Emission-Line Measurements

Emission-Line Parameters

The table below provides a compilation of emission-line parameters gathered through the development of the DAP. Many of them have not actually been fit by the DAP in any survey-level runs of the software and are simply collected here for reference.

Rest wavelengths are Ritz wavelengths in vacuum, collected from the NIST Atomic Spectra Database.

The “M1” and “E2” values are the Einstein \(A_{ki}\) coefficients for the magnetic dipole and electric quadrupole transitions, respectively. These are collected to fix the expected flux ratio between specific line doublets. The expected flux ratio is:

\[\frac{f_1}{f_2} = \frac{\lambda_2}{\lambda_1}\ \cdot\ \frac{M1_1+E2_1}{M1_2+E2_2}\]

where, e.g., \(\lambda_1\) is the rest wavelength of the first line in the doublet.

Additionally, we have defined some nominal passbands used for calculations of the line equivalent width (EW), including the main passband centered on the line and blue and red sidebands that are used to construct a linear continuum beneath the emission line.

Name

Rest \(\lambda\) (Å)

M1

E2

EW Passband (Å)

Blue Passband (Å)

Red Passband (Å)

HeII 3

3204.019

NeIII

3343.14

NeV

3346.783

1.38e-1

6.2e-5

NeV

3426.864

3.82e-1

3.9e-4

NI 3

3467.513

H25

3670.5155

H24

3672.5279

H23

3674.8110

H22

3677.4160

H21

3680.4065

H20

3683.8627

H19

3687.8871

H18

3692.6119

H17

3698.2103

H16

3704.9132

H15

3713.0334

H14

3723.0035

1

3706.3 – 3716.3

3738.6 – 3748.6

OII

3727.092

1.59e-4

1.86e-5

3716.3 – 3738.3

3706.3 – 3716.3

3738.6 – 3748.6

OII

3729.875

1.98e-6

2.86e-5

1

3706.3 – 3716.3

3738.6 – 3748.6

H13

3735.4365

1

3706.3 – 3716.3

3738.6 – 3748.6

H12 4

3751.2174

3746.2 – 3756.2

3738.6 – 3748.6

3756.6 – 3766.6

H11 4

3771.7012

3761.7 – 3781.7

3756.6 – 3766.6

3779.1 – 3789.1

\({\rm H}\theta\) 4

3798.9757

3789.0 – 3809.0

3776.5 – 3791.5

3806.5 – 3821.5

\({\rm H}\eta\) 4

3836.4720

3826.5 – 3846.5

3806.5 – 3826.5

3900.2 – 3920.2

NeIII

3869.86

1.74e-1

3859.9 – 3879.9

3806.5 – 3826.5

3900.2 – 3920.2

HeI 3

3889.749

1

3806.5 – 3826.5

3900.2 – 3920.2

\({\rm H}\zeta\) 4

3890.1506

3880.2 – 3900.2

3806.5 – 3826.5

3900.2 – 3920.2

NeIII

3968.59

5.40e-2

1

3938.6 – 3958.6

3978.6 – 3998.6

\({\rm H}\epsilon\) 4

3971.1951

3961.2 – 3981.2

3941.2 – 3961.2

3981.2 – 4001.2

HeI 3

4027.328

4017.3 – 4037.3

3997.3 – 4017.3

4037.3 – 4057.3

SII

4069.749

1.92e-1

9.53e-8

4062.7 – 4073.6

4049.7 – 4062.7

4082.0 – 4092.9

SII

4077.500

7.72e-2

1.16e-6

4073.6 – 4084.5

4049.7 – 4062.7

4082.0 – 4092.9

\({\rm H}\delta\) 4

4102.8922

4092.9 – 4112.9

4082.0 – 4092.9

4112.9 – 4132.9

\({\rm H}\gamma\) 4

4341.6837

4331.7 – 4351.7

4311.7 – 4331.7

4349.7 – 4358.7

OIII

4364.436

1.71e+0

