We present Multi Unit Spectroscopic Explorer (MUSE) integral field unit spectroscopic observations of the ∼150 kpc Lyα halo around the z = 4.1 radio galaxy TN J1338−1942. This 9-h observation maps ...the full two-dimensional kinematics of the Lyα emission across the halo, which shows a velocity gradient of Δv ∼ 700 km s−1 across 150 kpc in projection, and also identified two absorption systems associated with the Lyα emission from the radio galaxy. Both absorbers have high covering fractions (∼1) spanning the full ∼150 × 80 kpc2 extent of the halo. The stronger and more blueshifted absorber (Δv ∼ −1200 km s−1 from the systemic) has dynamics that mirror that of the underlying halo emission and we suggest that this high column material (n(H i) ∼ 1019.4 cm−2), which is also seen in C iv absorption, represents an outflowing shell that has been driven by the active galactic nuclei (AGN) or the star formation within the galaxy. The weaker (n(H i) ∼ 1014 cm−2) and less blueshifted (Δv ∼ −500 km s−1) absorber most likely represents material in the cavity between the outflowing shell and the Lyα halo. We estimate that the mass in the shell must be ∼1010 M⊙ – a significant fraction of the interstellar medium from a galaxy at z = 4. The large scales of these coherent structures illustrate the potentially powerful influence of AGN feedback on the distribution and energetics of material in their surroundings. Indeed, the discovery of high-velocity (∼1000 km s−1), group-halo-scale (i.e. >150 kpc) and mass-loaded winds in the vicinity of the central radio source is in agreement with the requirements of models that invoke AGN-driven outflows to regulate star formation and black hole growth in massive galaxies.
We present the Zurich Extragalactic Bayesian Redshift Analyzer (zebra). The current version of zebra combines and extends several of the classical approaches to produce accurate photometric redshifts ...down to faint magnitudes. In particular, zebra uses the template-fitting approach to produce Maximum Likelihood and Bayesian redshift estimates based on the following points.
An automatic iterative technique to correct the original set of galaxy templates to best represent the Spectral Energy Distributions (SEDs) of real galaxies at different redshifts.
A training set of spectroscopic redshifts for a small fraction of the photometric sample to improve the robustness of the photometric redshift estimates.
An iterative technique for Bayesian redshift estimates, which extracts the full two-dimensional redshift and template probability function for each galaxy.
We demonstrate the performance of zebra by applying it to a sample of 866 I
AB
≤ 22.5 COSMOS galaxies with available u*, B, V, g′, r′, i′, z′ and K
s
photometry and zCOSMOS spectroscopic redshifts in the range 0 < z < 1.3. Adopting a 5σ clipping that excludes ≤10 galaxies, both the Maximum Likelihood and Bayesian zebra estimates for this sample have an accuracy σΔz/(1+z) smaller than 0.03. Similar accuracies are recovered using mock galaxies.
zebra is made available at http://www.exp-astro.phys.ethz.ch/ZEBRA.
Contact. This paper presents the results obtained with the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO Very Large Telescope on the faint end of the Lyman-alpha luminosity function (LF) based ...on deep observations of four lensing clusters. The goal of our project is to set strong constraints on the relative contribution of the Lyman-alpha emitter (LAE) population to cosmic reionization. Aims. The precise aim of the present study is to further constrain the abundance of LAEs by taking advantage of the magnification provided by lensing clusters to build a blindly selected sample of galaxies which is less biased than current blank field samples in redshift and luminosity. By construction, this sample of LAEs is complementary to those built from deep blank fields, whether observed by MUSE or by other facilities, and makes it possible to determine the shape of the LF at fainter levels, as well as its evolution with redshift. Methods. We selected a sample of 156 LAEs with redshifts between 2.9 ≤ z ≤ 6.7 and magnification-corrected luminosities in the range 39 ≲ log LLyα erg s−1 ≲43. To properly take into account the individual differences in detection conditions between the LAEs when computing the LF, including lensing configurations, and spatial and spectral morphologies, the non-parametric 1/Vmax method was adopted. The price to pay to benefit from magnification is a reduction of the effective volume of the survey, together with a more complex analysis procedure to properly determine the effective volume Vmax for each galaxy. In this paper we present a complete procedure for the determination of the LF based on IFU detections in lensing clusters. This procedure, including some new methods for masking, effective volume integration and (individual) completeness determinations, has been fully automated when possible, and it can be easily generalized to the analysis of IFU observations in blank fields. Results. As a result of this analysis, the Lyman-alpha LF has been obtained in four different redshift bins: 2.9 < z < 6, 7, 2.9 < z < 4.0, 4.0 < z < 5.0, and 5.0 < z < 6.7 with constraints down to log LLyα = 40.5. From our data only, no significant evolution of LF mean slope can be found. When performing a Schechter analysis also including data from the literature to complete the present sample towards the brightest luminosities, a steep faint end slope was measured varying from α = −1.69−0.08+0.08 α = − 1 . 69 − 0.08 + 0.08 $ \alpha = -1.69^{+0.08}_{-0.08} $ to α = −1.87−0.12+0.12 α = − 1 . 87 − 0.12 + 0.12 $ \alpha = -1.87^{+0.12}_{-0.12} $ between the lowest and the highest redshift bins. Conclusions. The contribution of the LAE population to the star formation rate density at z ∼ 6 is ≲50% depending on the luminosity limit considered, which is of the same order as the Lyman-break galaxy (LBG) contribution. The evolution of the LAE contribution with redshift depends on the assumed escape fraction of Lyman-alpha photons, and appears to slightly increase with increasing redshift when this fraction is conservatively set to one. Depending on the intersection between the LAE/LBG populations, the contribution of the observed galaxies to the ionizing flux may suffice to keep the universe ionized at z ∼ 6.
The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band (NB) Hα+NII imaging survey carried out with MegaCam at the Canada–France–Hawaii Telescope. The survey ...covers the whole Virgo cluster region from its core to one virial radius (104 deg2). The sensitivity of the survey is of f(Hα) ~ 4 × 10−17 erg s−1 cm−2 (5σ detection limit) for point sources and Σ(Hα) ~ 2 × 10−18 erg s−1 cm−2 arcsec−2 (1σ detection limit at 3 arcsec resolution) for extended sources, making VESTIGE the deepest and largest blind NB survey of a nearby cluster. This paper presents the survey in all its technical aspects, including the survey design, the observing strategy, the achieved sensitivity in both the NB Hα+NII and in the broad-band r filter used for the stellar continuum subtraction, the data reduction, calibration, and products, as well as its status after the first observing semester. We briefly describe the Hα properties of galaxies located in a 4 × 1 deg2 strip in the core of the cluster north of M87, where several extended tails of ionised gas are detected. This paper also lists the main scientific motivations for VESTIGE, which include the study of the effects of the environment on galaxy evolution, the fate of the stripped gas in cluster objects, the star formation process in nearby galaxies of different type and stellar mass, the determination of the Hα luminosity function and of the Hα scaling relations down to ~106 M⊙ stellar mass objects, and the reconstruction of the dynamical structure of the Virgo cluster. This unique set of data will also be used to study the HII luminosity function in hundreds of galaxies, the diffuse Hα+NII emission of the Milky Way at high Galactic latitude, and the properties of emission line galaxies at high redshift.
We report on the measurement of the physical properties (rest-frame K-band luminosity and total stellar mass) of the hosts of 89 broad-line (type-1) active galactic nuclei (AGNs) detected in the ...zCOSMOS survey in the redshift range 1 < z < 2.2. The unprecedented multi-wavelength coverage of the survey field allows us to disentangle the emission of the host galaxy from that of the nuclear black hole in their spectral energy distributions (SEDs). We derive an estimate of black hole masses through the analysis of the broad Mg II emission lines observed in the medium-resolution spectra taken with VIMOS/VLT as part of the zCOSMOS project. We found that, as compared to the local value, the average black hole to host-galaxy mass ratio appears to evolve positively with redshift, with a best-fit evolution of the form, where the large asymmetric systematic errors stem from the uncertainties in the choice of initial mass function, in the calibration of the virial relation used to estimate BH masses and in the mean QSO SED adopted. On the other hand, if we consider the observed rest-frame K-band luminosity, objects tend to be brighter, for a given black hole mass, than those on the local M BH-MK relation. This fact, together with more indirect evidence from the SED fitting itself, suggests that the AGN hosts are likely actively star-forming galaxies. A thorough analysis of observational biases induced by intrinsic scatter in the scaling relations reinforces the conclusion that an evolution of the M BH-M * relation must ensue for actively growing black holes at early times: either its overall normalization, or its intrinsic scatter (or both) appear to increase with redshift. This can be interpreted as signature of either a more rapid growth of supermassive black holes at high redshift, a change of structural properties of AGN hosts at earlier times, or a significant mismatch between the typical growth times of nuclear black holes and host galaxies. In any case, our results provide important clues on the nature of the early co-evolution of black holes and galaxies and challenging tests for models of AGN feedback and self-regulated growth of structures.
ABSTRACT
We investigate the luminosity–metallicity (L–Z) relation in the local Universe (0 < z < 0.15) using spectra of 6387 star‐forming galaxies extracted from the 2dF Galaxy Redshift Survey. This ...sample is by far the largest to date used to perform such a study. We distinguish star‐forming galaxies from active galactic nuclei (AGNs) using ‘standard’ diagnostic diagrams to build a homogeneous sample of starburst galaxies for the L–Z study. We propose new diagnostic diagrams using ‘blue’ emission lines (O iiλ3727, O iiiλ5007 and Hβ) only to discriminate starbursts from AGNs in intermediate‐redshift (z > 0.3) galaxies. Oxygen‐to‐hydrogen (O/H) abundance ratios are estimated using the ‘strong‐line’ method, which relates the strength of following bright emission lines O iiλ3727, O iiiλ5007 and Hβ (parameters R23 and O32) to O/H. We used the N iiλ6584/Hα emission‐line ratio as a ‘secondary’ abundance indicator to break the degeneracy between O/H and R23. We confirm the existence of the L–Z relation over a large range of abundances (∼2 dex) and luminosities (∼9 mag). We find a linear relation between the gas‐phase oxygen abundance and both the ‘raw’ and extinction‐corrected absolute B‐band magnitude with a rms of ∼0.27. A similar relation, with nearly the same scatter, is found in the R band. This relation is in good agreement with that derived by Melbourne and Salzer using the Kitt Peak National Observatory (KPNO) International Spectroscopic Survey (KISS) data. However, our L–Z relation is much steeper than previous determinations using samples of ‘normal’ irregular and spiral galaxies. This difference seems to be primarily due to the choice of the galaxy sample used to investigate the L–Z relation rather than any systematic error affecting the O/H determination. We anticipate that this L–Z relation will be used as the local ‘reference’ for future studies of the evolution with cosmic time of fundamental galaxy scaling relations.
The estimate of radial abundance gradients in high-redshift galaxies allows to constrain their star formation history and their interplay with the surrounding intergalactic medium. The authors ...present VLT/SINFONI integral-field spectroscopy of a first sample of 50 galaxies at z similar to 1.2 in the MASSIV survey. Using the N2 ratio between the NII 6584 and H alpha rest-frame optical emission lines as a proxy for oxygen abundance in the interstellar medium, they measured the metallicity of the sample galaxies. Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting, and one is a chain galaxy. They suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. They also identify two interesting correlations in their sample: galaxies with higher gas velocity dispersion have shallower/positive gradients; and metal-poor galaxies tend to show a positive gradient, whereas metal-rich ones tend to show a negative one.
