School of Astronomy (SoA) - Weekly Seminar

Mr. Hadi Rahmani (IUCAA)   

Wednesday, 23 Farvardin ,11 April, Time: 14:00

IPM Larak Building, School of Astronomy 

Address: Larak Garden, opposite Araj, Artesh Highway,Tehran, Iran
E-mail: astro(at)ipm.ir

Abstract:
We present high resolution optical spectra obtained with the Ultraviolet and Visual Echelle Spectrograph (UVES) at the Very Large Telescope (VLT) and 21-cm absorption spectra obtained with the Giant Metrewave Radio Telescope (GMRT) and the Green Bank Telescope (GBT) of five quasars along the line of sight of which 21-cm absorption systems at 1.17 < z < 1.56 have been detected previously. We also present milliarcsec scale radioimages of these quasars obtained with the Very Large Baseline Array (VLBA). We use the data on four of these systems to constrain the time variation of x = g_p alpha^2 / μ where g_p is the proton gyromagnetic factor, alpha is the fine structure constant, and       μ is the proton-to-electron mass ratio. We carefully evaluate the systematic uncertainties in redshift measurements using cross-correlation analysis and repeated Voigt profile fitting. In two cases we also confirm ourresults by analysing    optical spectra obtained with the Keck telescope. We find the weighted and the simple means of dx/x to be respectively −(0.3 ± 1.3)× 10^−6  and −(0.2 ± 1.5) × 10^−6at the mean redshift of < z >= 1.36 corresponding to a look back time       of ~ 9 Gyr. This is the most stringent constraint ever obtained on dx/x. If we use only the two systems towards quasars unresolved at milliarcsec scales, we get the simple mean of dx/x = +(0.2±1.6)×10^−6.Assuming constancy of other constants we get dalpha/alpha = −(0.1 ± 0.7) × 10^−6 which is a factor of two better than the best constraints obtained so far using the Many Multiplet Method. On the other hand assuming alpha and g_p have not varied we derive            dμ/μ = +(0.2±1.5)×10^−6 which is again the best limit ever obtained on the variation of μ over this redshift range. Using independent constraints on dalpha/alpha at z < 1.8 and dμ/μ at z ~ 0.7 available in the literature we get dg_p/g_p < 3.5 × 10^−6. For two of the systems the spatial-dipole recently claimed in theliterature is ruled out at the ~ 2.5 sigma level