(Proposal ID) S17B-001

(PI) Misawa, Toru

(Proposal Title)
Transverse Proximity Effects around BAL Quasars

(Abstract)
The purpose of this proposal is to find out the reason why there exists an 
anisotropic H I absorption around quasars; i.e., the environments around 
quasars are highly biased toward producing strong H I absorption in transverse 
direction while there exists a significant deficit of H I absorption within a 
few Mpc of quasars along line-of-sight (i.e., proximity effect). The most 
plausible explanation for this opposite trend is that the transverse direction 
is shadowed from the quasar UV radiation due to dusty torus, a frequently 
invoked structure in AGN unification models.  However, a critical weakness of 
this idea is that we have no information on inclination angle of our sightline 
relative to the torus. In this program, we examine environments of foreground 
quasars with broad absorption troughs in their spectra (i.e., BAL quasars) 
because it is widely believed that BAL troughs are observed only if the 
central continuum is viewed from the side.  With closely separated (theta<60") 
quasar pairs at different redshift, we examine H I absorption at foreground 
BAL quasars in spectra of background quasars. We then confirm whether the 
anisotropic H I absorption (which is seen around non-BAL (i.e., face-on) 
quasars) is also observed around BAL (i.e., edge-on) quasars. We perform 
observations in S17B and S18A.