Lyman continuum leakage in faint star-forming galaxies at redshift z=3-3.5 probed by gamma-ray bursts

Context. The identification of the sources that reionized the Universe and their specific contribution to this process are key missing pieces of our knowledge of the early Universe. Faint star-forming galaxies may be the main contributors to the ionizing photon budget during the epoch of reionization (EoR), but their escaping photons cannot be detected directly due to inter-galactic medium opacity. Hence, it is essential to characterize the properties of faint galaxies with significant Lyman continuum (LyC) photon leakage up to z 4 to define indirect indicators allowing analogues to be found at the highest redshift. Aims. Long gamma-ray bursts (LGRB) explode typically in star-forming regions of faint, star-forming galaxies. Through LGRB afterglow spectroscopy it is possible to detect directly LyC photons. Our aim is to use LGRBs as tools to study LyC leakage from faint, star-forming galaxies at high redshift. Methods. Here we present the observations of LyC emission in the afterglow spectra of GRB 191004B at z = 3:5055, together with those of the other two previously known LyC-emitting LGRB (GRB 050908 at z = 3:3467, and GRB 060607A at z = 3:0749), to determine their LyC escape fraction and compare their properties. Results. From the afterglow spectrum of GRB 191004B we determine a neutral hydrogen column density at the LGRB redshift of og(NHI/cm. 2) =17:2 0:15, and negligible extinction (AV = 0:03 0:02 mag). The only metal absorption lines detected are C iv and Si iv. In contrast to GRB 050908 and GRB 060607A, the host galaxy of GRB 191004B displays significant Ly emission. From its Ly emission and the non-detection of Balmer emission lines we constrain its star-formation rate (SFR) to 1 SFR 4:7 M yr. 1. We fit the Ly emission with a shell model and find parameters values consistent with the observed ones. The absolute (relative) LyC escape fractions we find for GRB 191004B, GRB 050908 and GRB 060607A are of 0:35+0:10 .0:11 (0:43+0:12 .0:13 ), 0:08+0:05.0:04(0:08+0:05.0:04) and :20+0:05.0:05(0:45+ 0:15.0:15), respectively. We compare the LyC escape fraction of LGRBs to the values of other LyC emitters found from the literature, showing that LGRB afterglows can be powerful tools to study LyC escape for faint high-redshift star-forming galaxies. Indeed we could push LyC leakage studies to much higher absolute magnitudes. The host galaxies of the three LGRB presented here have all M1600 > .19:5 mag, with the GRB 060607A host at M1600 > .16 mag. LGRB hosts may therefore be particularly suitable for exploring the ionizing escape fraction in galaxies that are too faint or distant for conventional techniques. Furthermore the time investment is very small compared to galaxy studies

Washing our hands of the congenital cytomegalovirus disease epidemic

BACKGROUND: Each year in the United States, an estimated 40,000 children are born with congenital cytomegalovirus (CMV) infection, causing an estimated 400 deaths and leaving approximately 8000 children with permanent disabilities such as hearing or vision loss, or mental retardation. More children are affected by serious CMV-related disabilities than by several better-known childhood maladies, including Down syndrome, fetal alcohol syndrome, and spina bifida. DISCUSSION: Congenital CMV is a prime target for prevention not only because of its substantial disease burden but also because the biology and epidemiology of CMV suggest that there are ways to reduce viral transmission. Because exposure to the saliva or urine of young children is a major cause of CMV infection among pregnant women, it is likely that good personal hygiene, especially hand-washing, can reduce the risk of CMV acquisition. Experts agree that such measures are likely to be efficacious (i.e., they will work if consistently followed) and the American College of Obstetricians and Gynecologists recommends that physicians counsel pregnant women about preventing CMV acquisition through careful attention to hygiene. However, because of concerns about effectiveness (i.e., Will women consistently follow hygienic practices as the result of interventions?), the medical and public health communities appear reluctant to embrace primary CMV prevention via improved hygienic practices, and educational interventions are rare. Current data on the effectiveness of such measures in preventing CMV infection are promising, but limited. There is strong evidence, however, that educational interventions can prevent other infectious diseases with similar transmission modes, suggesting that effective interventions can also be found for CMV. Until a CMV vaccine becomes available, effective educational interventions are needed to inform women about congenital CMV prevention. SUMMARY: Perhaps no single cause of birth defects and developmental disabilities in the United States currently provides greater opportunity for improved outcomes in more children than congenital CMV. Given the present state of knowledge, women deserve to be informed about how they can reduce their risk of CMV infection during pregnancy, and trials are needed to identify effective educational interventions

Gamma-ray bursts as probes of high-redshift Lyman-alpha emitters and radiative transfer models

