The power spectrum of extended [C ii] haloes around high redshift galaxies

Abstract

ABSTRACT Atacama Large Millimeter/sub-millimeter Array (ALMA) observations have detected extended (≃10 kpc) [C$\scriptstyle \rm II$] haloes around high-redshift (z ≳ 5) star-forming galaxies. If such extended structures are common, they may have an impact on the line intensity mapping (LIM) signal. We compute the LIM power spectrum including both the central galaxy and the [C $\scriptstyle \rm II$] halo, and study the detectability of such signal in an ALMA LIM survey. We model the central galaxy and the [C $\scriptstyle \rm II$] halo brightness with a $\rm S\acute{e}rsic$ + exponential profile. The model has two free parameters: the effective radius ratio $f_{R_{\rm e}}$, and the central surface brightness ratio, fΣ, between the two components. [C $\scriptstyle \rm II$] haloes can significantly boost the LIM power spectrum signal. For example, for relatively compact [C $\scriptstyle \rm II$] haloes ($f_\Sigma =0.4$, $f_{R_{\rm e}}=2.0$), the signal is boosted by ≃20 times; for more extended and diffuse haloes ($f_\Sigma =0.1, f_{R_{\rm e}}=6.0$), the signal is boosted by ≃100 times. For the ALMA ASPECS survey (resolution θbeam = 1.13 arcsec, survey area $\Omega _{\rm survey}=2.9\, \rm arcmin^{2}$) the [C $\scriptstyle \rm II$] power spectrum is detectable only if the deL14d [C $\scriptstyle \rm II$]–SFR relation holds. However, with an optimized survey (θbeam = 0.232 arcsec, $\Omega _{\rm survey}=2.0\, \rm deg^{2}$), the power spectrum is detectable for all the [C $\scriptstyle \rm II$]–SFR relations considered in this paper. Such a survey can constrain $f_\Sigma$ ($f_{R_{\rm e}}$) with a relative uncertainty of $\sim 15~{{\ \rm per\ cent}}$ ($\sim 10~{{\ \rm per\ cent}}$). A successful LIM experiment will provide unique constraints on the nature, origin, and frequency of extended [C $\scriptstyle \rm II$] haloes, and the [C $\scriptstyle \rm II$]–SFR relation at early times.