The majority opinion favors cold dark matter, but there are a few who suggest warm dark matter as a solution for some problems, iincluding galacttic angular momentum. But hot dark matter is out, I think, because it's too hard to form structure as soon as we know it formed.

• Galaxy Formation and the Intergalactic Medium Research Group, University of Texas at Austin.
• Galaxy Formation, public pages from the Coamology Group at Cambridge University.
• Galaxy Formation and the Development of Large-Scale Structure: Caption, leads to super-computer developed movies of galaxy formation, and cosmic large scale structure formation. The simulation match observed structure characteristics fairly well, so it's hard to see such a radical solution as the electric cosmos is needed to handle any problems that do exist.

Of course, when I say "galaxy formation is pretty well understood at the basic level", I don't mean that we now know all there is to know, but rather that we understand the basic input from standard physics, and how it will lead to galaxy formation. But this is still an area of active research. Here are a few more or less randomly selected papers of interest.

Hierarchical galaxy formation
S. Cole, et al.
Monthly Notices of the Royal Astronomical Society 319(1): 168-204, November 21, 2000.
Abstract: We describe the GALFORM semi-analytic model for calculating the formation and evolution of galaxies in hierarchical clustering cosmologies. It improves upon, and extends, the earlier scheme developed by Cole et al. The model employs a new Monte Carlo algorithm to follow the merging evolution of dark matter haloes with arbitrary mass resolution. It incorporates realistic descriptions of the density profiles of dark matter haloes and the gas they contain; it follows the chemical evolution of gas and stars, and the associated production of dust; and it includes a detailed calculation of the sizes of discs and spheroids. Wherever possible, our prescriptions for modelling individual physical processes are based on results of numerical simulations. They require a number of adjustable parameters, which we fix by reference to a small subset of local galaxy data. This results in a fully specified model of galaxy formation which can be tested against other data. We apply our methods to the Lambda CDM cosmology (Omega (0) = 0.3, Lambda (0) = 0.7), and find good agreement with a wide range of properties of the local galaxy population: the B- and K-band luminosity functions, the distribution of colours for the population as a whole, the ratio of ellipticals to spirals, the distribution of disc sizes, and the current cold gas content of discs. Inspire of the overall success of the model, some interesting discrepancies remain: the colour-magnitude relation for ellipticals in clusters is significantly flatter than observed at bright magnitudes (although the scatter is about right), and the model predicts galaxy circular velocities, at a given luminosity, that are about 30 per cent larger than is observed. It is unclear whether these discrepancies represent fundamental shortcomings of the model, or whether they result from the various approximations and uncertainties inherent in the technique. Our more detailed methods do not change our earlier conclusion that just over half the stars in the Universe are expected to have formed since z less than or similar to 1.5.


The hierarchical origin of galaxy morphologies
M. Steinmetz & J.F. Navarro
New Astronomy 7(4): 155-160, June 2002
Abstract: We report first results from a series of N-body/gasdynamical simulations designed to study the origin of galaxy morphologies in a cold dark matter-dominated universe. The simulations include star formation and feedback and have numerical resolution sufficiently high to allow for a direct investigation of the morphology of simulated galaxies. We find, in agreement with previous theoretical work, that the presence of the main morphological components of galaxies-disks, spheroids, bars-is regulated by the mode of gas accretion and intimately linked to discrete accretion events. In the case we present, disks arise from the smooth deposition of cooled gas at the center of dark halos, spheroids result from the stirring of preexisting disks during mergers, and bars are triggered by tides generated by satellites. This demonstrates that morphology is a transient phenomenon within the lifetime of a galaxy and that the Hubble sequence reflects the varied accretion histories of galaxies in hierarchical formation scenarios. In particular, we demonstrate directly that disk/bulge systems can be built and rebuilt by the smooth accretion of gas onto the remnant of a major merger and that the present-day remnants of late dissipative mergers between disks are spheroidal stellar systems with structure resembling that of field ellipticals. The perplexing variety of galaxy morphologies is thus highly suggestive of-and may actually even demand-a universe where structures have evolved hierarchically.

The halo occupation distribution and the physics of galaxy formation
A.A. Berlind AA, et al.
Astrophysical journal 593(1): 1-25, Part 1, August 10 2003.
Abstract: The halo occupation distribution ( HOD) describes the bias between galaxies and dark matter by specifying (1) the probability P(dN/M) that a halo of virial mass M contains N galaxies of a particular class and (2) the relative spatial and velocity distributions of galaxies and dark matter within halos. We calculate and compare the HODs predicted by a smoothed particle hydrodynamics (SPH) simulation of a LambdaCDM cosmological model (cold dark matter with a cosmological constant) and by a semianalytic galaxy formation model applied to the same cosmology. Although the two methods predict different galaxy mass functions, their HOD predictions for samples of the same space density agree remarkably well. In a sample defined by a baryonic mass threshold, the mean occupation function [N](M) exhibits a sharp cutoff at low halo masses, a slowly rising plateau in which [N] climbs from 1 to 2 over nearly a decade in halo mass, and a more steeply rising high-occupancy regime at high halo mass. In the low-occupancy regime, the factorial moments [N(N - 1)] and [N(N-1)(N - 2)] are well below the values of [N](2) and [N](3) expected for Poisson statistics, with important consequences for the small-scale behavior of the two- and three-point correlation functions. The HOD depends strongly on galaxy age, with high-mass halos populated mainly by old galaxies and low-mass halos by young galaxies. The distribution of galaxies within SPH halos supports the assumptions usually made in semianalytic calculations: the most massive galaxy lies close to the halo center and moves near the halo's mean velocity, while the remaining, satellite galaxies have the same radial profile and velocity dispersion as the dark matter. The mean occupation at fixed halo mass in the SPH simulation is independent of the halo's larger scale environment, supporting both the merger tree approach of the semianalytic method and the claim that the HOD provides a complete statistical characterization of galaxy bias. We discuss the connections between the predicted HODs and the galaxy formation physics incorporated in the SPH and semianalytic approaches. These predictions offer useful guidance to theoretical models of galaxy clustering, and they will be tested empirically by ongoing analyses of galaxy redshift surveys. By applying the HODs to a large-volume N-body simulation, we show that both methods predict slight departures from a power-law galaxy correlation function, similar to features detected in recent observational analyses.

And a few other noteworthy efforts:

• Simulations of Galaxy Formation in a Lambda CDM Universe III: The Dissipative Formation of an Elliptical Galaxy
• Simulations of Galaxy Formation in a Lambda CDM Universe II: The Fine Structure of Simulated Galactic Disks
• Simulations of Galaxy Formation in a Lambda CDM Universe I: Dynamical and Photometric Properties of a Simulated Disk Galaxy
• The Properties of Spiral Galaxies: Confronting Hierarchical Galaxy Formation Models with Observations