Browsing by Author "Li, Aigen"

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    A tale of three galaxies: A "CLUMPY" view of the spectroscopically anomalous galaxies IRAS F10398+1455, IRAS F21013-0739 and SDSS J0808+3948
    (2016) Xie, Yanxia; Nikutta, Robert; Hao, Lei; Li, Aigen
    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 similar to 5-8 gm emission continuum, strong emission bands from polycyclic aromatic hydrocarbon (PAH) molecules, and prominent 10 mu m silicate emission. The steep similar to 5-8 mu m 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 PAHETT 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 similar to 5-8 mu m continuum to be consistent with that observed in IRAS F10398+1455 and IRAS F210130739. The flat similar to 5-8 mu m 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 and Lee (1984) "astronomical silicate" by a factor up to 2 in the similar to 5-8 mu m 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. (C) 2016 Elsevier Ltd. All rights reserved.
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    A TALE OF THREE GALAXIES: DECIPHERING THE INFRARED EMISSION OF THE SPECTROSCOPICALLY ANOMALOUS GALAXIES IRAS F10398+1455, IRAS F21013-0739, AND SDSS J0808+3948
    (IOP PUBLISHING LTD, 2015) Xie, Yanxia; Li, Aigen; Hao, Lei; Nikutta, Robert
    The Spitzer/Infrared Spectrograph spectra of three spectroscopically anomalous galaxies (IRAS F10398+ 1455, IRAS F21013-0739, and SDSS J0808+3948) are modeled in terms of a mixture of warm and cold silicate dust, and warm and cold carbon dust. Their unique infrared (IR) emission spectra are characterized by a steep similar to 5-8 mu m emission continuum, strong emission bands from polycyclic aromatic hydrocarbon (PAH) molecules, and prominent silicate emission. The steep similar to 5-8 mu m emission continuum and strong PAH emission features suggest the dominance of starbursts, while the silicate emission is indicative of significant heating from active galactic nuclei (AGNs). With warm and cold silicate dust of various compositions ("astronomical silicate," amorphous olivine, or amorphous pyroxene) combined with warm and cold carbon dust (amorphous carbon, or graphite), we are able to closely reproduce the observed IR emission of these galaxies. We find that the dust temperature is the primary cause in regulating the steep similar to 5-8 mu m continuum and silicate emission, insensitive to the exact silicate or carbon dust mineralogy and grain size a as long as a. 1 mm. More specifically, the temperature of the similar to 5-8 mu m continuum emitter (which is essentially carbon dust) of these galaxies is similar to 250-400 K, much lower than that of typical quasars, which is similar to 640 K. Moreover, it appears that larger dust grains are preferred in quasars. The lower dust temperature and smaller grain sizes inferred for these three galaxies compared with that of quasars could be due to the fact that they may harbor a young/weak AGNs that is not maturely developed yet.