Package astLib :: Module astSED

Module astSED

module for performing calculations on Spectral Energy Distributions (SEDs)

http://astlib.sourceforge.net

This module provides classes for manipulating SEDs, in particular the Bruzual & Charlot 2003, Maraston 2005, and Percival et al 2009 stellar population synthesis models are currently supported. Functions are provided for calculating the evolution of colours and magnitudes in these models with redshift etc., and for fitting broadband photometry using these models.

Classes

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Passband
This class describes a filter transmission curve.

TopHatPassband
This class generates a passband with a top hat response between the given wavelengths.

SED
This class describes a Spectral Energy Distribution (SED).

VegaSED
This class stores the SED of Vega, used for calculation of magnitudes on the Vega system.

StellarPopulation
This class describes a stellar population model, either a Simple Stellar Population (SSP) or a Composite Stellar Population (CSP), such as the models of Bruzual & Charlot 2003 or Maraston 2005.

M05Model
This class describes a Maraston 2005 stellar population model.

BC03Model
This class describes a Bruzual & Charlot 2003 stellar population model, extracted from a GALAXEV .ised file using the galaxevpl program that is included in GALAXEV.

P09Model
This class describes a Percival et al 2009 (BaSTI; http://albione.oa-teramo.inaf.it) stellar population model.

Functions

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list

makeModelSEDDictList(modelList, z, passbandsList, labelsList=[], EBMinusVList=[0.0], forceYoungerThanUniverse=True)
This routine makes a list of SEDDict dictionaries (see mags2SEDDict) for fitting using fitSEDDict.

source code

dictionary

fitSEDDict(SEDDict, modelSEDDictList)
Fits the given SED dictionary (made using mags2SEDDict) with the given list of model SED dictionaries.

source code

dictionary

mags2SEDDict(ABMags, ABMagErrs, passbands)
Takes a set of corresponding AB magnitudes, uncertainties, and passbands, and returns a dictionary with keys 'flux', 'fluxErr' 'wavelength'.

source code

list

mag2Flux(ABMag, ABMagErr, passband)
Converts given AB magnitude and uncertainty into flux, in erg/s/cm^2/Angstrom.

source code

list

flux2Mag(flux, fluxErr, passband)
Converts given flux and uncertainty in erg/s/cm^2/Angstrom into AB magnitudes.

source code

float

mag2Jy(ABMag)
Converts an AB magnitude into flux density in Jy

source code

float

Jy2Mag(fluxJy)
Converts flux density in Jy into AB magnitude

source code

Variables

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SED object VEGA = VegaSED()
The SED of Vega, used for calculation of magnitudes on the Vega system.

SED object AB = SED(wavelength= numpy.logspace(1, 8, 1e5), flux= numpy.on...
Flat spectrum SED, used for calculation of magnitudes on the AB system.

SED object SOL = SED()
The SED of the Sun.

Function Details

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makeModelSEDDictList(modelList, z, passbandsList, labelsList=[], EBMinusVList=[0.0], forceYoungerThanUniverse=True)

source code

This routine makes a list of SEDDict dictionaries (see mags2SEDDict) for fitting using fitSEDDict. This speeds up the fitting as this allows us to calculate model SED magnitudes only once, if all objects to be fitted are at the same redshift. We add some meta data to the modelSEDDicts (e.g. the model file names).

The effect of extinction by dust (assuming the Calzetti et al. 2000 law) can be included by giving a list of E(B-V) values.

If forceYoungerThanUniverse == True, ages which are older than the universe at the given z will not be included.

Parameters:

modelList (list of StellarPopulation model objects) - list of StellarPopulation models to include
z (float) - redshift to apply to all stellar population models in modelList
EBMinusVList (list) - list of E(B-V) extinction values to apply to all models, in magnitudes
labelsList (list) - optional list used for labelling passbands in output SEDDicts
forceYoungerThanUniverse (bool) - if True, do not allow models that exceed the age of the universe at z

Returns: list

list of dictionaries containing model fluxes, to be used as input to fitSEDDict.

fitSEDDict(SEDDict, modelSEDDictList)

source code

Fits the given SED dictionary (made using mags2SEDDict) with the given list of model SED dictionaries. The latter should be made using makeModelSEDDictList, and entries for fluxes should correspond directly between the model and SEDDict.

Returns a dictionary with best fit values.

Parameters:

SEDDict (dictionary, in format of mags2SEDDict) - dictionary of observed fluxes and uncertainties, in format of mags2SEDDict
modelSEDDictList (list of dictionaries, in format of makeModelSEDDictList) - list of dictionaries containing fluxes of models to be fitted to the observed fluxes listed in the SEDDict. This should be made using makeModelSEDDictList.

Returns: dictionary

results of the fitting - keys:

'minChiSq': minimum chi squared value of best fit
'chiSqContrib': corresponding contribution at each passband to the minimum chi squared value
'ageGyr': the age in Gyr of the best fitting model
'modelFileName': the file name of the stellar population model corresponding to the best fit
'modelListIndex': the index of the best fitting model in the input modelSEDDictList
'norm': the normalisation that the best fit model should be multiplied by to match the SEDDict
'z': the redshift of the best fit model
'E(B-V)': the extinction, E(B-V), in magnitudes, of the best fit model

mags2SEDDict(ABMags, ABMagErrs, passbands)

source code

Takes a set of corresponding AB magnitudes, uncertainties, and passbands, and returns a dictionary with keys 'flux', 'fluxErr' 'wavelength'. Fluxes are in units of erg/s/cm^2/Angstrom, wavelength in Angstroms. These dictionaries are the staple diet of the fitSEDDict routine.

Parameters:

ABMags (list or numpy array) - AB magnitudes, specified in corresponding order to passbands and ABMagErrs
ABMagErrs (list or numpy array) - AB magnitude errors, specified in corresponding order to passbands and ABMags
passbands (list of Passband objects) - passband objects, specified in corresponding order to ABMags and ABMagErrs

Returns: dictionary

dictionary with keys {'flux', 'fluxErr', 'wavelength'}, suitable for input to fitSEDDict

mag2Flux(ABMag, ABMagErr, passband)

source code

Converts given AB magnitude and uncertainty into flux, in erg/s/cm^2/Angstrom.

Parameters:

ABMag (float) - magnitude on AB system in passband
ABMagErr (float) - uncertainty in AB magnitude in passband
passband (Passband object) - Passband object at which ABMag was measured

Returns: list

[flux, fluxError], in units of erg/s/cm^2/Angstrom

flux2Mag(flux, fluxErr, passband)

source code

Converts given flux and uncertainty in erg/s/cm^2/Angstrom into AB magnitudes.

Parameters:

flux (float) - flux in erg/s/cm^2/Angstrom in passband
fluxErr (float) - uncertainty in flux in passband, in erg/s/cm^2/Angstrom
passband (Passband object) - Passband object at which ABMag was measured

Returns: list

[ABMag, ABMagError], in AB magnitudes

mag2Jy(ABMag)

source code

Converts an AB magnitude into flux density in Jy

Parameters:

ABMag (float) - AB magnitude

Returns: float

flux density in Jy

Jy2Mag(fluxJy)

source code

Converts flux density in Jy into AB magnitude

Parameters:

fluxJy (float) - flux density in Jy

Returns: float

AB magnitude

Variables Details

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AB

Flat spectrum SED, used for calculation of magnitudes on the AB system.

Type:: SED object

Value:

SED(wavelength= numpy.logspace(1, 8, 1e5), flux= numpy.ones(1e6))