arXiv subjects

G. Zamorani

Publications and source records attributed to G. Zamorani.

At least 217 records · Page 12Linked to original sources

arXiv2016

Limits on the LyC signal from z~3 sources with secure redshift and HST coverage in the E-CDFS field

Aim: We aim to measure the LyC signal from a sample of sources in the Chandra deep field south. We collect star-forming galaxies (SFGs) and active galactic nuclei (AGN) with accurate spectroscopic redshifts, for which Hubble Space Telescope (HST) coverage and multi-wavelength photometry are available. Method: We selected a sample of about 200 sources at z~3. Taking advantage of HST resolution, we applied a careful cleaning procedure and rejected sources showing nearby clumps with different colours, which could be lower-z interlopers. Our clean sample consisted of 86 SFGs (including 19 narrow-band selected Lya emitters) and 8 AGN (including 6 detected in X-rays). We measured the LyC flux from aperture photometry in four narrow-band filters covering wavelengths below a 912 A rest frame (3.11<z<3.53). We estimated the ratio between ionizing (LyC flux) and 1400 A non-ionizing emissions for AGN and galaxies. Results: By running population synthesis models, we assume an average intrinsic L(1400 A)/L(900 A) ratio of 5 as the representative value for our sample. With this value and an average treatment of the lines of sight of the inter-galactic medium, we estimate the LyC escape fraction relative to the intrinsic value (fesc_rel(LyC)). We do not directly detect ionizing radiation from any individual SFG, but we are able to set a 1(2)sigma upper limit of fesc_rel(LyC)<12(24)%. This result is consistent with other non-detections published in the literature. No meaningful limits can be calculated for the sub-sample of Lya emitters. We obtain one significant direct detection for an AGN at z=3.46, with fesc_rel(LyC) = (72+/-18)%. Conclusions: Our upper limit on fescrel(LyC) implies that the SFGs studied here do not present either the physical properties or the geometric conditions suitable for efficient LyC-photon escape.

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arXiv2016

AGN host galaxy mass function in COSMOS: is AGN feedback responsible for the mass-quenching of galaxies?

We investigate the role of supermassive black holes in the global context of galaxy evolution by measuring the host galaxy stellar mass function (HGMF) and the specific accretion rate i.e., lambda_SAR, distribution function (SARDF) up to z~2.5 with ~1000 X-ray selected AGN from XMM-COSMOS. Using a maximum likelihood approach, we jointly fit the stellar mass function and specific accretion rate distribution function, with the X-ray luminosity function as an additional constraint. Our best fit model characterizes the SARDF as a double power-law with mass dependent but redshift independent break whose low lambda_SAR slope flattens with increasing redshift while the normalization increases. This implies that, for a given stellar mass, higher lambda_SAR objects have a peak in their space density at earlier epoch compared to the lower lambda_SAR ones, following and mimicking the well known AGN cosmic downsizing as observed in the AGN luminosity function. The mass function of active galaxies is described by a Schechter function with a almost constant Mstar* and a low mass slope alpha that flattens with redshift. Compared to the stellar mass function, we find that the HGMF has a similar shape and that, up to log((Mstar/Msun)~11.5 the ratio of AGN host galaxies to star forming galaxies is basically constant (~10%). Finally, the comparison of the AGN HGMF for different luminosity and specific accretion rate sub-classes with the phenomenological model prediction by Peng et al. (2010) for the "transient" population, i.e. galaxies in the process of being mass-quenched, reveals that low-luminosity AGN do not appear to be able to contribute significantly to the quenching and that at least at high masses, i.e. Mstar>10^(10.7) Msun , feedback from luminous AGN (log(Lbol)>~46 [erg/s]) may be responsible for the quenching of star formation in the host galaxy.

