Search arXiv⌕ Search

arXiv subjects

Volker Springel

Publications and source records attributed to Volker Springel.

526 records · Page 30Linked to original sources

Where are the First Stars now?

We use high-resolution simulations to show that the current standard paradigm for the growth of structure in the Universe predicts the formation of a galaxy like our own to differ substantially from the classic ELS and Searle/Zinn pictures. On scales larger than the Local Group, the earliest star formation was extremely inhomogeneous, suggesting that the high redshift intergalactic medium should have large-scale abundance variations. The very oldest stars should be found today in the central regions of rich galaxy clusters. In the Milky Way's bulge and stellar halo little correlation is expected between age and metallicity. Some of the lowest metallicity stars may be relatively young. Many of the oldest stars may have high metallicity. Spheroid stars were formed before and during halo assembly, the oldest now lying preferentially at small radii, while low metallicity stars lie preferentially at large radii. The bulk of the Milky Way's stellar spheroid came from a small number of progenitors. It should show little spatial structure in the inner 5 to 15 kpc, but consist at each point of a superposition of hundreds of `cold' streams. Such streams have been detected in the Solar neighborhood.

astro-ph↗

Dynamics of pairwise motions

We derive a simple closed-form expression, relating $\vs(r)$ -- the mean relative velocity of pairs of galaxies at fixed separation $r$ -- to the two-point correlation function of mass density fluctuations, $ξ(r)$. We compare our analytic model for $\vs(r)$ with N-body simulations, and find excellent agreement in the entire dynamical range probed by the simulations ($0.1 \lsim ξ\lsim 1000$). Our results can be used to estimate the cosmological density parameter, $\Om$, directly from redshift-distance surveys, like Mark III.

astro-ph↗

Tidal tails in CDM cosmologies

We study the formation of tidal tails in pairs of merging disk galaxies with structural properties motivated by current theories of cold dark matter (CDM) cosmologies. In a recent study, Dubinski, Mihos & Hernquist (1996) showed that the formation of prominent tidal tails can be strongly suppressed by massive and extended dark haloes. For the large halo-to-disk mass ratio expected in CDM cosmologies their sequence of models failed to produce strong tails like those observed in many well-known pairs of interacting galaxies. In order to test whether this effect can constrain the viability of CDM cosmologies, we construct N-body models of disk galaxies with structural properties derived in analogy to the analytical work of Mo, Mao & White (1998). With a series of self-consistent collisionless simulations of galaxy-galaxy mergers we demonstrate that even the disks of very massive dark haloes have no problems developing long tidal tails, provided the halo spin parameter is large enough. We show that the halo-to-disk mass ratio is a poor indicator for the ability to produce tails. Instead, the relative size of disk and halo, or alternatively, the ratio of circular velocity to local escape speed at the half mass radius of the disk are more useful criteria. This result holds in all CDM cosmologies. The length of tidal tails is thus unlikely to provide useful constraints on such models.

astro-ph↗

Estimates for the Luminosity Function of Galaxies and its Evolution

A new method is presented to obtain a non-parametric maximum likelihood estimate of the luminosity function and the selection function of a flux limited redshift survey. The method parameterizes the selection function as a series of step-wise power laws and allows possible evolution of the luminosity function. We also propose a new technique to estimate the rate of evolution of the luminosity function. This is based on a minimization of the observed large-scale power with respect to the evolutionary model. We use an ensemble of mock surveys extracted from a N-body simulation to verify the power of this method. We apply our estimators to the 1.2-Jy survey of IRAS galaxies. We find a far-infrared luminosity function in good agreement with previously published results and evidence for rather strong evolution. If the comoving number density of IRAS galaxies is assumed to scale proportional to (1+z)^P, we estimate P=4.3 +/- 1.4 +/-1.

astro-ph↗