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Introduction: Semi-Analytic Galaxy Formation - Constrained Realization of the Local Universe

Constrained Simulations of the Local Universe were made in the frame of the GIF consortium, and involved :
H. Mathis¹, G. Lemson², V. Springel¹, G. Kauffmann¹, S. D. M. White¹, A. Eldar² and A.Dekel²

1 MPA Garching
2 Hebrew University

Our Constrained Realizations (CR) of the Local Universe simulate the formation and evolution of the neighbouring galaxy population starting from initial conditions with a smoothed linear density field which matches that derived from the IRAS 1.2 Jy galaxy survey. The simulations track the formation and evolution of all dark matter haloes more massive than 10¹¹ solar masses out to a distance of 8000 km/s from the Milky Way. We have implemented prescriptions similar to those of Kauffmann et al. (1999) to follow the assembly and evolution of the galaxies within these haloes. We have focused on two variants of the CDM cosmology: a LCDM and a TCDM model. Galaxy formation in each was adjusted to reproduce the I-band Tully-Fisher relation of Giovanelli et al. (1997).

We successfully compared the present-day luminosity functions, colours, morphology and spatial distribution of our simulated galaxies with those of the real local population, in particular with the Updated Zwicky Catalogue, the IRAS PSCz redshift survey, and with individual local clusters such as Coma, Virgo and Perseus. Although some discrepancies remain, our simulations recover the observed intrinsic properties and the observed spatial distribution of the local galaxies reasonably well.

These simulations can thus be used to calibrate methods which use the observed galaxy population to estimate the cosmic density parameter or to draw conclusions about the mechanisms of galaxy formation. To facilitate such work, we publically release our z=0 galaxy catalogues, together with the underlying mass distribution.

COLLISIONLESS RUNS

The simulations have been carried out on the CRAY T3E at the Computer Center (RZG) of the Max-Planck Society in Garching.

They used the parallel tree-code GADGET (Springel et al. 2001). Initially, both LCDM and TCDM simulated regions have approximatively spherical shapes and comoving radii of roughly 210 Mpc/h. They then evolve with free boundary conditions in an expanding universe. The 210 Mpc/h comoving radius includes an innermost high-resolution (hr) region, extending to 8000 km/s in radius, where the DM particles are the slightest, and an outermost low-resolution (lr) region, where the DM particles are more massive.

Note that the galaxy formation is followed exclusively in the high-resolution region, and that we discard all high-resolution DM haloes contaminated by low-mass particles.

• High resolution region : it extends to roughly 8000 km/s and contains low-mass particules. For each cosmology, the initial displacements and velocity fields for these particles have been contrained on scales greater than 5 Mpc/h by the IRAS 1.2 Jy survey, following the scheme of Kolatt et al. (1996). On smaller scales, additional unconstrained power (as required by the chosen cosmology) has been added up to the Nyquist frequency of the particles.
• Low resolution region : it extends from 8000 km/s to roughly 210 Mpc/h, and contains high-mass particules. In each cosmology, the initial displacement and velocity fields for these particles have been contrained on scales greater than 5 Mpc/h by the IRAS 1.2 Jy survey. No further power has been added on smaller scales.
  

SIMULATION PARAMETERS

We define H₀=100 h km/s/Mpc. The other parameters follow standard notation.

The subscripts "hr" and "lr" refer to the high and low resolution regions, respectively.

N is the number of (DM) particles, M the mass (units Msun/h) of one particle, and l_soft is the physical softening length (units kpc/h).

f_bar is the baryon fraction: f_bar=Omega_bar/Omega₀

alpha=star formation efficiency, epsilon=SNe feedback efficiency

f_bulge is the ratio of the satellite galaxy total mass to the central galaxy total mass beyond which a merger is supposed to trigger a starburst and form a bulge component

"Feedback" gives the hypothesis that we made for the fate of the cold gas which has been reheated by the SNe (either ejected from the DM halo and later reincorporated or always retained in the halo)

M_B,lum is the luminosity resolution limit of the simulations (in the B band), defined as the mean B band magnitude of the central galaxy of a 10 particle halo at z=0.

M_B,morpho the morphology resolution limit, defined as the mean B band magnitude of the central galaxy of a 100 particle halo at z=0.

Milky Way look-alikes are defined as galaxies of type Sb/Sc with a disk circular velocity betwen 200 and 240 km/s.

In the table below, masses are given in units of M_sun, disk star formation rates in units of M_sun/year, and we give our zero-point normalization of the Tully-Fisher realtion.

Data Download

Please click to go to the CR data-download page, including data on the galaxy and halo void test populations.

Images

Please click to go to the CR image page, including high resolution images, slices through simulations, slices with specific galaxy properties, and movies.

References

Simulating our cosmological neighbourhood: mock catalogs for velocity analysis, T. Kolatt, A. Dekel, G. Ganon and J. A. Willick, 1996, ApJ, 458, 419, astro-ph/9509066

Clustering of galaxies in a hierarchical universe -I. Methods and results at z=0, G. Kauffmann, J. Colberg, A. Diaferio and S. D. M. White, 1999, MNRAS, 303, 188, astro-ph/9805283

GADGET: A code for collisionless and gasdynamical cosmological simulations, V. Springel, N. Yoshida, S. D. M. White, New Astronomy, 2001, 6, 51, astro-ph/0003162

Simulating the Formation of the Local Galaxy Population, H. Mathis, G. Lemson, V. Springel, G. Kauffmann, S. D. M. White, A. Eldar and A. Dekel, MNRAS, submitted, astro-ph/0111099

Voids in the Simulated Local Universe, H. Mathis and S. D. M. White, MNRAS, submitted, astro-ph/0201193

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Comments to: H. Mathis hmathis@mpa-garching.mpg.de