arXiv subjects

L. Tresse

Publications and source records attributed to L. Tresse.

At least 55 records · Page 3Linked to original sources

arXiv2014

The VIMOS Ultra-Deep Survey: ~10,000 galaxies with spectroscopic redshifts to study galaxy assembly at early epochs 2<z<~6

We present the VIMOS Ultra Deep Survey (VUDS), a spectroscopic redshift survey of ~10.000 very faint galaxies to study the major phase of galaxy assembly 2<z<~6. The survey covers 1 deg^2 in 3 separate fields: COSMOS, ECDFS and VVDS-02h, with targets selection based on an inclusive combination of photometric redshifts and color properties. Spectra covering 3650<lambda<9350 A are obtained with VIMOS on the ESO-VLT with integration times of 14h. Here we present the survey strategy, the target selection, the data processing, as well as the redshift measurement process, emphasizing the specific methods adapted to this high redshift range. The spectra quality and redshift reliability are discussed, and we derive a completeness in redshift measurement of 91%, or 74% for the most reliable measurements, down to i_AB=25, and measurements are performed all the way down to i_AB=27. The redshift distribution of the main sample peaks at z=3-4 and extends over a large redshift range mainly in 2 < z < 6. At 3<z<5, the galaxies cover a large range of luminosities -23< M_U < -20.5, stellar mass 10^9 M_sun< M_star < 10^{11} M_sun, and star formation rates 1 M_sun/yr< SFR < 10^3 M_sun/yr. We discuss the spectral properties of galaxies using individual as well as stacked spectra. The comparison between spectroscopic and photometric redshifts as well as color selection demonstrate the effectiveness of our selection scheme. With ~6000 galaxies with reliable spectroscopic redshifts in 2<z<6 expected when complete, this survey is the largest at these redshifts and offers the opportunity for unprecedented studies of the star-forming galaxy population and its distribution in large scale structures during the major phase of galaxy assembly.

astro-ph.CO↗

arXiv2013

The VIMOS VLT Deep Survey final data release: a spectroscopic sample of 35016 galaxies and AGN out to z~6.7 selected with 17.5<=i_{AB}<=24.7

We describe the completed VIMOS VLT Deep Survey, and the final data release of 35016 galaxies and type-I AGN with measured spectroscopic redshifts up to redshift z~6.7, in areas 0.142 to 8.7 square degrees, and volumes from 0.5x10^6 to 2x10^7h^-3Mpc^3. We have selected samples of galaxies based solely on their i-band magnitude reaching i_{AB}=24.75. Spectra have been obtained with VIMOS on the ESO-VLT, integrating 0.75h, 4.5h and 18h for the Wide, Deep, and Ultra-Deep nested surveys. A total of 1263 galaxies have been re-observed independently within the VVDS, and from the VIPERS and MASSIV surveys. They are used to establish the redshift measurements reliability, to assess completeness, and to provide a weighting scheme taking into account the survey selection function. We describe the main properties of the VVDS samples, and the VVDS is compared to other spectroscopic surveys. In total we have obtained spectroscopic redshifts for 34594 galaxies, 422 type-I AGN, and 12430 Galactic stars. The survey has enabled to identify galaxies up to very high redshifts with 4669 redshifts in 1<=z_{spec}<=2, 561 in 2<=z_{spec}<=3 and 468 with z_{spec}>3, and specific populations like LAE have been identified out to z=6.62. We show that the VVDS occupies a unique place in the parameter space defined by area, depth, redshift coverage, and number of spectra. The VVDS provides a comprehensive survey of the distant universe, covering all epochs since z, or more than 12 Gyr of cosmic time, with a uniform selection, the largest such sample to date. A wealth of science results derived from the VVDS have shed new light on the evolution of galaxies and AGN, and their distribution in space, over this large cosmic time. A final public release of the complete VVDS spectroscopic redshift sample is available at http://cesam.lam.fr/vvds.

