Abstract
Abstract
In their third observing run, the LIGO–Virgo–KAGRA gravitational-wave (GW) observatory was sensitive to binary black hole (BBH) mergers out to redshifts z
merge ≈ 1. Because GWs are inefficient at shrinking the binary orbit, some of these BBH systems likely experienced long delay times τ between the formation of their progenitor stars at z
form and their GW merger at z
merge. In fact, the distribution of delay times predicted by isolated binary evolution resembles a power law
p
(
τ
)
∝
τ
α
τ
with slope −1 ≲ α
τ
≲ −0.35 and a minimum delay time of
τ
min
=
10
Myr
. We use these predicted delay time distributions to infer the formation redshifts of the ∼70 BBH events reported in the third GW transient catalog GWTC-3 and the formation rate of BBH progenitors. For our default α
τ
= –1 delay time distribution, we find that GWTC-3 contains at least one system (with 90% credibility) that formed earlier than z
form > 4.4. Comparing our inferred BBH progenitor formation rate to the star formation rate, we find that at z
form = 4, the number of BBH progenitor systems formed per stellar mass was
6.4
−
5.5
+
9.4
×
10
−
6
M
⊙
−
1
and this yield dropped to
0.134
−
0.127
+
1.6
×
10
−
6
M
⊙
−
1
by z
form = 0. We discuss implications of this measurement for the cosmic metallicity evolution, finding that for typical assumptions about the metallicity dependence of the BBH yield, the average metallicity at z
form = 4 was
〈
log
10
(
Z
/
Z
⊙
)
〉
=
−
0.3
−
0.4
+
0.3
, although the inferred metallicity can vary by a factor of ≈3 for different assumptions about the BBH yield. Our results highlight the promise of current GW observatories to probe high-redshift star formation.
Publisher
American Astronomical Society
Subject
Space and Planetary Science,Astronomy and Astrophysics