Clustering of Lyman Break Galaxies


Lyman break galaxies show clustering even at a redshift of z~3. At z=3 the universe is ~ 15% of its current age. Can structure grow that fast?

From Steidel etal 1998 (ApJ,. 492, 428):


FIG. 1.—Redshift histogram of the 67 color-selected objects with z > 2 that have been confirmed spectroscopically in an 8&farcm;7 by 17&farcm;6 strip. The dotted curve represents the smoothed redshift selection function obtained to date for our overall survey, normalized so as to have the same number of total galaxies as the SSA 22 sample. Approximately one-third of the confirmed redshifts are from the SSA 22 fields. The binning here is arbitrary; the formal boundaries of any "features" in the redshift distribution used for analysis were obtained using the method described in § 3 and in the Appendix.

In order to have that level of clustering, we must have a very high bias factor (remember: bias is the constrast factor between dark matter and galaxies):



FIG. 4.—Reconciling the observed galaxy overdensity with various cosmological scenarios. The smooth curves show the expected number of peaks in this field with linear overdensity greater than δL. The shaded boxes show the approximate peak height and number density deduced from our observations. The actual box position is slightly different for each of the cosmologies, but this difference is insignificant for our purposes. If a curve passes through the box, then the corresponding parameter values are at least roughly consistent with the existence of the spike in the redshift histogram. The x range of the box is a 68% confidence interval that takes into account only the (Poisson) uncertainties in δgal; the y range of the box 0.3 < npk < 2.5 is also an approximately 68% interval on the number density of similar structures at z ∼ 3, based on the fact that we have detected one such overdensity in the first densely sampled field. The two smooth curves for each cosmology give an idea of the uncertainty in npk. The upper curve applies if the true mass of the structure is 1 σlower than our best estimate and the normalization σ8 is 1 σ higher than the best estimate of Eke, Cole, & Frenk (1996). The lower curve applies if the mass of the structure is 1 σ higher and the normalization is 1 σlower than the best estimates. See text.