We analyze stellar masses of clumps drawn from a compilation of star-forming galaxies at 1.1 < z < 3.6. Comparing clumps selected in different ways, and in lensed or blank field galaxies, we examine ...the effects of spatial resolution and sensitivity on the inferred stellar masses. Large differences are found, with median stellar masses ranging from for clumps in the often-referenced field galaxies to for fainter clumps selected in deep-field or lensed galaxies. We argue that the clump masses, observed in non-lensed galaxies with a limited spatial resolution of ∼1 kpc, are artificially increased due to the clustering of clumps of smaller mass. Furthermore, we show that the sensitivity threshold used for the clump selection affects the inferred masses even more strongly than resolution, biasing clumps at the low-mass end. Both improved spatial resolution and sensitivity appear to shift the clump stellar mass distribution to lower masses, qualitatively in agreement with clump masses found in recent high-resolution simulations of disk fragmentation. We discuss the nature of the most massive clumps, and we conclude that it is currently not possible to properly establish a meaningful clump stellar mass distribution from observations and to infer the existence and value of a characteristic clump mass scale.
Abstract
The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the Epoch of Reionization ...is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with the Hubble Space Telescope Cosmic Origins Spectrograph for a
z
= 0.2–0.4 sample of 66 galaxies. After careful processing of the far-UV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.
We present a sample of synthetic massive stellar populations created using the Starburst99 evolutionary synthesis code and new sets of stellar evolutionary tracks, including one set that adopts a ...detailed treatment of rotation. Using the outputs of the Starburst99 code, we compare the populations' integrated properties, including ionizing radiation fields, bolometric luminosities, and colors. With these comparisons we are able to probe the specific effects of rotation on the properties of a stellar population. We find that a population of rotating stars produces a much harder ionizing radiation field and a higher bolometric luminosity, changes that are primarily attributable to the effects of rotational mixing on the lifetimes, luminosities, effective temperatures, and mass-loss rates of massive stars. We consider the implications of the profound effects that rotation can have on a stellar population, and discuss the importance of refining stellar evolutionary models for future work in the study of extragalactic, and particularly high-redshift, stellar populations.
Abstract
The relationship between galaxy characteristics and the reionization of the universe remains elusive, mainly due to the observational difficulty in accessing the Lyman continuum (LyC) at ...these redshifts. It is thus important to identify low-redshift LyC-leaking galaxies that can be used as laboratories to investigate the physical processes that allow LyC photons to escape. The weakness of the S
ii
nebular emission lines relative to typical star-forming galaxies has been proposed as a LyC predictor. In this paper, we show that the S
ii
deficiency is an effective method to select LyC-leaking candidates using data from the Low-redshift LyC Survey, which has detected flux below the Lyman edge in 35 out of 66 star-forming galaxies with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We show that LyC leakers tend to be more S
ii
deficient and that the fraction of their detections increases as S
ii
deficiency becomes more prominent. Correlational studies suggest that S
ii
deficiency complements other LyC diagnostics (such as strong Ly
α
emission and high O
iii
/O
ii
). Our results verify an additional technique by which reionization-era galaxies could be studied.
This work explores the generation of James Webb Space Telescope (JWSP) imagery via image-to-image translation from the available Hubble Space Telescope (HST) data. Comparative analysis encompasses ...the Pix2Pix, CycleGAN, TURBO, and DDPM-based Palette methodologies, assessing the criticality of image registration in astronomy. While the focus of this study is not on the scientific evaluation of model fairness, we note that the techniques employed may bear some limitations and the translated images could include elements that are not present in actual astronomical phenomena. To mitigate this, uncertainty estimation is integrated into our methodology, enhancing the translation's integrity and assisting astronomers in distinguishing between reliable predictions and those of questionable certainty. The evaluation was performed using metrics including MSE, SSIM, PSNR, LPIPS, and FID. The paper introduces a novel approach to quantifying uncertainty within image translation, leveraging the stochastic nature of DDPMs. This innovation not only bolsters our confidence in the translated images but also provides a valuable tool for future astronomical experiment planning. By offering predictive insights when JWST data are unavailable, our approach allows for informed preparatory strategies for making observations with the upcoming JWST, potentially optimizing its precious observational resources. To the best of our knowledge, this work is the first attempt to apply image-to-image translation for astronomical sensor-to-sensor translation.
Abstract
Direct observations of low-mass, low-metallicity galaxies at
z
≳ 4 provide an indispensable opportunity for detailed inspection of the ionization radiation, gas flow, and metal enrichment in ...sources similar to those that reionized the universe. Combining the James Webb Space Telescope (JWST), Very Large Telescope/MUSE, and Atacama Large Millimeter/submillimeter Array, we present detailed observations of a strongly lensed, low-mass (≈10
7.6
M
⊙
) galaxy at
z
= 3.98 (also see Vanzella et al.). We identify strong narrow nebular emission, including C
iv
λ
λ
1548, 1550, He
ii
λ
1640, O
iii
λ
λ
1661, 1666, Ne
iii
λ
3868, O
ii
λ
3727, and the Balmer series of hydrogen from this galaxy, indicating a metal-poor H
ii
region (≲0.12
Z
⊙
) powered by massive stars. Further, we detect a metal-enriched damped Ly
α
system (DLA) associated with the galaxy with the H
i
column density of
N
H I
≈ 10
21.8
cm
−2
. The metallicity of the associated DLA may reach the supersolar metallicity (≳
Z
⊙
). Moreover, thanks to JWST and gravitational lensing, we present the resolved UV slope (
β
) map at the spatial resolution of ≈100 pc at
z
= 4, with steep UV slopes reaching
β
≈ −2.5 around three star-forming clumps. Combining with low-redshift analogs, our observations suggest that low-mass, low-metallicity galaxies, which dominate reionization, could be surrounded by a high covering fraction of the metal-enriched, neutral-gaseous clouds. This implies that the metal enrichment of low-mass galaxies is highly efficient, and further supports that in low-mass galaxies, only a small fraction of ionizing radiation can escape through the interstellar or circumgalactic channels with low-column-density neutral gas.
Abstract
The Mg
ii
λλ
2796, 2803 doublet has been suggested as a useful indirect indicator for the escape of Ly
α
and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to ...date have focused on small samples of galaxies with strong Mg
ii
or strong LyC emission. Here, we present the first study of Mg
ii
to probe a large dynamic range of galaxy properties, using newly obtained high-signal-to-noise, moderate-resolution spectra of Mg
ii
, for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg
ii
profiles ranging from strong emission to P-Cygni profiles to pure absorption. We find that there is a significant trend (with a possibility of spurious correlations of ∼2%) that galaxies that are detected as strong LyC emitters (LCEs) show larger equivalent widths of Mg
ii
emission, while non-LCEs tend to show evidence of more scattering and absorption features in Mg
ii
. We then find that Mg
ii
strongly correlates with Ly
α
in both equivalent width and escape fraction, regardless of whether emission or absorption dominates the Mg
ii
profiles. Furthermore, we show that, for galaxies that are categorized as Mg
ii
emitters, one can use the information of Mg
ii
, metallicity, and dust to estimate the escape fraction of LyC within a factor of ∼3. These findings confirm that Mg
ii
lines can be used as a tool for selecting galaxies as LCEs and thus serve as an indirect indicator for the escape of Ly
α
and LyC.
PDF
