3.16 Instituto de Astrofísica

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Occultations stellaires pour l’étude des objets trans-neptuniens et les Centaures : applications aux anneaux de Chariklo
(2017) Leiva Espinoza, Rodrigo Andrés; Sicardy, Bruno; Vanzi, Leonardo; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
The present PhD thesis has been developed in the context of a cotutelle between the Pontificia Universidad Católica de Chile (PUC) and the Université Pierre et Marie Curie (UPMC). The first half of the PhD was done in the Instituto de Astrofísica at PUC and the second half at the Labora- toire d’Etudes Spatiales et d’Instrumentation en Astrophysique (LESIA) at the Observatoire de Paris, in the context of the European Research Council (ERC) project “Lucky Star", whose goal is to study the small objects of the outer Solar System using stellar occultations. Here, I address three important stages of the project: observations with fast cameras, data analysis and physical interpretation of the results. In the first part I describe tests performed on two occultation kits, each consisting in a fast camera, a time registration system and an acquisition software. I show that the EMCCD-based camera performs better than the alternative CMOS camera, reaching stars one magnitude fainter in equivalent conditions. The time registration system (the TimeBox device) has an accuracy below 20 ms with respect to the UTC reference time which is adequate for the timing of the observation of stellar occultations. Interactions with the acquisition software manufacturer lead to the adaptation of such software to the needs of the project. In the second part I study the physical characterization of three ob- ject with the analysis of stellar occultations. For the scattered disk object 2007 UK126 I derive the range and more probable density values analyzing the elliptical fits to a multi chord stellar occultation. For the plutino 2003 AZ84 I constrain the range of compatible density and orientation to a narrow region around ∼870 kg m−3 and opening angle B ∼ 48◦ analyzing two multi-chord stellar occultations. The main subject of this section is the adoption of a Bayesian-MCMC approach for analysis of five stellar occultations by the Centaur object Chariklo. Chariklo appears to be consistent with an ellipsoid with semiaxes a = 148+6−4 km, b = 132+6−5 km, and c = 102+10−8 km presenting topographic features of the order of 6 km. From this nominal model, I derive a body geometric albedo of 4.9±0.1% and a ring reflectivity of 3.7±0.3%. The topographic features for this model are ∼ 6 km, comparable to those of Saturnian icy satellites with similar size and density. In the third part, I consider Lindblad resonances between the mean motions of ring particles and the rotation of an irregular body. Mass excess departing from a spherical body exert strong torques on a collisional disk that clear the material from the corotation radius up to the outermost resonance. Application to Chariklo indicates very short clearing timescales ( < 105 years) and explains the current location of the rings.
A VLT/MUSE galaxy survey towards QSO Q1410 : looking for a WHIM traced by BLAs in inter-cluster filaments
(2018) Pessa Gutiérrez, Ismael Alejandro; Tejos, Nicolás; Barrientos, Luis Felipe; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Statistical study of neutron star glitches
(2018) Fuentes Baeza, José Rafael; Reisenegger, Andreas; Espinoza, Cristóbal; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
The extraplanar type II supernova ASASSN-14jb in the galaxy ESO 467-G051
(2018) Meza Retamal, Nicolás Eduardo; Clocchiatti, Alejandro; Prieto Katunaric, José Luis; Pontificia Universidad Católica de Chile. Facultad de Física
Stochastic ion acceleration by the ion cyclotron instability in collisionless plasmas with a growing magnetic field
(2018) Ley Quinteros, Francisco Javier; Reisenegger, Andreas; Riquelme Hernández, Mario Alejandro; Pontificia Universidad Católica de Chile. Facultad de Física
The exceptional x-ray evolution of SN 1996cr in high resolution
(2018) Quirola Vásquez, Jonathan Alexander; Bauer, Franz Erik; Pontificia Universidad Católica de Chile. Facultad de Física
En esta tesis presentamos un análisis de observaciones en rayos-X en múltiples épocas durante 18 años de la SN 1996cr, una de las cinco SNe más cercanas detectados en la época moderna. Observaciones de Chandra HETG en 2000, 2004 y 2009 nos permiten resolver espectralmente los perfiles de velocidad de líneas de emisión de Ne, Mg, Si, Sy Fe, así como monitorear su evolución como trazadores de la interacción ejecta-CSM. Para explicar la diversidad de líneas de emisión en rayos-X exploramos algunos posibles modelos geométricos. Basados en las observaciones del 2009 con alta señal-ruido, encontramos que una geometría polar con una configuración de dos distintos ángulos de apertura y obscuración interna puede exitosamente reproducir todos los perfiles de líneas observados. Ajustamos modelos que consideran C la convolución de los modelos geométricos con plasmas sin-equilibrio simples y dobles con componentes de absorción a la época 2009. Encontramos que el mejor modelo obtenido consiste de dos plasmas. Una componente es ligeramente absorbido (2×1021 cm−2), plasma frio (≈2 keV) con altas abundancias de Ne, Mg, Si