astro-ph.CO↗

arXiv2013

Proto-groups at 1.8<z<3 in the zCOSMOS-deep sample

We identify 42 candidate groups lying between 1.8<z<3.0 from a sample of 3502 galaxies with spectroscopic redshifts in the zCOSMOS-deep redshift survey within the same redshift interval. These systems contain three to five spectroscopic galaxies that lie within 500kpc in projected distance (in physical space) and within 700km/s in velocity. Based on extensive analysis of mock catalogues that have been generated from the Millennium simulation, we examine the likely nature of these systems at the time of observation, and what they will evolve into down to the present epoch. Although few of the "member" galaxies are likely to reside in the same halo at the epoch we observe them, 50% of the systems will eventually bring them all into the same halo, and almost all (93%) will have at least part of the member galaxies in the same halo by the present epoch. Most of the candidate groups can therefore be described as "proto-groups". An estimate of the overdensities is also consistent with the idea that these systems are being seen at the start of the assembly process. We also examine present-day haloes and ask whether their progenitors would have been seen amongst our candidate groups. For present-day haloes between 10^14-10^15Msun/h, 35% should have appeared amongst our candidate groups, and this would have risen to 70% if our survey had been fully-sampled, so we can conclude that our sample can be taken as representative of a large fraction of such systems. There is a clear excess of massive galaxies above 10^10Msun around the locations of the candidate groups in a large independent COSMOS photo-z sample, but we see no evidence in this latter data for any colour differentiation with respect to the field. This is however consistent with the idea that such differentiation arises in satellite galaxies, as indicated at z<1, if the candidate groups are indeed only starting to be assembled.

astro-ph.CO↗

arXiv2013

Spot the difference. Impact of different selection criteria on observed properties of passive galaxies in zCOSMOS 20-k sample

We present the analysis of photometric, spectroscopic, and morphological properties for differently selected samples of passive galaxies up to z=1 extracted from the zCOSMOS-20k spectroscopic survey. This analysis intends to explore the dependence of galaxy properties on the selection criterion adopted, study the degree of contamination due to star-forming outliers, and provide a comparison between different commonly used selection criteria. We extracted from the zCOSMOS-20k catalog six different samples of passive galaxies, based on morphology, optical colors, specific star-formation rate, a best fit to the observed spectral energy distribution, and a criterion that combines morphological, spectroscopic, and photometric information. The morphological sample has the higher percentage of contamination in colors, specific star formation rate and presence of emission lines, while the red & passive ETGs sample is the purest, with properties mostly compatible with no star formation activity; however, it is also the less economic criterion in terms of information used. The best performing among the other criteria are the red SED and the quiescent ones, providing a percentage of contamination only slightly higher than the red & passive ETGs criterion (on average of a factor of ~2) but with absolute values of the properties of contaminants still compatible with a red, passively evolving population. We also provided two revised definitions of early type galaxies based on restframe color-color and color-mass criteria, that better reproduce the observed bimodalities. The analysis of the number densities shows evidences of mass-assembly downsizing, with galaxies at 10.25<log(M/Msun)<10.75 increasing their number by a factor ~2-4 from z=0.6 to z=0.2, by a factor ~2-3 from z=1 to z=0.2 at 10.75<log(M/Msun)<11, and by only ~10-50% from z=1 to z=0.2 at 11<log(M/Msun)<11.5.

astro-ph.CO↗

arXiv2013

The VIMOS VLT Deep Survey. The different assembly history of passive and star-forming L_B >= L*_B galaxies in the group environment at z < 1

We use the VIMOS VLT Deep Survey to study the close environment of galaxies in groups at 0.2 <= z < 0.95. Close neighbours of L_B >= L*_B galaxies (Me_B = M_B + 1.1z <= -20) are identified with Me_B <= -18.25 and within a relative distance 5h^-1 kpc <= rp <= 100h^-1 kpc and relative velocity Delta v <= 500 km/s . The richness N of a group is defined as the number of Me_B <= -18.25 galaxies belonging to that group. We split our principal sample into red, passive galaxies with NUV - r >= 4.25 and blue, star-forming galaxies with NUV - r < 4.25. We find that blue galaxies with a close companion are primarily located in poor groups, while the red ones are in rich groups. The number of close neighbours per red galaxy increases with N, with n_red being proportional to 0.11N, while that of blue galaxies does not depend on N and is roughly constant. In addition, these trends are found to be independent of redshift, and only the average n_blue evolves, decreasing with cosmic time. Our results support the following assembly history of L_B >= L*_B galaxies in the group environment: red, massive galaxies were formed in or accreted by the dark matter halo of the group at early times (z >= 1), therefore their number of neighbours provides a fossil record of the stellar mass assembly of groups, traced by their richness N. On the other hand, blue, less massive galaxies have recently been accreted by the group potential and are still in their parent dark matter halo, having the same number of neighbours irrespective of N. As time goes by, these blue galaxies settle in the group potential and turn red and/or fainter, thus becoming satellite galaxies in the group. With a toy quenching model, we estimate an infall rate of field galaxies into the group environment of R_infall = 0.9 - 1.5 x 10^-4 Mpc^-3 Gyr^-1 at z ~ 0.7.

astro-ph.CO↗

arXiv2013

The VIMOS VLT Deep Survey: the redshift distribution N(z) of magnitude-limited samples down to iAB=24.75 and KsAB=22

We measure and analyse the redshift distribution N(z) of magnitude-selected samples using spectroscopic redshift measurement from the magnitude-selected VIMOS VLT Deep Survey (VVDS) with 17 2. Down to iAB<24.75 the sample has a mean redshift z=1.15 and 17.1% of the galaxies are beyond z=2. The projected sky density is 2.07+/-0.12 gal/arcmin2 at 1.4 2 than in colour-colour selected samples, and we use the magnitude-selected VVDS to emphasize the large uncertainties associated to other surveys using colour or colour-colour selected samples. Our results further demonstrate that semi-analytical models on dark matter simulations have yet to find the right balance of physical processes and time-scales to properly reproduce a fundamental galaxy population property like the observed N(z).

astro-ph.CO↗

arXiv2013

The dependence of Galactic outflows on the properties and orientation of zCOSMOS galaxies at z ~ 1

We present an analysis of cool outflowing gas around galaxies, traced by MgII absorption lines in the co-added spectra of a sample of 486 zCOSMOS galaxies at 1 < z < 1.5. These galaxies span a range of stellar masses (9.45< log[M*/Msun]<10.7) and star formation rates (0.14 < log [SFR/Msun/yr] < 2.35). We identify the cool outflowing component in the MgII absorption and find that the equivalent width of the outflowing component increases with stellar mass. The outflow equivalent width also increases steadily with the increasing star formation rate of the galaxies. At similar stellar masses the blue galaxies exhibit a significantly higher outflow equivalent width as compared to red galaxies. The outflow equivalent width shows strong effect with star formation surface density (ΣSFR) of the sample. For the disk galaxies, the outflow equivalent width is higher for the face-on systems as compared to the edge-on ones, indicating that for the disk galaxies, the outflowing gas is primarily bipolar in geometry. Galaxies typically exhibit outflow velocities ranging from -200 km/s to -300 km/s and on average the face-on galaxies exhibit higher outflow velocity as compared to the edge-on ones. Galaxies with irregular morphologies exhibit outflow equivalent width as well as outflow velocities comparable to face on disk galaxies. These galaxies exhibit minimum mass outflow rates > 5-7 Msun/yr and a mass loading factor (η = dMout/dt /SFR) comparable to the star formation rates of the galaxies.

astro-ph.CO↗

arXiv2013

HeII emitters in the VIMOS VLT Deep Survey: PopIII star formation or peculiar stellar populations in galaxies at 2<z<4.6?

The aim of this work is to identify HeII emitters at 2 1200km/s), 3 AGN, and an additional 12 possible HeII emitters. The properties of the individual broad emitters are in agreement with expectations from a W-R model. On the contrary, the properties of the narrow emitters are not compatible with such model, neither with predictions of gravitational cooling radiation produced by gas accretion. Rather, we find that the EW of the narrow HeII line emitters are in agreement with expectations for a PopIII star formation, if the episode of star formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1 only is enough to sustain the observed HeII flux. We conclude that narrow HeII emitters are either powered by the ionizing flux from a stellar population rare at z~0 but much more common at z~3, or by PopIII star formation. As proposed by Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of pristine gas at the periphery of galaxies from which PopIII may form, even down to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value predicted by Tornatore et al. (2007).

astro-ph.CO↗

arXiv2013

zCOSMOS 20k: Satellite galaxies are the main drivers of environmental effects in the galaxy population at least to z~0.7

