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M. Nonino

Publications and source records attributed to M. Nonino.

At least 145 records · Page 8Linked to original sources
arXiv2013

Chandra and optical/IR observations of CXOJ1415.2+3610, a massive, newly discovered galaxy cluster at z~1.5

(Abridged) We report the discovery of CXO J1415.2+3610, a distant (z~1.5) galaxy cluster serendipitously detected in a deep, high-resolution Chandra observation targeted to study the cluster WARP J1415.1+3612 at z=1.03. This is the highest-z cluster discovered with Chandra so far. Moreover, the total exposure time of 280 ks with ACIS-S provides the deepest X-ray observation currently achieved on a cluster at z>1.5. We perform an X-ray spectral fit of the extended emission of the intracluster medium (ICM) with XSPEC, and we detect at a 99.5% confidence level the rest frame 6.7-6.9 keV Iron K_αline complex, from which we obtain z_X=1.46\pm0.025. The analysis of the z-3.6μm color-magnitude diagram shows a well defined sequence of red galaxies within 1' from the cluster X-ray emission peak with a color range [5 < z-3.6 μm < 6]. The photometric redshift obtained by spectral energy distribution (SED) fitting is z_phot=1.47\pm 0.25. After fixing the redshift to z=1.46, we perform the final spectral analysis and measure the average gas temperature with a 20% error, kT=5.8^{+1.2}_{-1.0} keV, and the Fe abundance Z_Fe = 1.3_{-0.5}^{+0.8}Z_\odot. We fit the background subtracted surface brightness with a single beta--model out to 35" and derive the deprojected electron density profile. The ICM mass is 1.09_{-0.2}^{+0.3}\times 10^{13} M_\odot within 300 kpc. The total mass is M_{2500}= 8.6_{-1.7}^{+2.1} \times 10 ^{13} M_\odot for R_{2500}=(220\pm 55) kpc. Extrapolating the profile at larger radii we find M_{500}= 2.1_{-0.5}^{+0.7} \times 10 ^{14} M_\odot for R_{500} = 510_{-50}^{+55}$ kpc. This analysis establishes CXOJ1415.2+3610 as one of the best characterized distant galaxy clusters based on X-ray data alone.

astro-ph.CO↗
arXiv2012

The Cluster Lensing and Supernova Survey with Hubble (CLASH): Strong Lensing Analysis of Abell 383 from 16-Band HST WFC3/ACS Imaging

We examine the inner mass distribution of the relaxed galaxy cluster Abell 383 in deep 16-band HST/ACS+WFC3 imaging taken as part of the CLASH multi-cycle treasury program. Our program is designed to study the dark matter distribution in 25 massive clusters, and balances depth with a wide wavelength coverage to better identify lensed systems and generate precise photometric redshifts. This information together with the predictive strength of our strong-lensing analysis method identifies 13 new multiply-lensed images and candidates, so that a total of 27 multiple-images of 9 systems are used to tightly constrain the inner mass profile, $d\log Σ/d\log r\simeq -0.6\pm 0.1$ (r<160 kpc). We find consistency with the standard distance-redshift relation for the full range spanned by the lensed images, 1.01<z<6.03, with the higher redshift sources deflected through larger angles as expected. The inner mass profile derived here is consistent with the results of our independent weak-lensing analysis of wide-field Subaru images, with good agreement in the region of overlap. The overall mass profile is well fitted by an NFW profile with M_{vir}=(5.37^{+0.70}_{-0.63}\pm 0.26) x 10^{14}M_{\odot}/h and a relatively high concentration, c_{vir}=8.77^{+0.44}_{-0.42}\pm 0.23, which lies above the standard c-M relation similar to other well-studied clusters. The critical radius of Abell 383 is modest by the standards of other lensing clusters, r_{E}\simeq16\pm2\arcsec (for z_s=2.55), so the relatively large number of lensed images uncovered here with precise photometric redshifts validates our imaging strategy for the CLASH survey. In total we aim to provide similarly high-quality lensing data for 25 clusters, 20 of which are X-ray selected relaxed clusters, enabling a precise determination of the representative mass profile free from lensing bias. (ABRIDGED)