y S, y asociada con una región de interacción polar extendida (ángulo de semiapertura ≈58◦). Mientras que la otra componente tiene absorción moderada (2×1022 cm−2), un plasma caliente (∼30 keV) con abundancia de Fe alta y fuerte absorción interna, asociada con una región de interacción fuertemente polar (ángulo de semiapertura ≈20◦). Extendemos este modelo a otras siete épocas con baja señal-ruido y/o baja resolución espectral (XMM-Newton en 2001, 2013, 2014, 2016 y 2018), produciendo varias tendencias interesantes. El flujo, el cual es siempre dominado por el plasma caliente, alcanzando un punto máximo entre 2004–2009 y actualmente disminuyendo, indicando que la onda de choque esta pasando a través de un CSM de densidad más baja (viento de una gigante roja), de acuerdo con simulaciones hidrodinámicas previas. Las temperaturas del plasma y la velocidad de expansión muestran disminuciones suaves según las expectativas, mientras que las abundancias muestran aumentos leves, sugeriendo posibles influencias del material ejectado. Discutimos las implicaciones físicas de estos resultados y su impacto para identificar potenciales progenitores.
Stellar substructures in the southern galactic hemisphere
(2019) Navarrete Silva, Camila Andrea; Catelan, Márcio; Pontificia Universidad Católica de Chile. Facultad de Física
De acuerdo al modelo cosmológico actual, Λ-CDM (por sus iniciales en inglés), los halos de galaxias se ensamblan jerárquicamente, a través de la acumulación sucesiva de galaxias satélites más pequeñas. Los restos de eventos de asimilación pasados y en curso han sido encontrados en el halo galáctico en forma de sub-estructuras estelares, tanto en distribuciones espaciales como en el espacio de fase. La mayoría de estas detecciones han sido posibles gracias a estudios de imágenes de campo amplio observando cientos de miles de estrellas débiles en extensas áreas del halo galáctico visible desde el norte. Desde la última década, estudios de imágenes de campo amplio en el hemisferio sur galáctico han abierto el camino para estudios galácticos en áreas del cielo hasta ahora inexploradas. En esta tesis, exploré las dos sub-estructuras principales en el halo galáctico sur: la corriente estelar de Sagitario, la más prominente en el halo de la Vía Láctea, y la Nube Grande de Magallanes, galaxia satélite que podría albergar sub-estructura estelar en su propio halo. En el Capítulo 1 de esta tesis, presento el descubrimiento de colas de marea emergiendo del cúmulo globular NGC 7492, el que se encuentra inmerso en la corriente estelar de Sagitario. En el Capítulo 2, tracé la extensión más al sur de la corriente estelar de Sagitario, revelando una nueva bifurcación a lo largo de la línea de visión, la que abarca ∼40 grados en el cielo. El Capítulo 4 está dedicado al seguimiento espectroscópico de cuatro candidatos a corrientes estelares en las zonas más externas de la Gran Nube de Magallanes. La distribución de las estrellas observadas en el espacio de fase permitió trazar el halo estelar Magallánico hasta 40 grados desde el centrode la Gran Nube de Magallanes.
Dusty clumps in circumbinary discs.
(2019) Poblete Rivera, Pedro Pablo A.; Cuello, Nicolás; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Protoplanetary discs are structures formed by gas and dust that form during the first stages of the stellar evolution. Protoplanetary discs also are the birthplace of planets, moons, and asteroids like the ones we observe in our Solar System. However, protoplanetary disc structure varies amongst different systems. A good understanding of disc evolution and dynamics is required for a comprehensive view of planet formation. Recent observations have revealed that protoplanetary discs often exhibit cavities and azimuthal asymmetries such as dust traps and clumps. The presence of a stellar binary system in the inner disc regions has been proposed to explain the formation of these structures. In that case, the protoplanetary disc should be reclassified as circumbinary. Here, I study the dust and gas dynamics in circumbinary discs around eccentric and inclined binaries. This is done through two-fluid simulations of circumbinary discs, considering different values of the binary eccentricity and inclination. The simulations are made using phantom; a three-dimensional smoothed particle hydrodynamics code. I find that two kinds of dust structures can form in the disc: a single horseshoe-shaped clump, on top of a similar gaseous over-density; or numerous clumps, distributed along the inner disc rim. The latter features form through the complex interplay between the dust particles and the gaseous spirals caused by the binary. All these clumps survive between one and several tens of orbital periods at the feature location. I show that their evolution strongly depends on the gas–dust coupling and the binary parameters. Interestingly, these asymmetric features could in principle be used to infer or constrain the orbital parameters of a stellar companion — potentially unseen — inside the inner disc cavity. Finally, I apply these findings to the disc around AB Aurigae. The dusty clumps observed in this work suggest that circumbinary discs are promising places to form planetesimals and even planets, contrary to what was previously thought due to high relative velocity among solids.
