The disappearance of a narrow Mg II absorption system in quasar SDSS J165501.31+260517.4
aa r X i v : . [ a s t r o - ph . C O ] N ov D RAFT VERSION A UGUST
27, 2018
Preprint typeset using L A TEX style emulateapj v. 5/2/11
THE DISAPPEARANCE OF A NARROW MG II ABSORPTION SYSTEM IN QUASAR SDSS J165501.31+260517.4 Z HI -F U C HEN , Y I -P ING Q IN , M IN -F ENG G U Draft version August 27, 2018
ABSTRACTIn this letter, we present for the first time, the discovery of the disappearance of a narrow Mg II λλ , z e = 1 . z abs = 1 . ,
423 km s - with respect to the quasar. According tothe velocity offset and the line variability, this narrow Mg II λλ , λλ , z abs = 1 . Subject headings: galaxies: kinematics and dynamics—quasars: individual—quasars: absorption lines INTRODUCTION
It is known that absorption lines would be detected ina quasar spectra when the quasar sight line passes throughthe corresponding foreground absorbers. Absorption lines ofquasars are usually split into broad absorption lines (BALs),with the absorption troughs being broader than 2000 km s - atdepths >
10% below the continuum (Weymann et al. 1991),and narrow absorption lines (NALs), with line widths beingnarrower than 500 km s - . Absorption lines are traditionallydivided into two classes according to their relationship withthe corresponding quasars: (1) the cosmologically interveningabsorption lines, which are often believed to be caused by thecosmologically intervening galaxies lying on the quasar sightlines (Bergeron 1986; Bond et al. 2001) and hence are phys-ically unrelated with the quasars; (2) the intrinsic (or asso-ciated) absorption lines, which are physically associated withthe quasars. The intrinsic absorption lines are usually believedto be related with quasar outflows, for which, viewing at dif-ferent angles could give rise to different line types (BALs orNALs) (Murray et al. 1995).Variations of intrinsic absorption lines in equivalent widthand/or shape have been noted by various authors (e.g., Lund-gren et al. 2007; Leighly et al. 2009; Capellupo et al.2011; Hamann et al. 2011). It was revealed that the frac-tional change in equivalent width increases with rest-frametimescale over 0 . - Department of Physics and Telecommunication Engineering, BaiseUniversity, Baise, Guangxi 533000, China; [email protected] Center for Astrophysics, Guangzhou University, Guangzhou 510006,China; [email protected] Key Laboratory for Research in Galaxies and Cosmology, Shang-hai Astronomical Observatory, Chinese Academy of Sciences, 80 NandanRoad, Shanghai 200030, China; [email protected] Physics Department, Guangxi University, Nanning 530004, P. R.China be common, extreme events such as the disappearance andthe emergence of absorption troughs from the spectra are rare(which might consume many years of observation). So far,only a small number of these extreme events of BALs havebeen reported (e.g., Hall et al. 2011; Vivek et al. 2012; Filiz etal. 2012). Variations in the ionization state of absorption gasare also common. In a recent study, the coordinated line vari-ations of five narrow intrinsic absorption systems imprinted inone quasar spectra could be best explained by global changesin the ionization of absorption gas due to the changes in thequasar’s ionizing emission (Hamann et al. 2011). However,no disappearance and emergence of narrow absorption lineshave ever been reported.Quasars are capable of driving outflows with speeds up to30 ,
000 km s - (Ganguly et al. 2007). Therefore, the nar-row intrinsic absorption lines can occur at large velocity sep-arations from the quasars (e.g., Misawa et al. 2007; Gan-guly & Brotherton 2008; Hamann et al. 2011). In addition,narrow absorption lines imprinted in the quasar spectra arevery common for intervening absorption lines. Thus, in manycases, confirming a narrow absorption line to be intrinsic tothe quasar is very difficult (see Ganguly & Brotherton 2008for a review).In this letter, we analyze the spectra of quasar SDSSJ165501.31+260517.4 and report our discovery of the dis-appearance of a narrow Mg II λλ , Ω Λ = 0 . Ω M = 0 . H = 70 km s - Mpc - . ANALYSIS
