DLAs dominate the neutral gas, making DLA-based studies appropriate for determining its cosmic density. However, other cosmological quantities should be summed over all high-redshift objects rather than just DLAs or just Lyman break galaxies, which trace the bright end of the high-redshift rest-UV galaxy luminosity function. Another motivation for studying all types of objects is the search for the progenitors of typical spiral galaxies like the Milky Way, which have not yet been pinpointed amongst the zoo of high-redshift galaxies. In designing the Multiwavelength Survey by Yale-Chile (MUSYC, Gawiser et al. 2005a, http://www.astro.yale.edu/MUSYC), it was decided to focus on selecting all known populations of galaxies at z 3, where most objects are young and several selection techniques overlap (see review by Stern & Spinrad 1999). The various populations at this epoch are labelled by three-letter acronyms (TLAs). We discuss each below.
4.1. Lyman Break Galaxies (LBGs)
The Lyman break galaxies (LBGs) are selected via the Lyman break at 912Å in the rest-frame. Higher-energy photons are unable to escape the galaxies or travel far in the IGM due to the large cross-section for absorption of ionizing photons by neutral hydrogen (for an illustration of the technique first successfully applied by Steidel & Hamilton 1992, see Fig. 19 of Pettini 2004). At z 3, the Lyman break generates a very red color in U - V, which could also be observed for an intrinsically red object such as an M dwarf or elliptical galaxy, leading to the additional requirement of a blue continuum color in e.g. V - R, consistent with the expected starburst nature of young galaxies. This makes the LBG technique insensitive to heavily dust-reddened or evolved stellar populations.
The selected population of galaxies is described in detail by Giavalisco (2002) and Steidel et al. (2003). Star formation rates range from 10-1000 M yr-1 with a median value of ~ 50 M yr-1 after correction for reddening values ranging over 0 E(B - V) 0.4 (Pettini 2004). Inferred stellar masses range over 6 × 108 M M* 1011 M with median value 2 × 1010 M. Implied stellar ages range over 1 Myr t* 2 Gyr with median age 500 Myr (Shapley et al. 2005). Observed qualities of LBGs are summarized in Tables 1 and 2 below, giving values for the space density, clustering length and dark matter halo masses from Adelberger et al. (2005), the SFR and stellar mass per object and stellar mass density from Shapley et al. (2001) and the cosmic SFRD from Steidel et al. (1999).
4.2. Lyman Alpha Emitters (LAEs)
Starbursting galaxies can emit most of their ultraviolet luminosity in the Lyman line. Because Lyman photons are resonantly scattered in neutral hydrogen, even a small amount of dust will quench this emission. Hence, selecting objects with strong Lyman emission lines is expected to reveal a set of objects in the early phases of rapid star formation. These could either be young objects in their first burst of star formation or evolved galaxies undergoing a starburst due to a recent merger. Selecting galaxies with strong emission lines also allows us to probe the high-redshift luminosity function dimmer than the "spectroscopic" continuum limit of magnitude R = 25.5 that is used to select the Steidel et al. LBG samples, since continuum detection is not necessary for spectroscopic confirmation using the emission line.
Observed qualities of the Lyman Alpha Emitting galaxies (LAEs) are summarized in Tables 1 and 2 below, giving values for the SFR per object from Hu, Cowie, & McMahon (1998) and the space density, SFRD, clustering length and dark matter halo masses from MUSYC (Gawiser et al. 2005b).
4.3. Distant Red Galaxies (DRGs)
The inability of the Lyman break selection technique to find intrinsically red objects can be overcome by using observed NIR imaging to select high-redshift galaxies via their rest-frame Balmer/4000Å break. Looking for a continuum break in J - K selects objects at 2 < z < 4, labelled Distant Red Galaxies (DRGs) (Franx et al. 2003, van Dokkum et al. 2003). Reddy et al. (2005) offer a comparison of the redshift distributions of objects selected by LBG/star-forming colors, DRGs selected in J - K, and the passive evolution and star-forming samples selected through their BzK colors by Daddi et al. (2004). Note that this comparison is somewhat biased as the spectroscopic follow-up was performed on a sample originally selected only by the LBG/star-forming criteria. van Dokkum et al. (2005) report MUSYC results for an analogous comparison derived from a K-selected sample with inferred stellar masses > 1011 M.
Observed qualities of DRGs are summarized in Tables 1 and 2 below, giving values for the SFR and stellar mass per object from van Dokkum et al. (2004) and for the space density, SFRD, stellar mass density, clustering length and dark matter halo masses from MUSYC (Gawiser et al, in preparation).
4.4. Sub-Millimeter Galaxies (SMGs)
The Sub-millimeter galaxies (SMGs) are selected using sub-millimeter bolometer arrays, e.g. SCUBA or MAMBO, which have poor spatial resolution, ~ 15". Complementary high-resolution radio imaging is needed to obtain positions accurate enough to find optical counterparts or perform spectroscopy. This means that the SMGs with redshifts are really jointly selected in both sub-mm and radio. Observed qualities of SMGs are summarized in Tables 1 and 2 below, giving values for the space density from Chapman et al. (2003), the SFR per object and SFR density from Chapman et al. (2005), the clustering length from Webb et al. (2003) and the dark matter halo masses from MUSYC (Gawiser et al., in preparation).
4.5. Damped Lyman Absorption Systems (DLAs)
The Damped Lyman Absorption systems (DLAs) were introduced above in Section 2.1. Observed qualities of DLAs are summarized in Tables 1 and 2 below, giving the range of SFR per object for the two DLAs for which this quantity has been determined (Møller et al. 2002; Bunker 2004, see Wolfe et al. 2005 for a review). Also shown are the SFR density from Wolfe et al. (2003a) and the clustering length and dark matter halo masses determined by Cooke et al. (2005).