Modelling black hole accretion through an 𝛼-disc with a resolved interstellar medium in dwarf galaxies
We perform high-resolution simulations of an isolated dwarf galaxy with a virial mass of 1e10 Msun harbouring a 1e4 Msun intermediate mass black hole (IMBH) embedded in a nuclear star cluster (NSC) at its centre. To model a realistic interstellar medium (ISM), we incorporate IMF -sampled star formation, photo-ionisation feedback, H_II region modelling, photoelectric heating from a spatially varying far-ultraviolet field, and supernova feedback. Our approach employs a sub-grid Shakura-Sunyaev accretion disc model to accurately simulate the evolution of BH mass and spin. Using super-Lagrangian refinement techniques, we resolve spatial scales up to 0.01 pc, capturing the self-gravitating radius of the accretion disc, allowing accurate measurement of mass and angular momentum transfer to the IMBH . The gravitational potential of the NSC captures the ISM , forming a circumnuclear disc (CND), while its torques drive angular momentum loss from parsec to sub-parsec scales, circularising gas onto the 𝛼-accretion disc and fuelling IMBH accretion. We further investigate star formation in the vicinity of the IMBH . In the innermost regions, within 0.2 pc, star formation is highly suppressed. However, at distances of approximately 1 to 7 pc from the centre, the gas remains locally susceptible to fragmentation, leading to the formation of massive, young stars. The feedback from these stars can potentially disrupt the CND entirely and cut off the gas supply to the IMBH . Our study demonstrates the complexity of IMBH accretion once the resolved ISM is taken into account and paves the way for next-generation studies incorporating IMBH -driven feedback processes.
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Cygnus X-3 in 2024: many giant radio flares!
Cygnus X-3 is a `high mass X-ray binary’, which was first detected in the early days of X-ray astronomy, in 1966. It is also seen in the radio and the infra-red (but not optically due to obscuration). The emission is
due to accretion from the companion star onto the compact source, thought to be a Wolf-Rayet star and a black hole respectively. It occasionally shows giant fares, and has been monitored—approximately daily—for several years with the Arcminute Microkelvin Image (AMI) at Lord’s Bridge, SW of Cambridge. During 2022 and 2023 was placid, with little variation in its radio (or X-ray) emission, but in 2024 it showed five giant radio flares, brightening from a few mJy to > 10 Jy over a few days.
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arXiv:2502.07872v1 Announce Type: new
Abstract: Recent detections of carbon-bearing molecules in the atmosphere of a candidate Hycean world, K2-18 b, with JWST are opening the prospects for characterising potential biospheres on temperate exoplanets. Hycean worlds are a recently theorised class of habitable exoplanets with ocean covered surfaces and hydrogen-rich atmospheres. Hycean planets are thought to be conducive for hosting microbial life under conditions similar to those in the Earth's oceans. In the present work we investigate the potential for biological evolution on Hycean worlds and their dependence on the thermodynamic conditions. We find that a large range of evolutionary rates and origination times are possible for unicellular life in oceanic environments for a relatively marginal range in environmental conditions. For example, a relatively small (10 K) increase in the average ocean temperature can lead to over twice the evolutionary rates, with key unicellular groups originating as early as $\sim$1.3 billion years from origin of life. On the contrary, similar decreases in temperatures can also significantly delay the origination times by several billion years. This delay in turn could affect their observable biomarkers such as dimethylsulfide, which is known to be produced predominantly by Eukaryotic marine phytoplankton in Earth's oceans. Therefore, Hycean worlds that are significantly cooler than Earth may be expected to host simpler microbial life than Earth's oceans and may show weaker biosignatures, unless they orbit significantly older stars than the Sun. Conversely, Hycean worlds with warmer surface temperatures than Earth are more likely to show stronger atmospheric biosignatures due to microbial life if present.
