The starburst-AGN connection in the merger galaxy Mrk 938: an infrared and X-ray view

TL;DR

This study investigates the coexistence of starburst and AGN activity in the merger galaxy Mrk 938 using multi-wavelength data, revealing a predominantly starburst-driven infrared emission with a small AGN contribution and detailed dust properties.

Contribution

First detailed analysis of Mrk 938 combining Herschel far-IR imaging with archival data to characterize starburst and AGN contributions in a merger galaxy.

Findings

AGN contributes ~2% to total infrared luminosity

Infrared emission is dominated by a compact <2kpc region

Dust temperature is around 35K with a mass of 3x10^7 solar masses

Abstract

Mrk938 is a luminous infrared galaxy in the local Universe believed to be the remnant of a galaxy merger. It shows a Seyfert 2 nucleus and intense star formation according to optical spectroscopic observations. We have studied this galaxy using new Herschel far-IR imaging data in addition to archival X-ray, UV, optical, near-IR and mid-IR data. Mid- and far-IR data are crucial to characterise the starburst contribution, allowing us to shed new light on its nature and to study the coexistence of AGN and starburst activity in the local Universe. The decomposition of the mid-IR Spitzer spectrum shows that the AGN bolometric contribution to the mid-IR and total infrared luminosity is small (Lbol(AGN)/LIR~0.02), which agrees with previous estimations. We have characterised the physical nature of its strong infrared emission and constrained it to a relatively compact emitting region of <2kpc. It is in this obscured region where most of the current star formation activity is taking place as expected for LIRGs. We have used Herschel imaging data for the first time to constrain the cold dust emission with unprecedented accuracy. We have fitted the integrated far-IR spectral energy distribution and derived the properties of the dust, obtaining a dust mass of 3x10^7Msun. The far-IR is dominated by emission at 35K, consistent with dust heated by the on-going star formation activity.