From cwolf@astro.ox.ac.uk Sat Sep 27 19:49:41 2008
Date: Fri, 26 Sep 2008 11:14:09 +0100
From: Christian Wolf <cwolf@astro.ox.ac.uk>
To: STAGES Team <stages@lists.nottingham.ac.uk>
Subject: [STAGES] Fwd: MNRAS: MN-08-1460-MJ


> From: cg@ras.org.uk
> Date: 26 September 2008 08:16:20 BDT
> To: cwolf@astro.ox.ac.uk
> Subject: MNRAS: MN-08-1460-MJ
>
> Dear Dr Wolf
>
> I attach the reviewer's comments on your manuscript entitled "The  
> STAGES view of red spirals and dusty red galaxies: Mass-dependent  
> quenching of star-formation in cluster infall", ref. MN-08-1460-MJ,  
> which you submitted to Monthly Notices of the Royal Astronomical  
> Society.
>
> Minor revision of your manuscript is requested before it is  
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>
> Claire Geeson (Miss)
> Editorial Assistant
> "Monthly Notices"
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>
> Reviewer's Comments:
>
> The manuscript "The STAGES view of red spirals and dusty red  
> galaxies: Mass-dependent quenching of star formation in cluster  
> infall" by C. Wolf and collaborators provides a very interesting  
> look at the phenomenon of `dusty red spiral' galaxies, making use  
> of a unique data set including COMBO-17 SEDs and redshifts, as well  
> as Spitzer/MIPS imaging to probe for obscured star formation. Their  
> finding that most such dusty red galaxies are actually forming  
> stars (obscured from view) at a rate lower than that of normal blue  
> spirals, combined with their ability to trace this population as a  
> function of both mass and local environment, leads to some very  
> important insights on the quenching of star formation in cluster  
> spirals and the overall progression of galaxies from blue to red.  
> Particularly illuminating is the excellent discussion in S7  
> presenting a synthesized view of the various forms of 'anemic  
> spirals', 'passive spirals', and `red spirals' from their work and  
> the wider literature. I therefore recommend this manuscript for  
> publication in MNRAS, pending a response to a number of minor  
> suggestions and questions, most of which involve a request for more  
> clarity/specificity in discussing a number of the figures and the  
> selection of galaxy samples.
> I list these detailed comments below:
>
> S2.1, 2n par : The introduction of the photo-zs and comparison to  
> spectroscopic redshifts is confusing. I think you need to begin by  
> declaring that cluster members are identified via the COMBO-17  
> photo-zs, and you select a sample from the magnitude range xx < R <  
> xx. Then you can proceed to evaluate the accuracy of the photo-zs,  
> as you do in this paragraph. Finally, I think at the end of this  
> paragraph, you need to mention what your total sample size will  
> then be, based on this assessment of photo-z accuracy. At what  
> noise level/outlier rate do you make your cut?
>
> S2.2, 1st par: "the total SED will deviate from the aperture SED  
> underlying the M/L." This is confusingly worded. Perhaps clarify by  
> saying something like: "the SEDs constructed from total magnitudes  
> may be different from the SEDs based on aperture magnitudes. Since  
> our stellar mass estimates depend on M/L ratios from these SEDs,  
> aperture-based SEDs that are not representative of the total galaxy  
> will yield a stellar mass estimate that is incorrect."
>
> 2nd par:
> Where do the total colors you refer to come from? Are these also in  
> the G08 catalog, or do you get them somewhere else? How many  
> objects have you used in the comparison?
> Also, change "and E/S0 galaxies are reliable everywhere" to "and  
> masses of E/S0 galaxies..."
>
> I think it is also important to note here in this section that,  
> aside from just causing errors in the stellar mass, the SED fits to  
> photometry measured through these small central apertures can also  
> have the effect of identifying 'dusty red spirals' that aren't  
> "really" dusty red spirals (in other words, if you measured their  
> integrated photometry and did SED fitting, they would appear to be  
> just run of the mill blue spirals.) It appears that such a bias in  
> the sample should be limited to the most massive galaxies that  
> you've classified as 'dusty SF', but I think some explicit comments  
> on this are warranted, either here or in S3.1.
