kcorrect.kcorrect

Module Contents

Classes

Kcorrect

K-correction object

KcorrectSDSS

K-correction object for SDSS data

KcorrectGST

K-correction object for GALEX, SDSS, 2MASS data
class Kcorrect(filename=None, responses=None, templates=None, responses_out=None, responses_map=None, redshift_range=[0.0, 2.0], nredshift=4000, abcorrect=False, cosmo=None)[source]

Bases: kcorrect.fitter.Fitter

K-correction object

Parameters:

  • abcorrect (bool) – correct maggies to AB (default False)

  • filename (str) – input file to define kcorrect object (overrides responses, responses_out, responses_map, templates, redshift_range, nredshift, abcorrect)

  • responses (list of str) – names of input responses to base SED on

  • templates (list of kcorrect.template.SED) – templates to use (if None uses v4 default template set)

  • responses_out (list of str) – output responses for K-corrections (default to “responses”)

  • responses_map (list of str) – input responses to use for K-corrections (default to “responses”)

  • redshift_range (list of np.float32) – minimum and maximum redshifts (default [0., 2.])

  • nredshift (int or np.int32) – number of redshifts in interpolation grid (default 4000)

  • cosmo (astropy.cosmology.FLRW-like object) – object with distmod() method (default Planck18)

abcorrect

correct maggies to AB

Type:

bool

Amatrix

interpolation function for each template and input response

Type:

scipy.interpolate.interp1d object

AmatrixOut

interpolation function for each template and output response

Type:

scipy.interpolate.interp1d object

cosmo

object with luminosity_distance() method

Type:

astropy.cosmology.FLRW-like object

imap

for each responses_map element, its corresponding index in responses

Type:

ndarray of np.int32

nredshift

number of redshifts in interpolation grid

Type:

int or np.int32

redshift_range

minimum and maximum redshifts

Type:

list of np.float32

redshifts

redshifts in grid

Type:

ndarray of np.float32

responses

[Nin] names of input responses to use

Type:

list of str

responses_map

[Nout] input responses to use for K-corrections

Type:

list of str

responses_out

[Nout] output responses for K-corrections

Type:

list of str

templates

templates to use

Type:

kcorrect.template.Template object

Notes

K-corrections are magnitude shifts to account for the difference in the observed bandpass R and a desired output bandpass Q, denoted K_QR (see Blanton & Roweis 2007). The default behavior finds the K-corrections between each input bandpass with itself, i.e. K_QQ.

In detail:

“responses” corresponds to the observed bandpasses R.

“responses_out” corresponds to the observed bandpasses Q; it defaults to “responses”.

“responses_map” is the same length as “responses_out” and defines which bandpasses in “responses” to use for each output bandpass in “responses_out”. It defaults to “responses”.

Amatrix accepts a redshift as its argument and returns a matrix of shape [nresponses, ntemplates]. This matrix can be dotted into a set of coefficients for each template, and the result will be the observed bandpass maggies at the desired redshift for an SED corresponding to the coefficients. A ValueError results if the input redshift is outside redshift_range.

AmatrixOut is similar but returns a [nresponses_out, ntemplates] matrix for the output bandpasses.

Once defined, a Kcorrect object can be output to a FITS file with the method tofits(), and reimported with fromfits(). The filename parameter expects this format.

derived(redshift=None, coeffs=None, band_shift=0.0, distance=None)[source]

Return derived quantities based on coefficients

Parameters:

  • redshift (ndarray of np.float32, or np.float32) – [ngalaxy] redshift

  • coeffs (ndarray of np.float32) – [ngalaxy, ntemplates] coefficients for each template for each object

  • band_shift (np.float32) – band shift to apply for output response

  • distance (ndarray of np.float32 or np.float32) – [ngalaxy] luminosity distance in Mpc

Returns:

derived – dictionary with derived quantities (see below)

Return type:

dict()

Notes

If distance is not specified, then it is derived from the redshift assuming the cosmology in the cosmo attribute.

