PROBING QUASAR SIGHT LINES IN THREE DIMENSIONS Lise Bech Christensen Astrophysikalisches Institut Potsdam DISSERTATION ZUR ERLANGUNG DES NATURWISSENSCHAFTLICHEN GRADES DR. RER. NAT.; EINGEREICHT AN DER MATHEMATISCH-NATURWISSENSCHAFTLICHEN FAKULTAT¨ DER UNIVERSITAT¨ POTSDAM June 2005 ii iii PROBING QUASAR SIGHT LINES IN THREE DIMENSIONS by Lise Bech Christensen Astrophysikalisches Institut Potsdam Abstract This thesis explores the technique of integral field spectroscopy (IFS) to observe quasars at various redshifts, specifically to look for emission line objects close to the quasar sight lines. Observations with IFS allow simultaneous imaging and spectroscopy of a field in the sky. From the images objects can be identified right away. The spectra allow to determine the redshift and hence the distance of objects close to the quasar line of sight, thereby providing a three-dimensional view along the line of sight. The first part of the thesis presents a search for galaxy counterparts to intervening strong hydrogen absorption lines seen in quasar (QSO) spectra. Observations with IFS, contrary to other techniques, do not require previous knowledge of the location of the objects for follow- up spectroscopy. Since the redshifts of the intervening damped Lyman-® (DLA) systems are known, the IFS data can be searched for emission lines at known wavelengths anywhere in the field surrounding the QSO. By looking for emission from galaxies selected from absorption lines in background quasar spectra, we avoid the selection biases involved in flux-limited surveys so that we can probe the faint end of the galaxy luminosity function. Here we analyse two samples separated according to their redshifts: A sample at low redshifts (z < 1) for which optical emission lines are searched for, and a high redshift sample (z > 2) where the Ly® emission is redshifted to optical wavelengths. In the low redshift sample, we search for emission lines from known objects near the QSO sight line, and detect emission lines at the redshifts corresponding to those of the absorbers in six of eight systems investigated. Two of these objects have been confirmed recently by other authors using long-slit spectroscopy and photometric redshifts. We confirm the photometric redshift and identify four additional candidates to other systems. The offsets of the candidate emission lines to the QSOs probe the projected extension of the neutral gas disc. Using the spatial offsets as a proxy for the galaxy sizes, we estimate that the galaxies are consistent with having discs with an average scale length of 5 kpc, similar to local spiral galaxies. In the particular case of the z = 0.160 sub-DLA towards PHL 1226, we find an offset of 100 between the continuum and the line emission regions. However, such large offsets are not expected in higher redshift systems where galaxies typically appear as point sources with the spatial resolution in our datasets. For the sub-DLA galaxy towards PHL 1226, we determine a solar abundance in the emission region using strong line diagnostics. We discuss the possible presence of a metallicity bias in DLA (and sub-DLA) systems in cases where metallicity gradients would be similar to those in local galaxies. Because of the larger cross sections of the galaxy outskirts, such gradients could explain the large scatter and low metallicities found in DLAs that probe random sight lines through galaxy discs. In the high redshift sample that contains 21 DLAs and sub-DLAs, we find candidate Ly® emission lines from 8 systems, two of which are associated with sub-DLA systems. Line flux densities are similar to those of the few previously known systems. We find an average size of 20 kpc which is a few times larger than what is predicted by numerical simulations. Assuming that an exponential disc profile is a good representation of their morphologies, we derive an average disc iv scale length of 5 kpc, which is similar to the scale length determined for the low redshift sample. Because Ly® photons are resonantly scattered, converting the Ly® luminosities from the candidates into star-formation rates (SFR) will only provide a lower limit to the intrinsic SFR. ¡1 Hence we estimate lower limits of 1–10 M¯yr . We assume that the Schmidt-Kennicutt law, which relates the SFR per unit area to the surface density of gas, is valid for DLAs. This is used to argue that in order to achieve the measured SFRs, DLA galaxies must have radial sizes of »10 kpc in the neutral gas. Masses derived with a model of an exponential disc suggest that the average DLA galaxy at z ¼ 3 has a gas disc mass similar to that of the Milky Way and other local disc galaxies which is consistent with predictions from