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[[FrontPage]]
* re-submitted to ApJL on 19th June, 2015 [#gc42aa98]
** manuscript: [#r82347af]
- pdf: &ref(ms.pdf);
- tex source: &ref(ms.tex);
*** Figures & Table: [#efc30d3b]
- Tab. 1: &ref(Tab1.jpg,,50%);
- Fig. 1: &ref(f1.jpg,,25%); &ref(f1.eps);
- Fig. 2: &ref(f2.jpg,,25%); &ref(f2.eps);
- Fig. 3: &ref(f3.jpg,,25%); &ref(f3.eps);
- Fig. 4: &ref(f4.jpg,,25%); &ref(f4.eps);
*** &aname(RefereeReport){referee report (8th June, 2015)...
Report from Referee:
The manuscript "Discovery of Massive, Mostly Star-Format...
Galaxies with Extremely Strong Lyman-alpha Emission at z...
sample of nine massive galaxies at z~2.5-3.2 with Lyman-...
>100A and stellar mass log(M)>10.5
As described below, I believe that they Lya emission in ...
the sample of nine galaxies can be easily explained by s...
star formation or AGN activity. This reduces the sample ...
candidates to four.
The result that some quiescent-looking galaxies have str...
emission, but no hint of significant AGN activity, is so...
and may be worthy of publication. However there are many...
this analysis that need to be greatly extended and clari...
also good reason to believe that the Lya size measuremen...
much of the physical discussion in this letter are based...
completely unreliable. For all of these reasons I do not...
paper can be published in the ApJL in its current form.
Below I give some extended comments about the sample sel...
then give more comments about the rest of the analysis.
#####################
Sample selection:
Of the nine galaxies in this sample, two (ID numbers 1 a...
detected in the Chandra data. These galaxies can be clas...
since star formation cannot cause an x-ray detection at ...
redshifts. These galaxies also have high star formation ...
estimated from the SED fitting; hence it is not at all s...
they have Lya emission.
There is also a third galaxy (ID=9) that looks as if it ...
power-law SED, which would strongly suggest AGN activity...
claim that they used the Donley et al. (2012) criteria t...
from the IRAC colors, but since this object is not detec...
significantly at 8um, perhaps the authors didn't apply a...
selection criteria to this object?
Of the remaining galaxies, two (ID numbers 5 and 8) have
log(SFR)=1.8-2, so it is very difficult to describe thes...
"mostly quenched." In fact they are not all that far bel...
sequence of star formation at these redshifts (see e.g. ...
Schreiber et al 2010, and note that they use a Salpeter ...
to Chabrier as used in this work. Also, recall that the ...
scatter that is typically quoted for the main sequence i...
dex.). Finding Lya emission in some fraction of typical,...
star-forming galaxies is not surprising and is not worth...
publication (even if the galaxies are rather red, Lya em...
explained by radiative transfer effects; e.g. Finkelstei...
al. 2009).
This leaves a sample of four galaxies that are plausibly...
have no evidence of significant AGN activity, and have s...
emission (the sample increases to five if galaxy number ...
not to have IRAC colors consistent with an AGN). Such a ...
sample may be of marginal interest in itself, but it is ...
put them into an evolutionary scenario.
#############
Other comments:
-- Title: since the authors don't quote Lya fluxes (they...
equivalent widths), I don't think it is justified to say...
galaxies have "extremely strong Lyman-alpha emission." I...
authors have not shown that the Lya emission is very str...
is high, but that may only be because the rest-frame UV ...
is very faint. Indeed, the SFR estimates from Lya are qu...
low. For this reason I don't think it's fair to say that...
galaxies have "extreme" Lya emission. I would suggest th...
quote Lya fluxes, and compare them to the Lya luminosity...
(e.g. Gronwall et al. 2007), if they wish to claim that ...
emission is "extreme." Alternatively, a more accurate ti...
refer to "large Lyman-alpha equivalent widths"
-- Also, regarding the title, at least four of the galax...
significant, active star formation based on the SED fits...
explained above, the star formation rates are not strongly
depressed compared to the main sequence. If these galaxi...
the local universe they would be called extreme starburs...
is not accurate to describe them as "mostly quenched."
-- The authors discuss two possibilities for the cause o...
emission. One is winds that are blown out by AGN or supe...
the other is low-level star formation activity. The quoted
conclusion that the galaxies may represent a brief trans...
between star-forming and quiescence is completely unsupp...
the Lya emission is caused by low level star formation, ...
could suggest that the galaxies are not 100% quenched. I...
suggest that the galaxies are currently undergoing a min...
with a gas rich dwarf, that the Lya emission is related ...
mysterious Lya blobs, or that it is due to a projection ...
a nearby source; none of these possibilities are discuss...
authors, and neither can these possibilities be easily p...
an evolutionary scenario. Additionally, if the Lya emiss...
caused by AGN activity, then neither does that give any ...
evidence that the galaxies are in a brief transition pha...
-- Regarding the AGN activity, I found it very odd that ...
discuss how they removed AGN using radio/x-ray/IR indica...
Section 2, but then in Section 3 they explain that two o...
sources are detected in the x-ray. An x-ray detection at...
certainly means that the galaxies are AGN; it would take...
level of star formation to lead to an x-ray detection, a...
such star-formation can be ruled out by the SEDs and the...
24um detection. It would make sense to remove all AGNs f...
sample, or remove none of them. However if the AGNs are ...
sample then the authors would have to clearly specify wh...
galaxies are AGN in the table and figures.
-- Why have the authors not tried stacking the Chandra d...
to see if there is a weak detection?
-- If the galaxies do indeed represent a transition phas...
formation and quiescence, then there should be evidence ...
the SED fits and the colors. Do these galaxies have youn...
or larger tau/age, then typical quenched galaxies at sim...
However, given the very well-known degeneracies and syst...
uncertainties in stellar population properties inferred ...
SED-fitting, it is strange that the authors don't at lea...
this issue. The SFRs, in particular, are completely unre...
"quenched" galaxies. So to complement the discussion of ...
fitting, I would also strongly suggest including a U-V v...
color-color diagram, as this is a useful visual diagnost...
galaxy's colors, dust content, and age (e.g. Williams et
al. 2009). In this diagram there is a clear separation b...
star-forming and quenched galaxies, and recently-quenche...
would be found at the lower-left edge of the sequence of...
galaxies.
