2006AJ....131...34M

We carried out a Subaru and UKIRT near-infrared imaging survey for Hα-emitting galaxies around two pair quasar systems (Q0301-005/Q0302-003 and Q2343+125/Q2344+125) and a triple quasar system (KP 76/KP 77/KP 78). Narrowband near-infrared filters covering the Hα emission expected for galaxies at the confirmed C IV absorption redshift toward the quasar systems were used for this survey. These quasar pairs or triplet are separated at most by 17' (∼5 h^–1 Mpc in proper distance) from each other on the sky and have common C IV absorption lines at almost identical redshifts at z=2.24-2.43, which suggests there could be a megaparsec-scale absorbing system such as a cluster, or a group, of galaxies that covers all the lines of sight to the pair/triple quasars. Using narrowband deep images, we detected five candidates for Hα-emitting galaxies around two of the six fields, Q2343+125 and Q2344+125, whose apparent star formation rates are extremely high, 20-466 M_☉/yr. However, all or most of them are not likely to be galaxies at the absorption redshift but galaxies at lower redshift, because of their extreme brightness. In the fields of the other quasars, we detected no star-forming galaxies, nor did we find any number excess of galaxy counts around them. These nondetections could be because the luminosities and star formation rates of galaxies are lower than the detection limits of our observations (K'>21 and SFR<1.8-240 h^–2 M_☉/yr). They could be located outside of the observed field around Q0301 and Q0302, since our targeting field covers only 2% of this pair quasar field. But this is not the case for the other pair/triple quasar fields, because we found large field coverage fractions (∼33%-75%). Otherwise, most C IV absorption lines could be ascribed not to clusters of galaxies but to isolated star-forming pockets, far from bright galaxies, that could be analogous objects to weak Mg II absorbers.