Probing the early universe with lyman-alpha emitting galaxies

• Autores: Alberto Torralba Torregrosa
• Directores de la Tesis: Siddharta Gurung López (dir. tes.) , Pablo Arnalte-Mur (codir. tes.)
• Lectura: En la Universitat de València ( España ) en 2025
• Idioma: español
• Tribunal Calificador de la Tesis: R. M. González Delgado (presid.) , Mauro Stefanon (secret.) , Katherine Lucía Guaita Artieda (voc.)
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• Resumen

  • The Lyman-alpha emission line (Ly-alpha 121.567 nm) is typically one of the most luminous among the ultraviolet spectra of many galaxies. Ly-alpha emission mainly originates from recombination events of monoatomic hydrogen in the interstellar medium (ISM) of galaxies, typically powered by elevated star formation activity or the presence of an Active Galactic Nucleus (AGN). The Ly-alpha line carries valuable information about the properties of the ISM of galaxies (e.g., ionization state, gas dynamics, dust content, etc.). Moreover, due to its intrinsic resonant nature, Ly-alpha is highly sensitive to the presence of neutral hydrogen in the intergalactic medium (IGM), making it a valuable probe of the environmental conditions of galaxies at different redshifts.

    In this thesis, we study galaxy properties with Ly-alpha emission as the main driving feature. On the one hand, we make use of data from the wide-field multi-narrow band (multi-NB) surveys J-PAS and PAUS to select a sample of bright quasars with strong Ly-alpha emission, with the goal of estimating the Ly-alpha luminosity function (LF) as a function of redshift, from z=2 to z=5.3. We find a declining evolution of the total number of Ly-alpha-emitting quasars, consistent with the global evolution of the AGN population. We also compute the UV luminosity function of such a population, for which we measure a similar evolution, confirming a decreasing contribution to the ionizing photon budget of bright quasars toward the epoch of reionization. The multi-NB data of our selected populations also allowed us to obtain an average quasar spectrum across the probed redshift range, using only photometric data. We also measured the mean IGM attenuation due to the Ly-alpha forest from mean stacked spectra in redshift bins.

    We used data from the JWST Cycle 1 GO program #1933 to study the properties of an extremely luminous (MUV=-21.3) Ly-alpha emitter at z=6.6, dubbed COLA1. This galaxy presents a double-peaked Ly-alpha profile. At such a high redshift, cosmic reionization is still in progress, and the IGM is significantly neutral, implying that the blue peak of Ly-alpha should be completely absorbed. The visibility of the blue peak implies the existence of a highly ionized region around COLA1, allowing the resonant Ly-alpha photons to escape. We use JWST/NIRCam broad-band imaging and wide-field slitless spectroscopy to assess the ISM properties of COLA1 and the galaxies within its close environment. The analysis of COLA1's optical emission lines and broad-band photometry suggests a very high escape fraction of ionizing photons. Hence, we find that COLA1 could indeed be capable of powering the ionized region needed to explain its Ly-alpha double peak, with a minor contribution from other detected (fainter) galaxies. We find a mild overdensity of galaxies around COLA1, showing that the environment of this galaxy is normal when compared to galaxies with similar luminosities.