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arXiv2016

The VIMOS Ultra Deep Survey: Ly$α$ Emission and Stellar Populations of Star-Forming Galaxies at 2<z<2.5

The aim of this paper is to investigate spectral and photometric properties of 854 faint ($i_{AB}$<~25 mag) star-forming galaxies (SFGs) at 2 $0Å), and Ly$α$ emitters (LAEs; EW$\ge$20Å). The fraction of LAEs at these redshifts is $\sim$10%, which is consistent with previous observations. We compared best-fit SED-estimated stellar parameters of the SFG$_{\rm N}$, SFG$_{\rm L}$ and LAE samples. For the luminosities probed here ($\sim$L$^*$), we find that galaxies with and without Ly$α$ in emission have small but significant differences in their SED-based properties. We find that LAEs have less dust, and lower star-formation rates (SFR) compared to non-LAEs. We also find that LAEs are less massive compared to non-LAEs, though the difference is smaller and less significant compared to the SFR and E$_{\rm s}$(B-V). [abridged]

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arXiv2016

The Chandra COSMOS Legacy survey: overview and point source catalog

The COSMOS-Legacy survey is a 4.6 Ms Chandra program that has imaged 2.2 deg$^2$ of the COSMOS field with an effective exposure of $\simeq$160 ks over the central 1.5 deg$^2$ and of $\simeq$80 ks in the remaining area. The survey is the combination of 56 new observations, obtained as an X-ray Visionary Project, with the previous C-COSMOS survey. We describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2$\times 10^{-5}$. We also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft and hard band). The limiting depths are 2.2 $\times$ 10$^{-16}$, 1.5 $\times$ 10$^{-15}$ and 8.9$\times$ 10$^{-16}$ ${\rm erg~cm}^{-2}~{\rm s}^{-1}$ in the 0.5-2, 2-10 and 0.5-10 keV bands, respectively. The observed fraction of obscured AGN with column density $> 10^{22}$ cm$^{-2}$ from the hardness ratio (HR) is $\sim$50$^{+17}_{-16}$%. Given the large sample, we compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5-10%. For the first time, we compute number counts for obscured (HR$>$-0.2) and unobscured (HR$<$-0.2) sources and find significant differences between the two populations in the soft band. Due to the un-precedent large exposure, COSMOS-Legacy area is 3 times larger than surveys at similar depth and its depth is 3 times fainter than surveys covering similar area. The area-flux region occupied by COSMOS-Legacy is likely to remain unsurpassed for years to come.

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arXiv2015

The Chandra COSMOS Legacy survey: optical/IR identifications

We present the catalog of optical and infrared counterparts of the Chandra COSMOS-Legacy Survey, a 4.6 Ms Chandra program on the 2.2 square degrees of the COSMOS field, combination of 56 new overlapping observations obtained in Cycle 14 with the previous C-COSMOS survey. In this Paper we report the i, K, and 3.6 micron identifications of the 2273 X-ray point sources detected in the new Cycle 14 observations. We use the likelihood ratio technique to derive the association of optical/infrared (IR) counterparts for 97% of the X-ray sources. We also update the information for the 1743 sources detected in C-COSMOS, using new K and 3.6 micron information not available when the C-COSMOS analysis was performed. The final catalog contains 4016 X-ray sources, 97% of which have an optical/IR counterpart and a photometric redshift, while 54% of the sources have a spectroscopic redshift. The full catalog, including spectroscopic and photometric redshifts and optical and X-ray properties described here in detail, is available online. We study several X-ray to optical (X/O) properties: with our large statistics we put better constraints on the X/O flux ratio locus, finding a shift towards faint optical magnitudes in both soft and hard X-ray band. We confirm the existence of a correlation between X/O and the the 2-10 keV luminosity for Type 2 sources. We extend to low luminosities the analysis of the correlation between the fraction of obscured AGN and the hard band luminosity, finding a different behavior between the optically and X-ray classified obscured fraction.

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arXiv2015

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Environmental effects shaping the galaxy stellar mass function

We exploit the first public data release of VIPERS to investigate environmental effects in galaxy evolution between $z\sim0.5$ and $0.9$. The large number of spectroscopic redshifts over an area of about $10\,\mathrm{deg}^2$ provides a galaxy sample with high statistical power. The accurate redshift measurements, with $σ_z = 0.00047(1+z_\mathrm{spec})$, allow us to robustly isolate galaxies living in the lowest- and highest-density environments, as defined in terms of spatial 3D density contrast. We estimate the stellar mass function (SMF) of galaxies residing in these two environments, and constrain its high-mass end with unprecedented precision. We find that the galaxy SMF in the densest regions has a different shape than that measured at low densities, with an enhancement of massive galaxies and a hint of a flatter (less negative) slope at $z<0.8$. We normalise each SMF to the comoving volume occupied by the corresponding environment, and relate estimates from different redshift bins. We observe an evolution of the SMF of VIPERS galaxies in high densities, while the low-density one is nearly constant. We compare these results to semi-analytical models and find consistent environmental signatures. We discuss how the halo mass function and fraction of central/satellite galaxies depend on the environments considered, making intrinsic and environmental properties of galaxies physically coupled, and therefore difficult to disentangle. The evolution of our low-density regions is well described by the formalism introduced by Peng et al.~(2010), and is consistent with the idea that galaxies become progressively passive because of internal physical processes. The same formalism could also describe the evolution of the SMF in the high density regions, but only if a significant contribution from dry mergers is considered. [Abridged]

