A survey of faint galaxy pairs

Abstract

A sample of faint, V magnitude selected, galaxy pairs, having physical separations less than approximately 20h −1 kpc, is used to examine the rise in the merger rate with redshift and the statistical relations between close pairs and the field galaxy population. Redshifts have been obtained for 14 galaxies (V ≤ 22.5) that are in close (θ < 6 ′′ ) pairs, along with a comparison sample of 38 field galaxies. Two color photometry is available for about 1000 galaxies in the same fields. The average redshift of the V ≤ 22.5 field population is 0.36, statistically equal to the average redshift of 0.42 for the pairs. The similarity of the two redshift distributions, ∆z ≤ 0.1, limits any differential luminosity enhancement of close pairs to less than half a magnitude. The pairs are somewhat bluer than the field and have nearly twice the average [O II] detection rate of the field, but the differences are not statistically significant. The field population has an angular correlation at separations of θ ≤6 ′′ higher than the inward extrapolation of ω(θ) ∝ θ −0.8 , which may be a population of "companions" not present at the current epoch, or, luminosity enhancement of intrinsically faint galaxies in pairs. Physical pairs comprise about 7% of the faint galaxies in our survey fields. The same physical separation applied to local galaxies finds only 2.6% in pairs. If the rise in close low relatively velocity pairs with redshift is parameterized as (1 + z) m , then m = 2.9 ± 0.8. If all pairs at low velocities and r ≤ 20h −1 kpc merge, then the average galaxy mass would be 32% smaller at z = 0.4 than locally.

A Review of High-Redshift Merger Observations

“…A preliminary analysis of image bimodality (a robust parameter that in principle flags major mergers even at high redshift) amongst I < 22 mag peculiar systems with z < 1 suggests that around 40% the morphologically peculiar galaxies are strongly bimodal, and thus probably merging. This is consistent with a merger rate increases of ∼ (1 + z) 3 . Internal color analyses of morphologically peculiar systems is an interesting next step in probing high-redshift mergers, leading ultimately to kinematical investigations in the next few years.…”

Merging History as a Function of Halo Environment

“…This is consistent with the estimate of Burkey et al (1994), who used the pair fraction in deep HST images to derive a merger rate evolution of (1 ] z)2.5B0.5. Carlberg et al (1994), on the other hand, use the evolution of the close pair (h ¹ 6@@) fraction and conclude that the merger rate evolution is (1 ] z)3.4B1.0. Finally, Yee & Ellingson (1995) found a somewhat steeper redshift dependence, (1 ] z)4.0B1.5, for the close-pair (projected distance less than 20 h~1 kpc) evolution rate.…”

The Dawes Review 1: Kinematic Studies of Star-Forming Galaxies Across Cosmic Time

“…Before the advent of IFS surveys, the primary method of estimating the merger rate at high-redshift was via pair counts, starting with Zepf & Koo (1989) ;Carlberg, Pritchet, & Infante (1994);Le Fèvre et al (2000); Lin et al (2004), and many papers since. By trying to estimate the fraction of galaxies that were 'interacting pairs' f int (e.g.…”