Dynamical virial masses of Lyman-break galaxy haloes at z=3

We improve on our earlier dynamical estimate of the virial masses of the haloes of Lyman-break galaxies (LBGs) at redshift z=3 by accounting for the effects of seeing, slit width, and observational uncertainties. From an analysis of the small number of available rotation curves for LBGs we determine a relation Vc7=(1.9+/-0.2)sigma between circular velocity at a radius of 7kpc, and central line velocity width. We use this relation to transform the measured velocity widths of 32 LBGs to the distribution of circular velocities, for the population of LBGs brighter than R=25.5. We compare this distribution against the predicted distribution for the 'massive-halo' model in which LBGs pinpoint all of the highest mass dark matter haloes at that epoch. The observed LBG circular velocities are smaller than the predicted circular velocities by a factor >1.4+/-0.15. This is a lower limit as we have ignored any increase of circular velocity caused by baryonic dissipation. The massive-halo model predicts a median halo virial mass of 10^12.3 Msol, and a small spread of circular velocities. Our median estimated dynamical mass is <10^(11.6+/-0.3) Msol, which is significantly smaller; furthermore, the spread of our circular velocities is much larger than the massive-halo prediction. These results are consistent with a picture which leaves some of the most-massive haloes available for occupation by other populations which do not meet the LBG selection criteria. The median halo mass recently estimated by Adelberger et al. from the measured clustering of LBGs is 10^(11.86+/-0.3) Msol. Our dynamical analysis appears to favour lower masses and to be more in line with the median mass predicted by the collisional starburst model of Somerville et al., of 10^11.3 Msol. [abridged]Comment: 6 pages, 5 figures, MNRAS Letters, Accepte

HST Images of a Galaxy Group at z=2.81, and the Sizes of Damped Lyman Alpha Galaxies

We present HST WFPC2 observations in three bands (F450W, F467M and F814W) of a group of three galaxies at z=2.8 discovered in a ground-based narrow-band search for Lyman alpha emission near the z=2.8 quasar PKS0528-250. One of the galaxies is a damped (DLA) absorber and these observations bear on the relation between the DLA clouds and the Lyman-break galaxies and the stage in the evolution of galaxies they represent. We describe a procedure for combining the undersampled WFPC2 images pointed on a sub-pixel grid, which largely recovers the full sampling of the WFPC2 point spread function (psf). These three galaxies have similar properties to the Lyman-break galaxies except that they have strong Lyman alpha emission. The three galaxies are detected in all three bands, with average B~26, I~25. Two of the galaxies are compact with intrinsic (i.e. after correcting for the effect of the psf) half-light radii of ~0.1 arcsec (~0.4/h kpc, q_o=0.5). The third galaxy comprises two similarly compact components separated by 0.3 arcsec. The HST images and a new ground-based Lyman alpha image of the field provide evidence that the three galaxies are more extended in the light of Lyman alpha than in the continuum. The measured impact parameters for this DLA galaxy (1.17 arcsec), for a second confirmed system, and for several candidates, provide a preliminary estimate of the cross-section-weighted mean radius of the DLA gas clouds at z~3 of less than 13/h kpc, for q_o=0.5. Given the observed sky covering factor of the absorbers this implies that for q_o=0.5 the space density of DLA clouds at these redshifts is more than five times the space density of spiral galaxies locally, with the actual ratio probably considerably greater. For q_o=0.0 there is no evidence as yet that DLA clouds are more common than spiral galaxies locally.Comment: 11 pages, LaTeX, 6 Figures total (4 colour GIF-format, 2 PostScript), accepted for publication in MNRA

Cloud information for FIRE from surface weather reports

Surface weather observations of clouds were analyzed to obtain a global cloud climatology (Warren et al, 1986; 1988). The form of the synoptic weather code limits the types of cloud information which are available from these reports. Comparison of surface weather reports with instrumental observations during the FIRE field experiments can help to clarify the operational definitions which were made in the climatology because of the nature of the synoptic code. The long-term climatology from surface weather observations is also useful background for planning the location and timing of intensive field experiments

The lens and source of the optical Einstein ring gravitational lens ER 0047-2808

(Abridged) We perform a detailed analysis of the optical gravitational lens ER 0047-2808 imaged with WFPC2 on the Hubble Space Telescope. Using software specifically designed for the analysis of resolved gravitational lens systems, we focus on how the image alone can constrain the mass distribution in the lens galaxy. We find the data are of sufficient quality to strongly constrain the lens model with no a priori assumptions about the source. Using a variety of mass models, we find statistically acceptable results for elliptical isothermal-like models with an Einstein radius of 1.17''. An elliptical power-law model (Sigma \propto R^-beta) for the surface mass density favours a slope slightly steeper than isothermal with beta = 1.08 +/- 0.03. Other models including a constant M/L, pure NFW halo and (surprisingly) an isothermal sphere with external shear are ruled out by the data. We find the galaxy light profile can only be fit with a Sersic plus point source model. The resulting total M/L_B contained within the images is 4.7 h_65 +/-0.3. In addition, we find the luminous matter is aligned with the total mass distribution within a few degrees. The source, reconstructed by the software, is revealed to have two bright regions, with an unresolved component inside the caustic and a resolved component straddling a fold caustic. The angular size of the entire source is approx. 0.1'' and its (unlensed) Lyman-alpha flux is 3 x 10^-17 erg/s/cm^2.Comment: 13 pages, 5 figures. Revised version accepted for publication in MNRA