X‐shooter observations of QSO pairs

Observations of quasar pairs represent a powerful tool in the study of the intergalactic medium, providing in particular information on the quasar radiative feedback not only along the line of sight, but also in the transverse direction. In this paper, we present the spectra of the four quasar pairs we observed so far with X‐shooter, and we discuss two individual spectra affected by the presence of a close quasar in the foreground (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Lymanα forests and the evolution of the universe

The Lyα forest absorption lines in the spectra of quasars are interpreted as caused by the crossings of the light beam with the walls of a bubble structure (expanding with the Hubble flow only). Then, the typical separation between the absorption lines is proportional to the mean size of the bubbles. The variable factor is the expansion rate H[z]. The Friedmann regression analysis of the observed line separations determines the density parameter ω₀ and the normalized cosmological term λ₀ = λc²/3H²₀ of the appropriate cosmological model: ω₀ = 0.014 ± 0.002, λ₀ = 1.080 ± 0.006. Depending on the Hubble parameter this method reveals the values of the present mean matter density pm,0 = 2.6 h² · 10⁻²⁸ kg m⁻³ and of the cosmological constant Λ = 3.77 h² · 10⁻⁵² m⁻² (with h = H₀/(100 km/s·Mpc)). According to our analysis all models with Λ = 0 must be excluded. The curvature of space is positive. The curvature radius R₀ is 3.3 times the Hubble radius (c/H₀). The age t₀ is 2.8 times the Hubble age (H₀⁻¹).     

NICMOS imaging search for high-redshift damped Lyα galaxies

We are engaged in a programme of imaging with the STIS and NICMOS (NIC2) instruments aboard the Hubble Space Telescope ( HST ), to search for the galaxy counterparts of 18 high-redshift z >1.75 damped Ly α absorption lines and five Lyman-limit systems seen in the spectra of 16 target quasars. This paper presents the results of the imaging campaign with the NIC2 camera. We describe the steps followed in reducing the data and combining in mosaics, and the methods used for subtracting the image of the quasar in each field, and for constructing error frames that include the systematic errors associated with the PSF subtraction. To identify candidate counterparts, which are either compact or diffuse, we convolved the image and variance frames with circular top-hat filters of diameter 0.45 and 0.90 arcsec respectively, to create frames of summed S /N within the aperture. For each target quasar we provide catalogues listing positions and aperture magnitudes of all sources within a square of side 7.5 arcsec centred on the quasar, detected at S / N >6 . We find a total of 41 candidates, of which three have already been confirmed spectroscopically as the counterparts. We provide the aperture magnitude detection limits as a function of impact parameter, for both detection filters, for each field. The average detection limit for compact (diffuse) sources is H _AB =25.0 (24.4) at an angular separation of 0.56 (0.79) arcsec from the quasar, improving to H _AB =25.5 (24.8) at large angular separations. For the brighter sources we have measured the half-light radius and the n parameter of the best-fitting deconvolved Sersic-law surface brightness profile, and the ellipticity and orientation.     

Optical‐NIR spectra of quasars close to reionization (z ∼ 6)

X‐shooter, with its characteristics of resolution, spectral coverage and efficiency, provides a unique opportunity to obtain spectra of the highest‐redshift quasars (z ∼ 6) that will allow us to carry out successful investigations on key cosmological issues, from the details of the re‐ionization process, to the evolution of the first galaxies and AGNs. In this paper, we present the spectra of three z ∼ 6 quasars: one obtained during the commissioning of X‐shooter and two in the context of our ongoing GTO programme. Combining this sample with data in the literature, we update the value of the C IV cosmic mass density in the range 4.5 ≤ z ≤ 5, confirming the constant trend with redshift between 2.5 and 5 (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Integral field spectroscopy of QSO host galaxies

We describe a project to study the state of the ISM in ∼20 low redshift (z < 0.3) QSO host galaxies observed with the PMAS integral field spectrograph. We describe the development of the method to access the stellar and gas components of the spectrum without the strong nuclear emission, in order to access the host galaxy properties in the central region. It shows that integral field spectroscopy promises to be very efficient in studying the gas distribution and its velocity field, and also the spatially resolved stellar population in the host galaxies of luminous AGN. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Probing subparsec structure in the Lyman α forest with gravitational microlensing

We present the results of microlens ray-tracing simulations showing the effect of absorbing material between a source quasar and a lensing galaxy in a gravitational lens system. We find that, in addition to brightness fluctuations due to microlensing, the strength of the absorption line relative to the continuum varies with time, with the properties of the variations depending on the structure of the absorbing material. We conclude that such variations will be measurable via ultraviolet spectroscopy of image A of the gravitationally lensed quasar Q2237+0305 if the Lyman α clouds between the quasar and the lensing galaxy possess structure on scales smaller than ∼0.1 pc. The time-scale for the variations is on the order of years to decades, although very short-term variability can occur. While the Lyman α lines may not be accessible at all wavelengths, this approach is applicable to any absorption system, including metal lines.     

K-band imaging of strong Ca ii-absorber host galaxies at z∼1

We present K -band imaging of fields around 30 strong Ca  ii absorption-line systems, at  0.7 < z < 1.2  , three of which are confirmed damped Lyman α systems. A significant excess of galaxies is found within 6.0 arcsec (≃50 kpc) from the absorber line of sight. The excess galaxies are preferentially luminous compared to the population of field galaxies. A model in which field galaxies possess a luminosity-dependent cross-section for Ca  ii absorption of the form  ( L / L *)^0.7  reproduces the observations well. The luminosity-dependent cross-section for the Ca  ii absorbers appears to be significantly stronger than the established  ( L / L *)^0.4  dependence for Mg  ii absorbers. The associated galaxies lie at large physical distances from the Ca  ii -absorbing gas; we find a mean impact parameter of 24 kpc  ( H ₀= 70 km s⁻¹ Mpc⁻¹)  . Combined with the observed number density of Ca  ii absorbers the large physical separations result in an inferred filling factor of only ∼10 per cent. The physical origin of the strong Ca  ii absorption remains unclear, possible explanations vary from very extended discs of the luminous galaxies to associated dwarf galaxy neighbours, remnants of outflows from the luminous galaxies, or tidal debris from cannibalism of smaller galaxies.     

High spectral resolution X‐ray observations of AGN

A brief overview of some highlights of high spectral resolution X‐ray observations of AGN is given, mainly obtained with the RGS of XMM‐Newton. Future prospects for such observations with XMM‐Newton are given. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)