Masking line foregrounds in intensity-mapping surveys

Abstract

We address the problem of line confusion in intensity mapping surveys and explore the possibility to mitigate line foreground contamination by progressively masking the brightest pixels in the observed map. We consider experiments targeting CO(1-0) at z = 3, Lyα at z = 7, and CII at z = 7, and use simulated intensity maps, which include both clustering and shot noise components of the signal and possible foregrounds, in order to test the efficiency of our method. We find that for CO and Lyα it is quite possible to remove most of the foreground contribution from the maps via only 1%−3% pixel masking. The CII maps will be more difficult to clean, however, due to instrumental constraints and the high-intensity foreground contamination involved. While the masking procedure sacrifices much of the astrophysical information present in our maps, we demonstrate that useful cosmological information in the targeted lines can be successfully retrieved.

Spectral Line De-Confusion in an Intensity Mapping Survey

“…The masking technique makes use of an external galaxy catalog from galaxy surveys to identify and remove bright sources in order to reduce potential foreground contaminations (Breysse et al 2015;Silva et al 2015;Yue et al 2015). On the other hand, cross-correlation of an LIM survey with an external data set tracing the same cosmic volume can help extract signals of interest; the method has been proposed, in particular, in the studies of reionization (Lidz et al 2009;Visbal & Loeb 2010;Gong et al 2012Gong et al , 2014Chang et al 2015;Silva et al 2015), and has been successfully applied to extract LIM signals at lower redshifts against continuum foregrounds (Chang et al 2010;Masui et al 2013;Croft et al 2016).…”

On Estimation of Contamination from Hydrogen Cyanide in Carbon Monoxide Line-intensity Mapping

“…To motivate this mitigation, Breysse et al (2015) show that HCN significantly contaminates simulated CO surveys, with the HCN power spectrum sitting near or above the CO spectrum. However, the authors use an assumed galaxy power spectrum to simulate an intensity map with the expected clustering, rather than a cosmological simulation.…”

“…However, the authors use an assumed galaxy power spectrum to simulate an intensity map with the expected clustering, rather than a cosmological simulation. The work in Breysse et al (2015) is also limited to HCN contamination (and its mitigation) in 2D maps, for a single observed frequency channel. We must then ask whether high contamination in data products from 2D maps translates to equally high contamination in data products from a 3D cube, the latter of which is our concern.…”

“…We expect one of the brightest contaminant lines for COMAP and other CO(1-0) surveys to be a hydrogen cyanide (HCN) line, HCN(1-0), with a rest frequency of 88.63 GHz (Breysse et al 2015). CO emission from a redshift range of z ≈ 2.4-3.4, as targeted by COPSS and COMAP, mixes with HCN emission from z ≈ 1.6-2.4.…”

“…We derive line-luminosity relations from star-formation histories in cosmological simulations and observations of many local galaxies 1 . Furthermore, as in Li et al (2016), we use halo catalogues from dark matter simulations rather than analytically derived galaxy distributions as in Breysse et al (2015). This approach affords greater flexibility in generating mock galaxies and sky data 1 Visbal et al (2011) calibrate many of their line-luminosity relations solely based on M82, and do not examine HCN(1-0).…”