Hydrodynamic simulations of the triaxial bulge of M 31

Berman, S. L.

doi:10.1051/0004-6361:20010391

Cited by 31 publications

(57 citation statements)

References 33 publications

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“…Therefore, they were interpreted as a signature of bulge triaxiality. This idea is supported by the presence of non-circular gas motions (e.g., Gerhard & Vietri 1986;Bertola et al 1989;Gerhard et al 1989;Berman 2001) and a velocity gradient along the galaxy minor axis (Corsini et al 2003b;Coccato et al 2004Coccato et al , 2005. We improve the previous works in several aspects.…”

Section: Introductionmentioning

confidence: 77%

Structural properties of disk galaxies

Méndez-Abreu

Aguerri²,

Corsini³

et al. 2007

A&A

146

186

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Context. A variety of formation scenarios have been proposed to explain the diversity of properties observed in bulges. Studying their intrinsic shape can help to constrain the dominant mechanisms at the epochs of their assembly. Aims. The structural parameters of a magnitude-limited sample of 148 unbarred S0-Sb galaxies were derived in order to study the correlations between bulges and disks, as well as the probability distribution function of the intrinsic equatorial ellipticity of bulges. Methods. We present a new fitting algorithm (GASP2D) to perform two-dimensional photometric decomposition of the galaxy surface-brightness distribution. This was assumed to be the sum of the contribution of a bulge and disk component characterized by elliptical and concentric isophotes with constant (but possibly different) ellipticity and position angles. Bulge and disk parameters of the sample galaxies were derived from the J-band images, which were available in the Two Micron All Sky Survey. The probability distribution function of the equatorial ellipticity of the bulges was derived from the distribution of the observed ellipticities of bulges and misalignments between bulges and disks. Results. Strong correlations between the bulge and disk parameters were found. About 80% of bulges in unbarred lenticular and earlyto-intermediate spiral galaxies are not oblate but triaxial ellipsoids. Their mean axial ratio in the equatorial plane is B/A = 0.85. Their probability distribution function is not significantly dependent on morphology, light concentration or luminosity. The possible presence of nuclear bars does not influence our results. Conclusions. The interplay between bulge and disk parameters favors scenarios in which bulges have assembled from mergers and/or have grown over long times through disk secular evolution. However, all these mechanisms have to be tested against the derived distribution of bulge intrinsic ellipticities.

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Section: Introductionmentioning

confidence: 77%

Structural properties of disk galaxies

Méndez-Abreu

Aguerri²,

Corsini³

et al. 2007

A&A

146

186

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“…These features have been interpreted as the signature of bulge triaxiality. This idea is supported by the presence of non-circular gas motions (e.g., Gerhard & Vietri 1986;Bertola et al 1989;Gerhard et al 1989;Berman 2001;Falcón-Barroso et al 2006;Pizzella et al 2008) and a velocity gradient along the galaxy minor axis (e.g., Corsini et al 2003;Coccato et al 2004Coccato et al , 2005.…”

Section: Intrinsic Shape Of Disk Galaxiesmentioning

confidence: 99%

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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“…However previous attempts to fit former rotation curves of this galaxy found a higher mass-tolight ratio for the disk than for the bulge (Widrow et al 2003), which was unexpected given the older age of bulges relative to disks. Hydrodynamic simulations of the triaxial bulge of M 31 by Berman (2001) found a B-band mass-to-light ratio of 6.5 for the bulge i.e. a stellar mass of 10 10 M .…”

Section: Stellar Mass-to-light Ratiosmentioning

confidence: 99%

“…These have been observed along the major axis assumed to be at PA = 38 • and with i = 77 • . However, notice that this is shown not just to point out the consistency of the molecular and atomic gas velocities, but to emphasize one has to consider non-circular motion to properly trace the rotation curve in the inner region (Berman 2001;Berman & Loinard 2002). Hence we shall not use the CO data as well as the 21-cm data at radii smaller than 8 kpc.…”

Section: The Rotation Curve and The Radial Distribution Of The Baryonsmentioning

confidence: 99%

“…Detailed modelling of the surface brightness shows that at very least the bulge is an oblate spheroid with axis ratio of 0.8 (Kent 1983) but most likely it is a triaxial bulge (e.g. Berman 2001, and references therein). For the purpose of this paper, which is the dynamical mass modelling of the disk rotational velocities (beyond 8 kpc), we can neglect the asphericity of the bulge which affects the orbits in the innermost few kpc.…”

Section: The Bulge-disk Decomposition and The Stellar Distributionmentioning

confidence: 99%

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A wide-field H I mosaic of Messier 31

Corbelli

Lorenzoni

Walterbos³

et al. 2010

A&A

163

229

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Aims. We test cosmological models of structure formation using the rotation curve of the nearest spiral galaxy, M 31, determined using a recent deep, full-disk 21-cm imaging survey smoothed to 466 pc resolution. Methods. We fit a tilted ring model to the HI data from 8 to 37 kpc and establish conclusively the presence of a dark halo and its density distribution via dynamical analysis of the rotation curve. Results. The disk of M 31 warps from 25 kpc outwards and becomes more inclined with respect to our line of sight. Newtonian dynamics without a dark matter halo provide a very poor fit to the rotation curve. In the framework of modified Newtonian dynamic (MOND) however the 21-cm rotation curve is well fitted by the gravitational potential traced by the baryonic matter density alone. The inclusion of a dark matter halo with a density profile as predicted by hierarchical clustering and structure formation in a ΛCDM cosmology makes the mass model in newtonian dynamic compatible with the rotation curve data. The dark halo concentration parameter for the best fit is C = 12 and its total mass is 1.2 × 10 12 M . If a dark halo model with a constant-density core is considered, the core radius has to be larger than 20 kpc in order for the model to provide a good fit to the data. We extrapolate the best-fit ΛCDM and constant-density core mass models to very large galactocentric radii, comparable to the size of the dark matter halo. A comparison of the predicted mass with the M 31 mass determined at such large radii using other dynamical tracers, confirms the validity of our results. In particular the ΛCDM dark halo model which best fits the 21-cm data well reproduces the mass of M 31 traced out to 560 kpc. Our best estimate for the total mass of M 31 is 1.3 × 10 12 M , with 12% baryonic fraction and only 6% of the baryons in the neutral gas phase.

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Hydrodynamic simulations of the triaxial bulge of M 31

Cited by 31 publications

References 33 publications

Structural properties of disk galaxies

Structural properties of disk galaxies

Structural properties of disk galaxies

A wide-field H I mosaic of Messier 31

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