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Inaf OAR (Osservatorio Astronomico di Roma sede di Monte Porzio Catone)
LBC-Team (Large Binocular Camera Team)
HomePage: http://lbc.oa-roma.inaf.it
E-mails: fontana@oa-roma.inaf.it, grazian@oa-roma.inaf.it, gallozzi@oa-roma.inaf.it
LBC PHOTOMETRIC REDSHIFT CALCULATOR
Program Description
This document deals with the formulas of the Photometric Redshift Calculator
(ZPHOT) for LBC.
This tool enable the user to create a simulated photometric catalog of galaxies at various redshifts, with a high flexibility in defining the filters adopted and the S/N in each band.
This tool is primarily designed to compare the accuracy and efficiency of photo-z for different filter sets, adopting a standard recipe for photo-z.
It is to be emphasized that the result may be not completely realistic for two (opposite) reasons.
On the one side, with the given filter set and S/N, better results can be achived by using more tailored recipes for photo-Z, such as those using other spectral libraries or other information, such as sizes or luminosities; on the other side, the simulation is somewhat optimistic since the input spectra for galaxies have benn optained with spectral libraries, and hence are an incomplete representation of the complexity of real galaxy spectra.
Input catalogs may be created either by using the observed galaxies in the GOODS_S field or synthetic catalogs.
The flux of galaxies in the simulated catalog can be either normalized to a set of user-defined magnitudes (irrespective of colors and redshifts of simulated galaxies) or, in the case of GOODS_S catalog, kept to the observed level, which is useful to maintain the observed relations between redshifts, colors and magnitudes.
The output catalog can be made of an arbitrary number of filters, taken from the provided library.
For each filter, the user can specify a 1-sigma limiting magnitude for the sample.
The procedure adopted is the following: forfor each galaxy, the flux in each filter is computed and normalized according to the rules specified above. For each magnitude, the associated error is computed adopting a standard scaling of the S/N, computed from the 1-sigma magnitude limit.
Each flux is then perturbed with the corresponding noise, ...
This tool uses as input galaxies.
Input parameters
| Parameter | Var_Name | Type | Description |
| Input Catalog | INP_CAT | String, fixed choise | Name of input catalogs. |
| Spectral Library | LIB | String, fixed choise | Name of input spectral library. |
| Number of Filters | NFIL | Integer | Number of filters to be used. |
| Filters | FILT1,...,FILTn | Strings | Names of filters to be used. |
| Magnitude Limits | MLIM1,...,MLIMn | Float | Magnitude limit of the simulated sample. |
| Selection Magnitude | IREF | Integer | Column corresponding to the selection magnitude of the sample, used for flux normalization of the catalog. |
| Normalization Magnitudes | MREF | Float | Value(s) of the selection magnitudes, used to normalize the catalog. |
| Number of Iterations | NSIM | Integer | Each galaxy is inserted NSIM time in the output catalog, each time with a different noise. |
| Random Seed | IRAN | Integer (optional) | Random seed for noise computation. |
Interface Description
The ZPHOT is organized in three panels:
The main upper panel summarizes the input parameters, which should be necessary filled by the common user.
The second lower (left) panel operates with the Filter List.
The third lower (right) panel operates with the filter selected table to be considered.
Filters List
All filters available for this calculation are located in the Filters directory, with associate png image, to take a look.
Here is a sample of the U_LBCblue Filter:
Screnshots
One can start adding a filter to the filters list, simply pressing the "+" image.
As one can see the filter list is updated and it is possible to add other filters to the list.
It is also possible to delete the filter from the filters list pressing the "-" image.
If one wants to view a filter before to add/delete it he can press the view icon on the upper left of the filter name.
The final step is to insert the catalog list and the spectral library, then press the "calculate" button.
The output is retrieving in the output page.
download ZPHOT_help.ps
download ZPHOT_help.pdf
download ZPHOT_help.tex
gallozzi@oa-roma.inaf.it
2003-10-23
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