Near-ir integral field spectroscopy of high-Z galaxies

Abstract

Here we summarize the exciting prospect of near-infrared spatially-resolved spectroscopy of highredshift galaxies. This is now possible with the new integral field units on 8 m-class telescopes, such as the Cambridge IR Panoramic Survey Spectrograph (CIRPASS, Parry et al.: 2001, SPIE 4008, 1193). Line emission should be an instantaneous tracer of star formation activity, but measurements based on Lyman-α are unreliable because of the selective extinction of this resonant UV line. Using more robust lines such as Hα forces a move to the near-infrared at z > 1. Great sensitivity can be achieved in the J- and H-bands (1.2 & 1.6 µm) by pre-selecting galaxies with redshifts for which prominent rest-frame optical emission lines fall into these near-infrared windows, between atmospheric lines. On an 8 m-class telescope, star formation rates of < 1 M ⊙ yr−1 will be reached at z ≈ 1.4 with Hα in the H-band. Such star formation rates are well below L* for the high-z Lyman-break population, and are comparable locally to the luminous giant H II complexes in M 101. Line ratio indices will reveal the metallicity and extinction in star forming regions within the galaxy disks. The line widths and velocity offsets will provide a sensitive probe of the kinematics of the galaxies, to explore the evolution of fundamental scaling relations. Combining this spatially-resolved spectroscopy with deep, multi-colour, high-resolution imaging (e.g. from HST) will explore fundamental structural parameters (2D rotation velocity profiles, stellar masses, sizes and disk scale lengths), luminosities and star formation rates, and study their evolution with redshift. This will provide a stringent test of current models for the formation and evolution of galactic disks.