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desihub / fastspecfit

Fast spectral synthesis and emission-line fitting of DESI spectra.
https://fastspecfit.readthedocs.org
BSD 3-Clause "New" or "Revised" License
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consider tying narrow Balmer+helium lines to the forbidden lines #160

Closed moustakas closed 7 months ago

moustakas commented 9 months ago

In a recent GQP meeting, an argument was made that in objects with both broad and narrow line-emission, the narrow Balmer+helium line-widths should be tied to the forbidden lines.

moustakas commented 7 months ago

@Ragadeepika-Pucha @stephjuneau can you share a couple examples where the lack of this constraint led to some fitting issues?

Ragadeepika-Pucha commented 7 months ago

@moustakas @stephjuneau

There are two different cases where the lack of constraint between forbidden lines is leading to fitting issues. I have primarily focused on comparison of [NII] and Ha widths and its dependence on measuring emission-line fluxes and broad Ha component widths. I am going to add two separate comments, explaining each of these cases.

Ragadeepika-Pucha commented 7 months ago

Case 1 In some sources, the [NII] widths is quite broader than Ha and this eats up some of the existing broad Ha component, leading to a "narrower" broad Ha component, or in some cases from the narrow Ha component. As a result, both narrow and broad Ha components and of [NII] are not accurate, leading to inaccurate BPT positions and also lower black hole (BH) masses. This can be seen from the following plot (stellar mass-BH mass scaling relation), color coded by percentage difference between [NII] and Ha widths:

image

This plot shows that most of the "low BH mass" sources have [NII] widths >30-50% of Ha widths.

One example comparison between EmFit (my code) and Fastspecfit in [NII]+Ha spectra region is:

image

Example TARGETIDs: 39628005236015433, 39628005236015433, 39633049721244605, 39628522964128747

Ragadeepika-Pucha commented 7 months ago

Case 2

This case is the reverse, where the [NII] width is much narrower than the Ha width. In such cases, instead on one "narrow" and one "broad" component, fastspecfit is fitting two "broader" Ha components. This leads to very high Ha fluxes (>10 times of what I am measuring using my code) - clear BPT outliers

image

Example Fit in the [NII]+Ha region:

image

The fluxes mentioned are those of narrow Ha component.

Example TARGETIDs: 39627735873624156, 39627752483065233, 39628129861371535, 39633127848545072

Ragadeepika-Pucha commented 7 months ago

Based on the above two cases, I think it is important to have a constraint between forbidden lines and narrow Balmer lines. Maybe we can have Balmer line widths to vary within some percent of forbidden line widths. @stephjuneau can say more about it, especially regarding the physical reasoning for it.

stephjuneau commented 7 months ago

Based on the above two cases, I think it is important to have a constraint between forbidden lines and narrow Balmer lines. Maybe we can have Balmer line widths to vary within some percent of forbidden line widths. @stephjuneau can say more about it, especially regarding the physical reasoning for it.

Thanks for posting examples for these two different scenarios, Raga! Another useful piece of information is that you had made plots comparing the widths of the narrow lines measured independently to assess what range is reasonable if we wanted to allow a model to differ and I think that lead to something like a +/- 20% range capturing a lot of the possible intrinsic variation. (Is this value correct?) Based on this, your fitting code first lets the linewidth vary and checks if the difference is within that small range. If not, then it forces the linewidths to be the same for the narrow lines. This two-step fitting may not work well for Fastspecfit but given that the variations are quite small, just fixing them to be the same is probably a good approximation. Physically it would imply that we assume that the narrow-line emitting gas has consistent kinematics, which is reasonable in most cases though maybe less so in AGN hosts. However, the failure modes that you mention also will preferentially affect AGN hosts so I'd anticipate that this fix will be a net positive!

moustakas commented 7 months ago

@Ragadeepika-Pucha thanks for these specific examples. In a work-in-progress branch, I now constrain the narrow and forbidden line-widths and velocity shifts during narrow+broad-line fitting.

(During just narrow-line fitting, which impacts most objects, I haven't changed anything; the narrow Balmer+helium lines are tied separately from the forbidden lines.)

Here are your examples with this branch:

Case 1

39628005236015433 - not a good fit; the code likes a highly redshift broad component but only for Hbeta; the [SII] doublet is particularly poorly fit. I may need to just let this one go...but at least the reduced chi2 is relative high, so we should be able to find these problem children.

Screenshot 2024-01-11 at 9 50 35 PM

39633049721244605 - looks pretty good!

Screenshot 2024-01-11 at 9 51 29 PM

39628522964128747 - not perfect, but probably OK

Screenshot 2024-01-11 at 9 51 46 PM

Case 2

39627735873624156 - looks great

Screenshot 2024-01-11 at 10 01 06 PM

39627752483065233 - looks good!

Screenshot 2024-01-11 at 10 03 34 PM

39628129861371535 - not bad given it's a quasar...

Screenshot 2024-01-11 at 10 06 39 PM

39633127848545072 - looks great!

Screenshot 2024-01-11 at 10 12 27 PM
moustakas commented 7 months ago

After consulting with @stephjuneau and @Ragadeepika-Pucha and looking at several examples together, we've opted to make a small change to the constraints when fitting the broad- + narrow-line model. The change is that the [OIII] 4959,5007 doublet is now fitted separately from the other forbidden + narrow Balmer lines in order to allow for the possibility of a blue-shifted outflow. This change should help decompose the Halpha + [NII] complex (again, only when testing the broad-line hypothesis).

This readout is too much information, but I'm pasting it for completeness (for one particular low-redshift object):

Broad- + narrow-line model

--------------------------
Broad Balmer+helium lines:
--------------------------
h6_broad_amp              untied
h6_broad_sigma            tied to halpha_broad_sigma        with factor 1.0000
h6_broad_vshift           tied to halpha_broad_vshift       with factor 1.0000
hepsilon_broad_amp        untied
hepsilon_broad_sigma      tied to halpha_broad_sigma        with factor 1.0000
hepsilon_broad_vshift     tied to halpha_broad_vshift       with factor 1.0000
hdelta_broad_amp          untied
hdelta_broad_sigma        tied to halpha_broad_sigma        with factor 1.0000
hdelta_broad_vshift       tied to halpha_broad_vshift       with factor 1.0000
hgamma_broad_amp          untied
hgamma_broad_sigma        tied to halpha_broad_sigma        with factor 1.0000
hgamma_broad_vshift       tied to halpha_broad_vshift       with factor 1.0000
hei_broad_4471_amp        untied
hei_broad_4471_sigma      tied to halpha_broad_sigma        with factor 1.0000
hei_broad_4471_vshift     tied to halpha_broad_vshift       with factor 1.0000
heii_broad_4686_amp       untied
heii_broad_4686_sigma     tied to halpha_broad_sigma        with factor 1.0000
heii_broad_4686_vshift    tied to halpha_broad_vshift       with factor 1.0000
hbeta_broad_amp           untied
hbeta_broad_sigma         tied to halpha_broad_sigma        with factor 1.0000
hbeta_broad_vshift        tied to halpha_broad_vshift       with factor 1.0000
hei_broad_5876_amp        untied
hei_broad_5876_sigma      tied to halpha_broad_sigma        with factor 1.0000
hei_broad_5876_vshift     tied to halpha_broad_vshift       with factor 1.0000
halpha_broad_amp          untied
halpha_broad_sigma        untied
halpha_broad_vshift       untied

---------------------------
Narrow Balmer+helium lines:
---------------------------
h6_amp                    untied
h6_sigma                  tied to nii_6584_sigma            with factor 1.0000
h6_vshift                 tied to nii_6584_vshift           with factor 1.0000
hepsilon_amp              untied
hepsilon_sigma            tied to nii_6584_sigma            with factor 1.0000
hepsilon_vshift           tied to nii_6584_vshift           with factor 1.0000
hdelta_amp                untied
hdelta_sigma              tied to nii_6584_sigma            with factor 1.0000
hdelta_vshift             tied to nii_6584_vshift           with factor 1.0000
hgamma_amp                untied
hgamma_sigma              tied to nii_6584_sigma            with factor 1.0000
hgamma_vshift             tied to nii_6584_vshift           with factor 1.0000
hei_4471_amp              untied
hei_4471_sigma            tied to nii_6584_sigma            with factor 1.0000
hei_4471_vshift           tied to nii_6584_vshift           with factor 1.0000
heii_4686_amp             untied
heii_4686_sigma           tied to nii_6584_sigma            with factor 1.0000
heii_4686_vshift          tied to nii_6584_vshift           with factor 1.0000
hbeta_amp                 untied
hbeta_sigma               tied to nii_6584_sigma            with factor 1.0000
hbeta_vshift              tied to nii_6584_vshift           with factor 1.0000
hei_5876_amp              untied
hei_5876_sigma            tied to nii_6584_sigma            with factor 1.0000
hei_5876_vshift           tied to nii_6584_vshift           with factor 1.0000
halpha_amp                untied
halpha_sigma              tied to nii_6584_sigma            with factor 1.0000
halpha_vshift             tied to nii_6584_vshift           with factor 1.0000

----------------
Forbidden lines:
----------------
nev_3346_amp              untied
nev_3346_sigma            tied to nii_6584_sigma            with factor 1.0000
nev_3346_vshift           tied to nii_6584_vshift           with factor 1.0000
nev_3426_amp              untied
nev_3426_sigma            tied to nii_6584_sigma            with factor 1.0000
nev_3426_vshift           tied to nii_6584_vshift           with factor 1.0000
oii_3726_sigma            tied to nii_6584_sigma            with factor 1.0000
oii_3726_vshift           tied to nii_6584_vshift           with factor 1.0000
oii_3729_amp              untied
oii_3729_sigma            tied to nii_6584_sigma            with factor 1.0000
oii_3729_vshift           tied to nii_6584_vshift           with factor 1.0000
neiii_3869_amp            untied
neiii_3869_sigma          tied to nii_6584_sigma            with factor 1.0000
neiii_3869_vshift         tied to nii_6584_vshift           with factor 1.0000
oiii_4363_amp             untied
oiii_4363_sigma           tied to nii_6584_sigma            with factor 1.0000
oiii_4363_vshift          tied to nii_6584_vshift           with factor 1.0000
oiii_4959_amp             tied to oiii_5007_amp             with factor 0.3351
oiii_4959_sigma           tied to oiii_5007_sigma           with factor 1.0000
oiii_4959_vshift          tied to oiii_5007_vshift          with factor 1.0000
oiii_5007_amp             untied
oiii_5007_sigma           untied
oiii_5007_vshift          untied
nii_5755_amp              untied
nii_5755_sigma            tied to nii_6584_sigma            with factor 1.0000
nii_5755_vshift           tied to nii_6584_vshift           with factor 1.0000
oi_6300_amp               untied
oi_6300_sigma             tied to nii_6584_sigma            with factor 1.0000
oi_6300_vshift            tied to nii_6584_vshift           with factor 1.0000
siii_6312_amp             untied
siii_6312_sigma           tied to nii_6584_sigma            with factor 1.0000
siii_6312_vshift          tied to nii_6584_vshift           with factor 1.0000
nii_6548_amp              tied to nii_6584_amp              with factor 0.3399
nii_6548_sigma            tied to nii_6584_sigma            with factor 1.0000
nii_6548_vshift           tied to nii_6584_vshift           with factor 1.0000
nii_6584_amp              untied
nii_6584_sigma            untied
nii_6584_vshift           untied
sii_6716_amp              untied
sii_6716_sigma            tied to nii_6584_sigma            with factor 1.0000
sii_6716_vshift           tied to nii_6584_vshift           with factor 1.0000
sii_6731_sigma            tied to nii_6584_sigma            with factor 1.0000
sii_6731_vshift           tied to nii_6584_vshift           with factor 1.0000
oii_7320_amp              untied
oii_7320_sigma            tied to nii_6584_sigma            with factor 1.0000
oii_7320_vshift           tied to nii_6584_vshift           with factor 1.0000
oii_7330_amp              tied to oii_7320_amp              with factor 0.8163
oii_7330_sigma            tied to nii_6584_sigma            with factor 1.0000
oii_7330_vshift           tied to nii_6584_vshift           with factor 1.0000
siii_9069_amp             is NOT FITTED
siii_9069_sigma           tied to nii_6584_sigma            with factor 1.0000 and FIXED
siii_9069_vshift          tied to nii_6584_vshift           with factor 1.0000 and FIXED
siii_9532_amp             is NOT FITTED
siii_9532_sigma           tied to nii_6584_sigma            with factor 1.0000 and FIXED
siii_9532_vshift          tied to nii_6584_vshift           with factor 1.0000 and FIXED