4358.7 – 4374.4

4349.7 – 4358.7

4374.4 – 4384.4

HeI 3

4472.734

4462.7 – 4482.7

4442.7 – 4462.7

4482.7 – 4502.7

HeII 3

4687.015

4677.0 – 4697.0

4667.0 – 4677.0

4697.0 – 4707.0

ArIV 2

4712.58

9.6e-3

HeI 3

4714.466

4707.0 – 4722.0

4697.0 – 4707.0

4722.0 – 4732.0

ArIV

4741.45

7.2e-2

5.1e-3

\({\rm H}\beta\) 4

4862.6830

4852.7 – 4872.7

4798.9 – 4838.9

4885.6 – 4925.6

HeI

4923.3051

4913.3 – 4933.3

4898.3 – 4913.3

4933.3 – 4948.3

OIII

4960.295

6.21e-3

4.57e-6

4950.3 – 4970.3

4930.3 – 4950.3

4970.3 – 4990.3

OIII

5008.240

1.81e-2

3.52e-5

4998.2 – 5018.2

4978.2 – 4998.2

5028.2 – 5048.2

HeI

5017.0769

1

4988.2 – 4983.2

5028.2 – 5048.2

ArIII

5193.27

3.10e+0

NI

5199.349

1.60e-5

4.34e-6

5189.3 – 5209.3

5169.4 – 5189.3

5211.7 – 5231.7

NI

5201.705

9.71e-7

6.59e-6

1

5169.4 – 5189.4

5211.7 – 5231.7

OI

5578.887

1.26e+0

NII

5756.19

1.14e+0

HeI 3

5877.252

5867.2 – 5887.2

5847.2 – 5867.2

5887.2 – 5907.2

NaI

5891.583

NaI

5897.558

OI

6302.046

5.63e-3

2.11e-5

6292.0 – 6312.0

6272.0 – 6292.0

6312.0 – 6332.0

OI

6365.536

1.82e-3

3.39e-6

6355.5 – 6375.5

6335.5 – 6355.5

6375.5 – 6395.5

NII

6549.86

9.84e-4

9.22e-7

6542.9 – 6556.9

6483.0 – 6513.0

6623.0 – 6653.0

HeII 3

6561.890

\({\rm H}\alpha\) 4

6564.608

6557.6 – 6571.6

6483.0 – 6513.0

6623.0 – 6653.0

NII

6585.27

2.91e-3

8.65e-6

6575.3 – 6595.3

6483.0 – 6513.0

6623.0 – 6653.0

HeI

6679.9956

6670.0 – 6690.0

6652.0 – 6670.0

6690.0 – 6708.0

SII

6718.295

1.39e-5

1.88e-4

6711.3 – 6725.3

6690.0 – 6708.0

6748.0 – 6768.0

SII

6732.674

5.63e-4

1.21e-4

6725.7 – 6739.7

6690.0 – 6708.0

6748.0 – 6768.0

HeI 3

7067.144

7057.1 – 7077.1

7037.1 – 7057.1

7077.1 – 7097.1

HeI

7067.65683

ArIII

7137.76

3.21e-1

1.4e-3

7127.8 – 7147.8

7107.8 – 7127.8

7147.8 – 7167.8

ArIV

7172.67

8.1e-1

9.8e-2

ArIV

7239.77

4.44e-1

2.26e-1

ArIV

7265.33

4.88e-1

1.90e-1

HeI

7283.3571

OII

7320.94

5.19e-2

1

7291.0 – 7311.0

7342.8 – 7362.8

OII

7322.01

8.37e-3

9.07e-2

7313.8 – 7326.8

7291.0 – 7311.0

7342.8 – 7362.8

OII

7331.68

9.32e-3

7.74e-2

7326.8 – 7339.8

7291.0 – 7311.0

7342.8 – 7362.8

OII

7332.75

1.49e-2

3.85e-2

1

7291.0 – 7311.0

7342.8 – 7362.8

ArIV

7334.17

1.22e-1

ArIII

7753.24

8.3e-2

1.3e-4

7743.2 – 7763.2

7703.2 – 7743.2

7763.2 – 7803.2

ArIII

8038.73

2.9e-5

P20

8394.703

P19

8415.630

P18

8440.274

P17

8469.581

P16

8504.819

8494.8 – 8514.8

8474.8 – 8494.8

8514.8 – 8534.8

P15

8547.731

8534.8 – 8557.7

8514.8 – 8534.8

8557.7 – 8587.7

P14

8600.754

8587.7 – 8610.8

8557.7 – 8587.7

8610.8 – 8650.8

P13

8667.398

8657.4 – 8677.4

8617.4 – 8657.4

8677.4 – 8717.4

P12

8752.876

8742.9 – 8762.9

8702.9 – 8742.9

8762.9 – 8802.9

SIII

8831.8

5.25e-6

\({\rm P}\theta\)

