The Structure of Active Merger Remnant NGC 6240 from IRAC Observations

TL;DR

This study uses IRAC observations to analyze the structure and composition of the active merger remnant NGC 6240, revealing detailed distributions of stars and dust and insights into its transition from a disk galaxy to a spheroid.

Contribution

First high-sensitivity IRAC maps of NGC 6240's stellar and PAH distributions, providing new insights into its merger structure and evolution.

Findings

Radial profiles fit with r^.25 and exponential models reveal remnant structure.

IRAC detects extended low surface brightness features of stars and dust.

Correlation of outflows with IR emission supports merger-driven evolution.

Abstract

NGC 6240 is a rare object in the local universe: an active merger remnant viewed at the point of merging where two active galactic nuclei are visible. We present IRAC data of this object, providing high sensitivity maps of the stellar and PAH distribution in this complicated system. We use photometry to analyze the variation in these distributions with radius and provide an SED in the four IRAC bands: 3.6 microns, 4.5 microns, 5.8 microns and 8.0 microns. We fit the radial profiles of the 3.6 micron band to r^.25 and exponential profiles to evaluate the structure of the remnant. Finally, we compare the IRAC images with multi-wavelength data and examine how outflows in the X-ray, Halpha and CO correlate with 8 micron emission. The results support the general picture of NGC 6240 as a system experiencing a major merger and transitioning from a disk galaxy to a spheroid. The sensitivity of IRAC to low surface brightness mid-infrared features provides detailed information on the extended distributions of stars and dust in this rare system.