The cross-correlation among tracers of the underlying large-scale mass distribution in the universe

[eng] The work presented in this Ph.D. thesis is mostly related to the measurement and interpretation of the cross-correlation of different species. This is achieved using spectroscopic data from the BOSS survey of which I am a member. Along the thesis I will be visiting the cross-correlation of different tracers. This tracers include the Mg II absorbers, the Damped Lyα Systems (DLA), the Lyα forest, the quasars and the galaxies. Save the last mentioned, all tracers are measured from quasar spectra from BOSS. The galaxies are taken from the BOSS CMASS catalogue. The first cross-correlation I address is that of Mg II absorbers with CMASS galaxies. I present a new method for measuring the equivalent width of metal absorbers, developed in collaboration with Britt Lundgren and Jordi Miralda- Escud´e, and I apply it to the absorption doublet. Then I shift my attention to the DLAs and the Ly forest. Since the Lyα forest autocorrelation has already been studied (see e.g. Delubac et al. 2015; Blomqvist et al. 2015), the Lyα parameters are well constrained. I use those constraints to provide more accurate measurements of the DLA bias when analysing the cross-correlation of DLAs with the Lyα forest. The study has been made in collaboration with Andreu Font-Ribera, Nicol´as Busca, and Jordi Miralda-Escud´e. In particular, the estimator for the cross-correlation was orig- inally developed by Nicol´as Busca for the analysis of the Lyα autocorrelation and later adapted to the measurement of the cross-correlation. The first two cross-correlations studied and more importantly their interpre- tation, are mostly focused on large scales, where the linear theory is valid. At smaller scales, non-linear effects start to kick in and the linear approximation is no longer valid. I measure the cross-correlation of quasars with the Lyα forest, and focus on the small scales effects. I show that a contamination from metals is clearly present in the cross-correlation. Also, I discuss some of the possible non-linear effects and give a simple theoretical model to explain the effect that quasar radiation can have in the surrounding hydrogen clouds.[cat] El treball fet en aquesta tesi doctoral es basa principalment en la mesura i interpretació de la correlació creuada entre diferents traçadors. Els traçadors emprats en aquesta tesi són les galàxies del catàleg CMASS, els quàsars del catàleg de Baryon Oscillations Spectroscopic Survey (BOSS), els sistemes absorbidors de MgII, el bosc de Lya i els sistemes Lya esmorteïts o DLAs (els tres darrers són sistemes absorbidors detectats als espectres dels quàsars). El projecte BOSS és un dels quatre projectes que han composat la tercera fase de la col·laboració de l’Sloan Digital Sky Survey (SDSS) el principal objectiu del qual ha estat la detecció del senyal de les oscil·lacions acústiques dels barions (BAO, de l’anglès Baryon Acoustic Oscillations) i que ha estat recollint espectres electromagnètics de quàsars i galàxies des de la tardor de 2013 fins a la tardor de 2014. L’estructura d’aquesta tesi es divideix en tres capítols que fan referència a l’estudi de diferents traçadors. En el capítol ì els traçadors emprats són les galàxies de CMASS i els sistemes absorbidors de MgII; en el capítol 3, els DLA i el bosc de Lya, i en el capítol 5, els quàsars i el bosc de Lya. A més la tesi compta amb una introducció en català, una altra en anglès i un compendi de les conclusions obtingudes

A Strong Blend in the Morning: Studying the Circumgalactic Medium Before Cosmic Noon with Strong, Blended Lyman-α\alpha Forest Systems

