Redshifted formaldehyde from the gravitational lens B0218+357

Abstract

The gravitational lens toward B0218+357 offers the unique possibility to study cool moderately dense gas with high sensitivity and angular resolution in a cloud that existed half a Hubble time ago. Observations of the radio continuum and six formaldehyde (H2CO) lines were carried out with the VLA, the Plateau de Bure interferometer, and the Effelsberg 100-m telescope. Three radio continuum maps indicate a flux density ratio between the two main images, A and B, of ~ 3.4 +/- 0.2. Within the errors the ratio is the same at 8.6, 14.1, and 43 GHz. The 1_{01}-0_{00} line of para-H2CO is shown to absorb the continuum of image A. Large Velocity Gradient radiative transfer calculations are performed to reproduce the optical depths of the observed two cm-wave "K-doublet" and four mm-wave rotational lines. These calculations also account for a likely frequency-dependent continuum cloud coverage. Confirming the diffuse nature of the cloud, an n(H2) density of < 1000 cm^{-3} is derived, with the best fit suggesting n(H2) ~ 200 cm^{-3}. The H2CO column density of the main velocity component is ~5 * 10^{13} cm^{-2}, to which about 7.5 * 10^{12} cm^{-2} has to be added to also account for a weaker feature on the blue side, 13 km/s apart. N(H2CO)/N(NH3) ~ 0.6, which is four times less than the average ratio obtained from a small number of local diffuse (galactic) clouds seen in absorption. The ortho-to-para H2CO abundance ratio is 2.0 - 3.0, which is consistent with the kinetic temperature of the molecular gas associated with the lens of B0218+357. With the gas kinetic temperature and density known, it is found that optically thin transitions of CS, HCN, HNC, HCO+, and N2H+ (but not CO) will provide excellent probes of the cosmic microwave background at redshift z=0.68.

arXiv commentAccepted for A&A, 8 Pages, 3 Figures, 5 Tables

References in corpus (13)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Determination of Cosmological Parameters
• The Hubble constant from gravitational lens CLASS B0218+357 using the Advanced Camera for Surveys
• The Redshift of the Lensed Object in the Einstein Ring B0218+357
• Detection of water at z = 0.685 towards B0218+357
• The kinetic temperature of a molecular cloud at redshift 0.7: Ammonia in the gravitational lens B0218+357
• Detection of OH and wide HI absorption toward B0218+357
• Global 8.4-GHz VLBI observations of JVAS B0218+357
• Redshifted molecular absorption systems towards PKS1830-211 and B0218+357: submillimeter CO, CI and H2O data
• Free-free absorption in the gravitational lens JVAS B0218+357
• VLBI phase-reference observations of the gravitational lens JVAS B0218+357
• MERLIN/VLA imaging of the gravitational lens system B0218+357
• Distribution of the molecular absorption in front of the quasar B0218+357
• Intrinsic intraday variability in the gravitational lens system B0218+357

Cited by in corpus (9)

• Strong Limit on a Variable Proton-to-Electron Mass Ratio from Molecules in the Distant Universe
• A precise and accurate determination of the cosmic microwave background temperature at z=0.89
• Constraining changes in the proton-electron mass ratio with inversion and rotational lines
• The density, the cosmic microwave background, and the proton-to-electron mass ratio in a cloud at redshift 0.9
• Gravitational lensing reveals extreme dust-obscured star formation in quasar host galaxies
• The kinetic temperature of a molecular cloud at redshift 0.9: Ammonia in the gravitational lens PKS1830-211
• Isotopic ratios at z=0.68 from molecular absorption lines toward B 0218+357
• Formaldehyde Anti-Inversion at z=0.68 in the Gravitational Lens B0218+357
• Interstellar Silicate Dust in the z=0.685 Absorber Toward TXS 0218+357