Transformations of galaxies. I - Mergers of equal-mass stellar disks

Barnes, Joshua E.

doi:10.1086/171522

Cited by 500 publications

(525 citation statements)

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“…Dissipationless remnants are triaxial with a tendency to be more prolate, whereas dissipational remnants are triaxial and tend to be much closer to oblate. This result is consistent with previous studies of dissipationless and dissipational mergers (e.g., Barnes 1992;Hernquist 1992;Springel 2000;González-García & Balcells 2005). In addition, Hopkins et al (2010) used semi-empirical models to predict galaxy merger rates and contributions to bulge growth as functions of merger mass, redshift, and mass ratio.…”

Section: Discussionsupporting

confidence: 93%

Structural properties of disk galaxies

Méndez-Abreu

Simonneau

Aguerri

et al. 2010

A&A

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Context. Knowledge of the intrinsic shapes of galaxy components provides crucial information when constraining phenomena driving their formation and evolution. Aims. We analize the structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies to derive the intrinsic shape of their bulges. Methods. We developed a new method to derive the intrinsic shapes of bulges based on geometrical relationships between the apparent and intrinsic shapes of bulges and disks. Bulges were assumed to be triaxial ellipsoids sharing the same center and polar axis of their surrounding disks. Disks were assumed to be circular, infinitesimally thin, and to lie on the equatorial plane of bulges. The equatorial ellipticity and intrinsic flattening of bulges were obtained from the length of the apparent major and minor semi-axes of the bulge, the twist angle between the apparent major axis of the bulge and the galaxy line of nodes, and the galaxy inclination. Results. We find that the intrinsic shape is well constrained for a subsample of 115 bulges with favorable viewing angles. A large fraction of them are characterized by an elliptical section (B/A < 0.9). This fraction is 33%, 55%, and 43% if using their maximum, mean, or median equatorial ellipticity, respectively. Most are flattened along their polar axis (C < (A + B)/2). Only 18% of the observed bulges have a probability >50% and none has a probability >90% of being elongated along the polar axis. The distribution of triaxiality is strongly bimodal. This bimodality is driven by bulges with Sérsic index n > 2, or equivalently, by the bulges of galaxies with a bulge-to-total ratio B/T > 0.3. Bulges with n ≤ 2 and with B/T ≤ 0.3 follow a similar distribution, which differs from that of bulges with n > 2 and B/T > 0.3. In particular, bulges with n ≤ 2 and B/T ≤ 0.3 exhibit a larger fraction of oblate axisymmetric (or nearly axisymmetric) bulges, a smaller fraction of triaxial bulges, and fewer prolate axisymmetric (or nearly axisymmetric) bulges with respect to bulges with n > 2 and with B/T > 0.3, respectively. No correlation is found between the intrinsic shape and either the luminosity or velocity dispersion of bulges. Conclusions. According to predictions of the numerical simulations of bulge formation, bulges with n ≤ 2, which show a high fraction of oblate axisymmetric (or nearly axisymmetric) shapes and have B/T ≤ 0.3, may be the result of dissipational minor mergers. Both major dissipational and dissipationless mergers seem to be required to explain the variety of shapes found for bulges with n > 2 and B/T > 0.3.

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Section: Discussionsupporting

confidence: 93%

Structural properties of disk galaxies

Méndez-Abreu

Simonneau

Aguerri

et al. 2010

A&A

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“…Figure 2 shows edge-on views and velocity distributions for an unequal-mass merger remnant. Unlike the products of equal-mass mergers (Barnes 1992), this object is fairly oblate, with axial ratios b/a ≃ 0.9, c/a ≃ 0.6. A good deal of "fine structure" is still present due to incomplete phase-mixing, but the edge-on views show a distinctly disky morphology.…”

Section: Unequal-mass Mergersmentioning

confidence: 83%

Dynamics of Galaxy Interactions

Barnes

1998

Saas-Fee Advanced Courses

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Abstract. Interacting galaxies are a natural arena for studies of nonequilibrium stellar dynamics, gas dynamics, and thermodynamics. Only galaxy formation itself is as deeply concerned with as many different aspects of dynamics, and the connection between interactions and the formation of galaxies is probably no coincidence. This review discusses tidal interactions, halos and orbit decay, dissipative effects in galaxy interactions, properties of merger remnants, and origins of starbursts.

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“…The formation of a bh binary after the merger of two galaxies will be more complicated than in the simple experiments considered here: the bhs will have clusters of bound stars, and the surrounding galaxies will be greatly disturbed. Barnes (1992) simulated the merger of disk galaxies (without bhs) and found that the final collision of the two bulges was often remarkably head-on, suggesting that small values of L/L c might not be that improbable. But, as Barnes admits, the bulges in his galaxy models had unreasonably large core radii.…”

Section: The Results In Panel (A) Ofmentioning

confidence: 99%

The dynamical evolution of massive black hole binaries I. Hardening in a fixed stellar background

1996

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We use a hybrid N-body program to study the evolution of massive black hole binaries in the centers of galaxies, mainly to understand the factors affecting the binary eccentricity, the response of the galaxy to the binary merger, and the effect of loss-cone depletion on the merger time. The scattering experiments from paper I showed that the merger time is not sensitive to the eccentricity growth unless a binary forms with at least a moderate eccentricity. We find here that the eccentricity can become large under some conditions if a binary forms in a galaxy with a flat core or with a radial bias in its velocity distribution, especially if the dynamical friction is enhanced by resonances as suggested by Rauch and Tremaine (1996). But the necessary conditions all seem unlikely, and our prediction from paper I remains unchanged: in most cases the eccentricity will start and remain small. As a binary hardens it ejects stars from the center of a galaxy, which may explain why large elliptical galaxies have weaker density cusps than smaller galaxies. If so, the central velocity distributions in those galaxies should have strong tangential anisotropies. The wandering of a binary from the center of a galaxy mitigates the problems associated with loss-cone depletion and helps the binary merge.

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Transformations of galaxies. I - Mergers of equal-mass stellar disks

Cited by 500 publications

References 0 publications

Structural properties of disk galaxies

Structural properties of disk galaxies

Dynamics of Galaxy Interactions

The dynamical evolution of massive black hole binaries I. Hardening in a fixed stellar background

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