HST observations of the QSO pair Q1026-0045A,B

Abstract

The spatial distribution of the Lyalpha forest is studied using new HST data for the quasar pair Q 1026-0045 A and B at z_em = 1.438 and 1.520 respectively. The angular separation is 36 arcsec and corresponds to transverse linear separations between lines of sight of ~ 300h(-1}_{50) kpc (q_o = 0.5) over the redshift range 0.833 < z < 1.438. From the observed numbers of coincident and anti-coincident Lyalpha absorption lines, we conclude that, at this redshift, the Lyalpha structures have typical dimensions of ~ 500h(-1}_{50) kpc, larger than the mean separation of the two lines of sight. The velocity difference, Delta V, between coincident lines is surprisingly small (4 and 8 pairs with Delta V < 50 and 200 km s(-1) respectively). Metal line systems are present at z_abs = 1.2651 and 1.2969 in A, z_abs = 0.6320, 0.7090, 1.2651 and 1.4844 in B. In addition we tentatively identify a weak Mg ii system at z_abs = 0.11 in B. It is remarkable that the z_abs = 1.2651 system is common to both lines of sight. The system at z_abs = 1.4844 has strong O vi absorption. There is a metal-poor associated system at z_abs = 1.4420 along the line of sight to A with complex velocity profile. We detect a strong Lyalpha absorption along the line of sight to B redshifted by only 300 km s(-1) relatively to the associated system. It is tempting to interpret this as the presence of a disk of radius larger than 300h(-1}_{50) kpc surrounding quasar A. Based on observations obtained with the NASA/ESA Hubble Space Telescope by the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555