We study of the properties of a new class of circumgalactic medium absorbers identified in the Lyman-$\alpha$ forest: "Strong, Blended Lyman-$\alpha$" (or SBLA) absorption systems. We study SBLAs at $2.4<z<3.1$ in SDSS-IV/eBOSS spectra by their strong extended Lyman-$\alpha$ absorption complexes covering 138 km/s with an integrated $\log (N_{HI}/$cm$^{-2}) =16.04^{+0.05}_{-0.06}$ and Doppler parameter $b=18.1^{+0.7}_{-0.4}$ km/s. Clustering with the Lyman-$\alpha$ forest provides a large-scale structure bias of $b = 2.34\pm0.06$ and halo mass estimate of $M_h \approx 10^{12}{\rm h^{-1}M_{sol}}$ for our SBLA sample. We measure the ensemble mean column densities of 22 metal features in the SBLA composite spectrum and find that no single-population multiphase model for them is viable. We therefore explore the underlying SBLA population by forward modelling the SBLA absorption distribution. Based on covariance measurements and favoured populations we find that $\approx 25$% of our SBLAs have stronger metals. Using silicon only we find that our strong metal SBLAs trace gas with a $\log(n_H /$cm$^{-3}) > -2.45$ for $T=10^{3.5}$K and show gas clumping on $<255$ parsec scales. We fit multiphase models to this strong sub-population and find a low ionization phase with $n_H=1$cm$^{-3}$, $T=10^{3.5}$K and $[X/H]=0.8$, an intermediate ionization phase with $\log(n_H /$cm$^{-3}) = -3.35$, $T=10^{3.5}$K and $[X/H]=-1.1$, and a poorly constrained higher ionization phase. We find that the low ionization phase traces cold, dense super-solar metallicity gas with a clumping scale of just 0.009 parsecs.Comment: 28 pages, submitted to MNRA

Finestres al cel

We present an astronomy educational project intended for 16-year-old high school students that has been successfully deployed for 7 years under the Youth and Science Program of the Catalunya La Pedrera Foundation. The Youth and Science Program aims to encourage talented students to pursue careers in science and technology and a future as researchers. It consists of a two-week crash course covering all major topics in astronomy: stellar evolution, black holes, galaxy formation and evolution, cosmology, simulations, and gravitational waves, among many others. The classes focus on the relevant concepts in each of the aforementioned fields but without a detailed description of the math formalism or the most advanced concepts in modern physics, this to develop the students’ intuition and interest in the wonders of the Universe without overwhelming them. Theoretical sessions are complemented with a set of practical sessions that help students to consolidate the concepts. All theory and practical sessions in this project are being compiled in an outreach book addressed not only to the students of this project but also to the entire amateur astronomy community

The Cross-correlation of MgII Absorption and Galaxies in BOSS

We present a measurement of the cross-correlation of MgII absorption and massive galaxies, using the DR11 main galaxy sample of the Baryon Oscillation Spectroscopic Survey of SDSS-III (CMASS galaxies), and the DR7 quasar spectra of SDSS-II. The cross-correlation is measured by stacking quasar absorption spectra shifted to the redshift of galaxies that are within a certain impact parameter bin of the quasar, after dividing by a quasar continuum model. This results in an average MgII equivalent width as a function of impact parameter from a galaxy, ranging from 50 kpc to more than 10 Mpc in proper units, which includes all MgII absorbers. We show that special care needs to be taken to use an unbiased quasar continuum estimator, to avoid systematic errors in the measurement of the mean stacked MgII equivalent width. The measured cross-correlation follows the expected shape of the galaxy correlation function, although measurement errors are large. We use the cross-correlation amplitude to derive the bias factor of MgII absorbers, finding bMgII = 2.33 \pm? 0.19, where the error accounts only for the statistical uncertainty in measuring the mean equivalent width. This bias factor is larger than that obtained in previous studies and may be affected by modeling uncertainties that we discuss, but if correct it suggests that MgII absorbers at redshift z \simeq 0:5 are spatially distributed on large scales similarly to the CMASS galaxies in BOSS. Keywords: galaxies: haloes, galaxies: formation, quasars: absorption lines, large-scale structure of universeComment: Accepted for publication to MNRAS. Accepted 2014 December 12. Received 2014 November 29; in original form 2014 February

The cosmological bias factor of damped Lyman alpha systems: dependence on metal line strength

