southern african large telescope observations of act sz-selected clusters brian kirk catherine...
TRANSCRIPT
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
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
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/__cb20110216160051/saltsutherland/images/6/61/Primary.jpg
http://kelltrill.files.wordpress.com/2011/03/set-02-03.jpg
RSS Multi Object Spectroscopy
3 masks per cluster
20-30 galaxies per mask
2 exposures per mask
1000s exposures
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
SALT Spectra
Cluster J0320 Mask 2 Galaxy Members
Preliminary results show:
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 withredshift 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