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
Tension between cosmic microwave background–based and distance ladder–based determinations of the Hubble constant
H
0
motivates the pursuit of independent methods that are not subject to the ...same systematic effects. A promising alternative, proposed by Refsdal in 1964, relies on the inverse scaling of
H
0
with the delay between the arrival times of at least two images of a strongly lensed variable source such as a quasar. To date, Refsdal’s method has mostly been applied to quasars lensed by individual galaxies rather than by galaxy clusters. Using the three quasars strongly lensed by galaxy clusters (SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745) that have both multiband Hubble Space Telescope data and published time delay measurements, we derive
H
0
, accounting for the systematic and statistical sources of uncertainty. While a single time delay measurement does not yield a well-constrained
H
0
value, analyzing the systems together tightens the constraint. Combining the six time delays measured in the three cluster-lensed quasars gives
H
0
= 74.1 ± 8.0 km s
−1
Mpc
−1
. To reach 1% uncertainty in
H
0
, we estimate that a sample size of order of 620 time delay measurements of similar quality as those from SDSS J1004+4112, SDSS J1029+2623, and SDSS J2222+2745 would be needed. Improving the lens modeling uncertainties by a factor of two and a half may reduce the needed sample size to 100 time delays, potentially reachable in the next decade.
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.
Abstract We present a strong lensing analysis of COOL J1241+2219, the brightest known gravitationally lensed galaxy at z ≥ 5, based on new multiband Hubble Space Telescope (HST) imaging data. The ...lensed galaxy has a redshift of z = 5.043, placing it shortly after the end of the “Epoch of Reionization,” and an AB magnitude z AB = 20.47 mag (Khullar et al.). As such, it serves as a touchstone for future research of that epoch. The high spatial resolution of HST reveals internal structure in the giant arc, from which we identify 15 constraints and construct a robust lens model. We use the lens model to extract the cluster mass and lensing magnification. We find that the mass enclosed within the Einstein radius of the z = 1.001 cluster lens is M ( < 5 .″ 77 ) = 1.079 − 0.007 + 0.023 × 10 13 M ☉ , significantly lower than other known strong lensing clusters at its redshift. The average magnification of the giant arc is 〈 μ arc 〉 = 76 − 20 + 40 , a factor of 2.4 − 0.7 + 1.4 greater than previously estimated from ground-based data; the flux-weighted average magnification is 〈 μ arc 〉 = 92 − 31 + 37 . We update the current measurements of the stellar mass and star formation rate (SFR) of the source for the revised magnification to log ( M ⋆ / M ⊙ ) = 9.7 ± 0.3 and SFR = 10.3 − 4.4 + 7.0 M ⊙ yr −1 , respectively. The powerful lensing magnification acting upon COOL J1241+2219 resolves the source and enables future studies of the properties of its star formation on a clump-by-clump basis. The lensing analysis presented here will support upcoming multiwavelength characterization with HST and JWST data of the stellar mass assembly and physical properties of this high-redshift lensed galaxy.
Abstract
We report the discovery of COOL J0335−1927, a quasar at
z
= 3.27 lensed into three images with a maximum separation of 23.″3 by a galaxy cluster at
z
= 0.4178. To date, this is the highest ...redshift wide-separation lensed quasar known. In addition, COOL J0335−1927 shows several strong intervening absorbers visible in the spectra of all three quasar images with varying equivalent widths. The quasar also shows mini-broad line absorption. We construct a parametric strong gravitational lens model using ground-based imaging, constrained by the redshift and positions of the quasar images as well as the positions of three other multiply imaged background galaxies. Using our best-fit lens model, we calculate the predicted time delays between the three quasar images to be Δ
t
AB
=
499
−
146
+
141
(stat) and Δ
t
AC
=
−
127
−
17
+
83
(stat) days. Folding in systematic uncertainties, the model-predicted time delays are within the ranges 240 < Δ
t
AB
< 700 and −300 < Δ
t
AC
< −30. We also present
g
-band photometry from archival Dark Energy Camera Legacy Survey and Pan-STARRS imaging, and new multi-epoch observations obtained between 2022 September 18 UT and 2023 February 22 UT, which demonstrate significant variability in the quasar and will eventually enable the measurement of the time delay between the three quasar images. The currently available light curves are consistent with the model-predicted time delays. This is the fifth paper from the COOL-LAMPS collaboration.
