3.16 Tesis magíster

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A chemical survey of the proto-stellar system IRAS 16253-2429
(2023) Castillo Lara, Jaime; Guzmán Veloso, Viviana; Artur de la Villarmois, Elizabeth; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Presentamos un estudio químico de IRAS 16253-2429 (de aquí en adelante IRAS 16253), una proto-estrella de Clase 0 y de baja masa clasificada como un very low luminosity object (VeLLO) y localizada en el complejo de formación estelar ρ Ophiucus. Las moléculas CN, c-C3H2, y H2CO son detectadas por primera vez en IRAS 16253. H2CO se muestra compacta y simétrica en la región central, que incluye el disco y el envoltorio interior. c-C3H2 y CN también se presentan en la región central, pero con una emisión asimétrica y más extendida. También presentamos observaciones previas de 13CO, C17O, C18O, SO, CO, C2H y N2H+, con detecciones tentativas de DCO+ y N2D+. C2H se presenta en las paredes de la cavidad, en ambas direcciones de la ejección de gas, pero principalmente en la dirección norte. 13CO está presente en la región central y en la cavidad sur, C18O muestra una emisión compacta y simétrica, CO traza ambas direcciones de la ejección de gas, SO y C17O están centradas pero extendidas y asimétricas, y N2H+ está presente en el envoltorio exterior. A través de un diagrama rotacional para H2CO, estimamos una temperatura rotacional de ∼ 9.3K para la molecula. Esta baja temperatura rotacional sugiere un régimen sub-termal para H2CO, lo que a su vez implica que H2CO está presente sólo en el envoltorio interno, y no en el disco. A través de un ajuste de estructura hiperfina para N2H+, se estima una temperatura de excitación de ∼ 4 K para la molécula, esta baja temperatura de excitación también sugiere un régimen sub-termal, consistente con las bajas densidades del envoltorio exterior. Comparamos nuestros resultados con otros estudios de otras fuentes de Clase 0, pero más masivas. Encontramos que, en contra de nuestras expectativas, los trazadores de gas frío DCO+, N2H+ y N2D+ no son más abundantes en este VeLLO en comparación a otras proto-estrellas más masivas. Nuestros resultados sugieren que la química de IRAS 16253 es una versión a menor escala de la química encontrada en fuentes de Clase 0 más masivas.
An experiment in near field cosmology: A search for the Magellanic Wake
(2024) Cavieres Carrera, Manuel Antonio; Chanamé, Julio; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
The infall of the Magellanic Cloud system into the Milky Way halo hasstrong effects on the distribution of the stars and dark matter in the outerhalo of our Galaxy. In particular, N-body simulations predict a large-scaledensity asymmetry that spans the northern Galactic hemisphere (known as thecollective response), along with a localized overdensity (the Wake) that trailsthe LMC’s orbit. In this study, we collected wide-field deep near-infrared andoptical photometry from the VISTA and DECam instruments in four fieldsalong the expected position of the Magellanic Wake, covering most of thedensity range predicted to be found in the outer halo, as predicted by numericalmodels. This data allows us to select a clean sample of halo stars that reachthe oldest main sequence turn-off (MSTO) up to 100 kpc, with ∼ 400 stellarsources further than 60 kpc, on two separate tracers, near main sequence turnoff stars and red giant branch. We found that the Magellanic Wake overdensityis present in our data with a relative overdensity of 3.07 ± 0.7. Comparisonof the radial density profiles of near-MSTO stars with simulations of the MilkyWay/LMC interaction is best fitted by a massive LMC model with a total massof 2.5 × 10^11M⊙. This work provides the first unambiguous detection of thewake with consistent densities between two tracers.
