Abstract
Constraining the major contributors to the ionisation of the early universe is an ongoing endeavour of high-redshift galaxy research. We measure the ionising photon production efficiency and Lyman continuum escape fraction for a sample of 230 intermediate redshift (
1.3 less than z less than 2.6
1.3
<
z
<
2.6
$1.3\lt z\lt 2.6$
) sources observed as a part of the
OutThere survey
; a pure-parallel, wide-area JWST/NIRISS survey with accompanying JWST/NIRCam, NIRISS and HST photometry. The low threshold emission selection criteria for this sample makes for a large and robust control, against which other works may be contrasted, particularly for low-mass galaxies above
z greater than 5
z
>
5
$z\gt 5$
. This control sample allows us to verify the correlations between ionising and spectral/physical properties suggested by previous studies. We find no significant correlations between the ionising photon production efficiency (
xi Subscript normal i normal o normal n
ξ
i
o
n
$\mathrm{\xi_{ion}}$
) with the UV slope,
upper M Subscript upper U upper V
M
U
V
${M_{UV}}$
,
upper M Subscript asterisk
M
∗
$M_*$
or sSFR. We do find that
xi Subscript normal i normal o normal n
ξ
i
o
n
$\mathrm{\xi_{ion}}$
correlates with [OIII]5007 Å equivalent width (EW) (Spearman coefficient
rho equals 0.24
ρ
=
0.24
$\rho =0.24$
;
p less than 4 times 10 Superscript negative 4
p
<
4
×
10
−
4
$p\lt 4\times10^{-4}$
) and H
alpha
α
$\alpha$
EW (
rho equals 0.63
ρ
=
0.63
$\rho =0.63$
;
p less than less than 1 times 10 Superscript negative 6
p
<<
1
×
10
−
6
$p\lt\lt 1\times10^{-6}$
) hold even at low EW albeit with more scatter. We also find that our novel approach to determining the ionising photon escape fraction
normal f Subscript normal e normal s normal c
f
e
s
c
$\mathrm{f_{esc}}$
results in values within theoretical ranges (0–10%) though vary substantially in comparison to the empirical results (median
f Subscript normal e normal s normal c Baseline equals 0.9 percent sign Subscript negative 0.5 Superscript plus 1.1 Baseline
f
e
s
c
=
0.9
%
−
0.5
+
1.1
${f_{\rm esc}} = 0.9\%^{+1.1}_{-0.5}$
including non-detections, median
f Subscript normal e normal s normal c Baseline equals 1.9 percent sign Subscript negative 1.8 Superscript plus 8.9 Baseline
f
e
s
c
=
1.9
%
−
1.8
+
8.9
${f_{\rm esc}} = 1.9\%^{+8.9}_{-1.8}$
above a
0.01 percent sign
0.01
%
$0.01\%$
threshold). We find that this escape fraction method has consistently significant correlations with the redshift, SFR and M
Subscript upper U upper V
U
V
$_{UV}$
and sample-dependent correlations with [OIII]5007 Å EW,H
alpha
α
$\alpha$
EW and stellar mass.