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).