arXiv subjects

P. Merluzzi

Publications and source records attributed to P. Merluzzi.

At least 37 records · Page 2Linked to original sources

arXiv2010

Galaxy evolution as a function of environment and luminosity

We present an analysis of star formation and nuclear activity of about 28000 galaxies in a volume-limited sample taken from SDSS DR4 low-redshift catalogue (LRC) taken from the New York University Value Added Galaxy Catalogue (NYU-VAGC) of Blanton et al. 2005, with 0.005 ~ L*) galaxies. Moreover the fraction of galaxies with the optical signatures of an active galactic nucleus (AGN) decreases steadily from ~50\% at Mr~-21 to ~0 per cent by Mr~-18 closely mirroring the luminosity dependence of the passive galaxy fraction in low-density environments (see fig. 1 continuous lines). This result reflects the increasing importance of AGN feedback with galaxy mass for their evolution, such that the star formation histories of massive galaxies are primarily determined by their past merger history.

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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

ACCESS: NIR Luminosity Function and Stellar Mass Function of Galaxies in the Shapley Supercluster Environment

We present the NIR luminosity (LF) and stellar mass functions (SMF) of galaxies in the core of the Shapley supercluster at z=0.048, based on new K-band observations in conjunction with B- and R-band photometry and a subsample of ~650 galaxies spectroscopically confirmed supercluster members, allowing to investigate the galaxies down to M_K^*+6 and M=10^8.75 M_sun. For the 3 deg^2 field the K-band LF is described by a Schechter function with M_K^*=-24.96+-0.10 and α=-1.42+-0.03. We investigate the effect of environment by deriving the LF in three regions selected according to the local galaxy density, and observe a significant increase in the faint-end slope going from the high- (α=-1.33) to the low-density (α=-1.49) environments. The SMF is fitted well by a Schechter function with log_10(M^*)=11.16+-0.04 and α=-1.20+-0.02. The SMF of supercluster galaxies is also characterised by an excess of massive galaxies that are associated to the cluster BCGs. While the value of M* depends on environment the slope of the galaxy SMF does not vary with the environment. By comparing our findings with cosmological simulations, we conclude that the environmental dependences of the LF are not primary due to variations in the merging histories, but to processes which are not treated in the semi-analytical models, such as tidal stripping or harassment. In field regions the SMF shows a sharp upturn below M=10^9 M_sun, close to our mass limit, suggesting that the upturns seen in our K-band LFs, but not in the SMF, are due to this dwarf population. The environmental variations seen in the faint-end of the K-band LF suggests that dwarf galaxies, which are easier to strip than their more massive counterparts, are affected by tidal/gas stripping upon entering the supercluster.

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arXiv2009

LoCuSS: The mid-infrared Butcher-Oemler effect

We study the mid-infrared (MIR) properties of galaxies in 30 massive galaxy clusters at 0.02 5x10^10L_sun) within r_200, finding a steady increase in the fraction with redshift from ~3% at z=0.02 to ~10% by z=0.30, and an rms cluster-to-cluster scatter about this trend of 0.03. The best-fit redshift evolution model is of the form f_SF ~ (1+z)^5.7, which is stronger redshift evolution than that of L*_IR in both clusters and the field. We find that, statistically, this excess is associated with galaxies found at large cluster-centric radii, implying that the MIR Butcher-Oemler effect can be explained by a combination of both the global decline in star-formation in the universe since z~1 and enhanced star formation in the infall regions of clusters at intermediate redshifts. This picture is supported by a simple infall model based on the Millennium Simulation semi-analytic galaxy catalogs, whereby star-formation in infalling galaxies is instantaneously quenched upon their first passage through the cluster, in that the observed radial trends of f_SF trace those inferred from the simulations. We also find that f_SF does not depend on simple indicators of the dynamical state of clusters, including the offset between the brightest cluster galaxy and the peak of the X-ray emission. This is consistent with the picture described above in that most new star-formation in clusters occurs in the infall regions, and is thus not sensitive to the details of cluster-cluster mergers in the core regions.

