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prepared for next revision: 2015-06-30 †

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manuscript: †

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Figures & Table: †

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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.
↑

Reply to Referee (2015/07/02): †

> ===================================================
> Report from Referee:
>
> 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.

Thank you very much for your comments.
We have revised our paper taking account of your comments.
As for the details, please see below.

> 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.

As the additional information, we newly show the fraction of the cases
where GALFIT returned the "non-resolved" flag in the 200 simulations,
fnon-res, in new Table 2.  Non-zero value of fnon-res indicates that
the best-fit models could be fitted with the pure PSF in some cases,
and the object is resolved only marginally or not resolved.
Furthermore, following the referee's suggestion, we carried out the
additional simulations.  We convolved model galaxies with the best-fit
F814W-band light profile with the PSF of the IA-band data, then added
them into the IA-band image, and measured their sizes with GALFIT. 200
such simulations were done for two MAESTLOs with the extended Lya
emission.  As a result, we found that GALFIT retuned the
"non-resolved" flag in most cases (185/200 and 169/200 for Nos. 1 and
3, respectively).  Since the fnon-res for the observed IA-band data is
0/200 for both objects (see new Table 2), we consider that their Lya
emission is significantly extended relative to the rest-UV continuum
emission.  We described this issue in the third paragraph of Section
3.


> 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.

At first we had tried to fit with the Sersic profile, but our data are
not deep enough to resolve the well-known degeneracy between the
radius and Sersic index, and the radius cannot be strongly constrained
if n is free. Therefore we measured the sizes under the assumption of
n=1.  We added this explanation in Section 2.



> 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.

Thank you for this comment.  As you mentioned, this paper is not a
FULL-LENGTH but a LETTER one.  Therefore, we did not dare to give a
long review on possible physical mechanisms for the observed extended
Ly-alpha emission around our MAESTLOs.  Since we considered that the
most plausible interpretation is the super wind model, we focused on
the explanation adopting this model.

> 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.

Thank you for these comments. As you mentioned, the observed extended
Ly-alpha emission around our MAESTLOs may be related to LABs.
And, there are several  possible origins for LABs;

   (1) resonant scattering of Ly-alpha photons produced  in the central region 
         of a galaxy (Moller & Warren 1998),
   (2) the super windmodel (Taniguchi & Shioya 2000),
   (3) photoionization by nearby galaxies and/or AGNs (Cantalupo et al. 2005),  
and
   (4) gravitational cooling radiation (Keres et al. 2009, Dekel et al. 2009).

Among them, we consider that the super wind model is the most
plausible case for the extended Ly-alpha emission around the MAESTLOs.

First, the SEDs of MAESTLOs show that the aged stellar population is
dominant.  Thus, since there may be few ionizing photons in them, we
can rule out the case (3).  Also, the aged SEDs mean that little
photoionization occurs in them and thus it is expected that there are
few Ly-alpha photons in them.  Therefore, the resonance scattering
model (case 1) can also be ruled out.

From a theoretical point of view, we also consider that the
gravitational cooling radiation may be related to LAB
phenomena. However, we have not yet found any LABs caused by
gravitational cooling radiation to date.  One possible case is the LAB
in GOODS-S found by Norris et al. (2006).  Although this LAB has been
discussed as the best case for gravitational cooling radiation for
these years, Prescott et al. (2015, ApJ, 802, 32) have recently
identified 6 galaxies and one AGN are associated with this LAB.
Therefore, we now have no observational evidence for gravitational
cooling radiation.  Further, gravitational cooling radiation is a
quite unlikely case for the MAESTLOs because a very massive, aged
galaxy already exists in each MAESTLO.  Such gravitational cooling
radiation would be brighter in the forming phase of giant galaxies
since the cold gas accretion rate could be much higher.  Therefore, we
did not mention about case 4.

In our Letter, we show that the MAESTLOs are in a phase from intense
star formation to passive evolution. After such intense stay
formation, it is expected that a super wind occurs.  Therefore, we
concluded that the spewing model (case 2) is the most plausible
interpretation and thus focused on this interpretation concisely in
our LETTER paper.  We believe that this makes sense very much. 

Do you find much observational advantage for cases 1, 3, and 4 ?
If you find, please let us know.


That’s all. Thank you very much.

           Yoshi Taniguchi on behalf of the authors
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