arXiv subjects

E. Perez-Montero

Publications and source records attributed to E. Perez-Montero.

At least 55 records · Page 3Linked to original sources

arXiv2010

The zCOSMOS 10k-sample: the role of galaxy stellar mass in the colour-density relation up to z=1

[Abridged] With the first 10000 spectra of the flux limited zCOSMOS sample (I<=22.5) we study the evolution of environmental effects on galaxy properties since z=1.0, and disentangle the dependence among galaxy colour, stellar mass and local density (3D local density contrast `delta', computed with the 5th nearest neighbour approach). We confirm that within a luminosity-limited sample (M_B<=-20.5-z) the fraction of red (U-B>=1) galaxies 'f_red' depends on delta at least up to z=1, with red galaxies residing mainly in high densities. This trend weakens for increasing z, and it is mirrored by the behaviour of the fraction of galaxies with D4000A break >=1.4. We also find that up to z=1 the fraction of galaxies with log(EW[OII]) >=1.15 is higher for lower delta, and also this dependence weakens for increasing z. Given the triple dependence among galaxy colours, stellar mass and delta, the colour-delta relation found in the luminosity-selected sample can be due to the broad range of stellar masses. Thus, we fix the stellar mass and we find that in this case the colour-delta relation is flat up to z=1 for galaxies with log(M/M_sun)>=10.7. This means that for these masses the colour-delta relation found in a luminosity-selected sample is the result of the combined colour-mass and mass-delta relations. In contrast, we find that for 0.1<=z<=0.5 and log(M/M_sun)<=10.7 'f_red' depends on delta even at fixed mass. In these mass and z ranges, environment affects directly also galaxy colours. We suggest a scenario in which the colour depends primarily on stellar mass, but for relatively low mass galaxies the local density modulates this dependence. These galaxies formed more recently, in an epoch when evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate during longer periods of time.

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arXiv2010

Understanding the shape of the galaxy two-point correlation function at z~1 in the COSMOS field

We investigate how the shape of the galaxy two-point correlation function as measured in the zCOSMOS survey depends on local environment, quantified in terms of the density contrast on scales of 5 Mpc/h. We show that the flat shape previously observed at redshifts between z=0.6 and z=1 can be explained by this volume being simply 10% over-abundant in high-density environments, with respect to a Universal density probability distribution function. When galaxies corresponding to the top 10% tail of the distribution are excluded, the measured w_p(r_p) steepens and becomes indistinguishable from LCDM predictions on all scales. This is the same effect recognised by Abbas & Sheth in the SDSS data at z~0 and explained as a natural consequence of halo-environment correlations in a hierarchical scenario. Galaxies living in high-density regions trace dark matter halos with typically higher masses, which are more correlated. If the density probability distribution function of the sample is particularly rich in high-density regions because of the variance introduced by its finite size, this produces a distorted two-point correlation function. We argue that this is the dominant effect responsible for the observed "peculiar" clustering in the COSMOS field.

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arXiv2010

The XMM-Newton Wide-Field Survey in the COSMOS field (XMM-COSMOS): demography and multiwavelength properties of obscured and unobscured luminous AGN

We report the final optical identifications of the medium-depth (~60 ksec), contiguous (2 deg^2) XMM-Newton survey of the COSMOS field. XMM-Newton has detected ~800 X-ray sources down to limiting fluxes of ~5x10^{-16}, ~3x10^{-15}, and ~7x10^{-15} erg/cm2/s in the 0.5-2 keV, 2-10 keV and 5-10 keV bands, respectively. The work is complemented by an extensive collection of multi-wavelength data from 24 micron to UV, available from the COSMOS survey, for each of the X-ray sources, including spectroscopic redshifts for ~50% of the sample, and high-quality photometric redshifts for the rest. The XMM and multiwavelength flux limits are well matched: 1760 (98%) of the X-ray sources have optical counterparts, 1711 (~95%) have IRAC counterparts, and 1394 (~78%) have MIPS 24micron detections. Thanks to the redshift completeness (almost 100%) we were able to constrain the high-luminosity tail of the X-ray luminosity function confirming that the peak of the number density of logL_X>44.5 AGN is at z~2. Spectroscopically-identified obscured and unobscured AGN, as well as normal and starforming galaxies, present well-defined optical and infrared properties. We devised a robust method to identify a sample of ~150 high redshift (z>1), obscured AGN candidates for which optical spectroscopy is not available. We were able to determine that the fraction of the obscured AGN population at the highest (L_X>10^{44} erg s^{-1}) X-ray luminosity is ~15-30% when selection effects are taken into account, providing an important observational constraint for X-ray background synthesis. We studied in detail the optical spectrum and the overall spectral energy distribution of a prototypical Type 2 QSO, caught in a stage transitioning from being starburst dominated to AGN dominated, which was possible to isolate only thanks to the combination of X-ray and infrared observations.