There are about 8000 quasars included in both the SDSS-III (Sloan Digital Sky Survey-III) quasar catalog (Eisensteinet al. 2011; Ross et al. 2012) and the SDSS-II quasar cata-log (York et al. 2000; Schneider et al. 2010), meaning thatthese quasars have been observed twice by the Sloan Digi-tal Sky Survey. This large sample provides us a chance tosearch possible disappearance of absorption systems. Amongthese quasars, 33 were detected to possess obvious Mg II λλ , TABLE 1 P ARAMETERS OF DISAPPEARING ABSORPTION LINES
Species W r (Å) W r (Å) a Mg II λ ± Mg II λ ± Fe II λ ± N III λ ± Ni II λ ± Fe II λ ± Si II λ ± Fe II λ ± Ni II λ ± a The equivalent width limits estimated from the corresponding SDSS-IIIspectrum are also calculated by Equation (1). a combination of cubic splines for pseudo-continuum, andGaussians for line features. The Mg II λλ , λλ , z e = 1 . λλ , z abs = 1 . λλ , λλ , W r ). We estimate the uncertainty of the detectedabsorption lines via(1 + z ) σ w = qP i P ( λ i - λ ) σ f i P i P ( λ i - λ ) ∆ λ (1)here P ( λ i - λ ) , λ i , and σ f i represent the line profile centeredat λ , the wavelength, and the normalized flux uncertainty as afunction of pixel (Nestor et al. 2005; Quider et al. 2011). Thesum is performed over an integer number of pixels that coverat least ± DISCUSSION AND CONCLUSIONS
Although the disappearance of BALs was reported by var-ious authors previously (e.g., Hall et al. 2011; Vivek et al.2012; Filiz Ak et al. 2012), so far, the disappearance ofnarrow absorption lines has not been detected yet. Here,we show the first discovery of the disappearance of a nar-row Mg II λλ , z abs = 1 . z e =1 . ,
423 km s - . The line variability together with thevelocity offset suggest that this narrow Mg II λλ , λλ , λλ , λλ , z abs = 1 . ,
562 km s - (see Fig. 2). We found that this absorptiondoublet is very stable (within 1 σ error) during two epochs,with W r ( λ . ± .
09 and W r ( λ . ± . W r ( λ . ± .
17 and W r ( λ . ± .
15 from the SDSS-I/II spectrum. If thedisappearance of the z abs = 1 . λλ , z abs = 1 . λλ , λλ , D cont ∼ R S = 10 GM BH / c (Wise et al. 2004; Misawa et al. 2005).Here, let us take the virial black hole mass M BH = 10 . M ⊙ ,estimated based on the Mg II broad emission line (Shen etal. 2011), as the mass of the black hole. That gives rise to D cont = 1 . × . km . The disappearance of the narrow MgII λλ , - . Adopting the virial black hole mass and assum-ing that the shift velocity of the gas does not exceed the escapevelocity, we can constrain the location of the absorber relativeto the central region: the gas locates at a radius of r ∼ . pc (see, e.g., Misawa et al. 2005). According to the empiri-cal relationship between the radius and luminosity, the radiusof the broad emission line region (BLR) is R BLR ≈ . pc ,which was estimated from the continuum luminosity at 1350Å (Kaspi et al. 2007), where the continuum luminosity at1350 Å is directly taken from Shen et al. (2011). In this way,the absorber would locate at the vicinity of the broad emissionline region. ACKNOWLEDGEMENTS
We thank the anonymous referee for helpful comments andsuggestions. This work was supported by the 973 Programhe disappearance of a narrow Mg II absorption system 3 F IG . 1.— The spectra of quasar SDSS J165501.31+260517.4, observed by SDSS-I/II (the lower panel) and SDSS-III (the upper panel) respectively. The redsolid lines represent the pseudo-continua, and the solid green line presented in the lower panel is the pseudo-continuum shown in the upper panel.F IG . 2.— The pseudo-continuum normalized spectra of quasar SDSS J165501.31+260517.4, observed by SDSS-I/II (the lower panel) and SDSS-III (the upperpanel) respectively. The solid green lines represent the flux uncertainty levels which have been normalized by the corresponding pseudo-continuum, the solidblue curves represent the Gaussian fitting, and the dashed dark red lines show the positions of absorption lines. A Mg II λλ , z abs = 1 . Chen, Qin & Gu F IG . 3.— The Mg II λλ , z abs = 1 . (No. 2009CB824800), the National Natural Science Founda-tion of China (No. 11073007, and 11073039), the Guangzhoutechnological project (No. 11C62010685), and Guangxi Nat-ural Science Foundation (2012jjAA10090).(No. 2009CB824800), the National Natural Science Founda-tion of China (No. 11073007, and 11073039), the Guangzhoutechnological project (No. 11C62010685), and Guangxi Nat-ural Science Foundation (2012jjAA10090).