8865.216

8855.2 – 8875.2

8815.2 – 8855.2

8875.2 – 8915.2

\({\rm P}\eta\)

9017.384

9007.4 – 9027.4

8977.4 – 9007.4

9027.4 – 9057.4

SIII

9071.1

1.85e-2

3.94e-5

9061.1 – 9081.1

9026.1 – 9061.1

9081.1 – 9116.1

HeI 3

9212.862

\({\rm P}\zeta\)

9231.546

9221.5 – 9241.5

9181.5 – 9221.5

9241.5 – 9281.5

SIII

9533.2

4.78e-2

2.09e-4

9525.5 – 9540.9

9483.2 – 9523.2

9558.6 – 9598.6

\({\rm P}\epsilon\)

9548.588

9540.9 – 9556.3

9483.2 – 9523.2

9558.6 – 9598.6

HeI 3

9528.778

HeI 3

10030.470

\({\rm P}\delta\)

10052.123

10042.1 – 10062.1

10002.1 – 10042.1

10062.1 – 10102.1

Non-parametric Emission-Line Measurements

The DAP performs non-parametric measurements of the emission lines using a simple moment analysis. See mangadap.proc.emissionlinemoments and Emission-line Moments. In survey-level runs of the DAP, we have typically paired the set of moment measurements and Gaussian models; however, the number of emission-line moment measurements need not be matched to the number of emission-line Gaussian models and vice versa.

Input Data Format

The parameters that define the emission-line moments to calculate are provided via the EmissionMomentsDB object, which is built using an SDSS-style parameter file.

The columns of the parameter file are:

Parameter

Format

Description

index

int

Unique integer identifier of the emission line. Must be unique.

name

str

Name of the transition.

lambda

float

Rest frame wavelength of the emission line to analyze.

waveref

str

The reference frame of the wavelengths; must be either ‘air’ for air or ‘vac’ for vacuum.

primary

float[2]

A two-element vector with the starting and ending wavelength for the primary passband surrounding the emission line(s).

blueside

float[2]

A two-element vector with the starting and ending wavelength for a passband to the blue of the primary band.

redside

float[2]

A two-element vector with the starting and ending wavelength for a passband to the red of the primary band.

and an example file might look like this:

typedef struct {
    int index;
    char name[6];
    double lambda;
    char waveref[3];
    double primary[2];
    double blueside[2];
    double redside[2];
} DAPELB;

DAPELB   2  OIId    3728.4835  vac  { 3716.3  3738.3 } { 3706.3  3716.3 } { 3738.6  3748.6 }
DAPELB   3  OII     3729.875   vac  {   -1      -1   } {   -1      -1   } {   -1      -1   }

Note in the above example that the second set of parameters define nonsensical passbands with limits of {-1 -1}. This is used to signify that the moment parameters are “dummy” or placeholder parameters. This is used to create an empty channel in the output MAPS file and is used just to synchronize the channel indices between the non-parametric and Gaussian-fit results. That is, it’s used to ensure that, e.g., the \({\rm H}\alpha\) measurements are in the same channel for both the EMLINE_SFLUX and EMLINE_GFLUX extensions in the DAP MAPS file.

Changing the moment parameters

The moment measurements are performed by EmissionLineMoments; see Emission-line Moments. A set of parameter files that define a list of emission-line moment sets are provided with the DAP source distribution and located at $MANGADAP_DIR/mangadap/data/emission_bandpass_filters. The database you wish to use is selected by the passbands parameter in the relevant parameter block of the Analysis Plans file. The keyword is simply the capitalized name of the file without the “.par” extension. For example, to use the elbmpl9.par database, the plan file would include

[default.eline_moments]
 passbands = 'ELBMPL9'

To provide a user-defined database, simply replace the passbands keyword with the name of the local file defining the database (in the format given above). For example,

[default.eline_moments]
 passbands = '/path/to/my/local/file/my_elb_database.par'

Gaussian Emission-Line Modeling

The DAP models the emission lines using single-component Gaussian functions. See mangadap.proc.emissionlinemoments and Emission-line Modeling. In survey-level runs of the DAP, we have typically paired the set of moment measurements and Gaussian models; however, the number of emission-line moment measurements need not be matched to the number of emission-line Gaussian models and vice versa.

