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

Abstract

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 2000). 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 (z = 0.749) in the HDF North. If objects such as NGC 922 are common at highredshifts, 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 z = 0.7 and z = 1.2 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 z ∼ 0 template of Block & Puerari (1999) and Buta & Block (2001). 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.

The gravitational torque of bars in optically unbarred and barred galaxies

“…This variation might indicate some dynamical interaction between the two bars, such as an oscillation about the equilibrium aligned configuration. Block et al (2001) have suggested that a physically meaningful classification system for high-redshift galaxies may be more easily devised at rest-frame infrared wavelengths, rather than in the optical regime. Sub-mm observations indicate that at least some of these systems are heavily obscured by dust (Sanders 1999).…”

“…Lessons from our local Universe are that optical morphologies can be radically different from near-infrared ones; some optically flocculent galaxies, for example, may have beautiful grand design stellar disks when examined at K. The decoupling of gaseous and stellar disks can be dramatic (see e.g., Puerari et al 2000;Elmegreen et al 1999;Grosbøl & Patsis 1998;Block et al 1994). Block et al (2001) show that Fourier spectra may be generated on simulated Next Generation Space Telescope (NGST) rest-frame K post-stamp FITS images which may be as small as 1 on a side.…”

“…Recreated rest-frame K-band NGST images of the galaxies NGC 2997 and NGC 922 when moved out to redshifts of z = 0.7 and z = 1.2, are presented in Block et al (2001). We have applied our Q b method to NGC 922, which may serve as an excellent morphological interface between the low and high redshift universe (see Block et al 2001 for full details).…”

“…We have applied our Q b method to NGC 922, which may serve as an excellent morphological interface between the low and high redshift universe (see Block et al 2001 for full details).…”

Dust Penetrated Morphology in the High Redshift Universe

“…In this contribution, the images of NGC 922 are simulated at redshifts z = 0.7 and z = 1.2 in the K ′ restframe. The original image of NGC 922 was obtained at the NASA Infrared Telescope Facility with NSFCam (more details can be found in Block et al 2001).…”