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arXiv2015

CO luminosity function from Herschel-selected galaxies and the contribution of AGN

We derive the CO luminosity function (LF) for different rotational transitions (i.e. (1-0), (3-2), (5-4)) starting from the Herschel LF by Gruppioni et al. and using appropriate $L'_{\rm CO} - L_{\rm IR}$ conversions for different galaxy classes. Our predicted LFs fit the data so far available at $z\approx0$ and $2$. We compare our results with those obtained by semi-analytical models (SAMs): while we find a good agreement over the whole range of luminosities at $z\approx0$, at $z\approx1$ and $z\approx2$ the tension between our LFs and SAMs in the faint and bright ends increases. We finally discuss the contribution of luminous AGN ($L_{X}>10^{44}\,\rm{erg\,s^{-1}}$) to the bright end of the CO LF concluding that they are too rare to reproduce the actual CO luminosity function at $z\approx2$.

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arXiv2015

A higher efficiency of converting gas to stars push galaxies at z ~ 1.6 well above the star-forming main sequence

Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high-redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ~ 1.6) starburst galaxies with the Atacama Large (sub-)Millimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared detected galaxies having star formation rates (~300-800 Msolar/yr) elevated (>4x) above the star-forming `main sequence', and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ~ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (~30-50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as main-sequence outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical main-sequence star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the main sequence with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts such as being metal rich and having a higher ionization state of the interstellar medium.

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arXiv2015

An extreme [OIII] emitter at $z=3.2$: a low metallicity Lyman continuum source

[Abridged] We investigate the physical properties of a Lyman continuum emitter candidate at $z=3.212$ with photometric coverage from $U$ to MIPS 24$μ$m band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. Investigation of the UV spectrum confirms a direct spectroscopic detection of the Lyman continuum emission with $S/N>5$. Non-zero Ly$α$ flux at the systemic redshift and high Lyman-$α$ escape fraction suggest a low HI column density. The weak C and Si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. The [OIII]$λ\lambda4959,5007+\mathrm{H}β$ equivalent width is one of the largest reported for a galaxy at $z>3$ ($\mathrm{EW}([\mathrm{OIII}]λ\lambda4959,5007+\mathrm{H}β) \simeq 1600Å$, rest-frame) and the NIR spectrum shows that this is mainly due to an extremely strong [OIII] emission. The large observed [OIII]/[OII] ratio ($>10$) and high ionization parameter are consistent with prediction from photoionization models in case of a density-bounded nebula scenario. Furthermore, the $\mathrm{EW}([\mathrm{OIII}]λ\lambda4959,5007+\mathrm{H}β)$ is comparable to recent measurements reported at $z\sim7-9$, in the reionization epoch. We also investigate the possibility of an AGN contribution to explain the ionizing emission but most of the AGN identification diagnostics suggest that stellar emission dominates instead. This source is currently the first high-$z$ example of a Lyman continuum emitter exhibiting indirect and direct evidences of a Lyman continuum leakage and having physical properties consistent with theoretical expectation from Lyman continuum emission from a density-bounded nebula.

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arXiv2015

The Lyman Continuum escape fraction of galaxies at z=3.3 in the VUDS-LBC/COSMOS field

The Lyman continuum (LyC) flux escaping from high-z galaxies into the IGM is a fundamental quantity to understand the physical processes involved in the reionization epoch. We have investigated a sample of star-forming galaxies at z~3.3 in order to search for possible detections of LyC photons escaping from galaxy halos. UV deep imaging in the COSMOS field obtained with the prime focus camera LBC at the LBT telescope was used together with a catalog of spectroscopic redshifts obtained by the VIMOS Ultra Deep Survey (VUDS) to build a sample of 45 galaxies at z~3.3 with L>0.5L*. We obtained deep LBC images of galaxies with spectroscopic redshifts in the interval 3.27 28% but a detailed analysis of their properties reveals that, with the exception of two marginal detections (S/N~2) in the U band, all the other 8 galaxies are most likely contaminated by the UV flux of low-z interlopers located close to the high-z targets. The average escape fraction derived from the stacking of the cleaned sample was constrained to fesc_rel<2%. The implied HI photo-ionization rate is a factor two lower than that needed to keep the IGM ionized at z~3, as observed in the Lyman forest of high-z QSO spectra or by the proximity effect. These results support a scenario where high redshift, relatively bright (L>0.5L*) star-forming galaxies alone are unable to sustain the level of ionization observed in the cosmic IGM at z~3. Star-forming galaxies at higher redshift and at fainter luminosities (L<<L*) can be the major contributors to the reionization of the Universe only if their physical properties are subject to rapid changes from z~3 to z~6-10. Alternatively, ionizing sources could be discovered looking for fainter sources among the AGN population at high-z.

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arXiv2015

A high-dimensional look at VIPERS galaxies

We investigate how galaxies in VIPERS (the VIMOS Public Extragalactic Redshift Survey) inhabit the cosmological density field by examining the correlations across the observable parameter space of galaxy properties and clustering strength. The high-dimensional analysis is made manageable by the use of group-finding and regression tools. We find that the major trends in galaxy properties can be explained by a single parameter related to stellar mass. After subtracting this trend, residual correlations remain between galaxy properties and the local environment pointing to complex formation dependencies. As a specific application of this work we build subsamples of galaxies with specific clustering properties for use in cosmological tests.

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arXiv2015

The VIMOS Public Extragalactic Redshift Survey (VIPERS): Reconstruction of the redshift-space galaxy density field

Aims. Using the VIMOS Public Extragalactic Redshift Survey (VIPERS) we aim to jointly estimate the key parameters that describe the galaxy density field and its spatial correlations in redshift space. Methods. We use the Bayesian formalism to jointly reconstruct the redshift-space galaxy density field, power spectrum, galaxy bias and galaxy luminosity function given the observations and survey selection function. The high-dimensional posterior distribution is explored using the Wiener filter within a Gibbs sampler. We validate the analysis using simulated catalogues and apply it to VIPERS data taking into consideration the inhomogeneous selection function. Results. We present joint constraints on the anisotropic power spectrum as well as the bias and number density of red and blue galaxy classes in luminosity and redshift bins as well as the measurement covariances of these quantities. We find that the inferred galaxy bias and number density parameters are strongly correlated although these are only weakly correlated with the galaxy power spectrum. The power spectrum and redshift-space distortion parameters are in agreement with previous VIPERS results with the value of the growth rate $fσ_8 = 0.38$ with 18% uncertainty at redshift 0.7.

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arXiv2015

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Hierarchical scaling and biasing

We investigate the higher-order correlation properties of the VIMOS Public Extragalactic Redshift Survey (VIPERS) to test the hierarchical scaling hypothesis at z~1 and the dependence on galaxy luminosity, stellar mass, and redshift. We also aim to assess deviations from the linearity of galaxy bias independently from a previously performed analysis of our survey (Di Porto et al. 2014). We have measured the count probability distribution function in cells of radii 3 < R < 10 Mpc/h, deriving $σ_{8g}$, the volume-averaged two-,three-,and four-point correlation functions and the normalized skewness $S_{3g}$ and kurtosis $S_{4g}$ for volume-limited subsamples covering the ranges $-19.5 \le M_B(z=1.1)-5log(h) \le -21.0$, $9.0 < log(M*/M_{\odot} h^{-2}) \le 11.0$, $0.5 \le z < 1.1$. We have thus performed the first measurement of high-order correlations at z~1 in a spectroscopic redshift survey. Our main results are the following. 1) The hierarchical scaling holds throughout the whole range of scale and z. 2) We do not find a significant dependence of $S_{3g}$ on luminosity (below z=0.9 $S_{3g}$ decreases with luminosity but only at 1σ-level). 3) We do not detect a significant dependence of $S_{3g}$ and $S_{4g}$ on scale, except beyond z~0.9, where the dependence can be explained as a consequence of sample variance. 4) We do not detect an evolution of $S_{3g}$ and $S_{4g}$ with z. 5) The linear bias factor $b=σ_{8g}/σ_{8m}$ increases with z, in agreement with previous results. 6) We quantify deviations from the linear bias by means of the Taylor expansion parameter $b_2$. Our results are compatible with a null non-linear bias term, but taking into account other available data we argue that there is evidence for a small non-linear bias term.