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arXiv2010

The VIMOS-VLT Deep Survey: Evolution in the Halo Occupation Number since z $\sim$ 1

We model the evolution of the mean galaxy occupation of dark-matter halos over the range $0.1 0.1 M_0$ merger event occuring between redshifts of 0.5 and 1.0. Futhermore, we find that more luminous galaxies are found to occupy more massive halos irrespectively of the redshift. Finally, the average number of galaxies per halo shows little increase from redshift z$\sim$ 1.0 to z$\sim$ 0.5, with a sharp increase by a factor $\sim$3 from z$\sim$ 0.5 to z$\sim$ 0.1, likely due to the dynamical friction of subhalos within their host halos.

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arXiv2009

Properties and environment of Radio Emitting Galaxies in the VLA-zCOSMOS survey

We investigate the properties and the environment of radio sources with optical counterpart from the combined VLA-COSMOS and zCOSMOS samples. The advantage of this sample is the availability of optical spectroscopic information, high quality redshifts, and accurate density determination. By comparing the star formation rates estimated from the optical spectral energy distribution with those based on the radio luminosity, we divide the radio sources in three families, passive AGN, non-passive AGN and star forming galaxies. These families occupy specific regions of the 8.0-4.5 $μ$m infrared color--specific star formation plane, from which we extract the corresponding control samples. Only the passive AGN have a significantly different environment distribution from their control sample. The fraction of radio-loud passive AGN increases from ~2% in underdense regions to ~15% for overdensities (1+delta) greater than 10. This trend is also present as a function of richness of the groups hosting the radio sources. Passive AGN in overdensities tend to have higher radio luminosities than those in lower density environments. Since the black hole mass distribution is similar in both environments, we speculate that, for low radio luminosities, the radio emission is controlled (through fuel disponibility or confinement of radio jet by local gas pressure) by the interstellar medium of the host galaxy, while in other cases it is determined by the structure (group or cluster) in which the galaxy resides.

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arXiv2009

The optical spectra of Spitzer 24 micron galaxies in the COSMOS field: II. Faint infrared sources in the zCOSMOS-bright 10k catalogue

We have used the zCOSMOS-bright 10k sample to identify 3244 Spitzer/MIPS 24-micron-selected galaxies with 0.06< S(24um)< 0.50 mJy and I(AB)<22.5, over 1.5 deg^2 of the COSMOS field, and studied different spectral properties, depending on redshift. At 0.2<z<0.3, we found that different reddening laws of common use in the literature explain the dust extinction properties of around 80% of our infrared (IR) sources, within the error bars. For up to 16% of objects, instead, the Halpha/Hbeta ratios are too high for their IR/UV attenuations, which is probably a consequence of inhomogenous dust distributions. In only a few of our galaxies at 0.2<z<0.3 the IR emission could be mainly produced by dust heated by old rather than young stars. Besides, the line ratios of ~22% of our galaxies suggest that they might be star-formation/nuclear-activity composite systems. At 0.5<z<0.7, we estimated galaxy metallicities for 301 galaxies: at least 12% of them are securely below the upper-branch mass-metallicity trend, which is consistent with the local relation. Finally, we performed a combined analysis of the Hdelta equivalent-width versus Dn(4000) diagram for 1722 faint and bright 24um galaxies at 0.6<z<1.0, spanning two decades in mid-IR luminosity. We found that, while secondary bursts of star formation are necessary to explain the position of the most luminous IR galaxies in that diagram, quiescent, exponentially-declining star formation histories can well reproduce the spectral properties of ~40% of the less luminous sources. Our results suggest a transition in the possible modes of star formation at total IR luminosities L(TIR)=(3 +/-2)x10^11 Lsun.