Input Data Format

The parameters that define the emission-line models to fit are provided via the EmissionLineDB object, which is built using an SDSS-style parameter file.

The columns of the parameter file are:

Parameter

Format

Description

index

int

Unique integer identifier of the emission line. Must be unique. Specifically used when tying line parameters.

name

str

Name of the transition.

restwave

float

Rest frame wavelength of the emission line to analyze.

waveref

str

The reference frame of the wavelengths; must be either ‘air’ for air or ‘vac’ for vacuum.

action

str

A single character setting how the line should be treated. See Emission-Line “Actions”.

tie

str[4]

A sequence of 4 strings that indicate how the line should be tied to other lines. The first element specifies the line to which to tie the line specified in this row, indicated by its line index. The next three entries indicate how to tie each of the 3 Gaussian parameters: flux, velocity, and velocity dispersion. To leave the parameter untied, this should be None. To force the parameter to be identical to the parameter for the tied line, use =. For the flux, the flux can be specified to be a specific factor of the tied line; e.g., =0.30 forces the flux of this line to be 0.3 times the flux of the tied line. For the velocity and velocity dispersion, a single value can be used to set a the tied parameter to be within the specified fraction of the tied parameter. I.e., a value of 1.4 for the velocity dispersion parameter means the velocity dispersion of this line should be within \(\sigma_t/1.4 < \sigma < 1.4 \sigma_t\), where \(\sigma_t\) is the velocity dispersion of the tied line. When imposing these parameter inequalities, ppxf will require the cvxopt package.

blueside

float[2]

A two-element vector with the starting and ending wavelength for a passband to the blue of the primary band.

redside

float[2]

A two-element vector with the starting and ending wavelength for a passband to the red of the primary band.

and an example file might look like this:

typedef struct {
    int index;
    char name[6];
    double restwave;
    char waveref[3];
    char action;
    char tie[4][10];
    double blueside[2];
    double redside[2];
} DAPEML;

DAPEML   2  OII     3727.092   vac  f  {   34   None    = None }  {  3706.3  3716.3 }  {  3738.6  3748.6 }
DAPEML   3  OII     3729.875   vac  f  {    2   None    =    = }  {  3706.3  3716.3 }  {  3738.6  3748.6 }
DAPEML  23  Hb      4862.6830  vac  f  {   34   None    =  1.4 }  {  4798.9  4838.9 }  {  4885.6  4925.6 }
DAPEML  33  NII     6549.86    vac  f  {   35  =0.34    =    = }  {  6483.0  6513.0 }  {  6623.0  6653.0 }
DAPEML  34  Ha      6564.608   vac  f  { None   None None None }  {  6483.0  6513.0 }  {  6623.0  6653.0 }
DAPEML  35  NII     6585.27    vac  f  {   34   None    = None }  {  6483.0  6513.0 }  {  6623.0  6653.0 }

Note

  • Both the emission-line moments database and the emission-line modeling database define the sidebands used for the equivalent width calculations. Nominally, these should be the same, but it’s up to the person that writes the two parameter files to make sure that is true.

  • The format of this file has changed in version 3.1.0 in a way that removes many of the parameters used by the Elric fitter. That class is now deprecated.

Emission-Line “Actions”

The action parameter allows the emission-line database to be used both in masking during the stellar-continuum modeling (see SpectralPixelMask) and during the emission-line modeling itself.

The valid actions are:

  • i: ignore the line, as if the line were commented out.

  • f: fit the line and mask the line when fitting the stellar continuum.

  • m: mask the line when fitting the stellar continuum but do not fit the line itself

  • s: defines a sky line that should be masked. When masked, the wavelength of the line is not adjusted for the redshift of the object spectrum.

