Updated: 02/17/04 (CJMILLER)

The SDSS-C4 Galaxy Cluster Catalog

Summary:  

The current catalog contains galaxy clusters found in the SDSS DR2 spectroscopic database. The clusters are found in a seven dimensional space. Our algorithm is based on the fact that galaxies within clusters are co-evolving. Thus, galaxies will not only cluster in position, but the spectral energy distributions (SEDs) will look similar. We use galaxy colors as a proxy to the SEDs. We then find galaxies that are clustered in both position and color.

There are 748 clusters in this catalog (with keep = 1; i.e., good systems with < 10% contamination).  This is the largest spectroscopic cluster catalog ever made. The REFLEX X-ray cluster catalog (also with redshifts, but often 2-3 per cluster), contains ~400 clusters.

NOTE: The latest catalog version has been run on the official SDSS DR2 spectroscopic and photometric data (spec1d version 1d23 and photo version 5_4).

Authors: Christopher J. Miller, Robert C. Nichol (CMU), Daniel Reichart (UNC)

Main Collaborators: Risa Wechsler, Gus Evrard, and Tim McKay (UMichigan). Jim Annis (Fermilab), Larry Wasserman, Chris Genovese (CMU)

Other Collaborators: Hans Boehringer, Wolfgang Voges (MPE), Tomo Goto (ICRR), Neta Bahcall, Michael Strauss (Princeton), Marc Postman (Space Telescope), Andy Connolly, Andrew Hopkins (Pitt)

Page Contents:

1. Definition of the algorithm:
2. Definition of cluster properties
3. Summary of Comparison to simulations
4. Cluster catalog
5. Summary plots of clusters
6. Science
7. Conference Proceedings
   

C4 cluster catalog (DR2-Official) (ASCII format).

C4 cluster catalog (DR2-Official) (fits format).

    For every SDSS-C4 cluster, we have created 6 figures which attempt to fully describe the color and kinematic properties of each cluster.
    In all cases, the center of the cluster is RA_MEAN and DEC_MEAN and Z (see Properties).
   
    Please take a moment to read the following descriptions and keys before you proceed to the Summary Plots.  
    Note that the color-coding is usually consistent (RED means passive,  Green means starforming, Yellow means C4 galaxy, Blue is the BCG).

(Top-Left)   m(g) - m(r) versus m(r) color-magnitude plot. Uses Petrosian apparent magnitudes.  Uses galaxies within 1Mpc of the cluster.

KEY:

• Black filled circles are every spectroscopic galaxy projected onto the sky .
• Yellow filled circles are C4 galaxies within 1000kpc of the cluster center.
• Red outlines are galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster with H(alpha) equivalent widths < 4 angstroms.
• Green outlines are galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster with H(alpha) equivalent widths > 4 angstroms.
• Blue Cross is the Brightest Cluster Galaxy.
  
• The solid lines are the upper and lower 1 sigma limits to the fit to the galaxies with M(u) - M(r) >= 1.8 (k-corrected absolute magnitudes with h = 1. See Blanton et al. 2003).
  

(Top Right)  m(r) - m(i) versus m(r) color-magnitude plot. Uses Petrosian apparent magnitudes.  Uses galaxies within 1Mpc of the cluster.

KEY:

• Black filled circles are every spectroscopic galaxy projected onto the sky.
• Yellow filled circles are C4 galaxies within 1000kpc of the cluster center.
• Red outlines are galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster with H(alpha) equivalent widths < 4 angstroms.
• Green outlines are galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster with H(alpha) equivalent widths > 4 angstroms.
• Blue Cross is the Brightest Cluster Galaxy.
  
• The solid lines are the upper and lower 1 sigma limits to the robust line-fit to the galaxies with M(u) - M(r) >= 1.8 (k-corrected absolute magnitudes with h = 1. See Blanton et al. 2003).
  

(Center Left)   RA versus DEC. Uses galaxies within 1Mpc of the cluster.

KEY:

• Black filled circles are every spectroscopic galaxy projected onto the sky (extends beyond 1Mpc)
• Yellow filled circles are C4 galaxies within 1000kpc of the cluster center.
• Red outlines are galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster with H(alpha) equivalent widths < 4 angstroms.
• Green outlines are galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster with H(alpha) equivalent widths > 4 angstroms.
• Blue Cross is the Brightest Cluster Galaxy.
  
• The ellipse is fitted to galaxies within 1000kpc and for velocites less than 4 times the velocity dispersion of the cluster.