-- If there is significant Lya emission, there may also ...
with significant emission (Ha, OII, OIII). There is the ...
that these lines are affecting the SED fits. Do the SED ...
results change at all if the filters that are potentiall...
by these lines are removed from the fits?
-- The size measurements in the IA bands are potentially...
important, as they may help to shed light on the mechanism
responsible for the Lya emission. For this reason I thin...
is important to take great care in the measurements, in ...
know whether the ground-based measurements are reliable....
find the quoted measurements very problematic. For insta...
galaxies 6 and 2 the ground-based i*-band size measureme...
disagree *very strongly* with the F814 measurements. Thi...
to believe that ground-based size measurements are compl...
unreliable for small objects, and that the quoted uncert...
grossly underestimated. It is only for a single galaxy (...
there is any reason to believe that the ground-based mea...
are reliable. But note that this galaxy is both quite br...
very extended; hence this may be a special case. If we c...
the i*-band size measurements, why should we trust the I...
measurements? The authors would have to do careful tests...
that the measurements and the uncertainties are reliable...
unbiased. There are a number of examples in the literatu...
test; for just one particularly recent example, see Stra...
al. (2015).
-- The authors should state the FWHM of the IA and i* im...
-- At the end of the manuscript, the authors that that f...
will allow us to constrain the mechanisms that quench ga...
find this statement completely unsupported. Even if the ...
were transition objects, I am not sure how finding more ...
objects, or obtaining IFU observations, would shed any l...
the authors can specifically point out how studying MAES...
clearly reveal the quenching mechanism, then they should...
it.
*** &aname(ReplyToReferee){reply to referee report};: [#d...
- pdf: &ref(ReplyToReferee.pdf);
- text:
Dear Referee,
Thank you very much for your useful comments.
We have revised the manuscript taking your comments into...
> The manuscript "Discovery of Massive, Mostly Star-Form...
> Galaxies with Extremely Strong Lyman-alpha Emission at...
> a sample of nine massive galaxies at z~2.5-3.2 with Ly...
> equivalent width >100A and stellar mass log(M)>10.5
>
> As described below, I believe that they Lya emission i...
> the sample of nine galaxies can be easily explained by...
> star formation or AGN activity. This reduces the sampl...
> candidates to four.
>
> The result that some quiescent-looking galaxies have s...
> emission, but no hint of significant AGN activity, is ...
> and may be worthy of publication. However there are ma...
> this analysis that need to be greatly extended and cla...
> also good reason to believe that the Lya size measurem...
> much of the physical discussion in this letter are bas...
> completely unreliable. For all of these reasons I do n...
> paper can be published in the ApJL in its current form.
First of all, we agree with the referee's opinion that t...
detected with the Chandra X-ray Observatory can be regar...
Before the submission of this paper, only a part of Chan...
available for the COSMOS field. Therefore, we kept the ...
sources in the MAESTLO sample. However, now, we can use...
Chandra data for the entire COSMOS field. We have made ...
analysis and found that one more MAESTLO (previous ID, p...
Chandra source. Accordingly, we have removed the three ...
sources (pID 1, 2, and 3) from the MAESTLO sample in the...
manuscript. Therefore, we can discuss observational pro...
six MAESTLOs without any evidence for AGN activity, unam...
You also raised questions on the 3 MAESTLOs with pID 5, ...
As for these objects, we give our answers below.
To avoid confusion, we show the following list.
================================
Previous ID (pID) New ID
1 removed
2 removed
3 removed
4 1
5 2
6 3
7 4
8 5
9 6
================================
Sample selection:
=================
> Of the nine galaxies in this sample, two (ID numbers 1...
> detected in the Chandra data. These galaxies can be cl...
> AGN, since star formation cannot cause an x-ray detect...
> redshifts. These galaxies also have high star formatio...
> estimated from the SED fitting; hence it is not at all...
> that they have Lya emission.
As mentioned above, we have removed the three Chandra so...
pID 1, 2, and 3 from our sample. We then concentrate on...
well-defined sample of galaxies without any evidence for...
Therefore, the observed Ly alpha emission in the current...
is related either to star formation or to shock heated g...
superwind or to both.
> There is also a third galaxy (ID=9) that looks as if i...
> power-law SED, which would strongly suggest AGN activi...
> authors claim that they used the Donley et al. (2012) ...
> select AGNs from the IRAC colors, but since this objec...
> detected significantly at 8um, perhaps the authors did...
> IRAC AGN selection criteria to this object?
Thank you for your careful check. As you pointed out, w...
apply the Donley+12 criteria for this MAESTLO pID 9 beca...
non-detection in the IRAC Ch4. We have examined whether...
satisfies the Donley+12 criteria if it may have the redd...
Ch2-Ch4 by adopting the 3-sigma upper limit for Ch4. We...
that this object is located at nearly the edge of the cr...
the figure uploaded as Supplemental Material. Since the...
and optical SED appears to be well explained solely by t...
radiation (i.e., little [basically no] evidence for non-...
continuum from an AGN, it is reasonable to keep this obj...
MAESTLO without any evidence for AGN. Of course, it is ...
a very weak AGN is present in its nucleus. However, suc...
does not affect on our discussion given in this Letter.
> Of the remaining galaxies, two (ID numbers 5 and 8) have
> log(SFR)=1.8-2, so it is very difficult to describe th...
> "mostly quenched." In fact they are not all that far b...
> sequence of star formation at these redshifts (see e.g...
> Schreiber et al 2010, and note that they use a Salpete...
> to Chabrier as used in this work. Also, recall that th...
> scatter that is typically quoted for the main sequence...
> dex.). Finding Lya emission in some fraction of typica...
> star-forming galaxies is not surprising and is not wor...
> publication (even if the galaxies are rather red, Lya ...
> explained by radiative transfer effects; e.g. Finkelst...
> al. 2009).
Thank you for this comment. Actually, the MAESTLOs, pID...
a large SFR and appear to be close to the domain of the ...
sequence of star-forming galaxies at similar redshifts; ...
their new IDs are 2 and 5 in the revised manuscript. Ho...
the MAESTLO pID 5 (i.e., new ID 2) has a ratio of age/ta...
unity and shows a clear Balmer break, it is reasonable t...
this galaxy is in an quenching phase of star formation. ...
hand, as written explicitly in the footnote 16 in the ma...
