Close galaxy pairs with accurate photometric redshifts

Facundo Rodriguez, Elizabeth Johana Gonzalez, Ana Laura O'Mill, Enrique Gaztañaga, Pablo Fosalba, DIego García Lambas, Mar Mezcua, Małgorzata Siudek

Research output: Contribution to journalArticlepeer-review


Context: Studies of galaxy pairs can provide valuable information to jointly understand the formation and evolution of galaxies and galaxy groups. Consequently, taking the new high-precision photo-z surveys into account, it is important to have reliable and tested methods that allow us to properly identify these systems and estimate their total masses and other properties. 

Aims: In view of the forthcoming Physics of the Accelerating Universe Survey (PAUS), we propose and evaluate the performance of an identification algorithm of projected close isolated galaxy pairs. We expect that the photometrically selected systems can adequately reproduce the observational properties and the inferred lensing mass-luminosity relation of a pair of truly bound galaxies that are hosted by the same dark matter halo. 

Methods: We developed an identification algorithm that considers the projected distance between the galaxies, the projected velocity difference, and an isolation criterion in order to restrict the sample to isolated systems. We applied our identification algorithm using a mock galaxy catalog that mimics the features of PAUS. To evaluate the feasibility of our pair finder, we compared the identified photometric samples with a test sample that considers that both members are included in the same halo. Taking advantage of the lensing properties provided by the mock catalog, we also applied a weak-lensing analysis to determine the mass of the selected systems. 

Results: Photometrically selected samples tend to show high purity values, but tend to misidentify truly bounded pairs as the photometric redshift errors increase. Nevertheless, overall properties such as the luminosity and mass distributions are successfully reproduced. We also accurately reproduce the lensing mass-luminosity relation as expected for galaxy pairs located in the same halo.

Original languageEnglish
Article numberA123
Number of pages10
JournalAstronomy and Astrophysics
Publication statusPublished - 21 Feb 2020


  • galaxies: groups: general
  • galaxies: halos
  • gravitational lensing: weak

Cite this