[en] Full text: Several intercomparison exercises were organized by the International Atomic Energy Agency (IAEA) on the determination of operational quantities at the regional or interregional basis. These exercises revealed significant differences in the approach, methods and assumptions, and consequently in the measurement results obtained by participating laboratories. In the Latin America region, an intercomparison for determination of operational quantity Hp(10), organized within the frame of a technical cooperation regional project, was completed mid-2004, as a follow-up to previous exercises carried out during the 1990s. Eighteen laboratories from 19 member states participated in the first phase; the second phase grouped 15 laboratories from 16 member states. Dosimeter irradiations (5 different radiation qualities for photon simulating workplace fields) were done by 4 Secondary Standards Dosimetry Laboratories (SSDL). The preparations for the exercise involved an audit by the IAEA SSDL, where reference irradiations were provided to all participants for verification of their system. During the first phase (2002/03), only 9 out of 18 laboratories met the performance requirements for such monitoring services. Necessary corrective actions and procedure verification were implemented, and staff involved in these evaluations were subsequently trained. During the second phase (2004), 11 out of 15 laboratories fulfilled the performance criteria. The 4 laboratories still having difficulties in assessing occupational exposure participated in a results meeting, during which problem areas were identified. An ongoing technical cooperation mission is expected to assist these laboratories accordingly. There has been a definite improvement in the second phase and most laboratories demonstrated a good performance in the quantity tested. The technical results clearly show that the laboratories' capability in assessing occupational exposure from external sources of radiation is adequate. These results underline the importance of such an intercomparison programme as a key element towards the harmonization of quantities and units on an international level. This paper presents the intercomparison results. It must be noted that member states strongly recommend that the IAEA continue acting as a focal point for, inter alia, training in all forms, particularly in measurements and dosimetry techniques. This exercise also stressed the importance for the IAEA to take an active role in establishing a network of monitoring laboratories for radiation protection purposes, as it would provide for better information exchange for similar projects. (author)

[en] We present a model using both strong and weak gravitational lensing of the galaxy cluster MACS J0416.1-2403, constrained using spectroscopy from the Grism Lens-Amplified Survey from Space (GLASS) and Hubble Frontier Fields (HFF) imaging data. We search for emission lines in known multiply imaged sources in the GLASS spectra, obtaining secure spectroscopic redshifts of 30 multiple images belonging to 15 distinct source galaxies. The GLASS spectra provide the first spectroscopic measurements for five of the source galaxies. The weak lensing signal is acquired from 884 galaxies in the F606W HFF image. By combining the weak lensing constraints with 15 multiple image systems with spectroscopic redshifts and nine multiple image systems with photometric redshifts, we reconstruct the gravitational potential of the cluster on an adaptive grid. The resulting map of total mass density is compared with a map of stellar mass density obtained from the deep Spitzer Frontier Fields imaging data to study the relative distribution of stellar and total mass in the cluster. We find that the projected stellar mass to total mass ratio, f _⋆, varies considerably with the stellar surface mass density. The mean projected stellar mass to total mass ratio is $⟨<!--\; ???\; -->f_{\star <!--\; ???\; -->}⟩<!--\; ???\; -->=0.009\pm <!--\; ??\; -->0.003$ (stat.), but with a systematic error as large as 0.004–0.005, dominated by the choice of the initial mass function. We find agreement with several recent measurements of f _⋆ in massive cluster environments. The lensing maps of convergence, shear, and magnification are made available to the broader community in the standard HFF format.

[en] We present a new method to search for candidate z ≳ 2 Herschel 500 μm sources in the Great Observatories Origins Deep Survey-North field using a S_{500 μm}/S_{24 μm} “color deconfusion” technique. Potential high-z sources are selected against low-redshift ones from their large 500 to 24 μm flux density ratios. By effectively reducing the contribution from low-redshift populations to the observed 500 μm emission, we are able to identify counterparts to high-z 500 μm sources whose 24 μm fluxes are relatively faint. The recovery of known z ≳ 4 starbursts confirms the efficiency of this approach in selecting high-z  Herschel sources. The resulting sample consists of 34 dusty star-forming galaxies at z ≳ 2. The inferred infrared luminosities are in the range 1.5 × 10¹²–1.8 × 10¹³ L_⊙, corresponding to dust-obscured star formation rates (SFRs) of ∼260–3100 M_⊙ yr⁻¹ for a Salpeter initial mass function. Comparison with previous SCUBA $850\mathrm{\mu <!--\; ??\; -->}\mathrm{m}$-selected galaxy samples shows that our method is more efficient at selecting high-z dusty galaxies, with a median redshift of $z=3.07\pm <!--\; ??\; -->0.83$ and with 10 of the sources at z ≳ 4. We find that at a fixed luminosity, the dust temperature is ∼5 K cooler than that expected from the $T_d-<!--\; ???\; -->L_{\mathrm{I}\mathrm{R}}$ relation at $z\lesssim <!--\; ???\; -->$ 1, though different temperature selection effects should be taken into account. The radio-detected subsample (excluding three strong active galactic nucleus) follows the far-infrared (far-IR)/radio correlation at lower redshifts, and no evolution with redshift is observed out to $z\sim <!--\; ???\; -->5$, suggesting that the far-IR emission is star formation dominated. The contribution of the high-z  Herschel 500 μm sources to the cosmic SFR density is comparable to that of (sub)millimeter galaxy populations at $z\sim <!--\; ???\; -->2.5$ and at least 40% of the extinction-corrected UV samples at $z\sim <!--\; ???\; -->4$. Further investigation into the nature of these high-z dusty galaxies will be crucial for our understanding of the star formation histories and the buildup of stellar mass at the earliest cosmic epochs.