(Center Right)  The Dressler-Schectman (1988) substructure statistic. Uses galaxies within 1500kpc and with velocities less than four times the velocity dispersion of the cluster. The radius of the circle is proportional to e^DS, where DS is each galaxies Dressler-Schectman statistic.  Galaxies which within subclumps will appear as large circles.

KEY:

• Red open circles are galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster with H(alpha) equivalent widths < 4 angstroms.
• Green open circles are galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster with H(alpha) equivalent widths > 4 angstroms.

(Bottom Left)  Velocity Dispersion Profile. Uses the bi-weighted velocity dispersions for galaxies within 500,1000,1500,2000,2500 kpc of the cluster,

KEY:

• Black filled circles are every spectroscopic galaxy within the specified projected separation (500,1000,1500,2000,2500 kpc/
• Red filled circles are for red galaxies (in the E/S0 ridgeline)
• Yellow filled circles are for C4 galaxies.
  

(Bottom Right)  Velocity Histogram. Uses galaxies within 1000kpc of the cluster center and with velocities less than 4 times the velocity dispersion of the cluster.

KEY:

Also, on the summary plots, you will find links to:

• the NASA Extragalactic Database (NED)
•  the ROSAT All-Sky Survey data from SKYVIEW,
• The SDSS Footprint Server
• The SDSS Finding Chart
  

NOTE: If you have TABBED browsing (i.e. Netscape 7.0, Mozilla 1.1+), I suggest you open the Cluster Properties in a new tab (right click on the link below)

Click here for the list of Cluster Properties and links to Summary Plots

Science:

Published:

1. Gomez, P., Nichol, R.C., Miller, C.J., Balogh, M., Goto, T., Zabludoff, A., Romer, A.K., and others. 2003 ApJ, 584, 210
   
   We present in this paper a detailed analysis of the effect of environment on the star formation activity of galaxies within the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We have used the Hα emission line to derive the star formation rate (SFR) for each galaxy within a volume-limited sample of 8598 galaxies with 0.05<=z<=0.095 and M(r^*)<=-20.45. We find that the SFR of galaxies is strongly correlated with the local (projected) galaxy density, and thus we present here a density-SFR relation that is analogous to the density-morphology relation. The effect of density on the SFR of galaxies is seen in three ways. First, the overall distribution of SFRs is shifted to lower values in dense environments compared with the field population. Second, the effect is most noticeable for the strongly star-forming galaxies (Hα EW>5 Å) in the 75th percentile of the SFR distribution. Third, there is a ``break'' (or characteristic density) in the density-SFR relation at a local galaxy density of ~1 h^-2₇₅ Mpc^-2. To understand this break further, we have studied the SFR of galaxies as a function of clustercentric radius from 17 clusters and groups objectively selected from the SDSS EDR data. The distribution of SFRs of cluster galaxies begins to change, compared with the field population, at a clustercentric radius of 3-4 virial radii (at the >1 σ statistical significance), which is consistent with the characteristic break in density that we observe in the density-SFR relation. This effect with clustercentric radius is again most noticeable for the most strongly star-forming galaxies. Our tests suggest that the density-morphology relation alone is unlikely to explain the density-SFR relation we observe. For example, we have used the (inverse) concentration index of SDSS galaxies to classify late-type galaxies and show that the distribution of the star-forming (EW Hα>5 Å) late-type galaxies is different in dense regions (within 2 virial radii) compared with similar galaxies in the field. However, at present, we are unable to make definitive statements about the independence of the density-morphology and density-SFR relation. We have tested our work against potential systematic uncertainties including stellar absorption, reddening, SDSS survey strategy, SDSS analysis pipelines, and aperture bias. Our observations are in qualitative agreement with recent simulations of hierarchical galaxy formation that predict a decrease in the SFR of galaxies within the virial radius. Our results are in agreement with recent 2dF Galaxy Redshift Survey results as well as consistent with previous observations of a decrease in the SFR of galaxies in the cores of distant clusters. Taken together, these works demonstrate that the decrease in SFR of galaxies in dense environments is a universal phenomenon over a wide range in density (from 0.08 to 10 h^-2₇₅ Mpc ^-2) and redshift (out to z~=0.5).
   
