Himiko is one of the most luminous Ly emitters at z = 6.595. It has three star-forming clumps detected in the rest-frame UV, with a total SFR = 20 M yr−1. We report the Atacama Large ...Millimeter/submillimeter Array (ALMA) detection of the C ii158 m line emission in this Galaxy with a significance of 8 . The total C ii luminosity (LC ii = 1.2 × 108 L ) is fully consistent with the local LC ii-SFR relation. The ALMA high-angular resolution reveals that the C ii emission is made of two distinct components. The brightest C ii clump is extended over 4 kpc and is located on the peak of the Ly nebula, which is spatially offset by 1 kpc relative to the brightest UV clump. The second C ii component is spatially unresolved (size <2 kpc) and coincident with one of the three UV clumps. While the latter component is consistent with the local LC ii-SFR relation, the other components are scattered above and below the local relation. We shortly discuss the possible origin of the C ii components and their relation with the star-forming clumps traced by the UV emission.
We present the ancillary data and basic physical measurements for the galaxies in the ALMA Large Program to Investigate C+ at Early Times (ALPINE) survey-the first large multiwavelength survey that ...aims at characterizing the gas and dust properties of 118 main-sequence galaxies at redshifts 4.4 < z < 5.9 via the measurement of emission at (64% at >3.5 ) and the surrounding far-infrared continuum in conjunction with a wealth of optical and near-infrared data. We outline in detail the spectroscopic data and selection of the galaxies as well as the ground- and space-based imaging products. In addition, we provide several basic measurements including stellar masses, star formation rates (SFR), rest-frame ultra-violet (UV) luminosities, UV continuum slopes (β), and absorption line redshifts, as well as H emission derived from Spitzer colors. We find that the ALPINE sample is representative of the 4 < z < 6 galaxy population selected by photometric methods and only slightly biased toward bluer colors (Δβ ∼ 0.2). Using as tracer of the systemic redshift (confirmed for one galaxy at z = 4.5 out of 118 for which we obtained optical λ3727 emission), we confirm redshifted Ly emission and blueshifted absorption lines similar to findings at lower redshifts. By stacking the rest-frame UV spectra in the rest frame, we find that the absorption lines in galaxies with high specific SFR are more blueshifted, which could be indicative of stronger winds and outflows.
ABSTRACT
Most of the hydrogen in the intergalactic medium (IGM) was rapidly ionized at high redshifts. While observations have established that reionization occurred, observational constraints on the ...high-redshift ionizing emissivity remain elusive. Here, we present a new analysis of the Low-redshift Lyman Continuum Survey (LzLCS) and literature observations, a combined sample of 89 star-forming galaxies at redshifts near 0.3 with Hubble Space Telescope observations of their ionizing continua (or Lyman Continuum, LyC). We find a strong (6σ significant) inverse correlation between the continuum slope at 1550 Å (defined as F$_\lambda \propto \lambda ^{\beta ^{1550}_{\rm obs}}$) and both the LyC escape fraction (fesc, LyC) and fesc, LyC times the ionizing photon production efficiency (ξion). On average, galaxies with redder continuum slopes have smaller fesc, LyC than galaxies with bluer slopes mainly due to higher dust attenuation. More than 5 per cent (20 per cent) of the LyC emission escapes galaxies with $\beta _{\rm obs}^{1550}$ <−2.1 (−2.6). We find strong correlations between $\beta _{\rm obs}^{1550}$ and the O iii/O ii flux ratio (at 7.5σ significance), galaxy stellar mass (at 5.9σ), the gas-phase metallicity (at 4.6σ), and the observed far-ultraviolet absolute magnitude (at 3.4σ). Using previous observations of $\beta _{\rm obs}^{1550}$ at high redshift, we estimate the evolution of fesc, LyC with both redshift and galaxy magnitude. The LzLCS observations suggest that fainter and lower mass galaxies dominate the ionizing photon budget at higher redshift, possibly due to their rapidly evolving metal and dust content. Finally, we use our correlation between $\beta _{\rm obs}^{1550}$ and fesc, LyC × ξion to predict the ionizing emissivity of galaxies during the epoch of reionization. Our estimated emissivities match IGM observations, and suggest that star-forming galaxies emit sufficient LyC photons into the IGM to exceed recombinations near redshifts of 7–8.
