Southern African Large Telescope Observations of ACT SZ-Selected Clusters

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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
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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)?
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The Atacama Cosmology Telescope (ACT)
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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 ? s and as bright patches at mm
  ?s.

Visible X-ray
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SZ Effect Signals of Clusters
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Cluster Follow Up with SALT
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http//www.astro.wisc.edu/salt/SALT-suth.jpg
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Why we do optical follow-up

• 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

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SALT Specs

• 11m primary composed of 91 hexagonal mirrors
• Fixed altitude
• Spherical mirror
• Robert Stobie Spectrograph (RSS)
• It is the largest telescope in the Southern
  Hemisphere

http//images2.wikia.nocookie.net/__cb201102161600
51/saltsutherland/images/6/61/Primary.jpg
http//kelltrill.files.wordpress.com/2011/03/set-0
2-03.jpg
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Clusters lie within SDSS S82 allow visual
confirmation (include this slide?)
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RSS Multi Object Spectroscopy

• 3 masks per cluster
• 20-30 galaxies per mask
• 2 exposures per mask
• 1000s exposures

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SALT Spectra

• 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 (HK) confirmations were selected for
  velocity dispersion and mass estimates

Blue line is spectra, green line is template
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Membership criteria (include slide?)

• Ranked 3 or 4 in spectra quality
• Utilize shifty-gapper technique to remove
  non-member galaxies
• Remove galaxies outside R200

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Cluster J0320 Mask 2 Galaxy Members
Preliminary results show
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YM Relation Results

• 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.
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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