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Seven Broad Absorption Line Quasars With Excess Broadband Absorption Near 2250 Å

【标题】Seven Broad Absorption Line Quasars With Excess Broadband Absorption Near 2250 Å

【Title】

【DOI】10.1088/0004-637X/802/2/92

【作者】 张少华 ; 姜鹏; 周宏岩; Jingzhe Ma; Jian Ge; W. N. Brandt; Donald G. York; Pasquier Noterdaeme; Donald P. Schneider

【Author】 Zhang Shaohua ; Jiang Peng ; Zhou Hongyan ; Jingzhe Ma ; Jian Ge ; W. N. Brandt ; Donald G. York ; Pasquier Noterdaeme ; Donald P. Schneider

【期刊】The Astrophysical Journal

【Journal】

【期刊年份】2015

【卷】802

【期】2

【关键词】 dust; extinction; galaxies: ISM; quasars: absorption lines; quasars: general

【Keywords】 dust; extinction; galaxies: ISM; quasars: absorption lines; quasars: general

【摘要】We report the discovery of excess broadband absorption (EBBA) near 2250 Å in the spectra of seven broad absorption line (BAL) quasars. By comparing with the statistical results from the control quasar sample, the significance for the detections are all above the ≳ 4σ level, with five above \gt 5σ . The detections have also been verified by several other independent methods. The EBBAs present broader and weaker bumps at smaller wavenumbers than the Milky Way, and similar to the Large Magellanic Cloud. The EBBA bump may be related to the 2175 Å bump seen in the Local Group and may be a counterpart of the 2175 Å bump under different conditions in the early universe. Furthermore, five objects in this sample show low-ionization BAL (LoBALs), such as Mg ii and Al iii, in addition to the high-ionization BAL of C iv and Si iv. The fraction of LoBALs in our sample, ∼70%, is surprisingly high compared to that of general BAL quasars, ∼10%. Although the origin of the bump is still not clear, the coexistence of both BALs and bumps and the significantly high fraction of LoBALs may indicate that the bump carriers are closely related to the early evolution phase of quasars.

【Abstract】We report the discovery of excess broadband absorption (EBBA) near 2250 Å in the spectra of seven broad absorption line (BAL) quasars. By comparing with the statistical results from the control quasar sample, the significance for the detections are all above the ≳ 4σ level, with five above \gt 5σ . The detections have also been verified by several other independent methods. The EBBAs present broader and weaker bumps at smaller wavenumbers than the Milky Way, and similar to the Large Magellanic Cloud. The EBBA bump may be related to the 2175 Å bump seen in the Local Group and may be a counterpart of the 2175 Å bump under different conditions in the early universe. Furthermore, five objects in this sample show low-ionization BAL (LoBALs), such as Mg ii and Al iii, in addition to the high-ionization BAL of C iv and Si iv. The fraction of LoBALs in our sample, ∼70%, is surprisingly high compared to that of general BAL quasars, ∼10%. Although the origin of the bump is still not clear, the coexistence of both BALs and bumps and the significantly high fraction of LoBALs may indicate that the bump carriers are closely related to the early evolution phase of quasars.

【基金/项目】 the SOC program (CHINARE2012- 02-03) ; NSFC with grants NSFC-11233002 and NSFC-11203022 ; Chinese Natural Science Foundation by NSFC-11203021 ; National Basic Research Program of China (973 Program, 2013CB834905)

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