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Anomalously Steep Reddening Law in Quasars: An Exceptional Example Observed in IRAS 14026+4341

【标题】Anomalously Steep Reddening Law in Quasars: An Exceptional Example Observed in IRAS 14026+4341

【Title】Anomalously Steep Reddening Law in Quasars: An Exceptional Example Observed in IRAS 14026+4341

【DOI】10.1088/0004-6256/145/6/157

【作者】 姜鹏; 周宏岩; 纪拓; Xinwen Shu; Wenjuan Liu; 王建国; Xiaobo Dong; Jinming Bai; Huiyuan Wang; Tinggui Wang

【Author】 Jiang Peng ; Zhou Hongyan ; Ji Tuo ; Xinwen Shu ; Wenjuan Liu ; Wang Jianguo ; Xiaobo Dong ; Jinming Bai ; Huiyuan Wang ; Tinggui Wang

【期刊】The Astronomical Journal

【Journal】The Astronomical Journal

【期刊年份】2013

【卷】145

【期】6

【关键词】 dust, extinction, quasars: individual: IRAS 14026+4341

【Keywords】 dust, extinction, quasars: individual: IRAS 14026+4341

【摘要】A fraction of the heavily reddened quasars require a reddening curve that is even steeper than that of the Small Magellanic Cloud. In this paper, we thoroughly characterize the anomalously steep reddening law in quasars via an exceptional example observed in IRAS 14026+4341. By comparing the observed spectrum to the quasar composite spectrum, we derive a reddening curve in the rest-frame wavelength range of 1200-10000 Å. It has a steep rise at wavelengths shorter than 3000 Å, but no significant reddening at longer wavelengths. The absence of dust reddening in the optical continuum is confirmed by the normal broad-line Balmer decrement (the Hα/Hβ ratio) in IRAS 14026+4341. The anomalous reddening curve can be satisfactorily reproduced with a dust model containing silicate grains in a power-law size distribution, dn(a)/davpropa -1.4, truncated at a maximum size of a max = 70 nm. The unusual size distribution may be caused by the destruction of large "stardust" grains by quasar activities or a different dust formation mechanism (i.e., the in situ formation of dust grains in quasar outflows). It is also possible that the analogies of the dust grains observed near the Galactic center are responsible for the steep reddening curve. In addition, we find that IRAS 14026+4341 is a weak emission-line quasar (i.e., PHL 1811 analogies) with heavy dust reddening and blueshifted broad absorption lines.

【Abstract】A fraction of the heavily reddened quasars require a reddening curve that is even steeper than that of the Small Magellanic Cloud. In this paper, we thoroughly characterize the anomalously steep reddening law in quasars via an exceptional example observed in IRAS 14026+4341. By comparing the observed spectrum to the quasar composite spectrum, we derive a reddening curve in the rest-frame wavelength range of 1200-10000 Å. It has a steep rise at wavelengths shorter than 3000 Å, but no significant reddening at longer wavelengths. The absence of dust reddening in the optical continuum is confirmed by the normal broad-line Balmer decrement (the Hα/Hβ ratio) in IRAS 14026+4341. The anomalous reddening curve can be satisfactorily reproduced with a dust model containing silicate grains in a power-law size distribution, dn(a)/davpropa -1.4, truncated at a maximum size of a max = 70 nm. The unusual size distribution may be caused by the destruction of large "stardust" grains by quasar activities or a different dust formation mechanism (i.e., the in situ formation of dust grains in quasar outflows). It is also possible that the analogies of the dust grains observed near the Galactic center are responsible for the steep reddening curve. In addition, we find that IRAS 14026+4341 is a weak emission-line quasar (i.e., PHL 1811 analogies) with heavy dust reddening and blueshifted broad absorption lines.

【基金/项目】 grants NSFC 11233002, NSFC 11203022, NSFC 11033007 ; the SOC program CHINARE2012-02-03 ; the Fundamental Research Funds for the Central Universities

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