We present the updated census and statistics of Lyman-$\alpha$ emitting long gamma-ray bursts host galaxies (LAE-LGRBs). We investigate the properties of a sub-sample of LAE-LGRBs and test the shell model commonly used to fit Lyman-$\alpha$ (Ly$\alpha$) emission line spectra. Among the LAE-LGRBs detected to date, we select a golden sample of four LAE-LGRBs allowing us to retrieve information on the host galaxy properties and of its interstellar medium gas. We fit their Ly$\alpha$ spectra using the shell model, and constrain its parameters with the observed values. From the comparison of the statistics and properties of LAE-LGRBs to those of LAE samples in the literature, we find evidences of Ly$\alpha$ suppression in dusty systems, and a fraction of LAE-LGRBs among the overall LGRB hosts lower than that found for Lyman-break galaxy (LBG) samples at similar redshift range. However, we find that LAE-LGRBs are representative of Ly$\alpha$ emission from the bulk of UV-selected galaxies at z~2. We find that the golden sample of LAE-LGRBs are complex systems characterized by multiple emission blobs and by signs of possible galaxy interactions. The fitting procedure fails in recovering the HI column densities (NHI) measured from the afterglow spectra, and the other properties described by the shell-model parameters in the cases with very high NHI. The afterglows of most LGRBs and LAE-LGRBs show high NHI, implying that statistically the bulk of Ly$\alpha$ photons expected to be produced by massive stars in the star-forming region hosting the GRB will be surrounded by such opaque lines of sight. We interpret our results in the context of more sophisticated models and of different dominant Ly$\alpha$ emitting regions. We also compare LAE-LGRBs to LAE Lyman continuum (LyC) leakers in the literature in terms of properties identified as possible indirect indicators of LyC leakage

Gamma-ray bursts as probes of high-redshift Lyman-α emitters and radiative transfer models

International audienceAims. We present the updated census and statistics of Lyman-α emitting long gamma-ray burst host galaxies (LAE-LGRBs). We investigate the properties of a subsample of LAE-LGRBs and test the shell model that is commonly used to fit Lyman-α (Lyα) emission line spectra.Methods. We considered all LGRB host galaxies with relevant publicly available information. We defined a golden sample of four LAE-LGRBs (GRBs 011211, 021004, 060926, and 070110) with afterglow and host galaxy observations allowing us to constrain the shell modeling of the Lyα line.Results. The census results in 29 detected LAE-LGRBs. We present 5 new Lyα emission detections in host-galaxy spectra and the corresponding unpublished VLT/X-shooter data (GRBs 060926, 070110, 081121, 081222, and 100424A). From the comparison of the statistics and properties of LAE-LGRBs to those of LAE samples in the literature, we find evidence of Lyα suppression in dusty systems. The fraction of LAE-LGRBs in the overall LGRB hosts is lower than that found for Lyman-break galaxy (LBG) samples at similar redshift range. This result can arise because the selection criteria of the parent samples are different and the spectral observations of LGRB samples are shallower than those of LBG. However, we find that LAE-LGRBs are representative of Lyα emission from the bulk of UV-selected galaxies at z ∼ 2. We find that the golden sample of LAE-LGRBs we studied consists of complex systems characterized by multiple emission blobs and by signs of possible galaxy interactions. The fitting procedure recovers the HI column densities (NHI) measured from the afterglow spectra and the other properties described by the shell-model parameters in the two low-NHI cases, but it fails to do this in the other two cases with high NHI. The afterglows of most LGRBs and LAE-LGRBs show log(NHI/cm−2) > 20.3, implying that statistically, the bulk of Lyα photons that is expected to be produced by massive stars in the star-forming region hosting the GRB will be surrounded by these opaque lines of sight. We therefore interpret our results in the context of more sophisticated models and of different dominant Lyα-emitting regions. We also compare LAE-LGRBs to LAE Lyman continuum (LyC) leakers in the literature in terms of the properties that are identified as possible indirect indicators of LyC leakage. We find that only one LGRB (GRB 021004) would likely be a strong LyC leaker and discuss the validity of these indicators at high redshift. While our work shows that LGRBs are useful tools for probing LAEs and radiative transfer models, larger statistics are required to strengthen our findings

Deep MUSE observations in the HDFS. Morpho-kinematics of distant star-forming galaxies down to 108M⊙

Aims. Whereas the evolution of gas kinematics of massive galaxies is now relatively well established up to redshift z ~ 3, little is known about the kinematics of lower mass (M⋆≤ 1010M⊙) galaxies. We use MUSE, a powerful wide-field, optical integral-field spectrograph (IFS) recently mounted on the VLT, to characterize this galaxy population at intermediate redshift. Methods. We made use of the deepest MUSE observations performed so far on the Hubble Deep Field South (HDFS). This data cube, resulting from 27 h of integration time, covers a one arcmin2 field of view at an unprecedented depth (with a 1σ emission-line surface brightness limit of 1 × 10-19 erg s-1 cm-2 arcsec-2) and a final spatial resolution of ≈0.7′′. We identified a sample of 28 resolved emission-line galaxies, extending over an area that is at least twice the seeing disk, spread over a redshift interval of 0.