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arXiv2009

On the origin of the scatter around the Fundamental Plane: correlations with stellar population parameters

We present a fundamental plane (FP) analysis of 141 early-type galaxies in the Shapley supercluster at z=0.049 based on spectroscopy from the AAOmega spectrograph at the AAT and photometry from the WFI on the ESO/MPI 2.2m telescope. The key feature of the survey is its coverage of low-mass galaxies down to sigma_0~50km/s. We obtain a best-fitting FP relation log r_e=1.06 log sigma_0 - 0.82 log < I >_e + cst in the R band. The shallow exponent of sigma_0 is a result of the extension of our sample to low velocity dispersions. We investigate the origin of the intrinsic FP scatter, using estimates of age, metallicity and alpha/Fe. We find that the FP residuals anti-correlate (>3sigma) with the mean stellar age in agreement with previous work. However, a stronger (>4sigma) correlation with alpha/Fe is also found. These correlations indicate that galaxies with effective radii smaller than those predicted by the FP have stellar populations systematically older and with alpha over-abundances larger than average, for their sigma_0. Including alpha/Fe as a fourth parameter in the FP, the total scatter decreases from 0.088 dex to 0.075 dex and the estimated intrinsic scatter decreases from 0.068 dex to 0.049 dex. Thus, variations in alpha/Fe account for >> 30% of the total variance around the FP, and >> 50% of the estimated intrinsic variance. This result indicates that the distribution of galaxies around the FP are tightly related to the enrichment, and hence to the timescale of star-formation. Our results appear to be consistent with the merger hypothesis for the formation of ellipticals which predicts that a significant fraction of the scatter is due to variations in the importance of dissipation in forming merger remnants of a given mass.

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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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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

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

Eddington ratios of faint AGN at intermediate redshift: Evidence for a population of half-starved black holes

We use one of the deepest spectroscopic samples of broad line active galactic nuclei (AGN) currently available, extracted from the VIMOS VLT Deep Survey (VVDS), to compute MgII and CIV virial masses estimate of 120 super-massive black holes in the redshift range 1.0<z<1.9 and 2.6<z<4.3. We find that the mass-luminosity relation shows considerably enhanced dispersion towards low AGN luminosities (log L_bol ~ 45). At these luminosities, there is a substantial fraction of black holes accreting far below their Eddington limit (L_bol/L_Edd < 0.1), in marked contrast to what is generally found for AGN of higher luminosities. We speculate that these may be AGN on the decaying branch of their light-curves, well past their peak activity. This would agree with recent theoretical predictions of AGN evolution. In the electronic Appendix of this paper we publish an update of the VVDS type-1 AGN sample, including the first and most of the second epoch observations. This sample contains 298 objects of which 168 are new.

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arXiv2008

The SDSS-UKIDSS Fundamental Plane of Early-type Galaxies

We derive the Fundamental Plane (FP) relation for a sample of 1430 early-type galaxies in the optical (r band) and the near-infrared (K band), by combining SDSS and UKIDSS data. With such a large, homogeneous dataset, we are able to assess the dependence of the FP on the waveband. Our analysis indicates that the FP of luminous early-type galaxies is essentially waveband independent, with its coefficients increasing at most by 8% from the optical to the NIR. This finding fits well into a consistent picture where the tilt of the FP is not driven by stellar populations, but results from other effects, such as non-homology. In this framework, the optical and NIR FPs require more massive galaxies to be slightly more metal rich than less massive ones, and to have highly synchronized ages, with an age variation per decade in mass smaller than a few percent.