Computer simulations of modern cosmic microwave background experiments, and an application to the Cosmology Large Angular Scale Surveyor.
(2019) Fluxá Rojas, Pedro Antonio; Dünner Planella, Rolando; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
The study of the Cosmic Microwave Background is one of the corner-stones in the understanding of our universe. In recent years, ground and space born telescope have evidence that the observable universe is well described by a relatively simple model, the ΛCDM model. Ongoing and future experiments aim at going even further than ΛCDM by probing the very first moments of our universe using CMB polarization. Within this polarization field lies a possible signature of inflation, the leading theory that explains why do we observe a flat, isotropic and homogeneous universe. This signal corresponds to primordial B-modes, and its faintness makes its detection a major technical challenge. In this work, we present computer simulations of the CLASS Q-band telescope, one of the four telescopes of the CLASS experiment aiming at characterizing, among other things, primordial B-modes and thus inflation. This work is divided in several chapters. The first two briefly introduce the reader to the general concepts of cosmology and the Cosmic Microwave Background (CMB). The third chapter describes the method used to model the polarizing properties of antennas. Chapter four presents the algorithm and prototype implementation of a new computer simulation code for CMB, which was used to build simulations of the CLASS experiment. Chapter five generally describes the CLASS telescope, and presents the methodology and results from electromagnetic simulations. This work finalizes by presenting the results of an application of the simulation code to CLASS using realistic parameters for its scanning strategy, beams and sky models.
Supersoft X-rays nebulae in the Large Magellanic Cloud.
(2019) Farías Hinojosa, Diego Andrés; Clocchiatti, Alejandro; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Supersoft X-rays binaries sources (SSSs) are said to be potential SN Ia progenitors. Surrounding these sources, due to X-rays emission of a steady-state accreting white dwarf (WD), there should be an associated [O III]λ5007 nebulae. If a SN Ia occurs at this SSS phase, these nebulae should be present in early images surrounding supernova remnants (SNRs). The aim of this work is to find these expected nebulae surrounding four SSSs, CAL 83, CAL 87, RX J0513.9-6751 and RX J0550.0-7151, and three SNRs, SNR 0509-67.5, SNR 0519.69.0 and SNR N103B, in the Large Magellanic Cloud (LMC). In order to do this, we obtain images from the Inamori Magellan Areal Camera and Spectrograph (IMACS) using a broadband Bessell V filter, and a narrowband [O III] filter, centered at ≈ 5007 ˚A. The images were processed by the pipeline PHOTPIPE, which does the astrometry, stacking and differencing of the images, the last step using the well-known HOTPANTS code. By measuring the flux around the coordinates of the source, we study the surface brightness profiles up to 25 pc of the diffuse nebula, to later compare them to the theoretical profiles made by the photoionization code CLOUDY. Our [O III] flux measurements for CAL 83 are consistent within 2σ with previous results (Remillard et al., 1995), probably due to systematic effects in our calibration technique. In spite of this quantitative difference we confirm that CAL 83 is the only SSS with an associated [O III] ionized region of the seven candidates. The [O III] luminosity for the other objects at 7.5 pc from the central source, are . 15% of that of CAL 83. CLOUDY models of the nebulae allow us to constrain physical conditions, such as the ISM density of the source. For typical SSS parameters e.g., luminosity between 1037 − 1037.5 erg/s and effective temperature of the order of 5 × 105 K, the density of the CAL 83 nebula at 7.5 pc is suspected to be slightly lower than, but still consistent with, the range of 4 − 10 cm−3 found by Remillard et al. (1995). For all the other regions, CLOUDY models indicate ISM densities unrealistically low to be consistent with the observed luminosity upper limits.