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arXiv2015

The most obscured AGN in the COSMOS field

Highly obscured active galactic nuclei (AGN) are common in nearby galaxies, but are difficult to observe beyond the local Universe, where they are expected to significantly contribute to the black hole accretion rate density. Furthermore, Compton-thick (CT) absorbers (NH>10^24 cm^-2) suppress even the hard X-ray (2-10 keV) AGN nuclear emission, and therefore the column density distribution above 10^24 cm^-2 is largely unknown. We present the identification and multi-wavelength properties of a heavily obscured (NH>~10^25 cm^-2), intrinsically luminous (L(2-10keV)>10^44 erg s^-1) AGN at z=0.353 in the COSMOS field. Several independent indicators, such as the shape of the X-ray spectrum, the decomposition of the spectral energy distribution and X-ray/[NeV] and X-ray/6μm luminosity ratios, agree on the fact that the nuclear emission must be suppressed by a 10^25 cm^-2 column density. The host galaxy properties show that this highly obscured AGN is hosted in a massive star-forming galaxy, showing a barred morphology, which is known to correlate with the presence of CT absorbers. Finally, asymmetric and blueshifted components in several optical high-ionization emission lines indicate the presence of a galactic outflow, possibly driven by the intense AGN activity (L(Bol)/L(Edd) = 0.3-0.5). Such highly obscured, highly accreting AGN are intrinsically very rare at low redshift, whereas they are expected to be much more common at the peak of the star formation and BH accretion history, at z~2-3. We demonstrate that a fully multi-wavelength approach can recover a sizable sample of such peculiar sources in large and deep surveys such as COSMOS.

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arXiv2015

Evidence for Mature Bulges and an Inside-out Quenching Phase 3 Billion Years After the Big Bang

Most present-day galaxies with stellar masses $\geq10^{11}$ solar masses show no ongoing star formation and are dense spheroids. Ten billion years ago, similarly massive galaxies were typically forming stars at rates of hundreds solar masses per year. It is debated how star formation ceased, on which timescales, and how this "quenching" relates to the emergence of dense spheroids. We measured stellar mass and star-formation rate surface density distributions in star-forming galaxies at redshift 2.2 with $\sim1$ kiloparsec resolution. We find that, in the most massive galaxies, star formation is quenched from the inside out, on timescales less than 1 billion years in the inner regions, up to a few billion years in the outer disks. These galaxies sustain high star-formation activity at large radii, while hosting fully grown and already quenched bulges in their cores.

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arXiv2015

The SINS/zC-SINF Survey of z~2 Galaxy Kinematics: Rest-frame Morphology, Structure, and Colors from Near-infrared Hubble Space Telescope Imaging

We present the analysis of HST $J$- and $H$-band imaging for 29 galaxies on the star-forming main sequence at $z\sim2$, which have Adaptive Optics VLT SINFONI integral field spectroscopy from our SINS/zC-SINF program. The SINFONI H$α$ data resolve the on-going star-formation and the ionized gas kinematics on scales of $1-2$ kpc; the near-IR images trace the galaxies' rest-frame optical morphologies and distributions of stellar mass in old stellar populations at a similar resolution. The global light profiles of most galaxies show disk-like properties well described by a single Sérsic profile with $n\sim1$, with only $\sim15%$ requiring a high $n>3$ Sérsic index, all more massive than $10^{10}M_\odot$. In bulge+disk fits, about $40%$ of galaxies have a measurable bulge component in the light profiles, with $\sim15%$ showing a substantial bulge-to-total ratio $B/T\ge0.3$. This is a lower limit to the frequency of $z\sim2$ massive galaxies with a developed bulge component in stellar mass because it could be hidden by dust and/or outshined by a thick actively star-forming disk component. The galaxies' rest-optical half-light radii range between $1-7$ kpc, with a median of 2.1 kpc, and lie slightly above the size-mass relation at these epochs reported in the literature. This is attributed to differences in sample selection and definitions of size and/or mass measurements. The $(u-g)_{rest}$ color gradient and scatter within individual $z\sim2$ massive galaxies with $\ge10^{11}M_\odot$ are as high as in $z=0$ low-mass, late-type galaxies, and are consistent with the high star-formation rates of massive $z\sim2$ galaxies being sustained at large galactocentric distances.

