Fourier-space combination ofPlanckandHerschelimages

Abstract

Context. Herschel has revolutionized our ability to measure column densities (N H ) and temperatures (T ) of molecular clouds thanks to its far infrared multiwavelength coverage. However, the lack of a well defined background intensity level in the Herschel data limits the accuracy of the N H and T maps. Aims. We aim to provide a method that corrects the missing Herschel background intensity levels using the Planck model for foreground Galactic thermal dust emission. For the Herschel/PACS data, both the constant-offset as well as the spatial dependence of the missing background must be addressed. For the Herschel/SPIRE data, the constant-offset correction has already been applied to the archival data so we are primarily concerned with the spatial dependence, which is most important at 250 µm. Methods. We present a Fourier method that combines the publicly available Planck model on large angular scales with the Herschel images on smaller angular scales. Results. We have applied our method to two regions spanning a range of Galactic environments: Perseus and the Galactic plane region around l = 11 deg (HiGal-11). We post-processed the combined dust continuum emission images to generate column density and temperature maps. We compared these to previously adopted constant-offset corrections. We find significant differences ( 20%) over significant (∼15%) areas of the maps, at low column densities (N H 10 22 cm −2 ) and relatively high temperatures (T 20 K). We have also applied our method to synthetic observations of a simulated molecular cloud to validate our method. Conclusions. Our method successfully corrects the Herschel images, including both the constant-offset intensity level and the scaledependent background variations measured by Planck. Our method improves the previous constant-offset corrections, which did not account for variations in the background emission levels.

The history of dynamics and stellar feedback revealed by the H I filamentary structure in the disk of the Milky Way

“…Each point in the scatter plot corresponds to the values estimated using the Hessian analysis in the same 2 • × 2 • tile and 1.5-km s −1 velocity channel in both datasets. plane in the emission from molecular species, such as 13 CO (Goodman et al 2014;Ragan et al 2014;Wang et al 2015Wang et al , 2020cZucker et al 2015;Abreu-Vicente et al 2017). To establish a link between the HI filaments and the GMFs, without detailing individual objects, we also applied the Hessian analysis to the 13 CO (J = 1 → 0) emission observations in the GRS survey.…”

Physical Properties of Molecular Clouds at 2 pc Resolution in the Low-metallicity Dwarf Galaxy NGC 6822 and the Milky Way

“…We have tested several methods to remove the Galactic cirrus but failed to converge on robust results. In addition, we suspect problems in the Herschel PACS and SPIRE data products themselves (e.g., potentially related to the dynamic range or recovery of extended emission; see also Abreu-Vicente et al 2016) as individual bands show inconsistencies in their intensities (by a factor of a few) with any reasonable infrared SEDs in either faint or bright regions. For that reason, we reverted to using SPIREʼs m 350 m band as a dust proxy, but we note that results derived from more complex dust modeling (i.e., modified blackbody, Galliano et al, or Draine & Li model) agree within a factor of a few.…”

Intensity-corrected Herschel Observations of Nearby Isolated Low-mass Clouds*

“…These methods, however, are not easily applicable to the smaller Herschel maps of globules. The globule maps are typically 2 − 7 Planck beams across, which makes it difficult to reliably convolved them to Planck scales (Bernard et al 2010;Lombardi et al 2014) or to reliably bridge the spatial scales covered by each telescope in a Fourier analysis (Abreu-Vicente et al 2017). Zero-point corrections of the globule maps will require a different technique.…”