[Previous] | [Session 16] | [Next]
Y. Ohyama (Subaru telescope, NAOJ), T. Hamana, N. Kashikawa, M. Chiba (Nat. Astron. Obs. of Japan), T. Futamase (Astronomical Inst.,Tohoku Univ., Japan)
We present new optical spectroscopy of the lens elliptical galaxy in the ``Einstein Cross'' lens system HST 14176+5226, obtained with the Faint Object Camera and Spectrograph (FOCAS) of the Subaru telescope. Our spectroscopic observations are aimed at measuring the velocity dispersion of the lens galaxy, located at high redshift of zL=0.81, as an important component to lens models. We have measured this dispersion to be 230 ±14 km s-1 (1\sigma) inside 0.35 effective radii of the lens, based on the Fourier cross-correlation method for analyzing the obtained spectrum. To extract the significance of this information on the geometry of the universe which also affects the image splitting, we attempt to fit three different lens models to the available data of the lens system. Provided that the lens galaxy follows similar dynamical and structural properties to those of local ellipticals (i.e., velocity anisotropy, radial density profile, and core radius), our likelihood analysis suggests a nonvanishing, large cosmological constant, \Lambda, to explain both the observed image splitting and currently measured velocity dispersion of the lens simultaneously: 1\sigma lower limit on \Lambda in the flat universe is about 0.9 and 2\sigma lower limit ranges 0.2 to 0.6 depending on the lens models. These results are insensitive to usual ambiguities in astronomical observations, such as dust absorption and evolutionary effect for sample objects, to distinguish the world model. We also discuss the possible uncertainties in the current approach and further prospects in placing a much tighter constraint on \Lambda.
The author(s) of this abstract have provided an email address for comments about the abstract: ohyama@subaru.naoj.org