Narrow-line model only

--------------------------
Broad Balmer+helium lines:
--------------------------
h6_broad_amp              tied to halpha_broad_amp          with factor 1.0000
h6_broad_sigma            tied to halpha_broad_sigma        with factor 1.0000
h6_broad_vshift           tied to halpha_broad_vshift       with factor 1.0000
hepsilon_broad_amp        tied to halpha_broad_amp          with factor 1.0000
hepsilon_broad_sigma      tied to halpha_broad_sigma        with factor 1.0000
hepsilon_broad_vshift     tied to halpha_broad_vshift       with factor 1.0000
hdelta_broad_amp          tied to halpha_broad_amp          with factor 1.0000
hdelta_broad_sigma        tied to halpha_broad_sigma        with factor 1.0000
hdelta_broad_vshift       tied to halpha_broad_vshift       with factor 1.0000
hgamma_broad_amp          tied to halpha_broad_amp          with factor 1.0000
hgamma_broad_sigma        tied to halpha_broad_sigma        with factor 1.0000
hgamma_broad_vshift       tied to halpha_broad_vshift       with factor 1.0000
hei_broad_4471_amp        tied to halpha_broad_amp          with factor 1.0000
hei_broad_4471_sigma      tied to halpha_broad_sigma        with factor 1.0000
hei_broad_4471_vshift     tied to halpha_broad_vshift       with factor 1.0000
heii_broad_4686_amp       tied to halpha_broad_amp          with factor 1.0000
heii_broad_4686_sigma     tied to halpha_broad_sigma        with factor 1.0000
heii_broad_4686_vshift    tied to halpha_broad_vshift       with factor 1.0000
hbeta_broad_amp           tied to halpha_broad_amp          with factor 1.0000
hbeta_broad_sigma         tied to halpha_broad_sigma        with factor 1.0000
hbeta_broad_vshift        tied to halpha_broad_vshift       with factor 1.0000
hei_broad_5876_amp        tied to halpha_broad_amp          with factor 1.0000
hei_broad_5876_sigma      tied to halpha_broad_sigma        with factor 1.0000
hei_broad_5876_vshift     tied to halpha_broad_vshift       with factor 1.0000
halpha_broad_amp          is NOT FITTED
halpha_broad_sigma        is NOT FITTED
halpha_broad_vshift       is NOT FITTED

---------------------------
Narrow Balmer+helium lines:
---------------------------
h6_amp                    untied
h6_sigma                  tied to halpha_sigma              with factor 1.0000
h6_vshift                 tied to halpha_vshift             with factor 1.0000
hepsilon_amp              untied
hepsilon_sigma            tied to halpha_sigma              with factor 1.0000
hepsilon_vshift           tied to halpha_vshift             with factor 1.0000
hdelta_amp                untied
hdelta_sigma              tied to halpha_sigma              with factor 1.0000
hdelta_vshift             tied to halpha_vshift             with factor 1.0000
hgamma_amp                untied
hgamma_sigma              tied to halpha_sigma              with factor 1.0000
hgamma_vshift             tied to halpha_vshift             with factor 1.0000
hei_4471_amp              untied
hei_4471_sigma            tied to halpha_sigma              with factor 1.0000
hei_4471_vshift           tied to halpha_vshift             with factor 1.0000
heii_4686_amp             untied
heii_4686_sigma           tied to halpha_sigma              with factor 1.0000
heii_4686_vshift          tied to halpha_vshift             with factor 1.0000
hbeta_amp                 untied
hbeta_sigma               tied to halpha_sigma              with factor 1.0000
hbeta_vshift              tied to halpha_vshift             with factor 1.0000
hei_5876_amp              untied
hei_5876_sigma            tied to halpha_sigma              with factor 1.0000
hei_5876_vshift           tied to halpha_vshift             with factor 1.0000
halpha_amp                untied
halpha_sigma              untied
halpha_vshift             untied