Blue Stragglers in the Gaia Era: Galactic Open and Globular Clusters
(2023) Carrasco Varela, Francisco Felipe; Puzia, Thomas H.; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Blue Straggler Stars (BSSs) are one of the keys to understand in a better way how stars evolve and interact with each other in different star clusters. They appear to be hotter and brighter than the Main Sequence Turn Off Point (MSTO) and, therefore, they should have evolved off the Main-Sequence branch. We properly select, for Open Clusters (OCs) and Globular Clusters (GCs), star cluster members based on proper motions and parallaxes provided by Gaia Data Release 3 (DR3). Using isochrones models and selection criteria from previous studies, we select and classify stars as BSS, Yellow Straggler Stars and Red Stragglers Stars (evolved BSSs). We identify BSSs to be present in all our GCs and in 42/129 (∼ 33 %) of studied OCs. We counted a total of 4399 BSSs; 434 (∼ 10 %) located in OCs and 3965 (90 %) located in GCs. Clusters younger than ∼ 500 Myr do not show the presence of BSSs in our sample. We obtain astrophysical parameters from 3 different methods (color–temperature relations, isochrone–fitting models and parameters from Gaia DR3 spectra) such as the effective temperature Teff, star mass M, and surface gravity log(g). We find values for BSS Teff to be ∼ (6800 ± 585) K in GCs and ∼ (7570 ± 1400) K in OCs; and an average mass of ⟨MBSS⟩ = (1.75 ± 0.45) M⊙ in OCs and ⟨MBSS⟩ = (1.02 ± 0.1) M⊙ in GCs. For every BSS, we compute the difference of the BSS mass and the MSTO mass of its parent cluster, normalized by the MSTO mass, and called it Me based on previous studies. This parameter is classified as low–Me (Me < 0.5, BSS likely formed through mass-transfer) and high–Me (0.5 < Me < 1.0, BSS likely formed through mergers). For OCs we find a percentage 81.34 % high–Me and 18.66 % low–Me. For GCs, we find 94.25 % low–Me and 5.25 % high–Me. Comparing Me against the BSS age obtained with isochrone modes, we were able to detect: i) GC BSSs that are most likely to be formed through collisions show a “boost” in their percentage/fraction for stars with an age ∼ 1 − 2 Gyr, in agreement with reported age for core-collapse events in GCs found in previous studies; ii) a double sequence for GC BSSs, where we conclude that these sequences correspond to a pre merger/closer-binary interaction and post merger/closer-binary interaction of BSS formation
Characterization of molecular gas substructures in the protoplanetary disk HD 163296 using ALMA interferometric data
(2024) Maluenda Berna, Michel Yan Luis; Guzmán Veloso, Viviana; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
This thesis conducts an extensive examination of molecular gas substructures, specifically HCN and C2H, within the protoplanetary disk surrounding HD 163296. Utilizing ALMA interferometric data in two rotational transitions, the study resolves structures down to 10 au scales, focusing on characterizing gas substructures and comparing them with millimeter dust in the disk. The methodology involves parameterizing relative abundance, incorporating Gaussian functions, and employing MCMC analysis to model observed bright ring substructures. The study reveals three bright line emission rings for both HCN and C2H, indicating a high abundance within 150 au of the central star. Interestingly, no universal connection is found between dust and molecular substructures, suggesting complex dynamics. The inner disk (<150 au) exhibits a peak relative abundance of ∼6.8 × 10−11 for HCN and ∼5.0 × 10−11 for C2H, implying active organic chemistry or hidden molecular emissions. Furthermore, a significant overlap between dust and chemical substructures within 150 au is observed, diminishing in the outer disk. The outermost bright rings at approximately 309 and 385 au for HCN and C2H respectively lack correlation with CO substructures, challenging conventional understanding of protoplanetary disk composition and dynamics. Chemical conversion of CO into other species is proposed as a partial explanation for observed vertical substructures and high C/O ratios influencing C2H and HCN abundance. This research enhances our understanding of complex dynamics and chemical processes in protoplanetary disks, providing valuable insights for future planet formation studies.
Characterization of the dwarf galaxy population in the Centaurus A environment
(2020) Ribbeck Valenzuela, Karen X.; Puzia, Thomas H.; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
We report photometric properties of the dwarf galaxy population in the Centaurus A group, along with 51 new dwarf candidates based on the optical u’g’r’i’z’ imaging of 22 deg^2 centered on the nearby giant elliptical galaxy NGC 5128 as part of The Survey of Centaurus A’s Baryonic Structures (SCABS) program. Morphological analysis of the new candidates shows surface brightness profiles are well represented by a single component Sérsic models with an average Sérsic index of = 0.85 ± 0.05. The candidates present luminosities of -12 ≤ Mv ≤ -7 mag, corresponding to stellar masses of 7.5 ≥ log M/M☉ ≥ 4.5, which extend the size-luminosity relation toward fainter luminosities and smaller sizes for known dwarf galaxies outside the Local Group (LG), and are consistent with properties of nearby dwarf spheroidal galaxies. I will discuss the stellar population properties of the newly discovered galaxy sample and compare their properties to other dwarf galaxy samples in the nearby Universe.
