Ignacio del Moral-Castro
The majority of galaxies, including our Milky Way, have a supermassive black hole (SMBH) at their centre. These SMBHs have masses of millions to billions of times the mass of the Sun and a basic influence on the evolution of their host galaxies. In some cases, the black hole is ingesting the material surrounding it at a very high rate, emitting a large quantity of energy. In those cases we say that the galaxy has an active nucleus (AGN).
Studying the mechanisms which control the relation between the active nucleus and the rest of the galaxy is necessary to understand how these objects form and evolve, and to be able to throw light on this question we need to compare active and non-active galaxies. Previously, in the majority of studies the procedure used was the identification of a sample of active galaxies within a large survey, which were then compared to the rest of the galaxies in the survey having similar properties which do not show nuclear activity. However, here, we used a different method: we performed one-to-one comparisons. Firstly, we identified active spiral galaxies and for each of them we looked for a non-active galaxy which had equivalent global properties, i.e. with the same mass, brightness, orientation and so on, and very similar in appearance. We study galaxies which are almost twin, but with the difference being nuclear activity.
In this work, we make comparisons between the discs of several pairs of spiral galaxies (active and non-active). We conclude that in the discs of the former the rotational motion of the stars is of greater importance and put forward two scenarios to explain these dynamical differences. This result represents the first evidence of galaxy-scale differences between the dynamics of active and non-active spiral galaxies.
This poster shows part of my PHD thesis on nuclear activity in spiral galaxies. Nowadays, it is thought that all galaxies are active in some part of their evolution and this nuclear activity has a basic importance in their evolution. The main idea of my thesis is centred on comparison of isolated spiral galaxies which are almost twin, but with difference in the nuclear activity. In this way, we can identify the mechanisms which control the relation between the active nucleus and the rest of the galaxy
Slide 1 → Introduction
Observational evidences indicate that the majority of galaxies contain a supermassive black hole (SMBH) located at the galaxy's centre. In addition, they suggest that there is a co-evolution between the SMBHs and their host galaxies. Therefore, these SMBHs could regulate many of the most important properties such as mass or star formation of the galaxy.
In some galaxies, the SMBH is accreting the material surrounding it at a very high rate, emitting a large quantity of energy. In those cases, we say that the galaxy has an active nucleus (AGN). AGN are now understood as a short and likely episodic phase of galaxy evolution.
Slide 2 → Data
In my thesis, we use integral field spectroscopy (IFS) data. The traditional astronomical spectroscopy gives a single spectrum for the source that is being observed. However, using IFS three dimensional information is obtained. That is to say, we can get a spectrum for each spatial pixel and study the spatially resolved spectroscopic properties of galaxies. Specifically, in this work we use data from the CALIFA Survey (Calar Alto Legacy Integral Field Area). This survey contains IFS data for more than 600 galaxies in the Local Universe, taken at the Calar Alto Observatory in Almería.
Slide 3 → Methods
In the majority of previous studies the procedure used was the identification of a sample of active galaxies within a large survey, using different diagnostic diagrams (BPT diagram), which were then compared to the rest of the galaxies in the survey which do not show nuclear activity. However, in my thesis we develop a novel method: we performed one-to-one comparisons. For each isolated spiral active galaxy we look for a non-active one matched in global properties, i.e. with the same mass, brightness, orientation and so on, and very similar in appearance. Comparing these pairs of twin galaxies we can identify unique properties of active galaxies.
Slide 4 → Results
We assess the rotational support of the galaxies using the dimensionless lambda_Rspin parameter. This parameter is normalised and goes to unity when rotation dominates. We find that ~80 of the active galaxies show higher values than their corresponding non-active twins. That is to say, the active galaxies have larger rotational support. This result represents the first evidence of galaxy-scale differences between the dynamics of active and non-active spiral galaxies in the Local Universe.
Finding these kind of galaxy-scale differences appears puzzling because AGN are now understood as a short and likely episodic phase of galaxy evolution. However, this could then imply that not every galaxy goes through an active fase, at least in the redshift and mass range considered here.
More information and details in :
-) del Moral-Castro, I., et al. 2019, MNRAS, 485, 3794
-) del Moral-Castro, I., et al. 2020, A&A,639, L9
Press release:
https://www.iac.es/en/outreach/news/differences-between-discs-active-and-non-active-galaxies-detected-first-time