MUSTANG-2 Filtering

Like any other ground-based millimeter continuum observations, our default data processing attempts to remove the Earth’s atmosphere with either a common-mode subtraction or something quite similar to it (e.g. PCA).

There is an early memo on filtering which compared the results of observing simulated galaxy clusters using two different (Lissajous daisy) scan sizes and two different sets of filtering parameters. There is an executive summary here.

The following figures show transfer functions for a broad range of (Lissajous) scan sizes (from 2.5′ to 5.0′) with a fairly gentle filtering (3 components subtracted from the timestreams via PCA and a windowed filter, keeping frequencies between 0.06 Hz and 41.0 Hz).

Figure 1. Transfer functions for reduction parameters of PCA=3, and a Fourier window between 0.06 Hz and 41.0 Hz. Left: large-scale transmission by scan size (raw binned data). Right: fitted curves of the form Transmission = p[0] – (r/p[1])^p[2], by scan size (in arcminutes).

Below are the transfer functions from above with the same scan sizes but instead filtered with 5 components (via PCA) and a window between 0.08 Hz and 41.0 Hz. We note that the units of the wavenumber axes of all the plots on this page are 1/arcseconds.

Figure 2. Transfer functions for reduction parameters of PCA=5, and a Fourier window between 0.08 Hz and 41.0 Hz. Left: large-scale transmission by scan size (raw binned data). Right: fitted curves of the form Transmission = p[0] – (r/p[1])^p[2], by scan size (in arcminutes).

Below we show the differences between these two reductions (PCA=3 with a Fourier window between 0.06 Hz and 41.0 Hz vs PCA=5 with a Fourier window between 0.08 Hz and 41.0 Hz) by splitting the scan sizes used above among two plots:

Figure 3. Dashed lines indicate the harsher filtering (CA=5 with a Fourier window between 0.08 Hz and 41.0 Hz); solid lines are the gentler filtering (PCA=3 with a Fourier window between 0.06 Hz and 41.0 Hz).

A filtering with a highpass of 0.06 Hz is, unfortunately, a bit more gentler than we find is necessary. Rather, a highpass at 0.07 or 0.08 Hz often results in acceptable noise in our maps. There are still other datasets which require still more aggressive filtering, either a highpass at 0.09 Hz, or even 0.1 Hz.

Transfer Functions for Download

A repository of transfer functions (ascii files) is available here.