arXiv subjects

Luz Ángela García

Publications and source records attributed to Luz Ángela García.

10 recordsLinked to original sources

arXiv2026

Semi-Analytical Jeans Filtering Functions for Baryonic Density and Velocity Fields in Second-Order Cosmological Perturbation Theory

Cosmological perturbation theory provides the framework for describing the evolution of matter density fluctuations and the formation of large-scale structure in the $Λ$CDM paradigm. We present a semi-analytical approach for a mixed fluid composed of cold dark matter (CDM) and baryons. Assuming General Relativity, we derive the equations of motion from the Vlasov equation, incorporating baryonic effects through the stress tensor and retaining only baryonic pressure. We introduce Jeans Filtering Functions (JFF) as a biasing tool to describe baryonic fluctuations using CDM as a tracer. First- and second-order solutions are obtained with a semi-analytical method based on a single iteration of the equations of motion. These solutions can be evaluated at low computational cost and allow us to study the shift of the filtering scale beyond linear order and its impact on the matter power spectrum without computing the spectrum explicitly. In contrast to approaches based directly on the power spectrum, we quantify baryonic effects through the fluctuation fields themselves. We derive semi-analytical expressions for baryonic density and velocity fluctuations, with the velocity divergence field providing the most significant result. The method offers a readily evaluable description of baryonic effects in large-scale structure and shows how pressure shifts the filtering scale, with implications for quantities such as the filtering mass and the temperature of pressure-supported components.

astro-ph.CO↗

arXiv2026

The THESAN project: Lyman-alpha emitters as probes of ionized bubble sizes

We use the THESAN radiation-hydrodynamics simulations to investigate how Lyman-$α$ emitters (LAEs) trace ionized bubble sizes during the Epoch of Reionization. We generate realistic LAE catalogs by combining accurate intrinsic Ly$α$ production and intergalactic transmission with an empirical model for dust absorption and gas outflows. By calibrating to observationally-constrained Ly$α$ luminosity functions, we reproduce the rapid decline in Ly$α$ visibility toward higher redshifts while revealing mild tensions in LAE fractions near the end of reionization. Before the midpoint of reionization, galaxies within larger line-of-sight bubbles ($\gtrsim 10$ cMpc) have higher observed Ly$α$ luminosity and equivalent width (EW), demonstrating that the evolving LAE fraction provides a practical statistical tracer for bubble size. These correlations weaken as percolation progresses and the IGM becomes increasingly ionized. In LAE selected samples with $L_{\text{Ly}α} > 10^{41.5}\ \text{erg s}^{-1}$, Ly$α$ properties correlate with bubble size more strongly than UV magnitude, especially at $z \gtrsim 7$. This simulation-based framework maps LAE selections to bubble-size statistics, clarifies biases in more idealized models, and will supply public catalogs to interpret current and forthcoming JWST and narrow-band LAE surveys in terms of the evolving topology of reionization.

astro-ph.GA↗

arXiv2025

Search for host galaxies of unlocalized Fast Radio Bursts in the SDSS IV catalog

This theoretical work investigates different models to predict the redshift of Fast Radio Bursts (FRBs) from their observed dispersion measure (DM) and other reported properties. We performed an extensive revision of the FRBs with confirmed galaxy hosts in the literature and compiled an updated catalog. With this sample of FRBs, composed of 117 unique transients, we explore four physically motivated models that relate the DM and redshift ($z$): a linear trend (inspired by the Macquart relation), a log-parabolic function, a power-law, and a combined model from the above. We assess the success of these theoretical proposals by implementing different statistical metrics and ranking them. The DM-$z$ relations are also tested using 100 realizations of 500 simulated FRBs, which follow the observed DM trends. Relying on our theoretical modeling, we establish the probability of $\sim$1000 FRBs with unknown $z$ (from the latest CHIME data release) to be hosted by galaxies in the SDSS archival dataset. Our validation scheme allows us to predict the FRBs with a probability threshold of $\geq$0.95 to originate in these galaxies, using their 2D angular position in the sky, magnitude in the r-band, and redshift. This statistical proposal will be tested with upcoming data releases from DESI and new generations of galaxy surveys, such as Euclid, and it opens brilliant possibilities to localize these transients in an automatic pipeline.

