Arp220: extinction and merger-induced star formation

TL;DR

This study uses high-resolution spectroscopic and interferometric data to analyze the stellar populations, dust extinction, and kinematics of the merging galaxy system Arp220, revealing details about its starburst activity and nuclear structure.

Contribution

It provides a detailed spatially resolved analysis of Arp220's stellar populations, dust extinction, and kinematics, combining new spectroscopic data with re-analyzed CO observations.

Findings

Majority of K-band luminosity from a 10 Myr starburst

Western nucleus's kinematic center coincides with hot dust emission

Eastern nucleus is a kinematically coherent structure with differential extinction

Abstract

We analyse new spatially resolved integral field spectroscopic H- and K-band data at a resolution of 0.3arcsec (100pc) and re-analyse interferometric CO(2-1) line observations of the prototypical merging system Arp220. We find that the majority of the K-band luminosity is due to a 10Myr old starburst, with a significant contribution from an underlying ca 1Gyr old stellar population, and a small contribution from stars less than 8Myr old. The Calzetti (2000) reddening law provides the best fit to photometric datapoints spanning 0.45um -- 2.12um. Furthermore, estimates of the bolometric luminosity from IRAS fluxes in conjunction with our stellar population analysis indicate that we observe less than 10% of the emitted K-band light. The stellar and CO(2-1) kinematic centre of the western nucleus coincides with the compact hot dust emission, indicating that the latter marks the centre of the gravitational potential. In the eastern nucleus, the CO(2-1) data are well matched by a model in which the gas orbits around the peak of the dust emission. This, and the similarity of the K-band tracer kinematics, shows that despite the irregular morphology, the eastern nucleus is also a kinematically coherent structure. Comparison of the extinction map and EW_CO and EW_Br-gamma maps indicates that the lower half of the eastern nucleus is significantly more extincted than the upper half, suggesting that the lower half is buried in the larger-scale gas disk.