A Tale of Three Galaxies: A "Clumpy" View of the Spectroscopically Anomalous Galaxies IRAS F10398+1455, IRAS F21013-0739 and SDSS J0808+3948

TL;DR

This study analyzes the dust properties of three spectroscopically anomalous galaxies using infrared spectra, revealing complex starburst and AGN features and evaluating the effectiveness of the CLUMPY model in explaining their dust emission.

Contribution

It applies the PAHFIT and CLUMPY models to characterize dust and AGN contributions in these galaxies, highlighting limitations and suggesting the need for diverse dust species in future models.

Findings

CLUMPY model generally explains dust IR emission

Discrepancies in ~5-8 micron continuum suggest dust composition differences

Presence of both starburst and AGN features in the same galaxies

Abstract

We investigate the dust properties in three spectroscopically anomalous galaxies (IRAS F10398+1455, IRAS F21013-0739 and SDSS J0808+3948). Their Spitzer/IRS spectra are characterized by a steep ~5-8 micron emission continuum, strong emission bands from polycyclic aromatic hydrocarbon (PAH) molecules, and prominent 10 micron silicate emission. The steep ~5-8 micron continuum and strong PAH emission features suggest the presence of starbursts, while the silicate emission is indicative of significant heating from AGNs. The simultaneous detection of these two observational properties has rarely been reported on galactic scale. We employ the PAHFIT software to estimate their starlight contributions, and the CLUMPY model for the components contributed by the AGN tori. We find that the CLUMPY model is generally successful in explaining the overall dust infrared emission, although it appears to emit too flat at the ~5-8 micron continuum to be consistent with that observed in IRAS F10398+1455 and IRAS F21013-0739. The flat ~5-8 micron continuum calculated from the CLUMPY model could arise from the adopted specific silicate opacity of Ossenkopf et al. (1992) which exceeds that of the Draine & Lee (1984) "astronomical silicate" by a factor up to 2 in the ~5-8 micron wavelength range. Future models with a variety of dust species incorporated in the CLUMPY radiation transfer regime are needed for a thorough understanding of the dust properties of these spectroscopically anomalous galaxies.