Arp 65 interaction debris: massive H I displacement and star formation

¹ Korea Astronomy and Space Science Institute, 776, Daedeokdae ro, Yuseong gu, 305-348 Daejeon, Republic of Korea
e-mail: csg@kasi.re.kr
² Institute of Astrophysics and Space Sciences (IA), Rua das Estrelas, 4150-762 Porto, Portugal
³ Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield, AL10 9AB, UK
⁴ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, 411 007 Pune, India
⁵ Cotton College State University, Panbazar, 781 001 Guwahati, India
⁶ Raman Research Institute, 560 080 Bangalore, India

Received: 13 October 2014
Accepted: 24 August 2015

Abstract

Context. Pre–merger tidal interactions between pairs of galaxies are known to induce significant changes in the morphologies and kinematics of the stellar and interstellar medium components. Large amounts of gas and stars are often found to be disturbed or displaced as tidal debris. This debris then evolves, sometimes forming stars and occasionally forming tidal dwarf galaxies. Here we present results from our H i study of Arp 65, an interacting pair hosting extended H i tidal debris.

Aims. In an effort to understand the evolution of tidal debris produced by interacting pairs of galaxies, including in situ star and tidal dwarf galaxy formation, we are mapping H i in a sample of interacting galaxy pairs. The Arp 65 pair is the latest member of this sample to be mapped.

Methods. Our resolved H i 21 cm line survey is being carried out using the Giant Metrewave Radio Telescope. We used our H i survey data as well as available SDSS optical, Spitzer infra-red and GALEX UV data to study the evolution of the tidal debris and the correlation of H i with the star-forming regions within it.

Results. In Arp 65 we see a high impact pre–merger tidal interaction involving a pair of massive galaxies (NGC 90 and NGC 93) that have a stellar mass ratio of ~1:3. The interaction, which probably occurred ~1.0–2.5 × 10⁸ yr ago, appears to have displaced a large fraction of the H i in NGC 90 (including the highest column density H i) beyond its optical disk. We also find extended on-going star formation in the outer disk of NGC 90. In the major star-forming regions, we find the H i column densities to be ~4.7 × 10²⁰ cm^-2 or lower. But no signature of star formation was found in the highest column density H i debris SE of NGC 90. This indicates conditions within the highest density H i debris remain hostile to star formation and it reaffirms that high H i column densities may be a necessary but not sufficient criterion for star formation.