Abstract
At intermediate redshifts, many galaxies seem to be perturbed or suffering from an interaction. Considering that disk galaxies may have formed and evolved through minor mergers or through major mergers, it is important to understand the mechanisms at play during each type of merger in order to be able to establish the outcome of such an event. In some cases, only the use of both morphological and kinematical information can disentangle the actual configuration of an encounter at intermediate redshift. In this work, we present the morphological and kinematical analysis of a system at z=0.74 in order to understand its configuration, interacting stage and evolution. Using the integral field spectrograph GIRAFFE, long-slit spectroscopy by FORS2 and direct optical images from the HST-ACS and ISAAC near-infrared images, we disentangle the morphology of this system, its star-formation history and its extended kinematics in order to propose a possible configuration for the system. Numerical simulations are used to test different interacting scenarii. We identify this system as a face-on disk galaxy with a very bright bar in interaction with a smaller companion with a mass ratio of 3:1. The relevance of kinematical information and the constraints it imposes on the interpretation of the observations of distant galaxies is particularly strengthened in this case. This object is amongst the best example on how one may misinterpret morphology in the absence of kinematical information.
Highlights
Understanding how and when galaxies formed is a fundamental question in astrophysics
Earlier numerical simulations demonstrated that disks form around previously existing spheroids by means of the smooth accretion of gas from the intergalactic medium (e.g., Steinmetz & Navarro 2002), whereas spheroids represent the remnants of major merger events where disks are thrown together and mixed violently on a short timescale (e.g., Toomre 1977; Barnes & Hernquist 1992; Mihos & Hernquist 1994)
That there is almost no velocity gradient in the main component of the system can only be explained if the galaxy is seen face-on, in which case the bright, elongated structure seen in the direct images must be a bar lying on the disk of the main component
Summary
Understanding how and when galaxies formed is a fundamental question in astrophysics. Earlier numerical simulations demonstrated that disks form around previously existing spheroids by means of the smooth accretion of gas from the intergalactic medium (e.g., Steinmetz & Navarro 2002), whereas spheroids represent the remnants of major merger events where disks are thrown together and mixed violently on a short timescale (e.g., Toomre 1977; Barnes & Hernquist 1992; Mihos & Hernquist 1994). Two-dimensional spectroscopic observations of J033227.07274404.7 were taken with the integral field spectrograph FLAMES (Fibre Large Array Multi Element Spectrograph) with the medium-high (R = 5600–46 000) resolution spectrograph GIRAFFE (multi-IFU mode) as part of the IMAGES program (Yang et al 2008). A low-resolution (R = 860), large wavelength-range longslit spectrum (6000 Å to 10 800 Å) of the object was taken with the visual and near UV Focal Reducer and low dispersion Spectrograph, FORS2 as part of the ESO-GOODS program of spectroscopy of faint galaxies in the CDFS (Vanzella et al 2005). The 300I grism was used to obtain a spectral resolution of 3.2 Å per pixel and a spatial scale plate of 0.126 arcsec/pix
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