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

3204.038

NeV

3346.783

NeV

3426.863

H25

3670.5154

H24

3672.5279

H23

3674.8109

H22

3677.4160

H21

3680.4065

H20

3683.8627

H19

3687.8870

H18

3692.6119

H17

3698.2104

H16

3704.9133

H15

3713.0334

H14

3723.0035

1

3706.3 – 3716.3

3738.6 – 3748.6

OII

3727.092

3716.3 – 3738.3

3706.3 – 3716.3

3738.6 – 3748.6

OII

3729.875

1

3706.3 – 3716.3

3738.6 – 3748.6

H13

3735.4365

1

3706.3 – 3716.3

3738.6 – 3748.6

H12

3751.2243

3746.2 – 3756.2

3738.6 – 3748.6

3756.6 – 3766.6

H11

3771.7080

3761.7 – 3781.7

3756.6 – 3766.6

3779.1 – 3789.1

$${\rm H}\theta$$

3798.9826

3789.0 – 3809.0

3776.5 – 3791.5

3806.5 – 3821.5

$${\rm H}\eta$$

3836.4790

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

3889.749

1

3806.5 – 3826.5

3900.2 – 3920.2

$${\rm H}\zeta$$

3890.1576

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

$${\rm H}\epsilon$$

3971.2020

3961.2 – 3981.2

3941.2 – 3961.2

3981.2 – 4001.2

HeI

4027.3238

4017.3 – 4037.3

3997.3 – 4017.3

4037.3 – 4057.3

SII

4069.749

4062.7 – 4073.6

4049.7 – 4062.7

4082.0 – 4092.9

SII

4077.500

4073.6 – 4084.5

4049.7 – 4062.7

4082.0 – 4092.9

$${\rm H}\delta$$

4102.8991

4092.9 – 4112.9

4082.0 – 4092.9

4112.9 – 4132.9

$${\rm H}\gamma$$

4341.691

4331.7 – 4351.7

4311.7 – 4331.7

4349.7 – 4358.7

OIII

4364.435

4358.7 – 4374.4

4349.7 – 4358.7

4374.4 – 4384.4

HeI

4472.729

4462.7 – 4482.7

4442.7 – 4462.7

4482.7 – 4502.7

HeII

4687.015

4677.0 – 4697.0

4667.0 – 4677.0

4697.0 – 4707.0

ArIV

4712.58

HeI

4714.4578

4707.0 – 4722.0

4697.0 – 4707.0

4722.0 – 4732.0

ArIV

4741.45

$${\rm H}\beta$$

4862.691

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

NI

5199.3490

5189.3 – 5209.3

5169.4 – 5189.3

5211.7 – 5231.7

NI

5201.7055

1

5169.4 – 5189.4

5211.7 – 5231.7

NII

5756.19

HeI

5877.243

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

6365.535

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

$${\rm H}\alpha$$

6564.632

6557.6 – 6571.6

6483.0 – 6513.0

6623.0 – 6653.0

NII

6585.271

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

6718.294

6711.3 – 6725.3

6690.0 – 6708.0

6748.0 – 6768.0

SII

6732.674

6725.7 – 6739.7

6690.0 – 6708.0

6748.0 – 6768.0

HeI

7067.1252

7057.1 – 7077.1

7037.1 – 7057.1

7077.1 – 7097.1

ArIII

7137.76

3.21e-1

1.4e-3

7127.8 – 7147.8

7107.8 – 7127.8

7147.8 – 7167.8

ArIV

7172.68

ArIV

7239.76

ArIV

7265.33

OII

7321.003

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

ArIII

7753.24

8.3e-2

1.3e-4

7743.2 – 7763.2

7703.2 – 7743.2

7763.2 – 7803.2

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

$${\rm P}\theta$$

8865.216

8855.2 – 8875.2

8815.2 – 8855.2

8875.2 – 8915.2

SIII

8831.8

$${\rm P}\eta$$

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

$${\rm P}\zeta$$

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

$${\rm P}\delta$$

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. There are a few methods that you can use to change the set of emission-line parameters used by EmissionLineMoments: 1. To use one of the existing parameter databases, you can change the emission_passbands keyword in the EmissionLineMoments configuration file. The keyword should be the capitalized root of the parameter filename. E.g., to use $MANGADAP_DIR/mangadap/data/emission_bandpass_filters/elbmpl9.par, set the keyword to ELBMPL9.

