Figure 1.
Size growth of
quiescent galaxies
(normalized to fixed
stellar mass) from 17
surveys (including
GDDS), plotted as a
function of redshift
(bottom axis) and
time (top axis). The
left-hand panel shows
data for individual
galaxies, while the
right panel shows a
“box and whiskers”
plot summarizing
the data in quantiles.
The red line and the
gray shaded area in
both panels show the
best fit to the median
redshift points and
the ±1σ errors of the
best relation. Figure
taken from Damjanov
et al., 2011.
Cimatti et al. first reported a handful of these
objects in 2004. Later work by many groups
(including GDDS) has confirmed the basic
result. Our latest analyses focus on charting
the growth in their typical sizes (Damjanov
et al., 2011), while asking a more basic question: “just what are these things?” (Chevance
et al., 2012).
New Results
In the Damjanov et al. paper, we synthesize results from 17 spectroscopic surveys observed
at similar spatial resolution, augmented by
new measurements for GDDS galaxies. By
combining many separate surveys, we were
able to grow our sample to a respectable size;
ours contains structural data for 465 red galaxies in the redshift range 0.2 < z < 2.7.
The main result shows that size evolution of
passively-evolving compact red galaxies over
this redshift range is gradual and continuous
(Figure 1). We found no evidence for an end or
change to the process around z = 1, as has been
hinted at by some surveys that analyze subsets
of the data in isolation. Furthermore, the size
8
GeminiFocus
growth appears to be independent of stellar
mass, with the mass-normalized, half-light radius scaling with redshift as Re (1 + z) (-1.62 +/ -0.34).
Why are these results important? First, they
confirm that the size growth in massive galaxies is large, something like a factor of 3 out
=
to z 1; this was already fairly clear before
our work. Arguably more interesting is our
conclusion that the growth appears smooth
(at least on average), and that it does not end
at around z ~ 1, as suggested by some earlier
surveys of strongly star-forming blue galaxies.
A Bad Assumption?
Unfortunately, our results do not provide a response to the basic question we really wanted answered: namely, why are these massive
galaxies growing in size? In fact, in the most
recent GDDS paper (led by student Melanie Chevance and Toronto postdoc AnneMarie Weijmans) related to this question, we
seemed to have muddied the waters a little,
albeit in an interesting way, with the second
recent GDDS paper (Chevance et al., 2012).
June2012