We present results from a spectroscopic and imaging survey of galaxies in the fields of quasars from the Hubble Space Telescope (HST) Quasar Absorption Line Key Project. The aim of this survey is to identify galaxies within 3.5 ′ from the quasar sightline, to a limiting, integrated r-band magnitude m r = 22.5. The data are then compared to the HST homogeneous sample of Lyα-only absorbers in order to put constraints on the nature of these absorbers, and in particular on their relation to galaxies.We have obtained spectra for 81 objects in three quasar fields and identified 66 galaxies (success rate of 81%) at redshifts in the range z = 0.0500-0.7974, and at linear impact parameters to the quasar sightlines spanning D=57-2380 h −1 50 kpc. Among these galaxies, 19 are at less than 750 km s −1 from a Lyα absorber, and only one clearly does not give rise to any absorption. Three other galaxies are at the redshifts of metal-rich absorption systems, of which one belongs to a cluster with altogether 19 identified galaxies at the quasar redshift.The analysis of our sample combined with those of previous studies shows that: 1) the redshift agreements of the Lyα absorber-galaxy associations cannot be due to chance coincidence; 2) there is no clear anti-correlation between the Lyα rest-frame equivalent width and the impact parameter for the whole sample (w r,min =0.10Å). When only the strongest lines are considered (w r ≥ 0.24Å), w r (Lyα) and D are marginally anti-correlated. Lanzetta et al. (1995) found a stronger anti-correlation which could be due, at least in part, to the existence of metal-rich absorbers in their sample. Our results suggest that most Lyα absorbers are not gaseous clouds that belong in a strict sense to galaxies, as is the case for Mg ii absorbers. The size of Lyα galactic halos can be inferred from the variation with D of the fraction of associations to the total number of galaxies at impact parameters < D. This fraction drops from 1 to ∼ 0.65 at D ∼ 200h −1 50 kpc and flattens at larger values of D ( > ∼ 300h −1 50 kpc). This leads to Lyα galactic halos sizes about three times larger than the inner Mg ii halo region;3) there is no correlation between the galaxy luminosity and the impact parameter. This again suggests that a significant Lyα clouds do not belong to individual galaxies, but instead are distributed in the local large-scale structure. For the smaller impact parameters, this could reflect a link between D and the total galaxy mass rather than its luminous mass; 4) the HWHM=120 km s −1 of the relative velocity distribution of the Lyα absorber-galaxy associations is consistent with either galaxy rotation velocities or the local velocity dispersion in large-scale structures.Send offprint requests to: V. Le Brun ⋆ Based on observations made at the Canada-France-Hawaii-Telescope, Hawaii, USA

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Abstract. A new limit on the possible cosmological variation of the proton-to-electron mass ratio µ = m p /m e is estimated by measuring wavelengths of H 2 lines of Lyman and Werner bands from two absorption systems at z abs = 2.5947 and 3.0249 in the spectra of quasars Q 0405−443 and Q 0347−383, respectively. Data are of the highest spectral resolution (R = 53 000) and S/N ratio (30÷70) for this kind of study. We search for any correlation between z i , the redshift of observed lines, determined using laboratory wavelengths as references, and K i , the sensitivity coefficient of the lines to a change of µ, that could be interpreted as a variation of µ over the corresponding cosmological time. We use two sets of laboratory wavelengths, the first one, Set (A) (Abgrall et al. 1993, J. Mol. Spec., 157, 512), based on experimental determination of energy levels and the second one, Set (P) (Philip et al. 2004, Can. J. Chem., 82, 713), based on new laboratory measurements of some individual rest-wavelengths. We find ∆µ/µ = (3.05 ± 0.75) × 10 −5 for Set (A), and ∆µ/µ = (1.65 ± 0.74) × 10 −5 for Set (P). The second determination is the most stringent limit on the variation of µ over the last 12 Gyr ever obtained. The correlation found using Set (A) seems to show that some amount of systematic error is hidden in the determination of energy levels of the H 2 molecule.

Abstract.To investigate the presence of small scale structure in the spatial distribution of H 2 molecules we have undertaken repeated FUSE UV observations of the runaway O9.5V star, HD 34078. In this paper we present five spectra obtained between January 2000 and October 2002. These observations reveal an unexpectedly large amount of highly excited H 2 . Column densities for H 2 levels from (v = 0, J = 0) up to (v = 0, J = 11) and for several v = 1 and v = 2 levels are determined. These results are interpreted in the frame of a model involving essentially two components: i) a foreground cloud (unaffected by HD 34078) responsible for the H 2 (J = 0, 1), CI, CH, CH + and CO absorptions; ii) a dense layer of gas (n 10 4 cm −3 ) close to the O star and strongly illuminated by its UV flux which accounts for the presence of highly excited H 2 . Our model successfully reproduces the H 2 excitation, the CI fine-structure level populations as well as the CH, CH + and CO column densities. We also examine the time variability of H 2 absorption lines tracing each of these two components. From the stability of the J = 0, 1 and 2 damped H 2 profiles we infer a 3σ upper limit on column density variations ∆N(H 2 )/N(H 2 ) of 5% over scales ranging from 5 to 50 AU. This result clearly rules out any pronounced ubiquitous small scale density structure of the kind apparently seen in HI. The lines from highly excited gas are also quite stable (equivalent to ∆N/N ≤ 30%) indicating i) that the ambient gas through which HD 34078 is moving is relatively uniform and ii) that the gas flow along the shocked layer is not subject to marked instabilities.

Abstract. We present spectroscopic observations of the runaway reddened star HD 34078 acquired during the last three years at Observatoire de Haute Provence and McDonald Observatory as well as other spectra obtained since 1990. The drift of the line of sight through the foreground cloud due to the large transverse velocity of HD 34078 allows us to probe the spatial distribution of CH, CH + , CN and DIBs carriers at scales ranging from about 1 AU up to 150 AU. In particular, time variations in the equivalent width of absorption lines are examined. A few past and recent high resolution observations of CH and CH + absorption are used to search for line profile variations and to convert equivalent widths into column densities. The data set reveals a 20% increase in CH column density over the past 10 years with no corresponding variation in the column density of CH + or in the strengths of the 5780 and 5797 Å DIBs. CN observations indicate that its excitation temperature has significantly increased from <3.1 K in 1993 to 3.6 ± 0.17 K in 1998 while the CN column shows only a modest rise of ≈12±6%. The data also strongly suggest the existence of weak correlated variations in CH and CH + columns over periods of 6-12 months (or ≈10 AU). These results are discussed in relation to CH + production mechanisms. A dense newly intervening clump is considered in order to explain the long-term increase in the column density of CH, but such a scenario does not account for all observational constraints. Instead, the observations are best described by CH + production in a photodissociation region, like that suggested for the Pleiades and IC 348.

Context. The runaway star HD 34078, initially selected to investigate small scale structure in a foreground diffuse cloud, has been shown to be surrounded by highly excited H 2 , the origin of which is unclear. Aims. We first search for an association between the foreground cloud and HD 34078. Second, we extend previous investigations of temporal absorption line variations (CH, CH + , H 2 ) in order to better characterize them and understand their relation to small-scale structure in the molecular gas. Methods. We have mapped the 12 CO(2-1) emission at 12 resolution around HD 34078's position, using the 30 m IRAM antenna. The follow-up of CH and CH + absorption lines has been extended over 5 more years: 26 visible spectra have been acquired since 2003 at high or intermediate resolution. In parallel, CH absorption towards the reddened star ζ Per has been monitored to check the instrumental stability and homogeneity of our measurements. Three more FUSE spectra have been obtained to search for N(H 2 ) variations. Results. CO observations show a pronounced maximum near HD 34078's position, clearly indicating that the star and diffuse cloud are associated. The optical spectra confirm the reality of strong, rapid and correlated CH and CH + fluctuations (up to 26% for N(CH + ) between 2007 and 2008). On the other hand, N(H 2 , J = 0) has varied by less than 5% over 4 years, indicating the absence of marked density structure at scales below 100 AU. We also discard N(CH) variations towards ζ Per at scales less than 20 AU. Conclusions. Observational constraints from this work and from 24 μm dust emission appear to be consistent with H 2 excitation but inconsistent with steady-state bow shock models and rather suggest that the shell of compressed gas surrounding HD 34078 or lying at the boundary of a small foreground clump is seen at an early stage of the interaction. The CH and CH + time variations as well as their high abundances are likely due to chemical structure in the shocked gas layer located at the stellar wind/ambient cloud interface. Finally, the lack of variation in both N(H 2 , J = 0) towards HD 34078 and N(CH) towards ζ Per suggests that quiescent molecular gas is not subject to pronounced small-scale structure.

In order to investigate the origin of the excess of strong Mg ii systems towards GRB afterglows as compared to QSO sightlines, we have measured the incidence of Mg ii absorbers towards a third class of objects: the blazars. This class includes the BL Lac object population for which a tentative excess of Mg ii systems had already been reported. We observed with FORS1 at the ESO-VLT 42 blazars with an emission redshift 0.8 < z em < 1.9, to which we added the three high z northern objects belonging to the 1 Jy BL Lac sample. We detect 32 Mg ii absorbers in the redshift range 0.35-1.45, leading to an excess in the incidence of Mg ii absorbers compared to that measured towards QSOs by a factor ∼2, detected at 3σ. The amplitude of the effect is similar to that found along GRB sightlines. Our analysis provides a new piece of evidence that the observed incidence of Mg ii absorbers might depend on the type of background source. In front of blazars, the excess is apparent for both "strong" (w r (2796) > 1.0 Å) and weaker (0.3 < w r (2796) < 1.0 Å) Mg ii systems. The dependence on velocity separation with respect to the background blazars indicates, at the ∼1.5σ level, a potential excess for β ≡ v/c ∼ 0.1. We show that biases involving dust extinction or gravitational amplification are not likely to notably affect the incidence of Mg ii systems towards blazars. Finally we discuss the physical conditions required for these absorbers to be gas entrained by the powerful blazar jets. More realistic numerical modelling of jet-ambient gas interaction is required to reach any firm conclusions as well as repeat observations at high spectral resolution of strong Mg ii absorbers towards blazars in both high and low states.

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