which one would expect if they had disks.
This provides strong evidence that SMGs are
merger systems and the merging process
could trigger the intense star formation.
Quantifying a Merger
To find out how symmetrical SMGs are, we
run a “kinemetry” analysis, fitting ellipses to
the velocity and dispersion fields. The ellipses
are fit at increasing radii, and the properties
of the best-fitting ones at each radius are
used to establish the level of asymmetry.
Figure 2 shows the results of running this analysis on the SMG sample and also other galaxies. The SMGs have higher values of asymmetry in both the velocity and dispersion fields
than the more ”normal” star forming galaxies
of the SINS (Spectroscopic Imaging survey in
the Near-infrared with SINFONI) sample and
also the sample of low redshift spiral galaxies from the SINGS (Spitzer Infrared Nearby
Galaxies Survey) sample. This suggests that
SMGs have distinct dynamical properties to
other populations of star forming galaxies.
The background red-blue pixels in Figure 2
represent the results of running the kinemetry analysis on template disks and mergers.
The dotted line marks the division between
the two populations. We find that all the SMGs
lie in the red ”merger” region of the plot. This
provides further considerable evidence that
the SMGs are merger systems.
ponents. The division is shown by the green
dotted lines in Figure 1.
We note, however, that splitting the sources
into components does not necessarily represent the two distinct merging objects, since
these systems could have evolved to the
point where the gas and stars of the component systems have already started to mix.
However, this separation offers a starting
point to establish the types of systems that
might have merged and triggered the extreme star formation phase in the SMGs.
We find that the components often have
similar properties to the sample of star forming galaxies found at the same redshift as the
SMGs but with more moderate star formation
rates; the SINS sample of galaxies. This implies that two moderately star-forming, disklike, galaxies could merge together causing
this burst in extreme star formation.
SMGs in Massive Halos
The offsets in position and velocity between
the components within the merging systems can be used to constrain the average
halo mass of SMGs. We achieve this by com-
Figure 2.
The asymmetry
measures of the
velocity and disper ͥ