Stacking UV-selected Lyman-break galaxies in the ALMA frontier fields
(2019) Carvajal Pizarro, Rodrigo Alonso; Bauer, Franz Erik; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Los campos Frontier Fields (FF) ofrecen una ventana inusualmente profunda hacia el universo de alto corrimiento al rojo. Lo logran cubriendo un área sustancialmente más grande que el campo Hubble Ultra-Deep, que posee baja magnificación, sondeando 1–2 magnitudes más profundas en regiones con magnificaciones singularmente más altas. Este espacio de parámetros único, junto con excepcionales datos en múltiples longitudes de onda, permiten una mejor comprensión de las poblaciones de galaxias distantes. Se obtuvieron mosaicos en la banda 6 de ALMA (≈263GHz) en las porciones centrales de cinco campos FF para caracterizar las propiedades infrarrojas de 1821 Lyman-Break Galaxies (LBG), con corrimientos al rojo de z∼2–8, seleccionadas a través de observaciones en el ultravioleta. Investigamos flujos y excesos infrarrojos (IRX) tanto individuales como acumulados para la muestra de LBG en función de masas estelares, corrimientos al rojo, luminosidades ultravioleta y magnificaciones por lentes gravitacionales. Las muestras de LBG se han escogido con base en fotometría realizada con HST y confirmación fotométrica de corrimiento al rojo. Con plantillas de distribución espectral de energía (SED), obtenemos luminosidades, masas estelares y tasas de formación estelar para nuestros LBG. De las imágenes de ALMA, obtenemos flujos individuales y estimaciones de IRX así como valores medios de los cálculos acumulados en imágenes y visibilidades de ALMA. Tres LBG son detectados, individualmente, sobre un nivel de significancia de 4,1−σ, mientras las muestras acumuladas de los restantes LBG no entregan valores relevantes. Investigamos nuestras detecciones y límites superiores en el contexto de las relaciones entre IRX y masa estelar y entre IRX y la pendiente ultravioleta (β). Nuestros límites superiores ayudan a excluir grandes porciones del espacio de parámetros, lo que puede ser útil para modelización. En ciertos casos, nuestros límites son suficientemente profundos para crear una leve tensión con las, típicamente asumidas, relaciones de consenso en la literatura.
MUSE spectroscopy in dense stellar fields : a pilot study for VVV-CL001 cluster
(2020) Olivares Carvajal, Julio Ariel; Zoccali, Manuela; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
El Bulbo Galáctico es uno de los lugares más interesantes para estudiar debido a su gran concentración de estrellas viejas, por lo que su estudio nos ayuda a entender cómo fue la formación de la Galaxia. En nuestro esfuerzo para reconstruir la historia de formación estelar de la Vía Láctea, es esencial el estudio de la edad de sus estrellas, sin embargo, esta tarea es bastante difícil. Por ello, es que podemos usar la metalicidad de las estrellas, que se obtiene con menor dificultad, como otra forma de estimar la edad de las poblaciones estelares del bulbo. Es así como nos referimos a las estrellas pobres en metales como estrellas viejas, mientras que las estrellas ricas en metales serían estrellas jóvenes. Por otro lado, los cúmulos globulares generalmente tienen la misma edad, metalicidad y distancia, y además son trazadores de poblaciones estelares viejas, por lo que el estudio de los cúmulos globulares asociados al Bulbo Galáctico es crucial porque así obtenemos información confiable sobre esta región. En esta tesis, presentamos el primer estudio espectroscópico del nuevo cúmulo globular VVV-CL001 que se encuentra en dirección al Bulbo Galáctico. Se utilizó un nuevo método con espectros de baja resolución de MUSE para poder confirmar mediante cinemática y metalicidad la naturaleza del cúmulo CL001. Presentamos velocidades radiales, movimientos propios y metalicidades de 190 estrellas observadas en el campo de MUSE. Otro de los objetivos principales es estimar la distancia a CL001 para decidir a qué estructura de la Galaxia pertenece. Finalmente, aplicaremos el método utilizado en CL001 a un campo de MUSE observado en la región del bulbo interno para poder estudiar las velocidades radiales galactocéntricas y las metalicidades de estas estrellas. Se extrajeron espectros individuales de 190 estrellas en el campo del cúmulo VVV-CL001. También se derivaron velocidades radiales mediante correlación cruzada entre un espectro observado y un sintético. Las metalicidades se obtuvieron gracias al estudio de las variaciones del flujo pixel a pixel en el espectro observado comparado con el set de referencia proveniente del GES iDR3 usando The Cannon. Se asignaron movimientos propios y fotometría en el infrarrojo cercano a cada estrella del cúmulo haciendo un cruce de datos con el catálogo del VVV Survey. Se estimó la distancia a CL001 usando una estrella RR Lyrae encontrada en los surveys OGLE y VVV. Se estimó la órbita de CL001 con la distancia, la velocidad promedio y los movimientos propios absolutos del cúmulo usando galpy. Finalmente, las velocidades radiales galactocéntricas y las metalicidades de un campo del bulbo interior observado con MUSE fueron obtenidas gracias al mismo procedimiento que se utilizó para el cúmulo CL001. Derivamos la velocidad radial promedio del cúmulo RV = −336.5 ± 5.6 km s−1 usando las velocidades de 28 estrellas que son candidatas a ser parte del cúmulo, una de las velocidades más altas que se han encontrado en cúmulos de la Vía Láctea. Obtuvimos los movimientos propios de 25 estrellas en el cúmulo, confirmando que son miembros fidedignos de este. Obtuvimos la metalicidad promedio del cúmulo [Fe/H] = −1.92 ± 0.18 dex usando 28 miembros, esto quiere decir que su población es pobre en metales. También estimamos una distancia de D = 10.2 kpc a CL001, lo cual lo posicionaría más allá del centro galáctico. Con este resultado, estimamos la órbita de VVV-CL001 que lo clasificaría con mayor probabilidad como un cúmulo del halo. Por otro lado, derivamos resultados preliminares para el campo del bulbo observado con MUSE, obteniendo una distribución de velocidad galactocéntrica y una MDF que están de acuerdo con estudios previos en el bulbo interno.
