Hydrodynamic simulations of the triaxial bulge of M 31

doi:10.1051/0004-6361:20010391

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Hydrodynamic simulations of the triaxial bulge of M 31

Journal Article•DOI•

Hydrodynamic simulations of the triaxial bulge of M 31

S. Berman¹•Institutions (1)

University of Oxford¹

01 May 2001-Astronomy and Astrophysics (EDP Sciences)-Vol. 371, Iss: 2, pp 476-486

TL;DR: In this article, the potential of the stellar bulge is derived from its surface brightness prole, which is assumed to be triaxial and rotating in the same plane as the disk in order to explain the twisted nature of M 31's central isophotes and the non circular gas velocities in the inner disk.

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Abstract: The interstellar gas flow in the inner disk of M 31 is modelled using a new, two dimensional, grid based, hydrodynamics code. The potential of the stellar bulge is derived from its surface brightness prole. The bulge is assumed to be triaxial and rotating in the same plane as the disk in order to explain the twisted nature of M 31's central isophotes and the non circular gas velocities in the inner disk. Results are compared with CO observations and the bulge is found to be a fast rotator with a B-band mass-to-light ratio, B =6 .5 0.8, and a ratio of co-rotation radius to bulge semi-major axis,R =1 .2 0.1, implying that any dark halo must have a low density core in contradiction to the predictions of CDM. These conclusions would be strengthened by further observations conrming the model's o axis CO velocity predictions.

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Journal Article•DOI•

ΛCDM-based Models for the Milky Way and M31. I. Dynamical Models

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Anatoly Klypin¹, HongSheng Zhao², Rachel S. Somerville²•Institutions (2)

New Mexico State University¹, University of Cambridge²

10 Jul 2002-The Astrophysical Journal

TL;DR: In this article, the authors apply standard disk formation theory with adiabatic contraction within cuspy halo models predicted by the standard cold dark matter (?CDM) cosmology.

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Abstract: We apply standard disk formation theory with adiabatic contraction within cuspy halo models predicted by the standard cold dark matter (?CDM) cosmology. The resulting models are confronted with the broad range of observational data available for the Milky Way and M31 galaxies. We find that there is a narrow range of parameters that can satisfy the observational constraints, but within this range, the models score remarkably well. Our favored models have virial masses of 1012 and 1.6 ? 1012 M? for the Galaxy and for M31, respectively, average spin parameters ? ? 0.03-0.05, and concentrations Cvir = 10-17, typical for halos of this mass in the standard ?CDM cosmology. The models require neither dark matter modifications nor flat cores to fit the observational data. We explore two types of models, with and without the exchange of angular momentum between the dark matter and the baryons. The models without exchange give reasonable rotation curves, fulfill constraints in the solar neighborhood, and satisfy constraints at larger radii, but they may be problematic for fast rotating central bars. We explore models in which the baryons experience additional contraction due to loss of angular momentum to the surrounding dark matter. These models produce similar global properties, but the dark matter is only a 25% of the total mass in the central 3 kpc region, allowing a fast rotating bar to persist. According to preliminary calculations, our model galaxies probably have sufficient baryonic mass in the central ~3.5 kpc to reproduce recent observational values of the optical depth to microlensing events toward the Galactic center. Our dynamical models unequivocally require that about 50% of all the gas inside the virial radius must not be in the disk or in the bulge, a result that is obtained naturally in standard semianalytic models. Assuming that the Milky Way is typical, we investigate whether the range of virial masses allowed by our dynamical models is compatible with constraints from the galaxy luminosity function. We find that if the Milky Way has a luminosity MK = -24.0, then these constraints are satisfied, but if it is more luminous (as expected if it lies on the Tully-Fisher relation), then the predicted space density is larger than the observed space density of galaxies of the corresponding luminosity by a factor of 1.5-2. We conclude that observed rotation curves and dynamical properties of normal spiral galaxies appear to be consistent with standard ?CDM.

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737 citations

Cites background from "Hydrodynamic simulations of the tri..."

