Petrosian

class petrofit.petrosian.Petrosian(r_list, area_list, flux_list, area_err=None, flux_err=None, eta=0.2, epsilon=2.0, epsilon_fraction=0.99, total_flux_fraction=0.99, verbose=False, interp_kind='cubic', interp_num=5000)[source]

Bases: object

Class that computes and plots Petrosian properties.

Petrosian properties.

Parameters:

r_listnumpy.array: Array of radii in pixels.
area_listnumpy.array: Array of aperture areas.
flux_listnumpy.array: Array of photometric flux values.
area_errnumpy.array: Array of errors in the aperture areas. If None and flux_err is provided, errors are calculated with area_err set to zero.
flux_errnumpy.array: Array of errors in the flux values. If None and area_err is provided, errors are calculated with flux_err is set to zero.
etafloat, default=0.2: Eta is the petrosian value which defines the r_petrosian.
epsilonfloat: Epsilon value (used to determine r_total_flux). N.B: r_total_flux = r_petrosian * epsilon
epsilon_fraction: float, default=0.99: Fraction of total flux recovered by r_petrosian * epsilon.
total_flux_fractionfloat, default=0.99: Fraction of Sersic flux that defines the Petrosian total flux. Sersic total flux is the flux at infinity, thus a smaller fraction must be used to define the total flux when analysing images. total_flux_fraction can also be adjusted if the image has low signal-to-noise or if the profile extends too far out (for example profiles with high Sersic indices).
verbosebool: Prints info
interp_kindstr or int, optional: Specifies the kind of interpolation used on the curve of growth (i.e r_list vs flux_list)
interp_numint: Number of interpolation function sampling radii.

Attributes Summary

`area_err`
`area_list`
`c2080`	`c2080 = 5 * np.log10(r_80 / r_20)`
`c5090`	`c5090 = 5 * np.log10(r_90 / r_50)`
`epsilon`	Epsilon value (used to determine `r_total_flux`).
`epsilon_fraction`	Fraction of total flux recovered by `epsilon`
`eta`	Eta is the Petrosian value which defines the `r_petrosian`
`flux_err`
`flux_list`
`half_flux`	Returns the flux at `r_half_flux` or np.nan if out of range
`half_flux_err`	Returns the photometric uncertainty at `r_half_flux` or np.nan if out of range.
`r_50`
`r_50_err`
`r_epsilon`	r_epsilon = r_petrosian * epsilon
`r_epsilon_in_range`	True if `r_epsilon` is in input radii list
`r_half_light`	R_e or Radius containing half of the total Petrosian flux
`r_half_light_err`	Error estimate on r_e
`r_list`
`r_petrosian`	The Petrosian radius is defined as the radius at which the Petrosian profile equals eta.
`r_petrosian_err`	Estimated 1-sigma r_petrosian Error.
`r_total_flux`	The radius containing the total flux
`r_total_flux_err`	The radius containing the total flux
`total_flux`	Returns the flux at `r_total_flux` or np.nan if out of range
`total_flux_err`	Returns the photometric uncertainty at `r_total_flux` or np.nan if out of range.
`total_flux_fraction`	Fraction of Sersic flux that defines the Petrosian total flux.

Methods Summary

`concentration_index`([fraction_1, fraction_2])	Calculates Petrosian concentration index.
`fraction_flux_to_r`([fraction])	Given a fraction, compute the radius containing that fraction of the Petrosian total flux
`fraction_flux_to_r_err`([fraction])	Given a fraction, compute the radius containing that fraction of the Petrosian total flux
`imshow`([position, elong, theta, color, lw])	Make 2D plots of elliptical apertures with radii of `r_half_light`, `r_total_flux`, `r_20` and `r_80`.
`plot`([plot_r, title, radius_unit, ax, ...])	Plots the Petrosian profile.
`plot_cog`([plot_r, title, radius_unit, ...])	Plots the Curve of Growth (COG) for the Petrosian profile.
`r_half_light_arcsec`(wcs)	Given a wcs, compute the radius containing half of the total Petrosian flux in arcsec.
`r_total_flux_arcsec`(wcs)	Given a wcs, compute the radius containing the total Petrosian flux in arcsec.

Attributes Documentation

area_err

area_list

c2080: c2080 = 5 * np.log10(r_80 / r_20)

c5090: c5090 = 5 * np.log10(r_90 / r_50)

epsilon: Epsilon value (used to determine r_total_flux). N.B: r_total_flux = r_petrosian * epsilon

epsilon_fraction: Fraction of total flux recovered by epsilon

eta: Eta is the Petrosian value which defines the r_petrosian

flux_err

flux_list

half_flux: Returns the flux at r_half_flux or np.nan if out of range

half_flux_err: Returns the photometric uncertainty at r_half_flux or np.nan if out of range. Note that this includes errors in estimating r_half_flux.

r_50

r_50_err

r_epsilon: r_epsilon = r_petrosian * epsilon

r_epsilon_in_range: True if r_epsilon is in input radii list

r_half_light: R_e or Radius containing half of the total Petrosian flux

r_half_light_err: Error estimate on r_e

r_list

r_petrosian: The Petrosian radius is defined as the radius at which the Petrosian profile equals eta.

