Abstract
Exploiting broad- and narrowband images of the Hubble Space Telescope from the near-UV to
I
-band rest frame, we study the star-forming clumps of six galaxies of the GASP sample undergoing ...strong ram pressure stripping. Clumps are detected in H
α
and near-UV, tracing star formation on different timescales. We consider clumps located in galaxy disks and stripped tails and formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 H
α
-selected clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3745 UV-selected clumps (2021 disk, 825 extraplanar, and 899 tail clumps). Only ∼15% of star-forming clumps are spatially resolved, meaning that most are smaller than ∼140 pc. We study the luminosity and size distribution functions (LDFs and SDFs, respectively) and the luminosity–size relation. The average LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. The results suggest that the star formation is turbulence-driven and scale-free, as in main-sequence galaxies. All of the clumps, whether they are in the disks or tails, have an enhanced H
α
luminosity at a given size, compared to the clumps in main-sequence galaxies. Indeed, their H
α
luminosity is closer to that of clumps in starburst galaxies, indicating that ram pressure is able to enhance the luminosity. No striking differences are found among disk and tail clumps, suggesting that the different environments in which they are embedded play a minor role in influencing the star formation.
Recent work suggests that strong emission line, star-forming galaxies (SFGs) may be significant Lyman continuum leakers. We combine archival Hubble Space Telescope broadband ultraviolet and optical ...imaging (F275W and F606W, respectively) with emission line catalogs derived from WFC3 IR G141 grism spectroscopy to search for escaping Lyman continuum (LyC) emission from homogeneously selected z ∼ 2.5 SFGs. We detect no escaping Lyman continuum from SFGs selected on O ii nebular emission (N = 208) and, within a narrow redshift range, on O iii/O ii. We measure 1 upper limits to the LyC escape fraction relative to the non-ionizing UV continuum from O ii emitters, fesc 5.6%, and strong O iii/O ii > 5 ELGs, fesc 14.0%. Our observations are not deep enough to detect fesc ∼ 10% typical of low-redshift Lyman continuum emitters. However, we find that this population represents a small fraction of the star-forming galaxy population at z ∼ 2. Thus, unless the number of extreme emission line galaxies grows substantially to z 6, such galaxies may be insufficient for reionization. Deeper survey data in the rest-frame ionizing UV will be necessary to determine whether strong line ratios could be useful for pre-selecting LyC leakers at high redshift.
Abstract
We investigate the impact of field-to-field variation, deriving from cosmic variance, in measured Ly
α
emitter (LAE) luminosity functions (LFs) and this variation’s impact on inferences of ...the neutral fraction of the intergalactic medium (IGM) during reionization. We post-process a
z
= 7 IGM simulation to populate the dark matter halos with LAEs. These LAEs have realistic UV magnitudes, Ly
α
fluxes, and Ly
α
line profiles. We calculate the attenuation of Ly
α
emission in universes with varying IGM neutral fraction,
x
¯
H
I
. In a
x
¯
H
I
= 0.3 simulation, we perform 100 realizations of a mock 2 deg
2
survey with a redshift window Δ
z
= 0.5 and flux limit
f
Ly
α
> 1 × 10
−17
erg s
−1
cm
−2
; such a survey is typical in depth and volume of the largest LAE surveys conducted today. For each realization, we compute the LAE LF and use it to recover the input
x
¯
H
I
. Comparing the inferred values of
x
¯
H
I
across the ensemble of the surveys, we find that cosmic variance, deriving from large-scale structure and variation in the neutral gas along the sightline, imposes a floor in the uncertainty of
Δ
x
¯
H
I
∼
0.2
when
x
¯
H
I
= 0.3. We explore mitigation strategies to decrease this uncertainty, such as increasing the volume, decreasing the flux limit, or probing the volume with many independent fields. Increasing the area and/or depth of the survey does not mitigate the uncertainty, but composing a survey with many independent fields is effective. This finding highlights the best strategy for LAE surveys aiming at constraining the
x
¯
H
I
of the universe during reionization.
Abstract
Recent observations of GN-z11 with JWST have revealed a Ly
α
emission line with an equivalent width (EW) of 18 ± 2 Å. At
z
= 10.6, this galaxy is expected to lie in the heart of ...reionization. We use a series of inhomogeneous reionization simulations to derive the distribution of the Ly
α
EW after traveling through the neutral intergalactic medium with varying average neutral gas fraction,
x
H I
. We use these distributions to place an upper limit of
x
H I
< 0.88 at
z
= 10.6 at 95% confidence level. We compare our upper limit to different reionization history models, which include the recently identified enhancement at the bright end of the luminosity function at
z
> 8. We find that models in which faint galaxies have a higher escape fraction compared to bright galaxies are favored by the new data.
Abstract
Ly
α
emission is possibly the best indirect diagnostic of Lyman continuum (LyC) escape since the conditions that favor the escape of Ly
α
photons are often the same that allow for the escape ...of LyC photons. In this work, we present the rest-frame UV–optical spectral characteristics of 11 Ly
α
emitting galaxies at 3 <
z
< 6—the redshift range that optimizes between intergalactic medium attenuation effects and temporal proximity to the epoch of reionization. From a combined analysis of JWST/NIRSpec and MUSE data, we present the Ly
α
escape fraction and study its correlation with other physical properties of galaxies that might facilitate Ly
α
escape. We find that our galaxies have low masses (80% of the sample with
log
10
M
⋆
<
9.5
M
⊙
), compact sizes (median
R
e
∼ 0.7 kpc), low dust content, moderate O
iii
/O
ii
flux ratios (mean ∼ 6.8 ± 1.2), and moderate Ly
α
escape fractions (mean
f
esc
Ly
α
∼
0.11). Our sample shows characteristics that are broadly consistent with low-redshift galaxies with Ly
α
emission, which are termed as “analogs” of the high-redshift population. We predict the LyC escape fraction in our sample to be low (0.03–0.07), although larger samples in the postreionization epoch are needed to confirm these trends.
We present an investigation of clumpy galaxies in the Hubble Ultra Deep Field at in the rest-frame far-ultraviolet (FUV) using Hubble Space Telescope Wide Field Camera 3 broadband imaging in F225W, ...F275W, and F336W. An analysis of 1404 galaxies yields 209 galaxies that host 403 kpc scale clumps. These host galaxies appear to be typical star-forming galaxies, with an average of 2 clumps per galaxy and reaching a maximum of 8 clumps. We measure the photometry of the clumps and determine the mass, age, and star formation rates (SFR) using the spectral energy distribution fitting code FAST. We find that clumps make an average contribution of 19% to the total rest-frame FUV flux of their host galaxy. Individually, clumps contribute a median of 5% to the host galaxy SFR and an average of ∼4% to the host galaxy mass, with total clump contributions to the host galaxy stellar mass ranging widely from lower than 1% up to 93%. Clumps in the outskirts of galaxies are typically younger, with higher SFRs, than clumps in the inner regions. The results are consistent with clump migration theories in which clumps form through violent gravitational instabilities in gas-rich turbulent disks, eventually migrate toward the center of the galaxies, and coalesce into the bulge.
Abstract
Ly
α
emission from galaxies can be used to trace neutral hydrogen in the epoch of reionization, however, there is a degeneracy between the attenuation of Ly
α
in the intergalactic medium ...(IGM) and the line profile emitted by the galaxy. Large shifts of Ly
α
redward of systemic due to scattering in the interstellar medium can boost Ly
α
transmission in the IGM during reionization. The relationship between the Ly
α
velocity offset from systemic and other galaxy properties is not well established at high redshift or low luminosities, due to the difficulty of observing emission lines which trace the systemic redshift. Rest-frame optical spectroscopy with JWST/NIRSpec has opened a new window into understanding Ly
α
at
z
> 3. We present a sample of 12 UV-faint galaxies (−20 ≲
M
UV
≲ −16) at 3 ≲
z
≲ 6, with Ly
α
velocity offsets, Δ
v
Ly
α
, measured from the Very Large Telescope/MUSE and JWST/NIRSpec from the GLASS-JWST Early Release Program. We find a median Δ
v
Ly
α
of 205 km s
−1
and standard deviation of 75 km s
−1
, compared to 320 and 170 km s
−1
, respectively, for
M
UV
< −20 galaxies in the literature. Our new sample demonstrates the previously observed trend of decreasing Ly
α
velocity offset with decreasing UV luminosity and optical line velocity dispersion, which extends to
M
UV
≳ −20, consistent with a picture where the Ly
α
profile is shaped by gas close to the systemic redshift. Our results imply that during reionization Ly
α
from UV-faint galaxies will be preferentially attenuated, but that detecting Ly
α
with low Δ
v
Ly
α
can be an indicator of large ionized bubbles.