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arXiv2015

Extreme emission-line galaxies out to z$\sim$1 in zCOSMOS. I. Sample and characterization of global properties

We present a thorough characterization of a large sample of 183 extreme emission-line galaxies (EELGs) at redshift 0.11 < z < 0.93 selected from the 20k zCOSMOS Bright Survey because of their unusually large emission line equivalent widths. We use multiwavelength COSMOS photometry, HST-ACS I-band imaging and optical zCOSMOS spectroscopy to derive the main global properties of EELGs, such as sizes, masses, SFRs, reliable metallicities from both "direct" and "strong-line" methods. The EELGs are compact (R_50 ~ 1.3 kpc), low-mass (log(M*/Msol)~7-10) galaxies forming stars at unusually high specific SFR (log(sSFR/yr) up to ~ -7) compared to main sequence SFGs of the same stellar mass and redshift. At UV wavelengths, the EELGs are luminous and show high surface brightness and include strong Ly$α$ emitters, as revealed by GALEX spectroscopy. We show that zCOSMOS EELGs are high-ionization, low-metallicity systems, with median 12+log(O/H)=8.16, including a handful of extremely metal-deficient galaxies (<10% solar). While ~80% of the EELGs show non-axisymmetric morphologies, including clumpy and tadpole galaxies, we find that ~29% of them show additional low surface-brightness features, which strongly suggest recent or ongoing interactions. As star-forming dwarfs in the local Universe, EELGs are most often found in relative isolation. While only very few EELGs belong to compact groups, almost one third of them are found in spectroscopically confirmed loose pairs or triplets. We conclude that EELGs are galaxies caught in a transient and probably early period of their evolution, where they are efficiently building-up a significant fraction of their present-day stellar mass in an ongoing galaxy-wide starburst. Therefore, the EELGs constitute an ideal benchmark for comparison studies between low- and high-redshift low-mass star-forming galaxies.

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arXiv2015

Discovering extremely compact and metal-poor, star-forming dwarf galaxies out to z ~ 0.9 in the VIMOS Ultra-Deep Survey

We report the discovery of 31 low-luminosity (-14.5 > M_{AB}(B) > -18.8), extreme emission line galaxies (EELGs) at 0.2 < z < 0.9 identified by their unusually high rest-frame equivalent widths (100 < EW[OIII] < 1700 A) as part of the VIMOS Ultra Deep Survey (VUDS). VIMOS optical spectra of unprecedented sensitivity ($I_{AB}$ ~ 25 mag) along with multiwavelength photometry and HST imaging are used to investigate spectrophotometric properties of this unique sample and explore, for the first time, the very low stellar mass end (M* < 10^8 M$_{\odot}$) of the luminosity-metallicity (LZR) and mass-metallicity (MZR) relations at z < 1. Characterized by their extreme compactness (R50 < 1 kpc), low stellar mass and enhanced specific star formation rates (SFR/M* ~ 10^{-9} - 10^{-7} yr^{-1}), the VUDS EELGs are blue dwarf galaxies likely experiencing the first stages of a vigorous galaxy-wide starburst. Using T_e-sensitive direct and strong-line methods, we find that VUDS EELGs are low-metallicity (7.5 < 12+log(O/H) < 8.3) galaxies with high ionization conditions, including at least three EELGs showing HeII 4686A emission and four EELGs of extremely metal-poor (<10% solar) galaxies. The LZR and MZR followed by EELGs show relatively large scatter, being broadly consistent with the extrapolation toward low luminosity and mass from previous studies at similar redshift. However, we find evidences that galaxies with younger and more vigorous star formation -- as characterized by their larger EWs, ionization and sSFR -- tend to be more metal-poor at a given stellar mass.

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