Abstract
Extreme, young stellar populations are considered to be the primary contributor to cosmic reionization. How the Lyman continuum (LyC) escapes these galaxies remains highly elusive, and it is ...challenging to observe this process in actual LyC emitters without resolving the relevant physical scales. We investigate the Sunburst Arc, a strongly lensed LyC emitter at
z
= 2.37 that reveals an exceptionally small-scale (tens of parsecs) region of high LyC escape. The small (<100 pc) LyC-leaking region has extreme properties: a very blue UV slope (
β
= −2.9 ± 0.1), a high ionization state (O
iii
λ
5007/O
ii
λ
3727 = 11 ± 3 and O
iii
λ
5007/H
β
= 6.8 ± 0.4), strong oxygen emission (EW(O
iii
) = 1095 ± 40 Å), and a high Ly
α
escape fraction (0.3 ± 0.03), none of which are found in nonleaking regions of the galaxy. The leaking region’s UV slope is consistent with approximately “pure” stellar light that is minimally contaminated by the surrounding nebular continuum emission or extinguished by dust. These results suggest a highly anisotropic LyC escape process such that LyC is produced and escapes from a small, extreme starburst region where the stellar feedback from an ionizing star cluster creates one or more “pencil-beam” channels in the surrounding gas through which LyC can directly escape. Such anisotropic escape processes imply that random sight-line effects drive the significant scatters between measurements of galaxy properties and LyC escape fraction, and that strong lensing is a critical tool for resolving the processes that regulate the ionizing budget of galaxies for reionization.
Abstract
In the third paper from the COOL–LAMPS Collaboration, we report the discovery of COOL J0542-2125, a gravitationally lensed quasar at
z
= 1.84, observed as three images due to an intervening ...massive galaxy cluster at
z
= 0.61. The lensed quasar images were identified in a search for lens systems in recent public optical imaging data and have separations on the sky up to 25.″9, wider than any previously known lensed quasar. The galaxy cluster acting as a strong lens appears to be in the process of merging, with two subclusters separated by ∼1 Mpc in the plane of the sky, and their central galaxies showing a radial velocity difference of ∼1000 km s
−1
. Both cluster cores show strongly lensed images of an assortment of background sources, as does the region between them. A preliminary strong lens model implies masses of
M
<
250
k
p
c
=
1.79
−
0.01
+
0.16
×
10
14
M
⊙
and
M
<
250
k
p
c
=
1.48
−
0.10
+
0.04
×
10
14
M
⊙
for the east and west subclusters, respectively. This line of sight is also coincident with an ROSAT ALL-sky Survey source, centered between the two confirmed cluster halos reminiscent of other major cluster-scale mergers. Archival and new follow-up imaging show flux variability in the quasar images of up to 0.4 mag within ∼1 yr, and new multicolor imaging data reveal a 2
σ
detection of the underlying quasar host. A lens system with this configuration offers rare opportunities for a range of future studies of both the lensed quasar and its host and the foreground cluster merger causing the lensing.
Abstract
We report the discovery of five bright, strong gravitationally lensed galaxies at 3 <
z
< 4: COOL J0101+2055 (
z
= 3.459), COOL J0104−0757 (
z
= 3.480), COOL J0145+1018 (
z
= 3.310), COOL ...J0516−2208 (
z
= 3.549), and COOL J1356+0339 (
z
= 3.753). These galaxies have magnitudes of
r
AB
,
z
AB
< 21.81 mag and are lensed by galaxy clusters at 0.26 <
z
< 1. This sample nearly doubles the number of known bright lensed galaxies with extended arcs at 3 <
z
< 4. We characterize the lensed galaxies using ground-based
grz
/
giy
imaging and optical spectroscopy. We report model-based magnitudes and derive stellar masses, dust content, and star formation rates via stellar population synthesis modeling. Building lens models based on ground-based imaging, we estimate source magnifications ranging from ∼29 to ∼180. Combining these analyses, we derive demagnified stellar masses in the range
log
10
(
M
*
/
M
⊙
)
∼
9.69
−
10.75
and star formation rates in the youngest age bin in the range
log
10
(
SFR
/
(
M
⊙
yr
−
1
)
)
∼
0.39
−
1.46
, placing the sample galaxies on the massive end of the star-forming main sequence in this redshift interval. In addition, three of the five galaxies have strong Ly
α
emissions, offering unique opportunities to study Ly
α
emitters at high redshift in future work.