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arXiv2009

Integral field spectroscopy with SINFONI of VVDS galaxies. II. The mass-metallicity relation at 1.2 < z < 1.6

This work aims to provide a first insight into the mass-metallicity (MZ) relation of star-forming galaxies at redshift z~1.4. To reach this goal, we present a first set of nine VVDS galaxies observed with the NIR integral-field spectrograph SINFONI on the VLT. Oxygen abundances are derived from empirical indicators based on the ratio between strong nebular emission-lines (Halpha, [NII]6584 and [SII]6717,6731). Stellar masses are deduced from SED fitting with Charlot & Bruzual (2007) population synthesis models, and star formation rates are derived from [OII]3727 and Halpha emission-line luminosities. We find a typical shift of 0.2-0.4 dex towards lower metallicities for the z~1.4 galaxies, compared to the MZ-relation in the local universe as derived from SDSS data. However, this small sample of eight galaxies does not show any clear correlation between stellar mass and metallicity, unlike other larger samples at different redshift (z~0, z~0.7, and z~2). Indeed, our galaxies lie just under the relation at z~2 and show a small trend for more massive galaxies to be more metallic (~0.1 logarithmic slope). There are two possible explanations to account for these observations. First, the most massive galaxies present higher specific star formation rates when compared to the global VVDS sample which could explain the particularly low metallicity of these galaxies as already shown in the SDSS sample. Second, inflow of metal-poor gas due to tidal interactions could also explain the low metallicity of these galaxies as two of these three galaxies show clear signatures of merging in their velocity fields. Finally, we find that the metallicity of 4 galaxies is lower by ~0.2 to 0.4 dex if we take into account the N/O abundance ratio in their metallicity estimate.

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arXiv2009

The zCOSMOS survey: the role of the environment in the evolution of the luminosity function of different galaxy types

(Abridged) We studied the evolution in the B band luminosity function to z~1 in the zCOSMOS 10k sample, for which both accurate galaxy classifications and a detailed description of the local density field are available. The global LF exhibits a brightening of ~0.7 mag in M* from z~0.2 to z~0.9. At low z, late types dominate at faint magnitudes, while the bright end is populated mainly by early types. At higher z, late-type galaxies evolve significantly and, at z~1, the contribution from the various types to the bright end of the LF is comparable. The evolution for early types is in both luminosity and normalization. A similar behaviour is exhibited by late types, but with an opposite trend for the normalization. Studying the role of the environment, we find that the global LF of galaxies in overdense regions has always a brighter M* and a flatter slope. In low density environments, the main contribution to the LF is from blue galaxies, while for high density environments there is an important contribution from red galaxies to the bright end. The differences between the global LF in the two environments are not due to only a difference in the relative numbers of red and blue galaxies, but also to their relative luminosity distributions: the value of M* for both types in underdense regions is always fainter than in overdense environments. The "specular" evolution of late- and early-type galaxies is consistent with a scenario where a part of blue galaxies is transformed in red galaxies with increasing cosmic time, without significant changes in the fraction of intermediate-type galaxies. The bulk of this tranformation in overdense regions probably happened before z~1, while it is still ongoing at lower z in underdense environments.

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arXiv2009

The zCOSMOS Redshift Survey: How group environment alters global downsizing trends

We took advantage of the wealth of information provided by the first ~10000 galaxies of the zCOSMOS-bright survey and its group catalogue to study the complex interplay between group environment and galaxy properties. The classical indicator F_blue (fraction of blue galaxies) proved to be a simple but powerful diagnostic tool. We studied its variation for different luminosity and mass selected galaxy samples. Using rest-frame B-band selected samples, the groups galaxy population exhibits significant blueing as redshift increases, but maintains a lower F_blue with respect both to the global and the isolated galaxy population. However moving to mass selected samples it becomes apparent that such differences are largely due to the biased view imposed by the B-band luminosity selection, being driven by the population of lower mass, bright blue galaxies for which we miss the redder, equally low mass, counterparts. By focusing the analysis on narrow mass bins such that mass segregation becomes negligible we find that only for the lowest mass bin explored (logMass <= 10.6) does a significant residual difference in color remain as a function of environment, while this difference becomes negligible toward higher masses. Our results indicate that red galaxies of logMass >= 10.8 are already in place at z ~ 1 and do not exhibit any strong environmental dependence, possibly originating from so-called 'nature'/internal mechanisms. In contrast, for lower galaxy masses and redshifts lower than z ~ 1, we observe the emergence in groups of a population of 'nurture' red galaxies: slightly deviating from the trend of the downsizing scenario followed by the global galaxy population, and more so with cosmic time. These galaxies exhibit signatures of group-related secular physical mechanisms directly influencing galaxy evolution.

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arXiv2009

The Vimos VLT Deep Survey: Stellar mass segregation and large-scale galaxy environment in the redshift range 0.2<z<1.4

Hierarchical models of galaxy formation predict that the properties of a dark matter halo depend on the large-scale environment surrounding the halo. As a result of this correlation, we expect massive haloes to be present in larger number in overdense regions than in underdense ones. Given that a correlation exists between a galaxy stellar mass and the hosting dark matter halo mass, the segregation in dark matter halo mass should then result in a segregation in the distribution of stellar mass in the galaxy population. In this work we study the distribution of galaxy stellar mass and rest-frame optical color as a function of the large-scale galaxy distribution using the VLT VIMOS Deep Survey sample, in order to verify the presence of segregation in the properties of the galaxy population. We use the VVDS redshift measurements and multi-band photometric data to derive estimates of the stellar mass, rest-frame optical color, and of the large-scale galaxy density, on a scale of approximately 8 Mpc, for a sample of 5619 galaxies in the redshift range 0.2 0.7. However, when we consider only galaxies in narrow bins of stellar mass, in order to exclude the effects of the stellar mass segregation on the galaxy properties, we do not observe any more any significant color segregation.

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arXiv2009

The VIMOS VLT Deep Survey :Evolution of the major merger rate since z~1 from spectroscopicaly confirmed galaxy pairs

From the VIMOS VLT Deep Survey we use a sample of 6447 galaxies with I_{AB} < 24 to identify 251 pairs of galaxies, each member with a secure spectroscopic redshift, which are close in both projected separation and in velocity. We find that at z ~ 0.9, 10.9 +/- 3.2 % of galaxies with M_B(z) < -18-Qz are in pairs with separations dr < 20 kpc/h, dv < 500 km/s, and with dM_B < 1.5, significantly larger than 3.76 +/- 1.71 % at z ~ 0.5; we find that the pair fraction evolves as (1+z)^m with m = 2.49 +/- 0.56. For brighter galaxies with M_B(z=0) < -18.77, the pair fraction is higher and its evolution with redshift is somewhat flatter with m=1.88 \pm 0.40, a property also observed for galaxies with increasing stellar masses. Early type, dry mergers, pairs increase their relative fraction from 3 % at z ~ 0.9 to 12 % at z ~ 0.5. We find that the merger rate evolves as N_{mg}=(9.05 +/- 3.76) * 10^{-4}) * (1+z)^{2.43 +/- 0.76}. We find that the merger rate of galaxies with M_B(z) < -18-Qz has significantly evolved since z ~ 1. The merger rate is increasing more rapidly with redshift for galaxies with decreasing luminosities, indicating that the flat evolution found for bright samples is not universal. The merger rate is also strongly dependent on the spectral type of galaxies involved, late type mergers being more frequent in the past, while early type mergers are more frequent today, contributing to the rise in the local density of early type galaxies. About 20 % of the stellar mass in present day galaxies with log(M/M_{sun}) > 9.5 has been accreted through major merging events since z ~ 1, indicating that major mergers have contributed significantly to the growth in stellar mass density of bright galaxies over the last half of the life of the Universe.

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arXiv2009

Star Formation in HII Galaxies. Properties of the ionized gas

We propose a methodology to perform a self-consistent analysis of the physical properties of the emitting gas of HII galaxies adequate to the data that can be obtained with the XXI century technology. This methodology requires the production and calibration of empirical relations between the different line temperatures that should superseed currently used ones based on very simple, and poorly tested, photo-ionization model sequences. Then, these observations are analysed applying a methodology designed to obtain accurate elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the ionsied gas. Four electron temperatures and one electron density are derived from the observed forbidden line ratios using the five-level atom approximation. For our best objects errors of 1% in T([OIII]), 3% in T([OII]) and 5% in T([SIII]) are achieved with a resulting accuracy between 5 and 9% in total oxygen abundances, O/H. These accuracies are expected to improve as better calibrations based on more precise measurements, both on electron temperatures and densities, are produced.

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arXiv2008

Testing gravity on large scales. The skewness of the galaxy distribution at z~1

We study the evolution of the low-order moments of the galaxy overdensity distribution over the redshift interval 0.7<z<1.5. We find that the variance and the normalized skewness evolve over this redshift interval in a way that is remarkably consistent with predictions of first- and second-order perturbation theory. This finding confirms the standard gravitational instability paradigm over nearly 9 Gyrs of cosmic time and demonstrates the importance of accounting for the non-linear component of galaxy biasing to avoid disagreement between theory and observations.

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arXiv2008

Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey. II. Extending the mass-metallicity relation to the range z=0.89-1.24

Aims. We present a continuation of our study about the relation between stellar mass and gas-phase metallicity in the VIMOS VLT Deep Survey (VVDS). In this work we extend the determination of metallicities up to redshift = 1.24 for a sample of 42 star-forming galaxies with a mean redshift value of 0.99. Methods. For a selected sample of emission-line galaxies, we use both diagnostic diagrams and empirical calibrations based on [OII] emission lines along with the empirical relation between the intensities of the [OIII] and [NeIII] emission lines and the theoretical ratios between Balmer recombination emission lines to identify star-forming galaxies and to derive their metallicities. We derive stellar masses by fitting the whole spectral energy distribution with a set of stellar population synthesis models. Results. These new methods allow us to extend the mass-metallicity relation to higher redshift. We show that the metallicity determinations are consistent with more established strong-line methods. Taken together this allows us to study the evolution of the mass-metallicity relation up to z = 1.24 with good control of systematic uncertainties. We find an evolution with redshift of the average metallicity of galaxies very similar to those reported in the literature: for a given stellar mass, galaxies at z = 1 have, on average, a metallicity = 0.3 dex lower than galaxies in the local universe. However we do not see any significant metallicity evolution between redshifts z = 0.7 (Paper I) and z = 1.0 (this paper). We find also the same flattening of the mass-metallicity relation for the most massive galaxies as reported in Paper I at lower redshifts, but again no apparent evolution of the slope is seen between z = 0.7 and z = 1.0.

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arXiv2008

The VVDS-VLA Deep Field - IV: Radio-optical properties

(abridged) We use the 1.4 GHz VIMOS-VLA Deep Survey and the optical VVDS and the CFHT-LS to compare the properties of radio loud galaxies with respect to the whole population of optical galaxies. The availability of multiband photometry and high quality photometric redshifts allows to derive rest frame colors and radio luminosity functions down to a limit of a B rest-frame magnitude of M=-20. Galaxy properties and luminosity functions (LFs) are estimated up to z~1 for radio loud and radio quiet early and late type galaxies. Radio loud late type galaxies are redder than radio quiet objects of the same class and this is an effect related to the presence of more dust in stronger star forming galaxies. Moreover, we estimate optical LFs, stellar masses and star formation rate distributions for radio sources and compare them with those derived for a well defined control sample, finding that the probability for a galaxy to be a radio emitter significantly increases at high values of these parameters. Radio loud early type galaxies show luminosity evolution of their bivariate radio-optical LF, due to an evolution in the radio-optical ratio. The lack of evolution of the mass function of radio loud early type galaxies means that no new AGN are formed at z<1. On the contrary, radio loud late type objects show a strong evolution, both in luminosity and in density, of the radio LF for z>0.7. This evolution is the direct effect of the strong optical evolution of this class and no significant change with redshift of the radio-optical ratio is required. With the knowledge of the radio-optical ratio and the optical and radio LFs for late type galaxies, we estimated the star formation history of the Universe up to z~1.5, using optical galaxies as tracers of the global radio emission.

