Research results on clusters of galaxies
1. Identification of clusters of galaxies and updated catalog
Using photometric redshifts of galaxies, Wen, Han & Liu (2009, ApJS, 183, 197) identified 39,668 clusters from SDSS DR6. The sample is nearly three times of the famous previously largest cluster sample, maxBCG (Koester et al. 2007) and has a wide redshift range.
Improving the searching method, Wen, Han & Liu (2012, ApJS, 199, 34) identified 132,684 clusters from SDSS-III in the redshift range of 0.05<z<0.8.
Sky coverage (upper) of 132,684 clusters from Wen, Han & Liu (2012)
and typical distance distribution (lower)
Using the spectra data of SDSS DR9, we have updated the spectroscopic redshifts for 52,683 clusters. The updated catalog of galaxy clusters is now available here (cluster_dr9sz.dat) with the absolute magnitudes of BCGs included.
The format is
Col.(1): cluster ID;
Col.(2): R.A. (J2000) of cluster (or BCG) in degree
Col.(3): Decl. (J2000) of cluster (or BCG) in degree
Col.(4): photo-z of cluster
Col.(5): spectroscopic redshift of cluster
Col.(6): r-band magnitude of BCG
Col.(7): r200 of cluster in Mpc
Col.(8): cluster richness
Col.(9): absolute magnitude of BCG
Col.(10): number candidates of member candidates within r200
z=0.10 z=0.24 z=0.32 z=0.40
z=0.48 z=0.63 z=0.73 z=0.78
Examples of identified clusters from low to high redshift
Additionally, Wen & Han (2011, ApJ, 734, 68) identified 631, 202, 187 and 737 clusters in the redshift range of 0.1<z<1.6 from CFHT-wide, CFHT-deep, COSMOS and SWIRE fields. Merging these clusters samples gives 1644 clusters in the four survey fields, of which 1088 are newly identified.
Redshift distributions of identified clusters. The grey histograms show the distributions of previously known clusters
2. Strong lensing systems
Visually inspecting the color images, we found 13 strong lensing systems (Wen et al. 2009, RAA, 9, 5) from 39,668 clusters in Wen, Han & Liu (2009), of which 11 have been spectroscopically confirmed later.
Examples of lensing systems
Later, we found 68 strong lensing systems from 132,684 clusters (Wen, Han & Jiang 2011, RAA, 11, 1185). More importantly, we find that richer clusters have a higher probability for lensing.
Lensing probability as a function of cluster richness
3. Galaxy clusters as probes for cosmology
Wen, Han & Liu (2010, MNRAS, 407, 533) used the mass function of clusters to constrain the cosmology parameters, Ωm and σ8. With the scale relations between cluster mass and optical richness and total luminosity for 53 mass known clusters, the masses of clusters at 0.05<z<0.1 and 0.2<z<0.25 are estimated. Fittings the mass functions to a theoretical formula, we get σ8~0.85-0.9.
Mass functions for clusters of 0.05<z<0.1 (left) and 0.2<z<0.25 (right)
Hong et al. (2012, ApJ, 749, 81) used two point correlation of galaxy clusters to study the large scale structure of the universe. At scales of 10-50 Mpc, the correlation is well described by a power law with an index of -2.1. At the scale of ~110 Mpc, a baryon acoustic oscillation peak is detected.
Two point correlation of galaxy clusters at scales of 10-50 Mpc (left)
and 50-200 Mpc (right)