Star forming rates between z = 0.25 and z = 1.2 from the CADIS emission line survey

Free access article

Issue		A&A Volume 402, Number 1, April IV 2003


Page(s)		65 - 78
Section		Galactic structure and dynamics
DOI		http://dx.doi.org/10.1051/0004-6361:20021898

A&A 402, 65-78 (2003)
DOI: 10.1051/0004-6361:20021898

Star forming rates between z = 0.25 and z = 1.2 from the CADIS emission line survey

H. Hippelein¹, C. Maier¹, K. Meisenheimer¹, C. Wolf^{1, 2}, J. W. Fried¹, B. von Kuhlmann¹, M. Kümmel¹, S. Phleps¹ and H.-J. Röser¹

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
² Department of Physics, Denys Wilkinson Bldg., University of Oxford, Keble Road, Oxford, OX1 3RH, UK

(Received 15 May 2002 / Accepted 23 December 2002 )

Abstract
The emission line survey within the Calar Alto Deep Imaging Survey (CADIS) detects emission line galaxies by a scan with an imaging Fabry-Perot interferometer. It covers 5 fields of ${>} 100\,\sq \arcmin$ each in three wavelengths windows centered on $\lambda \simeq 700$ , 820, and 920 nm, and reaches to a typical limiting line flux of $3 \times 10^{-20}$ W m ^-2. This is the deepest emission line survey covering a field of several 100 $\sq \arcmin$ . Galaxies between z = 0.25 and z = 1.4 are detected by prominent emission lines (from H $\alpha$ to [O II]372.7) falling into the FP scans. Additional observations with a dozen medium band filters allow to establish the line identification and thus the redshift of the galaxies to better than $\sigma_{z} = 0.001$ . On the basis of a total of more than 400 emission line galaxies detected in H $\alpha$ (92 galaxies), [O III]500.7 (124 galaxies), or [O II]372.7 (222 galaxies) we measure the instantaneous star formation rate (SFR) in the range 0.24 < z < 1.21. With this purely emission line selected sample we are able to reach much fainter emission line galaxies than previous, continuum-selected samples. Thus completeness corrections are much less important. Although the relative [O III] emission line strength depends on excitation and metallicity and shows strong variation, the mean line ratios yield SFR[O III] values consistent with the SFR evolution. Our results substantiates the indications from previous studies (based on small galaxy samples) that the SFR decreases by a factor of ~20 between z = 1.2 and today. In fact, for a $\Omega_{\rm m} = 0.3, \Omega_\lambda = 0.7$ cosmology, we find an exponential decline $\dot{\rho}_{\rm SFR} \propto \exp(-t_{\rm lookback} / 2.6$ Gyr). This decrease of the SFR with time follows an exponential law which is compatible with the decreasing galaxy merger rate as expected from model calculations. The inferred SF density is in perfect agreement with that deduced from the FIR emission of optically selected galaxies which is explained by a large overlap between both populations. We show that self-consistent extinction corrections of both our emission lines and the UV continua lead to consistent results for the SF density.

Key words: stars: formation -- galaxies: general -- galaxies: high-redshift -- galaxies: luminosity function

Offprint request: H. Hippelein, hippelei@mpia-hd.mpg.de

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