>
> S2.5: When you mention the redshift interval for selecting cluster  
> members, please refer right away to Table 1.
> What do you mean by a "healthy flag" from STAGES?
> "For some purposes we select galaxies with..." Maybe clarify to  
> "For some purposes in this paper, we examine subsamples of galaxies  
> with..."
> Doesn't your low-redshift field galaxy sample (z=[0.05,0.14])  
> overlap in redshift with your low-mass cluster members  
> (z=0.122,0.205]?
>
> S2.6, 4th par: missing "log M_*/M_0" in "...all galaxies with > 10".
> Figure 4: You only very briefly discuss this figure, and it seems  
> to me that both panels show essentially the same thing: that few  
> galaxies in your sample at at r>1r_vir. I would suggest just  
> dropping one of the panels; while it is up to you, I think that the  
> left panel makes your point nicely.
>
> S3: The description of Figure 5 in the text is a bit confusing. I  
> think you need to be a bit more explicit in introducing the color- 
> color plot, what each axis measures, and then how the blue/black  
> points are selected in each case. Also, describe what the solid  
> black lines indicate. Perhaps you could consider adding panels to  
> this plot showing the CMR that you base the selection on, and/or  
> the spread of E(B-V) values versus some other quantity (V-I?, M*?).  
> Then mark those plots with blue or black points to illustrate how  
> you come to the coding for the color-color plots. Since this SF/non- 
> SF cut provides the basis for much of what follows, I think you  
> need to be very clear about how you arrive at it.
>
> S3.1, par 4: Can you give the specific constants of proportionality  
> that you adopt to convert L_280 and L_IR into SFRs?
> In the right panel of Fig 6, do you plot only those galaxies that  
> are detected both in the UV and IR?
> Also, referring back to your comparison of SEDs based on aperture  
> magnitudes versus total magnitudes, can you say anything about how  
> well the L_280 luminosity derived from the aperture SED compares to  
> L_280 derived from the total magnitude in this/the nearest band?  
> What is the scatter?
>
> par 6: "...dusty red ones is 3.9x lower." add "than in the blue  
> galaxies."
> Also, you find that SFR_IR/SFR_UV = 2 for the blue galaxies, but  
> aren't both of these SFR estimates calibrated to give the total  
> galaxy star formation rate from, respectively, the IR and UV flux?  
> So doesn't that imply that, say, your IR SFRs are just a factor of  
> 2 too high? Of course, your point that the dusty red galaxies have  
> *much* higher IR/UV SFR ratios remains valid, but I would think  
> that for the 'normal' blue galaxies, these two estimates of SFR  
> should give the same result?
>
> S3.2, 1st par: "the 99 light symbols" -> "light blue"?
> Figure 7, left: The correlations between UV excess and extinction  
> for the blue galaxies seems fairly weak: the slope of the best-fit  
> line is barely twice the rms about that line. Can you give any  
> statistic about whether this fit is meaningful or not? Also, what  
> is the typical COMBO-17 uncertainty in the determination of E(B-V)?  
> You mention that it reaches 0.15 for the lowest mass blue galaxies,  
> but what is typical?
>
> S3.3: It would greatly help the clarity of this section to be a bit  
> more specific when describing your panels in Fig 8., as you first  
> introduce them.  e.g., instead of saying "the top row of Fig 8 is a  
> star formation-mass diagram", say "we plot specific SFR versus  
> stellar mass, in each of three environments: field, infall region,  
> and cluster cores". There's a lot in this figure and some of the  
> next few, and I think you need to more slowly/explicitly lead the  
> reader through it.
>
> par 3: "The blue envelope...is of course the CMR cut...which causes  
> and artificial separations between blue and dusty red..." I'm not  
> sure I see this artificial separation. What panels are you  
> referring to here? It looks like maybe the U-V plots, but I'm not  
> sure. I understand that you are referring to how you've defined  
> 'dusty red' vs. 'blue cloud', but I am not sure what I should be  
> looking at here. Also, again, it would help if you had more  
> specifically defined the CMR cut that you used.