arXiv:2502.07872v1 Announce Type: new
Abstract: Recent detections of carbon-bearing molecules in the atmosphere of a candidate Hycean world, K2-18 b, with JWST are opening the prospects for characterising potential biospheres on temperate exoplanets. Hycean worlds are a recently theorised class of habitable exoplanets with ocean covered surfaces and hydrogen-rich atmospheres. Hycean planets are thought to be conducive for hosting microbial life under conditions similar to those in the Earth's oceans. In the present work we investigate the potential for biological evolution on Hycean worlds and their dependence on the thermodynamic conditions. We find that a large range of evolutionary rates and origination times are possible for unicellular life in oceanic environments for a relatively marginal range in environmental conditions. For example, a relatively small (10 K) increase in the average ocean temperature can lead to over twice the evolutionary rates, with key unicellular groups originating as early as $\sim$1.3 billion years from origin of life. On the contrary, similar decreases in temperatures can also significantly delay the origination times by several billion years. This delay in turn could affect their observable biomarkers such as dimethylsulfide, which is known to be produced predominantly by Eukaryotic marine phytoplankton in Earth's oceans. Therefore, Hycean worlds that are significantly cooler than Earth may be expected to host simpler microbial life than Earth's oceans and may show weaker biosignatures, unless they orbit significantly older stars than the Sun. Conversely, Hycean worlds with warmer surface temperatures than Earth are more likely to show stronger atmospheric biosignatures due to microbial life if present.
arXiv:2502.07887v1 Announce Type: new
Abstract: Studying the composition of exoplanets is one of the most promising approaches to observationally constrain planet formation and evolution processes. However, this endeavour is complicated for small exoplanets by the fact that a wide range of compositions is compatible with their bulk properties. To overcome this issue, we identify triangular regions in the mass-radius space where part of this degeneracy is lifted for close-in planets, since low-mass H/He envelopes would not be stable due to high-energy stellar irradiation. Planets in these Hot Water World triangles need to contain at least some heavier volatiles and are therefore interesting targets for atmospheric follow-up observations. We perform a demographic study to show that only few well-characterised planets in these regions are currently known and introduce our CHEOPS GTO programme aimed at identifying more of these potential hot water worlds. Here, we present CHEOPS observations for the first two targets of our programme, TOI-238 b and TOI-1685 b. Combined with TESS photometry and published RVs, we use the precise radii and masses of both planets to study their location relative to the corresponding Hot Water World triangles, perform an interior structure analysis and study the lifetimes of H/He and water-dominated atmospheres under these conditions. We find that TOI-238 b lies, at the 1-sigma level, inside the corresponding triangle. While a pure H/He atmosphere would have evaporated after 0.4-1.3 Myr, it is likely that a water-dominated atmosphere would have survived until the current age of the system, which makes TOI-238 b a promising hot water world candidate. Conversely, TOI-1685 b lies below the mass-radius model for a pure silicate planet, meaning that even though a water-dominated atmosphere would be compatible both with our internal structure and evaporation analysis, we cannot rule out the planet to be a bare core.
arXiv:2502.07887v1 Announce Type: new
Abstract: Studying the composition of exoplanets is one of the most promising approaches to observationally constrain planet formation and evolution processes. However, this endeavour is complicated for small exoplanets by the fact that a wide range of compositions is compatible with their bulk properties. To overcome this issue, we identify triangular regions in the mass-radius space where part of this degeneracy is lifted for close-in planets, since low-mass H/He envelopes would not be stable due to high-energy stellar irradiation. Planets in these Hot Water World triangles need to contain at least some heavier volatiles and are therefore interesting targets for atmospheric follow-up observations. We perform a demographic study to show that only few well-characterised planets in these regions are currently known and introduce our CHEOPS GTO programme aimed at identifying more of these potential hot water worlds. Here, we present CHEOPS observations for the first two targets of our programme, TOI-238 b and TOI-1685 b. Combined with TESS photometry and published RVs, we use the precise radii and masses of both planets to study their location relative to the corresponding Hot Water World triangles, perform an interior structure analysis and study the lifetimes of H/He and water-dominated atmospheres under these conditions. We find that TOI-238 b lies, at the 1-sigma level, inside the corresponding triangle. While a pure H/He atmosphere would have evaporated after 0.4-1.3 Myr, it is likely that a water-dominated atmosphere would have survived until the current age of the system, which makes TOI-238 b a promising hot water world candidate. Conversely, TOI-1685 b lies below the mass-radius model for a pure silicate planet, meaning that even though a water-dominated atmosphere would be compatible both with our internal structure and evaporation analysis, we cannot rule out the planet to be a bare core.