ABSTRACT
Finding reliable indicators of Lyman continuum (Ly C) photon leakage from galaxies is essential in order to infer their escape fraction in the epoch of reionization, where direct ...measurements of Ly C flux are impossible. To this end, here we investigate whether strong C iv λλ1548, 1550 emission in the rest-frame UV spectra of galaxies traces conditions ripe for ample production and escape of Ly C photons. We compile a sample of 19 star-forming galaxies in the redshift range $z$ = 3.1–4.6 from the VANDELS survey that exhibit strong C iv emission, producing a stacked spectrum where all major rest-UV emission lines are clearly detected. Best-fitting spectral energy distribution models containing both stellar and nebular emission suggest the need for low stellar metallicities ($Z=0.1--0.2\, Z_\odot$), young stellar ages ($\log (\rm {age\,yr^{-1}}) = 6.1--6.5$), a high ionization parameter (log U = −2) and little to no dust attenuation (E(B − V) = 0.00–0.01). However, these models are unable to fully reproduce the observed C iv and He ii line strengths. We find that the Ly α line in the stacked spectrum is strong and peaks close to the systemic velocity, features that are indicative of significant Ly C photon leakage along the line of sight. The covering fractions of low-ionization interstellar absorption lines are also low, implying Ly C escape fraction in the range ≈0.05–0.30, with signatures of outflowing gas. Finally, C iv/C iii ratios of >0.75 for a subset of individual galaxies with reliable detections of both lines are also consistent with physical conditions that enable significant Ly C leakage. Overall, we report that multiple spectroscopic indicators of Ly C leakage are present in the stacked spectrum of strong C iv emitting galaxies, potentially making C iv an important tracer of Ly C photon escape at $z$ > 6.
Context.
Finding and elucidating the properties of Lyman-continuum(LyC)-emitting galaxies is an important step in improving our understanding of cosmic reionization.
Aims.
Although the
z
∼ 0.3 − 0.4 ...LyC emitters found recently show strong optical emission lines, no consistent quantitative photoionization model taking into account the escape of ionizing photons and inhomogenous interstellar medium (ISM) geometry of these galaxies has yet been constructed. Furthermore, it is unclear to what extent these emission lines can be used to distinguish LyC emitters.
Methods.
To address these questions we construct one- and two-zone photoionization models accounting for the observed LyC escape, which we compare to the observed emission line measurements. The main diagnostics used include lines of O
III
, O
II
, and O
I
plus sulfur lines (S
II
, S
III
) and a nitrogen line (N
II
), which probe regions of different ionization in the ISM.
Results.
We find that single (one-zone) density-bounded photoionization models cannot reproduce the emission lines of the LyC leakers, as pointed out by earlier studies, because they systematically underpredict the lines of species of low ionization potential, such as O
I
and S
II
. Introducing a two-zone model, with differing ionization parameter and a variable covering fraction and where one of the zones is density-bounded, we show that the observed emission line ratios of the LyC emitters are well reproduced. Furthermore, our model yields LyC escape fractions, which are in fair agreement with the observations and independent measurements. The O
I
λ
6300 excess, which is observed in some LyC leakers, can be naturally explained in this model, for example by emission from low-ionization and low-filling-factor gas. LyC emitters with a high escape fraction (
f
esc
≳ 38%) are deficient both in O
I
λ
6300 and in S
II
λ
λ
6716,6731. We also confirm that a S
II
λ
λ
6716,6731 deficiency can be used to select LyC emitter candidates, as suggested earlier. Finally, we find indications for a possible dichotomy in terms of escape mechanisms for LyC photons between galaxies with relatively low (
f
esc
≲ 10%) and higher escape fractions.
Conclusions.
We conclude that two-zone photoionization models are sufficient and required to explain the observed emission line properties of
z
∼ 0.3 − 0.4 LyC emitters. This is in agreement with UV absorption line studies, which also show the co-existence of regions with high hydrogen column density (i.e., no escape of ionizing photons) and density-bounded or very low column density regions responsible for the observed escape of LyC radiation. These simple but consistent models provide a first step towards the use of optical emission lines and their ratios as quantitative diagnostics of LyC escape from galaxies.
