125 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
“But the skin of the earth is seamless”: Liberating Symbols of Nature in "Borderlands/The New Mestiza" by Gloria Anzaldúa
No full text“Build bridges, not walls!” Recently, this old slogan has boldly resounded in the streets of America. One of the greatest advocates of that belief was certainly Gloria Anzaldúa, author of Borderlands/La Frontera: The New Mestiza (1987) and co-author of This Bridge We Call Home (2002), among others. In Borderlands she offered a dramatic and revolutionary view on the life in the borderlands, nourishing with new life-blood the Latino, Feminist e Post-colonial studies. Being herself a Chicana grown up in the Texas-Mexico border area, Anzaldúa denounces the “terrorism” practiced by the U.S. government but also shows a possible path to follow in order to positively re-think the complex border identity: “I am participating in the creation of yet another culture, a new story to explain the world and our participation in it, a new value system with images and symbols that connect us to each other and to the planet” (81). Anzaldúa goes beyond the rationally cold, artificially created citizenship identity, towards a conception of the self more linked to the truth of being simply humans living on a planet whose surface is “seamless”. Nature is indeed central in her “new value system” and an endless source of symbols for her discourse. The aim of this article is to bring out the meanings attributed to Nature by Anzaldúa, proposing a close-reading of three poems included in Borderlands, where Nature (concreted in both natural space and animal life), becomes a symbol of the fight for liberation. “Horse”, “Wind tugging at my sleeve”, and “Dead”, are representative of the three main meanings we believe Anzaldúa ascribed to Nature: Nature as the strength we should – but frequently don’t - find in ourselves to fight oppression; Nature as the rebellion to the untruthful duality imposed by the border; Nature as the possibility of rebirth in a new identity
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
Italy: Legal Response to Covid-19
No full textScholarly report and analysis of national legal responses to Covid-19 around the world. The Compendium is composed of reports by country teams, headed by one or more Country or Territory Rapporteurs, who coordinate the production and updating of the relevant Country Reports. The reports are written by reference to a comprehensive Author Guidance Code (AGC). The AGC covers five topics:
I. Introduction
II. Applicable Legal Framework
III. Institutions and Oversight
IV. Public Health Measures, Enforcement and Compliance
V. Social and Employment Protection Measures
VI. Human Rights of Vulnerable Group
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
And Not Or, Kim Schoenstadt’s Composition for a Large Room in Three Parts
No full textThis essay focuses on the the relationship between spectator and art object as a Modernist dichotomy of author and viewer.https://digitalcommons.chapman.edu/art_books/1007/thumbnail.jp
L’autografia d'autore: Cambiamenti nella realizzazione e nella concezione del libro dal XII secolo all’invenzione della stampa
No full textIt is generally believed that the invention of printing triggered a cultural change, marking the passage between the medieval idea of the book and the modern one. It should be noted, though, that there was an important evolution through the Late Middle Ages, and that the printing revolution, however crucial, must be placed inside the wider process that from the XIIth century onwards transformed the use and function of writing, of reading and, consequently, the book itself, both theoretically and physically. The aim of this study is to track the cultural roots of the changes in the practices of intellectual work and, viceversa, to determine whether and how such changes may have influenced, through the literary production, late medieval culture. I have focused on the phenomenon of literary autography which, very unusual in the Early Middle Ages, is attested by a new and uninterrupted series of examples from the XIth-XIIth centuries onwards. The cultural landscape of the end of the Middle Ages appears therefore marked by the tension between a recurring drive towards an individualisation of the relation between an author and his work and a strict control by the author over the final product (both philologically and graphically) and an opposite trend leading to the loosening of the author's control over his work, as a natural result of the circulation of the texts but also of a different idea of the authorial role
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