We present the first results and design from the redshift z ∼ 9 − 10 Brightest of the Reionizing Galaxies Hubble Space Telescope survey BoRG[z9-10], aimed at searching for intrinsically luminous unlensed galaxies during the first 700 Myr after the Big Bang. is the continuation of a multi-year pure-parallel near-IR and optical imaging campaign with the Wide Field Camera 3. The ongoing survey uses five filters, optimized for detecting the most distant objects and offering continuous wavelength coverage from λ = 0.35µm to λ = 1.7µm. We analyze the initial ∼ 130 arcmin 2 of area over 28 independent lines of sight (∼ 25% of the total planned) to search for z > 7 galaxies using a combination of Lyman break and photometric redshift selections. From an effective comoving volume of (5 − 25) × 10 5 Mpc 3 for magnitudes brighter than m AB = 26.5 − 24.0 in the H 160 -band respectively, we find five galaxy candidates at z ∼ 8.3 − 10 detected at high confidence (S/N > 8), including a source at z ∼ 8.4 with m AB = 24.5 (S/N ∼ 22), which, if confirmed, would be the brightest galaxy identified at such early times (z > 8). In addition, BoRG[z9-10] data yield four galaxies with 7.3 z 8. These new Lyman break galaxies with m 26.5 are ideal targets for follow-up observations from ground and space based observatories to help investigate the complex interplay between dark matter growth, galaxy assembly, and reionization.

The Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) enabled the search for the first galaxies observed at z∼8-11 (500-700 Myr after the Big Bang). To continue quantifying the number density of the most luminous galaxies (M AB ∼ −22.0) at the earliest epoch observable with HST, we search for z∼10 galaxies (F125W-dropouts) in archival data from the Brightest of Reionizing Galaxies (BoRG[z8]) survey, originally designed for detection of z∼8 galaxies (F098M-dropouts). By focusing on the deepest 293 arcmin 2 of the data along 62 independent lines of sight, we identify six z∼10 candidates satisfying the color selection criteria, detected at S/N>8 in F160W with M AB =−22.8 to −21.1 if at z=10. Three of the six sources, including the two brightest, are in a single WFC3 pointing (∼4 arcmin 2 ), suggestive of significant clustering, which is expected from bright galaxies at z∼10. However, the two brightest galaxies are too extended to be likely at z∼10, and one additional source is unresolved and possibly a brown dwarf. The remaining three candidates have m AB ∼26, and given the area and completeness of our search, our best estimate is a number density of sources that is marginally higher but consistent at 2σ with searches in legacy fields. Our study highlights that z∼10 searches can yield a small number of candidates, making tailored follow-ups of HST pure-parallel observations viable and effective.

The selection of high redshift sources from broad-band photometry using the Lyman-break galaxy (LBG) technique is a well established methodology, but the characterization of its contamination for the faintest sources is still incomplete. We use the optical and near-IR data from four (ultra)deep Hubble Space Telescope legacy fields to investigate the contamination fraction of LBG samples at z ∼ 5 − 8 selected using a colour-colour method. Our approach is based on characterizing the number count distribution of interloper sources, that is galaxies with colors similar to those of LBGs, but showing detection at wavelengths shorter than the spectral break. Without sufficient sensitivity at bluer wavelengths, a subset of interlopers may not be properly classified, and contaminate the LBG selection. The surface density of interlopers in the sky gets steeper with increasing redshift of LBG selections. Since the intrinsic number of dropouts decreases significantly with increasing redshift, this implies increasing contamination from misclassified interlopers with increasing redshift, primarily by intermediate redshift sources with unremarkable properties (intermediate ages, lack of ongoing star formation and low/moderate dust content). Using Monte Carlo simulations, we estimate that the CANDELS deep data have contamination induced by photometric scatter increasing from ∼ 2% at z ∼ 5 to ∼ 6% at z ∼ 8 for a typical dropout color ≥ 1 mag, with contamination naturally decreasing for a more stringent dropout selection. Contaminants are expected to be located preferentially near the detection limit of surveys, ranging from 0.1 to 0.4 contaminants per arcmin 2 at J 125 =30, depending on the field considered. This analysis suggests that the impact of contamination in future studies of z > 10 galaxies needs to be carefully considered.

