Test equivalent width distributions in H alpha and [O III] at z<1

[yymao]

See LSSTDESC/DC2-production#31 for detail.

• code to reduce mock data
• code that works within DESCQA framework
• validation data
• validation criteria

[evevkovacs]

@egawiser @janewman-pitt-edu @yymao @rmandelb Eric G./Jeff N. suggested doing a validation test based on equivalent-width (EW) distributions. However, the Galacticus output has line strengths rather than EWs and the SED supplied is probably too coarse grained to estimate EWs accurately (although it could be tried). Are there other tests based on line strengths that we could do? What applicable validation data is available?

[egawiser]

It should be feasible to validate versus the H alpha, [O II], and [O III] luminosity functions. Adam Broussard has references assembled for H alpha, has been tasked with checking for [O III], and could add [O II] to that list. Note that for our specific LSS project, getting high enough line luminosities is actually what matters (not actually high EWs), so this is an entirely acceptable validation for that purpose.

[janewman-pitt-edu]

Getting EWs right is a better check that you're giving the correct fluxes to the correct objects, though... coarse spectrum is probably fine for EW.

Any existing [OIII] or H alpha luminosity functions for z~1 will be for tiny areas with huge cosmic variance, so that doesn't strike me as a great option. (There is an [OII] luminosity function from DEEP2 -- IIRC Johan Comparat did that -- but the EWs are better measured in the data anyways, as they are not affected by flux calibrations).

[adam-broussard]

Hi all, I have recently gotten a NERSC account so that I can access the protoDC2 catalog. I'm looking at the available quantities and it looks like I can access the band magnitudes, but not the emission line strengths. How can I get these added in?

[evevkovacs]

These are native quantities, available in the catalog but not yet exposed in the reader. Please see https://github.com/LSSTDESC/gcr-catalogs for instructions on how to use the GCR (you need the add_quantities method) and https://portal.nersc.gov/project/lsst/descqa/v2/?run=2017-11-27_4&test=ListQuantities for a list of the native quantities (click on native_quantities.txt under proto-dc2_v2.0)

[yymao]

@adam-broussard get_quantities() also accept native quantities.

@evevkovacs what's the native quantity names for the emission line strengths?

[evevkovacs]

@adam-broussard Examples are: (see also my comment above for helpful links)
emissionLines/diskLineLuminosity:balmerAlpha6563:rest
emissionLines/diskLineLuminosity:balmerAlpha6563:rest:contam_nitrogenII6584

[yymao]

@adam-broussard @evevkovacs see usage on the updated demo notebook (search for "accessing native quantities" subsection)

[evevkovacs]

Thanks Yao for the quick turn-around on this.

[adam-broussard]

Thanks a bunch for the help so far - I have been able to access the values, but I can't figure out the units. It looks like the values for "emissionLines/totalLineLuminosity:balmerAlpha6563:rest" are around unity though. Can anyone help with what the native units are or where to track them down?

[evevkovacs]

@adam-broussard Sorry for the delay in replying. We will have a units attribute soon, but in the mean time the units for luminosity (AB system) are 4.4659e13 W/Hz.

[adam-broussard]

@evevkovacs I see that the units are L_nu - can you tell me how I could convert this to a true luminosity? I assume that the wavelength bin size on the SED should work as a differential nu to integrate it, and if so what is it? Thank you again!

[adam-broussard]

Hi guys I hope everyone had a good winter break. I wanted to check in again now that we're on the other side of the new year. @evevkovacs @abensonca can you point me in the right direction for converting the emission lines from L_nu to L? Thanks in advance.

[abensonca]

For the emission lines the quantities are already L, not L_nu. Eve's comment is for broad-band stellar continuum luminosities (which are L_nu in units of 4.4659e13 W/Hz). The emission lines are in units of Solar luminosities (3.839e26 W). So, to get equivalent widths you should just need to convert the continuum L_nu to L_lambda, and then take the ratio.

[adam-broussard]

Great, thanks for the quick response!

[rmandelb]

@adam-broussard - have you been able to successfully access the emission line data? If you are actively working on this, perhaps you could summarize the status of what you are doing? In the issue page, I have not yet seen a concrete suggestion for how the validation test will be carried out, what validation dataset will be used, etc.

[adam-broussard]

Hi @rmandelb ! I apologize for the late response - I was preoccupied with a proposal which was due at the end of last week and had to stop work on this project for a bit. We have some ideas of plotting the equivalent width distribution and comparing to observations, but nothing is solidly formed just yet. Give me a few days this week to get everything in a row and I'll report back in by Thursday with an update and a more concrete plan.

[adam-broussard]

@evevkovacs Eric emailed me to say that I could pull the SED data from the GCR, and that they are named according to 'SED_l1_l2' where l1 and l2 are the starting and ending wavelengths respectively. I am seeing values such as 'sed_1000_246' - is it that this is instead the starting wavelength and the width (or something similar)? Also, can you tell me what the units are on these SED fluxes? Thanks!

