No abstract

The distribution of bar strengths in disk galaxies is a fundamental property of the galaxy population that has only begun to be explored. We have applied the bar-spiral separation method of Buta and coworkers to derive the distribution of maximum relative gravitational bar torques, Q b , for 147 spiral galaxies in the statistically welldefined Ohio State University Bright Galaxy Survey (OSUBGS) sample. Our goal is to examine the properties of bars as independently as possible of their associated spirals. We find that the distribution of bar strength declines smoothly with increasing Q b , with more than 40% of the sample having Q b 0:1. In the context of recurrent bar formation, this suggests that strongly barred states are relatively short-lived compared to weakly barred or nonbarred states. We do not find compelling evidence for a bimodal distribution of bar strengths. Instead, the distribution is fairly smooth in the range 0:0 Q b < 0:8. Our analysis also provides a first look at spiral strengths Q s in the OSUBGS sample, based on the same torque indicator. We are able to verify a possible weak correlation between Q s and Q b , in the sense that galaxies with the strongest bars tend to also have strong spirals.

Abstract. The distribution of gravitational torques and bar strengths in the local Universe is derived from a detailed study of 163 galaxies observed in the near-infrared. The results are compared with numerical models for spiral galaxy evolution. It is found that the observed distribution of torques can be accounted for only with external accretion of gas onto spiral disks. Accretion is responsible for bar renewal -after the dissolution of primordial bars -as well as the maintenance of spiral structures. Models of isolated, non-accreting galaxies are ruled out. Moderate accretion rates do not explain the observational results: it is shown that galactic disks should double their mass in less than the Hubble time. The best fit is obtained if spiral galaxies are open systems, still forming today by continuous gas accretion, doubling their mass every 10 billion years.

This paper reports on a near-infrared survey of early-type galaxies designed to provide information on bar strengths, bulges, disks, and bar parameters in a statistically well-defined sample of S0-Sa galaxies. Early-type galaxies have the advantage that their bars are relatively free of the effects of dust, star formation, and spiral structure that complicate bar studies in later type galaxies. We describe the survey and present results on detailed analysis of the relative Fourier intensity amplitudes of bars in 26 early-type galaxies. We also evaluate the symmetry assumption of these amplitudes with radius, used recently for bar-spiral separation in later-type galaxies. The results show a wide variety of radial Fourier profiles of bars, ranging from simple symmetric profiles that can be represented in terms of a single gaussian component, to both symmetric and asymmetric profiles that can be represented by two overlapping gaussian components. More complicated profiles than these are also found, often due to multiple bar-like features including extended ovals or lenses. Based on the gravitational bar torque indicator Q_b, double-gaussian bars are stronger on average than single-gaussian bars, at least for our small sample. We show that published numerical simulations where the bar transfers a large amount of angular momentum to the halo can account for many of the observed profiles. The range of possibilities encountered in models seems well-represented in the observed systems.Comment: Accepted for publication in AJ. 20 pages, 10 figures, uses emulateapj. Figures have been reduced in resolution here; a full-resolution preprint can be downloaded from http://bama.ua.edu/~rbuta/nirs0s/nirs0s_paper2.html . Further information on the Near-Infrared S0 Survey can be obtained from the NIRS0S website at http://bama.ua.edu/~rbuta/nirs0s/nirs0s.htm

We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 µm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T ≥ 0.1, the break radius to bar radius, r br /R bar , varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad Resonance (OLR) of the bar, and thus moves outwards as the bar grows. For galaxies with small bulges, B/T < 0.1, r br /R bar spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds.