Benedetta Vulcani

The JWST’s view on star formation in cluster galaxies

The goal of this project is to get unprecedented insights on the mechanisms that regulate star-formation in galaxies at z=0.1-1, exploiting for the first time integral and spatially resolved fluxes of some critical near infrared lines obtained with revolutionary space-based observations. The student will exploit data acquired with the James Webb Space Telescope (JWST), the most powerful space observatory ever built, which will open a new window, offering unprecedented resolution and sensitivity from the visible through the mid-IR range.
 The proposed analysis will based on one of the first ever observations obtained with JWST, taken in the context of the JWST Director’s Discretionary Early Release Science (ERS) Program. Specifically, the student will exploit the data of the Grism-Lens Amplified Survey from Space (GLASS)-ERS to investigate the Paschen and Balmer emission line fluxes in star forming galaxies in different environments to characterize the dust, gas and  star-formation rate distributions. Paschen lines suffer minimal extinction due to their longer wavelength than the Balmer ones and are optimal SFR tracers. The student will investigate the integrated and spatially resolved  star-formation rate for log M*/Msun>7 galaxies. Variations in the line ratios within and across galaxies would indicate a modification of the intrinsic ratio by reddening. Exploiting also ancillary FIR data that constrain the thermal dust emission the student will derive the dust properties and detect deviations from the typical relations, and eventually pin down an appropriate theoretical model for the hydrogen-emission-line region. Comparisons between galaxies in the different environments will shed light on the physical processes at work. Complementary studies of morphologies and structural parameters, obtained on ultra-deep imaging, will give additional insight on the galaxy assembly histories. The student will be immediately inserted in a vibrant international environment, and join the ERS team.

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The baryon cycle at cosmic noon as seen by JWST

The goal of this project is to get unprecedented insights on the mechanisms that regulate star-formation in galaxies at cosmic noon, exploiting observations obtained by the James Webb Space Telescope (JWST), the most powerful space observatory ever built. The proposed analysis will based on Parallel Application of Slitless Spectroscopy to Analyze Galaxy Evolution (PASSAGE, PI Malkann),  a field pure-parallel survey of emission line galaxies and  the Cycle 1 program awarded with the largest number of hours (591h). The PhD student will study star formation rates, gas ionization properties, and metallicities  for thousands of galaxies–the largest sample of this kind ever assembled,  reaching down to stellar masses of 1e7 Msun -- a completely uncharted territory. They will investigate the galaxy assembly across a wide range of redshift, capturing the transition between an epoch where galaxies were mostly irregular, highly star forming and dominated by random motions and a phase of more gentle assembly. At z<0.7, PASSAGE will provide Paschen alpha measurements for hundreds of galaxies, so we will be in the position of searching for heavily obscured and hidden star formation, for the first time in a statistically significant  sample. The student will perform detailed comparisons between the different SFR tracers and estimate the amount of obscured star formation that is typically missed when Halpha is used as a tracer. This analysis will have a huge impact in the community, providing an unbiased view of the star formation activity at low z.  At higher z (up to z<2.5) we will exploit the Ha line to study SFR distribution and gradients in the largest sample ever assembled. This study will shed light on the assembly of galaxies at cosmic noon, where the cosmic star formation was the highest and provide the crucial data to test “inside-out” scenarios of star-formation, whereby galaxies form the bulge first, and then grow disk structure. The student will be immediately inserted in a vibrant international environment, and join the PASSAGE team.

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The assembly of galaxy clusters through the cosmic time

Galaxy clusters are the largest known gravitationally bound structures in the Universe and contain up to thousands of galaxies. We currently have at least a broad-brush understanding of how local massive clusters affect their members, both via tidal and hydrodynamic processes. However, our knowledge is much more limited at higher redshift (z > 1-2), when structures are younger and still in formation and gas densities and star formation (SF) rates were much higher. Studies of the highest redshift progenitors of local clusters — called proto-clusters — are currently very sparse and limited. The goal of this project is to characterize the population of galaxies in protoclusters, either from a theoretical or observational point of view. 

Following a theoretical oriented approach, the PhD candidate will exploit the GAEA semi-analytic model to study the assembly of clusters through the cosmic time (from z=4 to 0), tackling the challenge of linking the high and low universe. The student will investigate the properties of galaxies in the different environments and at different epochs, to guide future observational requests. This analysis will be very important as it will assist the interpretation of observational results. From an observational point of view, the student will use archival and proprietary ALMA and JWST data to investigate the gas content and distribution, metallicity and star forming properties of galaxies in different environments.

By characterizing how star formation activity and mass assembly vary in different environments the student will be able to establish how environment primarily act when the Universe was a few billion years old. These results will pave the way to a physical understanding of how environment drives galaxy evolution in the early Universe.

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A few StePS forward in unveiling the complexity of galaxy evolution
One of the major goals of extragalactic astrophysics is to understand the physical processes that cause the formation and evolution of luminous structures. Recently, ground-breaking progress has been made in the low-redshift Universe in describing how the main galaxy properties vary with both galaxy mass and host halo mass. However, detailed observations of the evolutionary changes of galaxy properties as a function of look-back time are needed to establish which mechanisms dominate galaxy evolution, what drives the star formation history of galaxies and their mass assembly in the different environments. We propose a thesis to characterise in detail the stellar and gas content of galaxies at intermediate redshift in the different environments making use of the data of StePS, one of the eight surveys that will be carried out during the first five years of WEAVE operations. The main goals of the project are to understand 1) what physical mechanisms drive the star formation histories of galaxies and its quenching over two thirds of the life of the Universe? 2) what is the role of environment vs. intrinsic galaxy properties in this evolution? 3) how do galaxies assemble their mass during the last 7 Gyr?
The project will benefit from the high quality of StePS spectra that will allow to derive galaxy stellar ages, star-formation timescales, stellar and gas metallicities, and dust attenuation, and infer the past evolution of galaxies at different masses and redshift, relating their star formation histories to their intrinsic (e.g., stellar mass, galaxy morphology) and environmental properties. These spectra will also provide gas kinematics and stellar velocity dispersions, which will allow us to perform a dynamical classification of our galaxies and make a link between star formation history, mass assembly history and dynamics.
The student will be immediately inserted in a broad international context and will have the possibility to collaborate with other team members both in Italy and abroad.