Abstract
Luminous Compact Galaxies (LCGs) are enigmatic sources in many aspects. They can reach the luminosity of the Milky Way within a radius of only a few kpc. They also represent one of the most rapidly evolving populations of galaxies since they represent up to 1/5 of the luminous galaxies at redshift , while being almost absent in the local Universe. The measurement of their dynamics is crucial to our understanding of LCGs since this has the potential of telling us which physical process(es) drive(s) them and ultimately link them to the existing present-day galaxies. Here, we derive the 3-dimensional velocity fields and velocity dispersion (σ) maps of 17 LCGs selected from the Canada France Redshift Survey and the Hubble Deep Field South with redshifts ranging from to . We find that only 18% of them show rotational velocity fields typical of rotating disks while the others show more complex kinematics. Assuming that LCGs are not too far from equilibrium, about half of LCGs then appear to be either non-relaxed objects, or objects that are not supported by velocity dispersion alone. This supports the view that an important fraction of LCGs are probably mergers. It brings additional support to the “spiral rebuilding scenario” in which LCGs correspond to a previous or post-merger phase before the disk re-building.
Highlights
Luminous Compact Galaxies (LCGs) (MB < −20, rhalf < 5 h−501 kpc, and EW0([OII]) > 15 Å) correspond to the most rapidly evolving population seen in the UV (Lilly et al 1998): they represent ∼20% of the 1 > z > 0.4 galaxies (Zheng et al 2005), ∼50% of the emission line galaxies, and almost vanish in the local Universe, with their number density decreasing by factors of 7−10 (Jangren et al 2004; Garland et al 2003; Werk et al 2004)
We find that about 50% of LCGs could be supported by velocity dispersion, assuming they are not too far from equilibrium
Given that 18% of LCGs are classified as RD, one third of LCGs remain for which we cannot exclude the possibility that a rotational support could play a role in their dynamical state
Summary
Luminous Compact Galaxies (LCGs) (MB < −20, rhalf < 5 h−501 kpc, and EW0([OII]) > 15 Å) correspond to the most rapidly evolving population seen in the UV (Lilly et al 1998): they represent ∼20% of the 1 > z > 0.4 galaxies (Zheng et al 2005), ∼50% of the emission line galaxies (see Paper I, Flores et al 2006), and almost vanish in the local Universe, with their number density decreasing by factors of 7−10 (Jangren et al 2004; Garland et al 2003; Werk et al 2004). Merge, the “LCG phase” where all material from the progenitors fall into the mass barycenter of the system and form a bulge, and the “disk growing phase” where subsequently accreted material forms a rotating disk This scenario is partly supported by Östlin et al (1999 and 2001), who obtained very complex Hα velocity fields for local LCGs, characteristic of what is expected from merging galaxies. Another alternative is the one proposed by Barton & Van Zee (2001): comparing HI and optical emission line widths of nearby LCG candidates, they argued that interactions and minor mergers of disk galaxies may cause apparently compact morphology leading to the formation of a bulge. To make the interpretation easier, velocity fields and σ-maps are presented after a simple 5 × 5 linear interpolation
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