Computer vision and machine-learning method for the detection of low-surface brightness galaxies in the Fornax Cluster
(2024) Hernández Flores, Alejandra Valentina; Puzia, Thomas H.; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Detecting the faint luminosity in Low Surface Brightness Galaxies (LSBGs) poses significant challenges, primarily due to sky brightness and contamination from brighter sources while separating LSBGs from the background. Despite these challenges, the study of LSBGs holds great potential to advance our understanding of various fields, including cosmology, galaxy formation, evolution, and the characteristics of galaxy clusters. The primary goal of this study is to develop an automated code capable of effectively detecting LSBGs, including the more diffuse LSBGs that are only detectable through visual search. The initial focus is on the Fornax cluster of galaxies, with the possibility of extension to other galaxy clusters. The purpose is to significantly contribute to advancing research in LSBGs and its implications for broader astronomical studies. We have created an automated code that successfully detects LSBGs in digital images at a reasonable processing speed. We have incorporated an innovative algorithm to separate LSBGs from the background using a dynamic background kernel and threshold applied to image segments to achieve this. We have also implemented a bilateral filter that identifies the most diffuse LSBGs and preserves morphology, ensuring precise identification and classification. Additionally, we have developed and trained a One-Class Support Vector Machine (SVM) classifier using a gold sample of 143 LSBGs, resulting in a classifier with a low rate of false positives. The implemented code has successfully detected LSBGs, showcasing its ability to address the challenges associated with identifying the faint luminosity in these galaxies, even in the presence of brighter sources. The integrated algorithm has significantly improved the accuracy and efficiency of the detection process, allowing for the identification of a substantial number of LSBG candidates. Specifically, in the Fornax Cluster, our algorithm successfully identified 31,295 LSBG candidates, as documented in the comprehensive catalog available at GitHub Repository: \url{https://github.com/Alevhf/LSB_candidates/blob/main/Catalog_result.csv#L19304}.
Detection and characterization of hot Jupiters around hot stars
(2023) Torres Miranda, Pascal José; Jordán Colzani, Andrés Cristóbal; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
El objetivo principal de esta tesis es abordar el desafío de detectar y caracterizar Júpiteres calientes alrededor de estrellas calientes. La elevada temperatura de las estrellas dificulta la confirmación de exoplanetas debido a la rápida rotación estelar, lo que resulta en una menor precisión en las mediciones de velocidades radiales. Un método para caracterizar y confirmar planetas que orbitan este tipo de estrella es el de Tomografía Doppler (TD). En este trabajo, se desarrolló un método de TD, en un marco bayesiano y se probó en seis sistemas. Se utilizaron datos publicados de tres de ellos (WASP-19b, KELT-7b y HAT-P-56b), obteniendo resultados visuales similares a los publicados. Para dos sistemas (HD2685 y TOI-812), se predijeron y observaron los tránsitos, pero no fue posible recuperar la señal del planeta. Y un sistema que será publicado prontamente (TOI-3362-b, Espinoza et al. in prep) que es consistente con la alineación del sistema. También se construyó un catálogo de siete estrellas (incluyendo HD2685b) interesantes para nuestro estudio. Este catálogo se construyó a partir de una selección de estrellas calientes (hecha con datos de Gaia DR2) que poseían altas señales de tránsito en las curvas de luz obtenidas de TESS. De esas siete estrellas, cuatro poseen planetas ya confirmados y tres candidatos a planeta, de especial interés debido a las características únicas de cada sistema. También se desarrolló un código capaz de predecir la observabilidad de la Tomografía Doppler, considerando las características de la estrella, el planeta y el instrumento utilizado para la observación. Las conclusiones de este estudio indican que tanto el método de deconvolución como el modelo de predicción de Tomografía Doppler son útiles y consistentes con trabajos previos. Sin embargo, es necesario desarrollar nuevas herramientas para cuantificar la precisión de estos métodos.
Discovery and characterization of exoplanets in the TESS full frame images
(2022) Rojas Henríquez, Felipe Ignacio; Jordán Colzani, Andrés Cristóbal; Chanamé, Julio; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
En los últimos años la cantidad de exoplanetas ha ido en aumento. Hoy conocemos más de 5000 y este numero seguirá creciendo gracias a misiones como TESS, que monitorea constantemente estrellas cercanas desde el espacio. No obstante, de todos estos planetas descubiertos, menos de 1000 tienen mediciones de su masa y radio con una precisión del 20% o mejor. Conocer estos parámetros con precisión nos da una idea inicial de su composición y por ende, de cómo pudo haber sido su proceso de formación. Además, se conocen muy pocos planetas gigantes con órbitas con períodos superior a los 10 días. Este tipo de planetas (Gigantes Tibios) despiertan la pregunta de cómo es que se encuentran tan cerca de la estrella que orbitan. Al mismo tiempo, estos conservan posibles rastros de su evolución dinámica en sus órbitas, a diferencia de planetas con órbitas más pequeñas. El objetivo de este proyecto es implementar un sistema de procesamiento de las imágenes de la misión TESS y búsqueda de planetas gigantes tibios, en el marco de la colaboración WINE, dedicada al estudio de estos planetas. De los candidatos a planeta encontrados, se realizó el seguimiento, confirmación y caracterización de un Neptuno (TOI-883 b) y un sub-Saturno (TOI-899 b), que orbitan estrellas muy parecidas al Sol con períodos de 10 y 12 días, respectivamente.