We measure the cosmological bias factor of damped Ly α absorbers (DLAs) from their crosscorrelation with the Ly α forest absorption, as a function of the DLA metal strength, defined from an average of equivalent widths of the strongest detectable low-ionization metal lines. A clear increase of the bias factor with metal strength is detected, as expected from a relation of metallicity and velocity dispersion with host halo mass. The relation is stronger after the metal strength is corrected for the H I column density, to make it more related to metallicity instead of metal column density. After correcting for the effects of measurement errors of the metal strength parameter, we find that the bias factor of DLAs with the weakest metal lines is close to unity, consistent with an origin in dwarf galaxies with host halo masses ∼1010M , whereas the most metal rich DLAs have a bias factor as large as bDLA ∼ 3, indicative of massive galaxies or galaxy groups in host haloes with masses ∼1012M . Our result confirms the physical origin of the relation of bias factors measured from cross-correlation studies to the host haloes of the absorbers

The Mean Metal-line Absorption Spectrum of DLAs in BOSS

We study the mean absorption spectrum of the Damped Lyman alpha population at $z\sim 2.6$ by stacking normalized, rest-frame shifted spectra of $\sim 27\,000$ DLAs from the DR12 of BOSS/SDSS-III. We measure the equivalent widths of 50 individual metal absorption lines in 5 intervals of DLA hydrogen column density, 5 intervals of DLA redshift, and overall mean equivalent widths for an additional 13 absorption features from groups of strongly blended lines. The mean equivalent width of low-ionization lines increases with $N_{\rm HI}$, whereas for high-ionization lines the increase is much weaker. The mean metal line equivalent widths decrease by a factor $\sim 1.1-1.5$ from $z\sim2.1$ to $z \sim 3.5$, with small or no differences between low- and high-ionization species. We develop a theoretical model, inspired by the presence of multiple absorption components observed in high-resolution spectra, to infer mean metal column densities from the equivalent widths of partially saturated metal lines. We apply this model to 14 low-ionization species and to AlIII, SIII, SiIII, CIV, SiIV, NV and OVI. We use an approximate derivation for separating the equivalent width contributions of several lines to blended absorption features, and infer mean equivalent widths and column densities from lines of the additional species NI, ZnII, CII${}^{*}$, FeIII, and SIV. Several of these mean column densities of metal lines in DLAs are obtained for the first time; their values generally agree with measurements of individual DLAs from high-resolution, high signal-to-noise ratio spectra when they are available.Comment: Resubmitted after referee revision. Added evolution of metal-line equivalent widths with redshift (Section 5). Added assessment of result dependencies on sample and methodology. Comparison of relative abundances of DLAs vs Milky Way ISM and halo (Figure 16). Publicly available videos of composite quasar and DLA spectra realizations here: https://github.com/lluism

Origin of Metals around Galaxies. I. Catalogs of Metal-line Absorption Doublets from High-resolution Quasar Spectra

We present the first paper of the series Origin of Metals around Galaxies, which aims to explore the origin of the metals observed in the circumgalactic and intergalactic media. In this work we extract and build catalogs of metal absorbers that will be used in future analyses, and make our results publicly available to the community. We design a fully automatic algorithm to search for absorption metal-line doublets of the species C IV, N V, Si IV, and Mg II in high-resolution (R >=30,000) quasar spectra without human intervention, and apply it to the high-resolution and signal-to-noise ratio spectra of 690 quasars, observed with the UVES and HIRES instruments. We obtain 5656 C IV doublets, 7919 doublets of Mg II, 2258 of Si IV, and 239 of N V, constituting the largest high-resolution metaldoublet samples to date, and estimate the dependence of their completeness and purity on various doublet parameters such as equivalent width and redshift, using real and artificial quasar spectra. The catalogs include doublets with rest-frame line-equivalent widths down to a few mÅ, all detected at a significance above 3σ, and covering the redshifts between 1 < z =<5, properties that make them useful for a wide range of chemical evolution studies

Robustness of cosmic neutrino background detection in the cosmic microwave background