MAESTLO pID 8 (i.e., new ID 5) shows a relatively weak B...
break compared to the other MAESTLOs and its tau is esti...
highly uncertain. Therefore, to avoid any confusion, we...
mentioned this explicitly in the revised manuscript. We...
that we do not include these galaxies for the discussion...
duration of the MAESTLO phase although this does not aff...
discussion (i.e., only a factor of 4/6).
> This leaves a sample of four galaxies that are plausib...
> have no evidence of significant AGN activity, and have...
> emission (the sample increases to five if galaxy numbe...
> not to have IRAC colors consistent with an AGN). Such ...
> sample may be of marginal interest in itself, but it i...
> put them into an evolutionary scenario.
Following your comment given in “Other comments”, we have
investigated rest-frame UV-Opt-NIR colors of the six MAE...
comparing some star formation models. In this analysis,...
that the four MAESTLOs with a smaller sSFR are located a...
selection boundary for the quiescent galaxies in the res...
vs. V-J diagram studied by Muzzin et al. (2013, ApJ, 777...
Therefore, we have confirmed that these four MAESTLOs ar...
quenching phase. Thank you very much for your very usef...
We believe that the discovery of such quenching, massive...
~ 3 is very important because such populations have not ...
directly detected to date. It is interesting to note th...
quenching phase is manifested by the observed large EW_0...
MAESTLOs. If this is the case, EW_0(Lya) will provide u...
identify the quenching phase in future observational stu...
Other comments:
=================
> -- Title: since the authors don't quote Lya fluxes (th...
> equivalent widths), I don't think it is justified to s...
> galaxies have "extremely strong Lyman-alpha emission."...
> authors have not shown that the Lya emission is very s...
> is high, but that may only be because the rest-frame U...
> is very faint. Indeed, the SFR estimates from Lya are ...
> low. For this reason I don't think it's fair to say th...
> galaxies have "extreme" Lya emission. I would suggest ...
> quote Lya fluxes, and compare them to the Lya luminosi...
> (e.g. Gronwall et al. 2007), if they wish to claim tha...
> emission is "extreme." Alternatively, a more accurate ...
> refer to "large Lyman-alpha equivalent widths"
Let us note that the term of "strong emission line" refe...
"large line flux" but to "large EW" usually. For "large...
we usually use "bright emission line". As you see in th...
manuscript, we do not discuss Ly alpha luminosity of our...
galaxies explicitly.
However, in order to avoid any confusion to readers, we ...
the paper title to
"Discovery of Massive, Mostly Star-formation Quenched...
Extremely Large Lyman-alpha Equivalent Widths at z ~...
> -- Also, regarding the title, at least four of the gal...
> significant, active star formation based on the SED fi...
> explained above, the star formation rates are not stro...
> depressed compared to the main sequence. If these gala...
> the local universe they would be called extreme starbu...
> is not accurate to describe them as "mostly quenched."
Thank you for this comment. Now in the revised manuscri...
MAESTLOs; four galaxies have smaller sSFRs while the rem...
have typical SFR for galaxies at a concerned redshift. ...
that the fraction of small sSFR galaxies is 4/6 = 67%. ...
seems reasonable to mention that the majority of MAESTLO...
significantly smaller specific star formation rate, or o...
conclude that they are "mostly quenched".
As mentioned already above, we have found that the two g...
and 8 (their new IDs are 2 and 5 in the revised manuscri...
interpreted as that the star formation in them ceased re...
started to experience their passive evolution. Although...
observed SFRs are comparable to those in star-forming ga...
similar redshift range (i.e., z ~ 3), we can give consis...
interpretation on the all six galaxies in terms of the e...
quenching.
> -- The authors discuss two possibilities for the cause...
> emission. One is winds that are blown out by AGN or su...
> the other is low-level star formation activity. The qu...
> conclusion that the galaxies may represent a brief tra...
> between star-forming and quiescence is completely unsu...
> the Lya emission is caused by low level star formation...
> could suggest that the galaxies are not 100% quenched....
> suggest that the galaxies are currently undergoing a m...
> with a gas rich dwarf, that the Lya emission is relate...
> mysterious Lya blobs, or that it is due to a projectio...
> a nearby source; none of these possibilities are discu...
> authors, and neither can these possibilities be easily...
> an evolutionary scenario. Additionally, if the Lya emi...
> caused by AGN activity, then neither does that give an...
> evidence that the galaxies are in a brief transition p...
First, we have removed the discussion on the AGN winds/j...
have rejected all AGN-related objects in this revised ma...
Since the rest-frame UV, optical NIR color analysis sugg...
have reinforced that the four MAESTLOs have quite simila...
quiescent galaxies, we can conclude that the most MAESTL...
final (quenching) phase of active star formation.
We would like to note that the presence of LABs at high ...
not mysterious because a large number of LABs have been ...
to date (e.g., Matsuda+04, AJ, 128, 569, Matsuda+11, MN,...
Saito+06, ApJ, 648, 54) and it is found that they have m...
components (Uchimoto et al. 2012, ApJ, 750, 116, Kubo et...
ApJ, 799, 38). Therefore, it is not plausible that an i...
rich dwarf causes Lya blob.
As for the projection effect and so on, we have newly ad...
following comments in the revised manuscript. We think ...
comments provide enough information to readers.
"As for possible origins of the observed extended ...
we may have a projection effect. However, we cons...
a projection effect cannot be the origin of most M...
because of the small number densities of both mass...
with relatively low sSFR and LAEs with extremely l...
~ 3 (e.g., ~ 1.3x10^{-5} Mpc^{-3} for galaxies wit...
10^{10.5} Msun and sSFR = 0.03--0.3 Gyr^{-1}, and ...
Mpc^{-3} for LAEs with EW_0(Lya) >= 100 A). Namel...
projection probability of these objects with simil...
(e.g., Delta z < 0.5$) is expected to be extremely...
such chance alignments within 1" in our survey vol...
possibility is that a star-forming dwarf galaxy is...
merge onto these MAESTLOs. In this case, we have ...
a merging dwarf galaxy experiences such active sta...
Finally, jets and/or outflows from AGN are also po...
of such extended emission-line regions. However, ...
sample does not show any evidence for AGNs (Sectio...
weak AGN possibility is not completely rejected be...
limited depths of IRAC, XMM, Chandra, and radio da...
> -- Regarding the AGN activity, I found it very odd tha...
> discuss how they removed AGN using radio/x-ray/IR indi...
> Section 2, but then in Section 3 they explain that two...
> sources are detected in the x-ray. An x-ray detection ...
> certainly means that the galaxies are AGN; it would ta...
> level of star formation to lead to an x-ray detection,...
> such star-formation can be ruled out by the SEDs and t...
> 24um detection. It would make sense to remove all AGNs...
> sample, or remove none of them. However if the AGNs ar...
> sample then the authors would have to clearly specify ...
> are AGN in the table and figures.
We have already fixed this issue. Thank you very much f...
comment again.
> -- Why have the authors not tried stacking the Chandra...
> to see if there is a weak detection?
As for the stacking analysis for the six MAESTLOs that a...
detected in Chandra, we do not think that this works wel...
number of sources is only 6. Such stacking analysis wil...
much larger non-detection samples.
> -- If the galaxies do indeed represent a transition ph...
> star formation and quiescence, then there should be ev...
> that in the SED fits and the colors. Do these galaxies...
> ages, or larger tau/age, then typical quenched galaxie...
> mass? However, given the very well-known degeneracies...
> systematic uncertainties in stellar population propert...
> from SED-fitting, it is strange that the authors don't...
> mention this issue. The SFRs, in particular, are compl...
> unreliable for "quenched" galaxies. So to complement t...
> of the SED fitting, I would also strongly suggest incl...
> vs. V-J color-color diagram, as this is a useful visua...
> of galaxy's colors, dust content, and age (e.g. Willia...
> al. 2009). In this diagram there is a clear separation...
> star-forming and quenched galaxies, and recently-quenc...
> would be found at the lower-left edge of the sequence ...
> galaxies.
Thank you very much for this comment. Following your su...
have examined the distribution of the MAESTLOs in the re...
colors plane, U-V vs. V-J, which have been evaluated fro...
model SEDs. The result is shown in new Fig. 4. Compari...
quiescent galaxies studied by Muzzin+13 (ApJ, 777, 18), ...
found that our four MAESTLOs with a low sSFR (new IDs 1,...
are located around the selection boundary for quiescent ...
is thus suggested that they have been recently quenched ...
into the passive evolution phase. Therefore, this color...
reinforces our scenario. Although the colors of the oth...
MAESTLOs are consistent with the star-forming models, th...
also be interpreted as a galaxy that ceased its star for...
recently. The larger dust contents in these two galaxie...
expected if they are in an early phase of the superwind ...
i.e., most of dust grains may have not yet been blown ou...
superwind.
> -- If there is significant Lya emission, there may als...
> with significant emission (Ha, OII, OIII). There is th...
> that these lines are affecting the SED fits. Do the SE...
> results change at all if the filters that are potentia...
> by these lines are removed from the fits?
As you concerned, some MAESTLOs may also have other emis...
these lines may be detected in JHK bands. However, sinc...
of such emission lines is not expected to be serious bec...
very wide filter bandpasses in JHK, we use all JHK-band ...
some strong emission lines are expected to be in these b...
Although we have considered such case carefully in the s...
selection procedures, we have not described explicitly i...
manuscript. We have now described this treatment explic...
Section 2 of the revised manuscript.
> -- The size measurements in the IA bands are potential...
> important, as they may help to shed light on the mecha...
> responsible for the Lya emission. For this reason I th...
> is important to take great care in the measurements, i...
> know whether the ground-based measurements are reliabl...
> find the quoted measurements very problematic. For ins...
> galaxies 6 and 2 the ground-based i*-band size measure...
> disagree *very strongly* with the F814 measurements. T...
> to believe that ground-based size measurements are com...
> unreliable for small objects, and that the quoted unce...
> grossly underestimated. It is only for a single galaxy...
> there is any reason to believe that the ground-based m...
> are reliable. But note that this galaxy is both quite ...
> very extended; hence this may be a special case. If we...
> the i*-band size measurements, why should we trust the...
> measurements? The authors would have to do careful tes...
> that the measurements and the uncertainties are reliab...
> unbiased. There are a number of examples in the litera...
> test; for just one particularly recent example, see St...
> al. (2015).
Following your suggestion, we carried out the Monte Carl...
to estimate the uncertainty in the size measurements. W...
best-fit model profile at 200 random positions around th...
position (in a 2' x 2' region) per observed MAESTLO and ...
their sizes. The standard deviation of these 200 measur...
adopted as the uncertainty, where the systematic effects...
background fluctuation are taken into account. The esti...
uncertainty is systematically larger than the nominal er...
GALFIT as expected. We replace all the size errors in T...
those estimated from the simulation. As a result, we fo...
measurements in the Subaru i'-band data including old No...
cannot be distinguished from the point sources, which is...
with the very small sizes measured in the HST F814W band...
other hand, three out of new 6 MAESTLOs are significantl...
the Lya (intermediate-band) images considering the uncer...
estimated from the simulation, while the other three can...
distinguished from the point sources. Therefore, the co...
emission from all the MAESTLOs is very compact, while a ...
MAESTLOs show the extended Lya emission. We have added ...
description of the simulation to estimate the uncertaint...
measurements in Section 2, and describe these results in...
new error estimates in Section 3 in the revised manuscri...
> -- The authors should state the FWHM of the IA and i* ...
We describe these PSF sizes in the form of the half ligh...
which is used in the size measurements, in Section 2.
> -- At the end of the manuscript, the authors that that...
> will allow us to constrain the mechanisms that quench ...
> find this statement completely unsupported. Even if th...
> were transition objects, I am not sure how finding mor...
> objects, or obtaining IFU observations, would shed any...
> the authors can specifically point out how studying MA...
> clearly reveal the quenching mechanism, then they shou...
> it.
For example, observations to probe gas kinematics using ...
provide a useful constraint on the mechanism that quench...
formation in galaxies. If outflowing gas is detected, t...
mechanism is found to be strong stellar and/or supernova...
the other hand, if gas is not detected at all, the mecha...
strangulation, that is, the depletion of gas. We have a...
the end of the revised manuscript.
That's all. Thank you very much.
終了行:
[[FrontPage]]
* re-submitted to ApJL on 19th June, 2015 [#gc42aa98]
** manuscript: [#r82347af]
- pdf: &ref(ms.pdf);
- tex source: &ref(ms.tex);
*** Figures & Table: [#efc30d3b]
- Tab. 1: &ref(Tab1.jpg,,50%);
- Fig. 1: &ref(f1.jpg,,25%); &ref(f1.eps);
- Fig. 2: &ref(f2.jpg,,25%); &ref(f2.eps);
- Fig. 3: &ref(f3.jpg,,25%); &ref(f3.eps);
- Fig. 4: &ref(f4.jpg,,25%); &ref(f4.eps);
*** &aname(RefereeReport){referee report (8th June, 2015)...
Report from Referee:
The manuscript "Discovery of Massive, Mostly Star-Format...
Galaxies with Extremely Strong Lyman-alpha Emission at z...
sample of nine massive galaxies at z~2.5-3.2 with Lyman-...
>100A and stellar mass log(M)>10.5
As described below, I believe that they Lya emission in ...
the sample of nine galaxies can be easily explained by s...
star formation or AGN activity. This reduces the sample ...
candidates to four.
The result that some quiescent-looking galaxies have str...
emission, but no hint of significant AGN activity, is so...
and may be worthy of publication. However there are many...
this analysis that need to be greatly extended and clari...
also good reason to believe that the Lya size measuremen...
much of the physical discussion in this letter are based...
completely unreliable. For all of these reasons I do not...
paper can be published in the ApJL in its current form.
Below I give some extended comments about the sample sel...
then give more comments about the rest of the analysis.
#####################
Sample selection:
Of the nine galaxies in this sample, two (ID numbers 1 a...
detected in the Chandra data. These galaxies can be clas...
since star formation cannot cause an x-ray detection at ...
redshifts. These galaxies also have high star formation ...
estimated from the SED fitting; hence it is not at all s...
they have Lya emission.
There is also a third galaxy (ID=9) that looks as if it ...
power-law SED, which would strongly suggest AGN activity...
claim that they used the Donley et al. (2012) criteria t...
from the IRAC colors, but since this object is not detec...
significantly at 8um, perhaps the authors didn't apply a...
selection criteria to this object?
Of the remaining galaxies, two (ID numbers 5 and 8) have
log(SFR)=1.8-2, so it is very difficult to describe thes...
"mostly quenched." In fact they are not all that far bel...
sequence of star formation at these redshifts (see e.g. ...
Schreiber et al 2010, and note that they use a Salpeter ...
to Chabrier as used in this work. Also, recall that the ...
scatter that is typically quoted for the main sequence i...
dex.). Finding Lya emission in some fraction of typical,...
star-forming galaxies is not surprising and is not worth...
publication (even if the galaxies are rather red, Lya em...
explained by radiative transfer effects; e.g. Finkelstei...
al. 2009).
This leaves a sample of four galaxies that are plausibly...
have no evidence of significant AGN activity, and have s...
emission (the sample increases to five if galaxy number ...
not to have IRAC colors consistent with an AGN). Such a ...
sample may be of marginal interest in itself, but it is ...
put them into an evolutionary scenario.
#############
Other comments:
-- Title: since the authors don't quote Lya fluxes (they...
equivalent widths), I don't think it is justified to say...
galaxies have "extremely strong Lyman-alpha emission." I...
authors have not shown that the Lya emission is very str...
is high, but that may only be because the rest-frame UV ...
is very faint. Indeed, the SFR estimates from Lya are qu...
low. For this reason I don't think it's fair to say that...
galaxies have "extreme" Lya emission. I would suggest th...
quote Lya fluxes, and compare them to the Lya luminosity...
(e.g. Gronwall et al. 2007), if they wish to claim that ...
emission is "extreme." Alternatively, a more accurate ti...
refer to "large Lyman-alpha equivalent widths"
-- Also, regarding the title, at least four of the galax...
significant, active star formation based on the SED fits...
explained above, the star formation rates are not strongly
depressed compared to the main sequence. If these galaxi...
the local universe they would be called extreme starburs...
is not accurate to describe them as "mostly quenched."
-- The authors discuss two possibilities for the cause o...
emission. One is winds that are blown out by AGN or supe...
the other is low-level star formation activity. The quoted
conclusion that the galaxies may represent a brief trans...
between star-forming and quiescence is completely unsupp...
the Lya emission is caused by low level star formation, ...
could suggest that the galaxies are not 100% quenched. I...
suggest that the galaxies are currently undergoing a min...
with a gas rich dwarf, that the Lya emission is related ...
mysterious Lya blobs, or that it is due to a projection ...
a nearby source; none of these possibilities are discuss...
authors, and neither can these possibilities be easily p...
an evolutionary scenario. Additionally, if the Lya emiss...
caused by AGN activity, then neither does that give any ...
evidence that the galaxies are in a brief transition pha...
-- Regarding the AGN activity, I found it very odd that ...
discuss how they removed AGN using radio/x-ray/IR indica...
Section 2, but then in Section 3 they explain that two o...
sources are detected in the x-ray. An x-ray detection at...
certainly means that the galaxies are AGN; it would take...
level of star formation to lead to an x-ray detection, a...
such star-formation can be ruled out by the SEDs and the...
24um detection. It would make sense to remove all AGNs f...
sample, or remove none of them. However if the AGNs are ...
sample then the authors would have to clearly specify wh...
galaxies are AGN in the table and figures.
-- Why have the authors not tried stacking the Chandra d...
to see if there is a weak detection?
-- If the galaxies do indeed represent a transition phas...
formation and quiescence, then there should be evidence ...
the SED fits and the colors. Do these galaxies have youn...
or larger tau/age, then typical quenched galaxies at sim...
However, given the very well-known degeneracies and syst...
uncertainties in stellar population properties inferred ...
SED-fitting, it is strange that the authors don't at lea...
this issue. The SFRs, in particular, are completely unre...
"quenched" galaxies. So to complement the discussion of ...
fitting, I would also strongly suggest including a U-V v...
color-color diagram, as this is a useful visual diagnost...
galaxy's colors, dust content, and age (e.g. Williams et
al. 2009). In this diagram there is a clear separation b...
star-forming and quenched galaxies, and recently-quenche...
would be found at the lower-left edge of the sequence of...
galaxies.
