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This paper presents a new search for z >= 7.5 galaxies using the COSMOS2020 photometric catalogues. Finding galaxies at the reionisation epoch through deep imaging surveys remains observationally challenging. The larger area covered by ground-based surveys such as COSMOS enables the discovery of the brightest galaxies at these high redshifts. Covering 1.4 deg(2), our COSMOS catalogues were constructed from the latest UltraVISTA data release (DR4) combined with the final Spitzer/IRAC COSMOS images and the Hyper-Suprime-Cam Subaru Strategic Program DR2 release. We identified 17 new 7.5 < z < 10 candidate sources, and confirm 15 previously published candidates. Using deblended photometry extracted by fitting surface brightness models on multi-band images, we selected four candidates which would be rejected using fixed aperture photometry. We tested the robustness of all our candidates by comparing six different photometric redshift estimates. Finally, we computed the galaxy UV luminosity function in three redshift bins centred at z = 8, 9, 10. We find no clear evolution of the number density of the brightest galaxies M-UV < 21 .5, in agreement with previous works. Rapid changes in the quenching efficiency or attenuation by dust could explain such a lack of evolution between z similar to 8 and z similar to 9. A spectroscopic confirmation of the redshifts, already planned with JWST and the Keck telescopes, will be essential to confirm our results.

The Cosmic Evolution Survey (COSMOS) has become a cornerstone of extragalactic astronomy. Since the last public catalog in 2015, a wealth of new imaging and spectroscopic data have been collected in the COSMOS field. This paper describes the collection, processing, and analysis of these new imaging data to produce a new reference photometric redshift catalog. Source detection and multiwavelength photometry are performed for 1.7 million sources across the 2 deg2 of the COSMOS field, ∼966,000 of which are measured with all available broadband data using both traditional aperture photometric methods and a new profile-fitting photometric extraction tool, The Farmer, which we have developed. A detailed comparison of the two resulting photometric catalogs is presented. Photometric redshifts are computed for all sources in each catalog utilizing two independent photometric redshift codes. Finally, a comparison is made between the performance of the photometric methodologies and of the redshift codes to demonstrate an exceptional degree of self-consistency in the resulting photometric redshifts. The i < 21 sources have subpercent photometric redshift accuracy and even the faintest sources at 25 < i < 27 reach a precision of 5%. Finally, these results are discussed in the context of previous, current, and future surveys in the COSMOS field. Compared to COSMOS2015, it reaches the same photometric redshift precision at almost one magnitude deeper. Both photometric catalogs and their photometric redshift solutions and physical parameters will be made available through the usual astronomical archive systems (ESO Phase 3, IPAC-IRSA, and CDS).

We make use of JWST medium-band and broadband NIRCam imaging, along with ultradeep MIRI 5.6 mu m imaging, in the Hubble eXtreme Deep Field to identify prominent line emitters at z similar or equal to 7-8. Out of a total of 58 galaxies at z similar or equal to 7-8, we find 18 robust candidates ( similar or equal to 31%) for (H beta + [O III]) emitters, based on their enhanced fluxes in the F430M and F444W filters, with EW0(H beta +[O III]) similar or equal to 87-2100 angstrom. Among these emitters, 16 lie in the MIRI coverage area and 12 exhibit a clear flux excess at 5.6 mu m, indicating the simultaneous presence of a prominent Ha emission line with EW0(H alpha) similar or equal to 200-3000 angstrom. This is the first time that H alpha emission can be detected in individual galaxies at z > 7. The Ha line, when present, allows us to separate the contributions of H beta and [O III] to the (H beta +[O III]) complex and derive Ha-based star formation rates (SFRs). We find that in most cases [O III]/ H beta > 1. Instead, two galaxies have [O III]/H beta < 1, indicating that the NIRCam flux excess is mainly driven by H beta. Most prominent line emitters are very young starbursts or galaxies on their way to/from the starburst cloud. They make for a cosmic SFR density log(10)( rho(SFRH alpha) (M-circle dot yr(-1) Mpc))similar or equal to - 2.351 3 which is about a quarter of the total value (log(10)( SFR (M-circle dot yr(-1) Mpc))similar or equal to - 1.761 3 ) at z similar or equal to 7-8. Therefore, the strong Ha emitters likely had a significant role in reionization.

