Inhaltszusammenfassung:
This thesis presents the analysis of five XMM-Newton observations of the Draco
dwarf spheroidal galaxy (dSph) in X-rays. We performed source detection sepa-
rately for each image in each observation and for the total band mosaic image and
produced a catalogue of 70 X-ray sources. The sources were classified through
cross-correlation with catalogues of other wavelengths, spectral analysis, hardness
ratio diagrams, and variability studies. We classified 18 sources as active galac-
tic nuclei (AGNs) and 9 sources as galaxies and galaxy candidates. Six sources
were classified as foreground stars and one source as a foreground contact binary
system in the Milky Way. Four sources were classified as Low-mass X-ray bi-
nary (LMXB) candidates. One of them shows a significant pulsation, while the
others were classified based on the X-ray-to-optical flux ratio and their positionthe colour-magnitude diagram. We also found a symbiotic star, a candidate forcataclysmic variable, and a binary system in the Draco dSph. Based on hardness
ratios we classified 9 hard sources, which can be AGNs or LMXBs, in the fieldthe Draco dSph.
In the next step, the X-ray luminosity functions (XLFs) of the X-ray sourcesthe energy ranges of 2.0 − 10 keV and 0.5 − 2 keV were derived. The XLFs indicate
that X-ray sources in the field of the Draco dSph are strongly contaminated by
AGNs. The 0.2−5 keV XLF shows an excess of about ten sources, which are most likely objects
in Draco dSph.
The studies of XLFs were continued by deriving the XLFs of five other dwarf
galaxies, Phoenix, Fornax, Leo I, UMi, and UMa II, based on the observations
of XMM-Newton in the energy range of 0.5 − 2 keV. We studied the star forma-
tion history of each galaxy using literature, and showed that there is a correlation
between the population of X-ray binaries and the recent star formation history
of dwarf galaxies. The normalised XLF of Phoenix and Leo I dSphs represent
the XLF of dwarf galaxies before completely leaving the star forming ages. The
XLF shows that dwarf galaxies in this stage contain a population of LMXBs
with luminosities of log~ 34 − 35 erg/s. The XLFs of old dSph (Draco, UMi,
and UMa II) show that their X-ray sources have very low luminosity ranges log ~ 32 − 1034 erg /s . Therefore, it seems that they are dominated by white-dwarf
binaries and/or faint transient LMXBs. In the case of the Fornax dSph, we found
an unexpected luminosity range for its X-ray sources, inconsistent with the recent
star formation history of the galaxy. We suggested a possible correlation between
the nature of the X-ray sources of Fornax and the structure of the galaxy (its dark
matter halo). However, more studies of the nature of X-ray sources in this galaxy
are necessary.
In the last part of the studies, we estimated dark matter halo mass that is required
to keep the LMXBs of the Draco dSph, on the basis of the escape velocity of the
LMXBs. We considered dark matter halo masses, suggested by different models,
and showed that this galaxy could retain its LMXBs with speeds of 70 km/s assuming a dark halo mass of 10^9 solar masses.