Deep R-band counts of z~3 Lyman break galaxy candidates with the LBT

Aims. We present a deep multiwavelength imaging survey (UGR) in 3 different fields, Q0933, Q1623, and COSMOS, for a total area of ~1500arcmin^2. The data were obtained with the Large Binocular Camera on the Large Binocular Telescope. Methods. To select our Lyman break galaxy (LBG) candidates, we adopted the well established and widely used color-selection criterion (U-G vs. G-R). One of the main advantages of our survey is that it has a wider dynamic color range for U-dropout selection than in previous studies. This allows us to fully exploit the depth of our R-band images, obtaining a robust sample with few interlopers. In addition, for 2 of our fields we have spectroscopic redshift information that is needed to better estimate the completeness of our sample and interloper fraction. Results. Our limiting magnitudes reach 27.0(AB) in the R band (5\sigma) and 28.6(AB) in the U band (1\sigma). This dataset was used to derive LBG candidates at z~3. We obtained a catalog with a total of 12264 sources down to the 50% completeness magnitude limit in the R band for each field. We find a surface density of ~3 LBG candidates arcmin^2 down to R=25.5, where completeness is >=95% for all 3 fields. This number is higher than the original studies, but consistent with more recent samples.Comment: in press by A&A, full LBG candidates' catalog will be available in electronic form at the CD

The contribution of faint AGNs to the ionizing background at z~4

Finding the sources responsible for the hydrogen reionization is one of the most pressing issues in 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. 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 (M1450<~-26) which are known to ionize their surrounding IGM at z>~4. The LyC escape fraction has been detected with S/N ratio of ~10-120 and 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<M1450<-23.3, in agreement with the value found in the literature for much brighter QSOs (M1450<~-26) at the same redshifts. The LyC escape fraction of our faint AGNs does not show any dependence on the absolute luminosities or on the observed U-I colors. Assuming that the LyC escape fraction remains close to ~75% down to M1450~-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. 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 M1450~-23.Comment: Accepted for publication on A&A, 16 pages, 22 figure

AMBER/VLTI observations of 5 giant stars

While the search for exoplanets around main sequence stars more massive than the Sun have found relatively few such objects, surveys performed around giant stars have led to the discovery of more than 30 new exoplanets. The interest in studying planet hosting giant stars resides in the possibility of investigating planet formation around stars more massive than the Sun. Masses of isolated giant stars up to now were only estimated from evolutionary tracks, which led to different results depending on the physics considered. To calibrate the theory, it is therefore important to measure a large number of giant star diameters and masses as much as possible independent of physical models. We aim in the determination of diameters and effective temperatures of 5 giant stars, one of which is known to host a planet. AMBER/VLTI observations with the ATs were executed in low resolution mode on 5 giant stars. In order to measure high accurate calibrated squared visibilities, a calibrator-star-calibrator observational sequence was performed. We measured the uniform disk and limb-darkened angular diameters of 4 giant stars. The effective temperatures were also derived by combining the bolometric luminosities and the interferometric diameters. Lower effective temperatures were found when compared to spectroscopic measurements. The giant star HD12438 was found to have an unknown companion star at an angular separation of ~ 12 mas. Radial velocity measurements present in the literature confirm the presence of a companion with a very long orbital period (P ~ 11.4 years).}Comment: accepted for publication in A&

Elemental abundances of low-mass stars in the young clusters 25 Ori and lambda Ori

Aims. We aim to derive the chemical pattern of the young clusters 25 Orionis and lambda Orionis through homogeneous and accurate measurements of elemental abundances. Methods. We present FLAMES/UVES observations of a sample of 14 K-type targets in the 25 Ori and lambda Ori clusters; we measure their radial velocities, in order to confirm cluster membership. We derive stellar parameters and abundances of Fe, Na, Al, Si, Ca, Ti, and Ni using the code MOOG. Results. All the 25 Ori stars are confirmed cluster members without evidence of binarity; in lambda Ori we identify one non-member and one candidate single-lined binary star. We find an average metallicity [Fe/H]=-0.05+/-0.05 for 25 Ori, where the error is the 1sigma standard deviation from the average. lambda Ori members have a mean iron abundance value of 0.01+/-0.01. The other elements show close-to-solar ratios and no star-to-star dispersion. Conclusions. Our results, along with previous metallicity determinations in the Orion complex, evidence a small but detectable dispersion in the [Fe/H] distribution of the complex. This appears to be compatible with large-scale star formation episodes and initial non-uniformity in the pre-cloud medium. We show that, as expected, the abundance distribution of star forming regions is consistent with the chemical pattern of the Galactic thin disk.Comment: Accepted by Astronomy and Astrophysics. 14 pages, 10 figures, 7 table

