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© 2012 The Authors. © 2012 Monthly Notices of the Royal Astronomical Society © 2012 RAS. We thank the anonymous referee for a careful and constructive reading of the manuscript that helped us to improve the quality of the paper. We are grateful to Lulu Liu for providing us with their measurements of the fraction of galaxies with satellites obtained from the SDSS, used here as a local (z = 0) comparison. We thank Juan Betancort for his valuable input on several aspects of the statistical analysis in this paper. We are grateful to Sergio Pascual for his very useful help with programming questions. We would like also to acknowledge fruitful discussions with Javier Cenarro, Luis Díaz, Rosa Domínguez, César González, Carlos López San Juan, José Onorbe, Thorsten Naab and Vicent Quilis. IT is a Ramón y Cajal Fellow of the Spanish Ministry of Science and Innovation. This work has been supported by the 'Programa Nacional de Astronomía y Astrofísica' of the Spanish Ministry of Science and Innovation under grant AYA2010-21322-C03-02. PGP and GB acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2009-10368 and AYA2009-07723-E. This work has made use of the Rainbow Cosmological Surveys Data base, which is operated by the Universidad Complutense de Madrid (UCM)., The accretion of minor satellites has been postulated as the most likely mechanism to explain the significant size evolution of massive galaxies over cosmic time. Using a sample of 629 massive (M_star~ 10^11 M_⊙) galaxies from the near-infrared Palomar/DEEP-2 survey, we explore what fraction of these objects have satellites with 0.01 < M_sat/M_central < 1 (1:100) up to z= 1 and what fraction have satellites with 0.1 < M_sat/M_central < 1 (1:10) up to z= 2 within a projected radial distance of 100 kpc. We find that the fraction of massive galaxies with satellites, after background correction, remains basically constant and close to 30 per cent for satellites with a mass ratio down to 1:100 up to z= 1, and close to 15 per cent for satellites with a 1:10 mass ratio up to z= 2. The family of spheroid-like massive galaxies presents a 2–3 times larger fraction of objects with satellites than the group of disc-like massive galaxies. A crude estimation of the number of 1:3 mergers a massive spheroid-like galaxy has experienced since z~2 is around 2. For a disc-like galaxy this number decreases to ~1., Ministerio de Ciencia e Innovación (MICINN), Programa Nacional de Astronomía y Astrofísica (PNAyA), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2015. The American Astronomical Society. All rights reserved. We thank the two anonymous referees for contributing to significantly improve this work. M.H.C acknowledges D. Gratadour for kindly giving us access to the GPU cluster at LESIA. G.C.V gratefully acknowledges financial support from CONICYT-Chile through its doctoral scholarship and grant DPI20140090. S.M. acknowledges financial support from the Institut Universitaire de France (IUF), of which she is senior member. G.B., D.C.K., and S.M.F. acknowledge support from NSF grant AST-08-08133 and NASA grant HST-GO-12060.10A., We present a catalog of visual-like H-band morphologies of ~50.000 galaxies (H_f160w < 24.5) in the 5 CANDELS fields (GOODS-N, GOODS-S, UDS, EGS, and COSMOS). Morphologies are estimated using Convolutional Neural Networks (ConvNets). The median redshift of the sample is < z> 1.25. The algorithm is trained on GOODS-S, for which visual classifications are publicly available, and then applied to the other 4 fields. Following the CANDELS main morphology classification scheme, our model retrieves for each galaxy the probabilities of having a spheroid or a disk, presenting an irregularity, being compact or a point source, and being unclassifiable. ConvNets are able to predict the fractions of votes given to a galaxy image with zero bias and ~10% scatter. The fraction of mis-classifications is less than 1%. Our classification scheme represents a major improvement with respect to Concentration-Asymmetry-Smoothness-based methods, which hit a 20%–30% contamination limit at high z., Comisión Nacional de Investigación Científica y Tecnológica de Chile (CONICYT), Institut Universitaire de France (IUF), National Science Foundation (NSF), EE.UU., National Aeronautics and Space Administration (NASA), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2015 RAS. We thank the referee for helpful comments that have improved this paper. We also thank Johannes Buchner for helpful discussions and providing machine-readable results. We acknowledge helpful discussions with Ranjan Vasudevan. The scientific results reported in this article are based to a significant degree on observations made by the Chandra X-ray Observatory. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM). This study makes use of data from AEGIS, a multiwavelength sky survey conducted with the Chandra, GALEX, Hubble, Keck, CFHT, MMT, Subaru, Palomar, Spitzer, VLA, and other telescopes and supported in part by the National Science Foundation (NSF), NASA, and the STFC. Funding for the DEEP2 Galaxy Redshift Survey has been provided by NSF grants AST-95-09298, AST-0071048, AST-0507428, and AST-0507483 as well as NASA LTSA grant NNG04GC89G. Funding for the DEEP3 Galaxy Redshift Survey has been provided by NSF grants AST-0808133, AST-0807630, and AST-0806732. This work made use of images and/or data products provided by the NDWFS (Jannuzi & Dey 1999), which is supported by the National Optical Astronomy Observatory (NOAO). NOAO is operated by AURA, Inc., under a cooperative agreement with the NSF. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the NSF, and the US Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Some of the data used in this, We present new measurements of the evolution of the X-ray luminosity functions (XLFs) of unabsorbed and absorbed active galactic nuclei (AGNs) out to z ~ 5. We construct samples containing 2957 sources detected at hard (2-7 keV) X-ray energies and 4351 sources detected at soft (0.5-2 keV) energies from a compilation of Chandra surveys supplemented by wide-area surveys from ASCA and ROSAT. We consider the hard and soft X-ray samples separately and find that the XLF based on either (initially neglecting absorption effects) is best described by a new flexible model parametrization where the break luminosity, normalization, and faint-end slope all evolve with redshift. We then incorporate absorption effects, separately-modelling the evolution of the XLFs of unabsorbed (20 < log N_H < 22) and absorbed (22 < log N_H < 24) AGNs, seeking a model that can reconcile both the hard-and soft-band samples. We find that the absorbed AGN XLF has a lower break luminosity, a higher normalization, and a steeper faint-end slope than the unabsorbed AGN XLF out to z ~ 2. Hence, absorbed AGNs dominate at low luminosities, with the absorbed fraction falling rapidly as luminosity increases. Both XLFs undergo strong luminosity evolution which shifts the transition in the absorbed fraction to higher luminosities at higher redshifts. The evolution in the shape of the total XLF is primarily driven by the changing mix of unabsorbed and absorbed populations., Unión Europea (UE), Ministerio de Economía y Competitividad (MINECO), España, National Science Foundation (NSF), National Aeronautics and Space Administration (NASA), EE.UU., Science and Technology Facilities Council (STFC), Long Term Space Astrophysics Program (LTSA-NASA), National Optical Astronomy Observatory (NOAO), Alfred P. Sloan Foundation, US Department of Energy Office of Science, NASA Office of Space Science, COFUND Junior Research Fellowship from the Institute of Advanced Study, Durham University, ERC Advanced Grant FEEDBACK at the University of Cambridge, NSF CAREER, Greek Government, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. The authors acknowledge the referee's comments, which led to improvements in this work. They also thank Carlos Hernández Monteagudo for his very useful advice. LADG acknowledges support from the 'Caja Rural de Teruel' to develop this research. AJC is a Ramón y Cajal Fellow of the Spanish Ministry of Economy and Competitiveness. This work was supported by the 'Programa Nacional de Astronomía y Astrofísica' of the Spanish Ministry of Economy and Competitiveness under grants AYA2012-30789, AYA2010-21322-C03-02, AYA2009-10368 and AYA2009-07723-E. This work made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM)., Using a compilation of 379 massive (stellar mass M ≳ 10^11 M_⊙) spheroid-like galaxies from the near-infrared Palomar/DEEP-2 survey, we investigated, up to z ∼ 1, whether the presence of companions depends on the size of the host galaxy. We explored the presence of companions for mass ratios with respect to the central massive galaxy down to 1 : 10 and 1 : 100, and within projected distances of 30, 50 and 100 kpc of these objects. We found evidence that these companions are equally distributed around both compact and extended massive spheroid-like galaxies. This suggests that, at least since z ∼ 1, the merger activity in these objects is nearly homogeneous across the whole population and that the merger history is not affected