Galaxies Under the Cosmic Microscope - a GMOS study of the lensed disk-galaxy #289 in A2218

In this project, we exploit the gravitational potential of the rich cluster A2218 as a magnifying glass. We demonstrate that the magnification due to the cluster allows us to observe distant background galaxies at a comparable level of detail to galaxies at z~0.1. Using the GMOS Integral Field Unit on Gemini North we observed the spatially-resolved [OII](3727) emission line spectrum for a lensed disk-galaxy at z=1.034. Using a detailed model for the cluster mass distribution, we are able to correct for the lensing by the cluster and reconstruct the source morphology. We find that the overall magnification is a factor of 4.92 +/- 0.15, and the rest-frame absolute I-band magnitude is M_{I}^{rest} = -22.4 \pm 0.2, where the error bars include conservative estimates of the uncertainty in the source-plane reconstruction. The inclination-corrected circular velocity is 206 +/- 18km/s. The galaxy lies very close to the mean Tully-Fisher relation of present-day spirals. Although our results are based on a single object, they demonstrate that gravitational lensing can be viably used to make detailed studies of the evolution of the structure of distant field galaxies.

Richard Bower; Ian Smail; Mark Sullivan; Mark Swinbank: ICC, University of Durham

Andy Bunker; Joanna Smith: University of Cambridge

Richard Ellis; Graham Smith; Jean-Paul Kneib: Caltech Astronomy

HST image of cluster A2218

A2218

HST image of cluster A2218 (ra 66:35:49, dec +66:12:45)

Left: Arc #289 in A2218 generated by combining HST WFPC2 B, V and I drizzled images. Right: The reconstructed image of the arc corrected for lens magnification using the mass model of Smith et al. (2003).


Sky Frame

Source Frame

Left: The [OII] emission map of the arc measured from the GMOS IFU observations. The distribution of [OII] flux agrees well with the UV flux seen in the HST images above (the seeing for the observations was 0.7"). The contour map of the derived velocity field is overlaid. Right: The reconstructed IFU velocity field of the galaxy. The red and blue regions represent redshift and blueshift respectively and the contours map the velocity. The luminosity weighted magnification is 4.92 but varies from ~5.6 to ~4.9 from the northern to southern end of the arc. Without a lens, at z=1, 1" corresponds to 7.7kpc


Sky Frame

Source Frame

Arc 289 on the Tully Fisher Relation

Left: Arc\#289 on the Tully-Fisher relation in rest frame B-band compared to high redshift (z~0.83) field galaxies (Milvang-Jensen et al. 2001) and the high redshift sample from Vogt et al. (1999). For comparison we show the low redshift local fit from Pierce & Tully (1992). The solid triangle shows a massive disk galaxy (L451) at z=1.34 (van Dokkum & Stanford 2001). The galaxy rotation curve (inset) shows the peak-to-peak rotation velocity of the arc in [OII] emission built from the IFU image in the source plane. The error bars shown are formally 3-\sigma and alternate points are independent. The horizontal error bars show 0.7'' seeing transformed to the source plane. Right: The rest frame I-band Tully-Fisher relation compiled from Mathewson & Ford (1992) and from the Ursa-Major Cluster (Verheijen 2001). Arc #289 is shown by the solid point and lies very close to the mean TF relation for present day spirals. The small change in the I-band magnitude shown by arc#289 suggests a preference for hierarchical rather than the ``classical'' formation model.