Dust-penetrated morphology in the high-redshift universe: Clues from NGC 922

Results from the Hubble Deep Field (HDF) North and South show a large perce ntage of high-redshift galaxies whose appearance falls outside traditional classification systems. The nature of these objects is poorly understood, b ut sub-mm observations indicate that at least some of these systems are hea vily obscured (Sanders 2000). This raises the intriguing possibility that a physically meaningful classification system for high-redshift galaxies mig ht be more easily devised at rest-frame infrared wavelengths, rather than i n the optical regime. Practical realization of this idea will become possib le with the advent of the Next Generation Space Telescope (NGST). In order to explore the capability of NGST for undertaking such science, we present NASA-IRTF and SCUBA observations of NGC 922, a chaotic system in our local Universe which bears a striking resemblance to objects such as HDF 2-86 (z = 0.749) in the HDF North. If objects such as NGC 922 are common at high-re dshifts, then this galaxy may serve as a local morphological "Rosetta stone " bridging low and high-redshift populations. In this paper we demonstrate that quantitative measures of galactic structure are recoverable in the res t-frame infrared for NGC 922 seen at high redshifts using NGST, by simulati ng the appearance of this galaxy at redshifts z = 0.7 andz = 1.2 in rest-fr ame K'. While this object cannot be classified within any optical Hubble bi n, simulated NGST images at these redshifts can be readily classified using the dust penetrated z similar to 0 template of Block & Puerari (1999) and Buta & Block (2001). The near-infrared disk of NGC 922 is not peculiar at a ll; rather, it is remarkably regular, even presenting spiral arm modulation , a characteristic signature of several grand design galaxies. Our results suggest that the capability of efficiently exploring 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.