> And I'm not sure if you ever go back to address why the 'red  
> envelope of the dusty red galaxies appears to retreat..."
>
> Par 4/Fig 9: Again, it would help to be more specific up-front  
> about what you are plotting. The blue lines trace the SFR and  
> colors of the traditionally-defined blue cloud, while the black  
> lines follow the trends in the full 'star-forming sample'. I've  
> found the shorthand 'blue cloud' vs 'star-forming' you use to be a  
> bit confusing; I know you've made the distinction between them  
> earlier, but it would be good for readability to keep reminding the  
> reader which one is a traditional star-forming sample, and which  
> one includes those plus the dusty-red star forming galaxies.
>
> S6.1
> For both Figures 14 and 15, within each subsample in mass, how do  
> you choose the number and placing of Sigma_M points? Do you try to  
> assign equal numbers to each bin? Does each bin get assigned a  
> point on the Sigma axis that is equal to the mean density of the  
> galaxies making up that bin? the median? This all needs to be more  
> specific.
>
> In the discussion of Fig 14, you claim "from the field to the  
> outermost infall points there is already a change to less SF and  
> less extinction" Looking at the plots, this seems to only be true  
> in your lowest mass bins. In the 4 panels showing higher mass bins,  
> the field and 1st cluster points have error bars that seem to  
> overlap. Please correct this.
>
> In all of these bullet points discussing Fig 14 and 15, you may  
> want to put in parenthesis which row or column of panels you wish  
> to draw attention to to support each claim. Since there is so much  
> in these figures, telling the reader more explicitly how to parse  
> it will help to make your point.
>
> "Figure 15 shows trends in the fractions of..." ->shows  
> environmental trends or shows the fractions of Hubble types versus  
> Sigma_M. Again, this is a bit too vague in describing what the  
> figure is. Also, the "red fraction among spirals" and the "SF  
> fraction in a red sample" are too vaguely defined. How do you  
> define "red" for both of these? Red/passive, or red as in selected  
> by the CMD?
>
> 5th bullet for Fig 15: "...where the CMR cut enters crosses into  
> the ...blue cloud" enters or crosses, not both
>
> Also, at this 5th bullet and in the last par. of S6.1: Here you  
> mention that the field red sequence seems to be highly contaminated  
> by star forming galaxies (at low mass). This seems to be a strange  
> artifact of how you select your red sample, and is doubly confusing  
> without more info on what CMR cut you used, and whether it is the  
> same for the field and the cluster. If these low mass field  
> galaxies are being labeled as red or 'dusty-star-forming' by your  
> cut when another observer may look at the CMR and class the same  
> objects as obviously part of the blue cloud, then isn't this just  
> an indication that your CMR declines too steeply toward faint  
> magnitudes, so that you pick up too many faint blue galaxies in  
> your 'red sequence'? Is this problem limited to the field because  
> there are lots more SF galaxies there, or is it because the CMR is  
> actually different for the field galaxies? Also, for the cluster  
> you use a fixed cluster redshift for determining quantities like  
> rest colors and stellar masses, but for the field you must rely on  
> photo-zs. Does this introduce additional scatter in the CMR and  
> masses that could contribute to this contamination of the faint red  
> sequence?
>
> S6.2: I believe you need to refer to Table 4 somewhere in this  
> section.
>
> S7 This is a very nice discussion; my only comment is that you may  
> want to point out somewhere that you in fact *do* see some spirals  
> that are truly passive, rather than just 'semi-passive' or dusty- 
> SF. From your table 3, it looks to be about 20% of the cluster  
> spirals are non-SF. So you are actually seeing the whole  
> progression from lowered SF in the bulk of these red spirals, down  
> to truly passive spirals, and then apparently on into the S0 class,  
> which seems to happen on a longer timescale.
>

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