astro-ph.CO↗
arXiv2012

The Carina Project. V. The impact of NLTE effects on the iron content

We have performed accurate iron abundance measurements for 44 red giants (RGs) in the Carina dwarf spheroidal (dSph) galaxy. We used archival, high-resolution spectra (R~38,000) collected with UVES at ESO/VLT either in slit mode (5) or in fiber mode (39, FLAMES/GIRAFFE-UVES). The sample is more than a factor of four larger than any previous spectroscopic investigation of stars in dSphs based on high-resolution (R>38,000) spectra. We did not impose the ionization equilibrium between neutral and singly-ionized iron lines. The effective temperatures and the surface gravities were estimated by fitting stellar isochrones in the V, B-V color-magnitude diagram. To measure the iron abundance of individual lines we applied the LTE spectrum synthesis fitting method using MARCS model atmospheres of appropriate metallicity. We found evidence of NLTE effects between neutral and singly-ionized iron abundances. Assuming that the FeII abundances are minimally affected by NLTE effects, we corrected the FeI stellar abundances using a linear fit between FeI and FeII stellar abundance determinations. We found that the Carina metallicity distribution based on the corrected FeI abundances (44 RGs) has a weighted mean metallicity of [Fe/H]=-1.80 and a weighted standard deviation of sigma=0.24 dex. The Carina metallicity distribution based on the FeII abundances (27 RGs) gives similar estimates ([Fe/H]=-1.72, sigma=0.24 dex). The current weighted mean metallicities are slightly more metal poor when compared with similar estimates available in the literature. Furthermore, if we restrict our analysis to stars with the most accurate iron abundances, ~20 FeI and at least three FeII measurements (15 stars), we found that the range in iron abundances covered by Carina RGs (~1 dex) agrees quite well with similar estimates based on high-resolution spectra.

astro-ph.CO↗
arXiv2012

Abell 1758N from an optical point of view: new insights on a merging cluster with diffuse radio emission

We seek to explore the internal dynamics of the cluster Abell 1758N, which has been shown to host a radio halo and two relics, and is known to be a merging bimodal cluster. Our analysis is mainly based on new redshift data for 137 galaxies acquired at the Telescopio Nazionale Galileo, only four of which have redshifts previously listed in the literature. We also used photometric data from the Sloan Digital Sky Survey and from the Canada-France-Hawaii Telescope archive. We combined galaxy velocities and positions to select 92 cluster galaxies and analyzed the internal cluster dynamics. We estimate a cluster redshift of =0.2782 and quite a high line-of-sight (LOS) velocity dispersion of ~ 1300 km/s. Our 2D analysis confirms the presence of a bimodal structure along the NW-SE direction. We add several pieces of information to the previous merging scenario: the two subclusters (here A1758N(NW) and A1758N(SE)) cannot be separated in the velocity analyses and we deduce a small LOS velocity difference of ~300 km/s in the cluster rest-frame. The velocity information successfully shows that A1758N is surrounded by two small groups and active galaxies infalling onto, or escaping from, the cluster. Removing the two groups, we estimate ~1000 km/s and ~800 km/s for the velocity dispertions of A1758N(NW) and A1758N(SE), respectively. We find that Abell 1758N is a very massive cluster with a range of M=2-3 10^15 solar masses, depending on the adopted model. As expected for clusters that host powerful, extended, diffuse radio emissions, Abell 1758N is a major cluster merger just forming a massive system.

astro-ph.CO↗
arXiv2012

CLASH: Discovery of a Bright z~6.2 Dwarf Galaxy Quadruply Lensed by MACS J0329.6-0211