While the kinematics of galaxies up to z similar to 3 have been characterized in detail, only a handful of galaxies at high redshift (z > 4) have been examined in such a way. The Atacama Large Millimeter/submillimeter Array (ALMA) Large Program to INvestigate [C II] at Early times (ALPINE) survey observed a statistically significant sample of 118 star-forming main-sequence galaxies at z = 4.4-5.9 in [C. II]158 mu m emission, increasing the number of such observations by nearly 10 x . A preliminary qualitative classification of these sources revealed a diversity of kinematic types (i.e. rotators, mergers, and dispersion-dominated systems). In this work, we supplement the initial classification by applying quantitative analyses to the ALPINE data: a tilted ring model (TRM) fitting code ((3D)BAROLO), a morphological classification (Gini-M-20), and a set of disc identification criteria. Of the 75 [CM-detected ALPINE galaxies, 29 are detected at sufficient significance and spatial resolution to allow for TRM fitting and the derivation of morphological and kinematic parameters. These 29 sources constitute a high-mass subset of the ALPINE sample (M-* > 10(9.5) M-circle dot). We robustly classify 14 of these sources (six rotators, five mergers, and three dispersion-dominated systems); the remaining sources showing complex behaviour. By exploring the G-M-20 of z > 4 rest-frame far-infrared and [CII] data for the first time, we find that our 1 arcsec similar to 6 kpc resolution data alone are insufficient to separate galaxy types. We compare the rotation curves and dynamical mass profiles of the six ALPINE rotators to the two previously detected z similar to 4-6 unlensed main-sequence rotators, finding high rotational velocities (similar to 50-250 km s(-1)) and a diversity of rotation curve shapes.

Context. Galaxy mergers are thought to be one of the main mechanisms of the mass assembly of galaxies in the Universe, but there is still little direct observational evidence of how frequent they are at z greater than or similar to 4. Recently, many works have suggested a possible increase in the fraction of major mergers in the early Universe, reviving the debate on which processes (e.g., cold accretion, star formation, mergers) most contribute to the mass build-up of galaxies through cosmic time.Aims. To estimate the importance of major mergers in this context, we make use of the new data collected by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey, which attempted to observe the [CII] 158 mu m emission line from a sample of 75 main-sequence star-forming galaxies at 4.4 < z < 5.9.Methods. We used, for the first time, the morpho-kinematic information provided by the [CII] emission, along with archival multiwavelength data to obtain the fraction of major mergers (f(MM)) at z similar to 5. By combining the results from ALPINE with those at lower redshifts from the literature, we also studied the evolution of the merger fraction through cosmic time. We then used different redshift-evolving merger timescales (T-MM) to convert this fraction into the merger rate per galaxy (R-MM) and in the volume-averaged merger rate (Gamma(MM)).Results. We find a merger fraction of f(MM) similar to 0.44 (0.34) at z similar to 4.5 (5.5) from ALPINE. By combining our results with those at lower redshifts, we computed the cosmic evolution of the merger fraction which is described by a rapid increase from the local Universe to higher redshifts, a peak at z similar to 3, and a slow decrease toward earlier epochs. Depending on the timescale prescription used, this fraction translates into a merger rate ranging between similar to 0.1 and similar to 4.0 Gyr(-1) at z similar to 5, which in turn corresponds to an average number of major me

Star formation rate (SFR) measurements at z>4 have relied mostly on the rest-frame far-ultraviolet (FUV) observations. The corrections for dust attenuation based on the IRX-beta relation are highly uncertain and are still debated in the literature. Hence, rest-frame far-infrared (FIR) observations are necessary to constrain the dust-obscured component of the SFR. In this paper, we exploit the rest-frame FIR continuum observations collected by the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) to directly constrain the obscured SFR in galaxies at 4.4

Aims. Our aim is to analyze the variance of the intergalactic medium (IGM) transmission by studying this parameter in the rest-frame UV spectra of a large sample of high-redshift galaxies.Methods. We made use of the VIMOS Ultra Deep Survey and the VANDELS public survey to gain insight into the far UV spectrum of 2.7

