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prepared for next revision: 2015-06-30 †
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Report from Referee (2015/06/30): †
I thank the authors for their response, and they have satisfactorily
addressed most of my concerns. But there are two issues that I am
still unsatisfied with.
1) The first has to do with the size measurements. The updated
uncertainties on the fits seem to be more realistic. However I am
still quite worried about the size measurements. Now the only object
for which there is a measurement in the ground-based i'-band as well
as the ACS i-band still gives very different size measurements
(although they are consistent at ~2 sigma). So this does nothing to
alleviate my previous concern that the i'-band measurements may be
very biased... and if they are biased, then the IA measurements may
also be biased (especially since those bands have even worse
seeing). So the authors need to do more to convince readers that the
Lyman-alpha emission really is extended.
The authors state that "all the MAESTLOs cannot be distinguished from
the point sources in the Subaru i'-band data." How exactly have the
authors determined this? Can the authors definitively rule out that
the IA-band light profiles can be modeled as compact sources? (The
simulations performed by the authors in the new manuscript are useful,
but all they show is the accuracy with which it is possible to recover
large sizes measurements, which may themselves already be very
biased). There are several ways to test this. Perhaps the simplest would
be to do simulations as the authors have already done, placing model
light profiles at random locations, but use the best-fitting F814-band
light profiles rather than the IA-band light profiles. The authors
could do this in both the i'-band and the IA bands; this test would
show whether the updated uncertainties are reliable, and will also
show whether the ground-based size measurements are biased.
On a related point, in the updated text the authors state that "we fit the
observed surface brightnesses with an exponential law" (fourth
paragraph of section 2). I assume that they leave the Sersic index n
free in the fit, rather than forcing it to an exponential profile
(n=1). However if they have forced n=1 then they should explain why
this is necessary and justified.
2) I am still puzzled by the author's interpretation of the
Lyman-alpha emission as due to superwinds that are left over from a
star formation episode. Although this is certainly an interesting
idea, there are other possible explanations, and there is an extended
literature on the complicated physics and geometry of Lyman-alpha
emission that the authors do not address at all.
As the present manuscript is a Letter, and the focus is on the
observational result rather than a physical interpretation, an
extended discussion of the possible causes of the Lyman-alpha emission
is clearly not necessary. But the authors need to at least draw
attention to the fact that the physical explanation of superwinds is
quite speculative, and that there are other possible explanations.
For instance, the extended Lyman-alpha emission may be related to the
Lyman-alpha blobs (LABs). The LABs are indeed mysterious because, as
far as I know, the cause(s) of their emission is still completely
uncertain. As just one example from the literature, Dijkstra & Loeb
(2009) discussion several possible explanations for the origin of
LABs, and endorse the idea that the emission is due to the
gravitational energy of infalling gas. It is also worth noting that
Steidel et al. (2011) show that extended Lyman-alpha emission is
ubiquitous around ordinary star-forming galaxies at these
redshifts. Those authors discuss in detail the ways in which the
Lyman-alpha photons can originate from *within* the galaxies, rather
than outside of the galaxies.
Here I have picked just two well-known examples in the literature that
discuss possible origins of extended Lyman-alpha emission; there are a
number of others. Of course the nature of the Lyman-alpha emission
from the quenched galaxies discussed here may be very different than
the Lyman-alpha blobs or from ordinary star-forming galaxies, but on
the other hand they may all have the same underlying cause, and the
authors have not given any reason for preferring their physical
explanation over the various other explanations in the literature.
One interesting point which the authors may choose to purse is that,
based on the UVJ color-color diagram it seems that galaxies 1, 4, and
6 (and perhaps 3) are in a post-starburst phase. Since the typical
outflow velocities from star formation is well-known (AGN are faster),
and the authors have some estimate of the extent of the Lyman-alpha
emission, it would be trivial to estimate the approximate timescale of
the superwind (if that is what's causing the emission) and to
determine if it's consistent with the time since last significant star
formation from the SED fitting.
Regardless, the authors need to draw specific attention to the fact
that the physical explanation of superwinds is quite speculative, and
that there are other possible explanations.
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