arXiv:2502.08584v1 Announce Type: new
Abstract: Debris disks common around Sun-like stars carry dynamical imprints in their structure that are key to understanding the formation and evolution history of planetary systems. In this paper, we extend an algorithm (rave) originally developed to model edge-on disks to be applicable to disks at all inclinations. The updated algorithm allows for non-parametric recovery of the underlying (i.e., deconvolved) radial profile and vertical height of optically thin, axisymmetric disks imaged in either thermal emission or scattered light. Application to simulated images demonstrates that the de-projection and deconvolution performance allows for accurate recovery of features comparable to or larger than the beam or PSF size, with realistic uncertainties that are independent of model assumptions. We apply our method to recover the radial profile and vertical height of a sample of 18 inclined debris disks observed with ALMA. Our recovered structures largely agree with those fitted with an alternative visibility-space de-projection and deconvolution method (frank). We find that for disks in the sample with a well-defined main belt, the belt radius, fractional width and fractional outer edge width all tend to increase with age, but do not correlate in a clear or monotonic way with dust mass or stellar temperature. In contrast, the scale height aspect ratio does not strongly correlate with age, but broadly increases with stellar temperature. These trends could reflect a combination of intrinsic collisional evolution in the disk and the interaction of perturbing planets with the disk's own gravity.
arXiv:2502.08584v1 Announce Type: new
Abstract: Debris disks common around Sun-like stars carry dynamical imprints in their structure that are key to understanding the formation and evolution history of planetary systems. In this paper, we extend an algorithm (rave) originally developed to model edge-on disks to be applicable to disks at all inclinations. The updated algorithm allows for non-parametric recovery of the underlying (i.e., deconvolved) radial profile and vertical height of optically thin, axisymmetric disks imaged in either thermal emission or scattered light. Application to simulated images demonstrates that the de-projection and deconvolution performance allows for accurate recovery of features comparable to or larger than the beam or PSF size, with realistic uncertainties that are independent of model assumptions. We apply our method to recover the radial profile and vertical height of a sample of 18 inclined debris disks observed with ALMA. Our recovered structures largely agree with those fitted with an alternative visibility-space de-projection and deconvolution method (frank). We find that for disks in the sample with a well-defined main belt, the belt radius, fractional width and fractional outer edge width all tend to increase with age, but do not correlate in a clear or monotonic way with dust mass or stellar temperature. In contrast, the scale height aspect ratio does not strongly correlate with age, but broadly increases with stellar temperature. These trends could reflect a combination of intrinsic collisional evolution in the disk and the interaction of perturbing planets with the disk's own gravity.
Probing the early history of the Milky Way through ancient carbon-rich stars
The oldest, most metal-poor stars we find in the Milky Way today were born in pristine environments in the early Universe. These local, ancient stars contain unique clues about the First Stars and the early formation and evolution of our Galaxy. At low metallicity, many stars have been found to be enhanced in carbon, coming in two main types: some contain the fingerprints of the First Stars and others have experienced binary interaction with an evolved companion. I recently built a homogeneous sample of C-rich metal-poor stars using the Gaia XP spectra, employing a neural network and a dedicated training sample. I will present this recent paper and discuss how the change in frequency of C-rich stars with Galactic environment relates to globular clusters and clustered star formation in the early Universe.
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Statistical aspects in the determination of the proton's structure
The interpretation of the high energy physics data taken at the Large Hadron Collider (LHC), and the assessment of possible hints of physics beyond the Standard Model (SM) of particle physics, require the precise knowledge of the proton structure in terms of a set of functions parametrizing its content in terms of its elementary constituents, quarks and gluons. These functions are known as Parton Distribution Functions (PDFs). In this talk I will illustrate the statistical aspects involved in the solution of the inverse problem of determining PDFs from the LHC data, and how machine learning combined with Bayesian sampling techniques can be applied to obtain a faithful and robust determination of such functions.
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arXiv:2502.05406v1 Announce Type: new
Abstract: The filamentary nebula encompassing the central galaxy of the Perseus Cluster, NGC 1275, is a complex structure extending dozens of kiloparsecs from NGC 1275. Decades of previous works have focused on establishing the primary formation and ionization mechanisms in different filaments. These studies have pointed to a lack of star formation in the majority of the filaments, the importance of magnetic fields and turbulence in several regions, and the role of interactions between the intercluster medium (ICM) and the cool gas in the filaments, as well as the role of interaction between the central radio source, 3C84, and the filaments. In this paper, we present multi-filter observations of the entire filamentary system that cover the optical bandpass, using the SITELLE instrument at the Canada-France-Hawai'i Telescope. Here, we use the data analysis software, \href{https://crhea93.github.io/LUCI/index.html}{\texttt{LUCI}}, to produce flux maps of the prominent emission lines present in the filters: \oii{}$\lambda$3726/3729, \oiii{}$\lambda$5007, H$\beta$, \nii{}$\lambda$6548, \nii{}$\lambda$6583, and H$\alpha$. We use these maps to produce BPT and WHAN diagrams to study the ionization mechanisms at play in each distinct region of the filamentary nebula. First, we confirm the absence of \oiii{}$\lambda$5007 in the extended filaments, although we detect this line in the central core, revealing a compact region where photoionization by the AGN might affect local conditions. Our findings corroborate previous claims that the ionization in the extended filaments could be caused by the cooling ICM via collisional excitation and/or mixing. Moreover, they support the conclusion that magnetic fields play an important role in the formation and continued existence of the filaments.