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 and with the stellar mass, 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 and environmental 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 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 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 also increases with the overdensity. At a given overdensity and mass, the obtained relation between the environmental quenching and the satellite fraction agrees well with the satellite quenching efficiency, demonstrating that the environmental quenching in the overall population is consistent with being entirely produced through the 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.

astro-ph.CO↗

arXiv2013

Mass assembly in quiescent and star-forming galaxies since z=4 from UltraVISTA

We estimate the galaxy stellar mass function and stellar mass density for star-forming and quiescent galaxies with 0.2 10^10.7Msun. For the mass function of the quiescent galaxies, we do not find any significant evolution of the high-mass end at z<1; however we observe a clear flattening of the faint-end slope. From z~3 to z~1, the density of quiescent galaxies increases over the entire mass range. Their comoving stellar mass density increases by 1.6 dex between z~3 and z~1 and by less than 0.2dex at z<1. We infer the star formation history from the mass density evolution and we find an excellent agreement with instantaneous star formation rate measurements at z<1.5, while we find differences of 0.2dex at z>1.5 consistent with the expected uncertainties. We also develop a new method to infer the specific star formation rate from the mass function of star-forming galaxies. We find that the specific star formation rate of 10^10Msun galaxies increases continuously in the redshift range 1<z<4. Finally, we compare our results with a semi-analytical model and find that these models overestimate the density of low mass quiescent galaxies by an order of magnitude, while the density of low-mass star-forming galaxies is successfully reproduced.

astro-ph.CO↗

arXiv2013

Obscured AGN at z~1 from the zCOSMOS-Bright Survey I. Selection and Optical Properties of a [Ne v]-selected sample

A sample of 94 narrow line AGN with 0.65<z<1.20 has been selected from the 20k-Bright zCOSMOS galaxy sample by detection of the high-ionization [NeV]3426 line. Taking advantage of the large amount of data available in the COSMOS field, the properties of the [NeV]-selected Type-2 AGN have been investigated, focusing on their host galaxies, X-ray emission, and optical line flux ratios. Finally, the diagnostic developed by Gilli et al. (2010), based on the X-ray to [NeV] luminosity ratio, has been exploited to search for the more heavily obscured AGN. We found that [Ne v]-selected narrow line AGN have Seyfert 2-like optical spectra, although with emission line ratios diluted by a star-forming component. The ACS morphologies and stellar component in the optical spectra indicate a preference for our Type-2 AGN to be hosted in early-spirals with stellar masses greater than 10^(9.5-10)Msun, on average higher than those of the galaxy parent sample. The fraction of galaxies hosting [NeV]-selected obscured AGN increases with the stellar mass, reaching a maximum of about 3% at 2x10^11 Msun. A comparison with other selection techniques at z~1 shows that the detection of the [Ne v] line is an effective method to select AGN in the optical band, in particular the most heavily obscured ones, but can not provide by itself a complete census of AGN2. Finally, the high fraction of [NeV]-selected Type-2 AGN not detected in medium-deep Chandra observations (67%) is suggestive of the inclusion of Compton-thick sources in our sample. The presence of a population of heavily obscured AGN is corroborated by the X-ray to [NeV] ratio; we estimated, by mean of X-ray stacking technique and simulations, that the Compton-thick fraction in our sample of Type-2 AGN is 43+-4%, in good agreement with standard assumptions by the XRB synthesis models.

astro-ph.CO↗

arXiv2013

MASSIV: Mass Assembly Survey with SINFONI in VVDS. V. The major merger rate of star-forming galaxies at 0.9 < z < 1.8 from IFS-based close pairs

