A new perspective on the evolution of galaxies : from global to local scales
Author
Casado Gómez, JavierEntity
UAM. Departamento de Física TeóricaDate
2016-11-24Subjects
Galaxias - Tesis doctorales; FísicaNote
Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de lectura: 24-11-2016Esta obra está bajo una licencia de Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 Internacional.
Abstract
This thesis dissertation addresses the topic of galaxy formation and evolution with the
main purpose of shedding some light on the main mechanism(s) responsible for the selfregulation
of the star formation activity in the nearby Universe.
As a first step, we revisit the classic “nature or nurture” debate in this context by using
a sample of 82000 objects extracted from the Sloan Digital Sky Survey. Our analysis crosscorrelates
two proxies of the specific star formation rate, the equivalent width (EW) of the
H line and the (u-r) colour, with other physical properties (mass, metallicity, environment,
morphology, and the presence of close companions) leading to the discovery of a relatively
tight “ageing sequence” in the colour–EW plane. This trend favours a scenario where the
secular conversion of gas into stars (i.e. nature) is the main physical driver of star formation
and the gradual transition from a “chemically primitive” (metal-poor and intensely starforming)
state to a “chemically evolved” (metal-rich and passively-evolving) system.
To address the dependence on local and global properties, we investigate in further
detail the resolved colour-EW diagram of 40 matching objects from the CALIFA survey.
The IFS data reveal that the smooth “ageing” process always takes place, inside-out (i.e. the
central parts are more evolved than the outskirts), across the entire extent of all galaxies.
The current state of the different regions seems to be mostly driven by local processes, albeit
global properties (in particular, galaxy morphology) may play an important role.
The analysis of low signal-to-noise (S/N) measurements was critical in order to reach
these conclusions. To make an optimal use of this valuable information, we developed the
Bayesian Technique for Multi-image Analysis (BaTMAn) algorithm for the segmentation of
multidimensional data, with emphasis on the statistically-meaningful binning of IFS observations.
When applied to our dataset, the method significantly reduces the scatter in the
colour-EW diagram, convincingly demonstrating that there may be different ageing paths
depending on the details of the local star formation history.
In our view, the new generation of IFS surveys calls for new analysis tools and methodologies,
and a rigorous assessment of their accuracy (and that of the associated errors!)
requires a battery of realistic test cases where the correct solution is known. The final part
of this thesis describes the production of synthetic IFS observations, with similar characteristics
to the CALIFA products, based on hydrodynamical simulations. This ongoing project
will allow us to explore the optimal strategy to study galaxy ageing from current and forthcoming
IFS data, and it will provide the scientific community with a powerful tool to test
their analysis pipelines.
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Google Scholar:Casado Gómez, Javier
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