The derived dictionary contains the following keys with the associated quantities:

‘mremain’ndarray of np.float32, or np.float32

[ngalaxy] current stellar mass in solar masses

‘intsfh’ndarray of np.float32, or np.float32

[ngalaxy] current stellar mass in solar masses

‘mtol’ndarray of np.float32, or np.float32

[ngalaxy] mass-to-light ratio in each output band

‘b50’ndarray of np.float32, or np.float32

[ngalaxy] current (< 50 Myr) over past star formation

‘b300’ndarray of np.float32, or np.float32

[ngalaxy] current (< 300 Myr) over past star formation

‘b1000’ndarray of np.float32, or np.float32

[ngalaxy] current (< 1 Gyr) over past star formation

‘metallicity’ :

[ngalaxy] metallicity in current stars

All of these quantities should be taken with extreme caution and not accepted literally. After all, they are just the result of a template fit to a few bandpasses.

For the default template set, see Moustakas et al. (2013) for a comparison of the masses with other estimators.

For responses where solar_magnitude is not defined, mtol is in per maggy units (not per solar luminosity)

derived_mc(redshift=None, coeffs_mc=None, band_shift=0.0, distance=None)[source]

Return derived quantities based on coefficients

Parameters:

  • redshift (ndarray of np.float32, or np.float32) – [ngalaxy] redshift

  • coeffs_mc (ndarray of np.float32) – [ngalaxy, ntemplates, mc] coefficients for each template for each object

  • band_shift (np.float32) – band shift to apply for output response

  • distance (ndarray of np.float32 or np.float32) – [ngalaxy] luminosity distance in Mpc

Returns:

derived – dictionary with derived quantities (see below)

Return type:

dict()

Notes

Relies on repeated calls to the kcorrect.kcorrect.Kcorrect.derived() method.

The derived dictionary contains the following keys with the associated quantities:

‘mremain’ndarray of np.float32, or np.float32

[ngalaxy, mc] current stellar mass in solar masses

‘intsfh’ndarray of np.float32, or np.float32

[ngalaxy, mc] current stellar mass in solar masses

‘mtol’ndarray of np.float32, or np.float32

[ngalaxy, mc] mass-to-light ratio in each output band

‘b50’ndarray of np.float32, or np.float32

[ngalaxy] current (< 50 Myr) over past star formation

‘b300’ndarray of np.float32, or np.float32

[ngalaxy, mc] current (< 300 Myr) over past star formation

‘b1000’ndarray of np.float32, or np.float32

[ngalaxy, mc] current (< 1 Gyr) over past star formation

‘metallicity’ :

[ngalaxy, mc] metallicity in current stars

reconstruct_out(redshift=None, coeffs=None, band_shift=0.0)[source]

Reconstruct output maggies associated with coefficients

Parameters:

  • redshift (np.float32) – redshift

  • coeffs (ndarray of np.float32) – coefficients

  • band_shift (np.float32) – blueshift to apply to reconstructed bandpasses

Returns:

maggies – AB maggies in each output band

Return type:

ndarray of np.float32

kcorrect(redshift=None, coeffs=None, band_shift=0.0)[source]

Return K-correction in all bands

Parameters:

  • redshift (ndarray of np.float32, or np.float32) – redshift for K-correction

  • coeffs (ndarray of np.float32) – coefficients for each template for each object

  • band_shift (np.float32) – shift to apply for output responses

Returns:

kcorrect – K-correction from input to output magnitudes

Return type:

ndarray of np.float32

absmag(maggies=None, ivar=None, redshift=None, coeffs=None, band_shift=0.0, distance=None, reconstruct=False, limit=False)[source]

Return absolute magnitude in output bands

Parameters:

  • redshift (ndarray of np.float32, or np.float32) – [ngalaxy] redshift(s) for K-correction

  • maggies (ndarray of np.float32) – [ngalaxy, nbands] fluxes of each band in maggies

