Intensity-Corrected Herschel Observations of Nearby Isolated Low-Mass Clouds

TL;DR

This paper introduces a new technique to correct zero-point offsets in Herschel observations of 56 low-mass clouds, enabling more accurate temperature and optical depth measurements crucial for understanding cloud properties.

Contribution

We developed a novel method to measure and correct zero-point offsets in small Herschel maps using Planck data, improving the accuracy of dust temperature and optical depth estimates.

Findings

Most clouds have reliable offset measurements with the new technique.

Half of the clouds had underestimated SPIRE intensities in their outer regions.

Corrected maps show lower temperatures than previous studies that subtracted background levels.

Abstract

We present intensity-corrected Herschel maps at 100 um, 160 um, 250 um, 350 um, and 500 um for 56 isolated low-mass clouds. We determine the zero-point corrections for Herschel PACS and SPIRE maps from the Herschel Science Archive (HSA) using Planck data. Since these HSA maps are small, we cannot correct them using typical methods. Here, we introduce a technique to measure the zero-point corrections for small Herschel maps. We use radial profiles to identify offsets between the observed HSA intensities and the expected intensities from Planck. Most clouds have reliable offset measurements with this technique. In addition, we find that roughly half of the clouds have underestimated HSA-SPIRE intensities in their outer envelopes relative to Planck, even though the HSA-SPIRE maps were previously zero-point corrected. Using our technique, we produce corrected Herschel intensity maps for all 56 clouds and determine their line-of-sight average dust temperatures and optical depths from modified black body fits. The clouds have typical temperatures of ~ 14-20 K and optical depths of ~ 1e-5 - 1e-3. Across the whole sample, we find an anti-correlation between temperature and optical depth. We also find lower temperatures than what was measured in previous Herschel studies, which subtracted out a background level from their intensity maps to circumvent the zero-point correction. Accurate Herschel observations of clouds are key to obtain accurate density and temperature profiles. To make such future analyses possible, intensity-corrected maps for all 56 clouds are publicly available in the electronic version.