimated from the best-fit template (D_NB497 = NB497_obs - NB497_temp), which reflects the strength of the z = 3.1 HI Lya absorption lines because the mean IGM absorption is adopted for the template spectra. Finally we obtained the two-dimensional D_NB497 map with the mean separation of line-of-sights (LOS) of ~3 arcmin over the area of ~580 arcmin^2 in the SSA22 field. We found that the D_NB497 measurements in the SSA22 field are systematically higher than those in the control fields, which clearly suggests that the HI Lya absorptions are stronger in the proto-cluster region. In each field, interestingly, we found no notable correlation between the D_NB497 and the galaxy overdensity. There is a week trend that the D_NB497 is larger at smaller impact parameter from the nearest z = 3.1 galaxy. In this presentation, we discuss the interpretation about these results.