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Secular Evolution and the Formation of Pseudobulges in Disk Galaxies
Astrophysics · Submitted 16 Jul 2004
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim Thus a large variety of observational and theoretical results contribute to a new picture of galaxy evolution that complements hierarchical clustering and merging.
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The abstract, sentence by sentence
We review internal processes of secular evolution in galaxy disks, concentrating on the buildup of dense central features that look like classical, merger-built bulges but that were made slowly out of disk gas. We call these pseudobulges. As an existence proof, we review how bars rearrange disk gas into outer rings, inner rings, and gas dumped into the center. In simulations, this gas reaches high densities that plausibly feed star formation. In the observations, many SB and oval galaxies show central concentrations of gas and star formation. Star formation rates imply plausible pseudobulge growth times of a few billion years. If secular processes built dense central components that masquerade as bulges, can we distinguish them from merger-built bulges? Observations show that pseudobulges retain a memory of their disky origin. They have one or more characteristics of disks: (1) flatter shapes than those of classical bulges, (2) large ratios of ordered to random velocities indicative of disk dynamics, (3) small velocity dispersions, (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 rapid. So the cleanest examples of pseudobulges are recognizable. Thus a large variety of observational and theoretical results contribute to a new picture of galaxy evolution that complements hierarchical clustering and merging.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We review internal processes of secular evolution in galaxy disks, concentrating on the buildup of dense central features that look like classical, merger-built bulges but that were made slowly out of disk gas. | contribution 0.80 | 0.21 | 0.18 | asserted 0.75 |
| s1 | We call these pseudobulges. | background 0.46 | 0.36 | 0.05 | asserted 0.95 |
| s2 | As an existence proof, we review how bars rearrange disk gas into outer rings, inner rings, and gas dumped into the center. | method 0.45 | 0.12 | 0.05 | asserted 0.97 |
| s3 | In simulations, this gas reaches high densities that plausibly feed star formation. | result 0.68 | 0.21 | 0.04 | hedged possibility 0.82 |
| s4 | In the observations, many SB and oval galaxies show central concentrations of gas and star formation. | result 0.87 | 0.16 | 0.04 | asserted 0.99 |
| s5 | Star formation rates imply plausible pseudobulge growth times of a few billion years. | result 0.64 | 0.29 | 0.07 | hedged possibility 0.71 |
| s6 | If secular processes built dense central components that masquerade as bulges, can we distinguish them from merger-built bulges? | gap 0.89 | 0.06 | 0.05 | unclear 0.75 |
| s7 | Observations show that pseudobulges retain a memory of their disky origin. | result 0.87 | 0.17 | 0.24 | asserted 1.00 |
| s8 | They have one or more characteristics of disks: (1) flatter shapes than those of classical bulges, (2) large ratios of ordered to random velocities indicative of disk dynamics, (3) small velocity dispersions, (4) spiral structure or nuclear bars in the bulge part of the light profile, (5) nearly exponential brightness profiles, and (6) starbursts. | result 0.85 | 0.17 | 0.17 | asserted 1.00 |
| s9 | These structures occur preferentially in barred and oval galaxies in which secular evolution should be rapid. | result 0.71 | 0.25 | 0.07 | asserted 0.91 |
| s10 | So the cleanest examples of pseudobulges are recognizable. | interpretation 0.84 | 0.15 | 0.15 | asserted 0.99 |
| s11 | Thus a large variety of observational and theoretical results contribute to a new picture of galaxy evolution that complements hierarchical clustering and merging. | interpretation 0.96 | 0.11 | 0.63 | asserted 0.99 |
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The paper
Original abstract
We review internal processes of secular evolution in galaxy disks, concentrating on the buildup of dense central features that look like classical, merger-built bulges but that were made slowly out of disk gas. We call these pseudobulges. As an existence proof, we review how bars rearrange disk gas into outer rings, inner rings, and gas dumped into the center. In simulations, this gas reaches high densities that plausibly feed star formation. In the observations, many SB and oval galaxies show central concentrations of gas and star formation. Star formation rates imply plausible pseudobulge growth times of a few billion years. If secular processes built dense central components that masquerade as bulges, can we distinguish them from merger-built bulges? Observations show that pseudobulges retain a memory of their disky origin. They have one or more characteristics of disks: (1) flatter shapes than those of classical bulges, (2) large ratios of ordered to random velocities indicative of disk dynamics, (3) small velocity dispersions, (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 rapid. So the cleanest examples of pseudobulges are recognizable. Thus a large variety of observational and theoretical results contribute to a new picture of galaxy evolution that complements hierarchical clustering and merging.
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References
How the literature uses it
28 arXiv papers cite this in 49 sentences
Papers whose main result relates to this one's
States the same result 1 paper
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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.
Secular Evolution and the Growth of Pseudobulges in Disk Galaxies · 0.94
Papers citing it · 32 sentences without a confident label
Cites it as background 14 papers
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In contrast, pseudo-bulges arise gradually through long-term, internal (secular) processes within discs [ref] .
Age bimodality in pseudo-bulges of barred spiral galaxies: Bar-driven evolution across cosmic time · Introduction · 0.85
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Disk-like galaxies often suffer from gravitational instabilities that cause the formation of bars and spiral arms [ref] .
Discovery of a Barred-Spiral Galaxy at $z_{spec}$ = 3.16 II. The Star Formation History · Introduction · 0.95
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The evolution of galaxies via interactions with collective phenomena like bars and spiral structure is well-established [ref] . $N$-body simulations suggest that bars heat up in the axial direction and explain the morphology of so-called “box-shaped” bulges of some edge-on galaxies [ref] .
Detection of a Distinct Pseudobulge Hidden Inside the "Box-Shaped Bulge" of NGC 4565 · Motivation · 0.83
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