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

Abstract

A fraction of the heavily reddened quasars require a reddening curve which 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 1200Å-10000Å. It is featured with a steep rise at wavelengths shorter than 3000Å, but no significant reddening at longer wavelengths. The absence of dust reddening in 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 by a dust model containing silicate grains in a power-law size distribution, dn(a)/da ∝ a −1.4 , truncated at a maximum size 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 toward the Galactic center is 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.

Broad-band spectral energy distribution of 3000 Å break quasars from the Sloan Digital Sky Survey

“…We conclude that the reddening curve derived by Jiang et al (2013) for IRAS 14026+4341 does not provide a reasonable 13 There is an absorber system at z abs = 1.182. Since the absorber must be between the source and the observer, the only explanation would be an associated absorber moving towards the quasar with an unrealistic velocity v = c[R 2 − 1]/[R 2 + 1] ≈ −7300 km s −1 , where R = (1 + z em )/(1 + z abs ) (Foltz et al 1983).…”

“…3.2.2), reddening curves steeper than in the SMC were suggested for some samples or individual quasars Zhou et al 2006;Fynbo et al 2013;Jiang et al 2013;Leighly et al 2014). Presuming that the continuum of the dereddened broad-band SED is similar to that of the average quasar SED, Jiang et al (2013) have recently derived a reddening curve for the local 3000 Å break quasar IRAS 14026+4341 that steeply rises towards short wavelengths at λ < 3000 Å, which is very different from the reddening usually observed in nearby galaxies. These authors argue that such an unusual reddening law can be caused by the speculative assumption of an exotic dust grain size distribution that lacks large grains.…”

An X-Shooter composite of bright 1 <z< 2 quasars from UV to infrared

“…The quasar composite is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A87 Source code and composite is also made public at https://github.com/jselsing/QuasarComposite extinction curves are required (Fynbo et al 2013;Jiang et al 2013;Leighly et al 2014).…”

The Optical Variability of SDSS Quasars From Multi-Epoch Spectroscopy. Iii. A Sudden Uv Cutoff in Quasar SDSS J2317+0005

“…It is much steeper than the average Small Magellanic Cloud (SMC) bar extinction curve (Gordon et al 2003) at l > -2.5 1 . In recent years, although "gray" extinction curves are often claimed by many investigations (Czerny et al 2004;Gaskell et al 2004;Gaskell & Benker 2007), a growing number of heavily reddened quasars are detected (Wang et al 2005;Zafar et al 2012;Jiang et al 2013). We attempt to match our steep extinction curve with an SMC-like curve (Fitzpatrick & Massa 1990), since SMC-like curves have a steeper UV rise than other observed extinction curves like the Milky Way, Large Magellanic cloudsupernova (Gordon et al 2003;Fitzpatrick & Massa 2007;Gallerani et al 2010).…”

“…We are therefore lead to consider their other scenariowhere the dust cloud is a clump in an "Accreting Torus" much closer to the central engine (Jiang et al 2013;Zafar et al 2015).…”