Estimadores de metalicidad en SN tipo II-P
(2023) Castro Morales, Nicolás Manuel; Clocchiatti, Alejandro; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Uno de los parámetros más difíciles de estimar en supernovas es su metalicidad, basicamente por lo complejo de sus espectros y por la imposibilidad de haber observado con el detalle apropiado al progenitor en la gran mayoría de los casos. Los espectros de las supernovas de tipo IIP durante la fase fotosférica, sin embargo, revelan información directa sobre la metalicidad de la estrella progenitora que es posible interpretar. Los pseudo anchos equivalentes de los perfiles P Cygni de líneas de elementos químicos complejos ya han sido utilizados como indicadores de metalicidad, pero tienen algunas limitaciones. Presentamos un nuevo método que añade a las líneas de los espectros un indicador fotométrico basado en la evolución del brillo de las supernovas en la banda B, y/o la U, de Johnson, siempre en supernovas tipo IIP. Usando modelos teóricos de la atmósfera en estas supernovas encontramos que la variación de la magnitud en B entre las fases temprana y tardía de la curva de luz (EtoLC, por las siglas en inglés, de ``Early to Late Contrast'') está relacionada tanto con la masa como con la metalicidad del progenitor. Mostramos además que con el uso combinado de los anchos equivalentes de una línea de hierro y estos EtoLCS es posible discriminar con bastante sensibilidad y separar supernovas provenientes de la explosión de progenitores muy masivos de las provenientes de progenitores poco masivos, así como los que tenían metalicidad elevada de los que la tenían baja. Utilizando esta técnica a una muestra de supernovas reales, con buenos conjuntos de datos como para poder medir estos parámetros, se encuentra concordancia con lo ilustrado por los modelos indicando que, una vez calibrado, el método tendrá el potencial de poder encontrar con observaciones directas las características de masa y metalicidad de los progenitores de SN tipo IIP.
Evolution of the Galaxy Cluster Red Sequence from Redshift 0.2 to 1.5
(2022) Gutiérrez Hernández, Lorena; Barrientos, Luis Felipe; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
In this thesis, we present a study of the population of early-type galaxies in 115 clusters at 0.2 < z < 1.5, imaged with the F200LP/UVIS and F110W/IR filters of the Wide Field Camera 3 on the Hubble Space Telescope. We aim to investigate the evolution of the red sequence parameters (zero-point, slope, and intrinsic scatter) in the color-magnitude plane to constrain its members’ history and epoch of star formation. To accomplish this, we carefully selected the galaxies belonging to the red sequence, dismissing all contamination from the background and late-type galaxies into the clusters. Then, we used a robust linear fitting method to obtain the red sequence parameters in the rest frame. Finally, we compared the evolution of the zero-point with that of the color in stellar population synthesis models with different metallicity, formation red-shift, and e-folding time. We find that, as the redshift increases, the zero-point moves towards blue, the slope becomes steeper, and the observed scatter increases. On the other hand, the mean color of the clusters evolves slowly and is highly similar in systems at the same redshift, located in random directions in the universe. Therefore, the change of the zero-point is in agreement with the passive evolution of early galaxies in the present cosmological scenario. At the same time, we attribute the slope evolution to archaeological downsizing in conjunction with the progressive build-up of the red sequence. Finally, we constrain the epoch and period of stellar population formation to a strip diagonally crossing the τ - zf plane.
Exploring Super-Chandrasekhar Supernova SN2007if with radiative transfer code TARDIS
(2024) Silva Beyer, Joaquín; Clocchiatti, Alejandro; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Super-Chandrasekhar Supernovae (SNe) are a peculiar case of Type Ia SNthat show very high luminosities, slow light-curve evolution, and low expan-sion velocities, consistent with progenitor masses over the Chandrasekharlimit (≳ 1.4M⊙). SN 2007if is one of those events, with a still unknownexplosion scenario. Its early spectra are smooth and near featureless, butat later epochs, they seem to morph into a normal Type Ia. I exploredits spectra with radiative transfer code TARDIS, using three models, con-sidering the envelope interaction and the violent merger hypotheses. Thebest model, based on the envelope interaction scenario, resulted in a verygood match for early epochs, and a better match in the later epochs than theother models. I performed abundance tomography and adapted its chemicalstructure, resulting in my model 07if-tail. While it had a good agree-ment with the observed low velocities and some lines, many still featuredtoo deep absorption profiles, and the lines suggested a lower temperaturethan the overall continuum. I found that SN2007if probably lacks S and hasno Fe on its outer regions. In order to explain SN2007if’s light curve andspectra, a secondary source of continuum brightness is needed. My findingssupport the scenario of a WD-WD slow merger, forming a CO envelope thatinteracts with the explosion’s ejecta.
