Drastic changes in the molecular absorption at redshift z = 0.89 toward the quasar PKS 1830–211

Free access article

Issue		A&A Volume 491, Number 3, December I 2008


Page(s)		739 - 746
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:200810392
Published online		07 October 2008

A&A 491, 739-746 (2008)
DOI: 10.1051/0004-6361:200810392

Drastic changes in the molecular absorption at redshift z = 0.89 toward the quasar PKS 1830–211

S. Muller¹ and M. Guélin^{2, 3}

¹ Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), PO Box 23–141, Taipei, 106, Taiwan
e-mail: muller@asiaa.sinica.edu.tw
² Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la piscine, 38406 St Martin d'Hères, France
³ École Normale Supérieure/LERMA, 24 rue Lohmond, 75005 Paris, France

Received 16 June 2008 / Accepted 24 September 2008

Abstract
A 12 year-long monitoring of the absorption caused by a z = 0.89 spiral galaxy on the line of sight to the radio-loud gravitationally lensed quasar PKS 1830-211 reveals spectacular changes in the HCO⁺ and HCN (2–1) line profiles. The depth of the absorption toward the quasar NE image increased by a factor of ~ 3 in 1998–1999 and subsequently decreased by a factor $\geq$ 6 between 2003 and 2006. These changes were echoed by similar variations in the absorption line wings toward the SW image. Most likely, these variations result from a motion of the quasar images with respect to the foreground galaxy, which could be due to a sporadic ejection of bright plasmons by the background quasar. VLBA observations have shown that the separation between the NE and SW images changed in 1997 by as much as 0.2 mas within a few months. Assuming that motions of similar amplitude occurred in 1999 and 2003, we argue that the clouds responsible for the NE absorption and the broad wings of the SW absorption should be sparse and have characteristic sizes of 0.5–1 pc. 

Key words: galaxies: quasars: individual: PKS 1830-211 -- galaxies: quasars: absorption lines -- galaxies: ISM -- ISM: molecules

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