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arXiv2008

The VIMOS VLT Deep Survey: Tracing the galaxy stellar mass assembly history over the last 8Gyr

We selected a mass-limited sample of 4048 objects from the VIMOS VLT Deep Survey in the redshift interval 0.5<z<1.3. We used the amplitude of the 4000 Balmer break (Dn4000) to separate the galaxy population and the EW[OII]3727 line as proxy for the star formation activity. We discuss to what extent stellar mass drives galaxy evolution, showing for the first time the interplay between stellar ages and stellar masses over the past 8Gyr. Low-mass galaxies have small Dn4000 and at increasing stellar mass, the galaxy distribution moves to higher Dn4000 values as observed in the local Universe. As cosmic time goes by, we witness an increasing abundance of massive spectroscopically ET systems at the expense of the LT systems. This spectral transformation is a process started at early epochs and continuing efficiently down to the local Universe. This is confirmed by the evolution of our type-dependent stellar mass function. The underlying stellar ages of LT galaxies apparently do not show evolution, likely as a result of a continuous formation of new stars. All star formation activity indicators consistently point towards a star formation history peaked in the past for massive galaxies, with little or no residual star formation taking place in the most recent epochs. The activity and efficiency of forming stars are mechanisms that depend on stellar mass, and the mass assembly becomes progressively less efficient in massive systems as time elapses. The concepts of star formation downsizing and mass assembly downsizing describe a single scenario that has a top-down evolutionary pattern. The role of (dry) merging events seems to be only marginal at z<1.3, as our estimated efficiency in stellar mass assembly can possibly account for the progressive accumulation of passively evolving galaxies.

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arXiv2008

Global Properties of the Rich Cluster ABCG 209 at z~0.2. Spectroscopic and Photometric Catalogue

This paper is aimed at giving an overview of the global properties of the rich cluster of galaxies ABCG 209. This is achieved by complementing the already available data with new medium resolution spectroscopy and NIR photometry which allow us to i) analyse in detail the cluster dynamics, distinguishing among galaxies belonging to different substructures and deriving their individual velocity distributions, using a total sample of 148 galaxies in the cluster region, of which 134 belonging to the cluster; ii) derive the cluster NIR luminosity function; iii) study the Kormendy relation and the photometric plane of cluster early-type galaxies (ETGs). Finally we provide an extensive photometric (optical and NIR) and spectroscopic dataset for such a complex system to be used in further analyses investigating the nature, formation and evolution of rich clusters of galaxies. The observational scenario confirms that ABCG 209 is presently undergoing strong dynamical evolution with the merging of two or more subclumps. This interpretation is also supported by the detection of a radio halo (Giovannini et al. 2006) suggesting that there is a recent or ongoing merging. Cluster ETGs follow a Kormendy relation whose slope is consistent with previous studies both at optical and NIR wavelengths. We investigate the origin of the intrinsic scatter of the photometric plane due to trends of stellar populations, using line indices as indicators of age, metallicity and alpha/Fe enhancement. We find that the chemical evolution of galaxies could be responsible for the intrinsic dispersion of the Photometric Plane.

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arXiv2007

The VIMOS VLT Deep Survey. The Assembly History of the Stellar Mass in Galaxies: from the Young to the Old Universe

We present a detailed analysis of the Galaxy Stellar Mass Function of galaxies up to z=2.5 as obtained from the VVDS. We estimate the stellar mass from broad-band photometry using 2 different assumptions on the galaxy star formation history and show that the addition of secondary bursts to a continuous star formation history produces systematically higher (up to 40%) stellar masses. At low redshift (z=0.2) we find a substantial population of low-mass galaxies (<10^9 Msun) composed by faint blue galaxies (M_I-M_K=0.3). In general the stellar mass function evolves slowly up to z=0.9 and more significantly above this redshift. Conversely, a massive tail is present up to z=2.5 and have extremely red colours (M_I-M_K=0.7-0.8). We find a decline with redshift of the overall number density of galaxies for all masses (59+-5% for M>10^8 Msun at z=1), and a mild mass-dependent average evolution (`mass-downsizing'). In particular our data are consistent with mild/negligible (<30%) evolution up to z=0.7 for massive galaxies (>6x10^10 Msun). For less massive systems the no-evolution scenario is excluded. A large fraction (>=50%) of massive galaxies have been already assembled and converted most of their gas into stars at z=1, ruling out the `dry mergers' as the major mechanism of their assembly history below z=1. This fraction decreases to 33% at z=2. Low-mass systems have decreased continuously in number and mass density (by a factor up to 4) from the present age to z=2, consistently with a prolonged mass assembly also at z<1.

