Hydrodynamic simulations of the triaxial bulge of M 31

doi:10.1051/0004-6361:20010391

Home
/
Papers
/
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.

read less

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.

...read moreread less

Content maybe subject to copyright Report

Citations

PDF

Open Access

More filters

Journal Article•DOI•

Improving the triaxial bulge model of M31

[...]

S. L. Berman¹, Laurent Loinard²•Institutions (2)

University of Oxford¹, National Autonomous University of Mexico²

21 Oct 2002-Monthly Notices of the Royal Astronomical Society

TL;DR: In this article, a detailed hydrodynamical model of the gas flow in the triaxial gravitational potential of the bulge of the Andromeda galaxy (M31) has been proposed by Berman, and shown to provide excellent agreement with the CO emission-line velocities observed along its major axis.

...read moreread less

Abstract: A detailed hydrodynamical model of the gas flow in the triaxial gravitational potential of the bulge of the Andromeda galaxy (M31) has recently been proposed by Berman, and shown to provide excellent agreement with the CO emission-line velocities observed along its major axis. In the present paper, we confirm the validity of that model by showing that it can also reproduce the CO velocities observed off the major axis – a much more robust test. The CO observations, however, tend to span a wider range of velocities than a direct application of the original model of Berman would suggest. This situation can be improved significantly if the molecular disc is made thicker, a requirement already encountered in dynamical simulations of other spiral galaxies, and typically attributed to a broadening of the molecular layer in galactic fountain-like processes. In the central regions of M31, however, it is unclear whether there actually is a thick molecular disc, or whether broadening the molecular layer is merely an artificial theoretical means of accounting for some disc warping. Other effects not included in the model, such as hydraulic jumps, might also contribute to a widening of the range of velocities.

...read moreread less

14 citations

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

...…surface brightness (I0 = 21.6 mag arcsec −1, Walterbos & Kennicutt 1988) which when corrected for absorption and inclination using the values of Berman (2001) gives a central surface density of Σd =113 L⊙ pc −3, disk scale length (Rd = 5.8 kpc, Walterbos & Kennicutt 1988), and a conservative…...
[...]
...In this article, we show that hydrodynamical triaxial models of the bulge of the Andromeda galaxy (M31) previously presented by Berman (2001), and initially tested against CO emission observations along the apparent major axis only, can also account for the CO emission velocities observed off the…...
[...]
...The value of R = 1.2 found by Berman (2001) implies that the bulge of M31 is a fast rotator....
[...]
...By including a thick disk, the model initially proposed by Berman (2001) is able to match the 3D CO data of Loinard et al. (1999) reasonably well....
[...]
...The dynamical model developed by Berman (2001) takes into account a rotating, triaxial bulge, and an axisymmetric component that mimics the combined influence of the disk and halo....
[...]

Journal Article•DOI•

Evidence for non-axisymmetry in M 31 from wide-field kinematics of stars and gas

[...]

M. Opitsch¹, Maximilian Fabricius¹, Roberto P. Saglia¹, Ralf Bender¹, M. Blaña¹, Ortwin Gerhard¹ - Show less +2 more•Institutions (1)

Max Planck Society¹

01 Jan 2018-Astronomy and Astrophysics

TL;DR: In this article, the authors derived stellar line-of-sight velocity distributions from the stellar absorption lines, as well as velocity distributions and line fluxes of the emission lines H beta, [O III] and [N I].

...read moreread less

Abstract: Aims. As the nearest large spiral galaxy, M 31 provides a unique opportunity to study the structure and evolutionary history of this galaxy type in great detail. Among the many observing programs aimed at M 31 are microlensing studies, which require good three-dimensional models of the stellar mass distribution. Possible non-axisymmetric structures like a bar need to be taken into account. Due to M 31's high inclination, the bar is difficult to detect in photometry alone. Therefore, detailed kinematic measurements are needed to constrain the possible existence and position of a bar in M 31. Methods. We obtained approximate to 220 separate fields with the optical integral-field unit spectrograph VIRUS-W, covering the whole bulge region of M 31 and parts of the disk. We derived stellar line-of-sight velocity distributions from the stellar absorption lines, as well as velocity distributions and line fluxes of the emission lines H beta, [O III] and [N I]. Our data supersede any previous study in terms of spatial coverage and spectral resolution. Results. We find several features that are indicative of a bar in the kinematics of the stars, we see intermediate plateaus in the velocity and the velocity dispersion, and correlation between the higher moment h3 and the velocity. The gas kinematics is highly irregular, but is consistent with non-triaxial streaming motions caused by a bar. The morphology of the gas shows a spiral pattern, with seemingly lower inclination than the stellar disk. We also look at the ionization mechanisms of the gas, which happens mostly through shocks and not through starbursts.

