Author: Raffaella Schneider

Posted on

Available Thesis: High-z black hole populations with enhanced CAT

Supervisor: Raffaella Schneider
co-supervisors: Rosa Valiante, Tommaso Zana

Fig: Relation between the bolometric luminosity (Lbol) and BH mass (Mbh) predicted by Schneider+(2023) at 5 < z <11 using CAT (yellow, cyan and violet dots). The upper row shows the results of the Eddington-limited model (EL), and the bottom row the results for the super-Eddington model (SE). The diagonal dashed lines are reference values of 𝜆Edd = 𝐿bol/𝐿Edd = 0.01, 0.1, 1, and 10, and the vertical grey lines mark the initial heavy BH seed mass adopted in CAT (105 Msun). Starred data points show the luminosities and BH masses identified in JWST surveys. The properties of some of the observed systems at 𝑧 ∼ 5 are consistent with predictions of the EL model, but the luminosity and BH masses of the remaining systems at 𝑧 ∼ 5 and of most of the systems at 𝑧 ≳ 7 are better reproduced in the SE model.

A big question that remains unsolved pertains to the existence of hundreds of quasars at 6 ≤ z ≤ 7.64, which show that 10^9 − 10^10 Msun super massive black holes (SMBHs) can form in ∟ 700 Myr, by efficiently growing mass onto smaller black hole (BH) seeds (see Volonteri+2021; Inayoshi+2020). During the past year the advent of JWST has started to revolutionize this field: several tens of candidate Active Galactic Nuclei (AGNs) at z > 3 have been revealed by deep near-IR photometry, and dozens of AGNs have been identified via their broad emission lines, or as counterparts of X−ray sources. The general common features of these newly discovered AGNs are that these are orders of magnitudes fainter and lighter than quasars, with bolometric luminosities of Lbol ≈ 10^(43.5 – 46) erg/s and black hole masses Mbh ≈ 10^(5.3 – 8) Msun, with the lightest ones that border the mass range for the formation of heavy BH seeds. Intriguingly, the majority of these newly discovered accreting BHs appear to be over-massive compared to the stellar mass of their host galaxies, relative to local MBH − M⋆ relation. We used CAT to test various BH mass growth scenarios against new JWST observations (Schneider+23, see Figure). Our findings suggest that AGNs with properties similar to those observed with JWST can be explained by scenarios where BHs originate from Eddington-limited gas accretion onto heavy BH seeds, or through phases of super-Eddington accretion (Pezzulli+2016, Trinca+2022). However, our understanding of the conditions enabling super-Eddington growth is still limited. We aim to assess the conditions that allow for super-Eddington accretion of BH seeds, its duration, and the feedback it exerts on the host galaxy. High-resolution hydrodynamical simulations will be conducted, focusing on an isolated galaxy circumnuclear disk using the GIZMO code, where a novel BH accretion and momentum-driven feedback model has been recently implemented (Sala+21), which self-consistently account for the evolution of BH mass and spin (Cenci+21). This version will be accessible to our team through an established collaboration with the Institute for Computational Science at the University of Zurich (Pedro Capelo; Lucio Mayer). The results will be used to develop a simulation-informed analytic model to be integrated into CAT.

References:

Cenci+21, MNRAS, 500, 3719
Inayoshi+20, ARA&A, 58, 27
Pezzulli+16, MNRAS,458, 3087
Sala+21, MNRAS, 500, 4788
Schneider+23, MNRAS, 526, 3250
Trinca+22, MNRAS, 511, 616
Volonteri+21, Nat Rev Phys, 3, 732

Posted on

[NEW] Program: “Cosmic Origins: The First Billion Years” – Santa Barbara, California, USA, Jul 30, 2024 – Sep 20, 2024