We report the discovery of a z_{phot}=6.18^{+0.05}_{-0.07} (95% confidence level) dwarf galaxy, lensed into four images by the galaxy cluster MACS J0329.6-0211 (z_{l}=0.45). The galaxy is observed as a high-redshift dropout in HST/ACS/WFC3 CLASH and Spitzer/IRAC imaging. Its redshift is securely determined due to a clear detection of the Lyman-break in the 18-band photometry, making this galaxy one of the highest-redshift multiply-lensed objects known to date with an observed magnitude of F125W=24.00\pm0.04 AB mag for its highest-magnified image. We also present the first strong-lensing analysis of this cluster uncovering 15 additional multiply-imaged candidates of five lower-redshift sources spanning the range z_{s}~2-4. The mass model independently supports the high photometric redshift and reveals magnifications of 11.6^{+8.9}_{-4.1}, 17.6^{+6.2}_{-3.9}, 3.9^{+3.0}_{-1.7}, and 3.7^{+1.3}_{-0.2}, respectively, for the four images of the high-redshift galaxy. With this we construct a source image with a physical resolution of ~200 pc when the universe was ~0.9 Gyr old, where the z~6.2 galaxy occupies a source-plane area of approximately 2.2 kpc^{2}. Modeling the observed spectral energy distribution using population synthesis models, we find a demagnified stellar mass of ~10^{9} {M}_{sun}, subsolar metallicity (Z/Z_{sun}~0.5), low dust content (A_{V}~0.1 mag), a demagnified star formation rate (SFR) of ~3.2 {M}_{sun} yr^{-1}, and a specific SFR of ~3.4 Gyr^{-1}, all consistent with the properties of local dwarf galaxies.

astro-ph.CO↗
arXiv2011

CLASH: New Multiple-Images Constraining the Inner Mass Profile of MACS J1206.2-0847

We present a strong-lensing analysis of the galaxy cluster MACS J1206.2-0847 ($z$=0.44) using UV, Optical, and IR, HST/ACS/WFC3 data taken as part of the CLASH multi-cycle treasury program, with VLT/VIMOS spectroscopy for some of the multiply-lensed arcs. The CLASH observations, combined with our mass-model, allow us to identify 47 new multiply-lensed images of 12 distant sources. These images, along with the previously known arc, span the redshift range $1\la z\la5.5$, and thus enable us to derive a detailed mass distribution and to accurately constrain, for the first time, the inner mass-profile of this cluster. We find an inner profile slope of $d\log Σ/d\log θ\simeq -0.55\pm 0.1$ (in the range [1\arcsec, 53\arcsec], or $5\la r \la300$ kpc), as commonly found for relaxed and well-concentrated clusters. Using the many systems uncovered here we derive credible critical curves and Einstein radii for different source redshifts. For a source at $z_{s}\simeq2.5$, the critical curve encloses a large area with an effective Einstein radius of $θ_{E}=28\pm3\arcsec$, and a projected mass of $1.34\pm0.15\times10^{14} M_{\odot}$. From the current understanding of structure formation in concordance cosmology, these values are relatively high for clusters at $z\sim0.5$, so that detailed studies of the inner mass distribution of clusters such as MACS J1206.2-0847 can provide stringent tests of the $Λ$CDM paradigm.

astro-ph.CO↗
arXiv2011

Internal dynamics of Abell 2254: a merging galaxy cluster with a clumpy, diffuse radio emission

We explore the internal dynamics of Abell 2254, which has been shown to host a very clumpy and irregular radio halo. Our analysis is mainly based on redshift data for 128 galaxies acquired at the TNG. We also use new g',r',i' photometric data acquired at the INT and (V,i') photometric data available in the Subaru Archive. X-ray data from the XMM-Newton Science Archive are analyzed to study the hot gas component. We estimate the cluster redshift =0.177, a high line-of-sight (LOS) velocity dispersion, sigmaV about 1350 km/s, and X-ray temperature T about 6.4 keV. Both our optical and X-ray analyses reveal a complex dynamical activity. The analysis of the 2D galaxy distribution reveals the presence of two density peaks, one at the East and the other at the West. Using the full 3D information we detect a high LOS velocity (DeltaV about 3000 km/s), low mass group at the position of the 2D eastern peak. For the main system we compute a velocity dispersion sigmaV about 1000-1200 km/s. In the assumption of a bimodal system we estimate a mass M=1.5-2.9 10^15 solar masses.The X-ray morphological analysis confirms that Abell 2254 is a dynamically disturbed cluster. The X-ray isophotes are elongated toward the eastern direction, in agreement with a merger in the post core-crossing phase. A simple bimodal model finds that data are consistent with a bound, outgoing subcluster observed a few fractions of Gyr after the core crossing. However, both optical and X-ray analyses suggest that the main system is, at its time, a non relaxed structure, indicating N-S as a possible direction for a past accretion. We conclude that Abell 2254, for its mass and merging structure, fits well among typical clusters with radio halos. We shortly discuss as the particular irregularity of the radio halo might be linked to the complexity of the Abell 2254 structure.

astro-ph.CO↗
arXiv2011

On a new parameter to estimate the helium content in old stellar systems

We introduce a new parameter Δξ - the difference in magnitude between the red giant branch (RGB) bump and a point on the main sequence (MS) at the same color as the bump, the "benchmark" - to estimate the helium content in old stellar systems. Its sensitivity to helium is linear over the entire metallicity range, it is minimally affected by age, uncertainties in the photometric zero-point, reddening or the effects of evolution on the horizontal branch. The two main drawbacks are the need for precise and large photometric data sets, and a strong dependence of the ΔY/Δξ slope on metallicity. To test the Δξ parameter we selected 22 Galactic Globular Clusters (GGCs) with low foreground reddening, a broad range of iron abundance and precise, relatively deep, and homogeneous multi-band (B,V,I) photometry. We found that the observed Δξ and those predicted from α-enhanced models agree quite well if we assume Y=0.20. Comparison with canonical primordial helium content models (Y=0.245, ΔY/ΔZ=1.4) indicates that the observed Δξ values are systematically smaller than predicted. The outcome is the same if predicted parameters are based on models that take into account also CNO enhancements and becomes even larger if we consider He-enhanced models. These findings suggest that current stellar evolutionary models overestimate the luminosity of the RGB bump. We also found that including envelope overshooting can eliminate the discrepancy, as originally suggested by Alongi et al. (1993, aaps, 97, 851). The Δξ parameter of GGCs, in spite of the possible limitations concerning the input physics of current evolutionary models, provides an independent detection of pre-stellar helium at least at the 5σ level.

astro-ph.SR↗
arXiv2011

Early-Type galaxies at z ~ 1.3. III. On the dependence of Formation Epochs and Star Formation Histories on Stellar Mass and Environment

We study the environmental dependence of stellar population properties at z ~ 1.3. We derive galaxy properties (stellar masses, ages and star formation histories) for samples of massive, red, passive early-type galaxies in two high-redshift clusters, RXJ0849+4452 and RXJ0848+4453 (with redshifts of z = 1.26 and 1.27, respectively), and compare them with those measured for the RDCS1252.9-2927 cluster at z=1.24 and with those measured for a similarly mass-selected sample of field contemporaries drawn from the GOODS-South Field. Robust estimates of the aforementioned parameters have been obtained by comparing a large grid of composite stellar population models with extensive 8-10 band photometric coverage, from the rest-frame far-ultraviolet to the infrared. We find no variations of the overall stellar population properties among the different samples of cluster early-type galaxies. However, when comparing cluster versus field stellar population properties we find that, even if the (star formation weighted) ages are similar and depend only on galaxy mass, the ones in the field do employ longer timescales to assemble their final mass. We find that, approximately 1 Gyr after the onset of star formation, the majority (75%) of cluster galaxies have already assembled most (> 80%) of their final mass, while, by the same time, fewer (35%) field ETGs have. Thus we conclude that while galaxy mass regulates the timing of galaxy formation, the environment regulates the timescale of their star formation histories.