...read moreread less

12 citations

Book Chapter•DOI•

The intrinsic shape of galaxy bulges

[...]

Jairo Méndez-Abreu¹•Institutions (1)

University of St Andrews¹

01 Feb 2015-arXiv: Astrophysics of Galaxies

TL;DR: In this paper, the authors discuss the main developments and results in the quest to better understand the 3D shape of galaxy bulges and present the current view on the Milky Way bulge and future prospects in the field.

...read moreread less

Abstract: The knowledge of the intrinsic three-dimensional (3D) structure of galaxy components provides crucial information about the physical processes driving their formation and evolution. In this paper I discuss the main developments and results in the quest to better understand the 3D shape of galaxy bulges. I start by establishing the basic geometrical description of the problem. Our understanding of the intrinsic shape of elliptical galaxies and galaxy discs is then presented in a historical context, in order to place the role that the 3D structure of bulges play in the broader picture of galaxy evolution. Our current view on the 3D shape of the Milky Way bulge and future prospects in the field are also depicted.

...read moreread less

6 citations

Journal Article•DOI•

Simulations of dual morphology in spiral galaxies

[...]

S. L. Berman¹•Institutions (1)

University of Oxford¹

01 Dec 2003-Astronomy and Astrophysics

TL;DR: In this article, gas and stars in spiral galaxies are modelled with a combination of hydrodynamic and N-body techniques, revealing morphological dierences mirroring the dual morphologies seen in B and K 0 band observations of many spiral galaxies.

...read moreread less

Abstract: Gas and stars in spiral galaxies are modelled with a combination of hydrodynamic and N-body techniques. The sim- ulations reveal morphological dierences mirroring the dual morphologies seen in B and K 0 band observations of many spiral galaxies: gaseous images have tighter pitch angles, are more asymmetric, more flocculent and more likely to have multiple arms. Morphological decoupling increases as the stellar arm-interarm contrast and the Q parameter fall. The flocculence of a galaxy is quantified by decomposing the images into logarithmic spirals and defining a parameter closely related to the uniformity of the resulting 2D Fourier spectrum. Thus, a significant amount of morphological decoupling in spiral galaxies is shown to be due to the dierence in the dynamics of stars and gas, rather than dust, star formation or galaxy interactions.

...read moreread less

4 citations

Simulations of Dual Morphology in Spiral Galaxies

[...]

S. L. Berman¹•Institutions (1)

University of Oxford¹

01 Dec 2002

TL;DR: In this paper, gas and stars in spiral galaxies are modelled with a combination of hydrodynamic and N-body techniques, revealing morphological dierences mirroring the dual morphologies seen in B and K 0 band observations of many spiral galaxies.

...read moreread less

2 citations

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

...DUAL is a combination of the finite-difference hydrodynamic codeGALAHAD introduced in Berman (2001) and a particlemeshN-body code written by J. Sellwood....
[...]

1
…
2
3
4
5
6

Collapse

References

PDF

Open Access

More filters

Journal Article•DOI•

A Universal Density Profile from Hierarchical Clustering

[...]

Julio F. Navarro¹, Carlos S. Frenk², Simon D. M. White³•Institutions (3)

University of Arizona¹, Durham University², Max Planck Society³

01 Dec 1997-The Astrophysical Journal

TL;DR: In this article, the authors used high-resolution N-body simulations to study the equilibrium density profiles of dark matter halos in hierarchically clustering universes, and they found that all such profiles have the same shape, independent of the halo mass, the initial density fluctuation spectrum, and the values of the cosmological parameters.

