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Differences found between disks from active and inactive galaxies

Spiral galaxy

A study led by researchers from the Canary Institute of Astrophysics (IAC), comparing the disks of several pairs of spiral galaxies, active and inactive, concludes that in the disks of the previous rotation of stars is more important. This study, just accepted for publication in Letters on astronomy and astrophysics, is the first evidence of large-scale dynamic differences between active and inactive galaxies in the local universe. The participating astronomers are from the Institute of Astrophysics of the Canary Islands (IAC) and the University of La Laguna (ULL); as well as NatiAstronomical First: Discovered differences between the disks of an active and inactive galaxyseasonal autonomous university in Mexico (UNAM), the Madrid University of Competences (UCM) and the Instituto de Astrofísica de Andalucia (IAA).

There is already evidence that supermassive black holes in the centers of most galaxies have a major influence on their evolution. In some of them Black hole absorbs the material around it at a very high speed, emitting a large amount of energy. In these cases, we say that the galaxy has an active kernel (AGN). The material that powers the AGN must initially be quite far from the nucleus, in the disk of the galaxy revolving around its center. This gas must be “braked”

; in one way or another to enter the central zone, a process known as angular momentum loss.

Active IUD compared to inactive twin

Image illustrating the comparison between an active spiral galaxy (orange box) and its inactive twin (blue box). Credit: Gabriel Perez Diaz, SMM (IAC)

“Studying the mechanisms that control the relationship between the active core and the rest of the galaxy,” explains Ignacio del Moral Castro, a doctoral student at the IAC and the University of La Laguna (ULL) and first author of the article, “is needed to understand how these objects are forming and evolving, and in order to shed light on this question, we must compare active and inactive galaxies. To this end, the main idea of ​​my doctoral thesis is focused on the study and comparison of galaxies that are almost twins, but with the difference is nuclear activity. “

The work consists in comparing the dynamics of the galactic disks of different active / inactive pairs. The researchers used data from Caliph study (Calar Alto Legacy Integral Field Area). It contains spectroscopic data on complete 2D fields for more than 600 galaxies made at the Calar Alto Observatory in Almeria, which allows observations of almost the entire galaxy to be able to study its global characteristics.

The new methodology

Previously, in most studies, the procedure used was to identify a sample of active galaxies in a large study, which were then compared to the other galaxies in the study that have similar properties that do not show nuclear activity. This time, however, the researchers used a new method: they made one-to-one comparisons. First, they identified active spiral galaxies in the CALIFA sample and looked for an inactive galaxy for each of them that has equivalent global properties, i. with the same mass, brightness, orientation and so on and very similar in appearance.

Using this method, the team presented two scenarios to explain the dynamic differences between active and inactive galaxies. First, the explanation would be that this is a trace of the transmission of the angular momentum between the gas falling in the center and the material remaining in the disk. The second attributes the difference in gas flow from the outside by capturing small nearby satellite galaxies, in which case this capture must occur more frequently in active galaxies. Both scenarios are compatible with this result and are not mutually exclusive.

“The result surprised us; we really did not expect to find this type of differences on a large scale, as the duration of the active phase is very short compared to the life of the galaxy and the time required to obtain morphological and dynamic changes. says Begonia Garcia Lorenzo, an IAC researcher and co-author of the article.

“Until now, we thought that all galaxies went through active phases in their lives, but this result may mean that this is not the case, which would lead to a major change in current models,” added Christina Ramos Almeida, also an IAC researcher and co-author. of the article.

reference: “Bigger λR in the disk of isolated active spiral galaxies than in their inactive twins. “ from I. del Moral-Castro, B. García-Lorenzo, C. Ramos Almeida, T. Ruiz-Lara, J. Falcón-Barroso, SF Sánchez, P. Sánchez-Blázquez, I. Márquez and J. Masegosa, 14 July 2020 , Astronomy and astrophysics letters,,
DOI: 10.1051 / 0004-6361 / 202038091
arXiv: 2006.12654

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