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

¹ Dept. of Computational and Applied Mathematics, University of the Witwatersrand, Private Bag 3, WITS 2050, South Africa
² Instituto Nacional de Astrofísica, Optica y Electrónica, Calle Luis Enrique Erro 1, 72840 Tonantzintla, Puebla, México
³ Gemini Observatory, 670 North Aohoku Place, Hilo, HI 96720, USA
⁴ Department of Astronomy, University of Toronto, 60 St. George Str., Toronto, ON M5S 3H8, Canada
⁵ Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
⁶ Joint Astronomy Centre, Univ. Park, 660 North Aohoku Place, Hilo, HI 96720, USA

Corresponding author: D. L. Block, block@cam.wits.ac.za

Received: 16 November 2000
Accepted: 4 January 2001

Abstract

Results from the Hubble Deep Field (HDF) North and South show a large percentage of high-redshift galaxies whose appearance falls outside traditional classification systems. The nature of these objects is poorly understood, but sub-mm observations indicate that at least some of these systems are heavily obscured (Sanders [CITE]). This raises the intriguing possibility that a physically meaningful classification system for high-redshift galaxies might be more easily devised at rest-frame infrared wavelengths, rather than in the optical regime. Practical realization of this idea will become possible 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 () in the HDF North. If objects such as NGC 922 are common at high-redshifts, 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 rest-frame infrared for NGC 922 seen at high redshifts using NGST, by simulating the appearance of this galaxy at redshifts and in rest-frame K'. While this object cannot be classified within any optical Hubble bin, simulated NGST images at these redshifts can be readily classified using the dust penetrated template of Block & Puerari ([CITE]) and Buta & Block ([CITE]). The near-infrared disk of NGC 922 is not peculiar at all; 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.