Fe K line complex in the nuclear region of NGC 253

TL;DR

This study analyzes the Fe K line complex in NGC 253, revealing three distinct iron emission lines and suggesting their origins from supernova remnants and molecular clouds, indicating active star formation and complex nuclear activity.

Contribution

First clear detection of Fe I and Fe XXVI lines in NGC 253, providing insights into the nuclear region's composition and activity using multiple X-ray observatories.

Findings

Detected three Fe K lines at 6.4, 6.7, and 7.0 keV.

Emission region around the nucleus is ~60 arcsec^2.

Fe line fluxes suggest contributions from supernova remnants and molecular clouds.

Abstract

A bright, nearby edge-on starburst galaxy NGC 253 was studied using the Suzaku, XMM and Chandra X-ray observatories. We detected with Suzaku and XMM complex line structure of Fe K, which is resolved into three lines (Fe I at 6.4 keV, Fe XXV at 6.7 keV and Fe XXVI at 7.0 keV) around the center of NGC 253. Especially, the Fe I and Fe XXVI lines are the first clear detections, with a significance of >99.99 % and 99.89 % estimated by a Monte Carlo procedure. Imaging spectroscopy with Chandra revealed that the emission is distributed in ~60 arcsec^2 region around the nucleus, which suggests that the source is not only the buried AGN. The flux of highly ionized Fe lines can be explained by the accumulation of 10-1000 supernova remnants that are the result of high starforming activity, while the Fe I line flux is consistent with the fluorescent line emission expected with the molecular clouds in the region.