I used this code (before a few slight modifications to make it a stand-alone set of scripts) in Wijers & Schaye (2022; ADS link: https://ui.adsabs.harvard.edu/abs/2022MNRAS.514.5214W/abstract). Please cite this paper if you use this code (bibtex entry below). Please remember to also cite the sources for the backgrounds and response files you use.
It uses the instrument responses and instrumental + astrophysical background to calculate the minimum emission line surface brightness a source needs to reach a given signal-to-noise ratio in a given exposure time and spatial binning. Any systematic uncertainties, difficulties arising from Galactic emission or absorption features at the same energy, etc., are simply ignored in these calculations.
This code requires the following python packages:
- numpy
- scipy
- astropy
- pandas
- matplotlib
- sherpa : see https://cxc.cfa.harvard.edu/sherpa/python/ for instructions. As of writing (2023-03-02), this package works for python versions 3.8, 3.9, and 3.10. For conda installations, a specific channel needs to be used (see the website).
These can also be installed in a conda environment called 'minsb_xray' with:
conda env create -f condaenv_minsb_xray.yml
Note that this does require a somewhat up-to-date (ana)conda version: a system anaconda version 4 did not work here.
I have not put this together as a full installable package; this is just a collection of scripts best run from the directory they are in.
This code also requires models for the instrument responses and instrumental and astrophysical backgrounds. I have not included those there because the files would easily become outdated without maintenance, and the same configuration and response file might not be appropriate for every situation. (E.g., on-axis vs. off-axis, focussed vs. unfocussed, different options for in-development instruments.)
I have included a fiducial model for Galactic absorption (because I
wanted minimum intrinsic surface brightnesses for extragalactic
sources). This is a simple wabs model in Xspec, and you might need
to use a different model (or a model with a different hydrogen column
density) for your own applications.
For the paths and instrument responses, you will need to modify the
code under ##paths near the top of calc_minsb.py.
mdir is the directory where plotted images are stored.
dir_insfiles is the directory where response files and backgrounds
are stored. You will also need to modify the paths for the response
files and backgrounds for different instruments.
The Responses class handles the .arf and .rmf files; that should be
fairly straightforward. However, you will likely need to modify or add
instrument options for the InstrumentModel class. This is because
different instruments come with different background file formats,
e.g., saved in a single file or split into multiple components. Also
note that data on e.g., the opening angle over which the backgrounds
are given also differs between files. This needs to be added by hand.
The InstrumentModel class is the workhorse of the code, used to
calculate actual minimum surface brightness levels using its
getminSB_grid function. (The 'grid' refers to the fact that it can
take an array of line energies as input.)
getminSB_grid requires
- the line energies (rest-frame) and redshift,
- line width,
- signal-to-noise level (number of sigmas) required for detection,
- exposure time x spatial binning area,
- spectral range over which to measure the signal and the noise, and
- whether to include Galactic absorption in the minimum surface brightness to calculate the minimum surface brightness values.
Depending on the spectral resolution of the instrument and expected line widths, it might be useful to experiment with different line width values.
The spectral range over which signal and noise are measured can be be
explored using the explorepars_omegat_extr function. Just modify the
extr_ranges dictionary to try out different values (integer
extraction ranges specify a number of channels), and possibly different
instruments. Note that delta_E_chan (the channel widths in eV) is
simply used to report the size of the extraction range in eV.
I used savetable_sbmin to calculate the set of minimum surface
brightnesses used in Wijers & Schaye (2022). This can be modified to
calculate a different set of minima.
Please remember to also cite the sources for the backgrounds and response files you use. Some sources are only needed if you use the included line wavelength lists, Galactic absorption model, or plots.
Wijers & Schaye (2022): paper describing the calculations and applying calculated minimum observable surface brightnesses to investigate detectability of emission lines from galaxy haloes.
@ARTICLE{2022MNRAS.514.5214W,
author = {{Wijers}, Nastasha A. and {Schaye}, Joop},
title = "{The warm-hot circumgalactic medium around EAGLE-simulation galaxies and its detection prospects with X-ray-line emission}",
journal = {\mnras},
keywords = {galaxies: formation, galaxies: groups: general, galaxies: haloes, large-scale structure of Universe, X-rays: galaxies, Astrophysics - Astrophysics of Galaxies, Astrophysics - Cosmology and Nongalactic Astrophysics},
year = 2022,
month = aug,
volume = {514},
number = {4},
pages = {5214-5237},
doi = {10.1093/mnras/stac1580},
archivePrefix = {arXiv},
eprint = {2108.04847},
primaryClass = {astro-ph.GA},
adsurl = {https://ui.adsabs.harvard.edu/abs/2022MNRAS.514.5214W},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
If you used the included wabs absorption model, please cite:
for the wabs model (in xspec): Morrison & McCammon (1983; ADS link:
https://ui.adsabs.harvard.edu/abs/1983ApJ...270..119M/abstract)
@ARTICLE{1983ApJ...270..119M,
author = {{Morrison}, R. and {McCammon}, D.},
title = "{Interstellar photoelectric absorption cross sections, 0.03-10 keV.}",
journal = {\apj},
keywords = {Absorption Cross Sections, Cosmic Dust, Interstellar Chemistry, Interstellar Matter, X Ray Astronomy, Abundance, Electrophotometry, Ionization, Molecules, Astrophysics},
year = 1983,
month = jul,
volume = {270},
pages = {119-122},
doi = {10.1086/161102},
adsurl = {https://ui.adsabs.harvard.edu/abs/1983ApJ...270..119M},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
for the specific parameter value for the hydrogen column density: McCammon et al. (2002; ADS link: https://ui.adsabs.harvard.edu/abs/2002ApJ...576..188M/abstract), used for the Athena X-IFU background model
@ARTICLE{2002ApJ...576..188M,
author = {{McCammon}, D. and {Almy}, R. and {Apodaca}, E. and {Bergmann Tiest}, W. and {Cui}, W. and {Deiker}, S. and {Galeazzi}, M. and {Juda}, M. and {Lesser}, A. and {Mihara}, T. and {Morgenthaler}, J.~P. and {Sanders}, W.~T. and {Zhang}, J. and {Figueroa-Feliciano}, E. and {Kelley}, R.~L. and {Moseley}, S.~H. and {Mushotzky}, R.~F. and {Porter}, F.~S. and {Stahle}, C.~K. and {Szymkowiak}, A.~E.},
title = "{A High Spectral Resolution Observation of the Soft X-Ray Diffuse Background with Thermal Detectors}",
journal = {\apj},
keywords = {Instrumentation: Detectors, Instrumentation: Spectrographs- Galaxies: Intergalactic Medium, Space Vehicles: Instruments, X-Rays: Diffuse Background, X-Rays: ISM, Astrophysics},
year = 2002,
month = sep,
volume = {576},
number = {1},
pages = {188-203},
doi = {10.1086/341727},
archivePrefix = {arXiv},
eprint = {astro-ph/0205012},
primaryClass = {astro-ph},
adsurl = {https://ui.adsabs.harvard.edu/abs/2002ApJ...576..188M},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
For the line energies in the line_eng_ion dictionary near the top of
calc_minsb.py: CLOUDY v7.02, Ferland et al. (1998; ADS link:
https://ui.adsabs.harvard.edu/abs/1998PASP..110..761F/abstract)
@ARTICLE{1998PASP..110..761F,
author = {{Ferland}, G.~J. and {Korista}, K.~T. and {Verner}, D.~A. and {Ferguson}, J.~W. and {Kingdon}, J.~B. and {Verner}, E.~M.},
title = "{CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra}",
journal = {\pasp},
year = 1998,
month = jul,
volume = {110},
number = {749},
pages = {761-778},
doi = {10.1086/316190},
adsurl = {https://ui.adsabs.harvard.edu/abs/1998PASP..110..761F},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
For the line selection in the line_eng_ion dictionary near the top of
calc_minsb.py: Bertone et al. (2010;
ADS: https://ui.adsabs.harvard.edu/abs/2010MNRAS.407..544B/abstract)
@ARTICLE{2010MNRAS.407..544B,
author = {{Bertone}, Serena and {Schaye}, Joop and {Dalla Vecchia}, Claudio and {Booth}, C.~M. and {Theuns}, Tom and {Wiersma}, Robert P.~C.},
title = "{Metal-line emission from the warm-hot intergalactic medium - I. Soft X-rays}",
journal = {\mnras},
keywords = {radiation mechanisms: thermal, methods: numerical, galaxies: formation, intergalactic medium, cosmology: theory, diffuse radiation, Astrophysics - Cosmology and Nongalactic Astrophysics},
year = 2010,
month = sep,
volume = {407},
number = {1},
pages = {544-566},
doi = {10.1111/j.1365-2966.2010.16932.x},
archivePrefix = {arXiv},
eprint = {0910.5723},
primaryClass = {astro-ph.CO},
adsurl = {https://ui.adsabs.harvard.edu/abs/2010MNRAS.407..544B},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
For the Fe L-shell line energies in savetable_sbmin in calc_minsb.py:
CLOUDY v17.01, Ferland et al. (2017; ADS link:
https://ui.adsabs.harvard.edu/abs/2017RMxAA..53..385F/abstract)
@ARTICLE{2017RMxAA..53..385F,
author = {{Ferland}, G.~J. and {Chatzikos}, M. and {Guzm{\'a}n}, F. and {Lykins}, M.~L. and {van Hoof}, P.~A.~M. and {Williams}, R.~J.~R. and {Abel}, N.~P. and {Badnell}, N.~R. and {Keenan}, F.~P. and {Porter}, R.~L. and {Stancil}, P.~C.},
title = "{The 2017 Release Cloudy}",
journal = {\rmxaa},
keywords = {atomic processes, galaxies: active, methods: numerical, molecular processes, radiation mechanisms: general, Astrophysics - Astrophysics of Galaxies},
year = 2017,
month = oct,
volume = {53},
pages = {385-438},
doi = {10.48550/arXiv.1705.10877},
archivePrefix = {arXiv},
eprint = {1705.10877},
primaryClass = {astro-ph.GA},
adsurl = {https://ui.adsabs.harvard.edu/abs/2017RMxAA..53..385F},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
For the selection of those Fe L-shell lines: Ploeckinger & Schaye (2020; ADS: https://ui.adsabs.harvard.edu/abs/2020MNRAS.497.4857P/abstract)
@ARTICLE{2020MNRAS.497.4857P,
author = {{Ploeckinger}, Sylvia and {Schaye}, Joop},
title = "{Radiative cooling rates, ion fractions, molecule abundances, and line emissivities including self-shielding and both local and metagalactic radiation fields}",
journal = {\mnras},
keywords = {radiative transfer, ISM: general, intergalactic medium, galaxies: ISM, Astrophysics - Astrophysics of Galaxies},
year = 2020,
month = oct,
volume = {497},
number = {4},
pages = {4857-4883},
doi = {10.1093/mnras/staa2172},
archivePrefix = {arXiv},
eprint = {2006.14322},
primaryClass = {astro-ph.GA},
adsurl = {https://ui.adsabs.harvard.edu/abs/2020MNRAS.497.4857P},
adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}
If you used the plotting routines, please acknowledge Paul Tol, who put together the colorblind-friendly color schemes. See https://personal.sron.nl/~pault/ for background information and best usage of the schemes.