ABSTRACT
Using new Very Large Telescope (VLT)/XShooter spectral observations we analyse the physical properties of five z ∼ 0.3–0.4 confirmed Lyman continuum (LyC) leakers. Strong resonant Mg ...ii λλ2796, 2803 Å emission lines (I(λλ2796, 2803)/I(Hβ) ≃ 10–38 per cent) and non-resonant Fe ii* λλ2612, 2626 Å emission lines are observed in spectra of five and three galaxies, respectively. We find high electron densities Ne ∼ 400 cm−3, significantly higher than in typical low-z, but comparable to those measured in z ∼ 2–3 star-forming galaxies (SFGs). The galaxies have a mean value of log N/O = –1.16, close to the maximum values found for SFGs in the metallicity range of 12 + log O/H ≃ 7.7–8.1. All 11 low-z LyC emitting galaxies found by Izotov et al., including the ones considered in this study, are characterized by high equivalent width (EW) (Hβ) ∼ 200–400 Å, high ionization parameter (log(U) = –2.5 to –1.7), high average ionizing photon production efficiency ξ = 1025.54 Hz erg−1, and hard ionizing radiation. On the Baldwin–Phillips–Terlevich (BPT) diagram we find the same offset of our leakers from low-z main-sequence SFGs as that for local analogues of Lyman-break galaxies (LBGs) and extreme SFGs at z ∼ 2–3. We confirm the effectiveness of the He i emission lines diagnostics proposed by Izotov et al. in searching for LyC leaker candidates and find that their intensity ratios correspond to those in a median with low neutral hydrogen column density N(H i) = 1017–5 × 1017 cm−2 that permit leakage of LyC radiation, likely due to their density-bounded H ii regions.
Exposure to intrauterine heat stress during late gestation affects offspring performance into adulthood. However, underlying mechanistic links between thermal insult in fetal life and postnatal ...outcomes are not completely understood. We examined morphology, DNA methylation, and gene expression of liver and mammary gland for bull calves and heifers that were gestated under maternal conditions of heat stress or cooling (i.e. in utero heat stressed vs. in utero cooled calves). Mammary tissue was harvested from dairy heifers during their first lactation and liver from bull calves at birth. The liver of in utero heat stressed bull calves contained more cells and the mammary glands of in utero heat stressed heifers were comprised of smaller alveoli. We identified more than 1,500 CpG sites differently methylated between maternal treatment groups. These CpGs were associated with approximately 400 genes, which play a role in processes, such as development, innate immune defense, cell signaling, and transcription and translation. We also identified over 100 differentially expressed genes in the mammary gland with similar functions. Interestingly, fifty differentially methylated genes were shared by both bull calf liver and heifer mammary gland. Intrauterine heat stress alters the methylation profile of liver and mammary DNA and programs their morphology in postnatal life, which may contribute to the poorer performance of in utero heat stressed calves.
Using spectroscopic observations taken for the Visible Multi-Object Spectrograph (VIMOS) Ultra-Deep Survey (VUDS) we report here on the discovery of PCl J1001+0220, a massive proto-cluster of ...galaxies located at zspec ~ 4.57 in the COSMOS field. With nine spectroscopic members, the proto-cluster was initially detected as a ~12σ spectroscopic overdensity of typical star-forming galaxies in the blind spectroscopic survey of the early universe (2 < z ≲ 6) performed by VUDS. It was further mapped using a new technique developed which statistically combines spectroscopic and photometric redshifts, the latter derived from a recent compilation of incredibly deep multi-band imaging performed on the COSMOS field. Through various methods, the descendant mass of PCl J1001+0220 is estimated to be log (Mh/M⊙)z=0 $\log(\mathcal{M}_{h}/\mathcal{M}_{\odot})_{z=0}$log(Mh/M⊙)z=0 ~ 14.5–15 with a large amount of mass apparently already in place at z ~ 4.57. An exhaustive comparison was made between the properties of various spectroscopic and photometric member samples and matched samples of galaxies inhabiting less dense environments at the same redshifts. Tentative evidence is found for a fractional excess of older galaxies more massive in their stellar content amongst the member samples relative to the coeval field, an observation which suggests the pervasive early onset of vigorous star formation for proto-cluster galaxies. No evidence is found for the differences in the star formation rates (SFRs) of member and coeval field galaxies either through estimating by means of the rest-frame ultraviolet or through separately stacking extremely deep Very Large Array 3 GHz imaging for both samples. Additionally, no evidence for pervasive strong active galactic nuclei (AGN) activity is observed in either environment. Analysis of Hubble Space Telescope images of both sets of galaxies as well as their immediate surroundings provides weak evidence for an elevated incidence of galaxy–galaxy interaction within the bounds of the proto-cluster. The stacked and individual spectral properties of the two samples are compared, with a definite suppression of Lyα seen in the average member galaxy relative to the coeval field ( fesc, Lyα = 1.8−1.7+0.3 $f_{esc, \, \textrm{Ly}\alpha} = 1.8^{+0.3}_{-1.7}$fesc, Lyα=1.8−1.7+0.3% and 4.0−0.8+1.0 $4.0^{+1.0}_{-0.8}$4.0−0.8+1.0%, respectively). This observation along with other lines of evidence leads us to infer the possible presence of a large, cool, diffuse medium within the proto-cluster environment evocative of a nascent intracluster medium forming in the early universe.