https://www.kitp.ucsb.edu/activities/firstbillion24

We are witnessing an exciting revolution in our understanding of the first billion years of cosmic history. The launch of the JWST has enabled the discovery of galaxies in the first few hundred million years, and their detailed characterization in terms of chemical enrichment, stellar populations, nuclear black hole properties, morphologies, and environment is ongoing. In addition to these stunning discoveries, there have also been recent probes of the dust content of galaxies in the first billion years with ALMA, and robust theoretical predictions are also essential for interpreting future observations with ELTs and “deep-wide field” observations with the Nancy Grace Roman telescope. At the same time, GAIA and SDSS-V are probing the chemical abundances of individual stars in our own Galaxy and in nearby galaxies, which provide complementary “fossil evidence” on the properties of the first stars and how early galaxies were enriched with the heavy elements that eventually made life on Earth possible. This wealth of data has the potential to paint a picture of unprecedented clarity and detail of the first billion years of cosmic evolution — provided we have robust and detailed theoretical models with which to interpret and stitch them together. The goal of this program is to provide a unique forum for theorists and observers specializing in different subfields to interact intensively with each other developing links between several synergistic areas, including star formation, stellar evolution, chemistry, radiation, gas physics, and cosmology.

Associated KITP Conference: Cosmic Dawn Revealed by JWST: The Physics of the First Stars, Galaxies, and Black Holes

Posted on

Available Thesis: Imprints of a non-universal stellar IMF on the physics of early galaxies

Supervisor: Raffaella Schneider
co-supervisors: Rosa Valiante, Luca Graziani

Fig: Metallicity and redshift dependence of the stellar initial mass function. The panels show high-resolution simulations by Chon, Omukai & RS (2021) of a turbulent star forming cloud with different initial metallicities. Each panel shows a face-on view of the gas density in the star forming disk at the end of the simulation, with yellow asterisks and white dots representing individual stars with masses larger than and smaller than 1 Msun, respectively. It is clear that the number of low-mass stars rapidly increases with metallicity.

Chemical enrichment plays a crucial role in the thermal evolution of star-forming gas clouds. The metal abundance, both in the gas phase and in dust grains, is believed to be a key factor in the transition from a top-heavy Pop III IMF to a Kroupa-like Pop II/I IMF, occurring above a critical metallicity of Zcr=10^(-4Âą1) Zsun (Schneider+03; Omukai+05; Schneider+06; Schneider+12). Using high-resolution hydrodynamical simulations, we have recently shown that a more gradual transition in the stellar IMF occurs, with a larger fraction of massive stars persisting up to Z ≈ 10^(-2) Zsun (Chon+21). Moreover, the higher temperature of the CMB radiation at z ≥ 10 suppresses cloud fragmentation and reduces the number of low-mass stars in star forming regions with metallicities Z ≥ 10^(-2) Zsun (Schneider+10, Chon+22). As a result, we expect stellar populations with Z ≤ 10^(-2) Zsun or forming at z ≥ 10 to exhibit a mass spectrum consisting of a low-mass Kroupa-like component peaking at m∗ ≈ 0.1 Msun and a top-heavy component peaking at m∗ ≈ 10 Msun, with the mass fraction in the latter increasing with redshift and decreasing with metallicity. A non-universal IMF that depends on metallicity and redshift has far reaching implications for the evolution of the first galaxies. A top-heavy IMF has been recently advocated as a possible explanation for the number density of UV bright galaxies detected by JWST and its apparent lack of evolution between z ≈ 9 and z ≈ 13 – 17 (Trinca+23b), which are in tension with standard model predictions. At z > 10, spectroscopically confirmed galaxies are found to host ≈ 10^(7.2) – 10^9 Msun in stars, with stellar populations having formed half of their mass on timescales 16 – 70 Myr, and sub-solar metallicity (< 0.1 – 0.6 Zsun). As such, these galaxies are massive stars-dominated systems, and are therefore very sensitive to the shape of the high-mass end of the stellar IMF. In addition, stellar winds are believed to be weak at low metallicity, providing less kinetic energy

input to stellar environments. Metallicity also affects the stellar progenitor mass above which massive stars fail to explode and quietly collapse to BHs, with important implications for the timescales on which mechanical feedback due to supernova explosions operate. In this thesis project, we propose to investigate the implications of a non-Universal IMF on the physics of the first galaxies, implementing a parametric form of the IMF in the semi-analytical model CAT (Cosmic Archaeology Tool, Trinca+22). The project foresees comparison with JWST spectroscopic and photometric observations in collaboration with observers at the INAF/OAR.

References:

Chon+21  MNRAS, 508, 4175
Chon+22 MNRAS, 514, 4639
Omukai+05, ApJ, 626, 627
Schneider+03,  Nature, 422, 869
Schneider+06 MNRAS, 369, 1437
Schneider+10 MNRAS, 402, 429
Schneider+12 MNRAS, 419, 1566
Trinca+22  MNRAS, 511, 616
Trinca+23b arxiv:2305.04944

Posted on

“L’Universo invisibile svelato dal Telescopio Spaziale James Webb” – Conferenza pubblica di Roberto Maiolino – 29 Febbraio 2024 h.18:00 – Dipartimento di Fisica La Sapienza

https://www.phys.uniroma1.it/fisica/archivionotizie/le-scoperte-del-telescopio-spaziale-james-webb-alla-sapienza

Lingua: ITALIANO

Il 29 febbraio 2024, alle 18.00, il Prof. Roberto Maiolino dell’Università di Cambridge (Regno Unito) terrà una conferenza pubblica sul tema “L’Universo invisibile svelato dal Telescopio Spaziale James Webb” presso il Dipartimento di Fisica della Sapienza Università di Roma.

Il James Webb Space Telescope (JWST) è il piĂš grande telescopio spaziale mai costruito. Questa fenomenale macchina del tempo è capace di fotografare le prime stelle, i primi buchi neri e le prime galassie che si sono formate poco dopo il Big Bang e di studiare le atmosfere dei pianeti extrasolari, andando alla ricerca di quelli piĂš simili alla nostra Terra. Roberto Maiolino, parte del team di scienziati che ha seguito il progetto fin dall’inizio, racconterĂ  le complessitĂ  di questo straordinario telescopio e svelerĂ  i misteri che si celano dietro le sue immagini.

La conferenza è aperta alla cittadinanza e si terrà presso l’Aula Amaldi, Edificio Marconi del Dipartimento di Fisica della Sapienza Università di Roma. Sarà moderata dal Dr. Massimo Stiavelli, che dal 2012 guida il mission office di JWST presso lo Space Telescope Science Institute di Baltimora, negli Stati Uniti.

L’evento è organizzato in collaborazione tra la Pontificia Accademia delle Scienze e Sapienza Università di Roma. Fa parte del programma di public engagement del workshop “Astrophysics: The James Webb Space Telescope. From first light to new world views”, che riunisce ricercatrici e ricercatori da tutto il mondo presso la Pontificia Accademia delle Scienze tra il 27 e il 29 febbraio, per discutere dei primi, rivoluzionari risultati scientifici del potente osservatorio spaziale.

Il James Webb Space Telescope, lanciato il 25 dicembre 2021, è una collaborazione internazionale tra la NASA, l’Agenzia Spaziale Europea e l’Agenzia Spaziale Canadese. 

Per ulteriori informazioni:

Visita il sito web del Dipartimento di Fisica, Sapienza UniversitĂ  di Roma:
https://www.phys.uniroma1.it/fisica/ 

Leggi il programma del workshop “Astrophysics: The James Webb Space Telescope. From first light to new world views” sul sito della Pontificia Accademia delle Scienze:
https://www.pas.va/en/events/2024/astrophysics.html

Posted on

[NEW] NEW STRATEGIES FOR EXTRACTING COSMOLOGY FROM GALAXY SURVEYS – 2ND EDITION – Sexten, Italy, July 1-5, 2024

https://www.sexten-cfa.eu/event/new-strategies-for-extracting-cosmology-from-galaxy-surveys/

The next generation of large-scale structure surveys such as Euclid, DESI, LSST, SPHEREx, and SKA is going to provide an unprecedented amount of observational data. These surveys will map large portions of the sky, observing hundreds of millions of bright galaxies up to high redshifts, effectively transforming cosmology into a data-driven, precision science. It is more and more important to develop the right techniques to efficiently extract information from this data. The large number of ongoing efforts reach from new summary statistics for efficient data compression to full forward models for field level analysis and use an expanded range of statistical techniques. For any of these, blind mock data challenges are an important tool to demonstrate the unbiased inference of cosmological parameters, where complications can arise from uncertainties about non-linear galaxy formation as well as observational systematics. This is the second workshop with the aim to gather a broad range of proposed (new and established) methods for the data analysis of next-generation surveys. It will also offer a platform to discuss those methods in the light of ongoing data challenges and to plan future ones. The goal is to share expertise between groups and to identify common obstacles and solutions for establishing an end-to-end pipeline that can be applied to real data.