...read moreread less

Abstract: We use high-resolution N-body simulations to study the equilibrium density profiles of dark matter halos in hierarchically clustering universes. We find that all such profiles have the same shape, independent of the halo mass, the initial density fluctuation spectrum, and the values of the cosmological parameters. Spherically averaged equilibrium profiles are well fitted over two decades in radius by a simple formula originally proposed to describe the structure of galaxy clusters in a cold dark matter universe. In any particular cosmology, the two scale parameters of the fit, the halo mass and its characteristic density, are strongly correlated. Low-mass halos are significantly denser than more massive systems, a correlation that reflects the higher collapse redshift of small halos. The characteristic density of an equilibrium halo is proportional to the density of the universe at the time it was assembled. A suitable definition of this assembly time allows the same proportionality constant to be used for all the cosmologies that we have tested. We compare our results with previous work on halo density profiles and show that there is good agreement. We also provide a step-by-step analytic procedure, based on the Press-Schechter formalism, that allows accurate equilibrium profiles to be calculated as a function of mass in any hierarchical model.

...read moreread less

9,729 citations

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

...Hence, for a given value of Hubble’s constant, the halo circular speed curve is fully specified byv200 and c. Navarro et al. (1997) find a relationship between the characteristic density and radius (or, equivalently, betweenc andv200) of a halo in a given cosmology, thereby reducing the NFW…...
[...]
...If v200 = v0 = 257 km s−1, then the method of Navarro et al. (1997) gives a halo mass fraction at 3.5 kpc of 58% and a disk mass of only 5.8× 109M ....
[...]
...From Navarro et al. (1997), at a redshiftz = 0, r200 = ( h v200 km s−1 ) kpc....
[...]

Journal Article•DOI•

The Structure of cold dark matter halos

[...]

Julio F. Navarro¹, Carlos S. Frenk, Simon D. M. White•Institutions (1)

University of Arizona¹

01 May 1996-The Astrophysical Journal

TL;DR: In this article, high-resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple universal profile.

...read moreread less

Abstract: High resolution N-body simulations show that the density profiles of dark matter halos formed in the standard CDM cosmogony can be fit accurately by scaling a simple “universal” profile. Regardless of their mass, halos are nearly isothermal over a large range in radius, but significantly shallower than r -2 near the center and steeper than r -2 in the outer regions. The characteristic overdensity of a halo correlates strongly with halo mass in a manner consistent with the mass dependence of the epoch of halo formation. Matching the shape of the rotation curves of disk galaxies with this halo structure requires (i) disk mass-to-light ratios to increase systematically with luminosity, (ii) halo circular velocities to be systematically lower than the disk rotation speed, and (iii) that the masses of halos surrounding bright galaxies depend only weakly on galaxy luminosity. This offers an attractive explanation for the puzzling lack of correlation between luminosity and dynamics in observed samples of binary galaxies and of satellite companions of bright spiral galaxies, suggesting that the structure of dark matter halos surrounding bright spirals is similar to that of cold dark matter halos.

...read moreread less

7,622 citations

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

...One method of breaking this degeneracy is to represent the halo by an NFW profile (Navarro et al. 1996) derived from cosmologicalN -body simulations, ρ(r) ρs = 1 (r/rs)(1 + r/rs)2 , where ρs is a characteristic density,rs = r200/c is a characteristic radius andc is a dimensionless concentration…...
[...]
...This is in stark contrast to the predictions of Navarro et al. (1996), which imply that the halo mass fraction within 3.5 kpc is between 44% and 58%....
[...]
...However, Navarro et al. (1996) state that the maximum rotation velocity can be as high as1....
[...]

Journal Article•DOI•

Reddenings derived from H I and galaxy counts : accuracy and maps.

[...]

D. Burstein, C. Heiles

01 Aug 1982-The Astronomical Journal

1,025 citations

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

...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)…...
[...]
...…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)...
[...]

Journal Article•DOI•

The existence and shapes of dust lanes in galactic bars

[...]

E. Athanassoula

15 Nov 1992-Monthly Notices of the Royal Astronomical Society

TL;DR: In this article, the flow of gas in and around the bars or ovals of model barred galaxies is studied, and it is intimately linked to the properties of the periodic orbits.