...Those anomalies are attributed to the presence of a triaxial bar/bulge in M31 (e.g. Stark 1977; Stark & Binney 1994; Berman 2001)....
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Journal Article•DOI•

Spitzer/mips infrared imaging of m31: further evidence for a spiral/ring composite structure

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Karl D. Gordon¹, Jeremy Bailin², Charles W. Engelbracht¹, George H. Rieke¹, Karl Misselt¹, William B. Latter³, Eric T. Young¹, Matthew L. N. Ashby⁴, Pauline Barmby⁴, Brad K. Gibson⁵, Brad K. Gibson², Dean C. Hines⁶, Joannah L. Hinz¹, Oliver Krause¹, D. Levine³, Francine R. Marleau³, Alberto Noriega-Crespo³, Susan R. Stolovy³, David A. Thilker⁷, Michael W. Werner⁸ - Show less +16 more•Institutions (8)

University of Arizona¹, Swinburne University of Technology², California Institute of Technology³, Harvard University⁴, University of Central Lancashire⁵, Space Science Institute⁶, Johns Hopkins University⁷, Jet Propulsion Laboratory⁸

03 Feb 2006-The Astrophysical Journal

TL;DR: In this article, the two spiral arms appear to start at the ends of a bar in the nuclear region and extend beyond the star-forming ring, and the star forming ring is very circular except for a region near M32 where it splits.

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Abstract: New images of M31 at 24, 70, and 160 μm taken with the Multiband Imaging Photometer for Spitzer (MIPS) reveal the morphology of the dust in this galaxy. This morphology is well represented by a composite of two logarithmic spiral arms and a circular ring (radius ~10 kpc) of star formation offset from the nucleus. The two spiral arms appear to start at the ends of a bar in the nuclear region and extend beyond the star-forming ring. As has been found in previous work, the spiral arms are not continuous, but composed of spiral segments. The star-forming ring is very circular except for a region near M32 where it splits. The lack of well-defined spiral arms and the prominence of the nearly circular ring suggest that M31 has been distorted by interactions with its satellite galaxies. Using new dynamical simulations of M31 interacting with M32 and NGC 205, we find that, qualitatively, such interactions can produce an offset, split ring like that seen in the MIPS images.

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198 citations

Cites background from "Hydrodynamic simulations of the tri..."

...The location of these spots and appearance of the nuclear region (especially at 70 µm) is similar to the triaxial bulge simulations of Berman (2001)....
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Journal Article•DOI•

Molecular gas in the Andromeda galaxy

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Ch. Nieten¹, N. Neininger², N. Neininger¹, M. Guelin, H. Ungerechts, R. Lucas, Elly M. Berkhuijsen¹, Rainer Beck¹, Richard Wielebinski¹ - Show less +5 more•Institutions (2)

Max Planck Society¹, University of Bonn²

01 Jul 2006-Astronomy and Astrophysics

TL;DR: M 31, the closest large spiral galaxy to our own, is the best object for studying molecular clouds and their relation to the spiral structure as discussed by the authors, and it is also one of the best places where to estimate molecular clouds masses through the Virial Theorem.

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Abstract: M 31, the closest large spiral galaxy to our own, is the best object for studying molecular clouds and their relation to the spiral structure. As one of the astronomical objects with the best known distance (0.78 ± 0.02 Mpc), it is also one of the best places where to estimate molecular clouds masses through the Virial Theorem.

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193 citations

Cites background from "Hydrodynamic simulations of the tri..."

...Its non-circular orbit may be caused by the central bar (Berman 2001; Berman & Loinard 2002)....
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Journal Article•DOI•

A wide-field H I mosaic of Messier 31 - II. The disk warp, rotation, and the dark matter halo

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Edvige Corbelli¹, Silvio Lorenzoni¹, Rene A. M. Walterbos², Robert Braun³, David A. Thilker⁴ - Show less +1 more•Institutions (4)

INAF¹, New Mexico State University², Commonwealth Scientific and Industrial Research Organisation³, Johns Hopkins University⁴

01 Feb 2010-Astronomy and Astrophysics

TL;DR: In this article, a tilted ring model was used to fit the rotation curve of the nearest spiral galaxy, M 31, using a deep, full-disk 21-cm imaging survey smoothed to 466-pc resolution.

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Abstract: 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 Λ CDM 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 1012 . 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 Λ CDM 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 Λ CDM 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 1012 , with 12% baryonic fraction and only 6% of the baryons in the neutral gas phase.