Angular Diameters and Effective Temperatures of Twenty-five K Giant Stars from the CHARA Array

Using Georgia State University's CHARA Array interferometer, we measured angular diameters for 25 giant stars, six of which host exoplanets. The combination of these measurements and Hipparcos parallaxes produce physical linear radii for the sample. Except for two outliers, our values match angular diameters and physical radii estimated using photometric methods to within the associated errors with the advantage that our uncertainties are significantly lower. We also calculated the effective temperatures for the stars using the newly-measured diameters. Our values do not match those derived from spectroscopic observations as well, perhaps due to the inherent properties of the methods used or because of a missing source of extinction in the stellar models that would affect the spectroscopic temperatures

The VMC Survey. XXXII. Pre-main-sequence populations in the Large Magellanic Cloud

Context Detailed studies of intermediate- and low-mass pre-main-sequence (PMS) stars outside the Galaxy have so far been conducted only for small targeted regions harbouring known star formation complexes. The VISTA Survey of the Magellanic Clouds (VMC) provides an opportunity to study PMS populations down to solar masses on a galaxy-wide scale. Aims Our goal is to use near-infrared data from the VMC survey to identify and characterise PMS populations down to ∼ 1 M� across the Magellanic Clouds. We present our colour−magnitude diagram method, and apply it to a ∼ 1.5 deg2 pilot field located in the Large Magellanic Cloud. Methods The pilot field is divided into equal-size grid elements. We compare the stellar population in every element with the population in nearby control fields by creating Ks/(Y−Ks) Hess diagrams; the observed density excesses over the local field population are used to classify the stellar populations. Results Our analysis recovers all known star formation complexes in this pilot field (N 44, N 51, N 148, and N 138) and for the first time reveals their true spatial extent. In total, around 2260 PMS candidates with ages . 10 Myr are found in the pilot field. PMS structures, identified as areas with a significant density excess of PMS candidates, display a power-law distribution of the number of members with a slope of −0.86 ± 0.12. We find a clustering of the young stellar populations along ridges and filaments where dust emission in the far-infrared (FIR) (70 µm – 500 µm) is bright. Regions with young populations lacking massive stars show a lower degree of clustering and are usually located in the outskirts of the star formation complexes. At short FIR wavelengths (70 µm, 100 µm) we report a strong dust emission increase in regions hosting young massive stars, which is less pronounced in regions populated only by less massive (. 4 M�) PMS stars

Web of the giant: Spectroscopic confirmation of a large-scale structure around the z = 6.31 quasar SDSS J1030+0524

We report on the spectroscopic confirmation of a large-scale structure around the luminous z = 6.31 quasi-stellar object (QSO) SDSS J1030+0524, powered by a one billion solar mass black hole. The structure is populated by at least six members, namely, four Lyman-break galaxies (LBGs), and two Lyman alpha emitters (LAEs). The four LBGs were identified among a sample of 21 i-band dropouts with zAB &lt; 25.5 selected up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their redshifts were determined through multi-object spectroscopic observations at 8-10 m class telescopes lasting up to eight hours. The two LAEs were identified in a 6 h VLT/MUSE observation centered on the QSO. The redshifts of the six galaxies cover the range between 6.129-6.355. Assuming that the peculiar velocities are negligible, this range corresponds to radial separations of \ub15 physical Mpc from the QSO, that is comparable to the projected scale of the observed LBG distribution on the sky. We conservatively estimate that this structure is significant at a level &gt; 3.5\u3c3 and that the level of the galaxy overdensity is at least 1.5-2 within the large volume sampled ( 3c780 physical Mpc3). The spectral properties of the six member galaxies (Ly\u3b1 strength and UV luminosity) are similar to those of field galaxies at similar redshifts. This is the first spectroscopic identification of a galaxy overdensity around a supermassive black hole in the first billion years of the Universe. Our finding lends support to the idea that the most distant and massive black holes form and grow within massive (&gt;1012 M) dark matter halos in large-scale structures and that the absence of earlier detections of such systems is likely due to observational limitations

