The Duality of Spiral Structure, and a Quantitative Dust Penetrated Morphological Tuning Fork at Low and High Redshift

Abstract

In the near-infrared, the morphology of older star-dominated disks indicates a simple classification scheme (1) H$m$ where $m$ is the dominant harmonic, (2) a pitch angle (derived from the Fourier spectra) associated with the rate of shear A/$\omega$ in the stellar disk and (3) a `bar strength' parameter, robustly derived from the gravitational potential or torque of the bar. A spiral galaxy may present two radically different morphologies in the optical and near-infrared regime; there is no correlation between our quantitative dust penetrated tuning fork and that of Hubble. Applications of our $z\sim$0 Fourier template to the HDF are discussed using $L$ and $M$ band simulations from an 8-m NGST; the rest-wavelength IR morphology of high-$z$ galaxies should probably be a key factor in deciding the final choice of instruments for the NGST.

8 pages, 5 figures. To appear in ASP Conf. Ser. "Galaxy Disk and Disk Galaxies", Eds. J.G. Funes S.J. and E.M. Corsini (meeting held in Rome, June 12-16, 2000)