102 research outputs found
Massive and old quiescent galaxies at high redshift
No full textAims: Questions of how massive quiescent galaxies rapidly assembled and how abundant they are at high redshift are increasingly important in the study of galaxy formation. Looking at these systems can shed light on the processes of galaxy mass assembly and quenching of the star formation at early epochs. In order to address these questions, we aim to identify and characterize massive quiescent galaxies from z ̃ 2.5 out to the highest redshifts at which these systems can be found. The final purpose is to compare the results with the predictions of state-of-the-art semi-analytical models of galaxy formation and evolution.
Methods: We defined observer-frame color-color diagrams to optimally select quiescent galaxies at z > 2.5 and applied them to the COSMOS2015 catalog. We refined the spectral energy distribution (SED) fitting analysis for the selected candidates to confirm their quiescent nature, then derived their number density, mass density, and stellar mass functions. Finally, we compared the results with previous observations and some current semi-analytic models.
Results: We selected candidates for quiescent galaxies in the redshift range 2.5 ≲ z ≲ 4.5 from the COSMOS2015 catalog by means of two color-color diagrams. The additional SED fitting analysis allowed us to select 128 galaxies, consistent with being massive (log(M*/M☉)≥10.6), old (ages ≳0.5 Gyr), and quiescent (log(sSFR [yr-1]) ≤ -10.5) objects at high redshift (2.5 < z < 4.5). Their number and mass densities are in fair agreement with previous observations and, if confirmed, show a discrepancy with current semi-analytical models of galaxy formation and evolution, that underpredict the number of massive quiescent systems up to a factor of ̃12 at 2.5 ≤ z < 3.0 and ̃10 at z ̃ 4.0. The evolution of the stellar mass functions (SMFs) of these systems is similar to previous estimates and indicates a disagreement with models, particularly with regard to the shape of the SMF.
Conclusions: The present results add further evidence to the possibility that massive and quiescent galaxies can exist out to at least z ̃ 4. If future spectroscopic observations carried out with, for example, the James Webb Space Telecope (JWST), confirm the substantial presence of such a population, further work on modeling the stellar mass assembly, as well as supermassive black hole accretion and feedback processes at early cosmic epochs, is needed to understand how these systems formed, evolved, and quenched their star formatio
A comprehensive galaxy and AGN mock catalogue for the next generation of surveys
No full textCurrent and future large-sky surveys will produce unprecedented amounts of photometric and spectroscopic data for billions of sources. To fully exploit the scientific potential of these surveys, realistic simulations of astrophysical sources such as galaxies and Active Galactic Nuclei (AGN) have become essential tools. In this context, we introduce a new, flexible, and efficient computational model designed to simulate mock catalogues of galaxies and AGN that accurately replicate the statistical properties and observational features of these astrophysical sources. To achieve this, we followed a completely empirical approach, that is, we calibrated the model based on observed scaling relations. Specifically, we started with simulated dark matter (DM) haloes from an N-body simulation, to preserve the link with the cosmic web, and we populated them with galaxies and AGN using abundance matching techniques. To achieve this, we used several observational inputs, such as
stellar mass functions, host galaxy AGN mass functions, and AGN accretion rate distribution functions studied at different redshifts to assign, among other properties, stellar masses, the fraction of quenched galaxies, or the AGN activity (demography, obscuration, multiwavelength emission, etc.). As a proof test, we applied the method to a Millennium DM lightcone of 3.14 deg2 up to a redshift of z = 10. We show that the AGN population from the mock lightcone presented here reproduces with good accuracy various observables, such as state-of-the-art luminosity functions in the X-ray and in the ultraviolet, near-infrared colour-colour diagrams, and narrow emission line diagnostic diagrams. Finally, we demonstrate several applications of this catalogue. We computed several forecasts of Euclid observations, and we tested a pipeline for retrieving photometric redshifts on simulated AGN with Euclid-like photometry and a spectroscopic analysis pipeline on Euclid-like AGN spectral energy distributions. Finally, we show an application of this model for the preparation of an X-ray observational campaign
Searching for massive and quiescent galaxies at z > 3
No full textUno dei più grandi problemi aperti relativi alla formazione ed evoluzione delle galassie è la presenza di galassie massive e quiescenti nell’universo giovane, cioe` a z>3. In questo contesto, questa tesi si prefigge due obiettivi. Il primo è quello di trovare delle selezioni di colore atte ad identificare galassie quiescenti ad alto redshift. Tre nuove selezioni di colore sono proposte basate sulla presenza dei break D4000 e di Balmer che caratterizzano la distribuzione di energia spettrale di una popolazione stellare vecchia e sono ideati per selezionare questo tipo di oggetti a 2.5<z<4.5. Dal sotto-campione con m[4.5]≤24 del catalogo COSMOS2015, le galassie candidate sono selezionate tramite le selezioni di colore. Il secondo obiettivo di questo elaborato, è la conferma della natura quiescente dei candidati selezionati. Questo è realizzato attraverso un fit della distribuzione di energia spettrale dei candidati che permette di selezionare i candidati più evoluti e massivi. Un totale di 208 oggetti massivi quiescenti ad alto redshift sono identificati con età consistenti con l’essere vecchi quanto l’universo al loro redshift. Il campione finale così selezionato è utilizzato per rivisitare la densità numerica e in massa stellare della popolazione di galassie quiescenti ad alto redshift. Molti recenti modelli di formazione ed evoluzione delle galassie provano a spiegare la formazione di galassie massive e la loro trasformazione in sistemi quiescenti, tuttavia nessuno di essi è capace di riprodurre le osservazione degli ultimi anni. Sembra che i modelli sotto-stimino le densità numeriche ed in massa stellare di questi oggetti. Negli anni a venire, sarà fondamentale effettuare delle osservazioni spettroscopiche dei candidati quiescenti, utilizzando gli strumenti a disposizione nel prossimo futuro. Questo permetterà di valutare in modo più preciso le proprietà fisiche di questi oggetti e porterà ad una revisione dei modelli di formazione ed evoluzione delle galassie
Galaxy evolution in the VIMOS public extragalactic redshift survey (VIPERS)
No full textIn this work I present the first measurements of the galaxy stellar mass function (GSMF) from the first public release of the VIPERS catalogue, containing ∼55,000 objects.
First, I present the survey design, its scientific goal, the redshift measurements and validation. Then, I provide details about the estimate of galaxy stellar masses, star formation rates, and other physical quantities. I derive the GSMF of different galaxy types (e.g. active and passive galaxies) and as a function of the environment (defined through the local galaxy density contrast). These estimates represent new observational evidence useful to characterise the mechanism of galaxy evolution
Il mistero delle galassie quiescenti ad alto redshift
No full textNegli ultimi anni, osservazioni nell’ottico e nel vicino infrarosso hanno rivelato la presenza
di una popolazione di galassie massive ad alto redshift con debole o assente formazione stellare. L’esistenza di tali oggetti nell’universo primordiale è una grande sfida per i modelli di formazione delle galassie e per le simulazioni cosmologiche attuali; il fatto che una galassia sia massiccia e quiescente implica che abbia avuto un intenso episodio di formazione stellare ad alto redshift, seguito dall’invecchiamento della popolazione stellare che appare quindi già evoluta a z > 3. Questi oggetti appaiono quindi quasi vecchi quanto l’Universo al loro redshift. Tuttavia, le osservazioni di galassie quiescenti e massicce a z > 3 sono ancora incerte: a causa della loro debolezza, la maggior parte di queste galassie sono candidati fotometrici e il loro studio, in assenza di dati spettroscopici, si basa sull’analisi delle loro SED fotometriche. Lo scopo di questo progetto di tesi è uno studio dettagliato di queste galassie quiescenti e massive ad alto redshift. In particolare, è stato selezionato un campione affidabile di galassie quiescenti analizzando la loro distribuzione probabilistica dei redshifts fotometrici ed eseguendo un accurato SED fitting utilizzando una varietà di parametri e due modelli di popolazioni stellari semplici. Il campione così ottenuto è stato poi confrontato con i modelli di formazione delle galassie con lo scopo di imporre dei vincoli sui percorsi evolutivi che conducono alla loro esistenza. Questo confronto sembra attribuire un ruolo fondamentale all’accrescimento della massa del buco nero centrale che subisce un brusco arresto probabilmente dovuto ad un forte feedback negativo che riscalda il gas bloccando la formazione stellare. Osservazioni spettroscopiche in infrarosso, possibili con il futuro telescopio JWST, saranno fondamentali per confermare la presenza di questo tipo di oggetti ad alto redshift e determinarne le loro proprietà fisiche
LBT-MODS spectroscopy of high-redshift candidates in the Chandra J1030 field. A newly discovered z2.8 large scale structure
No full textWe present the results of a spectroscopic campaign with the Multi-Object
Double Spectrograph (MODS) instrument mounted on the Large Binocular Telescope
(LBT), aimed at obtaining a spectroscopic redshift for seven Chandra J1030
sources with a photometric redshift >=2.7 and optical magnitude
r_AB=[24.5-26.5]. We obtained a spectroscopic redshift for five out of seven
targets: all of them have z_spec>=2.5, thus probing the reliability of the
Chandra J1030 photometric redshifts. The spectroscopic campaign led to the
serendipitous discovery of a z~2.78 large scale structure (LSS) in the J1030
field: the structure contains four X-ray sources (three of which were targeted
in the LBT-MODS campaign) and two non-X-ray detected galaxies for which a
VLT-MUSE spectrum was already available. The X-ray members of the LSS are
hosted in galaxies that are significantly more massive
(log(M_*/M_sun)=[10.0-11.1]) than those hosting the two MUSE-detected sources
(log(M_*/M_sun)<10). Both observations and simulations show that massive
galaxies, and particularly objects having log(M_*/M_sun)>10, are among the best
tracers of large scale structures and filaments in the cosmic web.
Consequently, our result can explain why X-ray-detected AGN have also been
shown to be efficient tracers of large scale structures.Comment: 16 pages, 9 Figures. Accepted for publication in Astronomy and
Astrophysic
Quiescent galaxies at z ≳ 2.5: observations versus models
No full textThe presence of massive quiescent galaxies at high redshifts is still a challenge for most models of galaxy formation. The aim of this work is to compare the observed number density and properties of these galaxies with the predictions of state-of-the-art models. The sample of massive quiescent galaxies has been selected from the COSMOS2015 photometric catalog with z phot ≥ 2.5, {log}({M}* /{M}☉ )≥slant 10.5, and a specific star formation rate (sSFR) of {log}({sSFR} [{yr}}-1])≤slant -11. The photometric spectral energy distributions (SEDs) of the selected galaxies have been thoroughly analyzed based on different stellar population synthesis models. The final sample includes only those galaxies qualified as quiescent in all SED fitting runs. The observed properties have been compared to theoretical models: the number density of quiescent galaxies with 10.5≤slant {log}({M}* /{M}☉ )* /{M}☉ )≥slant 10.8 are underpredicted by most of the current models of galaxy formation: some of them, built on the CARNage simulation, are consistent with data up to z ∼ 4, while at higher redshifts the volume of the considered simulation is too small to find such rare objects. Simulated galaxies that match the observed properties in the sSFR-M * plane at z ∼ 3 have been analyzed by reconstructing their evolutionary paths: their merger trees suggest that AGN feedback could be the key process allowing for a rapid quenching of the star formation at z ≳ 4 and that its treatment should be improved in models
Characterization of a novel passive personal fast neutron dosimeter based on a CR-39 track detector in monochromatic neutron fields via Monte Carlo simulations and experiments
No full textInternational audienceThe response in terms of personal dose equivalent of a passive fast neutron dosimeter composed by a CR-39 detector coupled with a-cm-thick PMMA radiator is investigated in monochromatic neutron fields via simulations and experiments. In particular, the simulations were performed through the Monte Carlo FLUKA code (version 2011.2x.5), while the experimental fields were produced at the IRSN-AMANDE facility in Cadarache. The response is studied both with respect to the energy of the field and to its angle of incidence on the device. The simulated response shows a quite stationary trend in a wide energy range and also with respect to different irradiation geometries, and the agreement between simulated and experimental points individuates the simple and cheap dosimeter presented as promising for personal dosimetry applications in practical situations
The VIMOS Public Extragalactic Redshift Survey (VIPERS). Environmental effects shaping the galaxy stellar mass function
