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Tran,K.,et al. 2010, ApJin press,arXiv:0909.4079 |
WadaT.,etal., 2008, PASJ,60,517 |
arXiv:1001.0006v2 [astro-ph.CO] 4 May 2010Draft version November 2, 2018 |
Preprint typeset using L ATEX style emulateapj v. 11/10/09 |
COMPARISON OF HECTOSPEC VIRIAL MASSES WITH SZE MEASUREMENT S |
Kenneth Rines1,2, Margaret J. Geller2, and Antonaldo Diaferio3,4 |
Draft version November 2, 2018 |
ABSTRACT |
We present the first comparison of virial masses of galaxy clusters with their Sunyaev-Zel’dovich |
Effect (SZE) signals. We study 15 clusters from the Hectospec Clus ter Survey (HeCS) with |
MMT/Hectospec spectroscopy and published SZE signals. We measu re virial masses of these clusters |
from an average of 90 member redshifts inside the radius r100. The virial masses of the clusters are |
strongly correlated with their SZE signals (at the 99% confidence lev el using a Spearman rank-sum |
test). This correlation suggests that YSZcan be used as a measure of virial mass. Simulations predict |
a powerlaw scaling of YSZ∝Mα |
200withα≈1.6. Observationally, we find α=1.11±0.16, significantly |
shallower (given the formal uncertainty) than the theoretical pr ediction. However, the selection func- |
tion of our sample is unknown and a bias against less massive clusters c annot be excluded (such a |
selection bias could artificially flatten the slope). Moreover, our sam ple indicates that the relation |
between velocity dispersion (or virial mass estimate) and SZE signal has significant intrinsic scatter, |
comparable to the range of our current sample. More detailed stud ies of scaling relations are therefore |
needed to derive a robust determination of the relation between clu ster mass and SZE. |
Subject headings: galaxies: clusters: individual — galaxies: kinematics and dynamics — co smology: |
observations |
1.INTRODUCTION |
Clusters of galaxies are the most massive virialized |
systems in the universe. The normalization and evo- |
lution of the cluster mass function is therefore a sen- |
sitive probe of the growth of structure and thus cos- |
mology (e.g., Rines et al. 2007, 2008; Vikhlinin et al. |
2009; Henry et al. 2009; Mantz et al. 2008; Rozo et al. |
2008, and references therein). Many methods exist |
to estimate cluster masses, including dynamical masses |
from either galaxies (Zwicky 1937) or intracluster gas |
(e.g., Fabricant et al. 1980), gravitational lensing (e.g., |
Smith et al.2005;Richard et al.2010), andthe Sunyaev- |
Zel’dovich effect (SZE Sunyaev & Zeldovich 1972). In |
practice, these estimates are often made using simple |
observables, such as velocity dispersion for galaxy dy- |
namics or X-ray temperature for the intracluster gas. |
If one of these observable properties of clusters has a |
well-defined relation to the cluster mass, a large survey |
can yield tight constraints on cosmological parameters |
(e.g., Majumdar & Mohr 2004). There is thus much |
interest in identifying cluster observables that exhibit |
tight scaling relations with mass (Kravtsov et al. 2006; |
Rozo et al. 2008). Numerical simulations indicate that |
X-ray gas observables (Nagai et al. 2007) and SZE sig- |
nals (Motl et al. 2005) are both candidates for tight scal- |
ing relations. Both methods are beginning to gain ob- |
servational support (e.g., Henry et al. 2009; Lopes et al. |
2009; Mantz et al. 2009; Locutus Huang et al. 2009). |
Dynamical masses from galaxy velocities are unbiased |
kenneth.rines@wwu.edu |
1Department of Physics & Astronomy, Western Washington |
University, Bellingham, WA 98225; kenneth.rines@wwu.edu |
2Smithsonian Astrophysical Observatory, 60 Garden St, Cam- |
bridge, MA 02138 |
3Universit` a degli Studi di Torino, Dipartimento di Fisica G en- |
erale “Amedeo Avogadro”, Torino, Italy |
4Istituto Nazionale di Fisica Nucleare (INFN), Sezione di |
Torino, Torino, Italyin numerical simulations (Diaferio 1999; Evrard et al. |
2008), and recent results from hydrodynamical simula- |
tions indicate that virial masses may have scatter as |
small as ∼5% (Lau et al. 2010). |
Previous studies have compared SZE signals to hydro- |
staticX-raymasses(Bonamente et al.2008;Plagge et al. |
2010) and gravitational lensing masses (Marrone et al. |
2009, hereafter M09). Here, we make the first compar- |
ison between virial masses of galaxy clusters and their |
SZE signals. We use SZE measurements from the lit- |
erature and newly-measured virial masses of 15 clus- |
ters from extensive MMT/Hectospec spectroscopy. This |
comparison tests the robustness of the SZE as a proxy |
for cluster mass and the physical relationship between |
the SZE signal and cluster mass. Large SZ cluster sur- |
veys are underway and are beginning to yield cosmologi- |
calconstraints(Carlstrom et al.2010;Hincks et al.2010; |
Staniszewski et al. 2009). |
We assume a cosmology of Ω m=0.3, Ω Λ=0.7, and |
H0=70 km s−1Mpc−1for all calculations. |
2.OBSERVATIONS |
2.1.Optical Photometry and Spectroscopy |
We are completing the Hectospec Cluster Survey |
(HeCS), a study of an X-ray flux-limited sample of 53 |
galaxy clusters at moderate redshift with extensive spec- |
troscopy from MMT/Hectospec. HeCS includes all clus- |
ters with ROSAT X-ray fluxes of fX>5×10−12erg |
s−1at [0.5-2.0]keVfrom the Bright Cluster Survey (BCS |
Ebeling et al.1998)orREFLEXsurvey(B¨ ohringer et al. |
2004) with optical imaging in the Sixth Data Release |
(DR6) of SDSS (Adelman-McCarthy et al. 2008). We |
use DR6 photometry to select Hectospec targets. The |
HeCS targets are all brighter than r=20.8 (SDSS cata- |
logs are 95% complete for point sources to r≈22.2). Out |
of the HeCS sample, 15 clusters have published SZ mea- |
surements.2 Rines, Geller, & Diaferio |
2.1.1.Spectroscopy: MMT/Hectospec and SDSS |
HeCS is a spectroscopic survey of clusters in the red- |
shift range 0.10 ≤z≤0.30. We measure spectra with |
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