Simulating the joint evolution of quasars, galaxies and their large-scale distribution

Abstract

The cold dark matter model has become the leading theoretical paradigm for the formation of structure in the Universe. Together with the theory of cosmic inflation, this model makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability. Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations. Here we present a novel framework for the quantitative physical interpretation of such surveys. This combines the largest simulation of the growth of dark matter structure ever carried out with new techniques for following the formation and evolution of the visible components. We show that baryon-induced features in the initial conditions of the Universe are reflected in distorted form in the low-redshift galaxy distribution, an effect that can be used to constrain the nature of dark energy with next generation surveys.

Figures (11)

• Figure 1: The dark matter density field on various scales. Each individual image shows the projected dark matter density field in a slab of thickness $15\,h^{-1}{\rm Mpc}$ (sliced from the periodic simulation volume at an angle chosen to avoid replicating structures in the lower two images), colour-coded by density and local dark matter velocity dispersion. The zoom sequence displays consecutive enlargements by factors of four, centred on one of the many galaxy cluster halos present in the simulation.
• Figure 2: Differential halo number density as a function of mass and epoch. The function $n(M,z)$ gives the comoving number density of halos less massive than $M$. We plot it as the halo multiplicity function $M^2\rho^{-1}\,{\rm d}n/{\rm d}M$, where $\rho$ is the mean density of the universe. Groups of particles were found using a friends-of-friends algorithmDavis1985 with linking length equal to 0.2 of the mean particle separation. The fraction of mass bound to halos of more than 20 particles (vertical dotted line) grows from $6.42\times 10^{-4}$ at $z=10.07$ to 0.496 at $z=0$. Solid lines are predictions from an analytic fitting function proposed in previous workJenkins2001, while the dashed lines give the Press-Schechter modelPress1974 at $z=10.07$ and $z=0$.
• Figure 3: Environment of a 'first quasar candidate' at high and low redshifts. The two panels on the left show the projected dark matter distribution in a cube of comoving sidelength $10\,h^{-1}{\rm Mpc}$, colour-coded according to density and local dark matter velocity dispersion. The panels on the right show the galaxies of the semi-analytic model overlayed on a gray-scale image of the dark matter density. The volume of the sphere representing each galaxy is proportional to its stellar mass, and the chosen colours encode the restframe stellar $B-V$ colour index. While at $z=6.2$ (top) all galaxies appear blue due to ongoing star formation, many of the galaxies that have fallen into the rich cluster at $z=0$ (bottom) have turned red.
• Figure 4: Galaxy 2-point correlation function at the present epoch. Red symbols (with vanishingly small Poisson error-bars) show measurements for model galaxies brighter than $M_K = -23$. Data for the large spectroscopic redshift survey 2dFGRSHawkins2003 are shown as blue diamonds. The SDSSZehavi2002 and APMPadilla2003 surveys give similar results. Both, for the observational data and for the simulated galaxies, the correlation function is very close to a power-law for $r\le 20\, h^{-1}{\rm Mpc}$. By contrast the correlation function for the dark matter (dashed line) deviates strongly from a power-law.
• Figure 5: Galaxy clustering as a function of luminosity and colour. In the panel on the left, we show the 2-point correlation function of our galaxy catalogue at $z=0$ split by luminosity in the bJ-band (symbols). Brighter galaxies are more strongly clustered, in quantitative agreement with observationsNorberg2001 (dashed lines). Splitting galaxies according to colour (right panel), we find that red galaxies are more strongly clustered with a steeper correlation slope than blue galaxies. ObservationsMadgwick2003 (dashed lines) show a similar trend, although the difference in clustering amplitude is smaller than in this particular semi-analytic model.