arXiv:2502.05406v1 Announce Type: new
Abstract: The filamentary nebula encompassing the central galaxy of the Perseus Cluster, NGC 1275, is a complex structure extending dozens of kiloparsecs from NGC 1275. Decades of previous works have focused on establishing the primary formation and ionization mechanisms in different filaments. These studies have pointed to a lack of star formation in the majority of the filaments, the importance of magnetic fields and turbulence in several regions, and the role of interactions between the intercluster medium (ICM) and the cool gas in the filaments, as well as the role of interaction between the central radio source, 3C84, and the filaments. In this paper, we present multi-filter observations of the entire filamentary system that cover the optical bandpass, using the SITELLE instrument at the Canada-France-Hawai'i Telescope. Here, we use the data analysis software, \href{https://crhea93.github.io/LUCI/index.html}{\texttt{LUCI}}, to produce flux maps of the prominent emission lines present in the filters: \oii{}$\lambda$3726/3729, \oiii{}$\lambda$5007, H$\beta$, \nii{}$\lambda$6548, \nii{}$\lambda$6583, and H$\alpha$. We use these maps to produce BPT and WHAN diagrams to study the ionization mechanisms at play in each distinct region of the filamentary nebula. First, we confirm the absence of \oiii{}$\lambda$5007 in the extended filaments, although we detect this line in the central core, revealing a compact region where photoionization by the AGN might affect local conditions. Our findings corroborate previous claims that the ionization in the extended filaments could be caused by the cooling ICM via collisional excitation and/or mixing. Moreover, they support the conclusion that magnetic fields play an important role in the formation and continued existence of the filaments.
Exoplanet Clouds and Chemistry: A WASP-17b case study
In the short time since the start of JWST ’s science operations, it has caused a paradigm shift in the information and understanding of giant planet atmospheres. The spectroscopic IR capabilities have revealed absorption from H2O , CO2, and CO with exquisite precision, provided the first look at elusive methane absorption, and shown a diversity of photochemistry and disequilibrium processes at play in giant planet atmospheres. Previously obscuring aerosols that plagued UV-optical spectra are revealing themselves via distinct absorption and emission in the mid-IR confirming for the first time in irradiated exoplanets theoretical predictions of cloud formation. I will present a case study of one such planet which is revealing the roles of clouds and chemistry in exoplanet atmospheres and the feedback imparted between composition, dynamics, and detectability.
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Exoplanet Clouds and Chemistry: A WASP-17b case study
In the short time since the start of JWST ’s science operations, it has caused a paradigm shift in the information and understanding of giant planet atmospheres. The spectroscopic IR capabilities have revealed absorption from H2O , CO2, and CO with exquisite precision, provided the first look at elusive methane absorption, and shown a diversity of photochemistry and disequilibrium processes at play in giant planet atmospheres. Previously obscuring aerosols that plagued UV-optical spectra are revealing themselves via distinct absorption and emission in the mid-IR confirming for the first time in irradiated exoplanets theoretical predictions of cloud formation. I will present a case study of one such planet which is revealing the roles of clouds and chemistry in exoplanet atmospheres and the feedback imparted between composition, dynamics, and detectability.
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The Death Throes of Massive Stars
Core collapse supernovae play many important roles in astronomy and astrophysics. They trigger and regulate star formation through the energy they inject into the interstellar medium and they forge and disperse elements that seed the next generation of stars. On much more compact scales, which is the focus area of this talk, core collapsing stars are the birth sites of neutron stars and black holes, and therefore they are the gateway to the compact Universe. Numerical simulations of the core collapse have rapidly progressed in the last decade. Explosions are now readily obtained, the key ingredient being multidimensionality. This colloquium will review recent progress in understanding the central engines at the heart of core-collapse supernovae. I’ll touch upon how we can still use 1D simulations to understand the population as a whole, 2D simulations to systematically study theoretical uncertainties and explore the multimessenger signals, and 3D simulations to push our understanding of these extreme events.