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175 citations

Cites background from "Hydrodynamic simulations of the tri..."

...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)....
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...In particular Berman (2001); Berman & Loinard (2002) have shown that the anomalous velocities observed in the inner region of M31 can be explained as the response of the gas to the potential of a triaxial rotating bulge....
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...Detailed modelling of the surface brightness shows that at very least the bulge is an obl te spheroid with axis ratio of 0.8 (Kent 1983) but most likely it is a triaxial bulge (e.g. Berman 2001, and references therein)....
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...Hydrodynamic simulations of the triaxial bulge of M31 by Berman (2001) found a B-band mass-to-light ratio of 6.5 for the bulge i.e. a stellar mass of 1010 M⊙....
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Rotation of the Bulge Components of Disk Galaxies

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John Kormendy, G. Illingworth

01 Jan 1979

170 citations

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Journal Article•DOI•

Triaxial Models of the Bulge of M31

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Antony A. Stark

01 Apr 1977-The Astrophysical Journal

164 citations

"Hydrodynamic simulations of the tri..." refers background or methods in this paper

...This paper aims to build on the work of Stark (1977) and Stark and Binney (1994) in two ways....
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...Using the value for the mean B-band absorption in the bulge region ofAB = 0.98 mag, (van Genderen 1973), the gas density can be calibrated and an absorption map for the bulge can be determined....
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...Using the values ofAB = 0.32 mag for our Galaxy in the direction of M31 (Burstein and Heiles 1982),AB = 0.98 mag for the bulge region of M31 (van Genderen 1973) andM B = 5.48 for the absoluteB-band solar magnitude (Allen 1973), the value of Ie = 22.2 mag arcsec−2 in Walterbos and Kennicutt (1988) is transformed intoIe = 289L pc−2....
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...Observed parameters Distance of M31† D 690 kpc Total B-band absorption‡ AB 1.3 mag Inclination angle† θ 77◦ Systemic velocity† vsys −315 km s−1 Bulge effective radius∗ re 10′ Bulge surface brightness∗ Ie 22.2 mag arcsec−2 Axis ratio of inner isophotes∗ β 1.54 Bulge to disk isophote angle∗∗ ψ 10◦ Max. bulge isophote semi-major axis§ rmax 11′.4 At the distance of M31,1′ = 200 pc on the major axis † Hodge (1992),∗ Walterbos and Kennicutt (1988) ‡ Burstein and Heiles (1982) and van Genderen (1973) ∗∗ Lindblad (1956),§ Stark (1977)...
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...The potential of the bulge is derived from observations, using the method of Stark (1977) and the surface brightness profile of Walterbos and Kennicutt (1988) whilst the gas flows are modelled using a 2D, isothermal, hydrodynamics code....
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Journal Article•DOI•

Rotation of the bulge components of barred galaxies

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John Kormendy

01 Jun 1982-The Astrophysical Journal

TL;DR: In this article, Kormendy and Koo showed that the triaxial bulges are more disk-like than SA bulges and appear to have been formed with more dissipation than ordinary bulges, which is consistent with the hypothesis that part of the bulge in many SB galaxies consists of disk material (i.e., gas) which has been transported to the center by the bar.

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Abstract: Stellar rotation and velocity-dispersion measurements are presented for the bulge components of the SBO galaxies NGC 1023, 2859, 2950, 4340, 4371, and 7743. The kinematics of nine SB bulges with data available are compared with bulges of unbarred galaxies studied by Kormendy and Illingworth. All of the SB bulges are found to rotate at least as rapidly as oblate-spheroid dynamical models which are flattened by rotation. This result confirms the conclusion of Kormendy and Illingworth that bulges rotate very rapidly. Six SB bulges found by Kormendy and Koo to be triaxial rotate even more rapidly than the oblate models. In this respect, they resemble published n-body models of bars. That is, triaxial bulges are dynamically like bars and unlike elliptical galaxies, which are also believed to be triaxial, but which rotate slowly. Measured velocity anisotropies are found to be consistent with these conclusions. Two ordinary bulges whose rotation is well described by isotropic modes have a ratio of radial to azimuthal velocity dispersion of sigma/sub r//sigma/sub theta/ = 0.96 +- 0.03. In contrast, the triaxial bulge of NGC 3945, which rotates much faster than the isotropic models, has sigma/sub r//sigma/sub theta/ approx.1.31 +- 0.06. This is similar to the degreemore » of anisotropy, sigma/sub r//sigma/sub theta/approx.1.21 +- 0.03, found in a recent n-body bar model by Hohl and Zang. Altogether the kinematic observations imply the triaxial bulges are more disklike than SA bulges. They appear to have been formed with more dissipation than ordinary bulges. These results are consistent with the hypothesis that part of the bulge in many SB galaxies consists of disk material (i.e., gas) which has been transported to the center by the bar. The resulting star formation may produce a very centrally concentrated light distribution which resembles a bulge but which has dislike dynamics.« less