r_petrosian_err: Estimated 1-sigma r_petrosian Error.

r_total_flux: The radius containing the total flux

r_total_flux_err: The radius containing the total flux

total_flux: Returns the flux at r_total_flux or np.nan if out of range

total_flux_err: Returns the photometric uncertainty at r_total_flux or np.nan if out of range. Note that this includes errors in estimating r_total_flux.

total_flux_fraction: Fraction of Sersic flux that defines the Petrosian total flux. Sersic total flux is the flux at infinity, thus a smaller fraction must be used to define the total flux when analysing images. total_flux_fraction can also be adjusted if the image has low signal-to-noise or if the profile extends too far out (for example profiles with high Sersic indices).

Methods Documentation

concentration_index(fraction_1=0.2, fraction_2=0.8)[source]

Calculates Petrosian concentration index.

concentration_index = C_1_2 = 5 * np.log10( r(fraction_2) / r(fraction_1) )

Parameters:

fraction_1float: Fraction of total light enclosed by the radius in the denominator.
fraction_2float: Fraction of total light enclosed by the radius in the numerator.

Returns:

r_fraction_1, r_fraction_2, concentration_index

r_fraction_1float or np.nan
Radius containing fraction_1 of the total flux.
r_fraction_2: float or np.nan
Radius containing fraction_2 of the total flux.
concentration_indexfloat or np.nan
Concentration index

fraction_flux_to_r(fraction=0.5)[source]: Given a fraction, compute the radius containing that fraction of the Petrosian total flux

fraction_flux_to_r_err(fraction=0.5)[source]: Given a fraction, compute the radius containing that fraction of the Petrosian total flux

imshow(position=(0, 0), elong=1.0, theta=0.0, color=None, lw=None)[source]

Make 2D plots of elliptical apertures with radii of r_half_light, r_total_flux, r_20 and r_80.

Parameters:

positiontuple: (x, y) center of the apertures.
elongfloat: Elongation of the aperture.
thetafloat: The orientation of the aperture in rad.
colorstr: Color override that will change the color of the apertures in the plot.
lwfloat: Line width (thickness) of the plotted apertures.

plot(plot_r=True, title='Petrosian Profile', radius_unit='pix', ax=None, color='tab:blue', err_alpha=0.2, err_capsize=3, show_legend=True, legend_fontsize=None, ax_fontsize=None, tick_fontsize=None)[source]

Plots the Petrosian profile.

Parameters:

plot_rbool, optional: If True, plots the total flux and half-light radii. Default is True.
titlestr, optional: Title for the plot. Default is ‘Petrosian Profile’.
radius_unitstr, optional: Unit for the radius. Default is ‘pix’.
axmatplotlib.axis, optional: Matplotlib axis object to plot on. If None, creates a new axis.
colorstring: Matplotlib color for profile.
err_alphafloat, optional: Transparency for the error region. Default is 0.2.
err_capsizeint, optional: Cap size for the error bars. Default is 3.
show_legendbool, optional: If True, displays the legend. Default is True.
legend_fontsizeint or float, optional: Font size for the legend. If None, uses default font size.
ax_fontsizeint or float, optional: Font size for the axis labels. If None, uses default font size.
tick_fontsizeint or float, optional: Font size for the tick labels. If None, uses default font size.

Returns:

axmatplotlib.axis: Matplotlib axis object with the plot.

plot_cog(plot_r=True, title='Curve of Growth', radius_unit='pix', flux_unit='', ax=None, color='tab:blue', err_alpha=0.2, err_capsize=3, show_legend=True, legend_fontsize=None, ax_fontsize=None, tick_fontsize=None)[source]

Plots the Curve of Growth (COG) for the Petrosian profile.

Parameters:

plot_rbool, optional: If True, plots radii of interest including Petrosian radius. Default is True.
titlestr, optional: Title for the plot. Default is ‘Curve of Growth’.
radius_unitstr, optional: Unit for the radius. Default is ‘pix’.
flux_unitstr, optional: Unit for the cumulative flux. Default is ‘’
axmatplotlib.axis, optional: Matplotlib axis object to plot on. If None, creates a new axis.
colorstring: Matplotlib color for profile.
err_alphafloat, optional: Transparency for the error region. Default is 0.2.
err_capsizeint, optional: Cap size for the error bars. Default is 3.
show_legendbool, optional: If True, displays the legend. Default is True.
legend_fontsizeint or float, optional: Font size for the legend. If None, uses default font size.
ax_fontsizeint or float, optional: Font size for the axis labels. If None, uses default font size.
tick_fontsizeint or float, optional: Font size for the tick labels. If None, uses default font size.

Returns:

axmatplotlib.axis: Matplotlib axis object with the plot.

r_half_light_arcsec(wcs)[source]: Given a wcs, compute the radius containing half of the total Petrosian flux in arcsec.

r_total_flux_arcsec(wcs)[source]: Given a wcs, compute the radius containing the total Petrosian flux in arcsec.