----------------
Forbidden lines:
----------------
nev_3346_amp              untied
nev_3346_sigma            tied to oiii_5007_sigma           with factor 1.0000
nev_3346_vshift           tied to oiii_5007_vshift          with factor 1.0000
nev_3426_amp              untied
nev_3426_sigma            tied to oiii_5007_sigma           with factor 1.0000
nev_3426_vshift           tied to oiii_5007_vshift          with factor 1.0000
oii_3726_sigma            tied to oiii_5007_sigma           with factor 1.0000
oii_3726_vshift           tied to oiii_5007_vshift          with factor 1.0000
oii_3729_amp              untied
oii_3729_sigma            tied to oiii_5007_sigma           with factor 1.0000
oii_3729_vshift           tied to oiii_5007_vshift          with factor 1.0000
neiii_3869_amp            untied
neiii_3869_sigma          tied to oiii_5007_sigma           with factor 1.0000
neiii_3869_vshift         tied to oiii_5007_vshift          with factor 1.0000
oiii_4363_amp             untied
oiii_4363_sigma           tied to oiii_5007_sigma           with factor 1.0000
oiii_4363_vshift          tied to oiii_5007_vshift          with factor 1.0000
oiii_4959_amp             tied to oiii_5007_amp             with factor 0.3351
oiii_4959_sigma           tied to oiii_5007_sigma           with factor 1.0000
oiii_4959_vshift          tied to oiii_5007_vshift          with factor 1.0000
oiii_5007_amp             untied
oiii_5007_sigma           untied
oiii_5007_vshift          untied
nii_5755_amp              untied
nii_5755_sigma            tied to oiii_5007_sigma           with factor 1.0000
nii_5755_vshift           tied to oiii_5007_vshift          with factor 1.0000
oi_6300_amp               untied
oi_6300_sigma             tied to oiii_5007_sigma           with factor 1.0000
oi_6300_vshift            tied to oiii_5007_vshift          with factor 1.0000
siii_6312_amp             untied
siii_6312_sigma           tied to oiii_5007_sigma           with factor 1.0000
siii_6312_vshift          tied to oiii_5007_vshift          with factor 1.0000
nii_6548_amp              tied to nii_6584_amp              with factor 0.3399
nii_6548_sigma            tied to oiii_5007_sigma           with factor 1.0000
nii_6548_vshift           tied to oiii_5007_vshift          with factor 1.0000
nii_6584_amp              untied
nii_6584_sigma            tied to oiii_5007_sigma           with factor 1.0000
nii_6584_vshift           tied to oiii_5007_vshift          with factor 1.0000
sii_6716_amp              untied
sii_6716_sigma            tied to oiii_5007_sigma           with factor 1.0000
sii_6716_vshift           tied to oiii_5007_vshift          with factor 1.0000
sii_6731_sigma            tied to oiii_5007_sigma           with factor 1.0000
sii_6731_vshift           tied to oiii_5007_vshift          with factor 1.0000
oii_7320_amp              untied
oii_7320_sigma            tied to oiii_5007_sigma           with factor 1.0000
oii_7320_vshift           tied to oiii_5007_vshift          with factor 1.0000
oii_7330_amp              tied to oii_7320_amp              with factor 0.8163
oii_7330_sigma            tied to oiii_5007_sigma           with factor 1.0000
oii_7330_vshift           tied to oiii_5007_vshift          with factor 1.0000
siii_9069_amp             is NOT FITTED
siii_9069_sigma           tied to oiii_5007_sigma           with factor 1.0000 and FIXED
siii_9069_vshift          tied to oiii_5007_vshift          with factor 1.0000 and FIXED
siii_9532_amp             is NOT FITTED
siii_9532_sigma           tied to oiii_5007_sigma           with factor 1.0000 and FIXED
siii_9532_vshift          tied to oiii_5007_vshift          with factor 1.0000 and FIXED
moustakas commented 7 months ago

Done in #166.