Exploring the Green Valley with the dark energy survey: studying the evolution of galaxies
(2023) Gil Toriello, Santiago; Galaz, Gaspar; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
We investigate the properties of galaxies located at the so-called Green Valley, an intermediate region between the blue-cloud of active star- forming galaxies, and the red-sequence of quenched and "dead" galaxies, visible in a color vs stellar mass diagram for galaxies.We utilize data from multiple releases of the Dark Energy Survey (DES), to characterize galaxies based on their physical properties, and to correlate their location in a stellar mass vs color diagram with their morphologies.We selected a sample of high-quality photometric data from the Year 3 re- lease of the Dark Energy Survey, with redshifts ranging from local z ∼ 0, to intermediate z ∼ 1.5, and cleaned it by applying a set of different quality selection criteria. We obtained a number of measurements for the photometric redshifts of the galaxies, by employing different parametric algorithms, to study each evolution separately as a function of distance. With the use of LePHARE, a template fitting code, we measured a set of physical properties of the galaxies that are helpful to study their evo- lution, and to assess the transitional nature of galaxies inside the Green Valley. These are, mainly, the Absolute Magnitude, the Stellar Mass, the Star Formation Rate and the UV Luminosity.We made use of two catalogues for morphological prediction available for the Year 3 release. These catalogues allowed us to better constrain the relation between the morphological structures of galaxies and their evolutionary stage.Results show that combining SED template fitting algorithms with mor- phological analysis allows to constrain the bi-modality distribution even when working with optical surveys, up to redshifts of z = 1.5.This is a first approach on the use of these methods to pave the way more massive and intensive data treatment surveys, like the future LSST survey to be done with the Vera Rubin Telescope.
Exploring the intersection of Lyman-U Emitters & Lyman Break Galaxies behind the strongly lensed clusters : Abell370, Abell2744 and MACS0416
(2021) Prieto Lyon, Gonzalo; Bauer, Franz Erik; Guaita, Lucía; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
In this thesis, we present a study of star-forming galaxies between redshifts 2.9-6.7 split among four categories: Pure LAEs (73 galaxies) without UV detection; Pure LBGs (1015 galaxies) without Lyman-a detection; LAE-LBGs (193 galaxies), with both Lyman break and Lyman-a detected; and Other SFGs without any of these signatures (459 galaxies). We use Multi-Unit Spectroscopic Explorer (MUSE) and legacy Hubble Space Telescope (HST) data of the three Hubble Frontier Fields lensing clusters A370, A2744 and MACS0416, reaching magnitudes as faint as M1500 ≈ −13. We study the continuum and emission-line parameters of our sample, with the goal of finding and understanding any intrinsic differences between the aforementioned regimes of SFGs. We report a great diversity of high-redshift galaxies in the Lyman-a - M1500 plane, with a lack of massive galaxies above the SFR(Lya)=SFR(UV) line at M1500 < −18, with most pure LAEs near this line and log(Llya)<42.0. We measure the UV slope of pure LBGs and LAE-LBGs, with median values of ß=-1.75 and ß=-2.44 respectively, meaning that LAEs overall are near the dust-free domain while pure LBGs tend to be redder, and hence presumably more dust-obscured and/or older, the former being one of the probable reasons for their lack of Lyman-a; SFGs without LB or Lya show redder median slopes of ß=-1.59. LAE-LBGs tend to have a stronger sSFR than pure LBGs and other SFGs by a factor of 2 at every studied redshift. We find slight differences between the two LAE populations, with LAE-LBGs showing broader Lyman-a profiles, but further radiative transfer simulations are needed to clarify the contribution of HI velocity and column density.
Hierarchical triple systems in Gaia
(2022) Moraga Mejías, Víctor; Chanamé, Julio; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Investigación enfocada en la búsqueda de sistemas triples jerárquicos de estrellas en la Vía Láctea. Se usó como punto de partida una muestra de 224 sistemas de un catálogo de binarias anchas, los cuales fueron estudiados para determinar su real multiplicidad. Mediante una campaña de observaciones de espectroscopia, se determinaron nuevas velocidades radiales para 116 de estos sistemas. Al comparar con mediciones en la literatura existente, se encontraron 74 estrellas cuya variación en velocidad indica la presencia de un sistema espectroscópico no detectado hasta la fecha.
