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Variations in the 6.2 $μ$m polycyclic aromatic hydrocarbon band in Active Galactic Nuclei- and Starburst-dominated galaxies

Carla M. Canelo, Dinalva A. Sales, Vitor Avelaneda, Alexander G. G. M. Tielens, Miriani Pastoriza, Amâncio C. S. Friaça

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are fundamental to understanding the interstellar medium (ISM) of several astrophysical objects. Normally present in Starburst (SB) galaxies, they have also been more frequently detected in active galaxy nuclei (AGNs), suggesting an inner dusty torus that can shield the radiation from the central black role. In this work, we analyze the 6.2 $μ$m PAH band of SB-, AGN- and mixed-dominated spectra from 175 IDEOS database galaxies. After fitting of the band, the sources were distributed into the Peeters' A, B and C classes according to their profile peak positions. Class A objects are predominant in 80% of the entire sample, which could indicate the presence of PAHs with nitrogen incorporation. The water ice absorption at 6.0 $μ$m was also studied in eleven objects, and it affected the PAH band poorly. A prominent second spectral feature after 6.3 $μ$m is present in ten galaxies. Fitting both PAH profiles at 6.2 $μ$m changes all the fit results: the first profile is consistently blue-shifted and classified as class A due to the presence of the second component. Further studies are needed to better comprehend these PAH trends in galactic environments.

Variations in the 6.2 $μ$m polycyclic aromatic hydrocarbon band in Active Galactic Nuclei- and Starburst-dominated galaxies

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are fundamental to understanding the interstellar medium (ISM) of several astrophysical objects. Normally present in Starburst (SB) galaxies, they have also been more frequently detected in active galaxy nuclei (AGNs), suggesting an inner dusty torus that can shield the radiation from the central black role. In this work, we analyze the 6.2 m PAH band of SB-, AGN- and mixed-dominated spectra from 175 IDEOS database galaxies. After fitting of the band, the sources were distributed into the Peeters' A, B and C classes according to their profile peak positions. Class A objects are predominant in 80% of the entire sample, which could indicate the presence of PAHs with nitrogen incorporation. The water ice absorption at 6.0 m was also studied in eleven objects, and it affected the PAH band poorly. A prominent second spectral feature after 6.3 m is present in ten galaxies. Fitting both PAH profiles at 6.2 m changes all the fit results: the first profile is consistently blue-shifted and classified as class A due to the presence of the second component. Further studies are needed to better comprehend these PAH trends in galactic environments.
Paper Structure (15 sections, 10 figures)

This paper contains 15 sections, 10 figures.

Table of Contents

  1. Introduction
  2. The Peeters' classification
  3. Data Selection
  4. Data analysis
  5. Continuum subtraction
  6. Gaussian fit of the band
  7. Results and Discussion
  8. The band profile
  9. Water ice absorption feature
  10. A second PAH emission feature
  11. The Peeters' classes
  12. Advanced analysis
  13. Conclusions
  14. Comparison with previous analysis
  15. Fitting the continuum emission with PAHFIT-MCMC

Figures (10)

  • Figure 1: Example of the fits performed in the sample for Spline decomposition. The complete figure set (175 images) is available in the online journal.
  • Figure 2: Example of the fit results of one PAH band at 6.2 $\mu$m. The complete figure set (175 images) is available in the online journal.
  • Figure 3: Example of the fit results of water ice absorption at 6.0 $\mu$m and PAH band at 6.2 $\mu$m. The complete figure set (11 images) is available in the online journal.
  • Figure 4: Example of the fit results of two PAH bands at 6.2 and 6.3 $\mu$m. The complete figure set (10 images) is available in the online journal.
  • Figure 5: Comparison of the 6.2 $\mu$m PAH fit results amplitude, central wavelength and FWHM considering just one PAH profile (x axis) and fitting together with the water ice feature (y axis). The gray dashed line shows a slope of 1 for comparison. The black line shows the linear regression for each parameter, with the slope, interception and R-squared (R$^2$) values displayed within the panels.
  • ...and 5 more figures