Osservatorio Astronomico di Trieste

We investigate the 3-D matter distribution at z ∼ 2 with high resolution (R ∼ 40000) spectra of QSO pairs and groups obtained with the UVES spectrograph at ESO VLT. Our sample is unique for the number density of objects and the variety of separations, between ∼ 0.5 and 7 proper Mpc †. We compute the real space cross-correlation function of the Lyman-α forest transmitted fluxes. There is a significant clustering signal up to ∼ 2 proper Mpc, which is still present when absorption lines with high column density (log N 13.8) are excluded.

It has recently been shown that galaxy formation models within the ΛCDM cosmology predict that, compared to the observed population, small galaxies (with stellar masses < 10 11 M ⊙) form too early, are too passive since z ∼ 3 and host too old stellar populations at z = 0. We then expect an overproduction of small galaxies at z 4 that should be visible as an excess of faint Lyman-break galaxies. To check whether this excess is present, we use the MORGANA galaxy formation model and GRASIL spectro-photometric + radiative transfer code to generate mock catalogues of deep fields observed with HST-ACS. We add observational noise and the effect of Lyman-alpha emission, and perform color-color selections to identify Lymanbreak galaxies. The resulting mock candidates have plausible properties that closely resemble those of observed galaxies. We are able to reproduce the evolution of the bright tail of the luminosity function of Lyman-break galaxies (with a possible underestimate of the number of the brightest i-dropouts), but uncertainties and degeneracies in dust absorption parameters do not allow to give strong constraints to the model. Besides, our model shows a clear excess with respect to observations of faint Lyman-break galaxies, especially of z 850 ∼ 27 V-dropouts at z ∼ 5. We quantify the properties of these "excess" galaxies and discuss the implications: these galaxies are hosted in dark matter halos with circular velocities in excess of 100 km s −1 , and their suppression may require a deep rethinking of stellar feedback processes taking place in galaxy formation.

The cosmic evolution of the metal content of the intergalactic medium puts stringent constraints on the properties of galactic outflows and on the nature of UV background. In this paper, we present a new measure of the redshift evolution of the mass density of C iv, Ω CIV , in the interval 1.5 z 4 based on a sample of more than 1500 C iv lines with column densities 10 12 N (C iv) 10 15 cm −2. This sample more than doubles the absorption redshift path covered in the range z < 2.5 by previous samples. The result shows a significant increase of Ω CIV towards the lower redshifts at variance with the previously pictured constant behaviour.

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.

We explore new observationally-constrained sub-resolution models of galactic outflows and investigate their impact on the circumgalactic medium (CGM) in the redshift range z = 2 − 4. We perform cosmological hydrodynamic simulations, including star formation, chemical enrichment, and four cases of SNe-driven outflows: no wind (NW), an energy-driven constant velocity wind (CW), a radially varying wind (RVWa) where the outflow velocity has a positive correlation with galactocentric distance (r), and a RVW with additional dependence on halo mass (RVWb). Overall, we find that the outflows expel metal-enriched gas away from galaxies, significantly quench the star formation, reduce the central galactic metallicity and enrich the CGM. At z = 2, the radial profiles of gas properties around galaxy centers are most sensitive to the choice of the wind model for halo masses in the range (10 9 − 10 11)M ⊙. We infer that outflows in the RVWb model are least effective, with results similar to the NW case, except that the CGM is enriched more. Moreover, we find that the models CW and RVWa are similar, both showing the impact of effective winds, with the following notable differences. RVWa causes a greater suppression of star formation rate at z 5, and has a higher fraction of low-density (δ < 10), warm-hot (10 4 − 10 6 K) gas than in CW. Outflows in CW produce a higher and earlier enrichment of some IGM phases than in RVWa. By visual inspection, we note that the RVWa model shows galactic disks more pronounced than all the other wind models. We predict that some observational diagnostics are more promising to distinguish between different outflow driving mechanisms in galaxies: Z C of the CGM gas at r ∼ (30 − 300)h −1 kpc comoving, and CIV fraction of the inner gas at r < (4 − 5)h −1 kpc comoving.

