Found 28 talks width keyword high-redshift galaxies

Tuesday November 21, 2023
Astroparticle and Cosmology Laboratory (Paris)


Galaxies are embedded within a network of interconnected filaments, essential for their formation and growth. Simultaneously, they emit radiation and enriched matter back into their environment, influencing the evolution of the cosmic gas. Recent advancements in wide-field spectrographs offer a unique perspective, allowing us to probe the spatial distribution and properties of the circumgalactic medium at high redshift, particularly the Lyman-alpha line emitted by cold hydrogen gas. These insights are especially valuable in overdense regions, like protoclusters and groups, where we can explore most of the physical mechanisms at play. By combining data from instruments such as KCWI, MOSFIRE, IRAC, LRIS, and HST, we aim to decipher the various mechanisms that steer the evolution of galaxies and protocluster environments around the Cosmic Noon epoch, unveiling how mergers, AGN feedback, and galactic outflows influence both the large-scale gas distribution and the general properties of the galaxies themselves. Nonetheless, several degeneracies persist among the observed properties of the gas and the potential physical mechanisms responsible, underscoring the necessity for improved models of these cosmic phenomena and a larger statistical sample of protocluster environments.

Thursday March 2, 2023



Early-type galaxies: instructions to build them through mergers
Massive early-type galaxies (ETGs) are "red and dead" systems mainly composed of old and metal-rich stellar populations. In a cosmological context, present-day ETGs are believed to be the remnants of a complex stellar mass assembly history marked by several mergers, which are the consequence of the underlying hierarchical assembly of their host dark matter halos. In this talk, I will deal mainly with the merger-driven evolution of ETGs. Firstly, I will illustrate a comparison between observed ETGs from the MaNGA survey and simulated galaxies from the IllustrisTNG cosmological simulation suite. The aim of this study is to provide an interpretative scenario of the stellar mass assembly history of observed present-day ETGs, comparing the radial distributions of their stellar properties with those of simulated galaxies, in which it is possible to disentangle the contribution of stars formed in situ (i.e. within the main progenitor galaxy) and stars formed ex situ (i.e. in other galaxies) and then accreted through mergers. Then, I will describe how the scaling relation between the stellar mass and stellar velocity dispersion in ETGs evolves across cosmic time. Specifically, by extending the results of Cannnarozzo, Sonnenfeld & Nipoti (2020), I model the aforementioned relation through a Bayesian hierarchical approach, considering ETGs with log(M∗/M⊙) > 9 over the redshift range 0 ≲ z ≲ 4. Together with a new characterisation of the relation, I reconstruct the back-in-time evolutionary pathways of individual ETGs on the stellar mass-velocity dispersion plane to answer the question “how did high-redshift ETGs assemble through cosmic time to reach the functional form of the relation in the present-day Universe?“.
After the main topic, if time permits, I would like to spend a few minutes presenting another extra content (below you can find the title and a brief abstract of this further content). Feel free to include it or not in the announcement mail.
EXTRA - Inferring the Dark Matter halo mass in galaxies from other observables with Machine Learning
In the context of the galaxy-halo connection, it is widely known that the Dark Matter (DM) halos show correlations with some physical properties of the hosted galaxy: the most well-known relation is the so-called Stellar-to-Halo-Mass Relation. However, we know that there are several other empirical relations among galaxy properties, involving, for example, the stellar mass, the gas and stellar metallicities, the black hole mass, etc. Given the complexity of the problem and the high number of galaxy properties that might be related to DM halos, the study of the galaxy-halo connection can be approached by relying on machine learning techniques to shed light on this intricate network of relations. With the aim of inferring the DM halo mass and then finding a unique functional form able to link the halo mass to other observables in real galaxies, I rely on the state-of-the-art Explainable Boosting Machine, a novel implementation of generalised additive models with pairwise interactions, training a model on the IllustrisTNG simulation suite at different redshift.





Thursday February 23, 2023
University of Padova


I present a detailed analysis of the scaling relations of ETGs and suggest a way to predict the evolution of the distributions of galaxies in these planes. This new approach is able to account of several features observed in the FP projections and of the tilt of the Fundamental Plane.


Tuesday September 13, 2022


Cosmological observations (redshifts, cosmic microwave background radiation, abundance of light elements, formation and evolution of galaxies, large-scale structure) find explanations within the standard Lambda-CDM model, although many times after a number of ad hoc corrections. Nevertheless, the expression ‘crisis in cosmology’ stubbornly reverberates in the scientific literature: the higher the precision with which the standard cosmological model tries to fit the data, the greater the number of tensions that arise. Moreover, there are alternative explanations for most of the observations. Therefore, cosmological hypotheses should be very cautiously proposed and even more cautiously received.

There are also sociological and philosophical arguments to support this scepticism. Only the standard model is considered by most professional cosmologists, while the challenges of the most fundamental ideas of modern cosmology are usually neglected. Funding, research positions, prestige, telescope time, publication in top journals, citations, conferences, and other resources are dedicated almost exclusively to standard cosmology. Moreover, religious, philosophical, economic, and political ideologies in a world dominated by anglophone culture also influence the contents of cosmological ideas.

Thursday July 8, 2021


We summarize here some of the results reviewed recently by Sanchez (2020) and Sanchez  et al. (2021), comprising the advances in the comprehension of galaxies in the nearby universe based on integral field spectroscopic galaxy surveys. We review our current knowledge of the spatially resolved spectroscopic properties of low-redshift star-forming galaxies (and their retired counterparts) using results from the most recent optical integral field spectroscopy galaxy surveys. We briefly summarize the global spectroscopic properties of these galaxies, discussing the main ionization processes, and the global relations described by the star-formation rates, gas-phase oxygen abundances, and average properties of their stellar populations (age and metallicity) in comparison with the stellar mass. Then, we present the local distribution of the ionizing pro-cesses down to kiloparsec scales, and how the global scaling relations found using integrated parameters (like the star-formation main sequence, mass–metallicity relation, and Schmidt–Kennicutt law) have local/resolved counterparts, with the global ones being, for the most part, just integrated/average versions of the local ones.  The main conclusions of the most recent explorations are that the evolution of galaxies is mostly governed by local processes but clearly affected by global ones.

Tuesday January 29, 2019
CRAL - Observatoire de Lyon


Thanks to its unique capabilities, the MUSE integral field spectrograph at ESO VLT has given us new insight of the Universe at high redshift. In this talk I will review some breakthrough in the observation of the Hubble Ultra Deep field with MUSE including the discovery of a new population of faint galaxies without HST counterpart in the UDF and the ubiquitous presence of extended Lyman-alpha haloes around galaxies.

Wednesday November 28, 2018
Institute of Astrophysics and Space Sciences (IA)


There are galaxies that remain untouched since the ancient
Universe. These unique objects, the so-called relic galaxies, are several times
more massive than our Milky Way but with much smaller sizes, and
containing very old (>10 Gyr) stellar populations. For the very few of
them already found and analysed (most of them by our IAC colleagues),
they seem to host "too heavy" central
super massive black holes, also displaying an overabundance of low mass
versus high mass stars and retaining their primeval morphologies and
kinematics. How did they survive until the present day? Simulations
predict that they reside in galaxy overdensities whose large internal
random motions prevent galaxies from merging. However, we have not yet
determined observationally neither the environments these galaxies
inhabit nor how many there are (their number densities). We make use
of the GAMA survey, that allows us to conduct a complete
census of this elusive galaxy population, because of its large area and
spectroscopic completeness. After inspecting 180 square degrees of the sky
using the deepest photometric images available, we identified 29
massive ultracompact galaxies in the nearby Universe (0.02 < z < 0.3),
that are true windows to the ancient Universe. I will present the first paper
about this exceptional sample, describing their properties and
highlighting the fact that while some galaxies seem to be satellites
of bigger objects, others are not located in clusters, at odds with the
theoretical expectations.

Thursday October 15, 2015


Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter haloes. Although these predictions are unambiguous, the observational support has been indirect so far. I will report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of localized starbursts associated with gas having low metallicity. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr),  the observed metallicity inhomogeneities are only possible if the metal-poor gas producing stars fell onto the disk recently. I will analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. In addition, I will show model galaxies in cosmological numerical simulations with starbursts of low metallicity like to the star-forming regions in XMPs.

Tuesday June 30, 2015


Almost all cosmologists accept nowadays that the redshift of the galaxies is due to the expansion of the Universe (cosmological redshift), plus some Doppler effect of peculiar motions, but can we be sure of this fact by means of some other independent cosmological test? Here I will review some recent tests: CMBR temperature versus redshift, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczynski test. Some tests favour expansion and others favour a static Universe. Almost all the cosmological tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, an evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.

Tuesday June 2, 2015
Centro de Astrobiología CSIC-INTA


The importance of Luminous and Ultraluminous infrared galaxies (U/LIRGs) in the context of the cosmological evolution of the star-formation has been well established in the last decades. They have been detected in large numbers at high-z (z>1) in deep surveys with Spitzer and Herschel, and they seem to be the dominant component to the star formation rate (SFR) density of the Universe beyond z~2. Although rare locally, nearby U/LIRGs are valuable candidates to study extreme cases of compact star-formation and coeval AGN. In particular, the study of local U/LIRGs using near-IR integral field spectroscopic techniques allows us to disentangle the 2D distribution of the gas and the star-formation using high spatial resolution, and characterise dust-enshrouded, spatially-resolved star-forming regions with great amount of detail. In that context, we are carrying on a comprehensive 2D IFS near-IR survey of local 10 LIRGs and 12 ULIRGs, based on VLT-SINFONI observations. I will review different topics on the spatially resolved study of the ISM and the star-formation at different spatial scales. I will focus on the analysis of the multi-phase gas morphology and kinematics, and on the study of the spatially-resolved distribution of the extinction-corrected star-formation rate (SFR) and star-formation rate surface density (ΣSFR). In particular, I will present some recent results on the characterization of individual star-forming regions, in terms of their sizes and Paα luminosities.

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