Astronomy & Astrophysics

Free access article

Issue		A&A Volume 390, Number 1, July IV 2002
Page(s)		13 - 25
Section		Cosmology
DOI		10.1051/0004-6361:20020737

A&A 390, 13-25 (2002)
DOI: 10.1051/0004-6361:20020737

High matter density peaks from UVES observations of QSO pairs: Correlation properties and chemical abundances

V. D'Odorico¹, P. Petitjean^{1, 2} and S. Cristiani^{3, 4}

¹ Institut d'Astrophysique de Paris, 98bis Boulevard Arago, 75014 Paris, France
² LERMA, Observatoire de Paris, 61 Av. de l'Observatoire, 75014 Paris, France
³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
⁴ Osservatorio Astronomico di Trieste, via G.B. Tiepolo, 11, 34131 Trieste, Italy

(Received 6 February 2002 / Accepted 15 May 2002 )

Abstract
We study the transverse clustering properties of high matter density peaks as traced by high column density absorption systems (either Lyman limit systems characterized by N( $\ion$ $) \ge 2 \times 10^$ cm ^-2 or $\ion{C}{iv}$ systems with $W_{\rm r} > 0.5$ Å) at redshifts between 2 and 3 with UVES spectra of two QSO pairs (UM680/UM681 at 56 arcsec angular separation and Q2344+1228/Q2343+1232 at 5 arcmin angular separation) and a QSO triplet (Q2139-4433/Q2139-4434/Q2138-4427 at 1, 7 and 8 arcmin angular separation). We find 3 damped Lyman- $\alpha$ systems ( N( $\ion$ $) \ge 2 \times 10^$ cm ^-2): 2 coinciding with strong metal systems in the nearby line of sight and 1 matching the emission redshift of the paired QSO; plus 7 Lyman limit systems: 4 forming two matching couples and 3 without a corresponding metal system within ~3000 km s ^-1in the coupled line of sight. In summary, we detect five out of ten matching systems within 1000 km s ^-1, indicating a highly significant overdensity of strong absorption systems over separation lengths from ~1 to 8 h^-1 Mpc. The observed coincidences could arise in gas due to starburst-driven superwinds associated with a quasar or a galaxy, or gas belonging to large scale structures like filaments or sheets. We also determine chemical abundance ratios for three damped Lyman- $\alpha$ systems. In particular, for the damped system at $z\sim 2.53788$ in the spectrum of Q2344+1228, new estimates of the ratios O/Fe, C/Fe are obtained: $\rm -0.02< [C/Fe]<0.06$ , $\rm -0.06< [O/Fe]<0.2$ . They indicate that O and C are not over-solar in this system.

Key words: galaxies: abundances -- galaxies: high-redshift -- quasars: absorption lines -- cosmology: observations

Offprint request: V. D'Odorico, dodorico@ts.astro.it

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