We aim to measure the major merger rate of star-forming galaxies at 0.9 < z <1.8, using close pairs identified from integral field spectroscopy (IFS). We use the velocity field maps obtained with SINFONI/VLT on the MASSIV sample, selected from the star-forming population in the VVDS. We identify physical pairs of galaxies from the measurement of the relative velocity and the projected separation (r_p) of the galaxies in the pair. Using the well constrained selection function of the MASSIV sample we derive the gas-rich major merger fraction (luminosity ratio mu = L_2/L_1 >= 1/4), and, using merger time scales from cosmological simulations, the gas-rich major merger rate at a mean redshift up to z = 1.54. We find a high gas-rich major merger fraction of 20.8+15.2-6.8 %, 20.1+8.0-5.1 % and 22.0+13.7-7.3 % for close pairs with r_p <= 20h^-1 kpc in redshift ranges z = [0.94, 1.06], [1.2, 1.5) and [1.5, 1.8), respectively. This translates into a gas-rich major merger rate of 0.116+0.084-0.038 Gyr^-1, 0.147+0.058-0.037 Gyr^-1 and 0.127+0.079-0.042 Gyr^-1 at z = 1.03, 1.32 and 1.54, respectively. Combining our results with previous studies at z < 1, the gas-rich major merger rate evolves as (1+z)^n, with n = 3.95 +- 0.12, up to z = 1.5. From these results we infer that ~35% of the star-forming galaxies with stellar masses M = 10^10 - 10^10.5 M_Sun have undergone a major merger since z ~ 1.5. We develop a simple model which shows that, assuming that all gas-rich major mergers lead to early-type galaxies, the combined effect of gas-rich and dry mergers is able to explain most of the evolution in the number density of massive early-type galaxies since z ~ 1.5, with our measured gas-rich merger rate accounting for about two-thirds of this evolution.

astro-ph.CO↗

arXiv2013

The Colors of Central and Satellite Galaxies in zCOSMOS out to z ~ 0.8 and Implications for Quenching

We examine the red fraction of central and satellite galaxies in the large zCOSMOS group catalog out to z ~ 0.8 correcting for both the incompleteness in stellar mass and for the less than perfect purities of the central and satellite samples. We show that, at all masses and at all redshifts, the fraction of satellite galaxies that have been quenched, i.e., are red, is systematically higher than that of centrals, as seen locally in the Sloan Digital Sky Survey (SDSS). The satellite quenching efficiency, which is the probability that a satellite is quenched because it is a satellite rather than a central, is, as locally, independent of stellar mass. Furthermore, the average value is about 0.5, which is also very similar to that seen in the SDSS. We also construct the mass functions of blue and red centrals and satellites and show that these broadly follow the predictions of the Peng et al. analysis of the SDSS groups. Together, these results indicate that the effect of the group environment in quenching satellite galaxies was very similar when the universe was about a half its present age, as it is today.

astro-ph.CO↗

arXiv2013

Investigating the relationship between AGN activity and stellar mass in zCOSMOS galaxies at 0<z<1 using emission line diagnostic diagrams

We investigate the link between AGN activity, star-formation and stellar mass of the host galaxy at 0 10.2 threshold. Moreover, the stellar populations of AGN hosts are found to be older with respect to star-forming and composites galaxies. This could be due to the the tendency of AGN to reside in massive hosts. The dependence of the AGN classification on the stellar mass is in agreement with what has been already found in previous studies. It is consistent with, together with the evidence of older stellar populations inhabiting the AGN-like galaxies, the downsizing scenario. In particular, our evidence points to an evolutionary scenario where the AGN-feedback is capable of quenching the star formation in the most massive galaxies. Therefore, the AGN-feedback is the best candidate for initiating the passive evolutionary phase of galaxies.

astro-ph.CO↗

arXiv2013

The role of major mergers in shaping galaxies at 2<z<4 in the VUDS and VVDS surveys

The mass assembly of galaxies can proceed through different physical processes. Here we report on the spectroscopic identification of close physical pairs of galaxies at redshifts 2 <z < 4 and discuss the impact of major mergers in shaping galaxies at these early cosmological times. We aim to identify and characterize close physical pairs of galaxies destined to merge and use their properties to infer the contribution of merging processes to the early mass assembly of galaxies. We search for galaxy pairs with a transverse separation r_p < 25 h^{-1} kpc and a velocity difference Delta v < 500 km s^{-1} using the VIMOS VLT Deep Survey (VVDS) and early data from the VIMOS Ultra Deep Survey (VUDS) that comprise a sample of 1111 galaxies with spectroscopic redshifts measurements at redshifts 1.8 < z < 4 in the COSMOS, ECDFS, and VVDS-02h fields. We analyse their spectra and associated visible and near-infrared photometry to assess the main properties of merging galaxies that have an average stellar mass M_{star}=2.3 x 10^{10} M_{sun} at these redshifts. Using the 12 physical pairs found in our sample we obtain a first estimate of the merger fraction at these rdshifts, fmerg ~(15-20)%. The pair separations indicate that these pairs will merge within 1 Gyr, on average, with each producing a more massive galaxy by the time the cosmic star formation peaks at z~1-2. From the average mass ratio between galaxies in the pairs, the stellar mass of the resulting galaxy after merging will be ~60% larger than the most massive galaxy in the pair before merging. We conclude that major merging of galaxy pairs is on-going at 2<z<4 and significantly contributing to the major assembly phase of galaxies at this early epoch.