Abstract
We present a strong-lensing analysis of the cluster PSZ1 G311.65−18.48, based on Hubble Space Telescope imaging, archival VLT/MUSE spectroscopy, and Chandra X-ray data. This cool-core ...cluster (
z
= 0.443) lenses the brightest lensed galaxy known, dubbed the “Sunburst Arc” (
z
= 2.3703), a Lyman continuum (LyC) emitting galaxy multiply imaged 12 times. We identify in this field 14 additional strongly lensed galaxies to constrain a strong-lens model and report secure spectroscopic redshifts of four of them. We measure a projected cluster core mass of
M
(<250 kpc) =
2.93
−
0.02
+
0.01
×
10
14
M
⊙
. The two least magnified but complete images of the Sunburst Arc’s source galaxy are magnified by ∼13×, while the LyC clump is magnified by ∼4–80×. We present time delay predictions and conclusive evidence that a discrepant clump in the Sunburst Arc, previously claimed to be a transient, is not variable, thus strengthening the hypothesis that it results from an exceptionally high magnification. A source plane reconstruction and analysis of the Sunburst Arc finds its physical size to be 1 × 2 kpc and that it is resolved in three distinct directions in the source plane, 0°, 40°, and 75° (east of north). We place an upper limit of
r
≲ 50 pc on the source plane size of unresolved clumps and
r
≲ 32 pc for the LyC clump. Finally, we report that the Sunburst Arc is likely in a system of two or more galaxies separated by ≲6 kpc in projection. Their interaction may drive star formation and could play a role in the mechanism responsible for the leaking LyC radiation.
Extreme, young stellar populations are considered the primary contributor to cosmic re-ionization. How Lyman-continuum (LyC) escapes these galaxies remains highly elusive, and it is challenging to ...observe this process in actual LyC emitters without resolving the relevant physical scales. We investigate the Sunburst Arc: a strongly lensed, LyC emitter at \(z =2.37\) that reveals an exceptionally small scale (tens of parsecs) region of high LyC escape. The small (\(<\) 100 pc) LyC leaking region has extreme properties: a very blue UV slope (\(\beta = -2.9 \pm 0.1\)), high ionization state (O III\(\lambda 5007\)/O II\(\lambda 3727 \) \(= 11 \pm 3\) and O III\(\lambda 5007\)/H\(\beta\) \(=6.8 \pm 0.4\)), strong oxygen emission (EW(O III) \(= 1095 \pm 40 \ Å\)), and high Lyman-\(\alpha\) escape fraction (\(0.3 \pm 0.03\)), none of which are found in non-leaking regions of the galaxy. The leaking region's UV slope is consistent with approximately ``pure'' stellar light that is minimally contaminated by surrounding nebular continuum emission or extinguished by dust. These results suggest a highly anisotropic LyC escape process such that LyC is produced and escapes from a small, extreme starburst region where the stellar feedback from an ionizing star cluster creates one or more ``pencil beam'' channels in the surrounding gas through which LyC can directly escape. Such anisotropic escape processes imply that random sightline effects drive the significant scatters between measurements of galaxy properties and LyC escape fraction, and that strong lensing is a critical tool for resolving the processes that regulate the ionizing budget of galaxies for re-ionization.
ApJ, 950, 58 (2023) We report the discovery of five bright strong gravitationally lensed galaxies
at $3 < z < 4$: COOLJ0101$+$2055 ($z = 3.459$), COOLJ0104$-$0757 ($z = 3.480$),
COOLJ0145$+$1018 ($z ...= 3.310$), COOLJ0516$-$2208 ($z = 3.549$), and
COOLJ1356$+$0339 ($z = 3.753$). These galaxies have magnitudes of $r_{\rm AB},
z_{\rm AB} < 21.81$ mag and are lensed by galaxy clusters at $0.26 < z < 1$.
This sample nearly doubles the number of known bright lensed galaxies with
extended arcs at $3 < z < 4$. We characterize the lensed galaxies using
ground-based grz/giy imaging and optical spectroscopy. We report model-based
magnitudes and derive stellar masses, dust content, and star-formation rates
via stellar population synthesis modeling. Building lens models based on
ground-based imaging, we estimate source magnifications in the range $\sim$29
to $\sim$180. Combining these analyses, we derive demagnified stellar masses in
the range $\rm log_{10}(M_{*}/M_{\odot}) \sim 9.69 - 10.75$ and star formation
rates in the youngest age bin ranging from $\rm log_{10}(SFR/(M_{\odot}\cdot
yr^{-1})) \sim 0.39 - 1.46$, placing the sample galaxies on the massive end of
the star-forming main sequence in this redshift interval. In addition, three of
the five galaxies have strong Ly$\alpha$ emissions, offering unique
opportunities to study Ly$\alpha$ emitters at high redshift in future work.
