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[11.11] Seeing the Unvierse at redshift one with the AAT and CIRPASS: a multi-object near-infrared spectrograph

I.R. Parry (Institute of Astronomy, Cambridge), G.B. Dalton (Oxford Astrophysics), M. Doherty, R.G. Sharp, A.J. Dean, A.J. Bunker (Institute of Astronomy, Cambridge), I. Lewis, E. MacDonald, C. Wolf (Oxford Astrophysics), H. Hippelein, K. Meisenheimer (MPIA Heidelberg), L.A. Moustakas (STScI)

We present preliminary results from the CIRPASS instrument (Parry et al.\ 2000 SPIE 4008, 1193) -- a near-infrared fiber-fed spectrograph which was successfully commissioned in its multi-object spectroscopy (MOS) mode on the 4-m Anglo Australian Telescope in October 2002. The high resolving power of \lambda\,/\,\Delta\lambda_{\rm FWHM}\approx 5000 enables us to work effectively in the low-background regions between the OH sky lines in the J- and H-bands (1.0-1.7\,\mum). CIRPASS-MOS has 150 fibres each of 1.6^\prime\prime diameter, deployable over a 40^\prime-wide area. A natural project for CIRPASS-MOS is tracing star formation at z~1 using robust indicators such as H\alpha, redshifted into the near-infrared. We demonstrated this capability in our AAT observations last October, by observing some galaxies from the Calar Alto Deep Imaging Survey (CADIS) selected from a narrow redshift interval at z=0.88 by their [O{\scriptsize II}]\,3727\,Å\ line emission observed in extensive Fabry-Perot observations (Hippelein et al.\ 2003, astro-ph/0302116). The H\alpha is found at \approx 1.247\,\mum in a very clean (OH line-free) region of the night-sky spectrum, and we were able to detect H\alpha for a number of these galaxies. We demonstrated that CIRPASS achieved its design sensitivity: in a stacked 12-hour exposure we detected lines as faint as 4\times 10^-17\,{\rm ergs\,cm}^-2\,{\rm s}^-1 at 10\,\sigma (for \Delta v_FWHM~300\,km/s). This corresponds to an H\alpha flux at z~1 equivalent to an unobscured star formation rate of 2\,h₇₀^-2\,M_\odot\,{\rm yr}^-1 at z=1 (\Omega_M=0.3, \Omega_\Lambda=0.7), comparable to the star formation rate of the Milky Way today. We also successfully targeted a number of galaxies with photometric redshifts z~1, and broad-band colours indicating star formation. We are currently installing a 2k\times 2k detector on CIRPASS, which will double the wavelength coverage to 2100\,Å, and hence our ability to successfully target photometrically-selected galaxies over a range of redshifts will be greatly increased.

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The author(s) of this abstract have provided an email address for comments about the abstract: irp@ast.cam.ac.uk

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.