I.e., when using the emission-line database for the emission-line modeling, lines with the action set to f are fit, whereas all other lines are ignored.

Emission-Line “Modes”

Warning

This parameter is now DEPRECATED in favor of the tie parameter.

The mode parameter sets how the emission line should be treated with respect of the rest of the lines being modeled.

The valid modes are:

  • f: Fit the line independently of all others.

  • wN: Used by Elric only. Fit the line with untied parameters, but use a window that includes both this line and the line with index N.

  • xN: Used by Elric only. Fit the line with its flux tied to the line with index N.

  • vN: Fit the line with the velocity tied to the line with index N.

  • sN: Fit the line with the velocity dispersion tied to the line with index N.

  • kN: Fit the line with the velocity and velocity dispersion tied to the line with index N.

  • aN: Fit the line with the flux, velocity, and velocity dispersion tied to the line with index N.

As noted in the mode description, many of the modes are only available when using the Elric module. For the w mode, this is simply because the preferred module, Sasuke, fits the full spectrum instead of fitting the lines within small spectral windows. The other limitation are because Sasuke is based on the use of template spectra to fit the emission lines (see EmissionLineTemplates): To tie line fluxes, the lines to be tied are included in the same template spectrum, meaning that their kinematics are also automatically tied. That means that, for Sasuke, the x and a modes are identical.

In the Input Data Format example, the modes set the \({\rm H}\alpha\) line as the “reference” line. I.e., there should always be one line whose mode is f. This requirement is simply practical in setting up the tied parameter structure; there is no more weight given to the fit to the reference line than any other line. The blue [OII] and red [NII] lines have their velocities tied to the \({\rm H}\alpha\) line, all kinematics of the red [OII] line are tied to the blue [OII] line, and all parameters of the blue [NII] line are tied to the red [NII] line with a fixed flux ratio of NII-6550/NII-6585 == 0.34. By virtue of being tied to lines that have their velocites tied to the \({\rm H}\alpha\) line, the velocities of the red [OII] and blue [NII] lines are also tied to the \({\rm H}\alpha\) line. Again, this doesn’t mean that the fit to the \({\rm H}\alpha\) line is given any more weight than any other line, it just means that there is one model parameter that defines the velocity of all lines.

Changing the modeling parameters

The moment measurements are performed by EmissionLineMoments; see Emission-line Moments. A set of parameter files that define a list of emission-line moment sets are provided with the DAP source distribution and located at $MANGADAP_DIR/mangadap/data/emission_bandpass_filters. The database you wish to use is selected by the passbands parameters in the relevant parameter block of the Analysis Plans file. The keyword is simply the capitalized name of the file without the “.par” extension. To provide a user-defined database, simply replace the passbands keyword with the name of the local file defining the database (in the format given above).

The emission-line modeling is performed by EmissionLineModel; see Emission-line Modeling. A set of files that define a list of emission-line model parameter sets are provided with the DAP source distribution and located at $MANGADAP_DIR/mangadap/data/emission_lines. The database you wish to use is selected by the emission_lines parameter in the relevant parameter block of the Analysis Plans file. The keyword is simply the capitalized name of the file without the “.par” extension. For example, to use the elpmpl11.par database, the plan file would include

[default.eline_fits.fit]
 emissionpassbands = 'ELPMPL11'

To provide a user-defined database, simply replace the passbands keyword with the name of the local file defining the database (in the format given above). For example,

[default.eline_fits.fit]
 emissionpassbands = '/path/to/my/local/file/my_elp_database.par'
1(1,2,3,4,5,6,7,8,9)

No primary band defined because it overlaps with another line.

2

Provided magnetic dipole coefficient is actually its sum with the electric quadrupole coefficient.

3(1,2,3,4,5,6,7,8,9,10,11,12,13)

Wavelength based on a simple average of wavelengths for many fine-structure transitions.

4(1,2,3,4,5,6,7,8,9,10)

Center of gravity of the blending of fine-structure lines assuming Boltzmann populations in an optically thin plasma; see, e.g.: https://physics.nist.gov/cgi-bin/ASBib1/get_ASBib_ref.cgi?db=el&db_id=&comment_code=c69&element=H&spectr_charge=1&ref=&type=