Host galaxies of local hard X-ray selected AGN
(2022) Doll Carriel, Goran; Bauer, Franz Erik; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
We investigate the evolutionary state of galaxies hosting active galactic nuclei (AGN) for a sample of 138 hard X-ray selected AGN from the BAT AGN Spectroscopic Survey (BASS) catalog and which have high-resolution (R ∼ 5000), VLT/X-SHOOTER 0.3–1 µm spectroscopy. We perform a stellar population synthesis analysis via pPXF fitting of the stellar continuum, as well as fit specific emission and absorption features (e.g., Lick indices, line ratios), to estimate AGN/star formation contributions, dust obscuration, stellar age, metallicity and star formation histories. Additionally, we perform morphological classification on our sample to study possible correlations to said evolutionary state. We compare our results to AGN X-ray properties and infrared (IR) derived SFRs to estimate the potential for AGN feedback. Using several cuts and selection criteria, we construct a comparison sample from SDSS DR7 data in the MPA-JHU catalog to place our AGN sample in the context with overall galaxy evolution. The X-SHOOTER spectra primarily probe the central regions of the AGN hosts, which tend to be dominated by old (> 10 Gyr) stellar populations. However, we find our sample primarily composed of main-sequence spirals (46%), followed by green valley spirals (14%) and green valley ellipticals (14%), with almost no galaxies present in the red sequence according to our definition. Our spectral modeling suggests that most elliptical and blue spiral hosts of AGN experienced strong episodes of star formation at intermediate ages (∼ 1–6 Gyr), which strongly correlate with their apparent morphological features (tails, remnant features). In contrast, most red spirals seem to follow a completely secular evolution. Comparison of IR and optically derived SFRs for 57 AGN in the sample implies copious obscured star formation; this appears to push otherwise optically passive elliptical hosts into the green valley or main sequence. As for the effect of AGN feedback, we only find very mild correlations between the AGN and the host bulge properties, thereby implying weak links between the current AGN event and their intermediate-age populations.
Hα emission observations of nearby baryonic structures
(2022) Ziliotto, Tuila; Puzia, Thomas H.; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
A fundamental question in astronomy is how the environment affects galaxy evolution. Baryonic structures in the nearby universe can be used as laboratories to study the influence of the environment on galaxy evolution processes, since their close distances allow a detailed view of its member galaxies and their substructures. It is believed that the structures that we observe in the nearby universe form through the accretion of smaller groups of galaxies; thus, environmental processes can influence galaxies even before they enter larger clusters. The synergy between numerical simulations and surveys dedicated to observing large samples of galaxies is fundamental to trace and understand the physical properties of different galaxy components. In this context, star formation is one of the most fundamental parameters that characterizes galaxies, and can be heavily influenced by environmental conditions. We use data from the Next Generation Fornax Survey (NGFS) obtained with the Dark Energy Camera (DECam) g’r’i’ broadbands and N662 narrow-band covering the H-alpha + [N II] emission lines to study star formation in the central region (~R_vir/4) of the Fornax cluster of galaxies. We present a method for continuum subtraction in narrow-band images. From the continuum-subtracted H-alpha emission, we derived star formation rates (SFR) for a sample of dwarf galaxies in the central region of the Fornax cluster. Most of the dwarfs presenting H-alpha emission have large nuclei, with high temperatures in their very centers, suggesting the presence of a young stellar population. H-alpha emission concentrates in the centers of these galaxies. Considering the proposed scenarios for the formation of nucleated dwarf galaxies, our observations are in agreement with the model of in-situ star formation in their centers. We have found a spatial asymmetry in the distribution of H-alpha emitting nucleated dwarf galaxies around the Fornax center, suggesting different formation histories. We also discuss SFRs for NGC 1427A, a dwarf irregular galaxy with an intense burst of star formation. Broadband DECam data also allowed us to generate mass maps, from which we constructed diagrams of specific star formation rates versus pixel mass. In these diagrams, we can identify different substructures in the galaxies.
