University of Oulu

Signatures of secular evolution in disk galaxies

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Author: Díaz García, Simón1
Organizations: 1University of Oulu, Faculty of Science, Astronomy
Format: ebook
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 5.9 MB)
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Language: English
Published: 2016
Publish Date: 2016-09-16
Thesis type: Doctoral Dissertation
Defence Note: Academic dissertation to be presented with the assent of the Doctoral Training Committee for Technology and Natural Sciences of the University of Oulu for public discussion in the Auditorium L10, Linnanmaa, on September 30th, 2016, at 12 o’clock noon.
Tutor: Professor Heikki Salo
Doctor Eija Laurikainen
Reviewer: Professor Heikki Salo
Doctor Eija Laurikainen
Opponent: Professor Marc A. W. Verheijen
Kustos: Professor Heikki Salo


In this thesis we shed light on the formation and evolution of disk galaxies, which often host a stellar bar (about 2/3 of cases). In particular, we address the bar-driven secular evolution, that is, the steady redistribution of stellar and gaseous material through the disk induced by the bar torques and resonances. We characterize the mass distribution of the disks in the Spitzer Survey of Stellar Structure in Galaxies (S4G, Sheth et al. 2010) and study the properties of the different stellar structure components and the interplay between them.

We use 3.6µm photometry for ~ 1300 face-on and moderately inclined disk galaxies to analyze the frequency, dimensions, orientations and shapes of stellar bars, spiral arms, rings, (ring)lenses, and barlenses (i.e. lens-like structures embedded in the bars). We calculate the strength of the bars in the S4G via ellipse fitting, Fourier decomposition of the galaxy images, and from the gravitational tangential-to-radial forces. We also estimate the stellar contribution to the circular velocity, allowing us to analyze the coupling between non-baryonic and stellar matter within the optical disk. We average stellar density profiles (1D), the disk(+bulge) component of the rotation curve, and stellar bars (2D) as a function of fundamental galaxy parameters.

We complement the study with integral-field unit kinematic data from Seidel et al. (2015b) for a subsample of 16 S4G barred galaxies. We quantify the bar-induced perturbation strengths in the stellar and gaseous disk from the kinematics, and show that they agree with the estimates obtained from the images. We also use Hα Fabry-Perot observations from Erroz-Ferrer et al. (2015) for 29 S4G disk galaxies to study the inner slope of the rotation curves.

We provide possible observational evidence for the growth of bars in a Hubble time. We demonstrate the role of bars causing the spreading of the disk and the enhancement of the central stellar concentration. Our observations support the idea that Boxy/Peanut bulges in face-on perspective manifest as barlenses, that are often identfied in early-type galaxies hosting strong bars, and some of them also as inner lenses. We find that the amount of dark matter within the optical disk scales with the total stellar mass, as expected in the ΛCDM models. We also confirm that the observed inner velocity gradient is correlated with the central surface brightness, showing a strong connection between the inner shape of the potential well and the central stellar density.

We show that disks and bars in early-type (T < 5 ≡ Sc) and late-type (T ≥ 5) disk galaxies, or alternatively in galaxies having total stellar masses greater or smaller than 1010M, are characterized by very distinct properties. Late-type disks are less centrally concentrated (many galaxies are bulge-less) and present a larger halo-to-stellar mass ratio, what probably affects the disk stability properties. The detection of bars in late-type galaxies is strongly dependent on the identification criteria. On average, bars in early-type spirals (T = 0 − 2) are longer (both in physical units and relative to the disk) and have larger density amplitudes than the intermediate-type spirals (T ≈ 5), and the bar lengths among the latest-types in the S4G are also larger. In comparison to earlier types, the bars in late-type systems show larger tangential-to-radial force ratios. This result holds even when the estimated dark halo effect is included.

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Series: Report series in physical sciences
ISSN: 1239-4327
ISSN-L: 1239-4327
ISBN: 978-952-62-1318-7
ISBN Print: 978-952-62-1317-0
Issue: 102
Copyright information: This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited.