arXiv subjects

N. Menci

Publications and source records attributed to N. Menci.

At least 109 records · Page 6Linked to original sources

arXiv2002

The K20 survey. IV. The redshift distribution of Ks<20 galaxies: a test of galaxy formation models

We present the redshift distribution of a complete sample of 480 galaxies with Ks<20 distributed over two independent fields covering a total area of 52 arcmin^2. The redshift completeness is 87% and 98% respectively with spectroscopic and high-quality and tested photometric redshifts. The redshift distribution of field galaxies has a median redshift z_{med}\sim 0.80, with \sim 32% and \sim 9% of galaxies at z>1 and z>1.5 respectively. A ``blind'' comparison is made with the predictions of a set of the most recent LambdaCDM hierarchical merging and pure luminosity evolution (PLE) models. The hierarchical merging models overpredict and underpredict the number of galaxies at low-z and high-z respectively, whereas the PLE models match the median redshift and the low-z distribution, still being able to follow the high-z tail of N(z). We briefly discuss the implications of this comparison and the possible origins of the observed discrepancies. We make the redshift distribution publicly available.

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arXiv2002

The K20 survey. III. Photometric and spectroscopic properties of the sample

The K20 survey is an ESO VLT optical and near-infrared spectroscopic survey aimed at obtaining spectral information and redshifts of a complete sample of about 550 objects to K_s\leq20.0 over two independent fields with a total area of 52 arcmin^2. In this paper we discuss the scientific motivation of such a survey, we describe the photometric and spectroscopic properties of the sample, and we release the $K_s$-band photometric catalog. Extensive simulations showed that the sample is photometrically highly complete to K_s=20. The observed galaxy counts and the R-K_s color distribution are consistent with literature results. We observed spectroscopically 94% of the sample, reaching a spectroscopic redshift identification completeness of 92% to K_s\leq20.0 for the observed targets, and of 87% for the whole sample (i.e. counting also the unobserved targets). Deep spectroscopy was complemented with multi-band deep imaging in order to derive tested and reliable photometric redshifts for the galaxies lacking spectroscopic redshifts. The results show a very good agreement between the spectroscopic and the photometric redshifts with =0.01 and with a dispersion of σ_{Δz}=0.09. Using both the spectroscopic and the photometric redshifts, we reached an overall redshift completeness of about 98%. The size of the sample, the redshift completeness, the availability of high quality photometric redshifts and multicolor spectral energy distributions make the K20 survey database one of the most complete samples available to date for constraining the currently competing scenarios of galaxy formation and for a variety of other galaxy evolution studies.

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arXiv2002

The effect of non--gravitational gas heating in groups and clusters of galaxies

We present a set of gas-dynamical simulations of galaxy groups and clusters aimed at exploring the effect of non-gravitational heating. We use GASOLINE, a parallel Tree+SPH code, to simulate the formation of four cosmic halos with temperature 0.5<T<8 keV. Non-gravitational heating is implemented in two different ways: (1) by imposing a minimum entropy floor at a given redshift, 1<z<5; (2) by gradually heating gas, proportionally to the SN rate expected from semi-analytical modeling of galaxy formation. Our main results are the following. (a) An extra heating energy of about 1 keV per gas particle is required to reproduce the observed Lx-T relation, independent of whether it is provided so as to create an entropy floor of 50-100 keV cm^2, or is modulated in redshift; our SN feedback recipe provides only 1/3 keV/part. (b) The M-T relation is almost unaffected by non-gravitational heating and follows the M T^{3/2} scaling, with a normalization ~40% higher than observed, independent of the heating scheme. The inclusion of cooling in a run of a small group has the effects of increasing T_ew by ~30%, possibly reconciling simulated and observed M-T relations, and of decreasing Lx by ~40%. In spite of the inclusion of SN feedback energy, almost 40% of the gas becomes cold, in excess of current observational estimates. (abridged)

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arXiv2002

Binary Aggregations in Hierarchical Galaxy Formation: The Evolution of the Galaxy Luminosity Function

We develop a semi-analytic model of hierarchical galaxy formation with an improved treatment of the evolution of galaxies inside dark matter haloes. We take into account not only dynamical friction processes building up the central dominant galaxy, but also binary aggregations of satellite galaxies inside a common halo described using the kinetic Smoluchowski equation. The description of gas cooling, star formation and evolution, and Supernova feedback follows the standard prescriptions widely used in semi-analytic modelling. We find that binary aggregations are effective in depleting the number of small/intermediate mass galaxies over the redshift range 1 -16. We compare our predicted luminosity functions with those obtained from deep multicolor surveys in the rest-frame B and UV bands for the redshift ranges 0 1 and even more at z ~ 3 by the effect of binary aggregations. The predictions from our dynamical model are discussed and compared with the effects of complementary processes which may conspire in affecting the shape of the luminosity function.

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arXiv2002

The K20 survey. II. The Different Spatial Clustering of z~1 Old and Dusty Star-Forming EROs

We compare the 3D clustering of old passively-evolving and dusty star-forming z~1 EROs from the K20 survey. With detailed simulations of clustering, the comoving correlation length of dusty star-forming EROs is constrained to be less than r_0~2.5 Mpc/h. In contrast, the old EROs are much more positively correlated, with 5.5<~r_0/(Mpc/h)<~16, consistent with previous claims for z~1 field early-type galaxies based on analyses of ERO angular clustering. The low level of clustering of dusty star-forming EROs does not support these to be major mergers building up an elliptical galaxy, or typical counterparts of SCUBA sources, but it is instead consistent with the weak clustering of high redshift blue galaxies and of luminous local IRAS galaxies. Current hierarchical merging models can explain the large r_0 for z~1 field early-type galaxies, but fail in matching their high number density and overall old ages.

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arXiv2001

The K20 survey. I. Disentangling old and dusty star-forming galaxies in the ERO population

We present the results of VLT optical spectroscopy of a complete sample of 78 EROs with R-Ks\geq5 over a field of 52 arcmin^2. About 70% of the 45 EROs with Ks\leq19.2 have been spectroscopically identified with old passively evolving and dusty star-forming galaxies at 0.7<z<1.5. The two classes are about equally populated and for each of them we present and discuss the average spectrum. From the old ERO average spectrum and for Z=Z_{\odot} we derive a minimum age of \sim 3 Gyr, corresponding to a formation redshift of z_f \gtsima 2.4. PLE models with such formation redshifts well reproduce the density of old EROs (consistent with being passively evolving ellipticals), whereas the predictions of the current hierarchical merging models are lower than the observed densities by large factors (up to an order of magnitude). From the average spectrum of the star-forming EROs we estimate a substantial dust extinction with E(B-V) \gtsima 0.5. The star formation rates, corrected for the average reddening, suggest a significant contribution from EROs to the cosmic star-formation density at z \sim 1.

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arXiv2001

An Eulerian Perturbation Approach to Large Scale Structures: Extending the Adhesion Approximation

A description of the dynamics of a collisionless, self-gravitating fluid is developed and applied to follow the development of Large Scale Structures in the Universe. Such description takes on one of the assumptions of the Adhesion Approximation (AA) model, i.e., the introduction of an artificial viscosity $ν$ in the Euler equation, but extends it to deeper non-linear stages, where the extrapolation of the linear relation $ψ=-ϕ$ between the velocity and the gravitational potentials -- at the basis of both the Zel'dovich and the Adhesion models -- is no longer valid. This is achieved by expanding the relation bewteen the gravitational potential $ϕ$ and the velocity potential $ψ$, in powers of the small viscosity $ν$. When the results are compared to the outcomes of an N-body simulation, the proposed extension of the Adhesion approach provides a better description of small-scale, deeply non-linear regions, as it is quantitatively shown by the computation of some statistical indicators. At larger scales, the satisfactory description of the large scale texture and of the voids given by the canonical Adhesion Approximation is preserved in the extended model.

