Context.A severe problem for research in star-formation is that the masses of young stars are almost always estimated from evolutionary tracks alone. Since the tracks published by different groups differ, it is often only possible to give a rough estimate of the masses of young stars. It is thus crucial to test and calibrate the tracks. Up to now, only a few tests of the tracks could be carried out. However, it is now possible with the VLTI to set constrains on the tracks by determining the masses of many young binary stars precisely. Aims. In order to use the VLTI efficiently, a first step is to find suitable targets, which is the purpose of this work. Given the distance of nearby star-forming regions, suitable VLTI targets are binaries with orbital periods between at least 50 days and a few years. Although a number of surveys for detecting spectroscopic binaries have been carried out, most of the binaries found so far have periods that are too short. Methods. We thus surveyed the Chamaeleon, Corona Australis, Lupus, Sco-Cen, and ρ Ophiuci star-forming regions in order to search for spectroscopic binaries with periods longer than 50 days, which are suitable for the VLTI observations. Results. As a result of the 8 year campaign, we discovered 8 binaries with orbital periods longer than 50 days. Amongst the newly discovered long-period binaries is CS Cha, which is one of the few classical T Tauri stars with a circumbinary disk. The survey is limited to objects with masses higher than 0.1 to 0.2 M for periods between 1 and 8 years. Conclusions. We find that the frequency of binaries with orbital periods ≤3000 days is of 20 ± 5%. The frequency of long and short period pre-main sequence spectroscopic binaries is about the same as for stars in the solar neighbourhood. In total 14 young binaries are now known that are suitable for mass determination with the VLTI.

We report the discovery of a galaxy overdensity around a Compton-thick Fanaroff-Riley type II (FRII) radio galaxy at z=1.7 in the deep multiband survey around the z=6.3 quasi-stellar object (QSO) SDSS J1030+0524. Based on a 6hr VLT/MUSE and on a 4hr LBT/LUCI observation, we identify at least eight galaxy members in this structure with spectroscopic redshift z=1.687-1.699, including the FRII galaxy at z=1.699. Most members are distributed within 400 kpc from the FRII core. Nonetheless, the whole structure is likely much more extended, as one of the members was serendipitously found at ∼800 kpc projected separation. The classic radio structure of the FRII itself extends for ∼ 600 kpc across the sky. Most of the identified overdensity members are blue, compact galaxies that are actively forming stars at rates of ∼8-60 M yr −1 . For the brightest of them, a half-light radius of 2.2±0.8 kpc at 8000Å rest-frame was determined based on adaptive optics-assisted observations with LBT/SOUL in the Ks band. We do not observe any strong galaxy morphological segregation or concentration around the FRII core. This suggests that the structure is far from being virialized and likely constitutes the progenitor of a local massive galaxy group or cluster caught in its main assembly phase. Based on a 500ks Chandra ACIS-I observation, we found that the FRII nucleus hosts a luminous QSO (L 2−10keV = 1.3 × 10 44 erg s −1 , intrinsic and rest-frame) that is obscured by Compton-thick absorption (N H = 1.5±0.6×10 24 cm −2 ). Under standard bolometric corrections, the total measured radiative power (L rad ∼ 4 × 10 45 erg s −1 ) is similar to the jet kinetic power that we estimated from radio observations at 150MHz (P kin = 6.3 × 10 45 erg s −1 ), in agreement with what is observed in powerful jetted AGN. Our Chandra observation is the deepest so far for a distant FRII within a galaxy overdensity. It revealed significant diffuse X-ray emission within the region that is covered by the overdensity. In particular, X-ray emission extending for ∼240 kpc is found around the eastern lobe of the FRII. Four out of the six MUSE star-forming galaxies in the overdensity are distributed in an arc-like shape at the edge of this diffuse X-ray emission. These objects are concentrated within 200 kpc in the plane of the sky and within 450 kpc in radial separation. Three of them are even more concentrated and fall within 60 kpc in both transverse and radial distance. The probability of observing four out of the six z = 1.7 sources by chance at the edge of the diffuse emission is negligible. In addition, these four galaxies have the highest specific star formation rates of the MUSE galaxies in the overdensity and lie above the main sequence of field galaxies of equal stellar mass at z=1.7. We propose that the diffuse X-rays originate from an expanding bubble of gas that is shock heated by the FRII jet, and that star formation is promoted by the compression of the cold interstellar medium of the galaxies around the bubble, which may be remarkable evidence of pos...