[evevkovacs]

@adam-broussard l2 is the width of the tophat filter, not the ending wavelength.
For units see Andrew Benson's comment above: "The emission lines are in units of Solar luminosities (3.839e26 W). So, to get equivalent widths you should just need to convert the continuum L_nu to L_lambda, and then take the ratio."

[egawiser]

@evevkovacs great - does that make l1 the central wavelength of the tophat filter, or was I correct that it's the starting wavelength? And I think Adam was asking what kind of L_nu units the continuum values are in.

[yymao]

it's the start and width.

[abensonca]

L_nu is in units of 4.4659e13 W/Hz

[egawiser]

Awesome. Thank you all!

[adam-broussard]

That is indeed what I was looking for - thank you for the clarificaiton, Eric! It is also useful to know that these are L_nu rather than F_nu as I probably would have assumed that they were fluxes naively. I will work on this and have an equivalent width distribution posted tonight or tomorrow morning.

[adam-broussard]

Here is what I have found for the equivalent width distribution around a redshift of 1 (although I can do it for others). I am still searching out a paper which plots the equivalent width distribution for some redshift range. The closest I have been able to find is Marmo-Queralto et al. (2016) which deals with the average H-alpha equivalent width as a function of redshift.

[evevkovacs]

This is a great start. Can you make the same plot for protoDC2 (eg pick z> .9) for comparison?

[adam-broussard]

I did so, and it looks almost identical:

[janewman-pitt-edu]

I think there's ~0% chance [OIII] should generally be as strong as H alpha. The plot looks suspicious to me... E.g. in Moustakas et al. 2005, H beta fluxes are typical ~1/3 as large as H alpha, and [OIII]/H beta ratios span ~1/3 to 3x .

[egawiser]

@janewman-pitt-edu thanks for processing this through your well-trained neural network! I think the paper you mean is this one? http://adsabs.harvard.edu/abs/2006ApJ...642..775M That's low-redshift but does claim agreement with some z=1 observations. We know that [O III] gets much stronger at high redshift vs. [O II], and that should means it gets somewhat stronger vs. Ha, as reflected in this z=1 plot. In any case, hopefully @adam-broussard can generate the same plots for z=0 (say z<0.2) and z=0.5, where there's more literature to compare with.

[janewman-pitt-edu]

There's not much evolution in BPT diagrams by z~1 (especially for L* galaxies) -- things shift to lower metallicity at higher redshifts than that (the [OII] EW distribution is pretty invariant from redshift at z=0.8-1.4 as I recall, by the way).

I'd suggest looking at histograms of [OIII]/H alpha, [OIII]/H beta, and [OIII]/[OII]; that should show immediately if [OIII] is too tied to H alpha, for instance.

The simulations are somewhat incomplete at z<0.2, so z~0.5 would be probably a better place to do the comparison.

[janewman-pitt-edu]

PS Yes, that's the right paper. I found it via arxiv where the date was 2005.

[janewman-pitt-edu]

In case it's helpful, I've compiled plots for the [OII]/[OIII]/H beta flux ratios for DEEP2 galaxies (there's a limited redshift range where we can get all of these lines), as well as the [OII] EW distribution. I've produced plots of the ratios, etc. as a function of z (where dependence is weak and may just be due to the R=24.1 limit corresponding to more luminous objects at higher redshifts), as well as histograms. All of these are quantities you should be able to compare against (with the same R=24.1 cut applied).

(PS I'm applying a 3 sigma detection cut in [OII] EW for the plots with [OII], or in H beta EW for the [OIII]/Hb ratio).

[adam-broussard]

I have generated the plot for z = 0.5 but unfortunately I am getting the same results. I have also included a histogram showing the distribution of different equivalent width ratios, which seems to show that [OIII]/[OII] and H-alpha/[OII] EW is approximately 10, but H-alpha/[OIII] EW is approximately 1.

[janewman-pitt-edu]

Yeah, that's definitely not right. [OIII] should generally be less than [OII], not 10x higher, based on the real data.

[yymao]

@adam-broussard I see that you have made much progress on this. Do you think it is useful to create a test in DESCQA, basically porting what you have done into the framework? I can offer help, of course.

Also, how should we validate the results? @janewman-pitt-edu mentioned some potential validation data from DEEP2. Should we use them to compare with the catalog result when we implement this test in DESCQA? @egawiser @adam-broussard.

[adam-broussard]

@yymao Eric and I talked today and we think it would be a good idea to put this in DESCQA. We discussed some possible tests and came up with:

1. Fitting the exponential decline on the right side of the equivalent width distribution
2. The ratio of primary and secondary modes (essentially the modes of equivalent widths of the star forming vs quiescent population)
3. The equivalent width of the mode

[adam-broussard]

@janewman-pitt-edu could you send me the data you used to generate those example plots? That way I can easily compare between the data and protoDC2 as well as potentially use them for the tests I outlined above.

[yymao]

@adam-broussard sounds like a good plan. Let me know how I can help you putting this test into the framework!

[janewman-pitt-edu]

Sure, send me a direct email to janewman@pitt.edu and I can reply to it with files.

Best,

Jeff