CONCERTO: Extracting the power spectrum of the [C II ] emission line

Abstract: CONCERTO is the first experiment to perform a [CII] line intensity mapping survey to target $z>5.2$. Measuring the [CII] power spectrum allows us to study the role of dusty star-forming galaxies in the star formation history during the Reionization and post-Reionization. The main obstacle to this measurement is the contamination by bright foregrounds. We evaluate our ability to retrieve the [CII] signal in mock observations using the Simulated Infrared Dusty Extragalactic Sky. We compared two methods for dealing with the dust continuum emission from galaxies: the standard PCA and the arPLS method. For line interlopers, the strategy relies on masking low-redshift galaxies using external catalogues. As we do not have observations of CO or classical CO proxies ,we relied on the COSMOS stellar mass catalogue. To measure the power spectrum of masked data, we adapted the P of K EstimatoR and discuss its use on LIM data. The arPLS method achieves a reduction of the continuum background to a sub-dominant level of the [CII] at z=7 by a factor of>70. When using PCA, this factor is only 0.7. The masking lowers the power amplitude of line contamination down to $2 \times 10^2 Jy^2/sr$ This residual level is dominated by faint undetected sources. For our [CII] model, this results in a detection at z = 5.2 with a power ratio [CII]/(residual interlopers) = $62 \pm 32$ for a 22 % area survey loss. However, at z = 7, [C II ] / (residual interlopers)$=2.0 \pm 1.4$. Thanks to the large area covered by SIDES-Uchuu, we show that the power amplitude of line residuals varies by 12-15% for z=5.2-7. We present an end-to-end simulation of the extragalactic foreground removal that we ran to detect the [CII] at high redshift via its power spectrum. We show that dust continuum emission are not a limiting foreground for [CII] LIM. Residual CO and [CI] limits our ability to measure the [CII] power spectrum at z>7.