PhD Thesis (PDF) - Department of Astronomy - University of Virginia

not get a complete picture of the LMXB phenomena, and may completely miss rare
but very powerful types of LMXBs.
For observations of nearby E/S0 galaxies, we typically can only detect bright
active LMXBs ( 10 37 ergs s −1 ), and these LMXBs cannot be studied in as great a
level of detail as in the Milky Way. However, there are distinct advantages to E/S0
observations. All LMXBs in a given E/S0 share a common Galactic absorption column
and a common distance, which makes it easy to determine accurate luminosities. In
most cases, nearby E/S0 galaxies fit within the field-of-view (FOV) of a Chandra
observation, and thus all of the LMXBs in a given galaxy can be observed at the
same time. Thus, the instantaneous luminosity function (LF) of LMXBs can be easily
determined. Furthermore, individual E/S0s often have 50–200 sources brighter than
∼ 5×10 37 ergs s −1 , as opposed to the small number of bright sources in the Galaxy.
There are ∼30 early-type galaxies with good Chandra observations. Thus, it is much
easier to study the properties of the population of LMXBs in external galaxies, and
to do statistical studies. Moreover, there is a much greater chance of detecting rare
but luminous states of these systems.
1.4 The Galactic Connection Between Low-Mass
X-ray Binaries and Globular Clusters
Except for some galactic nuclei, the stellar densities in the field in galaxies are
quite low. For example, the local stellar mass density near the Sun is ∼ 0.1 M⊙ pc −3
(Binney & Merrifield 1998). At such low densities, individual stars in galaxies do not
interact with one another, either physically (collisions or tidal interactions) or even
gravitationally, unless they are formed together in a binary system. Thus, in the field
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