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arXiv2008

The close environment of 24 micron galaxies at 0.6<z<1.0 in the COSMOS field

We investigate the close environment of 203 Spitzer 24 micron-selected sources at 0.6 1.4. We find that LIRGs at 0.6 1.4 within 1 Mpc and +/- 500 km/s). The contrast between the activities of the close environments of LIRGs and ULIRGs appears especially enhanced in the COSMOS field density peak at z~0.67, because LIRGs on this peak have a larger fraction of passive neighbours, while ULIRGs have as active close environments as those outside the large-scale structure. The differential environmental activity is related to the differences in the distributions of stellar mass ratios between LIRGs/ULIRGs and their close neighbours, as well as in the general local density fields. At 0.8<z<1.0, instead, we find no differences in the environment densities of ULIRGs and other similarly massive galaxies, in spite of the differential activities. We discuss a possible scenario to explain these findings.

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arXiv2008

COSMOS Photometric Redshifts with 30-bands for 2-deg2

We present accurate photometric redshifts in the 2-deg2 COSMOS field. The redshifts are computed with 30 broad, intermediate, and narrow bands covering the UV (GALEX), Visible-NIR (Subaru, CFHT, UKIRT and NOAO) and mid-IR (Spitzer/IRAC). A chi2 template-fitting method (Le Phare) was used and calibrated with large spectroscopic samples from VLT-VIMOS and Keck-DEIMOS. We develop and implement a new method which accounts for the contributions from emission lines (OII, Hbeta, Halpha and Ly) to the spectral energy distributions (SEDs). The treatment of emission lines improves the photo-z accuracy by a factor of 2.5. Comparison of the derived photo-z with 4148 spectroscopic redshifts (i.e. Delta z = zs - zp) indicates a dispersion of sigma_{Delta z/(1+zs)}=0.007 at i<22.5, a factor of 2-6 times more accurate than earlier photo-z in the COSMOS, CFHTLS and COMBO-17 survey fields. At fainter magnitudes i<24 and z<1.25, the accuracy is sigma_{Delta z/(1+zs)}=0.012. The deep NIR and IRAC coverage enables the photo-z to be extended to z~2 albeit with a lower accuracy (sigma_{Delta z/(1+zs)}=0.06 at i~24). The redshift distribution of large magnitude-selected samples is derived and the median redshift is found to range from z=0.66 at 22<i<22.5 to z=1.06 at 24.5<i<25. At i<26.0, the multi-wavelength COSMOS catalog includes approximately 607,617 objects. The COSMOS-30 photo-z enable the full exploitation of this survey for studies of galaxy and large scale structure evolution at high redshift.

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arXiv2008

A test of the nature of cosmic acceleration using galaxy redshift distortions

Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion the physical cause of which is a mystery. Formally, this requires the inclusion of a term acting as a negative pressure in the equations of cosmic expansion, accounting for about 75 per cent of the total energy density in the Universe. The simplest option for this "dark energy" corresponds to a cosmological constant, perhaps related to the quantum vacuum energy. Physically viable alternatives invoke either the presence of a scalar field with an evolving equation of state, or extensions of general relativity involving higher-order curvature terms or extra dimensions. Although they produce similar expansion rates, different models predict measurable differences in the growth rate of large-scale structure with cosmic time. A fingerprint of this growth is provided by coherent galaxy motions, which introduce a radial anisotropy in the clustering pattern reconstructed by galaxy redshift surveys. Here we report a measurement of this effect at a redshift of 0.8. Using a new survey of more than 10,000 faint galaxies, we measure the anisotropy parameter b = 0.70 +/- 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 +/- 0.36. This is consistent with the standard cosmological-constant model with low matter density and flat geometry, although the error bars are still too large to distinguish among alternative origins for the accelerated expansion. This could be achieved with a further factor-of-ten increase in the sampled volume at similar redshift.

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