Found 46 talks width keyword galactic formation

Bosonic ultra-light dark matter (ULDM) in the mass range m ~ $10^{-22} - 10^{-21} \rm eV$ has been invoked as a motivated candidate with new input for the small-scale `puzzles' of cold dark matter. Numerical simulations show that these models form cored density distributions at the center of galaxies ('solitons'). These works also found an empirical scaling relation between the mass of the large-scale host halo and the mass of the central soliton. We show that this relation predicts that the peak circular velocity of the outskirts of the galaxy should approximately repeat itself in the central region. Contrasting this prediction to the measured rotation curves of well-resolved near-by galaxies, we show that ULDM in the mass range m ~ $10^{-22} - 10^{-21} \rm eV$ is in tension with the data.

In this talk I will discuss how the stellar, globular cluster (GC), and gas components of galaxies allow us to trace the assembly of galaxies and their dark matter (DM) haloes, and how they constrain the complex physics of galaxy formation. I will use examples from three studies: in the first one, I will describe how the study of the phase-space distribution of the MW GC system using Gaia in the context of the E-MOSAICS simulations provides a detailed quantitative picture of the formation of the Galaxy. In the second example, I will show how the unusual GC populations in galaxies like the infamous NGC1052-DF2 and DF4 can be used to rewind the clock and obtain a snapshot of their galactic progenitors at cosmic noon. A simple model of star cluster formation points to an extremely dense birth environment and strong structural evolution, providing clues of the effect of clustered star formation on galaxy evolution. In the last part I will describe a follow-up study of the impact of clustered star formation on galaxy structure that provides clues on the origin of ultra-diffuse galaxies (UDGs), which are difficult to explain in the current paradigm of galaxy formation. I will show how anchoring an analytical model on galaxy scaling relations and numerical simulations predicts the emergence of UDGs that lack DM driven by clustered feedback from young GCs.

The disc of galaxies is made of the superposition of a thin and a thick disc. Thick discs are seen in edge-on galaxies as excesses of light a few thin disc scale-heights above the mid-plane. Star formation occurs in the thin discs whereas thick discs are made of old stars. The formation mechanisms of thick discs are under debate. Thick discs might have formed either at high redshift on a short time-scale or might have been built slowly over the cosmic time. They may have an internal or an external origin. To solve the issue of the thick disc origin we studied the kinematics and the stellar populations of the nearby edge-on galaxies ESO 533-4 and ESO 243-49. We present the first Integral Field Unit (IFU) spectroscopy works with enough depth and quality to study the thick discs. This was done with VIMOS@VLT and MUSE@VLT.

Our results point that thick discs formed in a relatively short event at high redshift and that the thin disc has formed afterwards within it. We also find that the thick disc stars have an internal origin as opposed to have their stars accreted during encounters. The work regarding ESO 533-4 has recently been published in Comer?n et al. 2015, A&A, 584, 34.

The realism of hydrodynamical simulations of the formation and evolution of galaxies has improved considerably in recent years. I will try to give some insight into the reasons behind this success, focusing in particular on the importance of subgrid models and the associated limitations. I will also present recent results from the cosmological EAGLE simulations as well as from higher-resolution simulations of individual galaxies.

Major tests of cosmological and galaxy formation models can be constructed through dynamical and structural parameters of galaxies. Towards this end, we present the SHIVir (Spectroscopic and H-band Imaging of Virgo cluster galaxies) survey, which provides dynamical information and stellar population diagnostics for hundreds of galaxies. We construct scaling relations and dynamical profiles within the optical radius of most galaxies, paying close attention to the baryon-to-dark matter transition region and selected metrics which reduce scatter in fundamental scaling relations. Salient results include bimodal mass and surface brightness distributions for Virgo galaxies, a possible bifurcation in the stellar-to-halo mass relation for low-mass galaxies, and the need for deep velocity dispersions to extract meaningful science. Once complete, ours should be the most extensive mass catalogue ever assembled for a galaxy cluster.