by the size of the host galaxy. Our results could indicate that compact and extended massive spheroid-like galaxies are increasing in size at the same rate., Ministerio de Economía y Competitividad (MINECO), Caja Rural de Teruel, Programa Nacional de Astronomía y Astrofísica (PNAyA), España, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2010 The Authors. Journal compilation, © 2010 RAS. The authors wish to thank the anonymous referee for constructive suggestions that improved the paper and Alison Coil for useful comments. AG acknowledges financial support from the Marie-Curie Reintegration Grant PERG03-GA-2008-230644. PGP-G acknowledges support from the Spanish Ministry of Science and Innovation under grants AYA 2006-02358, AYA 2006-15698-C02-02 and CSD2006-100070, and from the Ramón y Cajal Program financed by the Spanish Government and the European Union. This study makes use of data from AEGIS, a multiwavelength sky survey conducted with the Chandra, GALEX, Hubble, Keck, CFHT, MMT, Subaru, Palomar, Spitzer, VLA and other telescopes and supported in part by the NSF, NASA and the STFC., We explore the nature of Infrared Excess sources (IRX), which are proposed as candidates for luminous [L_X(2–10 keV) > 10^43 erg s^−1] Compton thick (NH > 2 × 1024 cm−2) QSOs at z≈ 2. Lower redshift, z≈ 1, analogues of the distant IRX population are identified by first redshifting to z= 2 the spectral energy distributions (SEDs) of all sources with secure spectroscopic redshifts in the AEGIS (6488) and the GOODS-North (1784) surveys and then selecting those that qualify as IRX sources at that redshift. A total of 19 galaxies are selected. The mean redshift of the sample is z≈ 1. We do not find strong evidence for Compton thick QSOs in the sample. For nine sources with X-ray counterparts, the X-ray spectra are consistent with Compton thin active galactic nucleus (AGN). Only three of them show tentative evidence for Compton thick obscuration. The SEDs of the X-ray undetected population are consistent with starburst activity. There is no evidence for a hot dust component at the mid-infrared associated with AGN heated dust. If the X-ray undetected sources host AGN, an upper limit of L_X(2–10 keV) = 10^43 erg s^−1 is estimated for their intrinsic luminosity. We propose that a large fraction of the z≈ 2 IRX population is not Compton thick quasi-stellar objects (QSOs) but low-luminosity [L_X(2–10 keV) < 10^43 erg s^−1], possibly Compton thin, AGN or dusty starbursts. It is shown that the decomposition of the AGN and starburst contribution to the mid-IR is essential for interpreting the nature of this population, as star formation may dominate this wavelength regime., Unión Europea. FP7, Ministerio de Ciencia e Innovación (MICINN), Acciones Marie Skłodowska-Curie (UE), Gobierno de España, National Science Foundation (NSF), EE.UU., National Aeronautics and Space Administration (NASA), Science and Technology Facilities Council (STFC), Reino Unido, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2015. The American Astronomical Society. We would like to thank the referee for a useful and constructive report that clearly helped in improving the manuscript. M.H.C. warmly thanks P. Behroozi for kindly sharing the mass growth and merger rates of massive galaxies used in this paper. P.G.P.-G. acknowledges funding from Spanish Government MINECO Grant AYA2012-31277. G. C. V. gratefully acknowledges funding from CONICYT (Chile) through their Doctoral Scholarship. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM), partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC). This work is based on observations taken by the 3D-HST Treasury Program (GO 12177 and 1232) with the NASA/ESA HST, which is operated by the Association of Universities for Research in Astronomy, Inc, under NASA contract NAS5-26555., We quantify the morphological evolution of z ~ 0 massive galaxies (M_*/M_∼ ∼10^11.2 +/- 0.3) from z ~ 3 in the 5 CANDELS fields. The progenitors are selected using abundance matching techniques to account for the mass growth. At z < 1, the population matches the massive end of the Hubble sequence, with 30% of pure spheroids, 50% of galaxies with equally dominant disk and bulge components, and 20% of disks. At z ~ 2-3 however, there is a majority of irregular systems (~ 60%-70%) with still 30% of pure spheroids. We then analyze the stellar populations, star formation rates (SFRs), gas fractions, and structural properties for the different morphologies independently. Our results suggest two distinct channels for the growth of bulges in massive galaxies. Around ~ 30%-40% were