Observational constraints in Delta Gravity : CMB and supernovas
(2020) San Martín Hormazábal, Marco; Alfaro Solís, Jorge Luis; Pontificia Universidad Católica de Chile. Facultad de Física
I study the cosmological implications of Delta Gravity (DG), which is a gravitational model based on the extension of General Relativity (GR) by a new symmetry called δ ̃. In this model, new matter fields are added to the original matter fields, motivated by the additional symmetry. We call them δ ̃ matter fields. This theory predicts an accelerating Universe without introducing a Cosmological Constant Λ by hand in the equations. To test the Delta Gravity implications, I examine two critical observations in Cosmology: the rate of the Universe expansion through type Ia supernovae (SNe-Ia) and the power spectrum calculated from the cosmic microwave background radiation (CMB). To compare the observations with these model's predictions, I used a Markov Chain Monte Carlo (MCMC) analysis with the most updated SNe-Ia and Planck satellite data catalog. I obtain the fitted parameters needed to explain both SNe-Ia data and CMB measurements. I analyze the DG model's compatibility with both observations and constrain the cosmological parameters associated with the astrophysical evidence. Finally, I discuss if the Hubble Constant and the Accelerating Universe are compatible with the DG context's observational evidence.
New constraints for the initial-to-final mass relation of white dwarfs
(2020) Barrientos Laurence, Manuel Hernán; Chanamé, Julio; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
We present observational constraints for the initial-to-final mass relation (IFMR) derived from 11 white dwarfs (WDs) in wide binaries (WBs) that contain a turnoff/subgiant primary. Because the components of old-enough WBs are coeval to a good approximation, the age of the WD progenitor (and hence its mass) can be determined from the study of its wide companion. However, previous works that used wide binaries to constrain the IFMR suffered from large uncertainties in the initial masses because their MS primaries are difficult to age-date with good precision. Our more careful selection of wide binaries with evolved primaries avoids this problem by restricting to a region of parameter space where isochrone ages are significantly easier to determine with precision. We selected a sample of wide binary systems with adequate characteristics for our program by matching existing catalogs of WDs with the Gaia astrometric surveys. Having introduced the use of wide subgiant-WD binaries, the study of the IFMR of WDs is not limited anymore by the precision in initial mass, but now the pressure is on final mass, i.e., the mass of the WD today. Our results indicate a non-negligible spread in WD final masses within this initial-mass range. As already noted, improved determinations of the masses of the WDs in this regime would be important for settling this question.
Fast Radio Bursts : constraining possible astrophysical scenarios from a particle acceleration model
(2020) Zepeda González, Felipe; Reisenegger, Andreas; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Fast Radio Bursts (FRBs) are bright millisecond-long radio flashes that imply strong electromagnetic waves in their vicinity. We analyzed the acceleration experienced by particles under such intense fields, and we obtained that they will quickly become relativistic and move in the direction of the incident wave. In this process, the particles periodically reach a high Lorentz factor, which remains valid up to the radial distance r_f \sim 3 \times 10^{10} {\rm cm} \, (m/m_p)^{-1} L_{42}^{1/2} \nu_9^{-1}. We analyzed the possible formation of a charge separation region due to the different r_f of protons and electrons, and then we argued about the possible disruption of the electron acceleration process at r> r_f. We also analyzed the incoherent and coherent radiation processes experienced by the accelerating particles and concluded that the coherent radiation can substantially disperse the energy of the incident wave if the emission mechanism of the FRB is activated at r < r_{f,p^+}. Based on this, our model disfavours mechanisms in which the FRB is emitted from within the magnetosphere of a NS or magnetar as a progenitor scenario. Although the model was applied to FRBs, it is applicable to other FRB-like phenomena. We propose to extend our analysis by self-consistently solving the Maxwell equations and the equations of motion for the plasma.