astro-ph.CO↗
arXiv2011

The Carina Project. IV. radial velocity distribution

We present new and accurate radial velocity (RV) measurements of luminous stars of all ages (old horizontal branch, intermediate--age red clump, and young blue plume, as well as red giants of a range of ages; 20.6<V<22) in the Carina dwarf spheroidal galaxy, based on low-resolution spectra collected with the FORS2 multi-object slit spectrograph at the VLT. This data set was complemented by RV measurements based on medium and high-resolution archive spectra of brighter (V<20.6) Carina targets collected with the GIRAFFE multi-object fiber spectrograph at the VLT. The combined sample includes more than 21,340 individual spectra of ~2,000 stars covering the entire body of the galaxy. To further improve the statistics, the accurate RV measurements recently provided by Walker et al.(2007) were also added to the current data set. We ended up with a sample of ~1,370 RV measurements of candidate Carina stars that is ~75% larger than any previous Carina RV sample. The mean RV across the body of the galaxy varies from ~220 km/s at a distance of 7arcmin (~200 pc) from the center to ~223 km/s at 13arcmin, (~400 pc, 6sigma level) and flattens out to a constant value of ~221 km/s at larger distances (600 pc, 4sigma level). Moreover and even more importantly, we found that in the Carina regions where the mean RV is smaller the dispersion is also smaller, and the RV distribution is more centrally peaked (i.e. the kurtosis attains larger values). There is evidence of a secondary maximum in RV across the Carina center (|D|<200 pc). The occurrence of a secondary feature across the Carina center is also supported by the flat-topped radial distribution based on the photometric catalog.

astro-ph.GA↗
arXiv2011

Optical-NIR spectra of quasars close to reionization (z~ 6)

X-shooter, with its characteristics of resolution, spectral coverage and efficiency, provides a unique opportunity to obtain spectra of the highest-redshift quasars (z ~ 6) that will allow us to carry out successful investigations on key cosmological issues, from the details of the re-ionization process, to the evolution of the first galaxies and AGNs. In this paper, we present the spectra of three z ~ 6 quasars: one obtained during the commissioning of X-shooter and two in the context of our ongoing GTO programme. Combining this sample with data in the literature, we update the value of the C IV cosmic mass density in the range 4.5 < z < 5, confirming the constant trend with redshift between 2.5 and 5.

astro-ph.CO↗
arXiv2010

Star Formation Histories in a Cluster Environment at z~0.84

We present a spectrophotometric analysis of galaxies belonging to the dynamically young, massive cluster RX J0152.7-1357 at z~0.84, aimed at understanding the effects of the cluster environment on the star formation history (SFH) of cluster galaxies and the assembly of the red-sequence (RS). We use VLT/FORS spectroscopy, ACS/WFC optical and NTT/SofI near-IR data to characterize SFHs as a function of color, luminosity, morphology, stellar mass, and local environment from a sample of 134 spectroscopic members. In order to increase the signal-to-noise, individual galaxy spectra are stacked according to these properties. Moreover, the D4000, Balmer, CN3883, Fe4383 and C4668 indices are also quantified. The SFH analysis shows that galaxies in the blue faint-end of the RS have on average younger stars (Delta t ~ 2 Gyr) than those in the red bright-end. We also found, for a given luminosity range, differences in age (Delta t ~ 0.5 - 1.3 Gyr) as a function of color, indicating that the intrinsic scatter of the RS may be due to age variations. Passive galaxies in the blue faint-end of the RS are preferentially located in the low density areas of the cluster, likely being objects entering the RS from the "blue cloud". It is likely that the quenching of the star formation of these RS galaxies is due to interaction with the intracluster medium. Furthermore, the SFH of galaxies in the RS as a function of stellar mass reveals signatures of "downsizing" in the overall cluster.