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140 citations

"Hydrodynamic simulations of the tri..." refers background in this paper

...For many years, there has been ample evidence that bulges of barred spiral galaxies (SB bulges) are triaxial Kormendy (1982)....
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Journal Article•DOI•

An improved bulge model for M31

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Stephen M. Kent

01 Jun 1989-The Astronomical Journal

TL;DR: In this article, the authors derived new mass models with emphasis on determining the bulge mass/light ratio, and the best fitting model has an apparent bulge M/L = 5 and disk M/l = 10.

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Abstract: New mass models are derived with emphasis on determining the bulge mass/light ratio. Inside 6 kpc, the gas rotation curve is complex and probably does not measure the true circular velocity. Therefore, the bulge M/L ratio is constrained primarily by the bulge stellar velocity dispersion. The bulge kinematics inside 1 arcmin are consistent with the bulge being an oblate isotropic rotator. Overall, the best-fitting model has an apparent bulge M/L = 5 and disk M/L = 10. The rotation curve predicted by this model rises smoothly from the center to 1 kpc, and then is nearly flat out to 30 kpc. The predicted inner rotation curve forms an upper envelope to the observed complex gas kinematics. 27 refs.

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118 citations

"Hydrodynamic simulations of the tri..." refers background in this paper

...The maximum disk model of Kent (1989) implies a halo mass fraction of just 0.5% at 3.5 kpc and, although the model of minimumχ2/N is unable to make such a quantitative prediction, it is clearly at odds with the NFW halo predicted by CDM....
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Journal Article•DOI•

Positions of Emission Nebulae in M31.

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W. Baade, Halton Arp

01 May 1964-The Astrophysical Journal

84 citations

"Hydrodynamic simulations of the tri..." refers background in this paper

...The coordinate system is that of Baade and Arp (1964). be that the CO is very cold and difficult to detect in the inner disk (Loinard and Allen 1998) or simply not there (Melchior et al. 2000)....
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Journal Article•DOI•

A Complete CO Survey of M31. I. Distribution and Kinematics

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Thomas M. Dame, E. Koper, F. P. Israel, Patrick Thaddeus

01 Dec 1993-The Astrophysical Journal

TL;DR: The 1.2 m millimeter-wave telescope at the Center for Astrophysics has been used to carry out the first complete CO survey of M31 as discussed by the authors, which covers a 153'×45' area of the disk with half-beamwidth (4'.5) spacing.

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Abstract: The 1.2 m millimeter-wave telescope at the Center for Astrophysics has been used to carry out the first complete CO survey of M31. At 115 GHz, the frequency of the J=1→0 transition observed, the telescope has a beamwidth of 8'.7, corresponding to 1.7 kpc at the distance of M31. A total of 8 hr per day during two 6 month observing periods were devoted to the survey, which covers a 153'×45' area of the disk with half-beamwidth (4'.5) spacing. An average integration time of 100 minutes per point yielded an rms noise of 18 mK in each 1.3 km s -1 wide channel of our spectrometer. The entire galaxy has been observed out to a radius of at least 15 kpc-well beyond the optical disk and H I ring

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78 citations

"Hydrodynamic simulations of the tri..." refers background in this paper

...However, although there have been recent CO maps made of most of the Andromeda galaxy (Loinard et al. 1999, Dame et al. 1993), there is very little CO data available in the central bulge region....
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