No full textO.C. acknowledges the support from grants ASI-INAF I/023/12/0 “Attività relative alla fase B2/C per la missione Euclid”. L.G. and B.R.G. acknowledge support of the European Research Council through the Darklight E.R.C. Advanced Research Grant (# 291521). O.L.F. acknowledges the support of the European Research Council through the EARLY ERC Advanced Research Grant (# 268107). A.P., K.M., and J.K. have been supported by the National Science Centre (grants UMO-2012/07/B/ST9/04425 and UMO-2013/09/D/ST9/04030), the Polish-Swiss Astro Project (co-financed by a grant from Switzerland through the Swiss Contribution to the enlarged European Union). R.T. acknowledges financial support from the European Research Council under the European Community’s Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement n. 202686. E.B., F.M., and L.M. acknowledge the support from grants ASI-INAF I/023/12/0 and PRIN MIUR 2010-2011. LM also acknowledges financial support from PRIN INAF 2012. Y.M. acknowledges support from CNRS/INSU (Institut National des Sciences de l’Univers) and the Programme National Galaxies et Cosmologie (PNCG).We exploit the first public data release of VIPERS to investigate environmental effects in the evolution of galaxies between z ~ 0.5 and 0.9. The large number of spectroscopic redshifts (more than 50 000) over an area of about 10 deg2 provides a galaxy sample with high statistical power. The accurate redshift measurements (σz = 0.00047(1 + zspec)) allow us to robustly isolate galaxies living in the lowest and highest density environments (δ 4, respectively) as defined in terms of spatial 3D density contrast δ. We estimate the stellar mass function of galaxies residing in these two environments and constrain the high-mass end (ℳ ≳ 1011 ℳ⊙) with unprecedented precision. We find that the galaxy stellar mass function in the densest regions has a different shape than was measured at low densities, with an enhancement of massive galaxies and a hint of a flatter (less negative) slope at z< 0.8. We normalise each mass function to the comoving volume occupied by the corresponding environment and relate estimates from different redshift bins. We observe an evolution of the stellar mass function of VIPERS galaxies in high densities, while the low-density one is nearly constant. We compare these results to semi-analytical models and find consistent environmental signatures in the simulated stellar mass functions. We discuss how the halo mass function and fraction of central/satellite galaxies depend on the environments considered, making intrinsic and environmental properties of galaxies physically coupled, hence difficult to disentangle. The evolution of our low-density regions is described well by the formalism introduced by Peng et al. (2010, ApJ, 721, 193), and is consistent with the idea that galaxies become progressively passive because of internal physical processes. The same formalism could also describe the evolution of the mass function in the high density regions, but only if a significant contribution from dry mergers is considered.Peer reviewe
The stellar metallicities of massive quiescent galaxies at 1.0 < z < 1.3 from KMOS+VANDELS
No full textWe present a rest-frame UV-optical stacked spectrum representative of massive quiescent galaxies at 1.0<z<1.3 with log(M∗/M⊙)>10.8. The stack is constructed using VANDELS survey data, combined with new KMOS observations. We apply two independent full-spectral-fitting approaches, measuring a total metallicity, [Z/H]=−0.13±0.08 with Bagpipes, and [Z/H]=0.04±0.14 with Alf, a fall of ∼0.2−0.3 dex compared with the local Universe. We also measure an iron abundance, [Fe/H] =−0.18±0.08, a fall of ∼0.15 dex compared with the the local Universe. We measure the alpha enhancement via the magnesium abundance, obtaining [Mg/Fe]=0.23±0.12, consistent with similar-mass galaxies in the local Universe, indicating no evolution in the average alpha enhancement of log(M∗/M⊙)=11 quiescent galaxies over the last ∼8 Gyr. This suggests the very high alpha enhancements recently reported for several bright z∼1−2 quiescent galaxies are due to their extreme masses, log(M∗/M⊙)≳11.5, rather than being typical of the z≳1 population. The metallicity evolution we observe with redshift (falling [Z/H], [Fe/H], constant [Mg/Fe]) is consistent with recent studies. We recover a mean stellar age of 2.5+0.6−0.4 Gyr, corresponding to a formation redshift, zform=2.4+0.6−0.3. Recent studies have obtained varying average formation redshifts for z≳1 massive quiescent galaxies, and, as these studies report consistent metallicities, we identify different star-formation-history models as the most likely cause. Larger spectroscopic samples from upcoming ground-based instruments will provide precise constraints on ages and metallicities at z≳1. Combining these with precise JWST z>2 quiescent-galaxy stellar-mass functions will provide an independent test of formation redshifts derived from spectral fitting
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