Context. The reionization of the Universe is one of the most important topics of present day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the H i ionizing background at z 3. Aims. We aim at measuring the Lyman continuum escape fraction, which is one of the key parameters to compute the contribution of star-forming galaxies to the UV background. It provides the ratio between the photons produced at λ ≤ 912 Å rest-frame and those which are able to reach the CGM/IGM, not being absorbed by the neutral hydrogen or by the dust of the galaxy's ISM. Methods. We have used ultra-deep U-band imaging (U = 30.2mag at 1σ) by LBC/LBT in the CANDELS/GOODS-North field, as well as deep imaging in COSMOS and EGS fields, in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27 ≤ z ≤ 3.40 to faint magnitude limits (L = 0.2L * , or equivalently M 1500 ∼ −19). The narrow redshift range implies that the LBC U-band filter samples exclusively the λ ≤ 912 Å rest-frame wavelengths. Results. We have measured through stacks a stringent upper limit (<1.7% at 1σ) for the relative escape fraction of H i ionizing photons from bright galaxies (L > L * ), while for the faint population (L = 0.2L * ) the limit to the escape fraction is 10%. We have computed the contribution of star-forming galaxies to the observed UV background at z ∼ 3 and we have found that it is not enough to keep the Universe ionized at these redshifts, unless their escape fraction increases significantly (≥ 10%) at low luminosities (M 1500 ≥ −19). Conclusions. We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental to measure the Lyman continuum escape fraction down to faint magnitudes (M 1500 ∼ −16) which are inaccessible with the present instrumentation on blank fields. These results will be important in order to quantify the role of faint galaxies to the reionization budget.

Context. Finding the sources responsible for the hydrogen reionization is one of the most pressing issues in observational cosmology. Bright QSOs are known to ionize their surrounding neighborhood, but they are too few to ensure the required HI ionizing background. A significant contribution by faint AGNs, however, could solve the problem, as recently advocated on the basis of a relatively large space density of faint active nuclei at z > 4. Aims. This work is part of a long term project aimed at measuring the Lyman Continuum escape fraction for a large sample of AGNs at z ∼ 4 down to an absolute magnitude of M 1450 ∼ −23. We have carried out an exploratory spectroscopic program to measure the HI ionizing emission of 16 faint AGNs spanning a broad U − I color interval, with I ∼ 21 − 23 and 3.6 < z < 4.2. These AGNs are three magnitudes fainter than the typical SDSS QSOs (M 1450 −26) which are known to ionize their surrounding IGM at z 4. Methods. We acquired deep spectra of these faint AGNs with spectrographs available at the VLT, LBT, and Magellan telescopes, i.e. FORS2, MODS1-2, and LDSS3, respectively. The emission in the Lyman Continuum region, i.e. close to 900 Å rest frame, has been detected with S/N ratio of ∼ 10 − 120 for all the 16 AGNs. The flux ratio between the 900 Å rest frame region and 930 Å provides a robust estimate of the escape fraction of HI ionizing photons. Results. We have found that the Lyman Continuum escape fraction is between 44 and 100% for all the observed faint AGNs, with a mean value of 74% at 3.6 < z < 4.2 and −25.1 M 1450 −23.3, in agreement with the value found in the literature for much brighter QSOs (M 1450 −26) at the same redshifts. The Lyman Continuum escape fraction of our faint AGNs does not show any dependence on the absolute luminosities or on the observed U − I colors of the objects. Assuming that the Lyman Continuum escape fraction remains close to ∼ 75% down to M 1450 ∼ −18, we find that the AGN population can provide between 16 and 73% (depending on the adopted luminosity function) of the whole ionizing UV background at z ∼ 4, measured through the Lyman forest. This contribution increases to 25-100% if other determinations of the ionizing UV background are adopted from the recent literature. Conclusions. Extrapolating these results to z ∼ 5 − 7, there are possible indications that bright QSOs and faint AGNs can provide a significant contribution to the Reionization of the Universe, if their space density is high at M 1450 ∼ −23.

We report the discovery of the most distant radio galaxy to date, TGSS J1530+1049 at a redshift of z = 5.72, close to the presumed end of the Epoch of Reionisation. The radio galaxy was selected from the TGSS ADR1 survey at 150 MHz for having an ultra-steep spectral index, α 150 MHz 1.4 GHz = −1.4 and a compact morphology obtained using VLA imaging at 1.4 GHz. No optical or infrared counterparts for the radio source were found in publicly available sky surveys. Follow-up optical spectroscopy at the radio position using GMOS on Gemini North revealed the presence of a single emission line. We identify this line as Lyman alpha at z = 5.72, because of its asymmetric line profile, the absence of other optical/UV lines in the spectrum and a high equivalent width. With a Lyα luminosity of 5.7 × 10 42 erg s −1 and a FWHM of 370 km s −1 , TGSS J1530+1049 is comparable to 'non-radio' Lyman alpha emitters (LAEs) at a similar redshift. However, with a radio luminosity of log L 150 MHz = 29.1 W Hz −1 and a deconvolved physical size 3.5 kpc, its radio properties are similar to other known radio galaxies at z > 4. Subsequent J and K band imaging using LUCI on the Large Binocular Telescope resulted in non-detection of the host galaxy down to 3σ limits of J > 24.4 and K > 22.4 (Vega). The K band limit is consistent with z > 5 from the K − z relation for radio galaxies and helps rule out low redshifts. The stellar mass limit derived using simple stellar population models is M stars < 10 10.5 M . Its relatively low stellar mass and small radio and Lyα sizes suggest that TGSS J1530+1049 may be a radio galaxy in an early phase of its evolution.