arXiv subjects

B. Guiderdoni

Publications and source records attributed to B. Guiderdoni.

At least 37 records · Page 2Linked to original sources

arXiv2006

Modelling the Galaxy Bimodality: Shutdown Above a Critical Halo Mass

We reproduce the blue and red sequences in the observed joint distribution of colour and magnitude for galaxies at low and high redshifts using hybrid N-body/semi-analytic simulations of galaxy formation. The match of model and data is achieved by mimicking the effects of cold flows versus shock heating coupled to feedback from active galactic nuclei (AGNs), as predicted by Dekel & Birnboim (2006). After a critical epoch z=3, only haloes below a critical shock-heating mass 10^12MSun enjoy gas supply by cold flows and form stars, while cooling and star formation are shut down abruptly above this mass. The shock-heated gas is kept hot because being dilute it is vulnerable to feedback from energetic sources such as AGNs in their self-regulated mode. The shutdown explains in detail the bright-end truncation of the blue sequence at ~L*, the appearance of luminous red-and-dead galaxies on the red sequence starting already at z~2, the colour bimodality, its strong dependence on environment density and its correlations with morphology and other galaxy properties. Before z~2-3, even haloes above the shock-heating mass form stars by cold streams penetrating through the hot gas. This explains the bright star-forming galaxies at z~3-4, the early appearance of massive galaxies on the red sequence, the high cosmological star-formation rate at high redshifts and the subsequent low rate at low redshifts.

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arXiv2005

Active Galactic Nuclei In Cosmological Simulations - I. Formation of black holes and spheroids through mergers

The Active Galactic Nuclei In Cosmological Simulations (AGNICS) project includes AGN into the GalICS hybrid (N-body + semi-analytic) model to explore the quasar-galaxy link in a cosmological perspective. The key problems are the quasar fuelling mechanism, the origin of the BH to bulge mass relation, the causal and chronological link between BH growth and galaxy formation, the properties of quasar hosts and the role of AGN feedback in galaxy formation. This first paper has two goals: to describe the general structure and the assumptions of the method, and to apply AGNICS to studying the joint formation of BHs and spheroids in galaxy mergers. We investigate under what conditions this scenario can reproduce the local BH distribution and the evolution of the quasar population. AGNICS contains two star formation modes: a quiescent one in discs and a starburst one in protospheroids, the latter triggered by mergers and disc instabilities. We assume that BH growth is linked to the starburst mode. The simplest version of this scenario, in which the BH accretion rate and the star formation rate in the starburst component are simply related by a constant of proportionality, does not to reproduce the cosmic evolution of the quasar population. A model in which this relation is modulated by a scaling with the square root of the starburst gas density can explain the evolution of the quasar luminosity function in B-band and X-rays (accounting for the obscuration inferred from X-ray studies). The scatter and the tilt that this model introduces in the BH-to-bulge mass relation are within the observational constraints. The quasar contribution grows with bolometric luminosity and for a given bulge mass the most massive BHs are in the bulges with the oldest stars.

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arXiv2005

MoMaF : The Mock Map Facility

We present the Mock Map Facility, a powerful tool to generate mock catalogues or images from semi-analytically post-processed snapshots of cosmological N-body simulations. The paper describes in detail an efficient technique to create such mocks from the GALICS semi-analytic model, providing the reader with an accurate quantification of the artifacts it introduces at every step. We show that replication effects introduce a negative bias on the clustering signal -- typically peaking at less than 10 percent around the correlation length. We also thoroughly discuss how the clustering signal is affected by finite volume effects, and show that it vanishes at scales larger than about a tenth of the simulation box size. For the purpose of analysing our method, we show that number counts and redshift distributions obtained with GALICS and MOMAF compare well to K-band observations and to the 2dFGRS. Given finite volume effects, we also show that the model can reproduce the APM angular correlation function. The MOMAF results discussed here are made publicly available to the astronomical community through a public database. Moreover, a user-friendly Web interface (http://galics.iap.fr) allows any user to recover her/his own favourite galaxy samples through simple SQL queries. The flexibility of this tool should permit a variety of uses ranging from extensive comparisons between real observations and those predicted by hierarchical models of galaxy formation, to the preparation of observing strategies for deep surveys and tests of data processing pipelines.

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arXiv2005

GALICS -- VI. Modelling Hierarchical Galaxy Formation in Clusters

High-resolution N-body re-simulations of 15 massive (10^{14}-10^{15} Msun) dark matter haloes have been combined with the hybrid galaxy formation model GalICS (Hatton et al. 2003), to study the formation and evolution of galaxies in clusters, within the framework of the hierarchical merging scenario. New features in GalICS include a better description of galaxy positioning within dark matter haloes, a more reliable computation of the temperature of the inter-galactic medium as a function of redshift, and a description of the ram pressure stripping process. We focus on the luminosity functions, morphological fractions and colour distributions of galaxies in clusters and in cluster outskirts, at z=0. No systematic dependency on cluster richness is found either for the galaxy luminosity functions, morphological mixes, or colour distributions. Moving from higher density (cluster cores), to lower density environments (cluster outskirts), we detect a progressive flattening of the luminosity functions, an increase of the fraction of spirals and a decrease of that of ellipticals and S0s, and the progressive emergence of a bluer tail in the distributions of galaxy colours, especially for spirals. As compared to cluster spirals, early-type galaxies show a flatter luminosity function, and more homogeneous and redder colours. An overall good agreement is found between our results and the observations, particularly in terms of the cluster luminosity functions and morphological mixes. However, some discrepancies are also apparent, with too faint magnitudes of the brightest cluster members, especially in the B band, and galaxy colours tendentially too red (or not blue enough) in the model, with respect to the observations. Finally, ram pressure stripping appears to affect very little our results.

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arXiv2003

Comparison of two optical cluster finding algorithms for the new generation of deep galaxy surveys

We present a comparison between two optical cluster finding methods: a matched filter algorithm using galaxy angular coordinates and magnitudes, and a percolation algorithm using also redshift information. We test the algorithms on two mock catalogues. The first mock catalogue is built by adding clusters to a Poissonian background, while the other is derived from N-body simulations. Choosing the physically most sensible parameters for each method, we carry out a detailed comparison and investigate advantages and limits of each algorithm, showing the possible biases on final results. We show that, combining the two methods, we are able to detect a large part of the structures, thus pointing out the need to search for clusters in different ways in order to build complete and unbiased samples of clusters, to be used for statistical and cosmological studies. In addition, our results show the importance of testing cluster finding algorithms on different kinds of mock catalogues to have a complete assessment of their behaviour.

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arXiv2003

GALICS III: Predicted properties for Lyman Break Galaxies at redshift 3

This paper illustrates how mock observational samples of high-redshift galaxies with sophisticated selection criteria can be extracted from the predictions of GALICS, a hybrid model of hierarchical galaxy formation that couples the outputs of large cosmological simulations and semi-analytic recipes to describe dark matter collapse and the physics of baryons respectively. As an example of this method, we focus on the properties of Lyman Break Galaxies at redshift 3. With the MOMAF software package described in a companion paper, we generate a mock observational sample with selection criteria as similar as possible to those implied in the actual observations of z = 3 LBGs by Steidel et al.(1995). Our model predictions are in good agreement with the observed number density and 2D correlation function. We investigate the optical/IR luminosity budget as well as several other physical properties of LBGs and find them to be in general agreement with observed values. Looking into the future of these LBGs we predict that 75% of them end up as massive ellipticals today, even though only 35% of all our local ellipticals are predicted to have a LBG progenitor. In spite of some shortcomings, this new 'mock observation' method clearly represents a necessary first step toward a more accurate comparison between hierarchical models of galaxy formation and real observational surveys.

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arXiv2001

MIFS: A Mega Integral Field Spectrograph for the VLT

We describe MIFS, a second generation integral-field spectrograph for the VLT, operating in the visible wavelength range. It combines a 1'x1' field of view with the improved spatial resolution provided by multi-conjugate adaptive optics and covers a large simultaneous spectral range (0.6-1.0 microns). A separate mode exploits the highest spatial resolution provided by adaptive optics. With this unique combination of capabilities, MIFS has a wide domain of application and a large discovery potential. The MIFS low-spatial resolution mode (sampled at 0.2") combined with the initial MCAO capabilities planned for the VLT will provide ultra-deep fields with a limiting magnitude for spectroscopy of R~28. MIFS will improve the present day detection limit of Lyman alpha emitters by a factor of 100, and will detect low-mass star-forming galaxies to z~7. The MIFS high-spatial resolution mode (3"x3" field sampled at 0.01") is optimized for the next step in (MC)AO. It will probe, e.g., the relationship between supermassive central black holes and their host galaxy and the physics of winds from accretion disks in young stellar objects at unprecedented spatial resolution. MIFS will extend Europe's lead in integral-field spectroscopy. It capitalizes on new developments in adaptive optics, and is a key step towards instrumentation for OWL.

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arXiv2001

Star formation losses due to tidal debris in `hierarchical' galaxy formation

Bottom-up hierarchical formation of dark matter haloes is not as monotonic as implicitly assumed in the Press-Schechter formalism: matter can be ejected into tidal tails, shells or low density `atmospheres'. The implications that the possible truncation of star formation in these tidal `debris' may have for observational galaxy statistics are examined here using the ArFus N-body plus semi-analytical galaxy modelling software. Upper and lower bounds on stellar losses implied by a given set of N-body simulation output data can be investigated by choice of the merging/identity criterion of haloes between successive N-body simulation output times. A median merging/identity criterion is defined and used to deduce an upper estimate of possible star formation and stellar population losses. A largest successor merging/identity criterion is defined to deduce an estimate which minimises stellar losses. In the N-body simulations studied, the debris losses are short range in length and temporary; maximum loss is around 16%. The induced losses for star formation and luminosity functions are strongest (losses of 10%-30%) for low luminosity galaxies and at intermediate redshifts (1 < z < 3). This upper bound on likely losses is smaller than present observational uncertainties. Hence, Press-Schechter based galaxy formation models are approximately valid despite ignoring loss of debris, provided that dwarf galaxy statistics are not under study.

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arXiv2001

FIRBACK: III. Catalog, Source counts, and cosmological implications of the 170 micron ISO Deep survey

The FIRBACK (Far Infrared BACKground) survey is one of the deepest imaging surveys carried out at 170 microns with ISOPHOT onboard ISO, and is aimed at the study of the structure of the Cosmic Far Infrared Background. This paper provides the analysis of resolved sources. After a validated process of data reduction and calibration, we perform intensive simulations to optimize the source extraction, measure the confusion noise (sigma_c = 45 mJy), and give the photometric and astrometric accuracies. 196 galaxies with flux S > 3 sigma_c are detected in the area of 3.89 square degrees. Counts of sources with flux S > 4 sigma_c present a steep slope of 3.3 +/- 0.6 on a differential "logN-logS" plot between 180 and 500 mJy. As a consequence, the confusion level is high and will impact dramatically on future IR deep surveys. This strong evolution, compared with a slope of 2.5 from Euclidian geometry, is in line with models implying a strongly evolving Luminous Infrared Galaxy population. The resolved sources account for less than 10% of the Cosmic Infrared Background at 170 microns, which is expected to be resolved into sources in the 1 to 10 mJy range.

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arXiv2001

Simulating galaxy surveys with FIRST (PACS & SPIRE)

The next generation of submillimetre/millimetre instruments will provide us with a deeper insight into the mechanisms that rule galaxy formation. As the brightest starbursts are thought to be heavily obscured at optical wavelengths, the opening of this new window will complement the present observations, and enable a detailed investigation of the hierarchical merging of galaxies at remote epochs. In this context, we will present preliminary results of simulations currently developed for deep galaxy surveys with FIRST. N-body simulations of galaxy mergers are being developed to produce realistic morphologies and star formation histories. A Schmidt law is used to account for the evolution of the stellar and gas content of each particle. These simulations will be gathered in a library, including the temporal information with a timestep of 10 Myr. We then build consistent spectra accounting for this star formation history at each resolution element of the simulations. These morphologies will be included in the framework of the GalICS hybrid model of hierarchical galaxy formation, which reproduces the main observational constraints. We intend to present synthetic maps with the characteristics of the FIRST PACS/SPIRE instruments and discuss the optimal strategy for deep surveys complemented with the ground-based ALMA project.