  • ivar (ndarray of np.float32) – [ngalaxy, nbands] inverse variance of each band

  • coeffs (ndarray of np.float32) – [ngalaxy, ntemplates] coefficients for each template for each object

  • band_shift (np.float32) – shift to apply for output responses

  • distance (ndarray of np.float32 or np.float32) – [ngalaxy] distance in Mpc (or None)

  • reconstruct (bool) – if set, return absmag_reconstruct

  • limit (bool) – if set, return absmag_limit

Returns:

  • absmag (ndarray of np.float32) – [ngalaxy, nbands] AB absolute magnitude in each band for each object

  • absmag_reconstruct (ndarray of np.float32) – [ngalaxy, nbands] reconstructed AB absolute magnitude from SED fit (if reconstruct set)

  • absmag_limit (ndarray of np.float32) – [ngalaxy, nbands] 1-sigma bright limit on absolute mag from error

Notes

If distance is None, the distance is derived from the redshift using the cosmo attribute.

Depends on having run fit_coeffs on a consistent set of maggies and ivars.

Determines the distance modulus with the object’s “cosmo.distmod()” method. By default this is the Planck18 cosmology.

Returns the K-corrected absolute magnitude (or -9999 if there ivar=0, magggies are negative, or there is no valid value)

The “reconstructed” absolute magnitude is calculated from the kcorrect nonnegative fit instead of being a K-correction of the data. These values are -9999 if there is no valid value (usually meaning all of the coefficients input are zero).

The absolute magnitude “limit” is set to the 1-sigma limit from the error in each band (using the K-correction from the real fit). It is returned for every object with ivar != 0 and positive coefficients, and is -9999 otherwise.

If abcorrect is True, calls to_ab() method on input maggies to convert to AB.

absmag_mc(maggies_mc=None, ivar=None, redshift=None, coeffs_mc=None, band_shift=0.0, distance=None, reconstruct=False)[source]

Return absolute magnitude in output bands for Monte Carlo results

Parameters:

  • redshift (ndarray of np.float32, or np.float32) – [ngalaxy] redshift(s) for K-correction

  • maggies_mc (ndarray of np.float32) – [ngalaxy, nbands, mc] fluxes of each band in maggies

  • ivar (ndarray of np.float32) – [ngalaxy, nbands] inverse variance of each band

  • coeffs_mc (ndarray of np.float32) – [ngalaxy, ntemplates, mc] coefficients for each template for each object

  • band_shift (np.float32) – shift to apply for output responses

  • distance (ndarray of np.float32 or np.float32) – [ngalaxy] distance in Mpc (or None)

  • reconstruct (bool) – if set, return absmag_reconstruct

Returns:

  • absmag (ndarray of np.float32) – [ngalaxy, nbands, mc] AB absolute magnitude in each band for each object

  • absmag_reconstruct (ndarray of np.float32) – [ngalaxy, nbands] reconstructed AB absolute magnitude from SED fits (if reconstruct set)

Notes

Relies on multiple calls to kcorrect.kcorrect.Kcorrect.absmag() method.

tofits(filename=None)[source]

Output calculated information to FITS

Parameters:

filename (str) – name of output file

Notes

Overwrites file if it already exists.

Stores HDUs:

  • DATA : single row table with: ‘nredshift’, ‘redshift_range’, ‘abcorrect’

  • REDSHIFTS : redshift grid

  • RESPONSES : array of input response names

  • RESPONSES_OUT : array of output response names

  • RESPONSES_MAP : array of response mapping

  • A : A-matrix data

  • AOUT : A-matrix output data

fromfits(filename=None)[source]

Input from FITS file

Parameters:

filename (str) – name of input file

Notes

Expects format of tofits() output.

class KcorrectSDSS(responses=['sdss_u0', 'sdss_g0', 'sdss_r0', 'sdss_i0', 'sdss_z0'], templates=None, responses_out=None, responses_map=None, redshift_range=[0.0, 2.0], nredshift=4000, abcorrect=True, cosmo=None)[source]

Bases: Kcorrect

K-correction object for SDSS data

Parameters:

  • abcorrect (bool) – correct maggies to AB (default True)

  • templates (list of kcorrect.template.SED) – templates to use (if None uses v4 default template set)

  • responses (list of str) – names of input responses to base SED on (default to SDSS ugriz)

  • responses_out (list of str) – output responses for K-corrections (default to “responses”)

  • responses_map (list of str) – input responses to use for K-corrections (default to “responses”)

  • redshift_range (list of np.float32) – minimum and maximum redshifts (default [0., 2.])

