Mathematics – Logic
Scientific paper
Jun 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003phdt.........1m&link_type=abstract
PhD thesis, University of Nottingham
Mathematics
Logic
8
Galaxies: Spiral, Galaxies: Evolution, Galaxies: Clusters: Individual: Ms1054.4-0321
Scientific paper
This thesis studies spiral galaxies in the high redshift cluster MS1054-03 at z = 0.83 and field spirals at similar redshifts. The aim is to shed light on the processes governing the evolution of galaxies in clusters, in particular the processes responsible for the morphological transformation of spiral galaxies into S0s. The main diagnostic used is the Tully-Fisher relation. We have obtained spatially-resolved optical emission line spectra carried out at the VLT, from which we have measured rotation velocities. The sample analysed contains 7 spirals in MS1054-03 and 18 field spirals at z = 0.15-0.90. Rest-frame B-band magnitudes were derived using HST images, and the B-band Tully-Fisher relation for the sample was studied. With respect to a local relation, most of the high redshift galaxies were found on the high luminosity / low velocity side. The cluster sample was compared to the field sample. A difference in the Tully-Fisher residuals was found at 1.5-2 sigma significance. If interpreted as a difference in absolute magnitude at a fixed rotation velocity, the mean difference is ~1 mag in the sense that the cluster sample is brighter than the field sample. This could indicate a brightening due to enhanced levels of star formation. A similar analysis in the rest-frame H-band, but using unpublished magnitudes derived from images which we have not had access to, shows a cluster-field difference that is as large as in the B-band. This is at variance with our interpretation of the B-band results. If the H-band results are confirmed using published data we should consider the alternative interpretation that the Tully-Fisher residuals are driven by differences in rotation velocity rather than luminosity.
The size (stellar scale length)-velocity diagram showed no strong cluster-field difference. This indicates that the cluster and the field spirals are structurally similar. The gas scale lengths were compared to the stellar scale lengths, and the two were found to be well correlated. Their ratio was smaller for the cluster spirals than for the field spirals. This could indicate that centrally concentrated star formation is more common in cluster spirals than in field spirals, a phenomenon also found locally.
The B-band Tully-Fisher residuals were found to be correlated with the [OII] luminosity and with an estimate of the extinction-corrected star formation rate at ~2 sigma significance. Galaxies with large negative Tully-Fisher residuals (indicative of a brightening) had large [OII] luminosities and star formation rates. This directly supports the interpretation of the B-band Tully-Fisher residuals as due to a brightening caused by star formation.
Taken as a whole, the results indicate that at least some spiral galaxies in high redshift clusters experience a period of enhanced star formation. This fits into the emerging picture in which spirals at high redshift fall into clusters from the field, experience a star burst and then fade and morphologically transform into S0s. As a continuation of this work we are studying larger samples and other evolutionary phases to underpin the yet unknown physical mechanisms responsible for the morphological transformation.
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