already bulges at z ~ 2.5, with low average SFRs and gas fractions (10%-15%), high Sersic indices (n > 3-4), and small effective radii (R_e ∼1 kpc), pointing toward an even earlier formation through gas-rich mergers or violent disk instabilities. Between z ~ 2.5 and z ~ 0, they rapidly increase their size by a factor of ~ 4-5, are quenched, and slightly increase their Sersic indices (n ~ 5) but their global morphology remains unaltered. The structural evolution is independent of the gas fractions, suggesting that it is driven by ex situ events. The remaining 60% experience a gradual morphological transformation, from clumpy disks to more regular bulge +disk systems, essentially happening at z > 1. This results in the growth of a significant bulge component (n ~ 3) for 2/3 of the systems, possibly through the migration of clumps, while the remaining 1/3 retain a rather small bulge (n ~ 1.5-2). The transition phase between disturbed and relaxed systems and the emergence of the bulge is correlated with a decrease in the star formation activity and the gas fractions, suggesting a morphological quenching process as a plausible mechanism for the formation of these bulges., Ministerio de Economía y Competitividad (MINECO), España, Comisión Nacional de Investigación Científica y Tecnológica (CONICYT), Chile, Association of Universities for Research in Astronomy, NASA, EE.UU., Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Thanks to R. Sheth for comments on an early draft. Thanks to the anonymous referee for a constructive and quick report., We quantify the evolution of the stellar mass functions (SMFs) of star-forming and quiescent galaxies as a function of morphology from z ∼ 3 to the present. Our sample consists of ∼50 000 galaxies in the CANDELS fields (∼880 arcmin^2), which we divide into four main morphological types, i.e. pure bulge-dominated systems, pure spiral disc-dominated, intermediate two-component bulge+disc systems and irregular disturbed galaxies. At z ∼ 2, 80 per cent of the stellar mass density of star-forming galaxies is in irregular systems. However, by z ∼ 0.5, irregular objects only dominate at stellar masses below 10^9 M_⊙. A majority of the star-forming irregulars present at z ∼ 2 undergo a gradual transformation from disturbed to normal spiral disc morphologies by z ∼ 1 without significant interruption to their star formation. Rejuvenation after a quenching event does not seem to be common except perhaps for the most massive objects, because the fraction of bulge-dominated star-forming galaxies with M^*/M_⊙ > 10^10.7 reaches 40 per cent at z < 1. Quenching implies the presence of a bulge: the abundance of massive red discs is negligible at all redshifts over 2 dex in stellar mass. However, the dominant quenching mechanism evolves. At z > 2, the SMF of quiescent galaxies above M^* is dominated by compact spheroids. Quenching at this early epoch destroys the disc and produces a compact remnant unless the star-forming progenitors at even higher redshifts are significantly more dense. At 1 < z < 2, the majority of newly quenched galaxies are discs with a significant central bulge. This suggests that mass quenching at this epoch starts from the inner parts and preserves the disc. At z < 1, the high-mass end of the passive SMF is globally in place and the evolution mostly happens at stellar masses below 10^10 M_⊙. These low-mass galaxies are compact, bulge-dominated systems, which were environmentally quenched: destruction of the disc through ram-pressure stripping is the likely proc, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© ESO 2009. We thank the referee M. Bershady for his useful and constructive comments. We acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grant AYA 2006-02358. Partially funded by the Spanish MEC under the Consolider-Ingenio 2010 Program grant CSD2006-00070: First Science with the GTC (http://www.iac.es/consolider-ingenio-gtc/). Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut fur Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). This article is based on observations made with the WHT operated on the island of La Palma by the Instituto Astrofísico de Canarias in the Spanish Observatorio del Roque de los Muchachos. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, Caltech under NASA contract 1407. GALEX is a NASA Small Explorer launched in 2003 April. We gratefully acknowledge NASA's support for construction, operation, and scientific analysis of the GALEX mission. Based in part on data collected at Subaru Telescope and obtained from the SMOKA, which is operated by the Astronomy Data Center, National Astronomical Observatory of Japan. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii., Context. The galaxy number counts has been traditionally used to test models of galaxy evolution. However, the origin of significant differences in the shape of number counts at different wavelengths is still unclear. By relating the most remarkable features in the number counts with the underlying galaxy population it is possible to introduce further constraints on galaxy evolution. Aims. We aim to investigate the causes of the different shape of the K-band number counts when compared to other bands, analyzing in detail the presence of a change in the slope around K similar to 17.5. Methods. We present a near-infrared imaging survey, conducted at the 3.5 m telescope of the Calar Alto Spanish-German Astronomical Center (CAHA), covering two separated fields centered on the HFDN and the Groth field, with a total combined area of similar to 0.27 deg(2) to a depth of K similar to 19 (3 sigma, Vega). By combining our data with public deep K-band images in the CDFS (GOODS/ISAAC) and high quality imaging in multiple bands, we extract K-selected catalogs characterized with highly reliable photometric redshift estimates. We derive redshift binned number counts, comparing the results in our three fields to sample the effects of cosmic variance. We derive luminosity functions from the observed K-band in the redshift range [0.25-1.25], that are combined with data from the references in multiple bands and redshifts, to build up the K-band number count distribution. Results. The overall shape of the number counts can be grouped into three regimes: the classic Euclidean slope regime (d log N/dm similar to 0.6) at bright magnitudes; a transition regime at intermediate magnitudes, dominated by M* galaxies at the redshift that maximizes the product phi*dVc/d Omega; and an alpha dominated regime at faint magnitudes, where the slope asymptotically approaches -0.4(alpha + 1) controlled by post-M* galaxies. The slope of the K-band number counts presents an averaged decrement of similar t, Spanish Programa Nacional de Astronomia y Astrofísica, Spanish MEC, NASA, National Astronomical Observatory of Japan, National Science Foundation, Canada-France-Hawaii Telescope (CFHT), National Research Council (NRC) of Canada, Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, University of Hawaii, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2011 The Authors. © 201Monthly Notices of the Royal Astronomical Society. © 2011 RAS. CRA acknowledges financial support from STFC PDRA (ST/G001758/1). CRA, PGPG and GB acknowledge the Spanish Ministry of Science and Innovation (MICINN) through project Consolider-Ingenio 2010 Program grant CSD2006-00070: First Science with the GTC (http://www.iac.es/consolider-ingenio-gtc/). PGPG and GB acknowledge support from the Spanish Programa Nacional de Astronomía y Astrofísica under grants AYA2009-10368 and AYA2009-07723-E. KJI is supported through the Emmy Noether programme of the German Science Foundation (DFG). This work has made use of the Rainbow Cosmological Surveys Data base, which is operated by the Universidad Complutense de Madrid (UCM). This work is based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. This research has made use of the NED which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The authors specially acknowledge Tomer Tal for providing access to the OBEY images, as well as David Carter, Richard Pogge, Philip Massey, Giovanni Carraro and Carlos López SanJuan for their valuable help. We finally acknowledge useful comments from the anonymous referee., We present the results of a comparison between the optical morphologies of a complete sample of 46 southern 2 Jy radio galaxies at intermediate redshifts (0.05 < z < 0.7) and those of two control samples of quiescent early-type galaxies: 55 ellipticals at redshifts z ≤ 0.01 from the Observations of Bright Ellipticals at Yale (OBEY) survey, and 107 early-type galaxies at redshifts 0.2 < z < 0.7 in the Extended Groth Strip (EGS). Based on these comparisons, we discuss the role of galaxy interactions in the triggering of powerful radio galaxies (PRGs). We find that a significant fraction of quiescent ellipticals at low and intermediate redshifts show evidence for disturbed morphologies at relatively high surface brightness levels, which are likely the result of past or on-going galaxy interactions. However, the morphological features detected in the galaxy hosts of the PRGs (e.g. tidal tails, shells, bridges, etc.) are up to 2 mag brighter than those present in their quiescent