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arXiv2001

Cosmological History of Stars and Metals

We study the evolution of stellar content and the chemical enrichment of the universe averaged over the whole population of galaxies by means of a series of chemo-spectrophotometric models that take into account the metallicity and dust obscuration effects. We investigate various classes of cosmic star formation rates (CSFR) histories consistent with current estimations. We are able to reproduce a variety of observational constraints such as the emissivities at rest-frame 0.44, 25, 60 and 100 $μ$m of the local universe and also the overall shape of the extragalactic background light from UV/NIR galaxy counts and the cosmic infrared background (CIB) from DIRBE/FIRAS measurements. We find that the CIB at 140 $μ$m is crucial for discriminating between the CSFR histories. The best-fit model to this constraint seems to favour mid-infrared derived CSFR at low-$z$ and a flat CSFR at higher $z$ consistent with the most recent estimations, although the shape of the CSFR at high redshifts has little impact on the FIR/submm part of extragalactic background. We suggest that the bulk of the CIB energy is produced by a population of moderately obscured normal galaxies lying at $0\le z \le 1$. We then derive the global chemical enrichment and stellar content of the universe and find that this model predicts metallicities in good agreement with the metallicity in DLAs given that some outflow of metal-enriched gas from galaxies is assumed, but it overproduces the current present-day stellar mass density and NIR luminosity density.

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arXiv2000

Galaxy Modelling - II. Multi-Wavelength Faint Counts from a Semi-Analytic Model of Galaxy Formation

(Abridged) This paper predicts self-consistent faint galaxy counts from the UV to the submm wavelength range. The STARDUST spectral energy distributions described in Devriendt et al. (1999) are embedded within the explicit cosmological framework of a simple semi-analytic model of galaxy formation and evolution. We build a class of models which capture the luminosity budget of the universe through faint galaxy counts and redshift distributions in the whole wavelength range spanned by our spectra. In contrast with a rather stable behaviour in the optical and even in the far-IR, the submm counts are dramatically sensitive to variations in the cosmological parameters and changes in the star formation history. Faint submm counts are more easily accommodated within an open universe with a low value of $Ω_0$, or a flat universe with a non-zero cosmological constant. This study illustrates the implementation of multi-wavelength spectra into a semi-analytic model. In spite of its simplicity, it already provides fair fits of the current data of faint counts, and a physically motivated way of interpolating and extrapolating these data to other wavelengths and fainter flux levels.

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arXiv2000

FIRBACK Source Counts and Cosmological Implications

FIRBACK is a one of the deepest surveys performed at 170 microns with ISOPHOT onboard ISO, and is aimed at the study of cosmic far infrared background sources. About 300 galaxies are detected in an area of four square degrees, and source counts present a strong slope of 2.2 on an integral "logN-logS" plot, which cannot be due to cosmological evolution if no K-correction is present. The resolved sources account for less than 10% of the Cosmic Infrared Background at 170 microns. In order to understand the nature of the sources contributing to the CIB, and to explain deep source counts at other wavelengths, we have developed a phenomenological model, which constrains in a simple way the luminosity function evolution with redshift, and fits all the existing deep source counts from the mid-infrared to the submillimetre range. Images, materials and papers available on the FIRBACK web: http://wwwfirback.ias.u-psud.fr wwwfirback.ias.u-psud.fr

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arXiv2000

The extragalactic background and its fluctuations in the far-infrared wavelengths

