Welcome to Max' Foreground Center

Shop here for models, data and fortran code

Figure 7: The colored regions show the frequencies and angular scales where different foregrounds dominate over the microwave bacground fluctuations that we are trying to measure. The different panels are for our three scenarios and various polarization types.

What's a foreground?

The cosmic microwave background (CMB) is a goldmine of cosmological information, and has the potential to answer important questions about the origin and fate of the Universe. Exciting experiments are currently measuring it with increasing accuracy. The potential party-pooper is foregrounds, contamination of the pristine cosmological signal by microwave-emitting junk, for instance dust, free-free and synchrotron radiation from our galaxy and extragalactic objects. This page contains a detailed model of such foregrounds, described in the paper astro-ph/9905257 by Max Tegmark, Daniel Eisenstein, Wayne Hu and Angelica de Oliveira-Costa. This monstrously long paper also describes a method for removing foregrounds and computes the accuracy to which cosmolological parameters should be measurable in the end. Please click here to get the 660K compressed postscript file with the paper. To download a color postscript file with the figure above, just click on it. Click here if you are interested in other research of mine.

Stuff to download

The whole package in a single gzipped tar file (recommended if you're un a unix machine)
The fortran code foregmodel.f and the include files foreg_common.f, chan_common.f, cmb_common.f & physics_common.f
Foreground specification files for the optimistic, middle-of-the-road and pessimistic scenarios. The meaning of the parameters is explained in the paper. These three files give the models of our table 2, but you can of course change the numbers as you find appropriate before feeding the file to our software.
Experimental specification files for Boomerang, MAP and Planck. The four columns give the specifications for each channel: the frequency in GHz, the angular resolution (FWHM in arcminutes), the unpolarized and polarized sensitivities (10^6 times dT/T), just as in table 1 of the paper. The first line gives the useful sky fraction, although this is in fact never used by the parts of the code you'll find here.
The CMB model used in the paper (you can compute your own with CMBfast)
The point source source count model of Toffolatti et al 1998

What it does

The software evaluates the covariance matrix between different frequencies and polarization types as a function of angular scale. It includes demo subroutines that ourput some useful special cases such as

The power spectrum C_l for each foreground
The frequency dependence of each foreground
The rms foreground contribution to each channel of an experiment
Contours in the nu-ell plane

The code includes internal point source cleaning using source count models kindly provided by Luigi Toffolatti and his collaborators. The code should be pretty self-explanatory. It simply takes three files as input: one specifying the foreground model (e.g. mid_foregmodel.dat), one specifying the experiment (e.g. planck_specs.dat) and one specifying the assumed CMB model (e.g. lcdm_Cl.dat). You'll find sample input files above. The format of the CMB model is simply the format of CMBfast output, so it's easy to generate your own.

What it doesn't do

If you're interested (please email me if you are), I can tidy up more parts of the code used for our paper and put it here. It computes cleaned power spectra, attainable accuracy on cosmological parameters, etc.

The fine print

The package is public domain, which means that you may use it freely for any purpose whatsoever.
If you find it useful, we appreciate if you include an acknowledgement in publications that make use of it.

So here it is at last - our ridiculously long paper containing only 141 figure panels:

Foregrounds and Forecasts for the Cosmic Microwave Background

Authors:

Max Tegmark, Daniel Eisenstein, Wayne Hu & Angelica de Oliveira-Costa

Abstract:

One of the main challenges facing upcoming CMB experiments will be to distinguish the cosmological signal from foreground contamination. We present a comprehensive treatment of this problem and study how foregrounds degrade the accuracy with which the Boomerang, MAP and Planck experiments can measure cosmological parameters. Our foreground model includes not only the normalization, frequency dependence and scale dependence for each physical component, but also variations in frequency dependence across the sky. When estimating how accurately cosmological parameter can be measured, we include the important complication that foreground model parameters (we use about 500) must be simultaneously measured from the data as well. Our results are quite encouraging: despite all these complications, precision measurements of most cosmological parameters are degraded by less than a factor of 2 for our main foreground model and by less than a factor of 5 in our most pessimistic scenario. Parameters measured though large-angle polarization signals suffer more degradation: up to 5 in the main model and 25 in the pessimistic case. The foregrounds that are potentially most damaging and therefore most in need of further study are vibrating dust emission and point sources, especially those in the radio frequencies. It is well-known that E and B polarization contain valuable information about reionization and gravity waves, respectively. However, the cross-correlation between polarized and unpolarized foregrounds also deserves further study, as we find that it carries the bulk of the polarization information about most other cosmological parameters.

Reference info:

astro-ph/9905257, ApJ, 530, 133-165

Comment:

This removal method, first derived here, generalizes and supersedes the multifrequency Wiener filtering method of Tegmark & Efstathiou (1996) and Bouchet et al (1996).

Other foreground resources:

General CMB links:

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This page was last modified September 19, 2002.

max@physics.upenn.edu