Characterizing the Fe K-a line variability in a large sample of AGN
(2020) Andonie Bahamondes, Carolina Paz; Bauer, Franz Erik; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Varios Nucleos Activos de Galaxias (AGN) han mostrado variabilidad en su emisión en rayos X, en particular en el continuo entre 2-10 keV y en la línea de emisión de Hierro en 6.4 keV (Fe K-a). La línea Fe K-a es una característica obicua en el espectro de los AGN y es producida por procesos de reflección entre el continuo y la materia neutra que rodea el Agujero Negro Supermasivo (SMBH) que se encuentra en el centro del AGN. Varios estudios han constreñido la ubicación y el tamaño de las nubes reflectantes en algunos AGN estudiando la reacción de la línea a variaciones del continuo. En estre trabajo, constreñimos la relación entre la línea Fe K-a y el continuo para 19 fuentes, usando datos de los observatorios Chandra y XMM-Newton. Encontramos diferentes comportamientos, los cuales se pueden clasificar en 3 casos. Primero, en algunos AGN el flujo de la línea está dominado por nubes reflectantes ubicadas cerca de la corona de rayos X, como en el disco de acreción o la región de líneas anchas, por lo que la línea reacciona rápido frente a variaciones del continuum en las escalas de tiempo de las observaciones. Para estas fuentes, proporcionamos un límite superior para la región reflectiva. Segundo, en otros casos, la línea Fe K-a reacciona levemente frente a las variaciones del continuo, por lo que los flujos no están correlados, sugiriendo que las nubes reflectantes están localizadas mucho más lejos de la corona, como en el toro polvoriento. El último y tercer caso, son AGN que muestran variabilidad en el continuo y en la línea, pero los flujos no están correlacionados, indicando un escenario más complejo. Encontramos una leve correlación entre la relación Fe K-a-continuo y la masa del SMBH, indicando que a mayores masas las nubes reflectantes estarían ubicadas más cerca de la corona de rayos X. Para complementar los resultados espectrales, analizamos las imágenes de las observaciones de Chandra para ver si la emisión Fe K-a es extendida espacialmente. Encontramos que 14/15 fuentes analizadas son consistentes con una fuente puntual, para las cuales pudimos entregar un límite superior de la región reflectante emitiendo fotones Fe K-a, equivalente a la resolución espacial de Chandra (1.21 hasta 1419 pc).
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.
Identificando los mejores candidatos para la detección indirecta de materia oscura entre galaxias enanas esferoidales.
(2020) Calderón Galaz, César Jorge; Padilla, Nelson; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
La materia oscura (DM), cuya naturaleza y mecanismos de interacción son todavía un tema abierto, constituye alrededor del 25 % de la densidad de energía del Universo. Las partículas masivas de débil interacción (WIMPs) son consideradas como fuertes candidatos para las partículas DM. Su búsqueda, se lleva a cabo convenientemente a través de la detección de rayos gamma. Las galaxias enanas esferoidales (dSphs) clásicas o ultradébiles , ubicadas en las cercanías de la Galaxia, exhiben altos valores de la relación masa luminosidad, y por lo tanto se consideran objetos dominados por materia oscura. Estos objetos están al alcance del Cherenkov Telescope Array (CTA), que es el proyecto de astronomía de rayos gamma que llegará en esta década, con una mejor sensibilidad (un orden de magnitud) con respecto a los experimentos de la generación actual. El principal objetivo de este trabajo es sugerir posibles candidatos para el estudio con CTA, considerando sus respectivas incertezas. Para ello se obtuvo el J-factor de 5 distintas galaxias enanas, de modo de comprender cual de estas galaxias presenta los mayores valores, considerando que el J-factor nos dice la cantidad de materia oscura existente en una determinada región del espacio integrado a lo largo de la línea de visión. Para obtener este valor, es necesario realizar un análisis de Jeans, con los datos cinemáticos de cada galaxia, en donde encontramos carencia de datos en algunas de ellas, lo que imposibilita a obtener valores confiables para determinar un J-factor robusto. Se fija una cota inferior de 150 estrellas para obtener valores confiables de una galaxia esferoidal, este resultado se obtuvo del análisis de galaxias clásicas con una gran muestra de datos cinemáticos, de las cuales extrajimos datasets más pequeños simulando galaxias con menores datos estadísticos. El análisis de Jeans realizado, contempló el uso del método MCMC para obtener los parámetros de los perfiles de densidad de materia oscura para cada dSph. Finalmente, se denomina a la galaxia Sculptor como un excelente candidato para el estudio de una posible señal de rayos gamma con CTA, debido a su alto valor de J-factor y su poca incerteza en la medición, log J(α0,5) = 18,8 ± 0,1 [GeV2 cm −5 ]. Sin embargo, se deja la invitación a estudiar con más detalle la cinemática de las galaxias ultra-débiles como Triangulum II, quien presenta el J-factor más elevado, log J(α0,5) = 21,8±0,5 [GeV2 cm −5 ], pero con una gran incerteza en su medición, ya que consideramos que estas galaxias pueden ser la clave para comprender la naturaleza de la materia oscura en un futuro no muy lejano.