  • nredshift (int or np.int32) – number of redshifts in interpolation grid (default 4000)

  • cosmo (astropy.cosmology.FLRW-like object) – object with distmod() method (default Planck18)

abcorrect

correct maggies to AB

Type:

bool

Amatrix

interpolation function for each template and input response

Type:

scipy.interpolate.interp1d object

AmatrixOut

interpolation function for each template and output response

Type:

scipy.interpolate.interp1d object

cosmo

object with luminosity_distance() method

Type:

astropy.cosmology.FLRW-like object

imap

for each responses_map element, its corresponding index in responses

Type:

ndarray of np.int32

nredshift

number of redshifts in interpolation grid

Type:

int or np.int32

redshift_range

minimum and maximum redshifts

Type:

list of np.float32

redshifts

redshifts in grid

Type:

ndarray of np.float32

responses

[Nin] names of input responses to use

Type:

list of str

responses_map

[Nout] input responses to use for K-corrections

Type:

list of str

responses_out

[Nout] output responses for K-corrections

Type:

list of str

templates

templates to use

Type:

kcorrect.template.Template object

Notes

The ‘responses’ input defaults to [‘sdss_u0’, ‘sdss_g0’, ‘sdss_r0’, ‘sdss_i0’, ‘sdss_z0’]

This class provides the method fit_coeffs_asinh() to use SDSS-style asinh magnitudes (these are the magnitudes that the SDSS imaging reports).

If abcorrect is True, the to_ab() method is applied to the maggies input for absmag() and fit_coeffs() and fit_coeffs_asinh(), which adjusts from the SDSS system to the AB system.

to_ab(maggies=None, ivar=None)[source]

Convert input maggies to AB

Parameters:

  • maggies (ndarray of np.float32) – array of fluxes in standard SDSS system

  • ivar (ndarray of np.float32) – inverse variances in standard SDSS system (optional)

Returns:

  • ab_maggies (ndarray of np.float32) – array of fluxes converted to AB

  • ab_ivar (ndarray of np.float32) – inverse variances converted to AB (if ivar input)

Notes

Calls kcorrect.utils.sdss_ab_correct(), which does the following:

Uses the AB conversions produced by D. Eisenstein, in his message sdss-calib/1152

u(AB,2.5m) = u(database, 2.5m) - 0.036
g(AB,2.5m) = g(database, 2.5m) + 0.012
r(AB,2.5m) = r(database, 2.5m) + 0.010
i(AB,2.5m) = i(database, 2.5m) + 0.028
z(AB,2.5m) = z(database, 2.5m) + 0.040

fit_coeffs() and absmag() call this on their inputs if abcorrect is True.

fit_coeffs_asinh(redshift=None, mag=None, mag_err=None, extinction=None)[source]

Fit coefficients to asinh mags

Parameters:

  • redshift (np.float32 or ndarray of np.float32) – [N] or scalar redshift(s)

  • mag (ndarray of np.float32) – [N, 5] or [5] asinh magnitudes of each SDSS band

  • mag_err (ndarray of np.float32) – [N, 5] or [5] inverse variance of each band

  • extinction (ndarray of np.float32) – [N, 5] or [5] Galactic extinction in each band

Returns:

coeffs – coefficients for each template

Return type:

ndarray of np.float32

Notes

Converts mag, mag_err, and extinction to extinction-corrected maggies and ivar, and then (if abcorrect is True) calls to_ab() method to create AB maggies and ivar.

