Morphological evolution of z ~ 1 galaxies from deep K-band AO imaging in the COSMOS deep field *,**,***
LESIA-Paris Observatory, 5 place Jules Janssen, 92195 Meudon, France e-mail: firstname.lastname@example.org
2 IAA-C/ Camino Bajo de Huétor, 50-18008 Granada, Spain
3 Laboratoire d'Astrophysique de Toulouse-Tarbes, CNRS-UMR 5572 and Université Paul Sabatier Toulouse III, 14 avenue Belin, 31400 Toulouse, France
4 LAM-Marseille Observatory, Traverse du Siphon, Les trois Lucs, BP 8, 13376 Marseille Cedex 12, France
Accepted: 13 March 2007
Context.We present the results of an imaging program of distant galaxies () at high spatial resolution (~) aiming at studying their morphological evolution. We observed 7 fields of with the NACO Adaptive Optics system (VLT) in Ks (m) band with typical guide stars and 3 h integration time per field. Observed fields are selected within the COSMOS survey area, in which multi-wavelength photometric and spectroscopic observations are ongoing. High angular-resolution K-band data have the advantage of probing old stellar populations in the rest-frame, enabling a determination of galaxy morphological types unaffected by recent star formation, which are more closely linked to the underlying mass than classical optical morphology studies (HST). Adaptive optics on ground based telescopes is the only method today for obtaining such a high resolution in the K-band, but it suffers from limitations since only small fields are observable and long integration times are necessary.
Aims.In this paper we show that reliable results can be obtained and establish a first basis for larger observing programs.
Methods.We analyze the morphologies by means of B/D (bulge/disk) decomposition with GIM2D and C-A (concentration-asymmetry) estimators for 79 galaxies with magnitudes between and classify them into three main morphological types (late type, early type and irregulars). Automated and objective classification allows precise error estimation. Simulations and comparisons with seeing-limited (CFHT/Megacam) and space (HST/ACS) data are carried out to evaluate the accuracy of adaptive optics-based observations for morphological purposes.
Results.We obtain the first estimate of the distribution of galaxy types at redshift as measured from the near infrared at high spatial resolution. We show that galaxy parameters (disk scale length, bulge effective radius, and bulge fraction) can be estimated with a random error lower than for the bulge fraction up to () and that classification into the three main morphological types can be done up to () with at least 70% of the identifications correct. We used the known photometric redshifts to obtain a redshift distribution over 2 redshift bins (, ) for each morphological type.
Key words: galaxies: fundamental parameters / galaxies: high-redshift / galaxies: evolution / instrumentation: adaptive optics
Based on ESO observations at the VLT. Programmes P73.A-0814A and P75.A-0569A and 175.A-0839 (zCOSMOS).
Based on observations obtained with MegaPrime/MegaCam, a joint project of the CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at TERAPIX and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of the NRC and CNRS.
© ESO, 2007