Near-infrared imaging of NGC 5195

Spillar, Earl J.; Oh, Sree; Johnson, Paul E.; Wenz, M.

doi:10.1086/116101

Cited by 20 publications

(20 citation statements)

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“…We then see the underlying old stars that trace the mass distribution. The most important revelation is that bars are hidden in many galaxies that look unbarred in the optical (Block & Wainscoat 1991;Spillar et al 1992;Seigar & James 1998;Eskridge et al 2000Eskridge et al , 2002Block et al 2001;Laurikainen & Salo 2002;Whyte et al 2002). About two-thirds of all spiral galaxies look barred in the infrared.…”

Section: The Secular Evolution Of Unbarred Galaxiesmentioning

confidence: 99%

Secular Evolution and the Formation of Pseudobulges in Disk Galaxies

Kormendy¹,

Kennicutt

2004

Annu. Rev. Astron. Astrophys.

1,742

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: The Secular Evolution Of Unbarred Galaxiesmentioning

confidence: 99%

Secular Evolution and the Formation of Pseudobulges in Disk Galaxies

Kormendy¹,

Kennicutt

2004

Annu. Rev. Astron. Astrophys.

1,742

107

2,359

View full text Add to dashboard Cite

show abstract

“…They show us the old stars that trace the mass distribution. They reveal that bars are hidden in many galaxies that look unbarred in the optical (Block & Wainscoat 1991;Spillar et al 1992;Seigar & James 1998;Knapen et al 2000;Eskridge et al 2000Eskridge et al , 2002Block et al 2001;Laurikainen & Salo 2002;Whyte et al 2002). About two-thirds of all spiral galaxies look barred in the infrared.…”

Section: Secular Evolution Of "Unbarred" Galaxiesmentioning

confidence: 99%

Secular Evolution and the Growth of Pseudobulges in Disk Galaxies

Kormendy

Cornell

2004

Astrophysics and Space Science Library

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Galactic 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. A detailed review is in Kormendy & Kennicutt (2004). This paper provides a summary illustrated in part with different galaxies. Figure 2 summarizes how 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 are observed to have dense central concentrations of gas and star formation. Measurements of star formation rates show that bulge-like stellar densities are constructed on timescales of a few billion years. We conclude that secular evolution builds dense central components in disk galaxies that look like classical -that is, merger-builtbulges 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 σ with respect to the Faber-Jackson correlation between σ and bulge luminosity, (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.

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“…NGC 5195 (alternatively known as M51b) is the disky barred (SB0/SBa(s)) galaxy (Spillar et al 1992) that is the low-mass companion of NGC 5194 (alternatively known as M51a or "the Whirlpool Galaxy"), having undergone a 3:1 interaction roughly 340-500 Myr ago (Salo & Laurikainen 2000;Dobbs et al 2010;Mentuch Cooper et al 2012). NGC 5195 is a good case study of how star formation quenches for a galaxy a short time after an interaction, being nearby and showing signs of having recently transitioned.…”

Section: Introductionmentioning

confidence: 99%

After the Interaction: An Efficiently Star-Forming Molecular Disk in NGC 5195

Alatalo

Aladro

Nyland

et al. 2016

ApJ

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We present new molecular gas maps of NGC 5195 (alternatively known as M51b) from the Combined Array for Research in Millimeter Astronomy, including 12 CO(1-0), 13 CO(1-0), CN(1 0,2 -0 0,1 ), CS(2-1), and 3 mm continuum. We also detected HCN(1-0) and HCO + (1-0) using the Onsala Space Observatory. NGC 5195 has a 12 CO/ 13 CO ratio ( 12 13 =11.4 ± 0.5) consistent with normal star-forming galaxies. The CN(1-0) intensity is higher than is seen in an average star-forming galaxy, possibly enhanced in the diffuse gas in photo-dissociation regions. Stellar template fitting of the nuclear spectrum of NGC 5195 shows two stellar populations: an 80% mass fraction of old (10 Gyr) and a 20% mass fraction of intermediate-aged (≈1 Gyr) stellar populations. This provides a constraint on the timescale over which NGC 5195 experienced enhanced star formation during its interaction with M51a. The average molecular gas depletion timescale in NGC 5195 is t á ñ dep =3.08 Gyr, a factor of »2 larger than the depletion timescales in nearby star-forming galaxies, but consistent with the depletion seen in CO-detected early-type galaxies. While radio continuum emission at centimeter and millimeter wavelengths is present in the vicinity of the nucleus of NGC 5195, we find it is most likely associated with nuclear star formation rather than radio-loud AGN activity. Thus, despite having a substantial interaction with M51a ∼1/2 Gyr ago, the molecular gas in NGC 5195 has resettled and is currently forming stars at an efficiency consistent with settled early-type galaxies.

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Near-infrared imaging of NGC 5195

Cited by 20 publications

References 0 publications

Secular Evolution and the Formation of Pseudobulges in Disk Galaxies

Secular Evolution and the Formation of Pseudobulges in Disk Galaxies

Secular Evolution and the Growth of Pseudobulges in Disk Galaxies

After the Interaction: An Efficiently Star-Forming Molecular Disk in NGC 5195

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