Abstract
A tight positive correlation between the stellar mass and the gas-phase metallicity of galaxies has been observed at low redshifts. The redshift evolution of this correlation can strongly ...constrain theories of galaxy evolution. The advent of JWST allows probing the mass–metallicity relation at redshifts far beyond what was previously accessible. Here we report the discovery of two emission line galaxies at redshifts 8.15 and 8.16 in JWST NIRCam imaging and NIRSpec spectroscopy of targets gravitationally lensed by the cluster RX J2129.4+0005. We measure their metallicities and stellar masses along with nine additional galaxies at 7.2 <
z
spec
< 9.5 to report the first quantitative statistical inference of the mass–metallicity relation at
z
≈ 8. We measure ∼0.9 dex evolution in the normalization of the mass–metallicity relation from
z
≈ 8 to the local universe; at a fixed stellar mass, galaxies are 8 times less metal enriched at
z
≈ 8 compared to the present day. Our inferred normalization is in agreement with the predictions of FIRE simulations. Our inferred slope of the mass–metallicity relation is similar to or slightly shallower than that predicted by FIRE or observed at lower redshifts. We compare the
z
≈ 8 galaxies to extremely low-metallicity analog candidates in the local universe, finding that they are generally distinct from extreme emission line galaxies or “green peas,” but are similar in strong emission line ratios and metallicities to “blueberry galaxies.” Despite this similarity, at a fixed stellar mass, the
z
≈ 8 galaxies have systematically lower metallicities compared to blueberry galaxies.
Abstract
We characterize the morphological properties of a statistically relevant sample of H
α
and UV young star-forming clumps and optical complexes, observed with the Hubble Space Telescope in six ...galaxies of the GASP sample undergoing ram pressure stripping. The catalogs comprise 2406 (323 in the tails) H
α
clumps, 3750 (899) UV clumps, and 424 tail optical complexes. About 15%–20% of the clumps and 50% of the complexes are resolved in size. We find that more than half of the complexes contain no H
α
clumps, while most of them contain at least one UV clump. The clump number and size increase with the complex size, while the median complex filling factor is larger for UV clumps (0.27) than that for H
α
clumps (0.10) and does not correlate with almost any morphological property. This suggests that the clumps' number and size grow with the complex keeping the filling factor constant. When studying the position of the clumps inside their complexes, H
α
clumps, and UV clumps to a lesser extent, show a displacement from the complex center of 0.1–1 kpc, and in ∼60% of the cases, they are displaced away from the galactic disk. This is in accordance with the fireball configuration, already observed in the tails of stripped galaxies. Finally, the filling factor and the clump radius increase with the distance from the galactic disk, suggesting that the reciprocal displacement of the different stellar generations increases as a consequence of the velocity gradient caused by ram pressure.
We present near-infrared emission line counts and luminosity functions from the Hubble Space Telescope Wide Field Camera 3 Infrared Spectroscopic Parallels (WISP) program for 29 fields (0.037 deg ...super(2)) observed using both the G102 and G141 grism. We use simulations to correct for significant (>20%) incompleteness introduced in part by the non-dithered, non-rotated nature of the grism parallels. Our H alpha luminosity function contains a comparable number density of faint line emitters to that found by the Near IR Camera and Multi-Object Spectrometer near-infrared grism surveys, but significantly fewer (factors of 3-4 less) high-luminosity emitters. We also find that our high-redshift (z = 0.9-1.5) counts are in agreement with the high-redshift (z = 1.47) narrowband H alpha survey of HiZELS (Sobral et al.), while our lower redshift luminosity function (z = 0.3-0.9) falls slightly below their z = 0.84 result.
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