We use the LUQAS sample of 27 high resolution, high signal-to-noise QSO absorption spectra (Kim et al. 2004) and the results from Croft et al. (2002) together with a suite of highresolution hydro-dynamical simulations run with the GADGET-II code, to infer the linear dark matter power spectrum on scales of ∼ 0.3 − 30 Mpc at z = 2.125 and at z = 2.72.

We present results from high resolution (R≃ 28000) spectra of six highredshift QSOs taken at the ESO NTT telescope that allow the detailed study of the Lyman-α population in the redshift interval z = 2.8 − 4.1. The typical Doppler parameters found for the Lyman-α lines lie in the interval b = 20 ÷ 30 km s −1 , corresponding to temperatures T > 24000 K, with a fraction of the order 15% in the range 10 ≤ b ≤ 20 km s −1. These values are still consistent with models of low density, highly ionized clouds. The observed redshift and column density distributions obtained from these spectra and from the observations of 4 additional QSOs taken in the literature allow an accurate estimate of the proximity effect from a relatively large Lymanα sample (more than 1100 lines with log N HI ≥ 13.3) in the redshift interval z = 1.7 − 4.1. A Maximum Likelihood analysis has been applied to estimate simultaneously the best fit parameters of the Lyman-α statistics and of the UV background. After correcting for the blanketing of weak lines, we confirm that the column density distribution is best represented by a double power-law with a break at log N HI ≃ 14, with a slope β s = 1.8 for higher column densities and a flatter slope β f = 1.4 below the break. A value J LL = 5 ± 1 × 10 −22 erg cm −2 s −1 Hz −1 sr −1 is derived for the UV background in the redshift interval z = 1.7 − 4.1, consistent with the predicted QSO contribution. No evidence is found for redshift evolution of the UVB in the same redshift interval. The comoving volume density distributions of protogalactic damped systems, Lyman Limit systems and Lyman-α clouds with log N HI ∼ > 14 and radii R ≃ 200 kpc are found to be similar, suggesting a possible common association with-4galaxies.

We present a sample of 17 high-redshift (3.5 ∼ < z ∼ < 5.2) QSO candidates in the 320 arcmin 2 area of the Great Observatories Origins Deep Survey, selected in the magnitude range 22.45 < z 850 < 25.25 using deep imaging with the Advanced Camera for Surveys onboard the Hubble Space Telescope and the Advanced CCD Imaging Spectrometer onboard the Chandra X-ray Observatory. On the basis of seven spectroscopic and ten photometric redshifts we estimate that the final sample will contain between two and four QSOs with 4 < z < 5.2. A dearth of high-redshift, moderate-luminosity (M 145 ≃ −23) QSOs is observed with respect to predictions based on a) the extrapolation of the z ∼ 2.7 luminosity function (LF), according to a pure luminosity evolution calibrated by the results of the Sloan Digital Sky Survey; and b) a constant universal efficiency in the formation of super-massive black holes (SMBHs) in dark-matter halos. Evidence is gathered in favor of a density evolution of the LF at high redshift and of a suppression of the formation or feeding of SMBHs in low-mass halos.

Astronomy & Astrophysics manuscript no. (will be inserted by hand later) ... High matter density peaks from UVES observations of QSO ... V. D&#x27;Odorico1, P. Petitjean1,2, and S. Cristiani3,4 ... 1 Institut d&#x27;Astrophysique de Paris, 98bis Boulevard Arago, F-75014 Paris 2 LERMA, ...

We determined C, N and α-element relative abundances in the gas surrounding six quasi-stellar objects (QSOs) at an average redshift of 〈z〉≃ 2.4, by studying six narrow associated absorption systems in Ultraviolet Visual Echelle Spectrograph (UVES) high-resolution spectra. We ...