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arXiv2001

Pre-heating the ICM in high resolution simulations: the effect on the gas entropy

We present results from high-resolution Tree+SPH simulations of galaxy clusters and groups, aimed at studying the effect of non-gravitational heating on the entropy of the ICM. We simulate three systems, having emission-weighted temperature T=0.6,1 and 3 keV, with spatial resolution better than 1% of the virial radius. We consider the effect of different prescriptions for non-gravitational ICM heating, such as SN energy feedback, as predicted by semi-analytical models of galaxy formation, and two different minimum entropy floors, S_fl=50 and 100 keV cm^2, imposed at z=3. Simulations with only gravitational heating nicely reproduce predictions from self-similar ICM models, while extra heating is shown to break the self-similarity, by a degree which depends on total injected energy and on cluster mass. We use observational results on the excess entropy in central regions of galaxy systems, to constrain the amount of extra-heating required. We find that setting the entropy floor S_fl=50 keV cm^2, which corresponds to an extra heating energy of about 1 keV per particle, is able to reproduce the observed excess of ICM entropy.

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arXiv2001

The SZ Effect as a Probe of Non-Gravitational Entropy in Groups and Clusters of Galaxies

We investigate how strongly and at what scales the Sunyaev- Zel'dovich effect reflects the shifting balance between the two processes that compete for governing the density and the thermodynamic state of the hot intra-cluster medium pervading clusters and groups of galaxies: the hierarchical clustering of the DM; the non-gravitational energy and momentum fed back into the ICM by the condensing baryons. We base on a SAM of galaxy formation and clustering to describe how the baryons are partitioned among the hot, the cool and the stellar phase; the partition shifts as the galaxies cluster hierarchically, and as the feedback by stellar winds and SN explosions follows the star formation. Their impact is amplified by the same large scale accretion shocks that thermalize the gravitational energy of gas falling into the growing potential wells. We compute the Compton parameter $y$, and find a relation of $y$ with the ICM temperature, the $y-T$ relation, which departs from the self-similar scaling and bends down at temperatures typical of galaxy groups. We model-independently relate this with the analogous behaviour of the L_x - T relation, and discuss to what extent our results are generic of the hierarchical models of galaxy formation and clustering.

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arXiv2001

The Evolution of the Luminosity Function in Deep Fields: A Comparison with CDM Models

The galaxy Luminosity Function (LF) has been estimated in the rest frame B luminosity at 0<z<1.25 and at 1700 Å for 2.5<z<4.5 from deep multicolor surveys in the HDF-N, HDF-S, NTT-DF. The results have been compared with a recent version of galaxy formation models in the framework of hierarchical clustering in a flat Cold Dark Matter Universe with cosmological constant. The results show a general agreement for z<= 1, although the model LF has a steeper average slope at the faint end; at z~3 such feature results in an overprediction of the number of faint (I_{AB}~ 27) galaxies, while the agreement at the bright end becomes critically sensitive to the details of dust absorption at such redshifts. The discrepancies at the faint end show that a refined treatement of the physical processes involving smaller galaxies is to be pursued in the models, in terms of aggregation processes and/or stellar feedback heavily affecting the luminosity of the low luminosity objects. The implications of our results on the evolution of the cosmological star formation rate are discussed.

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arXiv2000

Comparing the Evolution of the Galaxy Disk Sizes with CDM Models: The Hubble Deep Field

The intrinsic sizes of the field galaxies with I<26 in the Hubble and ESO-NTT Deep Fields are shown as a function of their redshifts and absolute magnitudes using photometric redshifts derived from the multicolor catalogs and are compared with the CDM predictions. Extending to lower luminosities and to higher z our previous analysis performed on the NTT field alone, we find that the distribution of the galaxy disk sizes at different cosmic epochs is within the range predicted by typical CDM models. However, the observed size distribution of faint (M_B>-19) galaxies is skewed with respect to the CDM predictions and an excess of small-size disks (R_d<2 kpc) is already present at z~ 0.5. The excess persists up to z~3 and involves brighter galaxies . Such an excess may be reduced if luminosity-dependent effects, like starburst activity in interacting galaxies, are included in the physical mechanisms governing the star formation history in CDM models.

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arXiv1999

X-raying the Star Formation History of the Universe

The current models of early star and galaxy formation are based upon the hierarchical growth of dark matter halos, within which the baryons condense into stars after cooling down from a hot diffuse phase. The latter is replenished by infall of outer gas into the halo potential wells; this includes a fraction previously expelled and preheated, due to momentum and energy fed back by the SNe which follow the star formation. We identify such an implied hot phase with the medium known to radiate powerful X-rays in clusters and in groups of galaxies. We show that the amount of the hot component required by the current star formation models is enough to be observable out to redshifts $z \approx 1.5$ in forthcoming deep surveys from {\it Chandra} and {\it XMM}, especially in case the star formation rate is high at such and earlier $z$. These X-ray emissions constitute a necessary counterpart, and will provide a much wanted probe of the SF process itself (in particular, of the SN feedback), to parallel and complement the currently debated data from optical and IR observations of the young stars.

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arXiv1999

High redshift evolution of optically and IR-selected galaxies: a comparison with CDM scenarios

A combination of ground-based (NTT and VLT) and HST (HDF-N and HDF-S) public imaging surveys have been used to collect a sample of 1712 I-selected and 319 $K\leq 21$ galaxies. Photometric redshifts have been obtained for all these galaxies. The results have been compared with the prediction of an analytic rendition of the current CDM hierarchical models for galaxy formation. We focus in particular on two observed quantities: the galaxy redshift distribution at K<21 and the evolution of the UV luminosity density. The derived photometric redshift distribution is in agreement with the hierarchical CDM prediction, with a fraction of only 5% of galaxies detected at z>2. This result strongly supports hierarchical scenarios where present-day massive galaxies are the result of merging processes. The observed UV luminosity density in the I-selected sample is confined within a factor of 4 over the whole range 0 3. CDM models in $Λ$-dominated universe are in better agreement at 3<z<4.5, but predict a pronounced peak at z~1.5 and a drop by a factor of 8 from z=1.5 to z=4 that is not observed in the data. We conclude that improvements are required in the treatment of the physical processes directly related to the SFR, e.g. the starbust activity in merger processes and/or different feedback to the star formation activity.

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arXiv1999

The Evolution of the Galaxy Sizes in the NTT Deep Field: a Comparison with CDM Models

The sizes of the field galaxies with I<25 have been measured in the NTT Deep Field. Intrinsic sizes have been obtained after deconvolution of the PSF with a multigaussian method. The reliability of the method has been tested using both simulated data and HST observations of the same field. The distribution of the half light radii is peaked at r_{hl} 0.3 arcsec, in good agreement with that derived from HST images at the same magnitude. An approximate morphological classification has been obtained using the asymmetry and concentration parameters. The intrinsic sizes of the galaxies are shown as a function of their redshifts and absolute magnitudes using photometric redshifts derived from the multicolor catalog. While the brighter galaxies with morphological parameters typical of the normal spirals show a flat distribution in the range r_{d}=1-6 kpc, the fainter population at 0.4<z<0.8 dominates at small sizes. To explore the significance of this behaviour, an analytical rendition of the standard CDM model for the disc size evolution has been computed. The model showing the best fit to the local luminosity function and the Tully-Fisher relation is able to reproduce at intermediate redshifts a size distribution in general agreement with the observations, although it tends to underestimate the number of galaxies fainter than M_B~ -19 with disk sizes r_d~ 1-2 kpc.