ABSTRACT
We present a study designed to measure the average Lyman-continuum escape fraction (〈fesc〉) of star-forming galaxies at z ≃ 3.5. We assemble a sample of 148 galaxies from the VANDELS ...spectroscopic survey at 3.35 ≤ zspec ≤ 3.95, selected to minimize line-of-sight contamination of their photometry. For this sample, we use ultra-deep, ground-based, U-band imaging and Hubble Space Telescope V-band imaging to robustly measure the distribution of $\mathcal {R_{\rm obs}}\, =(L_{\rm LyC}/L_{\rm UV})_{\rm obs}$. We then model the $\mathcal {R_{\rm obs}}$ distribution as a function of 〈fesc〉, carefully accounting for attenuation by dust, the intergalactic medium and the circumgalactic medium. A maximum likelihood fit to the $\mathcal {R_{\rm obs}}$ distribution returns a best-fitting value of $\langle f_{\rm esc}\rangle =0.07^{+0.02}_{-0.02}$, a result confirmed using an alternative Bayesian inference technique (both techniques exclude 〈fesc〉 = 0.0 at >3σ). By splitting our sample in two, we find evidence that 〈fesc〉 is positively correlated with Ly α equivalent width (Wλ(Ly α)), with high and low Wλ(Lyα) subsamples returning values of $\langle f_{\rm esc}\rangle =0.12^{+0.06}_{-0.04}$ and $\langle f_{\rm esc} \rangle =0.02^{+0.02}_{-0.01}$, respectively. In contrast, we find evidence that 〈fesc〉 is anticorrelated with intrinsic UV luminosity and UV dust attenuation; with low UV luminosity and dust attenuation subsamples both returning best fits in the range 0.10 ≤ 〈fesc〉 ≤ 0.22. We do not find a clear correlation between fesc and galaxy stellar mass, suggesting stellar mass is not a primary indicator of fesc. Although larger samples are needed to further explore these trends, our results suggest that it is entirely plausible that the low dust, low-metallicity galaxies found at z ≥ 6 will display the 〈fesc〉 ≥ 0.1 required to drive reionization.
The estimate of stellar metallicities (
Z
*
) of high-
z
galaxies are of paramount importance in order to understand the complexity of dust effects and the reciprocal interrelations among stellar ...mass, dust attenuation, stellar age, and metallicity. Benefiting from uniquely deep far-UV spectra of > 500 star-forming galaxies at redshifts 2 <
z
< 5 extracted from the VANDELS survey and stacked in bins of stellar mass (
M
*
) and UV continuum slope (
β
), we estimate their stellar metallicities
Z
*
from stellar photospheric absorption features at 1501 and 1719 Å, which are calibrated with Starburst99 models and are largely unaffected by stellar age, dust, IMF, nebular continuum, or interstellar absorption. Comparing them to photometric-based spectral slopes in the 1250–1750 Å range, we find that the stellar metallicity increases by ∼0.5 dex from
β
∼ −2 to
β
∼ −1 (1 ≲
A
1600
≲ 3.2), and a dependence with
β
holds at fixed UV absolute luminosity
M
UV
and stellar mass up to ∼10
9.65
M
⊙
. As a result, metallicity is a fundamental ingredient for properly rescaling dust corrections based on
M
UV
and
M
*
. Using the same absorption features, we analyzed the mass-metallicity relation (MZR), and find it to be consistent with the previous VANDELS estimation based on a global fit of the FUV spectra. Similarly, we do not find a significant evolution between
z
∼ 2 and
z
∼ 3.5. Finally, the slopes of our MZR and
Z
*
−
β
relation are in agreement with the predictions of well-studied semi-analytic models (SAM) of galaxy formation, while some tensions remain concerning the absolute metallicity normalization. The relation between the UV slope and stellar metallicity is fundamental to the exploitation of large volume surveys with next-generation telescopes and for the physical characterization of galaxies in the first billion years of our Universe.
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