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arXiv2007

VVDS-SWIRE: Clustering evolution from a spectroscopic sample of galaxies with redshift 0.2<z<2.1 selected from Spitzer IRAC 3.6 micron and 4.5 micron photometry

By combining the VVDS with the SWIRE data, we have built the currently largest spectroscopic sample of galaxies selected in the rest-frame near-infrared. These allow us to investigate, for the first time using spectroscopic redshifts, the clustering evolution of galaxies selected from their rest-frame near-infrared luminosity in the redshift range 0.2<z<2.1. Therefore we use the projected two-point correlation function wp(rp) to study the three dimensional clustering properties of galaxies detected at 3.6 and 4.5 microns with IRAC and for which we have spectroscopic redshifts from first epoch VVDS. We find that in the flux limited samples at 3.6 and 4.5 microns, the clustering length does not change from redshift ~2 to the present. In addition, we find that the clustering lengths are systematically higher when galaxy samples are selected from increasingly redder wavelengths. These values are larger than the typical values found for I-band selected galaxies in the same redshift range, but we find that the difference in clustering length between I-band and 3.6/4.5 microns selected samples is decreasing with increasing redshift to become comparable at z~1.5. We interpret this as evidence that galaxies with older stellar populations and galaxies actively forming stars reside in comparably overdense environments at epochs earlier than z~1.5. The increasing difference in clustering length observed between rest-frame UV-optical and infrared selected samples could then be an indication that star formation is gradually shifting to lower density regions as cosmic time increases.

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arXiv2007

The SDSS-GALEX viewpoint of the truncated red sequence in field environments at z~0

We combine GALEX near-UV photometry with a volume-limited sample of local (0.005 2A. This contamination is greatest at faint magnitudes (Mr>-19) and in field regions where as many as three-quarters of red sequence galaxies are star-forming, and as such has important consequences for following the build-up of the red sequence. We find that the NUV-r colour instead allows a much more robust separation of passively-evolving and star-forming galaxies, which allows the build-up of the UV-selected red sequence with redshift and environment to be directly interpreted in terms of the assembly of stellar mass in passively-evolving galaxies. We find that in isolated field regions the number density of UV-optical red sequence galaxies declines rapidly at magnitudes fainter than Mr~-19 and appears completely truncated at Mr~-18. This confirms the findings of Haines et al. (2007) that no passively-evolving dwarf galaxies are found more than two virial radii from a massive halo, whether that be a group, cluster or massive galaxy. These results support the downsizing paradigm whereby the red sequence is assembled from the top down, being already largely in place at the bright end by z~1, and the faint end filled in at later epochs in clusters and groups through environment-related processes such as ram-pressure stripping or galaxy harassment.

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arXiv2007

The Different Physical Mechanisms that Drive the Star-Formation Histories of Giant and Dwarf Galaxies

We present an analysis of star-formation and nuclear activity in galaxies as a function of both luminosity and environment in the SDSS DR4 dataset. Using a sample of 27753 galaxies at 0.005 90% complete to Mr=-18.0 we find that the EW(Ha) distribution is strongly bimodal, allowing galaxies to be robustly separated into passive and star-forming populations about a value EW(Ha)=2A. In high-density regions ~70% of galaxies are passive independent of luminosity. In the rarefied field however, the fraction of passively-evolving galaxies is a strong function of luminosity, dropping from ~50% for Mr<-21 to zero by Mr~-18. Indeed for the lowest luminosity range covered (-18<Mr<-16) none of the ~600 galaxies in the lowest density quartile are passive. The few passively-evolving dwarf galaxies in field regions appear as satellites to bright (~L*) galaxies. The fraction of galaxies with optical AGN signatures decreases steadily from ~50% at Mr~-21 to ~0% by Mr~-18 closely mirroring the luminosity-dependence of the passive galaxy fraction in low-density environments. This result reflects the increasing importance of AGN feedback with galaxy mass for their evolution, such that the star-formation histories of massive galaxies are primarily determined by their past merger history. In contrast, the complete absence of passively-evolving dwarf galaxies more than ~2 virial radii from the nearest massive halo (i.e. cluster, group or massive galaxy) indicates that internal processes, such as merging, AGN feedback or gas consumption through star-formation, are not responsible for terminating star-formation in dwarf galaxies. Instead the evolution of dwarf galaxies is primarily driven by the mass of their host halo, probably through the combined effects of tidal forces and ram-pressure stripping.