[en] We present an analysis of deep Hubble Space Telescope (HST) multi-band imaging of the BDF field specifically designed to identify faint companions around two of the few Lyα emitting galaxies spectroscopically confirmed at z ∼ 7. Although separated by only 4.4 proper Mpc these galaxies cannot generate H ii regions large enough to explain the visibility of their Lyα lines, thus requiring a population of fainter ionizing sources in their vicinity. We use deep HST and VLT-Hawk-I data to select z ∼ 7 Lyman break galaxies around the emitters. We select six new robust z ∼ 7 LBGs at Y ∼ 26.5–27.5 whose average spectral energy distribution is consistent with the objects being at the redshift of the close-by Lyα emitters. The resulting number density of z ∼ 7 LBGs in the BDF field is a factor of approximately three to four higher than expected in random pointings of the same size. We compare these findings with cosmological hydrodynamic plus radiative transfer simulations of a universe with a half neutral IGM: we find that indeed Lyα emitter pairs are only found in completely ionized regions characterized by significant LBG overdensities. Our findings match the theoretical prediction that the first ionization fronts are generated within significant galaxy overdensities and support a scenario where faint, “normal” star-forming galaxies are responsible for reionization

[en] We analyze a sample of z-dropout galaxies in the CANDELS GOODS South and UDS fields that have been targeted by a dedicated spectroscopic campaign aimed at detecting their Lyα line. Deep IRAC observations at 3.6 and 4.5 μm are used to determine the strength of optical emission lines affecting these bands at z ∼ 6.5–6.9 in order to (1) investigate possible physical differences between Lyα emitting and non-emitting sources; (2) constrain the escape fraction of ionizing photons; and (3) provide an estimate of the specific star formation rate at high redshifts. We find evidence of strong [O iii]+Hβ emission in the average (stacked) SEDs of galaxies both with and without Lyα emission. The blue IRAC [3.6]–[4.5] color of the stack with detected Lyα line can be converted into a rest-frame equivalent width EW([O iii]+Hβ) = ${1500}_{-<!--\; ???\; -->440}^{+530}$Å assuming a flat intrinsic stellar continuum. This strong optical line emission enables a first estimate of $f_{\mathrm{e}\mathrm{s}\mathrm{c}}\lesssim <!--\; ???\; -->20\mathrm{\%<!--\; \%\; -->}$ on the escape fraction of ionizing photons from Lyα detected objects. The objects with no Lyα line show less extreme EW([O iii]+Hβ) = ${520}_{-<!--\; ???\; -->150}^{+170}$Å, suggesting different physical conditions of the H ii regions with respect to Lyα-emitting ones, or a larger $f_{\mathrm{e}\mathrm{s}\mathrm{c}}$. The latter case is consistent with a combined evolution of $f_{\mathrm{e}\mathrm{s}\mathrm{c}}$ and the neutral hydrogen fraction as an explanation of the lack of bright Lyα emission at z > 6. A lower limit on the specific star formation rate, SSFR > 9.1 Gyr⁻¹ for $M_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{r}}=2\times <!--\; ??\; -->{10}^9{M}_{\odot <!--\; ???\; -->}$ galaxies at these redshifts can be derived from the spectroscopically confirmed sample.