Posted on

[NEW] EAS Symposium S1: “Unveiling Black Hole Growth across Cosmic Time in the JWST and LISA era” – European Astronomical Society (EAS), Padova, Italy, July 1-5, 2024

https://eas.unige.ch/EAS2024/session.jsp?id=S1

Over the past two decades, observations have established samples of hundreds of luminous quasars, powered by accretion onto massive black holes, in the first billion years of the Universe. The James Webb Space Telescope (JWST) has significantly revised this sample by yielding unexpectedly numerous black holes with masses in the range of a few to a hundred million solar masses, within the first few hundred million years after the Big Bang, posing enormous challenges for black hole and galaxy formation models. On the other side of the redshift ladder, in the nearby Universe, JWST and ALMA are revealing the complex interplay of black hole accretion with their circumnuclear and galactic environment. Additionally, current and upcoming novel observations of stars torn apart by black holes? tides (a.k.a. Tidal Disruption Events, TDEs) by ZTF (Zwicky Transient Factory), the VRO/LSST and ULTRASAT hold promise to shedding light on the formation of massive black holes by uniquely expanding our knowledge of the scarcely populated low-mass end (less than one million solar masses) of the black hole mass function. Finally, massive black hole binaries (MBHBs) are sources of the gravitational waves (GWs) and naturally explain the stochastic GW background recently discovered by Pulsar Timing Arrays (PTAs). They will be detected by the Laser Interferometer Space Antenna (LISA) over the next decades, promising to directly reveal massive black holes with masses between 10 thousand and 10 million solar masses, virtually anywhere in the Universe.

Straddling the fields of cosmology, galaxy formation and black hole astrophysics, our symposium aims at bringing together communities working on different tracers of massive black hole formation and evolution, such as AGN, TDEs and MBHBs, both from the theoretical and observational standpoint, exploring and discussing constraints both in the local and distant Universe. The goals of the symposium are to discuss i) how the most recent observations can help establish a coherent picture of early black hole formation and their evolution through cosmic time, assess ii) what big and/or new questions remain open, and iii) how to address them with a combination of new theoretical developments and upcoming data.

By reviewing and discussing the most recent observational results, theoretical models and simulations, the symposium will provide a global perspective of how black hole formation, feeding and feedback happen in galaxies across cosmic time.

Image copyright: European Space Agency – ESA.

Posted on

[NEW] Massive Black Holes in the First Billion Years – Cork, Ireland / 29 April – 3 May, 2024

https://www.ucc.ie/en/physics/mbhconference/

We are on the cusp of significant advancements to our understanding of the origins and early growth of massive black holes with current and near-future electromagnetic observations by JWST and other upcoming missions which will be complemented by gravitational wave detections with LISA in the coming decade. The focus of this conference is on recent advancements in both observations and theory on the origin, growth and dynamics of MBHs in the early Universe.  Follow the pre-registration link above to let us know you are interested and you will receive an email when abstract submission is open!

Topics of interest:

  • Observations and predicted properties of AGN and their hosts at early times
  • Constraining MBH formation mechanisms with multimessenger observations at low and high redshift
  • Predictions for MBH seed masses from low redshift observations of dwarf galaxies
  • Challenges (both theoretical and observational) to observing and interpreting data on early MBHs
  • MBH-galaxy co-evolution and feedback in the early universe
  • Dynamics of MBHs and MBH binaries in the early Universe
  • How can we connect current and near-future E-M observations to future GW detections to do astrophysics?
  • Understanding the environment of high redshift MBHs and AGN and how it affects their early evolution
Posted on

EAS Symposium S12: “Breaking down the AGN frontiers: light and sound from early black holes” – European Astronomical Society (EAS), KrakĂłw, Poland, July 10-14, 2023

https://eas.unige.ch/EAS_meeting/session.jsp?id=S3

To date we have discovered more than 200 quasars at z>6 powered by accreting black holes with masses up to 109 – 1010 M⊙. The physical mechanisms driving/regulating their formation and evolution are among the most debated issues in Astrophysics.

With the first load of data incoming from JWST (with most Cycle 1 programs likely executed) and in view of the future campaigns/missions like Athena, LISA, ET, it is urgent to set the stage for interpreting observational information, refine/develp models, tools as well as selection strategies.

