EDP Sciences
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Volume 408, Number 2, September III 2003
Page(s) 455 - 463
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20031004

A&A 408, 455-463 (2003)
DOI: 10.1051/0004-6361:20031004

Integral-field spectrophotometry of the quadruple QSO HE 0435-1223: Evidence for microlensing

L. Wisotzki1, 2, T. Becker1, L. Christensen1, A. Helms2, K. Jahnke1, A. Kelz1, M. M. Roth1 and S. F. Sanchez1

1  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
2  Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany

(Received 9 April 2003 / Accepted 24 June 2003)

We present the first spatially resolved spectroscopic observations of the recently discovered quadruple QSO and gravitational lens HE 0435-1223. Using the Potsdam Multi-Aperture Spectrophotometer (PMAS), we show that all four QSO components have very similar but not identical spectra. In particular, the spectral slopes of components A, B, and D are indistinguishable, implying that extinction due to dust plays no major role in the lensing galaxy. While also the emission line profiles are identical within the error bars, as expected from lensing, the equivalent widths show significant differences between components. Most likely, microlensing is responsible for this phenomenon. This is also consistent with the fact that component D, which shows the highest relative continuum level, has brightened by 0.07 mag since Dec. 2001. We find that the emission line flux ratios between the components are in better agreement with simple lens models than broad band or continuum measurements, but that the discrepancies between model and data are still unacceptably large. Finally, we present a detection of the lensing galaxy, although this is close to the limits of the data. Comparing with a model galaxy spectrum, we obtain a redshift estimate of $z_{\mathrm{lens}}=0.44\pm 0.02$.

Key words: quasars: individual: HE 0435-1223 -- quasars: general -- gravitational lensing

Offprint request: L. Wisotzki, lwisotzki@aip.de

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