Constraining low redshift [CII] Emission by Cross-Correlating FIRAS and BOSS Data

TL;DR

This study uses a novel spherical harmonic tomography method to cross-correlate FIRAS and BOSS data, constraining low-redshift [CII] emission and demonstrating potential for future high-sensitivity measurements.

Contribution

It introduces a new SHT approach for intensity mapping and provides the first constraints on low-redshift [CII] emission using FIRAS and BOSS data.

Findings

Constraints on [CII] bias and intensity at z~0.35 and z~0.57

Results are consistent with current models and higher-redshift measurements

Future instruments like PIXIE could detect faint [CII] signals

Abstract

We perform a tomographic cross-correlation analysis of archival FIRAS data and the BOSS galaxy redshift survey to constrain the amplitude of [CII] $^2P_{3/2}\rightarrow$ $^2P_{1/2}$ fine structure emission. Our analysis employs spherical harmonic tomography (SHT), which is based on the angular cross-power spectrum between FIRAS maps and BOSS galaxy over-densities at each pair of redshift bins, over a redshift range of $0.24<z<0.69$. We develop the SHT approach for intensity mapping, where it has several advantages over existing power spectral estimators. Our analysis constrains the product of the [CII] bias and [CII] specific intensity, $b_{[CII]}I_{[CII]i}$, to be $<0.31$ MJy/sr at $z {\approx} 0.35$ and $<0.28$ MJy/sr at $z {\approx} 0.57$ at $95\%$ confidence. These limits are consistent with most current models of the [CII] signal, as well as with higher-redshift [CII] cross-power spectrum measurements from the Planck satellite and BOSS quasars. We also show that our analysis, if applied to data from a more sensitive instrument such as the proposed PIXIE satellite, can detect pessimistic [CII] models at high significance.