Simulation data

Introduction

The simulations process consists of modeling the sky using pre-Planck data, and then simulating the observations of that sky (actually those skies because they are simulated at many frequencies) using a model of the instruments and following the Planck scanning strategy. The first part is done by the Planck Sky Model (henceforth PSM), and the second part by the FFP6 (TBD- I guess this is the product, not the simulator) . A brief description of these is given below.

The Planck Sky Model

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The Planck Sky Model, a complete set data and code to simulate sky emission at millimeter-wave frequencies, is described in detail in the pre-launch PSM paper (Delabrouille et al., arXiv/1207.3675).

The main simulations used to test and validate the Planck data anaysis pipelines (and, in particular, component separation) makes use of simulations generated with version 1.7.7 of the PSM software. Sky emission comprises the following components: CMB, thermal dust, spinning dust, synchrotron, CO lines, free-free, thermal Sunyaev-Zel'dovich (SZ) effect (with first order relativistic corrections), kinetic SZ effect, radio and infrared sources, Cosmic Infrared Background (CIB).

The CMB is a based on adiabatic initial perturbations, with the following cosmological parameters:

• T_CMB = 2.725
• H = 0.684
• OMEGA_M = 0.292
• OMEGA_B = 0.04724
• OMEGA_NU = 0
• OMEGA_K = 0
• SIGMA_8 = 0.789
• N_S = 0.9732
• N_S_RUNNING = 0
• N_T = 0
• R = 0.0844
• TAU_REION = 0.085
• HE_FRACTION = 0.245
• N_MASSLESS_NU = 3.04
• N_MASSIVE_NU = 0
• W_DARK_ENERGY = -1
• K_PIVOT = 0.002
• SCALAR_AMPLITUDE = 2.441e-9

All other parameters are set to the default standard of the Jan 2012 version of CAMB. In addition, this simulated CMB contains non-gaussian corrections of the local type, with an f_NL parameter of 20.4075.

The Galactic ISM emission comprises 5 major components: Thermal dust, spinning dust, synchrotron, CO lines, and free-free emission. We refer the reader to the PSM publication for details. For the simulations generated here, however, the thermal dust model has been modified in the following way: Instead of being based on the 100 micron map of Schlegel, Finkbeiner and Davis (SFD; 1998), the dust template uses an internal release of the 857 GHz Planck observed map itself, in which point sources have been subtracted, and which has been locally filtered to remove CIB fluctuations in the regions of lowest column density. A caveat is that while this reduces the level of CIB fluctuations in the dust map in some of the regions, in regions of moderate dust column density the CIB contamination is actually larger than in the SFD map.

The other emissions of the galactic ISM are simulated using the prescription descibed in the PSM paper. Synchrotron, Free-free and spinning dust emission are based on WMAP observations, as analysed by Miville-Deschenes et al., 2008. Small scale fluctuations have been added to increase the variance on small scales and compensate the lower resolution of WMAP as compared to Planck (in particular HFI channels). The main limitation of these maps is the presence at high galactic latitude of fluctuations that may be imputable to WMAP noise. The presence of noise and of added Gaussian fluctuations on small scales may result in a few ocassional pixels being negative (e.g. in the spinning dust maps). Low frequency foreground maps are also contaminated by some residuals of bright radio sources that have not been properly subtracted from the templates of diffuse emission.

The CO maps are simulated using the CO J=1-0 observations of Dame et al. (2001). The main limitations are limited sky coverage, lower resolution than that of Planck high frequency channels, line ratios (J=2-1)/(J=1-0) and (J=3-2)/(J=2-1) constant over the sky. The CO in the simulation is limited to the three lowest 12CO lines.

Galaxy clusters are generated on the basis of cluster number counts, following the Tinker et al. (2008) mass function, for the cosmological parameters listed above. Clusters are assumed perfectly spherical, isothermal, and are modelled using the universal pressure profile of Arnaud et al. (2010). Relativistic corrections following Itoh et al. (1998) are included to first order. The simulated kinetic SZ effect assumes no bulk flow, and a redshift-dependent average cluster velocity compatible with the linear growth of structures.

Point sources comprise radio sources (based on extrapolations across frequencies of radio observations between 800 MHz and 5 GHz) and infrared sources (based on extrapolations in frequencies of IRAS sources). One small caveat that should be mentioned is that because of the un-evenness of the radio source surveys, the equatorial southern part of the sky has less faint radio sources than the northern part. Although all the missing sources are well below the Planck detaction level, this induces a small variation of the total emission background over the sky. Check the individual faint point source emission maps if this is a potential problem for your applications. See also the PSM publication for details about the PSM point source simulations.

Finally, the far infrared background due to high redshift galaxies has been simulated using a procedure is based on the distribution of galaxies in shells of density contrast at various redshifts (Castex et al., PhD thesis; paper in preparation). This simulation has been modified by gradually substituting an uncorrelated extra term of CIB emission at low frequencies, artifically added in particular to decorrelate the CIB at frequencies below 217 GHz from the CIB above that frequency, to mimick the apparent decorrelation observed in the Planck Early Paper on CIB power spectrum.

While the PSM simulations described here provide a reasonably representative multicomponent model of sky emission, the users are warned that it has been put together mostly on the basis of data se†s and knowledge pre-existing the Planck observations themselves. While it is sophisticated enough to include variations of emisison laws of major components of ISM emission, different emission laws for most sources, and a reasonably coherent global picture, it is not (and is not supposed to be) identical to the real sky emission. The users are warned to use these simulations with caution.

The Planck simulator a better name is welcome

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TBW by J. Borril

Products delivered

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What follows is the plan for the sims to be delivered as of mid Jan 2013. The text below is to be replaced by the description of the products described (AMo - 7/3/13)

Modelled sky (PSM outputs)

Full channel / nominal mission sky maps, Temperature only, in 9 Planck bands, of 10 components: cmb (lensed), CO, FIRB, free-free, synchrotron, thermal dust, spinning dust, kinetic SZ, thermal SZ, point sources

==> 10x9 maps for all components except CO) + 6 CO maps (present at freq > 100 GHz only) for a total of 96 maps which are to be grouped by frequency (as SkyMap products, into 10 FITS files, one for each component, names like COM_PSMMap-{component)_Nside_Relname.fits

Observed sky

A nominal mission map for each of the following

• a total map, i.e., sum of all components + noise
• a foregrounds map, i.e., sum of all components except cmb, including noise
• a point sources map, with the point sources alone
• the noise maps, with the noise alone

==> for a total of 36 maps grouped into 4 FITS files. Names like COM_SimMap-{total | foregrounds | sources | noise)_Nside_Relname.fits