Modelling of resolved scaling relations in simulated galaxies
(2023) Cornejo Cárdenas, Anell; Tissera, Patricia; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
We developed a new numerical tool, called SpecGSG (i.e. Spectra Generator of Simulated Galaxies), which aims to generate synthetic spectra of simulated galaxies in order to improve comparisons between simulations and observations. Through this code we can obtain spatially resolved spectral information that considers the contribution of stellar populations and the nebular emission produced by gas close to young stellar populations. A fundamental aspect of this tool, and what differentiates it from other previous works (e.g., Nanni et al. 2022), is that the nebular emission is calculated based on the properties of the gas surrounding recently born stellar populations. This code allowed us to study both the intrinsic properties of the simulations and the properties we derived from their synthetic spectra. From the intrinsic properties of the simulations we found an anti-correlation between the ionization parameter and gas metallicity. Additionally, we used SpecGSG to recover spatially resolved scaling relations using the synthetic spectra generated from the simulated galaxies in local regions. In particular, we focused on two scaling relations: (1) the spatially resolved star-forming main sequence (rSFMS), i.e. the relationship between the Star Formation Rate surface density (ΣSFR) and the stellar mass surface density (Σ∗), and (2) the spatially resolved mass-metallicity relation (rMZR), i.e. the relationship between the gas-phase metallicity and Σ∗. From these synthetic spectra, we found that the metallicity has a first dependence on Σ∗ and a second dependence on ΣSFR. This agrees with results obtained in observations of galaxies. Therefore, SpecGSG allows us to calculate the properties of the simulations from a more observational way, improving comparisons between observational and simulation data. At the moment, SpecGSG only implements a simple model of dust that downgrades the spectra due to its presence in the star-forming regions. The treatment of dust attenuation and re-emission along the line of sight between each emitting source and the observer, will be implemented in a future work.
Molecular outflows in local (U)LIRGs
(2022) Peñaloza Garrido, Fernando Felipe; Treister, Ezequiel; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Luminous infrared galaxies (LIRGs) and ultra luminous infrared galaxies (ULIRGs), defined for having L_IR > 10^11 L_⊙ and L_IR > 10^12 L_⊙ respectively, were observed in large numbers in the 1980s by the Infrared Astronomical Satellite (IRAS). Most of them are believed to form after a major merger of two similarly massive spiral galaxies and represent a key evolutionary stage, where events such as triggering of star formation and active galactic nucleus (AGN) occur, thereby deciding the fate of the galaxy. The study of (U)LIRGs and the processes taking place in them could lead to fundamental answers for understanding galaxy evolution. This thesis studies the CO(2–1) emission from a subset of the Great Observatories All-Sky LIRG Survey (GOALS), conformed by 18 local (U)LIRGs (mean z = 0.026) observed with the Atacama Compact Array (ACA), at the Atacama Large Millimeter/submillimeter Array (ALMA). The main goal was to search for high-velocity components that could indicate the presence of molecular outflows and determine their incidence in the host galaxies. This was done by modeling the data as rotating disk galaxies to separate the emission into systemic and non-systemic components and estimate their dynamical parameters (for example, escape velocities and galactic masses). Outflows with > 1% the total molecular mass were detected in 12 of the 18 sources at relatively low velocities, with only small fractions of the emission being able to escape the galactic potential. For the galaxies with stellar masses available in the literature, it was observed that they present higher star formation rates (SFRs) than those in the main sequence, although with lowering SFR for increasing M_star. Detailed analysis of mass outflow rates and AGN contributions to the bolometric luminosity support a scenario where feedback is produced mainly by stellar activity, as expected for starburst galaxies, finding that these outflows have little or no participation in the trend seen in the SFRs–M_star diagram.
