Polycyclic Aromatic Hydrocarbons, the Anomalous Microwave Emission, and Their Connection to the Cold Neutral Medium

Abstract

Using new large area maps of the cold neutral medium (CNM) fraction, $f_{\mathrm{CNM}}$, we investigate the relationship between the CNM, the abundance of polycyclic aromatic hydrocarbons (PAHs), and the anomalous microwave emission (AME). We first present our $f_{\mathrm{CNM}}$ map based on full-sky HI4PI data, using a convolutional neural network to covert the spectroscopic HI data to $f_{\mathrm{CNM}}$. We demonstrate that $f_{\mathrm{CNM}}$ is strongly correlated with the fraction of dust in PAHs as estimated from mid- and far-infrared dust emission. In contrast, we find no correlation between $f_{\mathrm{CNM}}$ and the amount of AME per dust emission, nor between $f_{\mathrm{CNM}}$ and the AME peak frequency. These results suggest PAHs preferentially reside in cold, relatively dense gas, perhaps owing to enhanced destruction in more diffuse media. The lack of correlation between $f_{\mathrm{CNM}}$ and AME peak frequency is in tension with expectations from theoretical models positing different spectral energy distributions of AME in the cold versus warm neutral medium. We suggest that different PAH abundances and emission physics in different interstellar environments may explain the weaker than expected correlation between 12$\mu$m PAH emission and AME even if PAHs are the AME carriers.

Submitted to ApJ. 12 pages, 4 figures, comments welcome

References in corpus (15)

• The NumPy array: a structure for efficient numerical computation
• Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Rotation-invariant convolutional neural networks for galaxy morphology prediction
• A refined model for spinning dust radiation
• GASS: The Parkes Galactic All-Sky Survey. Update: improved correction for instrumental effects and new data release
• A new, large-scale map of interstellar reddening derived from HI emission
• Modeling the Anomalous Microwave Emission with Spinning Nanoparticles: No PAHs Required
• The Polycyclic Aromatic Hydrocarbon Mass Fraction on a 10 pc scale in the Magellanic Clouds
• The Physical Nature of Neutral Hydrogen Intensity Structure
• Three Dimensional Hydrodynamic Simulations of Multiphase Galactic Disks with Star Formation Feedback: II. Synthetic HI 21 cm Line Observations
• Extracting the cold neutral medium from HI emission with deep learning: Implications for Galactic foregrounds at high latitude
• Characterizing Extragalactic Anomalous Microwave Emission in NGC 6946 with CARMA
• Investigation of the Origin of the Anomalous Microwave Emission in Lambda Orionis
• QUIJOTE Scientific results. III. Microwave spectrum of intensity and polarization in the Taurus molecular cloud Complex and L1527

Cited by in corpus (14)

• The Astrodust+PAH Model: A Unified Description of the Extinction, Emission, and Polarization from Dust in the Diffuse Interstellar Medium
• PHANGS-JWST First Results: Tracing the Diffuse ISM with JWST Imaging of Polycyclic Aromatic Hydrocarbon Emission in Nearby Galaxies
• Rotational spectra of interstellar N- and CN-PAHs: pyrene and coronene
• COMAP Early Science: VI. A First Look at the COMAP Galactic Plane Survey
• The stellar population responsible for a kiloparsec size superbubble seen in the JWST "phantom" images of NGC628
• Probing the cold neutral medium through HI emission morphology with the scattering transform
• BeyondPlanck XVI. Limits on Large-Scale Polarized Anomalous Microwave Emission from Planck LFI and WMAP
• QUIJOTE scientific results -- X. Spatial variations of Anomalous Microwave Emission along the Galactic plane
• QUIJOTE Scientific Results -- VII. Galactic AME sources in the QUIJOTE-MFI Northern Hemisphere Wide-Survey
• Far-ultraviolet Dust Extinction and Molecular Hydrogen in the Diffuse Milky Way Interstellar Medium
• Tracing PAH Emission in $\lambda$-Orionis Using COBE/DIRBE Data
• The End of the Road for Far-infrared Reddening Maps? Evidence for Reddening Errors Driven by Changes in PAH Abundance
• SPHEREx mapping of diffuse PAH and H II emission in the Galactic plane
• Modeling Long-Wavelength Amorphous Dust Emission Based on the Physically Motivated Soft-Potential Model