-- If there is significant Lya emission, there may also ...
with significant emission (Ha, OII, OIII). There is the ...
that these lines are affecting the SED fits. Do the SED ...
results change at all if the filters that are potentiall...
by these lines are removed from the fits?
-- The size measurements in the IA bands are potentially...
important, as they may help to shed light on the mechanism
responsible for the Lya emission. For this reason I thin...
is important to take great care in the measurements, in ...
know whether the ground-based measurements are reliable....
find the quoted measurements very problematic. For insta...
galaxies 6 and 2 the ground-based i*-band size measureme...
disagree *very strongly* with the F814 measurements. Thi...
to believe that ground-based size measurements are compl...
unreliable for small objects, and that the quoted uncert...
grossly underestimated. It is only for a single galaxy (...
there is any reason to believe that the ground-based mea...
are reliable. But note that this galaxy is both quite br...
very extended; hence this may be a special case. If we c...
the i*-band size measurements, why should we trust the I...
measurements? The authors would have to do careful tests...
that the measurements and the uncertainties are reliable...
unbiased. There are a number of examples in the literatu...
test; for just one particularly recent example, see Stra...
al. (2015).
-- The authors should state the FWHM of the IA and i* im...
-- At the end of the manuscript, the authors that that f...
will allow us to constrain the mechanisms that quench ga...
find this statement completely unsupported. Even if the ...
were transition objects, I am not sure how finding more ...
objects, or obtaining IFU observations, would shed any l...
the authors can specifically point out how studying MAES...
clearly reveal the quenching mechanism, then they should...
it.
*** &aname(ReplyToReferee){reply to referee report};: [#d...
- pdf: &ref(ReplyToReferee.pdf);
- text:
Dear Referee,
Thank you very much for your useful comments.
We have revised the manuscript taking your comments into...
> The manuscript "Discovery of Massive, Mostly Star-Form...
> Galaxies with Extremely Strong Lyman-alpha Emission at...
> a sample of nine massive galaxies at z~2.5-3.2 with Ly...
> equivalent width >100A and stellar mass log(M)>10.5
>
> As described below, I believe that they Lya emission i...
> the sample of nine galaxies can be easily explained by...
> star formation or AGN activity. This reduces the sampl...
> candidates to four.
>
> The result that some quiescent-looking galaxies have s...
> emission, but no hint of significant AGN activity, is ...
> and may be worthy of publication. However there are ma...
> this analysis that need to be greatly extended and cla...
> also good reason to believe that the Lya size measurem...
> much of the physical discussion in this letter are bas...
> completely unreliable. For all of these reasons I do n...
> paper can be published in the ApJL in its current form.
First of all, we agree with the referee's opinion that t...
detected with the Chandra X-ray Observatory can be regar...
Before the submission of this paper, only a part of Chan...
available for the COSMOS field. Therefore, we kept the ...
sources in the MAESTLO sample. However, now, we can use...
Chandra data for the entire COSMOS field. We have made ...
analysis and found that one more MAESTLO (previous ID, p...
Chandra source. Accordingly, we have removed the three ...
sources (pID 1, 2, and 3) from the MAESTLO sample in the...
manuscript. Therefore, we can discuss observational pro...
six MAESTLOs without any evidence for AGN activity, unam...
You also raised questions on the 3 MAESTLOs with pID 5, ...
As for these objects, we give our answers below.
To avoid confusion, we show the following list.
================================
Previous ID (pID) New ID
1 removed
2 removed
3 removed
4 1
5 2
6 3
7 4
8 5
9 6
================================
Sample selection:
=================
> Of the nine galaxies in this sample, two (ID numbers 1...
> detected in the Chandra data. These galaxies can be cl...
> AGN, since star formation cannot cause an x-ray detect...
> redshifts. These galaxies also have high star formatio...
> estimated from the SED fitting; hence it is not at all...
> that they have Lya emission.
As mentioned above, we have removed the three Chandra so...
pID 1, 2, and 3 from our sample. We then concentrate on...
well-defined sample of galaxies without any evidence for...
Therefore, the observed Ly alpha emission in the current...
is related either to star formation or to shock heated g...
superwind or to both.
> There is also a third galaxy (ID=9) that looks as if i...
> power-law SED, which would strongly suggest AGN activi...
> authors claim that they used the Donley et al. (2012) ...
> select AGNs from the IRAC colors, but since this objec...
> detected significantly at 8um, perhaps the authors did...
> IRAC AGN selection criteria to this object?
Thank you for your careful check. As you pointed out, w...
apply the Donley+12 criteria for this MAESTLO pID 9 beca...
non-detection in the IRAC Ch4. We have examined whether...
satisfies the Donley+12 criteria if it may have the redd...
Ch2-Ch4 by adopting the 3-sigma upper limit for Ch4. We...
that this object is located at nearly the edge of the cr...
the figure uploaded as Supplemental Material. Since the...
and optical SED appears to be well explained solely by t...
radiation (i.e., little [basically no] evidence for non-...
continuum from an AGN, it is reasonable to keep this obj...
MAESTLO without any evidence for AGN. Of course, it is ...
a very weak AGN is present in its nucleus. However, suc...
does not affect on our discussion given in this Letter.
> Of the remaining galaxies, two (ID numbers 5 and 8) have
> log(SFR)=1.8-2, so it is very difficult to describe th...
> "mostly quenched." In fact they are not all that far b...
> sequence of star formation at these redshifts (see e.g...
> Schreiber et al 2010, and note that they use a Salpete...
> to Chabrier as used in this work. Also, recall that th...
> scatter that is typically quoted for the main sequence...
> dex.). Finding Lya emission in some fraction of typica...
> star-forming galaxies is not surprising and is not wor...
> publication (even if the galaxies are rather red, Lya ...
> explained by radiative transfer effects; e.g. Finkelst...
> al. 2009).
Thank you for this comment. Actually, the MAESTLOs, pID...
a large SFR and appear to be close to the domain of the ...
sequence of star-forming galaxies at similar redshifts; ...
their new IDs are 2 and 5 in the revised manuscript. Ho...
the MAESTLO pID 5 (i.e., new ID 2) has a ratio of age/ta...
unity and shows a clear Balmer break, it is reasonable t...
this galaxy is in an quenching phase of star formation. ...
hand, as written explicitly in the footnote 16 in the ma...
