Physical Properties of a Pilot Sample of Spectroscopic Close Pair Galaxies at z ~ 2

TL;DR

This study uses HST imaging and Keck spectroscopy to identify and analyze the physical properties of galaxy pairs at z ~ 2, revealing insights into merger rates and star formation activity.

Contribution

It provides the first spectroscopic confirmation of close galaxy pairs at z ~ 2 and assesses their physical properties and merger fraction.

Findings

Approximately 50% false pair rate at small separations.

Detected pairs have typical star formation rates and masses.

Star formation rates can vary significantly within merging components.

Abstract

We use Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) rest-frame optical imaging to select a pilot sample of star-forming galaxies in the redshift range z = 2.00-2.65 whose multi-component morphologies are consistent with expectations for major mergers. We follow up this sample of major merger candidates with Keck/NIRSPEC longslit spectroscopy obtained in excellent seeing conditions (FWHM ~ 0.5 arcsec) to obtain Halpha-based redshifts of each of the morphological components in order to distinguish spectroscopic pairs from false pairs created by projection along the line of sight. Of six pair candidates observed, companions (estimated mass ratios 5:1 and 7:1) are detected for two galaxies down to a 3sigma limiting emission-line flux of ~ 10^{-17} erg/s/cm2. This detection rate is consistent with a ~ 50% false pair fraction at such angular separations (1-2 arcsec), and with recent claims that the star-formation rate (SFR) can differ by an order of magnitude between the components in such mergers. The two spectroscopic pairs identified have total SFR, SFR surface densities, and stellar masses consistent on average with the overall z ~ 2 star forming galaxy population.