We present analysis of two-and three-point correlation functions of Lyα forest (at 2 ≤ z ≤ 2.5) using X-Shooter spectra of three background quasar triplets probing transverse separations of 0.5-1.6 pMpc. We present statistics based on transmitted flux and clouds identified using Voigt profile fitting. We show that the observed two-, three-point correlation functions and reduced three-point correlation (i.e Q) are well reproduced by our simulations. We assign probabilities for realising all the observed correlation properties simultaneously using our simulations. Our simulations suggest an increase in correlation amplitudes and Q with increasing N HI . We roughly see this trend in the observations too. We identify a concurrent gap of 17Å (i.e 14.2 h −1 cMpc, one of the longest reported) wide in one of the triplets. Such gap is realised only in 14.2% of our simulated sightlines and most of the time belongs to a void in the matter distribution. In the second triplet, we detect DLAs along all three sightlines (with spatial separations 0.64 to 1.6 pMpc) within a narrow redshift interval (i.e ∆z = 0.088). Detection of a foreground quasar (∼ 1 pMpc from the triplet sightlines) and excess partial Lyman Limit systems around these DLAs suggest that we may be probing a large over-dense region. We also report positive C iv-C iv correlations up to ∼ 500 kms −1 only in the longitudinal direction. Additionally, we conclude a positive C iv-Lyα correlations for higher N HI thresholds up to a scale of ∼ 1000 kms −1 both in transverse and longitudinal directions.

Lyα forest absorption spectra decomposed into multiple Voigt profile components (clouds) allow us to study clustering of intergalactic medium (IGM) as a function of H i column density (NHI). Here, we explore the transverse three-point correlation (ζ) of Lyα clouds using mock triplet spectra from simulations at z ∼ 2 on scales of 1-5 h−1cMpc. We find ζ to depend strongly on NHI and scale and weakly on angle of the triplet configuration. We show that the ”hierarchical ansatz” is applicable for scales ≥ 3h−1cMpc, and obtain a median reduced three-point correlation (Q) in the range 0.2-0.7. We show, ζ is influenced strongly by the thermal and ionization state of the gas. As in the case of galaxies, the influence of physical parameters on Q is weaker compared to that on ζ. We show difference in ζ and Q between different simulations are minimized if we use appropriate NHI cut-offs corresponding to a given baryon over-density (Δ) using the NHI vs Δ relationship obtained from simulations. We study the effect of pressure broadening on ζ using a model with artificially boosted heating rates. However, for models with realistic thermal and ionization histories the effect of pressure broadening on ζ is sub-dominant compared to other local effects. We find the strong redshift evolution shown by ζ, mainly originating from the redshift evolution of thermal and ionization state of the IGM. We discuss the observational requirements for the detection of three-point correlation, specifically, in small intervals of configuration parameters and redshift.

The QUBRICS (QUasars as BRIght beacons for Cosmology in the Southern hemisphere) survey aims at constructing a sample of the brightest quasars with $z \lower.5ex\hbox{$\; \buildrel> \over \sim \;$}2.5$, observable with facilities in the Southern Hemisphere. QUBRICS makes use of the available optical and IR wide-field surveys in the South and of Machine Learning techniques to produce thousands of bright quasar candidates of which only a few hundred have been confirmed with follow-up spectroscopy. Taking advantage of the recent Gaia Data Release 3, which contains 220 million low-resolution spectra, and of a newly developed spectral energy distribution fitting technique, designed to combine the photometric information with the Gaia spectroscopy, it has been possible to measure 1672 new secure redshifts of QUBRICS candidates, with a typical uncertainty of σz = 0.02. This significant progress of QUBRICS brings it closer to (one of) its primary goals: providing a sample of bright quasars at redshift 2.5 < z < 5 to perform the Sandage test of the cosmological redshift drift. A Golden Sample of seven quasars is presented that makes it possible to carry out this experiment in about 1500 hours of observation in 25 years, using the ANDES spectrograph at the 39m ELT, a significant improvement with respect to previous estimates.

We study the statistical properties of O vi, C iv, and Ne viii absorbers at low-z (i.e., z < 0.5) using Sherwood simulations with ‘WIND’ only and ‘WIND+AGN’ feedback and Massive black-II simulation that incorporates both ‘WIND’ i.e. outflows driven by stellar feedback and AGN feedbacks. For each simulation, by considering a wide range of metagalactic ionizing UV background (UVB), we show the statistical properties such as distribution functions of column density (N), b-paramerer and velocity spread (ΔV90), the relationship between N and b-parameter and the fraction of Lyα absorbers showing detectable metal lines as a function of N(H i) are influenced by the UVB used. This is because UVB changes the range in density, temperature, and metallicity of gas contributing to a given absorption line. For simulations considered here, we show the difference in some of the predicted distributions between different simulations is similar to the one obtained by varying the UVB for a given simulation. Most of the observed properties of O vi absorbers are roughly matched by Sherwood simulation with ‘WIND+AGN’ feedback when using the UVB with a lower O vi ionization rate. However, this simulation fails to produce observed distributions of C iv and fraction of H i absorbers with detectable metals. Therefore, in order to constrain different feedback processes and/or UVBs, using observed properties of H i and metal ions, it is important to perform simultaneous analysis of various observable parameters.