2. To use a new parameter database, write the file and save it in the $MANGADAP_DIR/mangadap/data/emission_bandpass_filters/ directory, and then change the relevant configuration file in the same way as described above. 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. 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. action str A single character setting how the line should be treated. See Emission-Line “Actions”. relative_flux float Relative flux of the emission lines. This should most often be unity when the flux is not tied to another line; see Emission-Line “Modes”. mode str Fitting mode for the line. See Emission-Line “Modes”. profile str The name of the class used to construct the line profile. The available options are any of the classes in mangadap.util.lineprofiles. This functionality will likely be deprecated because the lineprofile should essentially always be FFTGaussianLSF; selected by setting this parameter to “FFTGaussianLSF”. ncomp int The number of components to fit. NOT TYPICALLY USED! output_model int Flag to include the best-fitting model of the line in the emission-line model spectrum. NOT TYPICALLY USED! par float[3] A list of the initial guess for the line profile parameters. NOT TYPICALLY USED! The number of parameters must match the struct declaration at the top of the file. The initial parameters are automatically adjusted to provide any designated flux ratios, and the center is automatically adjusted to the provided redshift for the spectrum. For example, for a GaussianLineProfile, this is typically set to “{1.0 0.0 100.0}”. fix int[3] A list of flags for fixing the input guess parameters during the fit. NOT TYPICALLY USED! Use 0 for a free parameter, 1 for a fixed parameter. The parameter value is only fixed AFTER adjusted in the flux and or center based on the redshift and the implied tied parameters. For a free set of parameters using a GaussianLineProfile, this is set to “{ 0 0 0 }”. lower_bound str[3] A list of lower bounds for the parameters. NOT TYPICALLY USED! For each parameter, use None to indicate no lower bound. For a GaussianLineProfile with positive flux and standard deviation, this is set to ‘{ 0.0 None 0.0 }’. upper_bound str[3] A list of upper bounds for the parameters. NOT TYPICALLY USED! For each parameter, use None to indicate no upper bound. For a GaussianLineProfile with maximum standard deviation of 800 km/s, this is set to ‘{ None None 800.0 }’. log_bounded int[3] A list of flags used when determining if a fit parameter is near the imposed boundary. NOT TYPICALLY USED! If true, the fraction of the boundary range used is done in logarithmic, not linear, separation. Use 0 for False, 1 for True. 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]; char action; double relative_flux; char mode[6]; char profile[30]; int ncomp; int output_model; double par[3]; int fix[3]; char lower_bound[3][10]; char upper_bound[3][10]; int log_bounded[3]; double blueside[2]; double redside[2]; } DAPEML; DAPEML 2 OII 3727.092 vac f 1.00 v34 FFTGaussianLSF 1 1 { 1.0 0.0 100.0 } { 0 0 0 } { 0.0 None 30.0 } { None None 400. } { 0 0 1 } { 3706.3 3716.3 } { 3738.6 3748.6 } DAPEML 3 OII 3729.875 vac f 1.00 k2 FFTGaussianLSF 1 1 { 1.0 0.0 100.0 } { 0 0 0 } { 0.0 None 30.0 } { None None 400. } { 0 0 1 } { 3706.3 3716.3 } { 3738.6 3748.6 } DAPEML 33 NII 6549.86 vac f 0.34 a35 FFTGaussianLSF 1 1 { 1.0 0.0 100.0 } { 0 0 0 } { 0.0 None 30.0 } { None None 400. } { 0 0 1 } { 6483.0 6513.0 } { 6623.0 6653.0 } DAPEML 34 Ha 6564.632 vac f 1.00 f FFTGaussianLSF 1 1 { 1.0 0.0 100.0 } { 0 0 0 } { 0.0 None 30.0 } { None None 400. } { 0 0 1 } { 6483.0 6513.0 } { 6623.0 6653.0 } DAPEML 35 NII 6585.271 vac f 1.00 v34 FFTGaussianLSF 1 1 { 1.0 0.0 100.0 } { 0 0 0 } { 0.0 None 30.0 } { None None 400. } { 0 0 1 } { 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. • Many of the current parameters in the emission-line modeling parameter file are hold-overs from when Elric was the standard class used for the emission-line fitting. Anything marked as “NOT TYPICALLY USED” hasn’t been adapted for use with the currently preferred module, Sasuke. 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”¶ 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 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. There are a few methods that you can use to change the set of emission-line parameters used by EmissionLineModel:

1. To use one of the existing parameter databases, you can change the emission_lines keyword in the EmissionLineModel configuration file. The keyword should be the capitalized root of the parameter filename. E.g., to use $MANGADAP_DIR/mangadap/data/emission_lines/elpmpl9.par, set the keyword to ELPMPL9. 2. To use a new parameter database, write the file and save it in the $MANGADAP_DIR/mangadap/data/emission_lines/ directory, and then change the relevant configuration file in the same way as described above.

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

No primary band defined because it overlaps with another line.