...read moreread less

Abstract: I study the flow of gas in and around the bars or ovals of model barred galaxies and show that it is intimately linked to the properties of the periodic orbits. Simulations show that the density of the gas in and around the bar region is low, except for the centre and two narrow lanes which are the loci of shocks. Such shocks form if the x 1 periodic orbits have either loops or large curvature values at their apocentres. The form of the shock loci depends on a number of parameters characterizing the bar and disc potentials. In order for shocks to be offset from the bar major axis towards its leading side, the x 2 and x 3 families must not only exist but also cover a sufficient extent along the bar major axis

...read moreread less

946 citations

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

...Athanassoula (1992) shows that these shocks are intimately linked to the dust lanes which appear in many barred galaxies....
[...]
...However, unlike the galaxy models of Athanassoula (1992), M31 is a real galaxy, modelled with a somewhat arbitrary bulge edge....
[...]
...…α 0.3 pc2M−1 yr −1 Initial gas density Σ0 1M pc−2 Constant mass radius rM 10 kpc Sound speed‡ cg 10 km s−1 Galaxy radius rG 10 kpc Courant number C 0.5 † Athanassoula (1992),‡ Cowie (1980) Simulations start with the gas at a uniform surface density Σ0 = 1 M pc−2 and on circular orbits at…...
[...]
...As in Athanassoula (1992), GALAHAD includes a routine to compensate for this by crudely simulating the interaction of stars with the ISM: star formation occurs and gas is removed in areas of high density, whereas stellar mass loss is assumed to take place at a steady rate across the galaxy....
[...]
...Following Athanassoula (1992), we set rco = R a, wherea is the length of the bulge semi-major axis....
[...]

Journal Article•DOI•

The Stellar Population Histories of Local Early-Type Galaxies. I. Population Parameters

[...]

Scott Trager¹, Scott Trager², Sandra M. Faber³, Guy Worthey⁴, J. Jesús González⁵ - Show less +1 more•Institutions (5)

Carnegie Institution for Science¹, Carnegie Learning², University of California, Santa Cruz³, St. Ambrose University⁴, National Autonomous University of Mexico⁵

01 Apr 2000-The Astronomical Journal

TL;DR: In this article, a series of investigations into the stellar populations of local elliptical galaxies as determined from their integrated spectra was conducted to determine the star formation and chemical evolution histories of present-day galaxies.

...read moreread less

Abstract: This paper commences a series of investigations into the stellar populations of local elliptical galaxies as determined from their integrated spectra. The goal of the series is to determine the star formation and chemical evolution histories of present-day elliptical galaxies. The primary galaxy sample analyzed is that of Gonzalez, which consists of 39 elliptical galaxies drawn primarily from the local field and nearby groups, plus the bulge of Messier 31. Single-burst stellar population (SSP)–equivalent ages, metallicities, and abundance ratios are derived from Hβ, Mg b, and Fe line strengths using an extension of the Worthey models that incorporates nonsolar line-strength "response functions" by Tripicco & Bell. These functions account for changes in the Lick/IDS indices caused by nonsolar abundance ratios, allowing us to correct the Worthey models for the enhancements of Mg and other α-like elements relative to the Fe-peak elements. SSP-equivalent ages of the Gonzalez elliptical galaxies are found to vary widely, 1.5 Gyr t 18 Gyr, while metallicities [Z/H] and enhancement ratios [E/Fe] are strongly peaked around [Z/H] = +0.26 and [E/Fe] = +0.20 (in an aperture of radius re/8). The enhancement ratios [E/Fe] are milder than previous estimates because of the application of nonsolar abundance corrections to both Mg b and Fe for the first time. While [E/Fe] is usually greater than zero, it is not the "E" elements that are actually enhanced but rather the Fe-peak elements that are depressed; this serves not only to weaken Fe but also to strengthen Mg b, accounting for the overall generally mild enhancements. Based on index strengths from the Lick/IDS galaxy library (Trager et al.), C is not depressed with Fe but rather seems to be on a par with other elements such as Mg in the E group. Gradients in stellar populations within galaxies are found to be mild, with SSP-equivalent age increasing by 25%, metallicity decreasing by [Z/H] = 0.20 dex, and [E/Fe] remaining nearly constant out to an aperture of radius re/2 for nearly all systems. Our ages have an overall zero-point uncertainty of at least ~25% because of uncertainties in the stellar evolution prescription, the oxygen abundance, the effect of [E/Fe] ≠ 0 on the isochrones, and other unknowns. However, the relative age rankings of stellar populations should be largely unaffected by these errors. In particular, the large spread in ages appears to be real and cannot be explained by contamination of Hβ by blue stragglers or hot horizontal-branch stars, or by fill-in of Hβ by emission. Correlations between these derived SSP-equivalent parameters and other galaxy observables will be discussed in future papers.

...read moreread less

663 citations