Aims. The aim of this paper is to study the stellar population of galaxies hosting an active galactic nucleus (AGN). We studied a subsample of hard X-ray emitting AGNs from the INTEGRAL and Swift catalogs, which were previously identified and characterized through optical spectroscopy. Our analysis provides complementary information, namely age and metallicity, which is necessary to complete the panoramic view of these interesting objects. Methods. We selected hard X-ray emitting objects, identified as AGNs, by checking their optical spectra in search of absorption lines suitable for the stellar population analysis. We obtained a final sample consisting of 20 objects with a redshift lower than 0.3. We used the full-spectrum fitting method; particularly, we use penalized pixel method and apply the PPXF code. After masking all the regions affected by emission lines, we fitted the spectra with the MILES single stellar population templates, and we derived mass-weighted ages and metallicities. Results. Most of the objects in our sample show an old stellar population; however, three of them are characterized by a bimodal distribution with a non-negligible contribution from young stars. The values of the mass-weighted metallicity span a wide range with most of them slightly above the solar value. No relations between the stellar population properties and the morphological ones have been found.

Cosmological surface brightness dimming of the form (1 + z) −4 affects all sources. The strong dependence of surface brightness dimming on redshift z suggests the presence of a selection bias when searching for high-redshift galaxies, i.e. we tend to detect only those galaxies with a high surface brightness (SB). However, unresolved knots of emission are not affected by SB dimming, thus providing a way to test the clumpiness of high-z galaxies. Our strategy relies on the comparison of the total flux detected for the same source in surveys characterized by different depth. For all galaxies, deeper images permit the better investigation of low-SB features. Cosmological SB dimming makes these low-SB features hard to detect when going to higher and higher redshifts. We used the GOODS and HUDF Hubble Space Telescope legacy datasets to study the effect of SB dimming on low-SB features of high-redshift galaxies and compare it to the prediction for smooth sources. We selected a sample of Lyman-break galaxies at z ∼ 4 (i.e. B 435 -band dropouts) detected in all of the datasets and found no significant trend when comparing the total magnitudes measured from images with different depth. Through Monte Carlo simulations we derived the expected trend for galaxies with different SB profiles. The comparison to the data hints at a compact distribution for most of the rest-frame ultraviolet light emitted from high-z galaxies.

We present a new technique to quantify the light contribution coming from the faint high redshift (z ∼ 6) galaxies below the detection threshold of imaging data, set conventionally at S/N = 4.5. We illustrate the technique with an application to Hubble Space Telescope Advanced Camera for Surveys images in the F775W and F850LP filters of the Ultra Deep Field parallel field NICP12. The aim of this analysis is to extend by a few magnitudes the faint end of the luminosity function at z ∼ 6. After masking all the detected sources in the field we apply a Fast Fourier Transform to obtain the spatial power spectrum of the background signal. The power spectrum permits us to separate the background noise signal, the residuals due to the data reduction of the wide field, and the overall signal produced by faint galaxies. The ratio of the signal in the i 775 and z 850 bands is used to estimate the contribution of the faint i-dropout objects. We rely on extensive Monte Carlo simulations to characterize various sources of uncertainty and quantify the number of faint i-dropout galaxies in the field. The analysis allows us to put constraints on the luminosity function at z ∼ 6 down to z 850 = 30 mag, 2.5 mag fainter than with standard techniques on the same data. The data are consistent with a faint end slope of the luminosity function of α = −1.9. Assuming a specific set of values for the clumping factor, escape fraction, and spectral energy distribution, we find that the z ∼ 6 undetected galaxies down to z 850 = 30 mag could have driven cosmic reionization.

Aims. The purpose of this work is to make available new gas-phase oxygen abundance measurements for a serendipitous sample of 27 galaxies with redshifts 0.35 ≤ z ≤ 0.52. Methods. We measured the equivalent widths of the [O ii]λ3727, Hβ, and [O iii]λλ4959, 5007 emission lines observed in the galaxy spectra obtained with the Visible Multi-Object Spectrograph mounted at the Very Large Telescope. For each galaxy, we derived the metallicity-sensitive emission-line ratio R 23 , ionization-sensitive emission-line ratio O 32 , and gas-phase oxygen abundance 12 + log(O/H).Results. The values of the gas-phase oxygen abundance 12 + log(O/H) that we obtained for all the sample galaxies are consistent with previous findings for galaxies at intermediate redshift.