This paper updates Kormendy & Kennicutt (2004): I review secular evolution of galaxy disks and the consequent growth of pseudobulges that often have been mistaken for true (i.e., merger-built) bulges. The evidence for secular evolution continues to get stronger. Studies of pseudobulge properties provide more clearcut criteria for recognizing the products of this evolution. Pseudobulge demographics clarify the problems for which secular evolution is important and the ones for which it is not important. An example of the latter is the energetics of active galactic nuclei (AGNs) and the mass budget of supermassive black holes: small black holes appear to reside in (necessarily small) pseudobulges, but their masses do not add up to a significant fraction of the total mass in AGN engines. On the other hand, the recognition of pseudobulges makes the biggest problem with cold dark matter galaxy formation still more acute: How can hierarchical clustering produce so many pure disk galaxies with no evidence for merger-built bulges?

The dynamics of a barred galaxy depends on the pattern speed of its bar. The only direct method for measuring it is the Tremaine-Weinberg technique. This method relies on the analysis of the distribution and dynamics of the stellar component. It is best suited to gas-poor galaxies and therefore it has been restricted to early-type barred galaxies. Nearly all the measured bars are as rapidly rotating as they can be. By comparing these results with recent high-resolution N-body simulations of bars in CDM halos, it is possible to conclude that these bars reside in maximal disks.

We present an elegant method of studying regular motions in oscillating potentials of double bars. This method relies on double-frequency orbits, which form the backbone of such systems. It is generally accepted that stationary potentials are mainly supported by particles trapped around stable periodic orbits, which in the plane of the galaxy represent oscillatory motion with only one frequency. Here we show that in oscillating potentials particles get trapped around parent orbits, which represent oscillatory motion with two frequencies. These orbits do not close in any reference frame, but they map onto loops, first introduced by Maciejewski & Sparke (1997). Loops enable studies of oscillating potentials in a manner analogous to how stationary potentials are studied with orbits that they admit.

The cold dark matter cosmology predicts that disk galaxies should be surrounded by hundreds to thousands of dark matter satellites with a mass function dn/dM~M-2. The largest satellites should contain stars and gas with masses and structure similar to the Large Magellanic Cloud while the smallest ones may have no stars and gas and therefore remain invisible. A disk galaxy like the Milky Way may experience dozens of encounters with satellite masses ranging from 108 to 1010 solar masses over cosmic history. While it has been argued that the existence of these satellites may lead to an unwelcome excess of vertical disk heating, we demonstrate the large number and amplitude of perturbations on the disk from dark satellites can be beneficial as a mechanism for generating recurrent transient spiral structure and in some cases the bar instability. The largest encounters lead to grand design forms while multiple smaller encounters can lead to ragged, multi-armed spiral structure. We use a stable, realistic N-body model of M31 as a platform for experiments. Satellite passages through the disk set up disturbances that are readily amplified into transient spiral waves. We demonstrate this behavior using idealized transient mass perturbations in the N-body disk plane. We also constructed 10 independent models with live orbiting satellites with mass distributions and orbital characteristics inspired by cosmological simulations. Half of these simulations develop a bar instability at some point during their evolution. Since satellites lose up to 80% of their mass via tidal stripping, we expect stronger perturbations on disks at higher redshifts and therefore more disturbed galaxy morphologies in accord with observation.

We compare N-body simulations performed in MOND with analogs in Newtonian gravity with dark matter. We have developed a code which solves the Poisson equation in both gravity models. It is a grid solver using adaptive mesh refinement technique, allowing us to study isolated galaxies as well as interacting galaxies. Galaxies in MOND are found to form bars faster and stronger than in the DM model. In Newton dynamics, it is difficult to reproduce the observed high frequency of strong bars, while MOND appears to fit better the observed bar frequency. Galaxy interactions and mergers, such as the Antennae, are also simulated with Newton and MOND dynamics. In the latter, dynamical friction is less important, and merging time-scales are longer. The formation of tidal dwarf galaxies in tidal tails will also be compared in MOND and Newton+DM models.

Galaxy disks evolve through angular momentum transfers between sub-components, like gas, stars, or dark matter halos, through non axisymmetric instabilities. The speed of this evolution is boosted in presence of a large fraction of the cold and dissipative gas component. When the visible matter dominates over the whole disk, angular momentum is exchanged between gas and stars only. The gas is driven towards the center by bars, stalled transiently in resonance rings, and driven further by embedded bars, which it contributes to destroy. From a small-scale molecular torus, the gas can then inflow from viscous torques, dynamical friction, or m=1 perturbations. In the weakened bar phases, multiple-speed spiral patterns can develop and help the galaxy to accrete external gas flowing from cosmic filaments. The various phases of secular evolution will be illustrated by numerical simulations.

Two types of bulges, boxy/peanut bulges and disky bulges, form from disk galaxy evolution. Boxy/peanut bulges are a result of a vertical instability of the bar, while disky bulges result from the inflow of mainly gaseous material to the inner parts of the disk. I will discuss their formation in the framework of disk evolution and their respective resulting properties.

Stellar bars are recognized as the most important internal factor that redistributes the angular momentum of the baryons and dark matter in disk galaxies. Yet, it is only now that we are starting to address the question of how bars impact the underlying disk galaxy over cosmological times and in different environments. I will present a review of our work on bars as a function of redshift and environment, focusing on three areas: (1) The evolution of barred disks in the field over the last 8 Gyr: We present results on the frequency and properties of barred disks in the rest-frame optical band, based on HST ACS images from the GEMS survey at z=0.24 to 1.0 (look-back times of 3 to 8 Gyr) and from the OSUBSGS survey of z~0 spirals (Jogee et al 2004; Marinova & Jogee 2007). Our results suggest that barred galaxies are abundant out to z~1, and the optical fraction of bright (M_V<-19.7) disk galaxies hosting strong large-scale bars (e>0.4, a>1.5 kpc) does not dramatically decline with redshift out to z~1. (2) Bars in disk-dominated vs bulge-dominated galaxies: To date, the vast majority of studies on bars have focused on relatively small samples that are dominated by bright galaxies of early Hubble type (Sa to Sc) and prominent classical bulges. Very little is known about bars in galaxies of late Hubble types and without a classical bulge -- the bulgeless galaxies that present a major challenge to hierarchical models. I will discuss our work based on 2000 disk galaxies at z=0.01-0.03 drawn from SDSS (Barazza, Jogee, Marinova 2007): we find that galaxies of late Hubble types with no bulge or a very low B/D display a remarkably higher optical bar fraction (>70% vs 40%) than galaxies with prominent classical bulges. Furthermore, barred galaxies show a larger fraction (31% vs 5%) of quasi bulgeless disk-dominated galaxies than do unbarred galaxies. I discuss possible interpretations of these new results in terms of the dark matter fraction and stabilizing effects of bulge. (3) Bars in dense environments (cluster) vs bars in the field: We present the first quantitative analysis of the properties of barred disks in dense clusters, using HST ACS data on the Abell 901/902 supercluster and in the Coma cluster, the richest cluster in the local Universe (Marinova & Jogee in prep.; Weinzirl & Jogee in prep). Cluster processes (e.g. galaxy tidal interactions, ram pressure stripping, accelerated evolution) lead to a different parameter space (larger tidal torques, lower disk gas content, larger tidal heating) for testing bar evolution scenarios.

Disks in isolated galaxies evolve continuously due to internally-driven processes. Bars, which are important agents of evolution, have received a great deal of attention in recent years. However, the importance of spiral patterns is less well known, yet their effects are also highly significant. Here I focus on the mechanisms and consequences of spiral behavior, and their implications for dynamical evolution.