astro-ph.CO↗

arXiv2025

Fast Radio Bursts as cosmological proxies: estimating the Hubble constant

One of the most challenging problems in cosmology is the Hubble tension, a discrepancy in the predicted expansion rate of the Universe. We leverage the sensitivity of the Dispersion Measure (DM) from Fast Radio Bursts (FRBs) with the Hubble factor to investigate the Hubble tension. We build a catalog of 98 localized FRBs and an independent mock catalog and employ 3 methods to calculate the best value of the $H_0$: i) the mean of $H_0$ values obtained through direct calculation, ii) the maximum likelihood estimate (MLE) and iii) the reconstruction of the cosmic expansion history $H(z)$ using two DM-$z$ relations. When the confirmed FRBs is employed, our predictions are compatible with reports from the Planck+2018, with $H_0=65.13\pm2.52\,\text{km/s/Mpc}$ and $57.67\pm11.99\,\text{km/s/Mpc}$ for MLE and the arithmetic mean, respectively. If we assume a linear and a power-law function for the DM-$z$ relation, our predictions for $H_0$ are $51.27^{+3.80}_{-3.31}\,\text{km/s/Mpc}$ and $77.09^{+8.89}_{-7.64}\,\text{km/s/Mpc}$, respectively. Using 100 mock catalogs of simulated FRBs, we obtain larger values for $H_0$ with all methods considered: $H_{0;\text{ Like}}=67.30\pm0.91\,\text{km/s/Mpc}$, $H_{0;\text{ Mean}}=66.21\pm3.46\,\text{km/s/Mpc}$, $H_{0;\text{ Median}}=66.10\pm1.89\,\text{km/s/Mpc}$, $H_{0;\text{Linear}}=54.34\pm1.57\,\text{km/s/Mpc}$ and $H_{0;\text{Power-law}}=91.84\pm1.82\,\text{km/s/Mpc}$ for the MLE, the arithmetic mean, and linear and power-law $\text{DM}-z$ relations, respectively. Our results for mock FRB catalogs increase the statistical precision, ranging from 1.4\% to 5.2\% for the MLE and arithmetic mean. Our result with the MLE applied to synthetic FRBs is at the same level of precision as reports from SH0ES. The increase in the number of confirmed FRBs will provide us, in combination with other observations, a robust prediction of the value of the Hubble constant.

astro-ph.CO↗

arXiv2023

Early dark energy induced by non-linear electrodynamics

In this work, we introduce a parametrization of early dark energy that mimics radiation at early times and governs the present acceleration of the Universe. We show that such parametrization models non-linear electrodynamics in the early Universe and investigate the cosmological viability of the model. In our scenario, the early dark energy is encoded in the non-linearity of the electromagnetic fields through a parameter $β$ that changes the Lagrangian of the system, and the parameters $γ_s$ and $α$, that define the departure from the standard model constant equation of state. We use a Bayesian method and the modular software \textsc{CosmoSIS} to find the best values for the model's free parameters with precomputed likelihoods from Planck 2018, primordial nucleosynthesis data, inferred distances from different wide galaxy surveys and luminosity distances of SNIa from Pantheon and SH0ES, such that $γ_s =$ 0.468 $\pm$ 0.026 and $α=$ -0.947 $\pm$ 0.032, as opposed to $Λ$CDM where $γ_s = β=$ 0 and there is no equivalence for the $α$ parameter. Our results predict an earlier formation of the structure and a shorter age of the Universe compared with the canonical cosmological model. One of the main findings of our work is that this kind of dark energy alleviates the ongoing tensions in cosmology, the Hubble tension and the so-called $σ_8$ tension, which predicted values by our model are H$_o =$ 70.2 $\pm$ 0.9 km/s/Mpc and $σ_8 =$ 0.798 $\pm$ 0.007. The reported values lie between the inferred values inferred from early and late (local) Universe observations. Future observations will shed light on the nature of the dark energy, its impact on the structure formation, and its dynamics.

gr-qc↗

arXiv2023

Analysis of the impact of broad absorption lines on quasar redshift measurements with synthetic observations

Accurate quasar classifications and redshift measurements are increasingly important to precision cosmology experiments. Broad absorption line (BAL) features are present in 15-20\% of all quasars, and these features can introduce systematic redshift errors, and in extreme cases produce misclassifications. We quantitatively investigate the impact of BAL features on quasar classifications and redshift measurements with synthetic spectra that were designed to match observations by the Dark Energy Spectroscopic Instrument (DESI) survey. Over the course of five years, DESI aims to measure spectra for 40 million galaxies and quasars, including nearly three million quasars. Our synthetic quasar spectra match the signal-to-noise ratio and redshift distributions of the first year of DESI observations, and include the same synthetic quasar spectra both with and without BAL features. We demonstrate that masking the locations of the BAL features decreases the redshift errors by about 1\% and reduces the number of catastrophic redshift errors by about 80\%. We conclude that identifying and masking BAL troughs should be a standard part of the redshift determination step for DESI and other large-scale spectroscopic surveys of quasars.

astro-ph.CO↗

arXiv2023

Constraining cosmological parameters from N-body simulations with Variational Bayesian Neural Networks

Methods based on Deep Learning have recently been applied on astrophysical parameter recovery thanks to their ability to capture information from complex data. One of these methods is the approximate Bayesian Neural Networks (BNNs) which have demonstrated to yield consistent posterior distribution into the parameter space, helpful for uncertainty quantification. However, as any modern neural networks, they tend to produce overly confident uncertainty estimates and can introduce bias when BNNs are applied to data. In this work, we implement multiplicative normalizing flows (MNFs), a family of approximate posteriors for the parameters of BNNs with the purpose of enhancing the flexibility of the variational posterior distribution, to extract $Ω_m$, $h$, and $σ_8$ from the QUIJOTE simulations. We have compared this method with respect to the standard BNNs, and the flipout estimator. We found that MNFs combined with BNNs outperform the other models obtaining predictive performance with almost one order of magnitude larger that standard BNNs, $σ_8$ extracted with high accuracy ($r^2=0.99$), and precise uncertainty estimates. The latter implies that MNFs provide more realistic predictive distribution closer to the true posterior mitigating the bias introduced by the variational approximation and allowing to work with well-calibrated networks.

astro-ph.IM↗

arXiv2021

The properties of high redshift galaxies

This work studies the connection between the first galaxies and their hosting dark matter halos in the early Universe when Reionization is concluding. Our numerical models (already presented in an earlier study) trace the star formation history at $z =$ 4 - 8, the galaxy stellar mass function, the stellar-to-halo mass distribution, and other high redshift galaxies statistics. All these predictions are consistent with observations to date and other high-resolution cosmological simulations. A key finding of this work is the robust estimate for the cosmic star formation history (through the implementation of galaxy and supernova winds and atomic and molecular cooling processes) and self-consistent chemical pollution of the intergalactic medium. The theoretical models are compatible with a faint-end slope of the galaxy luminosity function of $α=$ -2 at the end of the Reionization.

astro-ph.CO↗

arXiv2020

A novel early Dark Energy model

We present a theoretical study of an early dark energy (EDE) model. The equation of state $ω(z)$ evolves during the thermal history in a framework of a Friedmann-Lemaitre-Robertson-Walker Universe, following an effective parametrization that is a function of redshift $z$. We explore the evolution of the system from the radiation domination era to the late times, allowing the EDE model to have a non-negligible contribution at high redshift (as opposed to the cosmological constant that only plays a role once the structure is formed) with a very little input to the Big Bang Nucleosynthesis, and to do so, the equation of state mimics the radiation behaviour, but being subdominant in terms of its energy density. At late times, the equation of state of the dark energy model asymptotically tends to the fiducial value of the De Sitter domination epoch, providing an explanation for the accelerated expansion of the Universe at late times, emulating the effect of the cosmological constant. The proposed model has three free parameters, that we constrain using SNIa luminosity distances, along with the CMB shift parameter and the deceleration parameter calculated at the time of dark energy - matter equality. With full knowledge of the best fit for our model, we calculate different observables and compare these predictions with the standard$Λ$CDM model. Besides the general consent of the community with the cosmological constant, there is no fundamental reason to choose that particular candidate as dark energy. Here, we open the opportunity to consider a more dynamical model, that also accounts for the late accelerated expansion of the Universe.

astro-ph.CO↗

arXiv2018

The CGM and IGM at z$\sim$5: metal budget and physical connection

We present further results of a survey for absorption line systems in the spectra of four high redshift quasars (5.79 $\le$ z$_{\textrm{em}}$ $\le$ 6.13) obtained with the ESO Very Large Telescope X-Shooter. We identify 36 $\textrm{CIV}$ and 7 $\textrm{SiIV}$ systems with a $\ge$ 5$σ$ significance. The highest redshift $\textrm{CIV}$ and $\textrm{SiIV}$ absorbers identified in this work are at z = 5.80738 $\pm$ 0.00017 and z = 5.77495 $\pm$ 0.00038, respectively. We compute the comoving mass density of $\textrm{SiIV}$ ($Ω_{\textrm{SiIV}}$) and find that it evolves from $Ω_{\textrm{SiIV}}$ = 4.3$^{+2.1}_{-2.1}$ $\times$10$^{-9}$ at = 5.05 to $Ω_{\textrm{SiIV}}$ = 1.4$^{+0.6}_{-0.4}$ $\times$10$^{-9}$ at = 5.66. We also measure $Ω_{\textrm{CIV}}$ = 1.6$^{+0.4}_{-0.1}$ $\times$10$^{-8}$ at = 4.77 and $Ω_{\textrm{CIV}}$ = 3.4$^{+1.6}_{-1.1}$ $\times$10$^{-9}$ at = 5.66. We classify our $\textrm{CIV}$ absorber population by the presence of associated $\textit{low}$ and/or $\textit{high ionisation}$ systems and compute their velocity width ($Δ$v$_{90}$). We find that all $\textrm{CIV}$ systems with $Δ$v$_{90}$ > 200 kms$^{-1}$ have associated $\textit{low ionisation}$ systems. We investigate two such systems, separated by 550 physical kpc along a line of sight, and find it likely that they are both tracing a multi-phase medium where hot and cold gas is mixing at the interface between the CGM and IGM. We further discuss the \textrm{MgII} systems presented in a previous work and we identify 5 $\textrm{SiII}$, 10 $\textrm{AlII}$, 12 $\textrm{FeII}$, 1 $\textrm{CII}$, 7 $\textrm{MgI}$ and 1 $\textrm{CaII}$ associated transitions. We compute the respective comoving mass densities in the redshift range 2 to 6, as allowed by the wavelength coverage.

astro-ph.GA↗