On the equivalent effective temperature of massive young star clusters: The case of NGC 595

TL;DR

This paper evaluates the robustness of using the softness parameter to determine the equivalent effective temperature in giant HII regions, specifically NGC 595, despite uncertainties in stellar atmosphere models and variations in gas geometry and dust content.

Contribution

It demonstrates that the softness parameter provides a reliable measure of T* across different regions within a single giant HII region, even with complex geometries and dust variations.

Findings

The softness parameter reliably estimates T* in NGC 595.

Model uncertainties do not significantly affect T* determination.

T* varies consistently across different regions despite geometric differences.

Abstract

The softness parameter is based on the relative intensity of several optical emission lines emitted by the gas ionized by young massive star clusters and can be used to derive the equivalent effective temperature (T*) in those objects whose stellar population cannot be resolved. This method has several uncertainties due to the disagreement between different synthesis model atmospheres but it is robust to study the relative variations between objects. Following the 2D photoionization models of the giant HII region NGC 595 (P\'erez-Montero et al. 2011) we show that the determination of T* with the softness parameter is also robust in different regions of a same object with large variations in the geometry of the gas and in the dust-to-gas ratio.