期刊
ASTROPHYSICAL JOURNAL LETTERS
卷 728, 期 1, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/728/1/L12
关键词
atomic processes; galaxies: high-redshift; quasars: absorption lines
资金
- Department of Science and Technology, India
We report deep Green Bank Telescope spectroscopy in the redshifted NH3 (1,1), CS 1-0, and H2CO 0(00)-1(01) lines from the z similar to 0.685 absorber toward B0218+357. The inversion (NH3) and rotational (CS, H2CO) line frequencies have different dependences on the proton-electron mass ratio mu, implying that a comparison between the line redshifts is sensitive to changes in mu. A joint three-component fit to the NH3, CS, and H2CO lines yields [Delta mu/mu] = (-3.5 +/- 1.2) x 10(-7), from z similar to 0.685 to today, where the error includes systematic effects from comparing lines from different species and possible frequency-dependent source morphology. Two additional sources of systematic error remain, due to time variability in the source morphology and velocity offsets between nitrogen-bearing and carbon-bearing species. We find no statistically significant (>= 3 sigma) evidence for changes in mu and obtain the stringent 3 sigma constraint, [Delta mu/mu] < 3.6x10(-7), over 6.2 Gyr; this is the best present limit on temporal changes in mu from any technique, and for any look-back time, by a factor greater than or similar to 5.
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