Merger tree comparison : impact on the semi-analytic model GALFORM
(2020) Gómez, Jonathan; Padilla, Nelson; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Many previous studies using semi-analytic models have focused predominantly on improving the phenomenological prescriptions of the baryonic physics governing galaxy formation as the vast uncertainties in these processes are critical in understanding the observable Universe. On the other hand, studies dedicated to "the dark universe" imply that technical issues concerning dark matter (DM) halo merger trees can also impose other uncertainties when modeling the observable universe. We examine the effect of using four different merger tree building algorithms, SUBFIND, HBT, ROCKSTAR and VELOCIraptor, on galaxy properties using the semi-analytic model of galaxy formation and evolution GALFORM with fixed model parameters, run on the EAGLE simulation in its dark matter only version. The construction of each Halo Finder causes some to be able to find some haloes that other finders do not and vice versa affecting the total number of haloes that are found. The differences in definitions or limits to distinguish the satellite and central haloes present in the Halo Finders, produce haloes which are found in two different halo catalogs with different central/satellite classification which impacts the way in which the galaxies that reside in these haloes evolve as, by construction in GALFORM, central galaxies retain their hot gas whereas satellite galaxies do not. The results of GALFORM show that the number of central and type 1 satellite galaxies (those that are hosted by a dark matter satellite subhalo) depend directly on the halo finder and its definition for central and satellite subhalo, which results in the ROCKSTAR run having a slight excess of galaxies. In contrast the number of type 2 satellite galaxies, i.e. galaxies that are not hosted by a resolved dark matter subhalo also called orphan galaxies, depends strongly on the tree builder. The number of type 2 satellite galaxies (orphans) resulting from the VELOCIraptor run is up to ∼ 2x higher than HBT, ROCKSTAR and SUBFIND, in agreement with the excess of merged dark matter satellite subhalo progenitors of VELOCIraptor; but these are only a small fraction of the galaxy population. When matching individual GALFORM galaxies in the four finders we find that the hot gas mass MHot Gas, cold gas mass MCold Gas and instantaneous star formation rates are significantly affected by the satellite and central subhalo type. When we have a central subhalo that has a satellite subhalo as its counterpart, the satellite galaxy has MHot Gas= 0 by definition and, consequently, lower MCold Gas and instantaneous SFR for MStellar< 108h −1M than the central that it is matched to, independently of the halo finder algorithm. However, when comparing matched centrals and matched satellites, their average properties agree between the outputs from the different finders. Even though the scatter can be quite high, we find that the distributions of different baryon properties do not vary significantly between the different runs, even including orphan galaxies. Overall, the run with the strongest differences in the stellar mass function is that with HBT which contains ∼ 30% less galaxies, while in the other runs the match is excellent. Another discrepancy is that GALFORM run on VELOCIraptor is accompanied by higher star formation rate density and smaller sizes. However, in all cases the amplitude of these differences is small and insufficient to make an impact on any comparison to observational properties. The reason behind the small impact of the choice of finder lies in the homogenising effect of GALFORM in the merger trees, which ensures a small uncertainty on the model results coming from the dark matter halo finding procedure.Many previous studies using semi-analytic models have focused predominantly on improving the phenomenological prescriptions of the baryonic physics governing galaxy formation as the vast uncertainties in these processes are critical in understanding the observable Universe. On the other hand, studies dedicated to "the dark universe" imply that technical issues concerning dark matter (DM) halo merger trees can also impose other uncertainties when modeling the observable universe. We examine the effect of using four different merger tree building algorithms, SUBFIND, HBT, ROCKSTAR and VELOCIraptor, on galaxy properties using the semi-analytic model of galaxy formation and evolution GALFORM with fixed model parameters, run on the EAGLE simulation in its dark matter only version. The construction of each Halo Finder causes some to be able to find some haloes that other finders do not and vice versa affecting the total number of haloes that are found. The differences in definitions or limits to distinguish the satellite and central haloes present in the Halo Finders, produce haloes which are found in two different halo catalogs with different central/satellite classification which impacts the way in which the galaxies that reside in these haloes evolve