Spectroscopically Identified Emission Line Galaxy Pairs in the WISP survey

TL;DR

This study identifies emission line galaxy pairs up to redshift 1.6 using HST WISP survey data, revealing enhanced star formation rates and consistent emission line ratios, with a marginal increase in pair fraction over redshift.

Contribution

It provides the first large spectroscopic sample of ELG pairs at intermediate redshifts, quantifies star formation enhancement, and examines emission line properties and pair fraction evolution.

Findings

413 ELG pair systems identified in 0.5 deg$^{2}$ area.

Star formation rates are 40%-65% higher in pairs than isolated galaxies.

Pair fraction increases with redshift as (1+z)^0.58.

Abstract

We identify a sample of spectroscopically measured emission line galaxy (ELG) pairs up to z=1.6 from the WFC3 Infrared Spectroscopic Parallels (WISP) survey. WISP obtained slitless, near-infrared grism spectroscopy along with direct imaging in the J and H bands by observing in the pure-parallel mode with the Wide Field Camera Three (WFC3) on the Hubble Space Telescope (HST). From our search of 419 WISP fields covering an area of ~0.5 deg$^{2}$, we find 413 ELG pair systems, mostly Halpha emitters. We then derive reliable star formation rates (SFRs) based on the attenuation-corrected Halpha fluxes. Compared to isolated galaxies, we find an average SFR enhancement of 40%-65%, which is stronger for major pairs and pairs with smaller velocity separations (Delta_v < 300 km/s). Based on the stacked spectra from various subsamples, we study the trends of emission line ratios in pairs, and find a general consistency with enhanced lower-ionization lines. We study the pair fraction among ELGs, and find a marginally significant increase with redshift $f \propto (1+z)^\alpha$, where the power-law index \alpha=0.58$\pm$0.17 from $z\sim$0.2 to $z\sim$1.6. The fraction of Active galactic Nuclei (AGNs), is found to be the same in the ELG pairs as compared to isolated ELGs.