Resumen:

In this presentation we will analyze the physical origin of the primordial inhomogeneities during the inflation era. The proposed framework is based on semiclassical gravity, in which one only focuses on quantizing the matter fields, but the spacetime metric is always treated in a classical manner. The objective collapse mechanism is based on the Continuous Spontaneous Localization (CSL) model, and we apply it to the wave function associated with the perturbations of the inflaton field. The collapse given by the CSL model provides a satisfactory mechanism of breaking the initial symmetries of the Bunch-Davies vacuum. Additionally, we obtain a primordial spectrum that has the same distinctive features as the standard one, and which is consistent with the observations from the Cosmic Microwave Background (CMB). The novel aspect in this work is that the constructed CSL model arises from the simplest choices for the collapse parameter and operator.

Resumen:

Cosmic Dawn is an important open problem in Cosmology. The radiation produced by the first galaxies would not have been enough to maintain the ionization fraction of the IGM at large scales, therefore complementary ionization agents have been proposed, including cosmic rays (CR) that escape from those galaxies. In this talk, we investigate the ionization of the IGM produced by the electromagnetic cascades initiated by CR electrons, emphasizing the contribution of secondary photons, which has not been extensively explored yet. We simulated the transport of all the particles comprising the cascades and calculated the rate of ionization and the distribution of energy between the particles and the IGM. Our results show that high energy electrons carry energy far away from the source while ionizing the medium in their path, whilst those with kinetic energies lower than a few keV cool completely via ionization within a distance of kiloparsecs, reinforcing the results of previous works and extending their predictions to higher energy electrons and farther distances from the source. In addition, we show for the first time that photoionization by secondary photons produced in high-energy cascades may contribute significantly to the ionization of the IGM. This particular result implies a significant ionization rate in the far IGM that has not been considered by previous works. Finally, we evaluate the ionization rate at any point in the IGM in terms of the properties of the galaxy population present during the Cosmic Dawn as predicted by cosmological simulations of galaxy formation.

Resumen:

Our team is undertaking the Next Generation Fornax Survey (NGFS) in the optical u', g', and i' and the near-infrared (NIR) J and Ks filters. The NGFS is a deep multi-wavelength survey that covers the entire Fornax galaxy cluster out to its virial radius (1.4 Mpc) using optical photometry obtained with DECam at Blanco/CTIO and NIR observations from VIRCAM at VISTA/ESO. We have recently published catalogs and characterizations of more than 600 dwarf galaxies in the central region of the cluster u',g',i'. The unprecedented depth of our survey allows us to study in detail the stellar populations of dwarf galaxies via color maps in high and low-density environments. Galaxy colors arise from the dominant stellar populations within a galaxy and their ages. Hence, by examining the color of a galaxy one can determine the mix of stellar populations present in a stellar system. Studying color gradients and color maps within galaxies, i.e. the variations in color across their structures, reveals the spatial distribution of stellar populations within galaxies allowing for a more comprehensive understanding of the mechanisms that shape galaxy structures, their evolutionary paths, and the underlying physical mechanisms. By comparing the colors of galaxies in different regions, such as dense galaxy clusters versus less crowded field regions, we can investigate the impact of environmental factors on the evolution of galaxies. Color variations across a galaxy cluster can provide insights into processes like ram-pressure stripping, tidal interactions, or galaxy harassment that influence the properties of member galaxies. Significant differences in color gradients or maps between cluster galaxies and field galaxies can provide insights into the mechanisms that quench star formation in dense environments. These measurements aid in understanding the physical conditions, evolutionary processes, and feedback mechanisms that shape galaxies and their star formation histories.

Resumen:

The densest structures of the Universe formed at the knots of the cosmic web at high redshifts and constitute the present-day clusters of galaxies. They are nearly virialized systems, with a high density of gravitationally bound galaxies. The early stages of these structures are called protoclusters and they are the natural laboratories to observe the role of environmental effects on galaxy evolution. Protoclusters can be observationally identified by galaxy number density contrasts when compared to the field. In this work, we use submillimeter galaxies (SMGs), a population of dusty and distant starburst galaxies, which are expected to inhabit peaks of matter density, as targets for protocluster searches. We use combined wide-band and narrow-band optical photometry to identify Ly-alpha emitters (LAEs) around SMGs at $z\sim 4.5$ in the COSMOS field, as a means to identify typical star-forming galaxies that may trace the underlying structure containing our target SMGs. Using deep imaging, obtained by our team with the IMACS instrument on the Baade (6.5 m) telescope at the Las Campanas Observatory, we probe a physical scale of $\sim10 Mpc$ in size at $z=4.5$, consistent with protocluster scales. Our approach picks out line emitters as narrow-band excess objects. We denominate these objects as Ly-alpha candidates. We use additional IMACS spectroscopic data to confirm these candidates as bona fide LAEs and thus protoclusters members, eliminating low-redshfit interlopers. In comparisson with LAE density in the field, our preliminary results point to a mild excess in LAE density around SMGs at $z \sim 4.5$. These preliminary results are consistent with SMGs tracing typical moderate-mass structures of the Universe instead of the more massive ones, that grow into Coma-like clusters. SMGs may be thus an as-yet untapped population to understand the build-up of the more modest and more typical galaxy groups and clusters.