Period change rates of LMC classical cepheids using MESA
(2021) Espinoza Arancibia, Felipe Ignacio; Catelan, Márcio; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Las estrellas pulsantes, como las Cefeidas o las RR Lyrae, nos ofrecen una ventana para medir y estudiar los cambios debidos a la evolución estelar. Los cambios evolutivos en la densidad de la estrella producen cambios en el periodo de pulsación, que tienen un efecto acumulativo en los tiempos observados del brillo máximo o mínimo de la estrella. Por esta razón, las estrellas pulsantes son laboratorios de astrofísica estelar. En esta tesis calculamos un conjunto de modelos evolutivos de estrellas con 4 a 7 푀 utilizando el código de evolución estelar Modules for Experiments in Stellar Astrophysics (MESA), variando la tasa de rotación inicial y la metalicidad. Durante la fase de quema de helio, la luminosidad aumenta a medida que aumenta la rotación, mientras que variando la metalicidad el comportamiento de la luminosidad resulta no monotónico. Por otro lado, la extensión del blue loop muestra una dependencia con la masa y la rotación más compleja. La extensión del blue loop para estrellas con 푀 ≤ 5,5 푀 disminuye a medida que aumenta la tasa de rotación, mientras que el comportamiento es no monotónico para estrellas con 푀 > 5,5 푀 . Debido a la pérdida de momento angular durante la fase de quema de hidrógeno en una cáscara, las Cefeidas no alcanzan rotaciones cercanas a la rotación crítica. Utilizando Radial Stellar Pulsations (RSP), la nueva funcionalidad de MESA, obtuvimos los bordes de la banda de inestabilidad (IS) y los periodos lineales para el modo fundamental. Se obtuvieron relaciones período-edad, período-edad-temperatura, período-luminosidad y período-luminosidad-temperatura para tres tasas de rotación y metalicidades, que mostraron dependencias con el número de cruce, la posición en la IS, la 13 LIST OF FIGURES rotación y la metalicidad. Las tasas de cambio de periodo se calcularon directamente a partir de los periodos lineales. Los modelos durante el segundo cruce mostraron una dependencia no monontónica con la rotación, mientras que los modelos sin rotación muestran una mayor tasa de cambio de periodo durante el tercer cruce. Al variar el contenido de metales, los modelos con mayor metalicidad presentan una tasa ligeramente superior durante el segundo cruce. Comparamos nuestros modelos con los trabajos presentados en la literatura utilizando el código de Ginebra. Encontramos grandes diferencias entre los modelos dada la diferente implementación de la rotación entre los códigos. Además, comparamos nuestras tasas de cambio de periodo con las calculadas en trabajos recientes en la literatura, para las cefeidas de La Gran Nube de Magallanes (LMC). Encontramos un buen acuerdo en general, ya que 72,2% de los datos caen dentro de rango de 3-sigma de los modelos. La implementación de procesos aún no incluidos en MESA, como la pérdida de masa impulsada por la pulsación, podría ayudarnos a cubrir mejor las tasas de cambio de periodo empíricas en la literatura.
Primordial black holes as dark matter
(2021) Sureda Hernández, Joaquín Miguel; Padilla, Nelson; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Aún cuando se han postulado varios candidatos para resolver el problema de la materia oscura (DM), su verdadera naturaleza aún no está clara. En este trabajo, considero agujeros negros primordiales (PBHs) como un potencial candidato para resolver esta incógnita. Considerando un formalismo tipo Press-Schechter modificado, es derivada una función de masa extendida para PBHs, donde su formación ocurre en el Universo temprano por el colapso de fluctuaciones de densidad de energía. Asumiendo que estas fluctuaciones siguen estadística Gaussiana, éstas pueden ser relacionadas con el espectro de potencias primordial (PPS), donde además se considera un espectro de potencias partido con un índice espectral azul a escalas menores que una escala pivote, escogida como kpiv = 10 Mpc−1. Adicionalmente, se presenta un nuevo método para traducir restricciones observacionales en la fracción de DM compuesta por PBHs, f, calculadas para distribuciones de masa monocromáticas en restricciones sobre f para funciones de masa extendidas. Este método es muy general en el sentido de que uno solo necesita conocer la forma de la función f(MPBH ), sin tener que profundizar en los detalles del proceso físico relacionado con la observación. Además, toma en consideración el hecho de que algunas observaciones están relacionadas con algún proceso físico, el cual es sólo producido por una fracción de la población total de PBHs. Por lo tanto, solo esta fracción de los PBHs (o fracción de masa) es la que está siendo restringida. Por otro lado, este método considera la evolución de la función de masa, en el sentido de que algunos PBHs se están evaporando debido a la radiación de Hawking. Entonces, estos PBHs no son considerados en la función de masa luego de evaporarse por completo, debido a que no pueden ser parte de la DM. Debido a las características de las funciones de masa, se presenta una nueva restricción para funciones extendidas, relacionada con la función de masa de agujeros negros supermasivos (SMBH) y el hecho de que éstas funciones de masa tipo Press-Schechter no deberían, en ningún caso, predecir más SMBHs que los observados en el Universo. Utilizando un conjunto de distintas restricciones observacionales sobre f, para distribuciones monocromáticas, en conjunto con el método desarrollado para traducir restricciones a funciones de masa extendidas, se calcula la fracción de masa permitida f en las funciones de masa tipo PressSchechter. Combinando estas restricciones, junto con la que viene de los SMBH, se obtiene la fracción permitida f, de manera que no haya conflicto con las observaciones. Estos resultados se muestran como función de los parámetros de las funciones de masa tipo Press-Schechter. Considerando solo las restricciones bien definidas, aparece una región permitida en el espacio de parámetros, tal que toda la DM puede estar compuesta por PBHs. La región de mayor interés es la que cuyos parámetros permiten PBHs con masas ∼ 102M , dado que éstas masas son del mismo orden que las detectadas por LIGO y son difíciles de explicar solo considerando el colapso de estrellas.

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