The existence of a cosmic neutrino background can be probed indirectly by CMB experiments, not only by measuring the background density of radiation in the universe, but also by searching for the typical signatures of the fluctuations of free-streaming species in the temperature and polarisation power spectrum. Previous studies have already proposed a rather generic parametrisation of these fluctuations, that could help to discriminate between the signature of ordinary free-streaming neutrinos, or of more exotic dark radiation models. Current data are compatible with standard values of these parameters, which seems to bring further evidence for the existence of a cosmic neutrino background. In this work, we investigate the robustness of this conclusion under various assumptions. We generalise the definition of an effective sound speed and viscosity speed to the case of massive neutrinos or other dark radiation components experiencing a non-relativistic transition. We show that current bounds on these effective parameters do not vary significantly when considering an arbitrary value of the particle mass, or extended cosmological models with a free effective neutrino number, dynamical dark energy or a running of the primordial spectrum tilt. We conclude that it is possible to make a robust statement about the detection of the cosmic neutrino background by CMB experiments

The miniJPAS survey quasar selection IV: Classification and redshift estimation with SQUEzE

We present a list of quasar candidates including photometric redshift estimates from the miniJPAS Data Release constructed using SQUEzE. This work is based on machine-learning classification of photometric data of quasar candidates using SQUEzE. It has the advantage that its classification procedure can be explained to some extent, making it less of a `black box' when compared with other classifiers. Another key advantage is that using user-defined metrics means the user has more control over the classification. While SQUEzE was designed for spectroscopic data, here we adapt it for multi-band photometric data, i.e. we treat multiple narrow-band filters as very low-resolution spectra. We train our models using specialized mocks from Queiroz et al. (2022). We estimate our redshift precision using the normalized median absolute deviation, $\sigma_{\rm NMAD}$ applied to our test sample. Our test sample returns an $f_1$ score (effectively the purity and completeness) of 0.49 for quasars down to magnitude $r=24.3$ with $z\geq2.1$ and 0.24 for quasars with $z<2.1$. For high-z quasars, this goes up to 0.9 for $r<21.0$. We present two catalogues of quasar candidates including redshift estimates: 301 from point-like sources and 1049 when also including extended sources. We discuss the impact of including extended sources in our predictions (they are not included in the mocks), as well as the impact of changing the noise model of the mocks. We also give an explanation of SQUEzE reasoning. Our estimates for the redshift precision using the test sample indicate a $\sigma_{NMAD}=0.92\%$ for the entire sample, reduced to 0.81\% for $r<22.5$ and 0.74\% for $r<21.3$. Spectroscopic follow-up of the candidates is required in order to confirm the validity of our findings.Comment: Accepted in A&A 24 pages, 24 figures, 7 table

The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey

The Sloan Digital Sky Survey III (SDSS-III) presents the first spectroscopic data from the Baryon Oscillation Spectroscopic Survey (BOSS). This ninth data release (DR9) of the SDSS project includes 535,995 new galaxy spectra (median z=0.52), 102,100 new quasar spectra (median z=2.32), and 90,897 new stellar spectra, along with the data presented in previous data releases. These spectra were obtained with the new BOSS spectrograph and were taken between 2009 December and 2011 July. In addition, the stellar parameters pipeline, which determines radial velocities, surface temperatures, surface gravities, and metallicities of stars, has been updated and refined with improvements in temperature estimates for stars with T_eff<5000 K and in metallicity estimates for stars with [Fe/H]>-0.5. DR9 includes new stellar parameters for all stars presented in DR8, including stars from SDSS-I and II, as well as those observed as part of the SDSS-III Sloan Extension for Galactic Understanding and Exploration-2 (SEGUE-2). The astrometry error introduced in the DR8 imaging catalogs has been corrected in the DR9 data products. The next data release for SDSS-III will be in Summer 2013, which will present the first data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) along with another year of data from BOSS, followed by the final SDSS-III data release in December 2014.Comment: 9 figures; 2 tables. Submitted to ApJS. DR9 is available at http://www.sdss3.org/dr