Stars, the most fundamental building blocks of galaxies, are born within the clouds of gas and dust and and during their lives they enrich the gas and the interstellar medium (ISM) with heavy elements, magnetic fields, and cosmic rays all of which strongly affects the subsequent formation of stars and their host galaxy. To understand the evolution and appearance of galaxies it is therefore crucial to study the interplay between stars and the ISM. Putting together the infrared, submm, and radio observations of nearby galaxies, we have studied the physical properties of the dusty and magnetized ISM in nearby galaxies to address the pressing questions: How the ISM components are inter-connected and how their physical properties change in different galactic environments e.g. star forming regions, spiral arms, nucleus and outer disks? In what extent the star formation influences the physical properties and structure of the ISM in a galaxy? I will show the effect of star formation on the dust emission properties, interstellar magnetic fields, cosmic ray electron energy index and further discuss the important factors in the energy balance of the ISM at different scales in M33, M31, NGC6946, and other nearby galaxies.

Cold gas streaming along the dark-matter filaments of the cosmic web is predicted to be the major provider of resources for disc buildup and star formation in massive galaxies in the early universe. We use hydrodynamical simulations to study to what extent these cold streams are traceable in the extended circum-galactic environment of galaxies via Ly alpha emission, Ly alpha absorption and selected low ionisation metal absorption lines. We predict the strength of the absorption signal produced by the streams and find that it is consistent with observations in high redshift galaxies. The characteristics of the Ly alpha emission of our simulated galaxies are similar in luminosity, morphology and extent to the observed Ly alpha blobs, with distinct kinematic features. We analyse the characteristics of the cold streams in simulations and present scaling relations for the amount of infall, its velocity, distribution and its clumpiness and compare our findings with observations.

Most massive galaxies have supermassive black holes at their centres, and the masses of the black holes correlate with properties of the host-galaxy bulge component. These empirical scaling relations are important for distinguishing between various theoretical models of galaxy evolution, and they furthermore form the basis for all black-hole mass measurements at large distances. Observations have shown that the mass of the black hole is typically 0.1 per cent of the mass of the stellar bulge of the galaxy. Our spectroscopic survey with the Hobby-Eberly Telescope of 1000 nearby galaxies revealed several compact lenticular galaxies with extremely high velocity dispersions. The first example is NGC1277, which is a small, Re=1kpc, compact, lenticular galaxy with a mass of 1.2×10^11 solar masses. From the stellar kinematics we determined that the mass of the central black hole is 10^10 solar masses, more than 10 per cent of its bulge mass. I will present HST images and IFU spectroscopy of a dozen more compact galaxies that all appear to host extremely big black holes and have Salpeter-like IMFs. These local systems, with distances less than 100 Mpc, could be the passively evolved descendents of the quiescent compact nugget galaxies found at z~2 and the >10e9 Msun quasars that are found at z>6.

Any viable theory of the formation and evolution of galaxies should be able to broadly account for the emergent properties of the galaxy population, and their evolution with time, in terms of fundamental physical quantities. Yet, when citing the key processes we believe to be central to the story, we often find ourselves listing from a vast and confusing melee of modelling strategies & numerical simulations, rather than appealing to traditional analytic derivations where the connections to the underlying physics are more tangible. By re-examining both complex models and recent observational surveys in the spirit of the classic theories, we will investigate to what extent the trends in the galaxy population can still be seen as an elegant fingerprint of cosmology and fundamental physics.

The first galaxies are thought to have started the reionization of the Universe, that is the transformation of the cosmic hydrogen from its initial neutral to its present ionized state that occurred during the first few hundred million years after the Big Bang. I will review the key physics of reionization by the first galaxies and highlight the computational challenges of simulating the relevant processes, primarily the transport of ionizing photons. I will introduce the radiative transfer method TRAPHIC that we have developed to address these challenges. I will discuss the application of TRAPHIC in zoomed cosmological simulations of the first galaxies and evaluate the prospects for observing these galaxies with the upcoming James Webb Space Telescope. I will conclude by presenting first results from Aurora, a new suite of simulations to investigate reionization and galaxy formation across a large range of scales.