astro-ph.CO↗
arXiv2010

On the radial extent of the dwarf irregular galaxy IC10

We present new deep and accurate space (Advanced Camera for Surveys -- Wide Field Planetary Camera 2 at the Hubble Space Telescope) and ground-based (Suprime-Cam at Subaru Telescope, Mega-Cam at Canada-France-Hawaii Telescope) photometric and astrometric data for the Local Group dwarf irregular IC10. We confirm the significant decrease of the young stellar population when moving from the center toward the outermost regions. We find that the tidal radius of IC10 is significantly larger than previous estimates of $r_t \lesssim$ 10\min. By using the $I$,\vmi\ Color Magnitude Diagram based on the Suprime-Cam data we detect sizable samples of red giant (RG) stars up to radial distances of 18-23$'$ from the galactic center. The ratio between observed star counts (Mega-Cam data) across the tip of the RG branch and star counts predicted by Galactic models indicate a star count excess at least at a 3$σ$ level up to 34-42\min\ from the center. This finding supports the hypothesis that the huge H{\size{I}} cloud covering more than one degree across the galaxy is associated with IC10 \citep{huchtmeier79,cohen79}. We also provide new estimates of the total luminosity ($L_V\sim9\times$$10^7$ $L_\odot$, $M_V$$\sim$-15.1 mag) that agrees with similar estimates available in the literature. If we restrict to the regions where rotational velocity measurements are available (r$\approx13'$), we find a mass-to-light ratio ($\sim$10 $M_\odot$ $L_\odot$) that is at least one order of magnitude larger than previous estimates. The new estimate should be cautiously treated, since it is based on a minimal fraction of the body of the galaxy.

astro-ph.SR↗
arXiv2010

The hot horizontal-branch stars in omega Centauri

UV observations of some massive globular clusters have revealed a significant population of stars hotter and fainter than the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario where stars experience the helium flash while on the white dwarf cooling curve or by the progeny of the helium-enriched sub-population postulated to exist in some clusters. Previous spectroscopic analyses of blue hook stars in omega Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C and N enrichment cannot be verified. We compare the observed effective temperatures, surface gravities, helium abundances, and carbon line strengths (where detectable) of our targets stars with the predictions of the two aforementioned scenarios. Moderately high resolution spectra of hot HB stars in the globular cluster omega Cen were analysed for radial velocity variations, atmospheric parameters, and abundances using LTE and non-LTE model atmospheres. We find no evidence of close binaries among our target stars. All stars below 30,000K are helium-poor and very similar to HB stars observed in that temperature range in other globular clusters. In the temperature range 30,000K to 50,000K, we find that 28% of our stars are helium-poor (log(He/H) < -1.6), while 72% have roughly solar or super-solar helium abundance (log(He/H) >= -1.5). We also find that carbon enrichment is strongly correlated with helium enrichment, with a maximum carbon enrichment of 3% by mass. A strong carbon enrichment in tandem with helium enrichment is predicted by the late hot flasher scenario, but not by the helium-enrichment scenario. We conclude that the helium-rich HB stars in omega Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

astro-ph.SR↗
arXiv2010

Cluster galaxies in XMMU J2235-2557: galaxy population properties in most massive environments at z~1.4

We present a multi-wavelength study of galaxy populations in the core of the massive, X-ray luminous cluster XMMU J2235 at z=1.39, based on VLT and HST optical and near-infrared photometry. Luminosity functions in the z, H, and Ks bands show a faint-end slope consistent with being flat, and a characteristic magnitude M* close to passive evolution predictions of M* of local massive clusters, with a formation redshift z>2. The color-magnitude and color-mass diagrams show evidence of a tight red sequence of massive galaxies, with overall old stellar populations, generally early-type morphology, typically showing early-type spectral features and rest-frame far-UV emission consistent with very low star formation rates (SFR<0.2Msun/yr). Star forming spectroscopic members, with SFRs of up to ~100Msun/yr, are all located at clustercentric distances >~250kpc, with the central cluster region already appearing effectively quenched. Massive galaxies in the core of this cluster appear to be in an advanced evolutionary stage in terms of both star formation and mass assembly. The high-mass end of the galaxy stellar mass function is essentially already in place, and the stellar mass fraction estimated within r500 (~1%, Kroupa IMF) is already similar to that of local massive clusters. On the other hand, morphological analysis of the massive red sequence galaxies suggests that they are smaller than similarly massive local early-types. While possibly affected by systematics and biases, this result might imply that, in spite of the overall early assembly of these sources, their evolution is not complete, and processes like minor (and likely dry) merging might still shape their structural properties to resemble those of their local counterparts, without substantially affecting their stellar mass or host stellar populations.[abridged]

astro-ph.CO↗
arXiv2010

The Great Observatories Origins Deep Survey: Constraints on the Lyman Continuum Escape Fraction Distribution of Lyman--Break Galaxies at 3.4<z<4.5