astro-ph.CO↗

arXiv2013

Improved constraints on the expansion rate of the Universe up to z~1.1 from the spectroscopic evolution of cosmic chronometers

We present new improved constraints on the Hubble parameter H(z) in the redshift range 0.15 < z < 1.1, obtained from the differential spectroscopic evolution of early-type galaxies as a function of redshift. We extract a large sample of early-type galaxies (\sim11000) from several spectroscopic surveys, spanning almost 8 billion years of cosmic lookback time (0.15 < z < 1.42). We select the most massive, red elliptical galaxies, passively evolving and without signature of ongoing star formation. Those galaxies can be used as standard cosmic chronometers, as firstly proposed by Jimenez & Loeb (2002), whose differential age evolution as a function of cosmic time directly probes H(z). We analyze the 4000 Å break (D4000) as a function of redshift, use stellar population synthesis models to theoretically calibrate the dependence of the differential age evolution on the differential D4000, and estimate the Hubble parameter taking into account both statistical and systematical errors. We provide 8 new measurements of H(z) (see Tab. 4), and determine its change in H(z) to a precision of 5-12% mapping homogeneously the redshift range up to z \sim 1.1; for the first time, we place a constraint on H(z) at z \neq 0 with a precision comparable with the one achieved for the Hubble constant (about 5-6% at z \sim 0.2), and covered a redshift range (0.5 < z < 0.8) which is crucial to distinguish many different quintessence cosmologies. These measurements have been tested to best match a ΛCDM model, clearly providing a statistically robust indication that the Universe is undergoing an accelerated expansion. This method shows the potentiality to open a new avenue in constrain a variety of alternative cosmologies, especially when future surveys (e.g. Euclid) will open the possibility to extend it up to z \sim 2.

astro-ph.CO↗

arXiv2012

Mass Assembly of High-z Galaxies with MASSIV

MASSIV (Mass Assembly Survey with SINFONI in VVDS) is a sample of 84 distant star-forming galaxies observed with the SINFONI Integral Field Unit (IFU) on the VLT. These galaxies are selected inside a redshift range of 0.8 < z < 1.9, i.e. where they are between 3 and 5 billion years old. The sample aims to probe the dynamical and chemical abundances properties of representative galaxies of this cosmological era. On the one hand, close environment study shows that about a third of the sample is involved in major mergers. On the other hand, kinematical analysis revealed that 42% of the sample is rotating disks, in accordance with higher redshift samples. The remaining 58% show complex kinematics, suggesting a dynamical support based on dispersion, and about half of these galaxies is involved in major mergers. Spheroids, unrelaxed merger remnants, or extremely turbulent disks might be an explanation for such a behavior. Furthermore, the spatially resolved metallicity analysis reveals positive gradients, adding a piece to the puzzle of galaxies evolution scenarios.

astro-ph.CO↗

arXiv2012

The intriguing life of star-forming galaxies in the redshift range 1 < z < 2 using MASSIV

MASSIV (Massiv Assembly Survey with SINFONI in VVDS) is an ESO large program which consists of 84 star-forming galaxies, spanning in a wide range of stellar masses, observed with the IFU SINFONI on the VLT, in the redshift range 1 < z < 2. To be representative of the normal galaxy population, the sample has been selected from a well-defined, complete and representative parent sample. The kinematics of individual galaxies reveals that 58% of the galaxies are slow rotators, which means that a high fraction of these galaxies should probably be formed through major merger processes which might have produced gaseous thick or spheroidal structures supported by velocity dispersion rather than by rotation. Computations on the major merger rate from close pairs indicate that a typical star-forming galaxy underwent ~0.4 major mergers since ~9.5 Gyr, showing that merging is a major process driving mass assembly into the red sequence galaxies. These objects are also intriguing due to the fact that more than one galaxy over four is more metal-rich in its outskirts than in its center.

astro-ph.CO↗