AKARI Near-Infrared Spectroscopic Observations of Interstellar Ices in Edge-on Starburst Galaxy NGC253

TL;DR

This study uses AKARI near-infrared spectroscopy to analyze interstellar ices and PAHs in NGC253, revealing spatial variations and comparing ice abundances to those in our Galaxy, despite intense radiation fields.

Contribution

First spatially-resolved near-infrared spectra of interstellar ices in NGC253, showing differing distributions from PAHs and gas, and deriving ice abundance ratios in an external galaxy.

Findings

Detection of interstellar ices and PAHs near galaxy center

Different spatial distributions of ices compared to PAHs and gas

Ice abundance ratios similar to Galactic massive YSOs

Abstract

We present the spatially-resolved near-infrared (2.5-5.0 um) spectra of the edge-on starburst galaxy NGC253 obtained with the Infrared Camera onboard AKARI. Near the center of the galaxy, we clearly detect the absorption features of interstellar ices (H_2O: 3.05 um, CO_2: 4.27 um, and XCN: 4.62 um) and the emission of polycyclic aromatic hydrocarbons (PAHs) at 3.29 um and hydrogen recombination line Br alpha at 4.05 um. We find that the distributions of the ices differ from those of the PAH and gas. We calculate the column densities of the ices and derive the abundance ratios of N(CO_2)/N(H_2O) = 0.17 +- 0.05. They are similar to those obtained around the massive young stellar objects in our Galaxy (0.17 +- 0.03), although much stronger interstellar radiation field and higher dust temperature are expected near the center of NGC253.