VANDELS is an ESO Public Spectroscopic Survey designed to build a sample of high-signal-to-noise ratio, medium-resolution spectra of galaxies at redshifts between 1 and 6.5. Here we present the final Public Data Release of the VANDELS Survey, comprising 2087 redshift measurements. We provide a detailed description of sample selection, observations, and data reduction procedures. The final catalogue reaches a target selection completeness of 40% at i(AB)=25. The high signal-to-noise ratio of the spectra (above 7 in 80% of the spectra) and the dispersion of 2.5 angstrom allowed us to measure redshifts with high precision, the redshift measurement success rate reaching almost 100%. Together with the redshift catalogue and the reduced spectra, we also provide optical mid-infrared photometry and physical parameters derived through fitting the spectral energy distribution. The observed galaxy sample comprises both passive and star forming galaxies covering a stellar mass range of 8.3

We report the serendipitous discovery of a dust-obscured galaxy observed as part of the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [C II] at Early times (ALPINE). While this galaxy is detected both in line and continuum emissions in ALMA Band 7, it is completely dark in the observed optical/near-infrared bands and only shows a significant detection in the UltraVISTA K-s band. We discuss the nature of the observed ALMA line, that is [C II] at z similar to 4.6 or high-J CO transitions at z similar to 2.2. In the first case, we find a [C II]/FIR luminosity ratio of log(L-[C II]/L-FIR) similar to -2.5, consistent with the average value for local star-forming galaxies (SFGs). In the second case instead, the source would lie at larger CO luminosities than those expected for local SFGs and high-z submillimetre galaxies. At both redshifts, we derive the star formation rate (SFR) from the ALMA continuum and the physical parameters of the galaxy, such as the stellar mass (M-*), by fitting its spectral energy distribution. Exploiting the results of this work, we believe that our source is a 'main-sequence', dusty SFG at z = 4.6 (i.e. [C II] emitter) with log(SFR/M-circle dot yr(-1)) similar to 1.4 and log(M-*/M-circle dot) similar to 9.9. As a support to this scenario our galaxy, if at this redshift, lies in a massive protocluster recently discovered at z similar to 4.57, at only similar to 1 proper Mpc from its centre. This work underlines the crucial role of the ALPINE survey in making a census of this class of objects, in order to unveil their contribution to the global SFR density at the end of the Reionization epoch.

We report the detection of [C II] lambda 158 mu m emission from a system of three closely separated sources in the Cosmic Evolution Survey (COSMOS) field at z similar to 4.56 , as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Large Program to INvestigate C II at Early times (ALPINE). The two most luminous sources are closely associated, both spatially (1.6 arcsec similar to 11 kpc) and in velocity (similar to 100 km s(-1)), while the third source is slightly more distant (2.8 arcsec similar to 18 kpc, similar to 300 km s(-1)). The second most luminous source features a slight velocity gradient, while no significant velocity gradient is seen in the other two sources. Using the observed [C II] luminosities, we derive a total log(10)(SFR[C II] [M-circle dot Yr(-1)]) = 2.8 +/- 0.2, which may be split into contributions of 59, 31, and 10 per cent from the central, east, and west sources, respectively. Comparison of these [C II] detections to recent zoom-in cosmological simulations suggests an ongoing major merger. We are thus witnessing a system in a major phase of mass build-up by merging, including an ongoing major merger and an upcoming minor merger, which is expected to end up in a single massive galaxy by z similar to 2.5.

The molecular gas content of normal galaxies at z> 4 is poorly constrained because the commonly used molecular gas tracers become hard to detect at these high redshifts. We use the [CII] 158 mu m luminosity, which was recently proposed as a molecular gas tracer, to estimate the molecular gas content in a large sample of main sequence star-forming galaxies at z=4.4-5.9, with a median stellar mass of 10(9.7) M-circle dot, drawn from the ALMA Large Program to INvestigate [CII] at Early times survey. The agreement between the molecular gas masses derived from [CII] luminosities, dynamical masses, and rest-frame 850 mu m luminosities extrapolated from the rest-frame 158 mu m continuum supports [CII] as a reliable tracer of molecular gas in our sample. We find a continuous decline of the molecular gas depletion timescale from z=0 to z=5.9, which reaches a mean value of (4.6 +/- 0.8) x 10(8) yr at z similar to 5.5, only a factor of between two and three shorter than in present-day galaxies. This suggests a mild enhancement of the star formation efficiency toward high redshifts. Our estimates also show that the previously reported rise in the molecular gas fraction flattens off above z similar to 3.7 to achieve a mean value of 63%+/- 3% over z=4.4-5.9. This redshift evolution of the gas fraction is in line with that of the specific star formation rate. We use multi-epoch abundance-matching to follow the gas fraction evolution across cosmic time of progenitors of z=0 Milky Way-like galaxies in similar to 10(13) M-circle dot halos and of more massive z=0 galaxies in similar to 10(14) M-circle dot halos. Interestingly, the former progenitors show a monotonic increase of the gas fraction with redshift, while the latter show a steep rise from z=0 to z similar to 2 followed by a constant gas fraction from z similar to 2 to z=5.9. We discuss three possible effects, namely outflows, a pause in gas supply, and over-efficient star formation, which may jointly contribute to the

We present ALMA observations of a merging system at z similar to 4.57, observed as a part of the ALMA Large Program to INvestigate [CII] at Early times (ALPINE) survey. Combining ALMA [CII]158 mu m and far-infrared continuum data with multi-wavelength ancillary data, we find that the system is composed of two massive (M-star greater than or similar to 10(10) M-circle dot) star-forming galaxies experiencing a major merger (stellar mass ratio r(mass)greater than or similar to 0.9) at close spatial (similar to 13 kpc; projected) and velocity (Delta v<300 km s(-1)) separations, and two additional faint narrow [CII]-emitting satellites. The overall system belongs to a larger scale protocluster environment and is coincident to one of its overdensity peaks. Additionally, ALMA reveals the presence of [CII] emission arising from a circumgalactic gas structure, extending up to a diameter-scale of 30 kpc. Our morpho-spectral decomposition analysis shows that about 50% of the total flux resides between the individual galaxy components, in a metal-enriched gaseous envelope characterised by a disturbed morphology and complex kinematics. Similarly to observations of shock-excited [CII] emitted from tidal tails in local groups, our results can be interpreted as a possible signature of interstellar gas stripped by strong gravitational interactions, with a possible contribution from material ejected by galactic outflows and emission triggered by star formation in small faint satellites. Our findings suggest that mergers could be an efficient mechanism of gas mixing in the circumgalactic medium around high-z galaxies, and thus play a key role in the galaxy baryon cycle at early epochs.

We present dust attenuation properties of spectroscopically confirmed star forming galaxies on the main sequence at a redshift of similar to 4.4-5.8. Our analyses are based on the far infrared continuum observations of 118 galaxies at rest-frame 158 mu m obtained with the Atacama Large Millimeter Array (ALMA) Large Program to INvestigate [CII] at Early times (ALPINE). We study the connection between the ultraviolet (UV) spectral slope (beta), stellar mass (M-star), and infrared excess (IRX = L-IR/L-UV). Twenty-three galaxies are individually detected in the continuum at > 3.5 sigma significance. We perform a stacking analysis using both detections and nondetections to study the average dust attenuation properties at z similar to 4.4-5.8. The individual detections and stacks show that the IRX-beta relation at z similar to 5 is consistent with a steeper dust attenuation curve than typically found at lower redshifts (z<4). The attenuation curve is similar to or even steeper than that of the extinction curve of the Small Magellanic Cloud. This systematic change of the IRX- relation as a function of redshift suggests an evolution of dust attenuation properties at z> 4. Similarly, we find that our galaxies have lower IRX values, up to 1 dex on average, at a fixed mass compared to previously studied IRX-M-star relations at z less than or similar to 4, albeit with significant scatter. This implies a lower obscured fraction of star formation than at lower redshifts. Our results suggest that dust properties of UV-selected star forming galaxies at z greater than or similar to 4 are characterised by (i) a steeper attenuation curve than at z less than or similar to 4, and (ii) a rapidly decreasing dust obscured fraction of star formation as a function of redshift. Nevertheless, even among this UV-selected sample, massive galaxies (log M-star/M-circle dot> 10) at z similar to 5-6 already exhibit an obscured fraction of star formation of similar to 45%, indicating a

Aims. We present the detailed characterisation of a sample of 56 sources serendipitously detected in ALMA band 7 as part of the ALMA Large Program to INvestigate CII at Early Times (ALPINE). These sources, detected in COSMOS and ECDFS, have been used to derive the total infrared luminosity function (LF) and to estimate the cosmic star formation rate density (SFRD) up to z similar or equal to 6.Methods. We looked for counterparts of the ALMA sources in all the available multi-wavelength (from HST to VLA) and photometric redshift catalogues. We also made use of deeper UltraVISTA and Spitzer source lists and maps to identify optically dark sources with no matches in the public catalogues. We used the sources with estimated redshifts to derive the 250 mu m rest-frame and total infrared (8-1000 mu m) LFs from z similar or equal to 0.5 to 6.Results. Our ALMA blind survey (860 mu m flux density range: similar to 0.3-12.5 mJy) allows us to further push the study of the nature and evolution of dusty galaxies at high-z, identifying luminous and massive sources to redshifts and faint luminosities never probed before by any far-infrared surveys. The ALPINE data are the first ones to sample the faint end of the infrared LF, showing little evolution from z similar or equal to 2.5 to z similar or equal to 6, and a "flat" slope up to the highest redshifts (i.e. 4.5

The [CII] 158 mu m line is one of the strongest IR emission lines, which has been shown to trace the star formation rate (SFR) of galaxies in the nearby Universe, and up to z similar to 2. Whether this is also the case at higher redshift and in the early Universe remains debated. The ALPINE survey, which targeted 118 star-forming galaxies at 4.4 6 [CII] measurements (detections and upper limits) do not behave very differently to the z similar to 4-6 data. We find a weak dependence of L([CII])/SFR on the Ly alpha equivalent width. Finally, we find that the ratio L([CII])/L-IR similar to (1-3) x 10(-3) for the ALPINE sources, comparable to that of "normal" galaxies at lower redshift. Our analysis, which includes the largest sample (similar to 150 galaxies) of [CII] measurements at z>4 available so far, suggests no or little evolution of the [CII]-SFR relation over the last 13 Gyr of cosmic time.

Context. The Lyman-alpha line in the ultraviolet (UV) and the [CII] line in the far-infrared (FIR) are widely used tools to identify galaxies in the early Universe and to obtain insights into interstellar medium (ISM) properties in high-redshift galaxies. By combining data obtained with ALMA in band 7 at similar to 320 GHz as part of the ALMA Large Program to INvestigate [CII] at Early Times (ALPINE) with spectroscopic data from DEIMOS at the Keck Observatory, VIMOS and FORS2 at the Very Large Telescope, we assembled a unique sample of 53 main-sequence star-forming galaxies at 4.4

The ALMA-ALPINE [CII] survey is aimed at characterizing the properties of a sample of normal star-forming galaxies (SFGs). The ALMA Large Program to INvestigate (ALPINE) features 118 galaxies observed in the [CII]-158 mu m line and far infrared (FIR) continuum emission during the period of rapid mass assembly, right after the end of the HI reionization, at redshifts of 4 5). Based on a visual inspection of the [CII] data cubes together with the large wealth of ancillary data, we find a surprisingly wide range of galaxy types, including 40% that are mergers, 20% extended and dispersion-dominated, 13% compact, and 11% rotating discs, with the remaining 16% too faint to be classified. This diversity indicates that a wide array of physical processes must be at work at this epoch, first and foremost, those of galaxy mergers. This paper sets a reference sample for the gas distribution in normal SFGs at 4

We present a new prospective analysis of deep multi-band imaging with the James Webb Space Telescope (JWST). In this work, we investigate the recovery of high-redshift 5 6 and redshifts of 0 5 galaxy samples can be reduced to <0.01 arcmin(-2) with a limited impact on galaxy completeness. We investigate multiple high-redshift galaxy selection techniques and find that the best compromise between completeness and purity at 5

Aims. Our aim is to estimate the intergalactic medium (IGM) transmission towards UV-selected star-forming galaxies at zx2004;greater than or similar to& x2004;4 and study the effect of the dust attenuation on these measurements.Methods. The UV spectrum of high-redshift galaxies is a combination of their intrinsic emission and the effect of the IGM absorption along their line of sight. Using data coming from the unprecedentedly deep spectroscopy from the VANDELS ESO public survey carried out with the VIMOS instrument, we compute both the dust extinction and the mean transmission of the IGM as well as its scatter from a set of 281 galaxies at zx2004;> x2004;3.87. Because of a degeneracy between the dust content of the galaxy and the IGM, we first estimate the stellar dust extinction parameter E(B - V) and study the result as a function of the dust prescription. Using these measurements as constraint for the spectral fit we estimate the IGM transmission Tr(Ly alpha). Both photometric and spectroscopic spectral energy distribution fits are performed using the SPectroscopy And photometRy fiTting tool for Astronomical aNalysis which is able to fit the spectral continuum of the galaxies as well as photometric data.Results. Using the classical Calzetti attenuation law we find that E(B - V) goes from 0.11 at zx2004;=& x2004;3.99 to 0.08 at zx2004;=& x2004;5.15. These results are in very close agreement with published measurements. We estimate the IGM transmission and find that the transmission is decreasing with increasing redshift from Tr(Ly alpha) = 0.53 at zx2004;=& x2004;3.99 to 0.28 at zx2004;=& x2004;5.15. We also find a large standard deviation around the average transmission that is more than 0.1 at every redshift. Our results are in very good agreement with both previous measurements from AGN studies and with theoretical models.

