Crowded Field Galaxy Photometry: Precision Colors in the CLASH Clusters

Thomas Connor, Megan Donahue, Daniel D. Kelson, John Moustakas, Dan Coe, Marc Postman, Larry D. Bradley, Anton M. Koekemoer, Peter Melchior, Keiichi Umetsu, G. Mark Voit

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


We present a new method for photometering objects in galaxy clusters. We introduce a mode-filtering technique for removing spatially variable backgrounds, improving both detection and photometric accuracy (roughly halving the scatter in the red sequence compared to previous catalogs of the same clusters). This method is based on robustly determining the distribution of background pixel values and should provide comparable improvement in photometric analysis of any crowded fields. We produce new multiwavelength catalogs for the 25 CLASH cluster fields in all 16 bandpasses from the UV through the near-IR, as well as rest-frame magnitudes. A comparison with spectroscopic values from the literature finds a ∼30% decrease in the redshift deviation from previously released CLASH photometry. This improvement in redshift precision, in combination with a detection scheme designed to maximize purity, yields a substantial upgrade in cluster member identification over the previous CLASH galaxy catalog. We construct luminosity functions for each cluster, reliably reaching depths of at least 4.5 mag below M∗ in every case, and deeper still in several clusters. We measure M∗, α, and their redshift evolution, assuming the cluster populations are coeval, and find little to no evolution of a, -0.9 ≲ 〈α〉 ≲ -0.8, and M∗ values consistent with passive evolution. We present a catalog of galaxy photometry, photometric and spectroscopic redshifts, and rest-frame photometry for the full fields of view of all 25 CLASH clusters. Not only will our new photometric catalogs enable new studies of the properties of CLASH clusters, but mode-filtering techniques, such as those presented here, should greatly enhance the data quality of future photometric surveys of crowded fields.

Original languageEnglish (US)
Article number37
JournalAstrophysical Journal
Issue number1
StatePublished - Oct 10 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • galaxies: clusters: general
  • methods: data analysis
  • techniques: photometric


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