Magnification and evolution biases in large-scale structure surveys

Abstract

Measurements of the galaxy number density in upcoming surveys such as Euclid and the SKA will be sensitive to distortions from lensing magnification and Doppler effects, beyond the standard redshift-space distortions. The amplitude of these contributions depends sensitively on magnification bias and evolution bias in the galaxy number density. Magnification bias quantifies the change in the observed number of galaxies gained or lost by lensing magnification, while evolution bias quantifies the physical change in the galaxy number density relative to the conserved case. These biases are given by derivatives of the number density, and consequently are very sensitive to the form of the luminosity function. We give a careful derivation of the magnification and evolution biases, clarifying a number of results in the literature. We then examine the biases for a variety of surveys, encompassing optical/NIR, 21cm galaxy and 21cm intensity mapping surveys.

Anti-symmetric clustering signals in the observed power spectrum

“…A.4 HI galaxies with SKAO As for optical galaxies, the number density of HI galaxies is dependent on the sensitivity threshold of the instrument. In [46] we find an explanation how such flux cut S cut is computed from instrumental specifications. We follow their results and descriptions for SKAO and SKAO2.…”

“…For intensity mapping we recover the correct HI transfer function in equation (2.14) by setting s HI = 0.4. The evolution bias is computed in [46]. In figure 9 we plot the HI biases in thick dotted purple.…”

“…In the case of SKAO's MID HI IM with DESI-like BGS samples and Euclid-like spectroscopic Hα galaxy survey, we will assume a 10 000 deg 2 . For more details on the calculation of magnification and evolution bias please refer to [46].…”

“…Once we obtain {c 1 , c 2 , c 3 } as a function of redshift and flux cut we follow [46] to compute the magnification and evolution biases. For SKAO2 we will further divide into a "faint" and "bright" sample with the redshift dependent cut Note that the flux cut between the two samples should also contribute to the faint magnification bias.…”

Multi-wavelength spectroscopic probes: biases from neglecting light-cone effects

“…The key point is that, in order to avoid serious bias on the best-fit values of f NL and cosmological parameters, the effect of lensing magnification on the galaxy power spectrum must be included in upcoming surveys which cover high redshifts. The inclusion of lensing in the theoretical modeling highlights the importance of good-precision estimates of the lensing magnification bias parameter (see also [5,7,8,15,24,25,[30][31][32][33][34]). The lensing magnification and associated parameter s are given by [31, Here ng is the comoving number density at the source, which is given by an apparent magnitude integral of the luminosity function φ, with limiting apparent magnitude m c .…”