Abstract
Abstract
Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-redshift Universe with a small volume. Such uncertainties produce the field-to-field variance σ
g
of galaxy numbers in observational astronomy, which significantly affects the luminosity function (LF) measurement of Lyα emitters (LAEs). For most previous Lyα LF studies, σ
g
is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for z ≈ 2.2 Lyα LFs. The LAE candidates are observed using the narrow band and broad band of the Subaru/Hyper Suprime-Cam in eight independent fields, making the total survey area ≃11.62 deg2 and a comoving volume of ≃8.71 × 106 Mpc3. We report a best-fit Schechter function with parameters α = −1.75 (fixed),
L
Ly
α
*
=
5.95
−
0.96
+
1.22
×
10
42
erg s−1, and
ϕ
Ly
α
*
=
5.26
−
1.27
+
1.65
× 10−4 Mpc−3 for the overall Lyα LFs. After clipping out the regions that may bias the cosmic variance measurements, we calculate σ
g
by sampling LAEs within multiple pointings on the field image. We investigate the relation between σ
g
and survey volume V, and fit a simple power-law
σ
g
=
k
×
V
10
5
Mpc
3
β
. We find best-fit values of
−
1.399
−
0.156
+
0.160
for β and
1.249
−
0.193
+
0.213
for k. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs is likely larger than that of general star-forming galaxies.
Publisher
American Astronomical Society
Subject
Space and Planetary Science,Astronomy and Astrophysics