Images

Abstract

We present a first combined analysis of the morphological and dynamical properties for the intermediate-mass Galaxy Evolution Sequence (IMAGES) sample. It is a representative sample of 52 z ∼ 0.6 galaxies with M stell from 1.5 to 15×10 10 M that possesses 3D resolved kinematics and HST deep imaging in at least two broad band filters. We aim at evaluating the evolution of rotating spirals robustly since z ∼ 0.6, as well as at testing the different schemes for classifying galaxies morphologically. We used all the information provided by multi-band images, color maps, and 2D light fitting to assign a morphological class to each object. We divided our sample into spiral disks, peculiar objects, compact objects, and mergers. Using our morphological classification scheme, 4/5 of the identified spirals are rotating disks, and more than 4/5 of identified peculiar galaxies show complex kinematics, while automatic classification methods such as concentration-asymmetry and GINI-M20 severely overestimate the fraction of relaxed disk galaxies. Using this methodology, we find that the fraction of undisturbed rotating spirals has increased by a factor ∼2 during the past 6 Gyr, a much higher fraction than was found previously based on morphologies alone. These rotating spiral disks are forming stars very rapidly, even doubling their stellar masses over the past 6 Gyr, while most of their stars were formed a few Gyr earlier, which reveals a large gas supply. Because they are the likely progenitors of local spirals, we can conjecture how their properties are evolving. Their disks show some evidence of inside-out growth, and the gas supply/accretion is not random since the disk needs to be stable in order to match the local disk properties.

A giant bar induced by a merger event at z = 0.4?

“…to features that resemble tidal arms (one blue at the upper right on the sky and another on the left), although very irregular, with several blue clumps. Closed to its center, there is a significant concentration of light that we sometimes refer to as the core, which is probably a small bulge Its color is roughly b − z = 1.8, as found for galaxies of late type to Sbc (Neichel et al 2008). The bar is asymmetric, extending spatially far more towards the upper-right side of the core.…”

“…Its center is dominated by an elongated structure, most likely a giant, thin bar of semi-major axis 0.85 arcsec or about 6 kpc. Neichel et al (2008) found that its color is approximately b − z = 0.8, i.e. typical of a starburst (see their Figs.…”

“…Table 1 summarizes its overall properties, including photometry, morphological parameters, and kinematical measurements (provided by the IMAGES data base that can be retrieved from Yang et al 2008;Neichel et al 2008;Puech et al 2008). This object has a stellar mass of 2.0 × 10 10 M , a K-band magnitude of M K = −20.94, and displays a peculiar morphology and kinematics.…”

“…Using the GIRAFFE spectrograph at the VLT, the kinematic properties of 65 of these galaxies, for instance J033239.72-275154.7, have been derived. This galaxy lies at z = 0.41, is classified as a merger from an analysis lead by Neichel et al (2008), and exhibits a large, young bar. This bar has a size of 6 kpc, i.e.…”

Stellar mass and velocity functions of galaxies

“…Ziegler et al 2009), although it is still being debated (e.g. Neichel et al 2008). Finally, it has also been shown that models of the chemical and spectro-photometric evolution of the Milky Way and nearby disk galaxies, when rolled backwards, fit the properties of redshift ∼0.7 star forming galaxies in a very reasonable way (Buat et al 2008).…”