University of Oulu

Study of the morphological features in the Spitzer Survey of Stellar Structure in Galaxies (S4G)

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Author: Herrera Endoqui, Martín1
Organizations: 1University of Oulu, Faculty of Science, Astronomy
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 7.9 MB)
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Language: English
Published: 2016
Publish Date: 2016-09-19
Thesis type: Doctoral Dissertation
Defence Note: Academic dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in the Auditorium GO101, on September 23rd, 2016, at 12 o’clock noon.
Tutor: Doctor Eija Laurikainen
Professor Heikki Salo
Reviewer: Doctor Irene A. Cruz-González Espinosa
Doctor J. Alfonso López Aguerri
Opponent: Doctor Isabel Pérez Martín
Kustos: Professor Heikki Salo


Conspicuous morphological features such as rings, ringlenses, lenses, barlenses, and spiral arms are observed in many nearby disk galaxies. These features are believed to form due to the so-called secular evolution after the galaxies were formed, which means that their disks evolve in a more passive fashion and in longer timescales, compared to their formation processes. This slow evolution of disks is due to the effect of non-axisymmetric potentials, among which, a bar potential is perhaps the most effective of all. Strong rotating bars redistribute angular momentum and material through the disks of galaxies very effciently, and produce resonances. At these resonances the material is trapped and starts forming stars, creating beautiful rings. However, rings are not the only structure observed in disk galaxies. There are also spiral arms that, might or might not be created by bars. Other type of structures are lenses, which in images appear as flat light distributions with sharp edges, and ringlenses, whose appearance is intermediate between those of rings and lenses. Also, there are barlenses, which are conspicuous lens-like structures embedded in bars, and have been suggested to be the more face-on counterparts of Boxy/Peanut/X-shaped bulges. The study of the physical properties of all these structures provides a tool to investigate the mechanisms that create them and hence, to determine which are the processes that drive the slow evolution of galaxies.

In this thesis I study the morphological structures using mainly data from the Spitzer Survey of Stellar Structure in Galaxies (S4G), by means of their sizes, orientations, shapes and colors. The S4G contains images of ~ 2500 nearby galaxies of all Hubble types at 3.6 and 4.5 μm, allowing a dust free view of the old stellar population which is subject of the secular evolution.

Among the results presented in this thesis and the respective companion papers are the following. A catalog that contains the sizes, ellipticities and position angles of the morphological features in the S4G was created. This catalog also includes the measurements of the pitch angles of spiral arms. There is a corroboration of previous results showing that different types of morphological features appear in galaxies with different Hubble stages and bar families, and a confirmation of the resonant nature of rings but also of a high fraction of lenses and ringlenses. There is also an observation indicating that low mass galaxies lack nuclear structures such as nuclear rings due to the lack of inner Lindblad resonances caused by their low central mass concentrations. Observational evidence is presented indicating that a fraction of inner lenses in unbarred galaxies might be former barlenses of which the "thin bar" has probably dissolved or it is too faint to be detected.

The sizes of barlenses show a tight linear correlation with those of bars, being the size of the barlens typically half the size of the bar. The study of the optical colors of barlenses reveals their similarity with bars, giving observational evidence that their stellar populations are similar, and distinguishes them from disks and nuclear regions. The orientations of barlenses with respect to that of bars and disks reveal that barlenses are vertically thick structures. All these results support the idea that barlenses are the vertically thick inner parts of bars and hence relate them observationally to Boxy/Peanut/X-shaped bulges.

These results and others are published in a series of original papers in which I have collaborated and that are appended at the end of this work.

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Series: Report series in physical sciences
ISSN: 1239-4327
ISSN-L: 1239-4327
ISBN: 978-952-62-1323-1
ISBN Print: 978-952-62-1322-4
Issue: 103
Copyright information: This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.