Abstract. Using HST/WFPC2 imaging in F606W (or F450W) and F814W filters, we obtained the color maps in observed frame for 36 distant (0.4 < z < 1.2) luminous infrared galaxies (LIRGs, L IR (8−1000 µm) ≥ 10 11 L ), with average star formation rates of ∼100 M yr −1 . Stars and compact sources are taken as references to align images after correction of geometric distortion. This leads to an alignment accuracy of 0.15 pixel, which is a prerequisite for studying the detailed color properties of galaxies with complex morphologies. A new method is developed to quantify the reliability of each pixel in the color map without any bias against very red or blue color regions. Based on analyses of two-dimensional structure and spatially resolved color distribution, we carried out morphological classification for LIRGs. About 36% of the LIRGs were classified as disk galaxies and 22% as irregulars. Only 6 (17%) systems are obvious ongoing major mergers. An upper limit of 58% was found for the fraction of mergers in LIRGs with all the possible merging/interacting systems included. Strikingly, the fraction of compact sources is as high as 25%, similar to that found in optically selected samples. From their K band luminosities, LIRGs are relatively massive systems, with an average stellar mass of about 1.1 × 10 11 M . They are related to the formation of massive and large disks, from their morphologies and also from the fact that they represent a significant fraction of distant disks selected by their sizes. If sustained at such large rates, their star formation can double their stellar masses in less than 1 Gyr. The compact LIRGs show blue cores, which could be associated with the formation of the central region of these galaxies. We find that all LIRGs are distributed along a sequence which relate their central color to their concentration index. This sequence links compact objects with blue central color to extended ones with relatively red central color, which are closer to the local disks. We suggest that there are many massive disks which have been forming a large fraction of their stellar mass since z = 1. For most of them, their central parts (bulge?) were formed prior to the formation of their disks.

Abstract.To address how the galaxy Hubble sequence is established and what physical processes are involved, we studied morphological properties and internal structures of field galaxies in the past (0.4 < z < 1). In addition to structural parameters derived from bulge+disk decomposition, Zheng et al. (2004, A&A, 421, 847) introduced color maps in recognizing galaxies and properly classified morphologies of 36 luminous infrared galaxies (LIRGs, L IR (8−1000 µm) ≥ 10 11 L ). Here we presented morphological classification of a parallel 75 non-LIRG sample. Our examination revealed that a significant fraction of the galaxies shows remarkable morphological evolution, most likely related to the present-day spiral galaxies. Comparison of the morphological properties between LIRGs and non-LIRGs shows that the LIRGs contain a higher fraction of ongoing major mergers and systems with signs of merging/interaction. This suggests that the merging process is one of the major mechanisms to trigger star formation. We found that spiral LIRGs probably host much fewer bars than spiral non-LIRGs, suggesting that a bar is not efficient in triggering violent star formation. Differing from Abraham et al. (1999, MNRAS, 308, 569), no dramatic change of the bar frequency is detected up to redshift z ∼ 0.8. The bar frequency of the distant spirals is similar to (and may be higher than) the present-day spirals in the rest-frame B band. We conclude that bar-driven secular evolution is not a major mechanism to drive morphological evolution of field galaxies, especially their bulge formation, which is more likely related to multiple intense star formation episodes during which the galaxies appear as LIRGs (Hammer et al. 2005, A&A, 430, 115).

A new method to simulate turbulent phase is investigated in this paper. The goal of this method is to be able to simulate very long exposure times as well as time evolving turbulence conditions. But contrary to existing methods, our method allows to simulate such effects without using the whole memory space required by the simulated exposure time, making it particularly suited to the simulation of adaptive optics systems for very large apertures telescopes.

Integral field spectrographs are major instruments with which to study the mechanisms involved in the formation and the evolution of early galaxies. When combined with multi-object spectroscopy, those spectrographs can behave as machines used to derive physical parameters of galaxies during their formation process. Up to now, there has been only one available spectrograph with multiple integral field units, i.e. FLAMES/GIRAFFE on the European Southern Observatory (ESO) Very Large Telescope (VLT). However, current ground-based instruments suffer from a degradation of their spatial resolution due to atmospheric turbulence. In this article we describe the performance of FALCON, an original concept of a new-generation multi-object integral field spectrograph with adaptive optics for the ESO VLT. The goal of FALCON is to combine high angular resolution (0.25 arcsec) and high spectral resolution (R > 5000) in the J and H bands over a wide field of view (10 × 10 arcmin 2 ) in the VLT Nasmyth focal plane. However, instead of correcting the whole field, FALCON will use multiobject adaptive optics (MOAO) to perform the adaptive optics correction locally on each scientific target. This requires us then to use atmospheric tomography in order to use suitable natural guide stars for wavefront sensing. We will show that merging MOAO and atmospheric tomography allows us to determine the internal kinematics of distant galaxies up to z ≈ 2 with a sky coverage of 50 per cent, even for objects observed near the Galactic pole. The application of such a concept to extremely large telescopes seems therefore to be a very promising way to study galaxy evolution from z = 1 to redshifts as high as z = 7. Wavelength rangeAs explained in the Introduction, dynamical information is required to improve our knowledge of the mechanisms responsible for the formation of galaxies. The velocity field of the galaxies has therefore to be probed by measuring the redshifts of emission lines, which we choose to peak in the 1.00-1.85 μm wavelength range (covering the J and H bands), thus avoiding the thermal domain (λ > 1.95 μm) where the instrumental thermal background will dominate the noise. Several emission lines can then be used, such as [O II] (λ = 3727 Å), Hβ (λ = 4861 Å), [O III] (λ = 5007 Å) and in particular Hα (λ = 6563 Å). Indeed, this latter suffers less from extinction than the other emission lines (Liang et al. 2004), and can be used to map the dynamical information up to z = 1.8. The use of shorter wavelength emission lines will allow the observation of galaxies up to z = 2.5, although extinction may then be a problem (Liang et al. 2004). Angular resolutionMorphological studies of galaxies located in the Hubble Deep Fields and the Great Observatories Origins Deep Survey (GOODS) fields have shown that galaxies with z 1 have half-light radii r 1/2 smaller than 0.5 arcsec (Marleau & Simard 1998;Ferguson et al. 2004), with an average r 1/2 = 0.25 arcsec at z = 2 (Bouwens et al. 2004). As we want to study the dynamical processes occurring within...