P21	March 1998

¹ Institut d'Astrophysique de Paris - CNRS, 98bis Bd Arago, F-75014, Paris, France
² UA CNRS 173-DAEC, Observatoire de Paris-Meudon, F92195, Meudon Principal Cedex, France
³ Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium
⁴ NASA-Goddard Space Flight Center, Code 681, Greenbelt, MD 20771, USA
⁵European Southern Observatory, Schwarzschild Strasse 2, D-80547 Garching, Germany
⁶ Astrophysikalisches Institut Postdam, An der Sternwarte 16, D-14482 Postdam, Germany

^* Directeur de Recherches FNRS, Belgium

⁺ Based on observations obtained with the NASA/ESA Hubble Space Telescope, by the Space Telescope Science Institute, which is operated by the AURA, Inc., under NASA contract NAS5-26555

Abstract

     The spatial distribution of the Ly forest is studied using new HST data of the quasar pair Q1026-0045 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 ~300 h₅₀^-1 kpc (q₀ = 0) over the redshift range 0.833 < z < 1.438. From the observed number of coincident and anti-coincident Ly absorption lines, we conclude that, at this redshift, the Ly structures have typical dimensions of ~500 h₅₀^-1 kpc, larger than the mean separation of the two lines of sight. The velocity difference, V, between coincident lines is surprinsingly small (4 and 8 pairs with 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, 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 line of sight. The system at z_abs = 1.4844 has strong OVI 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 Ly 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 ~300 h₅₀^-1 kpc surrounding quasar A.