If redshift is an array, even with just one element, coeffs is returned as an [nredshift, ntemplate] array.

Otherwise coeffs is returned as an [ntemplate] array.

class KcorrectGST(responses=['galex_FUV', 'galex_NUV', 'sdss_u0', 'sdss_g0', 'sdss_r0', 'sdss_i0', 'sdss_z0', 'twomass_J', 'twomass_H', 'twomass_Ks'], templates=None, responses_out=None, responses_map=None, redshift_range=[0.0, 2.0], nredshift=4000, abcorrect=False, cosmo=None)[source]

Bases: Kcorrect

K-correction object for GALEX, SDSS, 2MASS data

Parameters:

  • abcorrect (bool) – correct maggies to AB (default True)

  • templates (list of kcorrect.template.SED) – templates to use (if None uses v4 default template set)

  • responses (list of str) – names of input responses to base SED on (default to FNugrizJHK)

  • responses_out (list of str) – output responses for K-corrections (default to “responses”)

  • responses_map (list of str) – input responses to use for K-corrections (default to “responses”)

  • redshift_range (list of np.float32) – minimum and maximum redshifts (default [0., 2.])

  • nredshift (int or np.int32) – number of redshifts in interpolation grid (default 4000)

  • cosmo (astropy.cosmology.FLRW-like object) – object with distmod() method (default Planck18)

abcorrect

correct maggies to AB

Type:

bool

Amatrix

interpolation function for each template and input response

Type:

scipy.interpolate.interp1d object

AmatrixOut

interpolation function for each template and output response

Type:

scipy.interpolate.interp1d object

cosmo

object with luminosity_distance() method

Type:

astropy.cosmology.FLRW-like object

imap

for each responses_map element, its corresponding index in responses

Type:

ndarray of np.int32

nredshift

number of redshifts in interpolation grid

Type:

int or np.int32

redshift_range

minimum and maximum redshifts

Type:

list of np.float32

redshifts

redshifts in grid

Type:

ndarray of np.float32

responses

[Nin] names of input responses to use

Type:

list of str

responses_map

[Nout] input responses to use for K-corrections

Type:

list of str

responses_out

[Nout] output responses for K-corrections

Type:

list of str

templates

templates to use

Type:

kcorrect.template.Template object

Notes

The ‘responses’ input defaults to [‘galex_FUV’, ‘galex_NUV’, ‘sdss_u0’, ‘sdss_g0’, ‘sdss_r0’, ‘sdss_i0’, ‘sdss_z0’, ‘twomass_J’, ‘twomass_H’, ‘twomass_Ks’]

abcorrect is by default False and the input maggies are assumed to be AB. If abcorrect is set to True, the to_ab() method is applied to the maggies input for absmag() and fit_coeffs() and fit_coeffs_asinh(), which adjusts from the SDSS system to the AB system. However, there is no change applied to the 2MASS or or GALEX inputs.

to_ab(maggies=None, ivar=None)[source]

Convert FNugrizJHK input maggies to AB

Parameters:

  • maggies (ndarray of np.float32) – array of fluxes in standard SDSS system

  • ivar (ndarray of np.float32) – inverse variances in standard SDSS system (optional)

Returns:

  • ab_maggies (ndarray of np.float32) – array of fluxes converted to AB

  • ab_ivar (ndarray of np.float32) – inverse variances converted to AB (if ivar input)

Notes

Leaves FN and JHK alone, and fixes ugriz with kcorrect.utils.sdss_ab_correct(), which does the following:

Uses the AB conversions produced by D. Eisenstein, in his message sdss-calib/1152

u(AB,2.5m) = u(database, 2.5m) - 0.036
g(AB,2.5m) = g(database, 2.5m) + 0.012
r(AB,2.5m) = r(database, 2.5m) + 0.010
i(AB,2.5m) = i(database, 2.5m) + 0.028
z(AB,2.5m) = z(database, 2.5m) + 0.040

fit_coeffs() and absmag() call this on their inputs if abcorrect is True.