A review of elliptical and disc galaxy structure, and modern scaling laws

A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their models to describe the radial distribution of stars in `nebulae'. This article reviews the progress since then, providing both an historical perspective and a contemporary review of the stellar structure of bulges, discs and elliptical galaxies. The quantification of galaxy nuclei, such as central mass deficits and excess nuclear light, plus the structure of dark matter halos and cD galaxy envelopes, are discussed. Issues pertaining to spiral galaxies including dust, bulge-to-disc ratios, bulgeless galaxies, bars and the identification of pseudobulges are also reviewed. An array of modern scaling relations involving sizes, luminosities, surface brightnesses and stellar concentrations are presented, many of which are shown to be curved. These 'redshift zero' relations not only quantify the behavior and nature of galaxies in the Universe today, but are the modern benchmark for evolutionary studies of galaxies, whether based on observations, N-body-simulations or semi-analytical modelling. For example, it is shown that some of the recently discovered compact elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to appear in "Planets, Stars and Stellar Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references incl. many somewhat forgotten, pioneer papers. Original submission to Springer: 07-June-201

Secular Evolution and the Growth of Pseudobulges in Disk Galaxies

Galaxy evolution is in transition from an early universe dominated by hierarchical clustering to a future dominated by secular processes. These result from interactions involving collective phenomena such as bars, oval disks, spiral structure, and triaxial dark halos. This paper summarizes a review by Kormendy & Kennicutt (2004) using, in part, illustrations of different galaxies. In simulations, bars rearrange disk gas into outer rings, inner rings, and galactic centers, where high gas densities feed starbursts. Consistent with this picture, many barred and oval galaxies have dense central concentrations of gas and star formation rates that can build bulge-like stellar densities on timescales of a few billion years. We conclude that secular evolution builds dense central components in disk galaxies that look like classical, merger-built bulges but that were made slowly out of disk gas. We call these pseudobulges. Many pseudobulges can be recognized because they have characteristics of disks: (1) flatter shapes than those of classical bulges, (2) correspondingly large ratios of ordered to random velocities, (3) small velocity dispersions, (4) spiral structure or nuclear bars, (5) nearly exponential brightness profiles, and (6) starbursts. These structures occur preferentially in barred and oval galaxies in which secular evolution should be most rapid. Thus a variety of observational and theoretical results contribute to a new paradigm of secular evolution that complements hierarchical clustering.Comment: 19 pages, 9 Postscript figures; requires kapproc.cls and procps.sty; to appear in "Penetrating Bars Through Masks of Cosmic Dust: The Hubble Tuning Fork Strikes a New Note", ed. Block, Freeman, Puerari, Groess, and Block, Dordrecht: Kluwer, in press; for a version with full resolution figures, see http://chandra.as.utexas.edu/~kormendy/ar3ss.htm

DUST PENETRATED ARM CLASSES: INSIGHT FROM RISING AND FALLING ROTATION CURVES

We present near-infrared K-band images of 15 galaxies. We have performed a Fourier analysis on the spiral structure of these galaxies in order to determine their pitch angles and dust-penetrated arm classes. We have also obtained rotation curve data for these galaxies and calculated their shear rates. We show that there is a correlation between pitch angle and shear rate and conclude that the main determinant of pitch angle is the mass distribution within the galaxy. This correlation provides a physical basis for the dust-penetrated classification scheme of Block &amp; Puerari (1999)