numerical simulations. We argue that according to numerical simulations, DLA galaxy masses including stellar masses could be only 10% of the mass of a present day luminous L¤ galaxy, where L¤ is the characteristic luminosity in the Schechter luminosity function. To further determine the nature of the emission line candidates, it is crucial not only to obtain confirmation of the candidates by deeper spectroscopic measurements, but also to investigate rest-frame optical emission lines. This is necessary to constrain the dust effects for the derived SFRs. The second part of this thesis investigates emission lines at the QSO redshifts. The low redshift sample contains three QSOs at z < 1, where the redshifted optical emission lines are covered by the observed wavelength range. Two radio-loud quasars are lobe-dominated and show extended [O II] emission line regions, while we detect no extended emission for the core-dominated quasar. Alignment of the extended emission nebulae with the radio jets, together with large velocities, suggest an interaction between the radio jets and the surrounding material. Extended nebulae with narrow Ly® emission lines are found around a sample of high redshift (2:7 < z < 4:5) radio-quiet QSOs and one radio-loud, core-dominated QSO. The nebular emission lines are much more narrow than the nuclear Ly® emission line from the QSOs. IFS allows us to explore the velocity structure of the two brightest emission line nebulae and we find evidence for velocity gradients extending over a few arcseconds. Our results support theoretical predictions for the nebulae extensions and surface brightness. 1–2% of the QSO flux within a 20 A˚ narrow-band is re-emitted by the nebulae around the radio- quiet quasars. This is an order of magnitude smaller than what has been seen for lobe-dominated radio-loud QSOs investigated in the literature. We discuss these differences in the nebulae around radio-loud and radio-quiet QSOs. Analyses of correlations between the QSO ionising flux, radio flux densities, nebulae emission line flux, and nebulae sizes indicate that the ionising flux does not determine the nebular properties. More luminous nebulae are found to be larger, and we argue that interactions with the radio jets could be an additional factor which causes brighter emission in the surroundings. Alternatively, differences in the environments could affect the extended emission. In conclusion, our use of IFS to search for faint emission lines, both from point sources and extended nebulae provides exciting new results within the scientific areas studied here. v Contents 1 Introduction 1 1.1 QSO absorption systems . 1 1.2 DLA metallicities . 5 1.2.1 Chemical composition . 5 1.2.2 Chemical evolution . 7 1.2.3 Absorption line profiles . 7 1.3 Ly® photon properties . 8 1.4 Galaxies associated with DLAs . 9 1.4.1 Surveys for DLA galaxies . 9 1.4.2 Metallicities of DLA galaxies . 10 1.4.3 DLA cloud sizes . 11 1.4.4 Morphologies of DLA galaxies . 11 1.4.5 Simulations of DLA galaxies . 12 1.4.6 DLA galaxy star formation rates . 13 1.5 Relation to high redshift galaxies . 13 1.5.1 Lyman break galaxies . 14 1.5.2 Gamma-Ray burst selected DLA systems . 15 1.6 Goals and outline of this work . 15 1.6.1 Emission line survey . 16 1.6.2 Structure of this thesis . 16 2 Abundances and kinematics of a candidate sub-damped Lyman® galaxy toward PHL 1226 21 2.1 Introduction . 21 2.2 Observations and data reduction . 23 2.3 Galaxy and QSO spectra . 24 2.3.1 Emission line images . 26 2.3.2 High surface brightness region . 26 2.4 Derived properties . 28 2.4.1 Dust reddening . 28 2.4.2 Chemical abundances . 29 2.4.3 Star formation rate . 31 2.5 Kinematics . 32 2.6 Discussion . 33 2.6.1 Relationship with DLAs, sub-DLAs and Mg II systems . 33 2.6.2 Abundance gradient effect . 34 2.6.3 Sub-DLA cloud properties . 34 2.7 Conclusions . 35 vi 3 Integral-field spectroscopic observations of damped Lyman-® galaxies at z<1 39 3.1 Introduction . 39 3.2 Sample selection . 40 3.3 Observations and data reduction . 41 3.4 Search for DLA optical counterparts . 44 3.5 Notes on individual objects . 45 3.6 Impact parameters . 51 3.7 Conclusions and discussion . 52 4 Integral Field Spectroscopy of Extended Ly® Emission from the DLA Galaxy in Q2233+131 57 4.1 Introduction . 57 4.2 Observations and data reduction . 59 4.3 The QSO spectrum . 59 4.4 The spectrum of the DLA galaxy . 61 4.4.1 Velocity structure . 63 4.4.2 The double peaked Ly® line . 65 4.4.3 Artificial slit spectra . 66 4.5 HST deep imaging . 66 4.6 Ly® emission from high redshift objects . 68 4.7 Origin of the extended emission . 70 4.7.1 Ly® emission indicative of star formation . 70 4.7.2 Origin of the double peaked emission line .