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arXiv2007

The cosmic star formation rate evolution from z=5 to z=0 from the VIMOS VLT Deep Survey

We present the evolution of the comoving SFR density in the redshift range 0 < z < 5 using the first epoch data release of the VVDS, that is 11564 spectra selected at I_AB=24 over 2200 arcmin^2 in two fields of view, the VVDS-0226-04 and the VVDS-CDFS-0332-27, and the cosmological parameters (Omega_M, Omega_L, h)=(0.3, 0.7, 0.7). We study the multi-wavelength non dust-corrected luminosity densities at 0 < z < 2 from the rest-frame FUV to the optical passbands, and the rest-frame 1500A luminosity functions and densities at 2.7 < z < 5. They evolve from z=1.2 to 0.05 according to (1+z)^{x} with x = 2.05, 1.94, 1.92, 1.14, 0.73, 0.42, 0.30 in the FUV-1500, NUV-2800, U-3600, B-4400, V-5500, R-6500, and I-7900 passbands, respectively. From z = 1.2 to 0.2 the B-band density for the irregular-like galaxies decreases markedly by a factor 3.5 while it increases by a factor 1.7 for the elliptical-like galaxies. We identify several SFR periods; from z = 5 to 3.4 the FUV-band density increases by at most 0.5dex, from z=3.4 to 1.2 it decreases by 0.08dex, from z=1.2 to 0.05 it declines steadily by 0.6dex. For the most luminous M_AB(1500) < -21 galaxies the FUV-band density drops by 2dex from z = 3.9 to 1.2, and for the intermediate -21 < M_AB(1500) < -20 galaxies it drops by 2dex from z = 0.2 to 0. Comparing with dust corrected surveys, at 0.4 < z < 2 the FUV seems obscured by a constant factor of ~1.8-2 mag, while at z < 0.5 it seems progressively less obscured by up to ~0.9-1 mag when the dust-deficient early-type population is increasingly dominating the B-band density. The VVDS results agree with a downsizing picture where the most luminous sources cease to efficiently produce new stars 12 Gyrs ago (at z~4), while intermediate luminosity sources keep producing stars until 2.5 Gyrs ago (at z~0.2).(abridged)

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arXiv2007

The VVDS type-1 AGN sample: The faint end of the luminosity function

In a previous paper (Gavignaud et al. 2006), we presented the type-1 Active Galactic Nuclei (AGN) sample obtained from the first epoch data of the VIMOS-VLT Deep Survey (VVDS). The sample consists of 130 faint, broad-line AGN with redshift up to z=5 and 17.5< I <24.0, selected on the basis of their spectra. In this paper we present the measurement of the Optical Luminosity Function up to z=3.6 derived from this sample, we compare our results with previous results from brighter samples both at low and at high redshift. Our data, more than one magnitude fainter than previous optical surveys, allow us to constrain the faint part of the luminosity function up to high redshift. By combining our faint VVDS sample with the large sample of bright AGN extracted from the SDSS DR3 (Richards et al., 2006b) and testing a number of different evolutionary models, we find that the model which better represents the combined luminosity functions, over a wide range of redshift and luminosity, is a luminosity dependent density evolution (LDDE) model, similar to those derived from the major X-surveys. Such a parameterization allows the redshift of the AGN space density peak to change as a function of luminosity and explains the excess of faint AGN that we find at 1.0< z <1.5. On the basis of this model we find, for the first time from the analysis of optically selected samples, that the peak of the AGN space density shifts significantly towards lower redshift going to lower luminosity objects. This result, already found in a number of X-ray selected samples of AGN, is consistent with a scenario of "AGN cosmic downsizing", in which the density of more luminous AGN, possibly associated to more massive black holes, peaks earlier in the history of the Universe, than that of low luminosity ones.

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