Dinámica de agujeros negros supermasivos

Abstract

Black holes are one of the most intriguing objects that astrophysics is capable of studying, but they are not easy to detect. It is necessary for them to be surrounded by an accretion disk in order for us to observe them. Each galaxy has a central supermassive black hole with a mass on the order of several million times that of the Sun. When it starts accreting matter, it becomes an Active Galactic Nucleus (AGN), which is classified based on its activity type such as quasars, Seyfert galaxies, LINERs, and so on. In this project, we will analyze a population of AGN galaxies that exhibit a continuum energy distribution dominated by the emission from the accretion disk surrounding the central supermassive black hole. The objective is to find a direct relationship between the mass of a black hole and the temperature of the surrounding accretion disk. To establish the desired relationship, the emission of coronal lines [Si VI] and [Ne V] in these galaxies will be studied, and they will be normalized by dividing their fluxes by the broad and narrow components of Brγ. Once these ratios are obtained, they will be compared with the mass of the central black hole in the galaxies to observe the trend they describe. The initial starting point is the publication by Prieto (2022), which we will aims to continue their research and expand it with a new population of galaxies, as well as with new relationships that were inconclusive in that work. The data for the new galaxies is obtained from the PARSEC project, taken with adaptive optics and in very high spatial resolution. Once the list of galaxies is obtained, the Seyfert nuclear activity classification will be searched to exclude those that do not meet the desired criteria. A data screening process is also necessary, where galaxies with high levels of noise near the target lines will be eliminated, as well as those where the flux measurements are unclear. All the data, including MBH, [Si VI], [Ne V], Brγbroad and Brγnarrow fluxes, and Seyfert classification of each galaxy, will be compiled into a single table. From this table, the values will be extracted and used to determine the desired relationships. The first relationship obtained in this study is the one found by Prieto (2022), which relates MBH and the [Si VI]/Brγbroad ratio in the galaxies of that publication. The goal is to validate the dual trend observed in their results by adding the rest of the galaxies and creating another graph for comparison. In the published study, they obtained a Pearson coefficient of -0.76, while our study yields a coefficient of -0.71, resulting in a slightly lower but equally consistent data correlation. Furthermore, by adding the new galaxies, the dual trend in the results is still maintained. This study does not provide an explanation for the differentiation between the two groups of galaxies. 2 To continue, the normalizing factor for [Si VI] has been changed to Brγnarrow, and the wanted relationship has been explored in the same manner as before. This change was made because the research on which this study is based proposed the narrow component of Brγ as a potential improvement for the relationship between black hole mass and [Si VI]. This is due to the coinciding formation region of these lines, which is not the case for Brγbroad. For this relationship, a correlation coefficient of -0.38 was obtained, significantly lower than when we use the broad component. This discrepancy could be attributed to the possibility that some of the emission from Brγnarrow may be contaminated by circumnuclear star-forming regions that emit in this spectral line. The next coronal line used in this study is [Ne V], and although it doesn't have the same high ionization potential as [Si VI]. It was chosen because it has an advantage over the other: all the detectable [Ne V] emission will be in the form of gas and will be observable in the spectrum, while with [Si VI], some of the emission will be blocked due to being in a solid form as a metal. In the relationship between MBH and the flux of [Ne V] normalized to Brγbroad, a correlation coefficient of -0.61 is obtained, which is quite consistent, similar to the correlation observed with the [Si VI] coronal line. When plotting these results, three galaxies were identified that did not follow the general trend of the rest. These outliers were marked and not considered in the regression analysis of the most galaxies. Further study of these galaxies and the inclusion of more data points will be necessary to understand how this trend is modified. Finally, the last relationship obtained is the trend of [Ne V] flux normalized to Brγnarrow with MBH, resulting in two distinct trends again, with correlation coefficients of -0.84 and -0.78. Studying these two groups of galaxies, no definitive factor causing this significant differentiation between them has been identified. A potential solution for finding an explanation is to review the spectra of the [Ne V] flux in these galaxies and see if any data points exhibit high levels of noise. Further analysis in this direction may provide insights into the observed discrepancy. In conclusion, the objectives initially set for this study have been achieved. It has successfully contributed additional results to the research published by Prieto (2022) and discussed the findings presented therein. Trends have been established between each of the proposed data relationships, some showing stronger correlations than others, but all of them consistent with an unique trend: an increase of the temperature of the accretion disc with decreasing MBH. This confirmation is evidenced by observing that each of the obtained trends has a negative slope. Thanks to this study, we have been able to gain a broader understanding of one of the least known objects in the astrophysical landscape: black holes. Also, with this work we are contributing to enlarge a bit the understanding of the accretion disc and its black hole at its center in the scientific community.