MAESTLO pID 8 (i.e., new ID 5) shows a relatively weak B...
break compared to the other MAESTLOs and its tau is esti...
highly uncertain. Therefore, to avoid any confusion, we...
mentioned this explicitly in the revised manuscript. We...
that we do not include these galaxies for the discussion...
duration of the MAESTLO phase although this does not aff...
discussion (i.e., only a factor of 4/6).
> This leaves a sample of four galaxies that are plausib...
> have no evidence of significant AGN activity, and have...
> emission (the sample increases to five if galaxy numbe...
> not to have IRAC colors consistent with an AGN). Such ...
> sample may be of marginal interest in itself, but it i...
> put them into an evolutionary scenario.
Following your comment given in “Other comments”, we have
investigated rest-frame UV-Opt-NIR colors of the six MAE...
comparing some star formation models. In this analysis,...
that the four MAESTLOs with a smaller sSFR are located a...
selection boundary for the quiescent galaxies in the res...
vs. V-J diagram studied by Muzzin et al. (2013, ApJ, 777...
Therefore, we have confirmed that these four MAESTLOs ar...
quenching phase. Thank you very much for your very usef...
We believe that the discovery of such quenching, massive...
~ 3 is very important because such populations have not ...
directly detected to date. It is interesting to note th...
quenching phase is manifested by the observed large EW_0...
MAESTLOs. If this is the case, EW_0(Lya) will provide u...
identify the quenching phase in future observational stu...
Other comments:
=================
> -- Title: since the authors don't quote Lya fluxes (th...
> equivalent widths), I don't think it is justified to s...
> galaxies have "extremely strong Lyman-alpha emission."...
> authors have not shown that the Lya emission is very s...
> is high, but that may only be because the rest-frame U...
> is very faint. Indeed, the SFR estimates from Lya are ...
> low. For this reason I don't think it's fair to say th...
> galaxies have "extreme" Lya emission. I would suggest ...
> quote Lya fluxes, and compare them to the Lya luminosi...
> (e.g. Gronwall et al. 2007), if they wish to claim tha...
> emission is "extreme." Alternatively, a more accurate ...
> refer to "large Lyman-alpha equivalent widths"
Let us note that the term of "strong emission line" refe...
"large line flux" but to "large EW" usually. For "large...
we usually use "bright emission line". As you see in th...
manuscript, we do not discuss Ly alpha luminosity of our...
galaxies explicitly.
However, in order to avoid any confusion to readers, we ...
the paper title to
"Discovery of Massive, Mostly Star-formation Quenched...
Extremely Large Lyman-alpha Equivalent Widths at z ~...
> -- Also, regarding the title, at least four of the gal...
> significant, active star formation based on the SED fi...
> explained above, the star formation rates are not stro...
> depressed compared to the main sequence. If these gala...
> the local universe they would be called extreme starbu...
> is not accurate to describe them as "mostly quenched."
Thank you for this comment. Now in the revised manuscri...
MAESTLOs; four galaxies have smaller sSFRs while the rem...
have typical SFR for galaxies at a concerned redshift. ...
that the fraction of small sSFR galaxies is 4/6 = 67%. ...
seems reasonable to mention that the majority of MAESTLO...
significantly smaller specific star formation rate, or o...
conclude that they are "mostly quenched".
As mentioned already above, we have found that the two g...
and 8 (their new IDs are 2 and 5 in the revised manuscri...
interpreted as that the star formation in them ceased re...
started to experience their passive evolution. Although...
observed SFRs are comparable to those in star-forming ga...
similar redshift range (i.e., z ~ 3), we can give consis...
interpretation on the all six galaxies in terms of the e...
quenching.
> -- The authors discuss two possibilities for the cause...
> emission. One is winds that are blown out by AGN or su...
> the other is low-level star formation activity. The qu...
> conclusion that the galaxies may represent a brief tra...
> between star-forming and quiescence is completely unsu...
> the Lya emission is caused by low level star formation...
> could suggest that the galaxies are not 100% quenched....
> suggest that the galaxies are currently undergoing a m...
> with a gas rich dwarf, that the Lya emission is relate...
> mysterious Lya blobs, or that it is due to a projectio...
> a nearby source; none of these possibilities are discu...
> authors, and neither can these possibilities be easily...
> an evolutionary scenario. Additionally, if the Lya emi...
> caused by AGN activity, then neither does that give an...
> evidence that the galaxies are in a brief transition p...
First, we have removed the discussion on the AGN winds/j...
have rejected all AGN-related objects in this revised ma...
Since the rest-frame UV, optical NIR color analysis sugg...
have reinforced that the four MAESTLOs have quite simila...
quiescent galaxies, we can conclude that the most MAESTL...
final (quenching) phase of active star formation.
We would like to note that the presence of LABs at high ...
not mysterious because a large number of LABs have been ...
to date (e.g., Matsuda+04, AJ, 128, 569, Matsuda+11, MN,...
Saito+06, ApJ, 648, 54) and it is found that they have m...
components (Uchimoto et al. 2012, ApJ, 750, 116, Kubo et...
ApJ, 799, 38). Therefore, it is not plausible that an i...
rich dwarf causes Lya blob.
As for the projection effect and so on, we have newly ad...
following comments in the revised manuscript. We think ...
comments provide enough information to readers.
"As for possible origins of the observed extended ...
we may have a projection effect. However, we cons...
a projection effect cannot be the origin of most M...
because of the small number densities of both mass...
with relatively low sSFR and LAEs with extremely l...
~ 3 (e.g., ~ 1.3x10^{-5} Mpc^{-3} for galaxies wit...
10^{10.5} Msun and sSFR = 0.03--0.3 Gyr^{-1}, and ...
Mpc^{-3} for LAEs with EW_0(Lya) >= 100 A). Namel...
projection probability of these objects with simil...
(e.g., Delta z < 0.5$) is expected to be extremely...
such chance alignments within 1" in our survey vol...
possibility is that a star-forming dwarf galaxy is...
merge onto these MAESTLOs. In this case, we have ...
a merging dwarf galaxy experiences such active sta...
