Transcript ppt - Rencontres du Vietnam

Southern African Large Telescope
Observations of ACT SZ-Selected
Clusters
Brian Kirk
Catherine Cress, Matt Hilton, Steve Crawford, Jack Hughes, Felipe Menanteau, etc
Centre for High Performance Computing, UKZN, SAAO, Rutgers Univ
Recontres du Vietnam July 28 – August 3, 2013
Quy Nhon, Vietnam
http://mcdonaldobservatory.org/sites/default/files/images/news/gallery/salt.
startrails.jpg
Evolution of Structure through Time
Structure of galaxies, clusters of galaxies,
super clusters, etc. form through
gravitational collapse of density
fluctuations seen in the CMB.
How structure evolves and how it appears
to us depends on cosmological
parameters.
Our goal is to sample galaxy clusters as a
function of z to constrain these
cosmological parameters.
w value has an affect on the number
density of clusters over a given SZ
detection threshold
w value of curve peak from top to bottom: 1, -0.6, -0.3, 0
Haiman et al (2001)
The Atacama Cosmology Telescope
(ACT)
Sunyaev-Zeldovich effect:
Hot gas (107K) exists in galaxy cluster
environments.
CMB photons colliding with the hot gas
get up-scattered to higher
frequencies by the inverse Compton
effect.
Hot e-’s give up their energy to radio
photons.
ACT maps show galaxy clusters as
holes in the CMB sky at radio λ ’s
and as bright patches at mm λ’s.
Visible
X-ray
SZ Effect Signals of Clusters
Cluster Follow Up with SALT
http://www.astro.wisc.edu/salt/SALT-suth.jpg
Why we do optical follow-up
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Sunyaev Zel-Dovich – Mass
Relation (YM relation)
Calibrate YM relation with
cluster masses
Using the cluster locations
identified by ACT, we
measure redshifts of galaxies
and velocity dispersions of
the cluster so masses can be
estimated
SALT Specs
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11m primary composed of 91
hexagonal mirrors
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Fixed altitude
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Spherical mirror
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Robert Stobie Spectrograph
(RSS)
http://images2.wikia.nocookie.net/__cb20110216160051/saltsutherland/images/6/61/Primary.jpg
It is the largest telescope in
the Southern Hemisphere
http://kelltrill.files.wordpress.com/2011/03/set-02-03.jpg
RSS Multi Object Spectroscopy
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3 masks per
cluster
20-30 galaxies
per mask
2 exposures per
mask
1000s exposures
SALT Spectra
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Once spectra is reduced it is
correlated with galaxy
templates.
7 different galaxy templates
from SDSS
Of the spectra acquired, only
those with multiple line (H+K)
confirmations were selected
for velocity dispersion and
mass estimates
Blue line is spectra, green line is template
Cluster J0320 Mask 2 Galaxy Members
Preliminary results show:
YM Relation Results
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SALT observations
will help us to
characterize the
scaling relation
between SZ signal
and cluster mass –
as well as improving
our understanding of
this relation's
redshift evolution
SALT observations
are ongoing through
2013.
Y200 –dynamical mass relation derived from 2010B Gemini/VLT observations
of southern ACT clusters (solid line, Sifon et al., 2012). The slope of the
relation is consistent with the self-similar prediction; more observations
are needed to improve this result and constrain the evolution with
redshift of the relation. Note the Battaglia et al. result is
from numerical simulations, and the Planck result is from
stacking clusters at much lower redshifts than the ACT sample.
In Summary
* cluster counts as a function of redshift constrain cosmology
* need to measure cluster masses accurately
* using SALT to collect spectra of galaxy clusters detected by ACT
* measuring mass of clusters using velocity dispersions to help calibrate YM
relation