The James Webb Space Telescope (JWST) will provide deep imaging and spectroscopy for sources at redshifts above 6, covering the entire Epoch of Reionization (EoR, 6 < z < 10), and enabling the detailed exploration of the nature of the different sources during the first 1 Gyr of the history of the Universe. The Medium Resolution Spectrograph (MRS) of the mid-IR Instrument (MIRI) will be the only instrument on board JWST able to observe the brightest optical emission lines Hα and [OIII]0.5007 μm at redshifts above 7 and 9, respectively, providing key insights into the physical properties of sources during the early phases of the EoR. This paper presents a study of the Hα fluxes predicted by state-of-the-art FIRSTLIGHT cosmological simulations for galaxies at redshifts of 6.5–10.5, and its detectability with MIRI. Deep (40 ks) spectroscopic integrations with MRS will be able to detect (signal-to-noise ratio > 5) EoR sources at redshifts above 7 with intrinsic star formation rates (SFR) of more than 2 M⊙ yr−1, and stellar masses above 4–9 × 107 M⊙. These limits cover the upper end of the SFR and stellar mass distribution at those redshifts, representing ∼6% and ∼1% of the predicted FIRSTLIGHT population at the 6.5–7.5 and 7.5–8.5 redshift ranges, respectively. In addition, the paper presents realistic MRS simulated observations of the expected rest-frame optical and near-infrared spectra for some spectroscopically confirmed EoR sources recently detected by ALMA as [OIII]88 μm emitters. The MRS simulated spectra cover a wide range of low metallicities from about 0.2–0.02 Z⊙, and different [OIII]88 μm/[OIII]0.5007 μm line ratios. The simulated 10 ks MRS spectra show S/N in the range of 5–90 for Hβ, [OIII]0.4959,0.5007 μm, Hα and HeI1.083 μm emission lines of the currently highest spectroscopically confir

Context. Ultraviolet (UV) emission-line spectra are used to spectroscopically confirm high-z galaxies and increasingly also to determine their physical properties.Aims. We construct photoionization models to interpret the observed UV spectra of distant galaxies in terms of the dominant radiation field and the physical condition of the interstellar medium (ISM). These models are applied to new spectroscopic observations from the VIMOS Ultra Deep Survey (VUDS).Methods. We construct a large grid of photoionization models, which use several incident radiation fields (stellar populations, active galactic nuclei (AGNs), mix of stars and AGNs, blackbodies, and others), and cover a wide range of metallicities and ionization parameters. From these models we derive new spectral UV line diagnostics using equivalent widths (EWs) of [CIII]lambda 1909 doublet, CIV lambda 1549 doublet and the line ratios of [CIII], CIV, and He II lambda 1640 recombination lines. We apply these diagnostics to a sample of 450 [CIII]-emitting galaxies at redshifts z = 2-4 previously identified in VUDS.Results. We demonstrate that our photoionization models successfully reproduce observations of nearby and high-redshift sources with known radiation field and/or metallicity. For star-forming galaxies our models predict that [CIII] EW peaks at sub-solar metallicities, whereas CIV EW peaks at even lower metallicity. Using the UV diagnostics, we show that the average star-forming galaxy (EW([CIII]) similar to 2 angstrom) based on the composite of the 450 UV-selected galaxies' spectra The inferred metallicity and ionization parameter is typically Z = 0.3-0.5 Z(circle dot) and logU = 2.7 to 3, in agreement with earlier works at similar redshifts. The models also indicate an average age of 50-200 Myr since the beginning of the current star-formation, and an ionizing photon production rate, xi(ion), of log xi(ion)/erg(-1) Hz = 25.3-25.4. Among the sources with EW([CIII]) > = 10 angs