The Absorption Spectrum of the QSO PKS 2126-158 (zem= 3.27) and the Clustering Properties of Metal Systems Valentina D&#x27;Odorico International School for Advanced Studies, SISSA, via Beirut 2-4, 1-34014 Trieste, Italy Abstract. We report the detection of a significant ...

We report on our serendipitous discovery that the objects Q 01323-4037 and Q 0132-4037, listed in the Véron-Cetty & Véron catalog (2006) as two different quasars, are actually a quasar and a star. We briefly discuss the origin of the misidentification, and provide a refined ...

The evolution of QSO clustering is investigated with a new sample of 388 QSOs with 0.3 < z ≤ 2.2, B ≤ 20.5 and MB < −23. Evidence is found for an increase of the clustering amplitude with increasing redshift. These measurements allow to further distinguish among the various physical scenarios proposed to interpret the QSO phenomenon. A single population model is inconsistent with the observations. The general properties of the QSO population would arise naturally if quasars are short-lived events connected to a characteristic halo mass ∼ 5 • 10 12 M .

Abstract. We present the results of the detailed surface photometry of a sample of elliptical galaxies in the Hubble Deep Field. In the &lt; µe &gt;–re plane the elliptical galaxies of the HDF turn out to follow a &#x27;rest frame&#x27; Kormendy relation, once the appropriate K + E corrections are ...

This is the second paper of a series describing the Asiago-ESO/RASS QSO survey, a project aimed at the construction of an all-sky statistically well-defined sample of very bright QSOs (B J ≤ 15). Such a survey is required to remove the present uncertainties about the properties of the local QSO population and constitutes an homogeneous database for detailed evolutionary studies of AGN. We present here the complete Southern Sample, which comprises 243 bright (12.60 ≤ B J ≤ 15.13) QSO candidates at high galactic latitudes (|b gal | ≥ 30 •). The area covered by the survey is 5660 sq. deg. Spectroscopy for the 137 still unidentified objects has been obtained. The total number of AGN turns out to be 111, 63 of which are new identifications. The properties of the selection are discussed. The completeness and the success rate for this survey at the final stage are 63% and 46%, respectively.

The evolution of galaxy clustering from z = 0 to z 4.5 is analyzed using the angular correlation function and the photometric redshift distribution of galaxies brighter than I AB ≤ 28.5 in the Hubble Deep Field North. The reliability of the photometric redshift estimates is discussed on the basis of the available spectroscopic redshifts, comparing different codes and investigating the effects of photometric errors. The redshift bins in which the clustering properties are measured are then optimized to take into account the uncertainties of the photometric redshifts. The results show that the comoving correlation length r 0 has a small decrease in the range 0 ∼ < z ∼ < 1 followed by an increase at higher z. We compare these results with the theoretical predictions of a variety of cosmological models belonging to the general class of Cold Dark Matter scenarios, including Einstein-de Sitter models, an open model and a flat model with nonzero cosmological constant. The comparison with the expected mass clustering evolution indicates that the observed high-redshift galaxies are biased tracers of the dark matter with an effective bias b strongly increasing with redshift. Assuming an Einstein-de Sitter universe, we obtain b 2.5 at z 2 and b 5 at z 4. These results support theoretical scenarios of biased galaxy formation in which the galaxies observed at high redshift are preferentially located in more massive halos. Moreover, they suggest that the usual parameterization of the clustering evolution as ξ(r, z) = ξ(r, 0) (1 + z) −(3+) is not a good description for any value of. A comparison of the clustering amplitudes that we measured at z 3 with those reported by Adelberger et al. (1998) and Giavalisco et al. (1998), based on a different selection, suggests that the clustering depends on the abundance of the objects: more abundant objects are less clustered, as expected in the paradigm of hierarchical galaxy formation. The strong clustering and high bias measured at z 3 are consistent with the expected density of massive haloes predicted in the frame of the various cosmologies considered here. At z 4, the strong clustering observed in the Hubble Deep Field requires a significant fraction of massive haloes to be already formed by that epoch. This feature could be a discriminant test for the cosmological parameters if confirmed by future observations.