A Catalog of Isolated Galaxy Pairs Limited to Absolute Magnitude -18.5 Drawn from HyperLEDA Database

Abstract

The present paper is devoted to the construction of a catalog of isolated galaxy pairs extracted from the HyperLEDA extragalactic database. The radial velocities of the galaxies in the pairs are in the range $[3000,16000]$ km.s$^{-1}$. In order to get an unbiased pair catalog as complete as possible, we have limited the absolute magnitude of the galaxies to $M \leq-18.5$). The criteria used to define the isolated galaxy pairs are the following: 1) Velocity criterion: radial velocity difference between the pair members $\Delta V<500$ km.s$^{-1}$; 2) Interdistance criterion: projected distance between the members $r_p<1$ Mpc; 3) Reciprocity criterion: each member is the closest galaxy to the other one, which excludes multiplets; 4) Isolation criterion: we define a pair as isolated if the ratio $\rho=r_3/r_p$ of the projected distance of the pair to its closest galaxy (this one having a velocity difference lower than 500 km.s$^{-1}$ with respect to the pair) and the members projected interdistance $r_p$ is larger than 2.5. We have searched for these closest galaxies first in HyperLEDA M-limited source catalog, then in the full one. We have managed not to suppress the small number of pairs having close-by but faint dwarf galaxy companions. The galaxy pair catalog lists the value of $\rho$ for each isolated pair. This method allows the user of the catalog to select any isolation level (beyond the chosen limit $\rho>2.5$). Our final catalog contains 13114 galaxy pairs, of which 57\% are fairly isolated with $\rho>5$, and 30 \% are highly isolated with $\rho \geq 10$.