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I have a template spectral energy distribution (SED) at z=0. I want to shift the template SED to an arbitrary redshift (z>0), how to do this in python?

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    $\begingroup$ What have you tried so far? Why do you want to do this? You must show a little background search and context. Please take the astronomy.stackexchange.com/tour $\endgroup$ – J. Chomel May 14 '18 at 9:01
  • $\begingroup$ I have created spectra of simulated galaxy using library from Bruzual & Charlot 2003. I tried to create mock observation (eg AB magnitude in several bands) so I need to redshift my template spectra before applying filter response. I did shift it using (1+z)*wavelength but I did not change the flux (literally just shift the spectrum along the wavelength), and I got wrong result compared to more established sed code. $\endgroup$ – Dian Puspita Triani May 18 '18 at 1:34
  • $\begingroup$ Most template fitting codes do exactly this, and provide what you are looking for as an intermediate result. Have you looked into Le Phare (Ilbert 2009) or Phosphoros (ui.adsabs.harvard.edu/abs/2017IAUS..325...73D/abstract)? $\endgroup$ – usernumber Jan 15 at 13:01
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$\lambda_{rest} \times (1 + z) = \lambda_{obs}$

where $\lambda_{rest}$ is your restframe wavelength template.

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  • $\begingroup$ This is not enough. Since photons are spread out in wavelength, the flux density decreases by (1+z). For broadband photometry, that means that the flux decreases, but if your flux is line-dominated, the SED stays more or less the same. $\endgroup$ – pela May 15 '18 at 20:30
  • $\begingroup$ The question asked about shifting the restframe wavelength from the template, so the relationship is as stated. Calibrating flux is a different story. At least, that is what I have been done in my research. I would love to hear different approaches though. $\endgroup$ – Kornpob Bhirombhakdi May 16 '18 at 11:52
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    $\begingroup$ I can explain further in an answer, but I think J. Chomel is right: the OP should first explain what she tried. $\endgroup$ – pela May 16 '18 at 21:14
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    $\begingroup$ I guess the person might try ti fit the template with observation. In that case, you shift with the known redshift, and let scale parameter as a fitting parameter. Therefore, you do not need to know flux/mad system. Anyway, again, flux/mag system seems irrelevant in this question to me. So, why don't we just wait if there will be more info? $\endgroup$ – Kornpob Bhirombhakdi May 17 '18 at 14:38
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    $\begingroup$ Sounds like a good idea :) $\endgroup$ – pela May 19 '18 at 16:44

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