ISO-LWS observations of C+ and O lines in absorption toward SgrB2

TL;DR

This study uses high-resolution ISO-LWS observations to analyze the absorption features of C+ and O lines in the Sagittarius B2 complex, revealing multiple layers and implications for interstellar medium cooling in star-forming regions.

Contribution

It provides the first detailed analysis of C+ and O line absorption in SgrB2, identifying multiple layers consistent with PDR models and discussing implications for galaxy observations.

Findings

Detection of [OI] and [CII] lines in absorption.

Identification of three atomic oxygen layers.

Implication of optically thick [CII] lines in star-forming regions.

Abstract

High spectral resolution ISO-LWS observations of the [OI] 63.2 and 145.5 microns and [CII] 157.7 microns fine structure lines are presented for the center of the Sagittarius B2 complex (SgrB2). Both the [OI] 63.2 microns and the [CII] 157.7 microns lines are detected in absorption. Using observations of the CO isotopes and of the HI lines, absorption components can be associated with many clouds along the Sgr B2 line of sight. From these data, we were able to disentangle three different layers, as predicted by PDR models, which contain atomic oxygen. We derive lower limits for the column densities of C and O. The fact that the [CII] 157.7 microns line is detected in absorption implies that the main cooling line of the interstellar medium can be optically thick especially in the direction of large star-forming complexes or in the nuclei of galaxies. This could partially account for the deficiency in the [CII] 157.7 microns line which has been recently found toward infrared bright galaxies in ISO data.