In this Symposium we will discuss the most recent advances in theoretical and observational studies of supermassive black holes at the reionization epoch as well as the cosmic evolution of the seeds out of which they form. In detail, we will review the state of the art of:

1. theoretical studies for the formation and growth of early black holes (from the seeds to the supermassive) including black hole dynamics, comparing the results of different approaches (e.g. analytical models and numerical/hydro simulations). We foresee to foster discussion on the relevant processes operating on different scales and in different physical regimes relevant to black holes.

2. observational campaigns devoted to study both high-z quasars and seed black hole relics in the local Universe with the aim of i) characterizing the population of (rare) titans at the reionization epoch and their less luminous counterparts (fainter AGN) and i) to build ?complete? mass/luminosity functions across cosmic epochs.

3. development of observational, multi-wavelength/messenger strategies to detect signatures of accreting and merging black holes.

The final goal of the meeting is to discuss ongoing and future projects, foster and consolidate collaborations within the scientific community.

Posted on

Reionization with galaxies and active galactic nuclei

In this work we investigate the properties of the sources that reionized the intergalactic medium (IGM) in the high-redshift Universe. Using a semi-analytical model aimed at reproducing galaxies and black holes in the first ∼1.5 Gyr of the Universe, we revisit the relative role of star formation and black hole accretion in producing ionizing photons that can escape into the IGM. Both star formation and black hole accretion are regulated by supernova feedback, resulting in black hole accretion being stunted in low-mass haloes. We explore a wide range of combinations for the escape fraction of ionizing photons (redshift-dependent, constant, and scaling with stellar mass) from both star formation ( ⟨fsfesc⟩ ) and AGN ( fbhesc ) to find: (I) the ionizing budget is dominated by stellar radiation from low stellar mass ( M∗<10^9M⊙ ) galaxies at z > 6 with the AGN contribution (driven by Mbh>10^6M⊙ black holes in M∗≳10^9M⊙ galaxies) dominating at lower redshifts; (II) AGN only contribute 10−25 per cent to the cumulative ionizing emissivity by z = 4 for the models that match the observed reionization constraints; (III) if the stellar mass dependence of ⟨fsfesc⟩ is shallower than fbhesc , at z < 7 a transition stellar mass exists above which AGN dominate the escaping ionizing photon production rate; (IV) the transition stellar mass decreases with decreasing redshift. While AGN dominate the escaping emissivity above the knee of the stellar mass function at z ∼ 6.8, they take-over at stellar masses that are a tenth of the knee mass by z = 4.

https://ui.adsabs.harvard.edu/abs/2020MNRAS.495.3065D/abstract

Posted on

Unveiling early black hole growth with multifrequency gravitational wave observations

Third-generation ground-based gravitational wave interferometers, like the Einstein Telescope (ET), Cosmic Explorer, and the Laser Interferometer Space Antenna (LISA), will detect coalescing binary black holes over a wide mass spectrum and across all cosmic epochs. We track the cosmological growth of the earliest light and heavy seeds that swiftly transit into the supermassive domain using a semi-analytical model for the formation of quasars at z = 6.4, 2, and 0.2, in which we follow black hole coalescences driven by triple interactions. We find that light-seed binaries of several 102M⊙ are accessible to ET with a signal-to-noise ratio (S/N) of 10-20 at 6 < z < 15. They then enter the LISA domain with larger S/N as they grow to a few 10^4M⊙ . Detecting their gravitational signal would provide first time evidence that light seeds form, grow, and dynamically pair during galaxy mergers. The electromagnetic emission of accreting black holes of similar mass and redshift is too faint to be detected even for the deepest future facilities. ET will be our only chance to discover light seeds forming at cosmic dawn. At 2 < z < 8, we predict a population of ‘starved binaries’, long-lived marginally growing light-seed pairs, to be loud sources in the ET bandwidth (S/N > 20). Mergers involving heavy seeds ( ∟10^5−10^6M⊙ ) would be within reach up to z = 20 in the LISA frequency domain. The lower z model predicts 11.25 (18.7) ET (LISA) events per year, overall.

https://ui.adsabs.harvard.edu/abs/2021MNRAS.500.4095V/abstract