counterparts. Indeed, if we consider the same surface brightness limits, the fraction of disturbed morphologies is considerably smaller in the quiescent population (53 per cent at z < 0.2 and 48 per cent at 0.2 ≤ z < 0.7) than in the PRGs (93 per cent at z < 0.2 and 95 per cent at 0.2 ≤ z < 0.7 considering strong-line radio galaxies only). This supports a scenario in which PRGs represent a fleeting active phase of a subset of the elliptical galaxies that have recently undergone mergers/interactions. However, we demonstrate that only a small proportion (≲20 per cent) of disturbed early-type galaxies are capable of hosting powerful radio sources., Ministerio de Ciencia e Innovación (MICINN), Science and Technology Facilities Council (STFC), Reino Unido, Programa Nacional de Astronomía y Astrofísica (PNAyA), España, Deutsche Forschungsgemeinschaft (DFG), Alemania, National Aeronautics and Space Administration (NASA), Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

© 2017. The American Astronomical Society. All rights reserved. G.B. and M.K. acknowledge support from HST-AR-12847 and HST-AR-14552. P.G.P.-G. acknowledge support from grants AYA2015-63650-P and AYA2015-70815-ERC. W.R. is supported by JSPS KAKENHI grant number JP15K17604 and the Thailand Research Fund/Office of the Higher Education Commission grant number MRG6080294. This Letter makes use of the following ALMA data: ADS/JAO.ALMA#2015.1.00907.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc., We present high spatial resolution (FWHM similar to 0."14) observations of the CO(8-7) line in GDS-14876, a compact star-forming galaxy at z = 2.3 with a total stellar mass of log(M-*/M-circle dot) = 10.9. The spatially resolved velocity map of the inner r less than or similar to 1 kpc reveals a continuous velocity gradient consistent with the kinematics of a rotating disk with v(rot)(r = 1 kpc) = 163. +/-. 5 km.s(-1) and v(rot)/s similar to 2.5. The gas-to-stellar ratios estimated from CO(8-7) and the dust continuum emission span a broad range, f(gas)(CO) = M-gas/M-* = 13%-45% and f(gas)(CO) = 50%-67% but are nonetheless consistent given the uncertainties in the conversion factors. The dynamical modeling yields a dynamical mass of log(M-dyn/M-circle dot.) = 10.5(-0.2)(+0.5), which is lower, but still consistent with the baryonic mass, log(M-bar = M-circle dot + M-gas(CO)/M-circle dot)= 11.0 if the smallest CO-based gas fraction is assumed. Despite a low, overall gas fraction, the small physical extent of the dense, star-forming gas probed by CO(8-7), similar to 3x smaller than the stellar size, implies a strong relative concentration that increases the gas fraction up to f(gas)(CO) similar to 85% , 1 kpc in the central 1 kpc. Such a gas-rich center, coupled with a high star formation rate (SFR) similar to 500. M-circle dot yr(-1), suggests that GDS-14876 is quickly assembling a dense stellar component (bulge) in a strong nuclear starburst. Assuming its gas reservoir is depleted without replenishment, GDS-14876 will quickly (t(depl) similar to 27 Myr) become a compact quiescent galaxy that could retain some fraction of the observed rotational support., Ministerio de Economía y Competitividad (MINECO), JSPS KAKENHI, Thailand Research Fund/Office of the Higher Education Commission, Depto. de Física de la Tierra y Astrofísica, Fac. de Ciencias Físicas, TRUE, pub

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 greater than or similar to 3. Aims. We measure the Lyman continuum escape fraction, which is one of the key parameters used to compute the contribution of star-forming galaxies to the UV background. It provides the ratio between the photons produced at lambda <= 912 angstrom rest-frame and those that are able to reach the inter-galactic medium, i.e. that are not absorbed by the neutral hydrogen or by the dust of the galaxy's inter-stellar medium. Methods. We used ultra-deep U-band imaging (U = 30.2 mag at 1 sigma) from Large Binocular Camera at the Large Binocular Telescope (LBC/LBT) in the CANDELS/GOODS-North field and deep imaging in the 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 similar to -19). The narrow redshift range implies that the LBC U-band filter exclusively samples the lambda <= 912 angstrom rest-frame wavelengths. Results. We measured through stacks a stringent upper limit (<1.7% at 1 sigma) 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 less than or similar to 10%. We computed the contribution of star-forming galaxies to the observed UV background at z similar to 3 and find that it is not sufficient 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 Lym