Summary of Models

This page contains high-level description of the models available within the mapsims package, this models are specific to the Simons Observatory, more general PySM models are instead available in the so_pysm_models package, see the documentation about those models.

Model templates

Model templates or more in general model data are stored on the Simons Observatory project pages at NERSC in the folder:

/global/cfs/cdirs/sobs/www/so_mapsims_data

Which is then made publicly available via web at https://portal.nersc.gov/project/sobs/so_mapsims_data

For example all the available hitmaps are available there. In order to copy data at that location:

  • run collabsu sobs (you need permissions by the allocation PI)

  • copy data there

  • run bash update_html_list.sh in the /global/cfs/cdirs/sobs/www/so_mapsims_data folder, this creates the html pages that list the files and also fixes permissions.

Noise power spectra and hitmaps

The SONoiseSimulator class provides a wrapper to call so_noise_models to simulate power spectra of the noise taking into account the expected performance of the whole experiment. The noise simulator accepts a number of parameters to configure the simulation, see the documentation in the so_noise_models repository.

It also includes simulated relative hitmaps simulated in time domain with TOAST. We currently have 1 hitmap per tube and they are the first split of the MSS-0001 Mission Scale simulation (~18 days of data), see the wiki (restricted to members of Simons Observatory) for more documentation.

As an example:

>>> from mapsims import noise
>>> import healpy as hp
>>> noise_sim = noise.SONoiseSimulator(nside=128)
>>> hp.mollview(noise_sim.get_hitmaps("ST0")[0][0], title="Relative hitmap")
>>> noise_maps = noise_sim.simulate(tube="ST0")
>>> hp.mollview(noise_maps[0][0][1], min=-10, max=10, unit="uK_CMB", title="Q noise map ST0")

Cosmic Microwave Background simulations

The so_pysm_models package provides a generic so_pysm_models.PrecomputedAlms PySM component that can load a set of \(a_{\ell m}\) coefficients and generate a map at the requested \(N_{side}\).

mapsims has 2 classes that derive from PrecomputedAlms:

  • the class SOPrecomputedCMB provides a specific naming convention tailored to the Simons Observatory simulations that are already available

  • the class SOStandalonePrecomputedCMB is useful to simulate CMB only maps, in this case it is wasteful to use PySM because it first creates a map and then performs other 2 spherical harmonics transforms to apply the beam smoothing. This class instead keeps the input in spherical harmonics domain, first applies the beam and then returns a map. The SOStandalonePrecomputedCMB.simulate() method gets a Channel object and returns a map already convolved with the channel’s beam.

Available Cosmic Microwave Background simulations

Lensed CMB

Available at NERSC at: /global/cfs/cdirs/sobs/v4_sims/mbs/cmb

  • Input theory spectrum and parameters: The input spectra are based on a best-fit Planck cosmology. The unlensed power spectra are available at https://github.com/ACTCollaboration/actsims/blob/master/data/cosmo2017_10K_acc3_scalCls.dat. The maps are generated at \(\ell_{max}\) = 8000 but are saved only at \(\ell_{max}\) = 5100 (to save disk space).

  • The lensing (i.e. kappa or \(\phi\)) maps are Gaussian random fields obtained with the same cosmology. The lensing is done at one-arcminute resolution using the routine pixell.lensing.rand_map(). We pass separate random seeds to make the CMB and \(\phi\) maps, meaning that there is no correlation between T and \(\phi\) (or E and \(\phi\)) arising from the ISW effect (this might have an impact for people studying primordial non-Gaussianity). The input \(\phi\) \(a_{\ell m}\) are available at /global/cfs/cdirs/sobs/v4_sims/mbs/cmb/input_phi/ and can be accessed using the SOPrecomputedCMB.get_phi_alm() function.

  • The lensed power spectra, which represent the lensed maps to a very good approximation are at https://github.com/ACTCollaboration/actsims/blob/master/data/cosmo2017_10K_acc3_lensedCls.dat

  • There are no primordial B modes (and similarly no contribution from tensors to the T maps).

  • See all the cosmological parameters used in the CAMB configuration file