CR Main

Constrained Simulations of the Local Galaxy Population

Constrained Simulations of the Local Universe were made in the frame of the GIF consortium, and involved :

H. Mathis (1), G. Lemson (2), V. Springel (1), G. Kauffmann (1), S. D. M. White (1), A. Eldar (2) and A.Dekel (2)

(1) MPA Garching, (2) Hebrew University

introduction/ collisionless runs/ simulation parameters/ references/ HIGH RESOLUTION PICTURES for astro-ph/0111099 and astro-ph/0201193/ DATA-DOWNLOAD/ slices through the simulation/ movies/ smoothed fields/ Mark III and mock Mark III catalogues/ voids/ links/

INTRODUCTION

Our Constrained Realizations (CR) of the Local Universe simulate the formation and evolution of the neihgbouring 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.

Cosmological parameters

Model Omega0 Lambda h Gamma Sigma8

LCDM 0.3 0.7 0.7 0.21 0.9

TCDM 1.0 0.0 0.5 0.21 0.6

Collisionless simulation parameters

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).

Model N_hr M_hr (Msun/h) l_soft,hr (kpc/h) N_lr M_lr (Msun/h) l_soft,lr (kpc/h)

LCDM 50730389 0.357 x 10¹⁰ 20 20506522 14.386 x 10¹⁰ 120

TCDM 53302154 1.18978 x 10¹⁰ 20 20442823 47.952 x 10¹⁰ 120

Semi-analytic parameters

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.

Model f_bar alpha epsilon f_bulge Feedback M_B,lum M_B,morpho

LCDM 0.12 0.05 0.05 0.1 retention -16.25 -18.46

TCDM 0.2 0.15 0.03 0.1 ejection -18.45 -20.61

Masses for Milky-Way look-alikes

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.

Model Stellar mass Cold Gas mass disk SFR M_B- 5 log h M_I- 5 log h B-V Number

LCDM 9.32 x 10¹⁰ 1.05 x 10¹⁰ 1.78 -20.02 -22.01 0.74 229

TCDM 1.58 x 10¹¹ 1.15 x 10¹⁰ 3.37 -20.04 -21.99 0.71 941

REFERENCES

Some selected publications :

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

HIGH RESOLUTION PICTURES

high resolution versions of the Figures 1 and 3 of the paper "Simulating the Formation of the Local Galaxy Population" (astro-ph/0111099).

high resolution version of the Figure 1 of the paper "Voids in the Simulated Local Universe" (astro-ph/0201193).

DATA DOWNLOAD

The CR data-download page is available, including the galaxy and halo void test populations.

SLICES THROUGH THE SIMULATIONS

Detailed pictures of various sizes for the dark matter distribution, made by Volker Springel, are available here.

The following images show further projections of slices encompassing the supergalactic plane, and cut through our LCDM and TCDM cosmologies. A different colour scale than previously has been used.

SLICES WITH SPECIFIC GALAXY PROPERTIES

More images showing specific properties of the galaxies on top of the dark matter, for the LCDM model at various redshifts are also available.

MOVIES

A short movie shows the galaxy distribution on spherical shells. (caution : the movie will play at the rate of the connexion).

SMOOTHED DENSITY FIELDS

To get a more qualitative visual impression, we have smoothed the galaxy distribution with a gaussian filter, and then projected the resulting density field on the sky, in FK4 coordinates and on the supergalactic plane, in SG coordinates (caution: both pages host large pictures: download may be slow).

MarkIII and mock Mark III catalogues

Based on the results above, we (eldar@phys.huji.ac.il) have also constructed mock Mark III catalogues of peculiar velocities.

Voids

Constrained crealizations of the Local Universe are also ideal to study the simulated population of galaxies in voids and to evaluate to which extent semi-analytic models (to their luminosity resolution limit) successfully reproduce voids as large and as empty as the nearby ones. We have checked (astro-ph/0201193) whether various galaxy and halo populations selected according to observationally relevant quantities could be considered to be homogeneously distributed with respect to the bright spirals.

Down to M_B=-16.3, we came up wih negative conclusions for a possible homogeneous population.

Pictures are available here, and halo and galaxy catalogues used for the prospection of simulated voids can be downloaded there.

Back to the Galaxy Formation Group at MPA
Back to NumCos

Last modified: Feb 12, 2002. For Questions / Comments / Remarks : hmathis@mpa-garching.mpg.de

Model	Omega0	Lambda	h	Gamma	Sigma8
LCDM	0.3	0.7	0.7	0.21	0.9
TCDM	1.0	0.0	0.5	0.21	0.6

Model	N_hr	M_hr (Msun/h)	l_soft,hr (kpc/h)	N_lr	M_lr (Msun/h)	l_soft,lr (kpc/h)
LCDM	50730389	0.357 x 10¹⁰	20	20506522	14.386 x 10¹⁰	120
TCDM	53302154	1.18978 x 10¹⁰	20	20442823	47.952 x 10¹⁰	120

Model	f_bar	alpha	epsilon	f_bulge	Feedback	M_B,lum	M_B,morpho
LCDM	0.12	0.05	0.05	0.1	retention	-16.25	-18.46
TCDM	0.2	0.15	0.03	0.1	ejection	-18.45	-20.61

Model	Stellar mass	Cold Gas mass	disk SFR	M_B- 5 log h	M_I- 5 log h	B-V	Number
LCDM	9.32 x 10¹⁰	1.05 x 10¹⁰	1.78	-20.02	-22.01	0.74	229
TCDM	1.58 x 10¹¹	1.15 x 10¹⁰	3.37	-20.04	-21.99	0.71	941