Finally, jets and/or outflows from AGN are also po...
of such extended emission-line regions. However, ...
sample does not show any evidence for AGNs (Sectio...
weak AGN possibility is not completely rejected be...
limited depths of IRAC, XMM, Chandra, and radio da...
> -- Regarding the AGN activity, I found it very odd tha...
> discuss how they removed AGN using radio/x-ray/IR indi...
> Section 2, but then in Section 3 they explain that two...
> sources are detected in the x-ray. An x-ray detection ...
> certainly means that the galaxies are AGN; it would ta...
> level of star formation to lead to an x-ray detection,...
> such star-formation can be ruled out by the SEDs and t...
> 24um detection. It would make sense to remove all AGNs...
> sample, or remove none of them. However if the AGNs ar...
> sample then the authors would have to clearly specify ...
> are AGN in the table and figures.
We have already fixed this issue. Thank you very much f...
comment again.
> -- Why have the authors not tried stacking the Chandra...
> to see if there is a weak detection?
As for the stacking analysis for the six MAESTLOs that a...
detected in Chandra, we do not think that this works wel...
number of sources is only 6. Such stacking analysis wil...
much larger non-detection samples.
> -- If the galaxies do indeed represent a transition ph...
> star formation and quiescence, then there should be ev...
> that in the SED fits and the colors. Do these galaxies...
> ages, or larger tau/age, then typical quenched galaxie...
> mass? However, given the very well-known degeneracies...
> systematic uncertainties in stellar population propert...
> from SED-fitting, it is strange that the authors don't...
> mention this issue. The SFRs, in particular, are compl...
> unreliable for "quenched" galaxies. So to complement t...
> of the SED fitting, I would also strongly suggest incl...
> vs. V-J color-color diagram, as this is a useful visua...
> of galaxy's colors, dust content, and age (e.g. Willia...
> al. 2009). In this diagram there is a clear separation...
> star-forming and quenched galaxies, and recently-quenc...
> would be found at the lower-left edge of the sequence ...
> galaxies.
Thank you very much for this comment. Following your su...
have examined the distribution of the MAESTLOs in the re...
colors plane, U-V vs. V-J, which have been evaluated fro...
model SEDs. The result is shown in new Fig. 4. Compari...
quiescent galaxies studied by Muzzin+13 (ApJ, 777, 18), ...
found that our four MAESTLOs with a low sSFR (new IDs 1,...
are located around the selection boundary for quiescent ...
is thus suggested that they have been recently quenched ...
into the passive evolution phase. Therefore, this color...
reinforces our scenario. Although the colors of the oth...
MAESTLOs are consistent with the star-forming models, th...
also be interpreted as a galaxy that ceased its star for...
recently. The larger dust contents in these two galaxie...
expected if they are in an early phase of the superwind ...
i.e., most of dust grains may have not yet been blown ou...
superwind.
> -- If there is significant Lya emission, there may als...
> with significant emission (Ha, OII, OIII). There is th...
> that these lines are affecting the SED fits. Do the SE...
> results change at all if the filters that are potentia...
> by these lines are removed from the fits?
As you concerned, some MAESTLOs may also have other emis...
these lines may be detected in JHK bands. However, sinc...
of such emission lines is not expected to be serious bec...
very wide filter bandpasses in JHK, we use all JHK-band ...
some strong emission lines are expected to be in these b...
Although we have considered such case carefully in the s...
selection procedures, we have not described explicitly i...
manuscript. We have now described this treatment explic...
Section 2 of the revised manuscript.
> -- The size measurements in the IA bands are potential...
> important, as they may help to shed light on the mecha...
> responsible for the Lya emission. For this reason I th...
> is important to take great care in the measurements, i...
> know whether the ground-based measurements are reliabl...
> find the quoted measurements very problematic. For ins...
> galaxies 6 and 2 the ground-based i*-band size measure...
> disagree *very strongly* with the F814 measurements. T...
> to believe that ground-based size measurements are com...
> unreliable for small objects, and that the quoted unce...
> grossly underestimated. It is only for a single galaxy...
> there is any reason to believe that the ground-based m...
> are reliable. But note that this galaxy is both quite ...
> very extended; hence this may be a special case. If we...
> the i*-band size measurements, why should we trust the...
> measurements? The authors would have to do careful tes...
> that the measurements and the uncertainties are reliab...
> unbiased. There are a number of examples in the litera...
> test; for just one particularly recent example, see St...
> al. (2015).
Following your suggestion, we carried out the Monte Carl...
to estimate the uncertainty in the size measurements. W...
best-fit model profile at 200 random positions around th...
position (in a 2' x 2' region) per observed MAESTLO and ...
their sizes. The standard deviation of these 200 measur...
adopted as the uncertainty, where the systematic effects...
background fluctuation are taken into account. The esti...
uncertainty is systematically larger than the nominal er...
GALFIT as expected. We replace all the size errors in T...
those estimated from the simulation. As a result, we fo...
measurements in the Subaru i'-band data including old No...
cannot be distinguished from the point sources, which is...
with the very small sizes measured in the HST F814W band...
other hand, three out of new 6 MAESTLOs are significantl...
the Lya (intermediate-band) images considering the uncer...
estimated from the simulation, while the other three can...
distinguished from the point sources. Therefore, the co...
emission from all the MAESTLOs is very compact, while a ...
MAESTLOs show the extended Lya emission. We have added ...
description of the simulation to estimate the uncertaint...
measurements in Section 2, and describe these results in...
new error estimates in Section 3 in the revised manuscri...
> -- The authors should state the FWHM of the IA and i* ...
We describe these PSF sizes in the form of the half ligh...
which is used in the size measurements, in Section 2.
> -- At the end of the manuscript, the authors that that...
> will allow us to constrain the mechanisms that quench ...
> find this statement completely unsupported. Even if th...
> were transition objects, I am not sure how finding mor...
> objects, or obtaining IFU observations, would shed any...
> the authors can specifically point out how studying MA...
> clearly reveal the quenching mechanism, then they shou...
> it.
For example, observations to probe gas kinematics using ...
provide a useful constraint on the mechanism that quench...
formation in galaxies. If outflowing gas is detected, t...
mechanism is found to be strong stellar and/or supernova...
the other hand, if gas is not detected at all, the mecha...
strangulation, that is, the depletion of gas. We have a...
the end of the revised manuscript.
That's all. Thank you very much.
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