We use ultra-deep ultraviolet VLT/VIMOS intermediate-band and VLT/FORS1 narrow-band imaging in the GOODS Southern field to derive limits on the distribution of the escape fraction (f_esc) of ionizing radiation for L >~ L*(z=3) Lyman Break Galaxies (LBGs) at redshift 3.4--4.5. Only one LBG, at redshift z=3.795, is detected in its Lyman continuum (LyC; S/N~5.5), the highest redshift galaxy currently known with a direct detection. Its ultraviolet morphology is quite compact (R_eff=0.8, kpc physical). Three out of seven AGN are also detected in their LyC, including one at redshift z=3.951 and z850 = 26.1. From stacked data (LBGs) we set an upper limit to the average f_esc in the range 5%--20%, depending on the how the data are selected (e.g., by magnitude and/or redshift). We undertake extensive Monte Carlo simulations that take into account intergalactic attenuation, stellar population synthesis models, dust extinction and photometric noise in order to explore the moments of the distribution of the escaping radiation. Various distributions (exponential, log-normal and Gaussian) are explored. We find that the median f_esc is lower than ~6% with an 84% percentile limit not larger than 20%. If this result remains valid for fainter LBGs down to current observational limits, then the LBG population might be not sufficient to account for the entire photoionization budget at the redshifts considered here, with the exact details dependent upon the assumed ionizing background and QSO contribution thereto. It is possible that f_esc depends on the UV luminosity of the galaxies, with fainter galaxies having higher f_esc, and estimates of f_esc from a sample of faint LBG from the HUDF (i775<28.5) are in broad quantitative agreement with such a scenario.

astro-ph.CO↗
arXiv2010

The bright end of the z ~ 7 UV Luminosity Function from a wide and deep HAWK-I survey

(Abridged) We present here the second half of an ESO Large Programme, which exploits the unique combination of area and sensitivity provided in the near-IR by the camera Hawk-I at the VLT. We have obtained - 30 observing hours with Hawk-I in the Y-band of two high galactic latitude fields. We combined the Y-band data with deep J and K Hawk-I observations, and with FORS1/FORS2 U, B, V, R, I, and Z observations to select z-drop galaxies having Z - Y > 1, no optical detection and flat Y - J and Y - K colour terms. We detect 8 high-quality candidates in the magnitude range Y = 25.5 - 26.5 that we add to the z-drop candidates selected in two Hawk-I pointings over the GOODS-South field. We use this full sample of 15 objects found in -161 arcmin^2 of our survey to constrain the average physical properties and the evolution of the number density of z ~ 7 LBGs. A stacking analysis yields a best-fit SED with photometric redshift z= 6.85 +0.20 -0.15 and an E(B-V)=0.05 +0.15 -0.05. We compute a binned estimate of the z ~ 7 LF and explore the effects of photometric scatter and model uncertainties on the statistical constraints. After accounting for the expected incompleteness through MonteCarlo simulations, we strengthen our previous finding that a Schechter luminosity function constant from z=6 to z=7 is ruled out at a >99% confidence level, even including the effects of cosmic variance. For galaxies brighter than M_1500= -19.0, we derive a luminosity density rho_UV = 1.5^{+2.1}{-0.8} x 10^25 erg/s/Hz/Mpc^3, implying a decrease by a factor 3.5 from z=6 to z=6.8. We find that, under standard assumptions, the emission rate of ionizing photons coming from UV bright galaxies is lower by at least a factor of two than the value required for reionization. Finally, we exploit deep Hawk-I J and K band observations to derive an upper limit on the number density of M1500<~ -22.0 LBGs at z-8 (Y-dropouts).

astro-ph.CO↗