   
   
2. Miller, C.J., Nichol, R.C., Gomez, P.L., Hopkins, A.M., and Bernardi, M. 2003, ApJ, 597, 142
   
   We present the observed fraction of galaxies with an Active Galactic Nucleus (AGN) as a function of environment in the Early Data Release of the Sloan Digital Sky Survey (SDSS). Using 4921 galaxies between 0.05 <= z <= 0.095, and brighter than M_r* = -20.0 (or M* +1.45), we find at least ~ 20% of these galaxies possess an unambiguous detection of an AGN, but this fraction could be as high as ~40% after we model the ambiguous emission line galaxies in our sample. We have studied the environmental dependence of galaxies using the the distance to the 10^th nearest neighbor. As expected, we observe that the fraction of star--forming galaxies decreases with density, while the fraction of passive galaxies increases with density. In contrast, the fraction of galaxies with an AGN remains constant from the cores of galaxy clusters to the rarefied field population. We conclude that the presence of an AGN is independent of the disk component of a galaxy. Our analyses are robust against measurement error, definition of an AGN, aperture bias, stellar absorption, survey geometry and signal--to--noise. Our observations are consistent with the hypothesis that a supermassive black hole resides in the bulge of all massive galaxies and ~40% of these black holes are seen as AGNs in our sample. A high fraction of local galaxies with an AGN suggests that either the mean lifetime of these AGNs is longer than previously thought (>10^8 years), or that the AGN burst more often than expected; ~40 times over the redshift range of our sample.
   
   
3. Michael L. Balogh, Ivan K. Baldry, Robert Nichol, Chris Miller, Richard Bower, Karl Glazebrook, 2004, ApJ, 615, L101
   
   
   We analyse the u-r color distribution of 24346 galaxies with Mr<=-18 and z<0.08, drawn from the Sloan Digital Sky Survey first data release, as a function of luminosity and environment. The color distribution is well fit with two Gaussian distributions, which we use to divide the sample into a blue and red population. At fixed luminosity, the mean color of the blue (red) distribution is nearly independent of environment, with a weakly significant (~3sigma) detection of a trend for colors to become redder by 0.1-0.14 (0.03-0.06) mag with a factor ~100 increase in local density, as characterised by the surface density of galaxies within a +/-1000 km/s redshift slice. In contrast, at fixed luminosity the fraction of galaxies in the red distribution is a strong function of local density, increasing from ~10-30 per cent of the population in the lowest density environments, to ~70 per cent at the highest densities. The strength of this trend is similar for both the brightest (-23
   
4. Finn, R. A.; Balogh, M.; Miller, C.; Nichol, R. C.; Zaritsky, D.
   
   We present results on our efforts to measure total star-formation rates (SFRs) for a sample of 471 0.05 < z < 0.09 galaxy clusters drawn from the C4 catalog. The C4 catalog is a spectroscopic and color-selected cluster sample selected from the Sloan Digital Sky Survey. We investigate how the total SFR, the fraction of star-forming galaxies, and the average SFR per stellar mass depend on cluster mass, redshift, and substructure. The C4 cluster sample provides an ideal low-redshift benchmark for cluster evolution studies. Characterizing cluster star formation properties in terms of the total SFR per cluster mass, we compare the C4 clusters to published H surveys for higher redshift (0.2 < z < 0.85) clusters.
   
5. 
   Balogh, Miller, Nichol, Zabludoff, and Goto, MNRAS, 2005, in press
   
   Near-infrared imaging of 222 nearby Hdelta-strong galaxies from the SDSS. k+a and e(a) galaxies reside in environments typical of normal galaxies and not simply clusters.
   
   

1. Wechsler, R., Everad, G. et al.
   
   Mock SDSS galaxy catalogs and their use in clustering algorithms and in populating dark matter halos. Uses Jim Annis' maxBCG and the C4 clusters.
   
2. Miller, C.J., Nichol, R.C., and Sheth, R., et al. (to be submitted in Fall 2003)
   
   Radial profiles for C4 clusters using the galaxies.
   
   
3. Miller, C.J., Nichol, R.C., Romer, A.K., Voges, W., Boehringer, W., et al. (to be submitted in Fall 2003)
   
   ROSAT All-Sky Survey X-ray properties of C4 clusters.
   
   
4. Miller, C.J., et al.
   
   Spectroscopic, Photometric, and Dynamical Properties of Brightest Cluster Galaxies in C4 clusters.
   

1. Nichol, R.C. 2003:   http://xxx.lanl.gov/abs/astro-ph/0305041
   
   
2. Nichol, R.C., Miller, C.J., Goto, T. 2003: http://xxx.lanl.gov/abs/astro-ph/0301306
   
   
3. Nichol, R.C. 2001: http://xxx.lanl.gov/abs/astro-ph/0110231
   
   
4. Nichol, R.C., Miller, C.J., et al. 2000: http://xxx.lanl.gov/abs/astro-ph/0011557