Aims. The knowledge of the number and physical nature of low-metallicity massive galaxies is crucial for determining and interpreting the mass-metallicity relation (MZR). Methods. Using VLT-ISAAC ...near-infrared (NIR) spectroscopy of 39 zCOSMOS 0.5 <z< 0.9 galaxies, we have measured Hα and N II λ 6584 emission line fluxes for galaxies with O II λ 3727, Hβ, and O III λ 5007 available from VIMOS optical spectroscopy. The NIR spectroscopy enables us to break the degeneracy of the R23 method to unambiguously derive O/H gas metallicities and star formation rates (SFRs) from extinction-corrected Hα fluxes. Results. We used the position in the D4000 vs. O III λ 5007/Hβ diagram of galaxies with reliable O/Hs from NIR spectroscopy as a benchmark. This enabled us to break the lower or upper branch R23 degeneracy of additional 900 zCOSMOS galaxies at 0.5 <z< 0.9, which do not have measurements of Hα and N II λ 6584. Additionally, the Hα-based SFR measurements were used to find the best SFR calibration based on O II λ 3727 for the 0.5 <z< 0.9 zCOSMOS galaxies without Hα measurements. With a larger zCOSMOS sample of star-forming galaxies at z ≈ 0.7 with reliable O/H and SFR measurements, we studied the MZR at z ≈ 0.7 and its dependence on (specific) SFR. We find a fraction of 19% of lower mass 9.5 < log (M/M⊙) < 10.3 zCOSMOS galaxies that shows a larger evolution of the MZR relation than is found in higher mass galaxies; they are more metal poor at a given mass by a factor of 2−3 than SDSS. This indicates that the low-mass MZR slope steepens at z ≈ 0.7 compared to local galaxies. Many of these galaxies with lower metallicity would be missed by studies that assume upper branch R23 solution for all galaxies. The existence of these metal-poor galaxies at z ≈ 0.7 can be interpreted as the chemical version of galaxy downsizing. Moreover, the sample of zCOSMOS galaxies shows direct evidence that the SFR influences the MZR at these redshifts. The measured metallicities for the zCOSMOS sample broadly agree with the values expected for a non-evolving fundamental metallicity relation. This comparison also reveals that galaxies with lower metallicities and typically higher (specific) SFRs, such as found in our zCOSMOS sample at z ≈ 0.7, agree with the predictions of a non-evolving Z(M, SFR).
We explore the role of environment in the evolution of galaxies over 0.1 < z < 0.7 using the final zCOSMOS-bright data set. Using the red fraction of galaxies as a proxy for the quenched population, ...we find that the fraction of red galaxies increases with the environmental overdensity δ and with the stellar mass M
*, consistent with previous works. As at lower redshift, the red fraction appears to be separable in mass and environment, suggesting the action of two processes: mass m(M
*) and environmental ρ(δ) quenching. The parameters describing these appear to be essentially the same at z ∼ 0.7 as locally. We explore the relation between red fraction, mass and environment also for the central and satellite galaxies separately, paying close attention to the effects of impurities in the central-satellite classification and using carefully constructed samples well matched in stellar mass. There is little evidence for a dependence of the red fraction of centrals on overdensity. Satellites are consistently redder at all overdensities, and the satellite quenching efficiency, sat(δ, M
*), increases with overdensity at 0.1 < z < 0.4. This is less marked at higher redshift, but both are nevertheless consistent with the equivalent local measurements. At a given stellar mass, the fraction of galaxies that are satellites, f
sat(δ, M
*), also increases with overdensity. The obtained ρ(δ)/f
sat(δ, M
*) agrees well with sat(δ, M
*), demonstrating that the environmental quenching in the overall population is consistent with being entirely produced by a satellite quenching process at least up to z = 0.7. However, despite the unprecedented size of our high-redshift samples, the associated statistical uncertainties are still significant and our statements should be understood as approximations to physical reality, rather than physically exact formulae.
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