The Interaction between Spiral Galaxies IC 2163 and NGC 2207. I. Observations

Abstract

Original article can be found at: http://adsabs.harvard.edu/abs/ Copyright American Astronomical Society. DOI: 10.1086/176374 [Full text of this article is not available in the UHRA]High-resolution H I observations taken at the VLA of the interacting pair of galaxies NGC 2207 and IC 2163 are presented, compared with optical and radio continuum images, and analyzed with detailed computer simulations (in Paper II) in order to determine the orbits and study the effects of in-plane and out-of-plane tidal forcing during a recent, close, nonmerging encounter between galaxies of comparable mass. IC 2163 has an ocular shape (an eye-shaped central oval with a sharp apex at each end) and a double- parallel arm structure on the side opposite NGC 2207. Our observations of IC 2163 find (1) an intrinsically oval shape to the disk, (2) large streaming motions along the oval, (3) H I tidal arms located symmetrically on opposite sides of the nucleus (even though one side is obscured by NGC 2207 at optical wavelengths), and (4) a line-of-sight velocity difference of 70-100 km s-1 between the two components of the double-parallel arm. Optical surface photometry of IC 2163 indicates that most of the stars in the interarm region have been cleared away and put into the central oval and tidal arms. The kinematic and structural anomalies of IC 2163 are consistent with the predictions of N-body galaxy encounter simulations if NGC 2207 moved approximately in the plane of IC 2163 in a prograde sense. The companion, NGC 2207, shows different types of disturbances. The main body of H I gas in NGC 2207 forms a broad, clumpy ring that contains relatively thin stellar arms and corresponds to a plateau in the radial distribution of optical light. The most massive H I clouds in the ring do not always coincide with the stellar arms. The ring is broken in the south, and a filamentary pool of H I extends 40 kpc farther south. The velocity field in the main disk of NGC 2207 is highly distorted with isovelocity contours that are shaped like an open trailing spiral, and the H I line profiles in this region are very broad with Gaussian dispersions of 40-50 km s-1. The kinematic disturbances in NGC 2207 suggest that the main tidal force on NGC 2207 was perpendicular to its disk. The companion side of the H I ring is unusually bright in ??20 cm radio continuum emission, perhaps indicating a shock front. There is no significant excess of star formation in these galaxies, but there are several 108 Msun gas clouds in each disk, some of which may eventually become detached dwarf galaxies

NGC 2207/Ic 2163: A Grazing Encounter With Large-Scale Shocks

“…The radio continuum flux density of NGC 2207/IC 2163 is about three times higher than expected from the IRAS far-infrared flux (Elmegreen et al 1995b), yet neither galaxy contains a radio-loud active galactic nucleus (AGN). The global value of the Helou q FIR parameter (the logarithm of the ratio of FIR to λ20 cm radio continuum flux density) is 1.81 for NGC 2207/IC 2163, whereas Condon (1992) finds the median value of q FIR for galaxies that are not radio-loud AGNs to be 2.3 with an rms scatter of 0.2.…”

“…The spiral galaxies NGC 2207 and IC 2163, at a distance of 35 Mpc (1 =170 pc; Elmegreen et al 1995b) and partially overlapping in projection, are involved in a nearly grazing encounter with closest approach 200-400 Myr ago. We have studied this pair extensively (Elmegreen et al 1995a(Elmegreen et al , 1995b(Elmegreen et al , 1998(Elmegreen et al , 2000(Elmegreen et al , 2001(Elmegreen et al , 2006Thomasson 2004;Struck et al 2005) throughout the electromagnetic spectrum with Hubble Space Telescope (HST) WFPC2 observations in UBVI bands, groundbased Hα, Spitzer/IRAC (3.6-8 μm), and MIPS (24-160 μm) observations, Very Large Array (VLA) H i and radio continuum, and 12 CO J = 1 → 0 (Swedish ESO Submillimeter Telescope (SEST)) observations and reproduced many of the observed features with N-body and smoothed particle hydrodynamics encounter simulations.…”

“…We have studied this pair extensively (Elmegreen et al 1995a(Elmegreen et al , 1995b(Elmegreen et al , 1998(Elmegreen et al , 2000(Elmegreen et al , 2001(Elmegreen et al , 2006Thomasson 2004;Struck et al 2005) throughout the electromagnetic spectrum with Hubble Space Telescope (HST) WFPC2 observations in UBVI bands, groundbased Hα, Spitzer/IRAC (3.6-8 μm), and MIPS (24-160 μm) observations, Very Large Array (VLA) H i and radio continuum, and 12 CO J = 1 → 0 (Swedish ESO Submillimeter Telescope (SEST)) observations and reproduced many of the observed features with N-body and smoothed particle hydrodynamics encounter simulations. Relative to IC 2163, the encounter is prograde and nearly in-plane, producing the observed eyeshaped (ocular) oval and two long tidal arms in IC 2163.…”

Major-Merger Galaxy Pairs at Z = 0: Dust Properties and Companion Morphology

“…The standard model for gas redistribution is of a tidal torque delivering gas to the galaxy nucleus as in the simulations of Di Matteo et al (2008). Merging galaxies have increased velocity dispersion in their ISM (Elmegreen et al 1995). The increase in dispersion is dominated by supersonic gas turbulence in the cold star forming phase of the ISM (Burkert 2006).…”

[ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of Dust and Star-forming Regions in the Ocular Galaxy IC 2163 and Its Spiral Companion NGC 2207

“…Ground-based observations in optical, H I, and radio continuum show evidence for the interaction in the form of tidal arms and 100 km s~1 streaming motions in an eye-shaped central oval of IC 2163, regions with H I velocity dispersion of up to 50 km s~1 in both galaxies, and a strongly warped disk in NGC 2207 (Elmegreen et al 1995b, hereafter Paper I). The ocular (eyelike) shape is common for prograde, in-plane tidal interactions (Sundin 1989, 215 ;Elmegreen et al 1991 ;Donner, Engstrom, & Sundelius 1991).…”