David Thomas Hill PhD Thesis - Research@StAndrews:FullText ...

Chapter 1. Introduction: The luminosity distribution and total luminosity density of
galaxies
from the Schmidt Telescope were scanned, and 20 million objects were detected. A magni-
tude limited (mbj = 20.5mag) catalogue of 2 million galaxies was taken from this sample.
Preparation for SDSS (Gunn & Knapp, 1993) and 2MASS (Kleinmann, 1992) began in
the early nineties. SDSS was a successor survey to the DSS: a predominantly northern sky
survey based at the same site, with the advantage of 50 years of technological advancement
including, importantly, the switch from photographic plates to direct measurement using
CCDs. SDSS imaging provides the majority of the optical data used within this thesis,
and it is further described in Chapter 2. 2MASS had a similar relationship to IRc, with the
great advances in NIR technology giving it the capacity to observe 11 magnitudes deeper
and with ∼ 100% sky coverage in three filters (JHKs). This increase in scope allowed it
to examine the L and T dwarf star populations for the first time (Kirkpatrick et al., 1999),
and sources obscured by the dust in the Galactic plane (e.g. the overdensity of sources
in Canis Major that may be a dwarf galaxy, Martin et al. 2004). 2MASS was followed
up by UKIDSS (Lawrence et al., 2007), which began observing in 2005, is 3 magnitudes
deeper than 2MASS, and observes using four filters (YJHK). UKIDSS imaging provides
the NIR data for this thesis, and is described in Chapter 2.
1.1.3 The advancement in redshift surveys
However, progressively deeper photometry alone cannot answer most cosmological prob-
lems. Some form of distance indicator to the detected sources is necessary, such as using
Cepheid variables (Leavitt & Pickering, 1912) or supernovae (Colgate, 1979) as standard
candles. Cepheid variables are stars with a characteristic, periodic variation in brightness
(due to an obscuring outer envelope of Helium that expands and contracts), with the pe-
riod of the variation proportional to the luminosity of the star itself. Type Ia supernova
have a similarly invariant property: the peak of their luminous output is constant, as is the
rate at which the luminosity decays from that peak. From the observed apparent magni-
tude and the theoretical absolute magnitude, the distance to the galaxies containing these
sources can be surmised. However, these techniques are not feasible indicators for large
samples of sources. Firstly, they require source variability to be measured, thus requiring a
large amount of telescope time. Secondly, the Cepheid variable method requires a specific
stellar type to be resolvable within the source, and the supernova technique requires a
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