Evidence for acoustic communication among bottom foraging humpback whales

Humpback whales (Megaptera novaeangliae), a mysticete with a cosmopolitan distribution, demonstrate marked behavioural plasticity. Recent studies show evidence of social learning in the transmission of specific population level traits ranging from complex singing to stereotyped prey capturing behaviour. Humpback whales have been observed to employ group foraging techniques, however details on how individuals coordinate behaviour in these groups is challenging to obtain. This study investigates the role of a novel broadband patterned pulsed sound produced by humpback whales engaged in bottom-feeding behaviours, referred to here as a ‘paired burst’ sound. Data collected from 56 archival acoustic tag deployments were investigated to determine the functional significance of these signals. Paired burst sound production was associated exclusively with bottom feeding under low-light conditions, predominantly with evidence of associated conspecifics nearby suggesting that the sound likely serves either as a communicative signal to conspecifics, a signal to affect prey behaviour, or possibly both. This study provides additional evidence for individual variation and phenotypic plasticity of foraging behaviours in humpback whales and provides important evidence for the use of acoustic signals among foraging individuals in this species

STEP: the VST survey of the SMC and the Magellanic Bridge - I : Overview and first results

STEP (the SMC in Time: Evolution of a Prototype interacting late-type dwarf galaxy) is a Guaranteed Time Observation survey being performed at the VST (the ESO VLT Survey Telescope). STEP will image an area of 74 sq. deg. covering the main body of the Small Magellanic Cloud (32 sq. deg.), the Bridge that connects it to the Large Magellanic Cloud (30 sq. deg.) and a small part of the Magellanic Stream (2 sq. deg.). Our g, r, i, Hα photometry is able to resolve individual stars down to magnitudes well below the main-sequence turn-off of the oldest populations. In this first paper, we describe the observing strategy, the photometric techniques and the upcoming data products of the survey. We also present preliminary results for the first two fields for which data acquisition is completed, including some detailed analysis of the two stellar clusters IC 1624 and NGC 419.Peer reviewedFinal Accepted Versio

Redshift identification of X-ray-selected active galactic nuclei in the J1030 field: searching for large-scale structures and high-redshift sources

We publicly release the spectroscopic and photometric redshift catalog of the sources detected with Chandra in the field of the z = 6.3 quasar SDSS J1030+0525. This is currently the fifth-deepest extragalactic X-ray field, and reaches a 0.5 2 keV flux limit of f0:5-2 = 6 × 10-17 erg s-1 cm-2. Using two independent methods, we measure a photometric redshift for 243 objects, while 123 (51%) sources also have a spectroscopic redshift, 110 of which come from an INAF-Large Binocular Telescope (LBT) Strategic Program.We use the spectroscopic redshifts to determine the quality of the photometric ones, and find it to be in agreement with that of other X-ray surveys which used a similar number of photometric data points. In particular, we measure a sample normalized median absolute deviation of NMAD = 1.48 × median(||zphot - zspec||/(1 + zspec)) = 0.065. We use these new spectroscopic and photometric redshifts to study the properties of the Chandra J1030 field.We observe several peaks in our spectroscopic redshift distribution between z = 0.15 and z = 1.5, and find that the sources in each peak are often distributed across the whole Chandra field of view. This confirms that X-ray-selected AGNs can efficiently track large-scale structures over physical scales of several megaparsecs. Finally, we computed the Chandra J1030 z > 3 number counts: while the spectroscopic completeness of our sample is limited at high redshift, our results point towards a potential source excess at z ≥ 4, which we plan to either confirm or reject in the near future with dedicated spectroscopic campaigns