The Bulge/Disk Connection in Late-Type Spirals

Courteau, Stéphane

doi:10.1007/978-94-009-0335-7_31

Cited by 2 publications

(4 citation statements)

References 70 publications

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“…From this, they conclude that: "Our measurements of exponential stellar density profiles [in bulges] as well as a restricted range of [bulge-to-disk] scale lengths provide strong observational support for secular evolution models. Self-consistent numerical simulations of disk galaxies evolve toward a double exponential profile with a typical ratio between bulge and disk scale lengths near 0.1 (D. Friedli 1995, private communication) in excellent agreement with our measured values" (see Courteau et al 1996 for details). MacArthur, Courteau, & Holtzman (2003) find that h b /h d = 0.13 ± 0.06 for late-type spirals and again note the connection with secular evolution.…”

Section: Exponential Bulgessupporting

confidence: 75%

“…Also, some bulge colors found in the above studies are indicative of young ages, especially for Sc -Sm galaxies (de Jong 1996c). Bulge and disk scale lengths and surface brightnesses also correlate (see the above papers; Courteau, de Jong, & Broeils 1996;Courteau 1996b). Courteau and collaborators interpret these correlations as products of "secular dynamical evolution .…”

Section: Stellar Populations In Classical Bulges and Pseudobulgesmentioning

confidence: 94%

“…As a diagnostic of formation processes, Courteau et al (1996) go on to examine the ratio h b /h d of the scale lengths of the inner and outer exponentials. For the combined sample, they find that h b /h d = 0.08±0.05, and for the de Jong sample, they find that h b /h d = 0.09 ± 0.04.…”

Section: Exponential Bulgesmentioning

confidence: 99%

“…Many reviews discuss secular evolution in barred and oval galaxies (Kormendy 1979a, b;, 1982aNorman 1984;Bosma 1992;Martinet 1995;Friedli & Benz 1995;Pfenniger 1996aPfenniger , b, 2000Sellwood & Debattista 1996;Buta 1995Buta , 1999Athanassoula 2002;Maciejewski 2003;Wada 2003;; and especially Wilkinson 1993, hereafter SW93, and. Discussions of pseudobulge formation include, besides the above, Pfenniger & Norman (1990); Courteau (1996b) ;Wyse, Gilmore, & Franx (1997) ;; Kormendy & Gebhardt (2001); Balcells (2002); and especially and Carollo (2003).…”

Section: Introductionmentioning

confidence: 99%

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Secular Evolution and the Formation of Pseudobulges in Disk Galaxies

Kormendy¹,

Kennicutt

2004

Annu. Rev. Astron. Astrophys.

1,764

107

2,359

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The Universe is in transition. At early times, galactic evolution was dominated by hierarchical clustering and merging, processes that are violent and rapid. In the far future, evolution will mostly be secular: the slow rearrangement of energy and mass that results from interactions involving collective phenomena such as bars, oval disks, spiral structure, and triaxial dark halos. Both processes are important now. This paper reviews internal secular evolution, concentrating on one important consequence, the buildup of 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.We begin with an "existence proof" -a review of how bars rearrange disk gas into outer rings, inner rings, and stuff dumped onto the center. Simulation results correspond closely to the morphology of barred galaxies. In the simulations, gas transported to small radii reaches high densities that plausibly feed star formation. In the observations, many SB and oval galaxies have dense central concentrations of gas and star formation. Optical colors and spectra often imply young stellar populations. So the formation of pseudobulges is well supported by theory and observations. It is embedded in a broader evolution picture that accounts for much of the richness observed in galaxy structure.If secular processes built dense central components that masquerade as bulges, how can we distinguish them from merger-built bulges? Observations show that pseudobulges retain a memory of their disky origin. 2That is, they have one or more characteristics of disks: (1) flatter shapes than those of classical bulges, (2) correspondingly large ratios of ordered to random velocities indicative of disk dynamics, (3) small velocity dispersions σ with respect to the Faber-Jackson correlation between σ and bulge luminosity, (4) spiral structure or nuclear bars in the "bulge" part of the light profile, (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. So the cleanest examples of pseudobulges are recognizable.Are their formation timescales plausible? We use measurements of central gas densities and star formation rates to show that pseudobulges of the observed densities form on reasonable timescales of a few billion years.Thus a large variety of observational and theoretical results contribute to a new picture of galaxy evolution that complements hierarchical clustering and merging. Secular evolution consists of more than the aging of stellar populations. Every galaxy is dynamically evolving.

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Section: Exponential Bulgessupporting

confidence: 75%

Section: Stellar Populations In Classical Bulges and Pseudobulgesmentioning

confidence: 94%

Section: Exponential Bulgesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Secular Evolution and the Formation of Pseudobulges in Disk Galaxies

Kormendy¹,

Kennicutt

2004

Annu. Rev. Astron. Astrophys.

1,764

107

2,359

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Pseudobulges in the Disk Galaxies NGC 7690 and NGC 4593

Kormendy

Cornell

Block

et al. 2006

ApJ

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We present Ks-band surface photometry of NGC 7690 (Hubble type Sab) and NGC 4593 (SBb). We find that, in both galaxies, a major part of the "bulge" is as flat as the disk and has approximately the same color as the inner disk. In other words, the "bulges" of these galaxies have disk-like properties. We conclude that these are examples of "pseudobulges" -- that is, products of secular dynamical evolution. Nonaxisymmetries such as bars and oval disks transport disk gas toward the center. There, star formation builds dense stellar components that look like -- and often are mistaken for -- merger-built bulges but that were constructed slowly out of disk material. These pseudobulges can most easily be recognized when, as in the present galaxies, they retain disk-like properties. NGC 7690 and NGC 4593 therefore contribute to the growing evidence that secular processes help to shape galaxies. NGC 4593 contains a nuclear ring of dust that is morphologically similar to nuclear rings of star formation that are seen in many barred and oval galaxies. The nuclear dust ring is connected to nearly radial dust lanes in the galaxy's bar. Such dust lanes are a signature of gas inflow. We suggest that gas is currently accumulating in the dust ring and hypothesize that the gas ring will starburst in the future. The observations of NGC 4593 therefore suggest that major starburst events that contribute to pseudobulge growth can be episodic.Comment: 10 pages, 3 Postscript figures; requires emulateapj.cls, apjfonts.sty, and psfig.sty; accepted for publication in ApJ; for a version with full resolution figures, see http://chandra.as.utexas.edu/~kormendy/n7690.pd

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The Bulge/Disk Connection in Late-Type Spirals

Cited by 2 publications

References 70 publications

Secular Evolution and the Formation of Pseudobulges in Disk Galaxies

Secular Evolution and the Formation of Pseudobulges in Disk Galaxies

Pseudobulges in the Disk Galaxies NGC 7690 and NGC 4593

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