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Yu-Ying Zhang
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Research interests and selected ongoing projects
My main research interests are in the field of cosmology, in
particular the study of the nature and distribution of matter in
galaxy clusters, the determination of the cosmological parameters, and
the formation of galaxies and galaxy clusters. I make intensive use of
interplay between observations, modeling, and theory, in which I
worked on data from hard X-rays to the radio, but mostly in the X-ray
and optical. (see
my publications). Below
is a list of selected ongoing projects.
- Galaxy clusters at medium
redshifts
Expanded from the REFLEX-DXL Sample (e.g. Zhang et al. 2006), my main
project in the last few years has been leading an X-ray XMM-Newton
survey of a sample of more than 80 galaxy clusters at the redshift of
z~0.2 including being the Principal Investigator of four XMM-Newton
surveys totaling ~1.5Msec. With a subsample of 37
clusters, Zhang et
al. (2008) and Zhang
et al. (2010)tested the assumption of hydrostatic equilibrium in
galaxy clusters combining X-ray and weak lensing approaches in
comparison with
simulations. In Zhang
et al. (2007), Zhang et
al. (2008), Okabe et
al. (2010), we attempted to find out whether/how the shape,
normalization and scatter of the cluster mass-observable scaling
relations depend on the dynamical state of clusters, and to
characterize the systematic uncertainties in dark energy experiments
that rely on counting galaxy clusters as a function of mass and
redshift. Zhang
et al. (2012) demonstrated the advantage to probe the astrophysics
of galaxy cluster assembly, e.g. whether/how group infall and star
formation affests cluster assembly within clusters.
- HIghest X-ray FLUx Galaxy Cluster Sample (HIFLUGCS)
The HIFLUGCS sample is a complete sample of galaxy clusters with X-ray flux
limit (0.1-2.4 keV) of 2.e-11 erg/s/cm2 and galactic latitude |bII| >= 20.0
deg covering 2/3 of the sky (Reiprich
& Boehringer 2002, Chen
et al. 2007).
Sixty-three out of 64 clusters in this sample have been followed-up
with XMM-Newton observations. I have developed a new method via
spectrally measured 2-D maps to quantify the subtructure and its
impact on the scaling relations using the Newton observations which
have sufficient photon statistics (
Zhang et al. 2009). I
led a release of the two-dimensional density, temperature, entropy,
and pressure maps and corresponding spectra for four HIFLUGCS clusters
at the Multivariate Archive of
X-Ray Images (MAXI) at
the German Astrophysical Virtual
Observatory (GAVO). Release of more clusters is in progress and
the influence of the substructure in the precision cluster cosmology
is under investigation.
I also led the efforts to carry out detailed X-ray analyses of the
intra-cluster medium with XMM-Newton and ROSAT data and detailed
dynamical analyses of the structures of galaxies clusters with optical
spectroscopic data based on ~14000 cluster galaxy redshifts in total,
and investigated the origin of the scatter in the X-ray luminosity
vs. velocity dispersion relation via a thorough comparison between
observations and simulations
(Zhang et
al. 2011a).
We also made the efforts to calibrate the baryon content in those
nearby clusters and investigate their star-formation efficiency and
metal-enrichment history
(Zhang et
al. 2011b; Lagana et
al. 2011b).
Recently, we investigate 14-195 keV spectra from the
Swift Burst Alert Telescope (BAT) all-sky survey for evidence of
non-thermal excess emission above the exponentially decreasing tail of
thermal emission in the flux-limited HIFLUGCS sample. To account for
the thermal contribution at BAT energies, XMM-Newton EPIC spectra are
extracted from coincident spatial regions so that both thermal and
non-thermal spectral components can be determined simultaneously. We
find marginally significant IC components in six clusters, though
after closer inspection and consideration of systematic errors we are
unable to claim a clear detection in any of
them. (Wik et
al. 2012)
Funded projects
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Curriculum Vitae
