Galaxy mergers and interactions

The merger history of a given population is estimated measuring its merger fraction fm, i.e., the fraction of galaxies in a sample suffering a merging process, both by morphological criteria (highly distorted galaxies are merger remnants) and by close pair statistics (two galaxies close in the sky plane and in redshift space, Dv ≤ 500 km/s, that will lead to a merger).

ALHAMBRA merger fraction of MB ≤ -20 galaxies from PDF analysis

Figure 1 - ALHAMBRA merger fraction of MB ≤ -20 galaxies from PDF analysis (orange stars). Red symbols are from spectroscopic studies (from lower to higher redshifts: SSRS2, Patton+00; MGC, López-Sanjuan+10; CNOC2, Patton+02; VVDS, López-Sanjuan+15a; DEEP2, Lin+04, Lin+08). The dashed line is the best-fitting power-law to the data.

The definition of a close pair in photometric redshift surveys is limited by the Dv ≤ 500 km/s condition, since typical errors in photometric redshifts are larger. This leads to false pairs due to projection effects. The PDF-based method presented in López-Sanjuan+15a, that uses the full PDF of the sources in redshift space, provides robust and accurate merger fractions and rates when comparing with spectroscopically derived measurements (Fig. 1). The method outlined in López-Sanjuan+15a will be generalised to estimate the merger fraction and rate in J-PAS.

PHASE: Development phase.