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arXiv1999

The History of Cosmic Baryons: X-ray Emission vs. Star Formation Rate

We relate the star formation from cold baryons in virialized structures to the X-ray properties of the associated diffuse, hot baryonic component. Our computations use the standard ``semi-analytic'' models to describe i) the evolution of dark matter halos through merging after the hierarchical clustering, ii) the star formation governed by radiative cooling and by supernova feedback, iii) the hydro- and thermodynamics of the hot gas, rendered with our Punctuated Equilibria model. So we relate the X-ray observables concerning the intra-cluster medium to the thermal energy of the gas pre-heated and expelled by supernovae following star formation, and then accreted during the subsequent merging events. We show that at fluxes fainter than $F_X\approx 10^{-15}$ erg/cm$^2 $ s (well within the reach of next generation X-ray observatories) the X-ray counts of extended extragalactic sources (as well as the faint end of the luminosity function, the contribution to the soft X-ray background, and the $L_X-T$ correlation at the group scales) increase considerably when the star formation rate is enhanced for z>1 as indicated by growing optical/infrared evidence. Specifically, the counts in the range 0.5-2 keV are increased by factors $\sim 4$ when the the feedback is decreased and star formation is enhanced as to yield a flat shape of the star formation rate for 2<z<4.

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arXiv1999

X-raying the Cosmic Star Formation Rate

Using current semi-analytic models of structure and star formation based on hierarchical clustering, we connect the cosmic star formation rate (SFR) to the X-ray emission properties of groups and clusters of galaxies. We show that when the baryons cool down from a hot phase to condense into stars with a SFR flat for z>2, then such hot phase yields deep X-ray source counts (at fluxes F=10^{-15} erg/cm^2 s in the energy band 0.5-2 keV) about 5 times larger than in the case of a SFR peaked at z ~ 1.5. We also discuss the effect of the SFR on the shape and evolution of the X-ray L-T relation.

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arXiv1999

Hot Gas in Clusters of Galaxies: the Punctuated Equilibria Model

We develop a model to describe the evolution of the intra-cluster X-ray emitting baryons, as they are included in the dark matter potential wells of galaxy clusters evolving through subsequent merging events in the framework of hierarchical clustering. The gas is assumed to re-adjusts to a new hydrostatic equilibrium after each merging event. Before merging it is gravitationally heated at the local virial temperature when bound in subclusters; at early $z$ the gas is preheated by supernova activity following star formation. In detail, we compute analytically the following steps: the dynamic histories of dark matter halos with their merging events; the associated infall of gas into a halo, with compressions and shocks estabilishing the conditions at the cluster boundary; the updated disposition of the gas in the potential well matching such conditions; the statistical convolution of the key quantities over the merging histories. The model predicts the density and surface brightness profiles with no free parameters; the so-called $β$ parameter is itself an outcome of the model, and the polytropic index $γ$ is internally constrained to a narrow range. We obtain declining temperature profiles, and profiles for the density and for the surface brightness shallower in groups compared with clusters. Our model groups also contain a lower baryonic fraction on average, but with a scatter considerably larger than at cluster scales. Various statistics are obtained analytically upon averaging over the merging histories. In particular, we predict in different cosmologies the statistical correlation $L-T$ of luminosity with temperature; similarly we derivethe correlation $R_X-T$ for the size of the X-ray emitting region. The intrinsic scatter in both correlations is also predicted.

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arXiv1998

A Physical Model for Baryons in Clusters of Galaxies

The X-ray emission from clusters of galaxies is one of the best observational probe to investigate the distribution of dark matter at intermediate and high redshifts. Since the disposition of the intracluster plasma (ICP) responsible of the emission is crucial to link X-ray properties to the global properties of the dark matter halos, we propose a semi--analytical approach for the diffuse baryons. This comprises the following blocks: Monte Carlo merging histories to describe the dynamics of dark matter halos; the central hydrostatic disposition for the ICP; conditions of shock, or of closely adiabatic compression at the boundary with the external gas, preheated by stellar energy feedbacks. From our model we predict the $L-T$ correlation, consistent with the data as for shape and scatter.

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