[en] Improving the capabilities of detecting faint X-ray sources is fundamental for increasing the statistics on faint high-z active galactic nuclei (AGNs) and star-forming galaxies (SFGs). We performed a simultaneous maximum likelihood point-spread function fit in the [0.5–2] keV and [2–7] keV energy bands of the 4 Ms Chandra Deep Field South (CDFS) data at the position of the 34,930 CANDELS H-band selected galaxies. For each detected source we provide X-ray photometry and optical counterpart validation. We validated this technique by means of a ray-tracing simulation. We detected a total of 698 X-ray point sources with a likelihood $\mathcal{L}><!--\; >\; -->4.98$ (i.e., >2.7σ). We show that prior knowledge of a deep sample of optical–NIR galaxies leads to a significant increase in the detection of faint (i.e., ∼10⁻¹⁷ cgs in the [0.5–2] keV band) sources with respect to “blind” X-ray detections. By including previous X-ray catalogs, this work increases the total number of X-ray sources detected in the 4 Ms CDFS, CANDELS area to 793, which represents the largest sample of extremely faint X-ray sources assembled to date. Our results suggest that a large fraction of the optical counterparts of our X-ray sources determined by likelihood ratio actually coincides with the priors used for the source detection. Most of the new detected sources are likely SFGs or faint, absorbed AGNs. We identified a few sources with putative photometric redshift z > 4. Despite the low number statistics and the uncertainties on the photo z, this sample significantly increases the number of X-ray-selected candidate high-z AGNs.

[en] Star-forming galaxies are considered to be the leading candidate sources dominating cosmic reionization at $z><!--\; >\; -->7$: the search for analogs at moderate redshift showing Lyman continuum (LyC) leakage is currently an active line of research. We have observed a star-forming galaxy at z = 3.2 with Hubble/WFC3 in the F336W filter, corresponding to the 730–890 Å rest-frame, and detected LyC emission. This galaxy is very compact and also has a large Oxygen ratio $[\mathrm{O}\mathrm{I}\mathrm{I}\mathrm{I}]\mathrm{\lambda <!--\; ??\; -->}5007$/$[\mathrm{O}\mathrm{I}\mathrm{I}]\mathrm{\lambda <!--\; ??\; -->}3727$ ($\gtrsim <!--\; ???\; -->10$). No nuclear activity is revealed from optical/near-infrared spectroscopy and deep multi-band photometry (including the 6 Ms X-ray Chandra observations). The measured escape fraction of ionizing radiation spans the range 50%–100%, depending on the intergalactic medium (IGM) attenuation. The LyC emission is measured at $m_{\mathrm{F}336\mathrm{W}}=27.57\pm <!--\; ??\; -->0.11$ (with signal-to-noise ratio (S/N) = 10) and is spatially unresolved, with an effective radius of $R_e<<!--\; <\; -->200$ pc. Predictions from photoionization and radiative transfer models are in line with the properties reported here, indicating that stellar winds and supernova explosions in a nucleated star-forming region can blow cavities generating density-bounded conditions compatible to optically thin media. Irrespective of the nature of the ionizing radiation, spectral signatures of these sources over the entire electromagnetic spectrum are of central importance for their identification during the epoch of reionization when the LyC is unobservable. Intriguingly, the Spitzer/IRAC photometric signature of intense rest-frame optical emissions ([O iii]λλ4959,5007 + Hβ) recently observed at $z\simeq <!--\; ???\; -->7.5\text{--}8.5$ is similar to what is observed in this galaxy. Only the James Webb Space Telescope will measure optical line ratios at $z><!--\; >\; -->7$, allowing a direct comparison with the lower-redshift LyC emitters, such as that reported here.

[en] We present the public release of the stellar mass catalogs for the GOODS-S and UDS fields obtained using some of the deepest near-IR images available, achieved as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey project. We combine the effort from 10 different teams, who computed the stellar masses using the same photometry and the same redshifts. Each team adopted their preferred fitting code, assumptions, priors, and parameter grid. The combination of results using the same underlying stellar isochrones reduces the systematics associated with the fitting code and other choices. Thanks to the availability of different estimates, we can test the effect of some specific parameters and assumptions on the stellar mass estimate. The choice of the stellar isochrone library turns out to have the largest effect on the galaxy stellar mass estimates, resulting in the largest distributions around the median value (with a semi interquartile range larger than 0.1 dex). On the other hand, for most galaxies, the stellar mass estimates are relatively insensitive to the different parameterizations of the star formation history. The inclusion of nebular emission in the model spectra does not have a significant impact for the majority of galaxies (less than a factor of 2 for ∼80% of the sample). Nevertheless, the stellar mass for the subsample of young galaxies (age <100 Myr), especially in particular redshift ranges (e.g., 2.2 < z < 2.4, 3.2 < z < 3.6, and 5.5 < z < 6.5), can be seriously overestimated (by up to a factor of 10 for <20 Myr sources) if nebular contribution is ignored