as, by construction in GALFORM, central galaxies retain their hot gas whereas satellite galaxies do not. The results of GALFORM show that the number of central and type 1 satellite galaxies (those that are hosted by a dark matter satellite subhalo) depend directly on the halo finder and its definition for central and satellite subhalo, which results in the ROCKSTAR run having a slight excess of galaxies. In contrast the number of type 2 satellite galaxies, i.e. galaxies that are not hosted by a resolved dark matter subhalo also called orphan galaxies, depends strongly on the tree builder. The number of type 2 satellite galaxies (orphans) resulting from the VELOCIraptor run is up to ∼ 2x higher than HBT, ROCKSTAR and SUBFIND, in agreement with the excess of merged dark matter satellite subhalo progenitors of VELOCIraptor; but these are only a small fraction of the galaxy population. When matching individual GALFORM galaxies in the four finders we find that the hot gas mass MHot Gas, cold gas mass MCold Gas and instantaneous star formation rates are significantly affected by the satellite and central subhalo type. When we have a central subhalo that has a satellite subhalo as its counterpart, the satellite galaxy has MHot Gas= 0 by definition and, consequently, lower MCold Gas and instantaneous SFR for MStellar< 108h −1M than the central that it is matched to, independently of the halo finder algorithm. However, when comparing matched centrals and matched satellites, their average properties agree between the outputs from the different finders. Even though the scatter can be quite high, we find that the distributions of different baryon properties do not vary significantly between the different runs, even including orphan galaxies. Overall, the run with the strongest differences in the stellar mass function is that with HBT which contains ∼ 30% less galaxies, while in the other runs the match is excellent. Another discrepancy is that GALFORM run on VELOCIraptor is accompanied by higher star formation rate density and smaller sizes. However, in all cases the amplitude of these differences is small and insufficient to make an impact on any comparison to observational properties. The reason behind the small impact of the choice of finder lies in the homogenising effect of GALFORM in the merger trees, which ensures a small uncertainty on the model results coming from the dark matter halo finding procedure.
The complex gaseous and stellar environments of the nearby dual active galactic nucleus Mrk 739 as unveiled by optical VLT/MUSE observations
(2021) Tubín Arenas, Dusán Mile; Treister, Ezequiel; Pontificia Universidad Católica de Chile. Instituto de Astrofísica
Dual active galactic nuclei (Dual AGN) represent a critical stage in a major galaxy merger (M/m <3), where both supermassive black holes (SMBHs) are rapidly accreting. Studying these systems can yield valuable insights into the physical processes that affect galaxy evolution, both in terms of nuclear activity and galactic collisions. In this context, we present integral field spectroscopic (IFS) observations of the nearby (z∼0.03) dual AGN Mrk 739, whose projected nuclear separation is∼3.4 kpc, obtained with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). We find that the galaxy has an extended AGN-ionized emission-line region extending up to ∼20 kpc away from the nuclei, while star-forming regions are more centrally concentrated within 2-3 kpc. We model the kinematics of the ionized gas surrounding the eastern nucleus using a circular disk profile, resulting in a peak velocity of 237+26−28km s−1at a distance of ∼1.2 kpc. The enclosed dynamical mass within 1.2 kpc is log M(M) = 10.20±0.06, ∼1,000 times larger than the estimated supermassive black hole (SMBH) mass of Mrk739E. The morphology and dynamics of the dual AGN Mrk 739 are consistent with an early stage of the collision, where the foreground galaxy (Mrk 739W) is a young star-forming galaxy in an ongoing first passage with its background companion (Mrk739E). Since Mrk 739W’s AGN does not show evidence of being actively accreting as its companion, we claim that the gas of the northern spiral arms of Mrk 739W are cross-ionized by the nuclear activity of Mrk 739E. The subsequent MUSE Narrow Field Mode (NFM) analysis reveals an unprecedented spatial resolution for Mrk 739E, where star-forming clumps, traced by Hα emission, form a ring-like structure inside a rotating disk. These star-forming clouds are surrounding an active SMBH at the center of an elliptical galaxy undergoing a merger process with a young spiral galaxy. Kinematically, we note that the disk is rotating with a velocity of Vmed,rot= 280.5±32.7 km s−1,∼50 km s−1larger than the velocity derived from the WFM analysis. The flux distribution of the NFM data reveal Hα clouds that also belong to Mrk 739W. Based on our schematic representation of the merger process, this emission would be part of the north side of the Mrk 739W’sbar and the beginning of the leading arm that gives origin to the large-scale spiraling crest.

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