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The Death Throes of Massive Stars
Core collapse supernovae play many important roles in astronomy and astrophysics. They trigger and regulate star formation through the energy they inject into the interstellar medium and they forge and disperse elements that seed the next generation of stars. On much more compact scales, which is the focus area of this talk, core collapsing stars are the birth sites of neutron stars and black holes, and therefore they are the gateway to the compact Universe. Numerical simulations of the core collapse have rapidly progressed in the last decade. Explosions are now readily obtained, the key ingredient being multidimensionality. This colloquium will review recent progress in understanding the central engines at the heart of core-collapse supernovae. I’ll touch upon how we can still use 1D simulations to understand the population as a whole, 2D simulations to systematically study theoretical uncertainties and explore the multimessenger signals, and 3D simulations to push our understanding of these extreme events.
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arXiv:2501.14408v2 Announce Type: replace
Abstract: The Euclid mission is generating a vast amount of imaging data in four broadband filters at high angular resolution. This will allow the detailed study of mass, metallicity, and stellar populations across galaxies, which will constrain their formation and evolutionary pathways. Transforming the Euclid imaging for large samples of galaxies into maps of physical parameters in an efficient and reliable manner is an outstanding challenge. We investigate the power and reliability of machine learning techniques to extract the distribution of physical parameters within well-resolved galaxies. We focus on estimating stellar mass surface density, mass-averaged stellar metallicity and age. We generate noise-free, synthetic high-resolution imaging data in the Euclid photometric bands for a set of 1154 galaxies from the TNG50 cosmological simulation. The images are generated with the SKIRT radiative transfer code, taking into account the complex 3D distribution of stellar populations and interstellar dust attenuation. We use a machine learning framework to map the idealised mock observational data to the physical parameters on a pixel-by-pixel basis. We find that stellar mass surface density can be accurately recovered with a $\leq 0.130 {\rm \,dex}$ scatter. Conversely, stellar metallicity and age estimates are, as expected, less robust, but still contain significant information which originates from underlying correlations at a sub-kpc scale between stellar mass surface density and stellar population properties.
arXiv:2501.14408v2 Announce Type: replace
Abstract: The Euclid mission is generating a vast amount of imaging data in four broadband filters at high angular resolution. This will allow the detailed study of mass, metallicity, and stellar populations across galaxies, which will constrain their formation and evolutionary pathways. Transforming the Euclid imaging for large samples of galaxies into maps of physical parameters in an efficient and reliable manner is an outstanding challenge. We investigate the power and reliability of machine learning techniques to extract the distribution of physical parameters within well-resolved galaxies. We focus on estimating stellar mass surface density, mass-averaged stellar metallicity and age. We generate noise-free, synthetic high-resolution imaging data in the Euclid photometric bands for a set of 1154 galaxies from the TNG50 cosmological simulation. The images are generated with the SKIRT radiative transfer code, taking into account the complex 3D distribution of stellar populations and interstellar dust attenuation. We use a machine learning framework to map the idealised mock observational data to the physical parameters on a pixel-by-pixel basis. We find that stellar mass surface density can be accurately recovered with a $\leq 0.130 {\rm \,dex}$ scatter. Conversely, stellar metallicity and age estimates are, as expected, less robust, but still contain significant information which originates from underlying correlations at a sub-kpc scale between stellar mass surface density and stellar population properties.
Exoplanet Clouds and Chemistry: A WASP-17b case study
In the short time since the start of JWST ’s science operations, it has caused a paradigm shift in the information and understanding of giant planet atmospheres. The spectroscopic IR capabilities have revealed absorption from H2O , CO2, and CO with exquisite precision, provided the first look at elusive methane absorption, and shown a diversity of photochemistry and disequilibrium processes at play in giant planet atmospheres. Previously obscuring aerosols that plagued UV-optical spectra are revealing themselves via distinct absorption and emission in the mid-IR confirming for the first time in irradiated exoplanets theoretical predictions of cloud formation. I will present a case study of one such planet which is revealing the roles of clouds and chemistry in exoplanet atmospheres and the feedback imparted between composition, dynamics, and detectability.
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