The inhomogeneous ISM toward PKS1830-211 SW - A detailed view on molecular gas at a look-back time of 7.5 Gyr

Abstract

Based on measurements with the Effelsberg 100-m telescope, a multi-line study of molecular species is presented toward the south-western source of the gravitational lens system PKS 1830-211, which is by far the best known target to study molecular gas in absorption at intermediate redshift. Determining line parameters and optical depths and performing Large Velocity Gradient radiative transfer calculations, the aims of this study are (1) to evaluate physical parameters of the absorbing foreground gas at z~0.89, in particular its homogeneity, and (2) to monitor the spectroscopic time variability caused by fluctuations of the z~2.5 background continuum source. We find, that the gas is quite inhomogeneous with n(H2)~2 x 10^3 cm^-3 for most molecular species but with higher values for H2CO and lower ones for SO. Measuring the CS J=1-0 transition during a time interval of more than a decade, from 2001 to 2012, the peak absorption depth of the line remains approximately constant, while the line shape undergoes notable variations. Covering the time between 1996 and 2013, CS, HCO+, and CH3OH data indicate maximal integrated optical depths in ~2001 and 2011/2012. This is compatible with a ~10 yr periodicity, which, however, needs confirmation by substantially longer time monitoring. Comparing molecular abundances with those of different types of Galactic and nearby extragalactic clouds we find that the observed cloud complex does not correspond to one particular type but to a variety of cloud types with more diffuse and denser components as can be expected for an observed region with a transverse linear scale of several parsec and a likely larger depth along the line-of-sight. A tentative detection of Galactic absorption in the c-C3H2 1(10)-1(01) line at 18.343 GHz is also reported.

Accepted for publication in A&A, 11 pages, 10 figures, 4 tables

References in corpus (7)

• Search for TeV Gamma-ray Emission from GRB 100621A, an extremely bright GRB in X-rays, with H.E.S.S
• Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe
• Probing isotopic ratios at z = 0.89: molecular line absorption in front of the quasar PKS 1830-211
• An ALMA Early Science survey of molecular absorption lines toward PKS1830-211 -- Analysis of the absorption profiles
• Drastic changes in the molecular absorption at redshift z=0.89 toward the quasar PKS 1830-211
• Detection of chloronium and measurement of the 35Cl/37Cl isotopic ratio at z=0.89 toward PKS1830-211
• Submillimeter water and ammonia absorption by the peculiar z~0.89 interstellar medium in the gravitational lens of the PKS 1830-211 system

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• A study of submillimeter methanol absorption toward PKS1830-211: Excitation, invariance of the proton-electron mass ratio, and systematics
• Detection of deuterated molecules, but not of lithium hydride, in the z=0.89 absorber toward PKS1830-211
• Cosmo-tomography toward PKS1830-211: Variability of the quasar and of its foreground molecular absorption monitored with ALMA
• The ortho-to-para ratio of H${}_2$Cl${}^{+}$: Quasi-classical trajectory calculations and new simulations in light of new observations
• Methanol absorption in PKS B1830-211 at milliarcsecond scales
• Discovery of Hydrogen Radio Recombination Lines at z=0.89 towards PKS 1830-211
• Emergence of a new HI 21-cm absorption component at z~1.1726 towards the gamma-ray blazar PKS~2355-106
• A sub-ppm upper limit on the cosmological variations of the fine structure constant alpha
• New constraints on the values of the fundamental constants at a look-back time of 7.3 Gyr
• The 107 GHz methanol transition is a dasar in G0.253+0.016