Insights from Synthetic Star-forming Regions: II. Verifying Dust Surface Density, Dust Temperature & Gas Mass Measurements with Modified Blackbody Fitting

TL;DR

This study evaluates the accuracy of dust surface density, temperature, and gas mass measurements from modified blackbody fitting of synthetic Herschel observations, highlighting significant errors near star-forming regions and the limitations in high-background environments.

Contribution

It provides a comprehensive assessment of the reliability and limitations of modified blackbody fitting for measuring physical properties of star-forming regions using synthetic data.

Findings

Pixel-based measurements near star-formation sites can be highly inaccurate.

Modified blackbody fitting estimates of total gas mass are reliable within 10 kpc in moderate backgrounds.

Convolving images to the largest common beam size reduces information and affects measurement quality.

Abstract

We use a large data-set of realistic synthetic observations (PaperI) to assess how observational techniques affect the measurement of physical properties of star-forming regions. In this paper (PaperII), we explore the reliability of the measured total gas mass, dust surface density and dust temperature maps derived from modified blackbody fitting of synthetic Herschel observations. We found from our pixel-by-pixel analysis of the measured dust surface density and dust temperature a worrisome error spread especially close to star-formation sites and low-density regions, where for those "contaminated" pixels the surface densities can be under/overestimated by up to three orders of magnitude. In light of this, we recommend to treat the pixel-based results from this technique with caution in regions with active star formation. In regions of high background typical in the inner Galactic plane, we are not able to recover reliable surface density maps of individual synthetic regions, since low-mass regions are lost in the FIR background. When measuring the total gas mass of regions in moderate background, we find that modified blackbody fitting works well (absolute error:+9%;-13%) up to 10kpc distance (errors increase with distance). Commonly, the initial images are convolved to the largest common beam-size, which smears contaminated pixels over large areas. The resulting information loss makes this commonly-used technique less verifiable as now chi^2-values cannot be used as a quality indicator of a fitted pixel. Our control measurements of the total gas mass (without the step of convolution to the largest common beam size) produce similar results (absolute error:+20%;-7%) while having much lower median errors especially for the high-mass stellar feedback phase. In upcoming papers (III&IV) we test the reliability of measured star-formation rate with direct and indirect techniques.