A Cosmic Far-InfraRed Background (CFIRB) has long been predicted that would traces the intial phases of galaxy formation. It has been first detected by Puget et al.(1996) using COBE data and has been later confirmed by several recent studies (Fixsen et al. 1998, Hauser et al. 1998, Lagache et al. 1999). We will present a new determination of the CFIRB that uses for the first time, in addition to COBE data, two independent gas tracers: the HI survey of Leiden/Dwingeloo (hartmann, 1998) and the WHAM H$_α$ survey (Reynolds et al 1998). We will see that the CFIRB above 100 micron is now very well constrained. The next step is to see if we can detect its fluctuations. To search for the CFIRB fluctuations, we have used the FIRBACK observations. FIRBACK is a deep cosmological survey conducted at 170 micron with ISOPHOT (Dole et al., 2000). We show that the emission of unresolved extra-galactic sources clearly dominates, at arcminute scales, the background fluctuations in the lowest galactic emission regions. This is the first detection of the CFIRB fluctuations.

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arXiv1999

The spectral appearance of primeval galaxies

The current and forthcoming observations of large samples of high-redshift galaxies selected according to various photometric and spectroscopic criteria can be interpreted in the context of galaxy formation, by means of models of evolving spectral energy distributions (SEDs). We hereafter present STARDUST which gives synthetic SEDs from the far UV to the submm wavelength range. These SEDs are designed to be implemented into semi-analytic models of galaxy formation.

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arXiv1999

Galaxy Modelling -- I. Spectral Energy Distributions from Far-UV to Sub-mm Wavelengths

(abridged) We present STARDUST, a new self-consistent modelling of the spectral energy distributions (SEDs) of galaxies from far-UV to radio wavelengths. In order to derive the SEDs in this broad spectral range, we first couple spectrophotometric and (closed-box) chemical evolutions to account for metallicity effects on the spectra of synthetic stellar populations. We then use a phenomenological fit for the metal-dependent extinction curve and a simple geometric distribution of the dust to compute the optical depth of galaxies and the corresponding obscuration curve. This enables us to calculate the fraction of stellar light reprocessed in the infrared range. In a final step, we define a dust model with various components and we fix the weights of these components in order to reproduce the IRAS correlation of IR colours with total IR luminosities. This allows us to compute far-IR SEDs that phenomenologically mimic observed trends. We are able to predict the spectral evolution of galaxies in a broad wavelength range, and we can reproduce the observed SEDs of local spirals, starbursts, luminous infrared galaxies (LIRGs) and ultra luminous infrared galaxies (ULIRGs). This modelling is so far kept as simple as possible and depends on a small number of free parameters, namely the initial mass function (IMF), star formation rate (SFR) time scale, gas density, and galaxy age, as well as on more refined assumptions on dust properties and the presence (or absence) of gas inflows/outflows.

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arXiv1999

Far-infrared Point Sources

The analysis of the submm anisotropies that will be mapped by the forthcoming MAP and PLANCK satellites requires careful foreground subtraction before measuring CMB fluctuations. Among these, the foreground due to IR/submm thermal radiation from dusty sources was poorly known until recent observational breakthroughs began unveiling the properties of these objects. We hereafter briefly review the observational evidence for a strong evolution of IR/submm sources with respect to the local universe explored by IRAS. We present the basic principles of a new modeling effort where consistent spectral energy distributions of galaxies are implemented into the paradigm of hierarchical clustering with the fashionable semi-analytic approach. This model provides us with specific predictions in IR/submm wavebands, that seem to reproduce the current status of the observations and help assessing the capabilities of forthcoming instruments to pursue the exploration of the deep universe at IR/submm wavelengths. Finally, the ability of the PLANCK High Frequency Instrument all-sky survey to produce a catalogue of dusty sources at submm wavelengths is briefly described.

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arXiv1999

FIRBACK Far Infrared Survey with ISO: Data Reduction, Analysis and First Results

FIRBACK is one of the deepest cosmological surveys performed in the far infrared, using ISOPHOT. We describe this survey, its data reduction and analysis. We present the maps of fields at 175 microns. We point out some first results: source identifications with radio and mid infrared, and source counts at 175 microns. These two results suggest that half of the FIRBACK sources are probably at redshifts greater than 1. We also present briefly the large follow-up program.

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