Reconstructing the emergence of the Milky Way’s stellar population with Gaia, SDSS-V and JWST

Project Information

EMERGE

Grant agreement ID: 833031

DOI

10.3030/833031

EC signature date 15 April 2019

Start date 1 October 2019

End date 30 September 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 859 375,00

EU contribution

€ 1 859 375,00

Coordinated by

TEL AVIV UNIVERSITY
Israel

Periodic Reporting for period 4 - EMERGE (Reconstructing the emergence of the Milky Way’s stellar population with Gaia, SDSS-V and JWST)

Reporting period: 2024-04-01 to 2025-09-30

Summary of the context and overall objectives of the project

Supernovae (SNe) of all types play critical roles in numerous places in astrophysics: they are the main sources of most of the elements of the periodic table; the kinetic energy released in their explosions are central to the growth and evolution of galaxies; their remnants are the sites where cosmic rays are accelerated to huge energies. However,
our empirical understanding of these events is still quite limited. Little is known about the progenitor stars or stellar systems of the different types of supernovae, or about the distribution of delay times between formation of a stellar population and the explosion of some of its members as supernovae of different types. The detailed element yields of every type are also poorly known, as are the relative numbers and the importance of different SN stypes. A resulting problem is, apart from the fact that we are in the dark regarding all of these aspects of such an important univresal process, is that the other aforementioned processes (chemical evolution of galaxies via SN element production, cosmic ray production,etc.) remain poorly understood, and their modeling can only be based on highly uncertain theoretical constructs. The objective of my EMERGE project is, through astronomical observations and analysis, to put on an empirical basis, as many as possible of the above properties of SNe. This is becoming particularly feasible thanks to the data froma number of massive new observational projects, including Gaia, TESS, SDSS-V, and JWST. Specifically: I am measuring the demographics of binary populations in our Galaxy, from among which come the progenitor systems of many SN types; with mew measurements and analysis, I am refining measurements of the SN delay-time dsitribution; and I am analyzing large photometric and spectroscopic SN datasets to systematically determine the elemnt yields of the various SN types.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

1. The demographics of short-period binary populations: we analyzed the joint TESS-Gaia database to derive a sample of 15,000 short-period (P~1 day) binary star sytems, revealed via their mutual ellipsoidal tidal distortions. This full sample was incorporated as an Open-Fiber Target program in SDSS-V, and observations have begun. A publication analyzing the characteristics of the close-binary population in this uncharted territory was published in MNRAS (Green et al. 2023).

2. The separation and mass-ratio distribution of close double white dwarfs: We have obtained multi-epoch radial-velocity data for most of the double-white-dwarf (DWD) candidates (the favored SN Ia progenitors) that we previously found from the SDSS and SPY surveys, using a number of large telescopes (ESO-VLT, GTC, LBT, SALT). One system is a remarkable system consisting of a hot WD strongly irradiating a brown-dwarf companion. A paper analyzing this system was published in Nature Astronomy (Hallakoun et al. 2023).

3. The delay-time distribution of supernovae in galaxy-cluster environments: we re-analyzed Hubble Space Telescope data on supernovae in galaxy clusters, taking into account the star-formation present in clusters that are observed at high redshift. We have derived the Type Ia SN (SN Ia) delay-time distribution, and confirmed the puzzling high efficiency of SN Ia production in clusters compared to field-galaxy environments. A paper with the results was published in MNRAS (Freundlich and Maoz 2021). My planned proposal to discover SNe in clusters at even higher redshifts with JWST was submitted in January and October 2023, but were unsuccessful. I will resubmit in upcoming cycles.

4. The SN Ia DTD from IFU data in nearby galaxies: We have collected several available codes for reconstruction of stellar populations from optical spectra, and performed tests and simulations to evaluate and compare their performance, systematics and problems, toward applying the codes to several large integral-field spectroscopy datasets for nearby galaxies that have hosted SNe, to determine the DTD based on spatially resolved stellar populations. However, this specific program has not succeeded to date and I am seeking alternative paths.

5. The element yields of different SN types: We have systematically analyzed light curves and spectra for hundreds of SNe, developing new physical tools to determine reliably their element yields. A paper determining the distribution of iron yields of Type-II SNe was published in MNRAS (Rodriguez et al. 2021).
A paper on the iron yields of stripped-envelope SNe was published in ApJ (Rodriguez et al. 2023). A follow-up paper on the energetics of stripped-envelope SNe was published in Nature (Rodriguez et al. 2024). A paper on r-process-element from neutron-star mergers has been submitted to ApJ (Maoz and Nakar 2024). We continue work using nebular-phase spectra of all types of SNe to determine empirical yields of additional elements.

6. The initial mass functions of different stellar populations: we used Gaia data to discover that the so-called "blue-halo" population of Milky Way stars, has a peculiar "bottom-heavy" initial mass function (IMF), similar to that in the massive elliptical galaxies in clusters. Published in MNRAS (Hallakoun and Maoz 2021).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The above results constitute progress toward the stated objective of placing the properties of SNe and their progenitors on an empirical and physical footing. By the end of the project I expect that we will have a much clearer picture than today on the close-binary population, based on the ellipsoidal TESS sample that we published and its further observations with SDSS-V, but also from additional binary samples. We will complete the RV analysis of the DWD data, which will provide the first characterization of this population and a critical test of its viability as the progenitors of SNe Ia. My next attempted JWST proposal to discover and measure the rates of supernovae in protoclusters at redshifts 2-4 will hopefully be accepted, and that program can then progress. I plan to adapt the originally foreseen analysis of the DTD based on resolved stellar populations in nearby galaxies to a new, better, dataset, based on data obtained in SDSS-V: spectra at the host locations of all known nearby supernovae to date. The current analysis of nebular-phase SN spectra will hopefully lead to the fullest possible empirical inventory of SN element yields.

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