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Institute of Astronomy

 

Studying stellar populations in Omega Centauri with phylogenetics

Recent IoA Publications - Wed, 25/06/2025 - 10:10
arXiv:2504.01813v2 Announce Type: replace Abstract: The nature and formation history of our Galaxy's largest and most enigmatic stellar cluster, known as Omega Centauri (ocen) remains debated. Here, we offer a novel approach to disentangling the complex stellar populations within ocen based on phylogenetics methodologies from evolutionary biology. These include the Gaussian Mixture Model and Neighbor-Joining clustering algorithms applied to a set of chemical abundances of ocen stellar members. Instead of using the classical approach in astronomy of grouping them into separate populations, we focused on how the stars are related to each other. In this way, we could identify stars that likely formed in globular clusters versus those originating from prolonged in-situ star formation and how these stars interconnect. Our analysis supports the hypothesis that ocen might be a nuclear star cluster of a galaxy accreted by the Milky Way with a mass of about 10^9M_sun. Furthermore, we revealed the existence of a previously unidentified in-situ stellar population with a distinct chemical pattern unlike any known population found in the Milky Way to date. Our analysis of ocen is an example of the success of cross-disciplinary research and shows the vast potential of applying evolutionary biology tools to astronomical datasets, opening new avenues for understanding the chemical evolution of complex stellar systems.

Studying stellar populations in Omega Centauri with phylogenetics

Stars and stellar evolution - Wed, 25/06/2025 - 10:10
arXiv:2504.01813v2 Announce Type: replace Abstract: The nature and formation history of our Galaxy's largest and most enigmatic stellar cluster, known as Omega Centauri (ocen) remains debated. Here, we offer a novel approach to disentangling the complex stellar populations within ocen based on phylogenetics methodologies from evolutionary biology. These include the Gaussian Mixture Model and Neighbor-Joining clustering algorithms applied to a set of chemical abundances of ocen stellar members. Instead of using the classical approach in astronomy of grouping them into separate populations, we focused on how the stars are related to each other. In this way, we could identify stars that likely formed in globular clusters versus those originating from prolonged in-situ star formation and how these stars interconnect. Our analysis supports the hypothesis that ocen might be a nuclear star cluster of a galaxy accreted by the Milky Way with a mass of about 10^9M_sun. Furthermore, we revealed the existence of a previously unidentified in-situ stellar population with a distinct chemical pattern unlike any known population found in the Milky Way to date. Our analysis of ocen is an example of the success of cross-disciplinary research and shows the vast potential of applying evolutionary biology tools to astronomical datasets, opening new avenues for understanding the chemical evolution of complex stellar systems.

An LBT view of the co-rotating group of galaxies around NGC 2750: Deep imaging and new satellite candidates

Recent IoA Publications - Wed, 25/06/2025 - 10:02
arXiv:2506.19001v1 Announce Type: new Abstract: Some galaxies such as the Milky Way and Andromeda display coherently rotating satellite planes, posing tensions with cosmological simulations. NGC 2750 has emerged as an additional candidate system hosting a co-rotating group of galaxies. We aim to assess the presence of a coherent satellite plane around NGC 2750 by identifying new candidate dwarf galaxies and low surface brightness features. We conducted deep, wide-field photometric observations of NGC 2750 using the Large Binocular Telescope in the g- and r-bands. Standard data reduction techniques were applied to enhance the detection of low-surface-brightness features down to about 31 mag/arcsec^2 in r. Our observations led to the discovery of six new candidate dwarf galaxies, including one with properties consistent with an ultra-diffuse galaxy. We also identified tidal features around NGC 2750, indicating past interactions with nearby satellites. The spatial distribution of satellites suggests a moderate flattening, further supported by the newly identified candidates. Follow-up spectroscopic measurements will be critical in confirming or challenging the strong kinematic coherence observed previously. The luminosity function of NGC 2750 reveals an excess of bright satellites compared to similar systems, adding to the growing tension between observed satellite populations and cosmological simulations.

An LBT view of the co-rotating group of galaxies around NGC 2750: Deep imaging and new satellite candidates

Cosmology and Fundamental physics - Wed, 25/06/2025 - 10:02
arXiv:2506.19001v1 Announce Type: new Abstract: Some galaxies such as the Milky Way and Andromeda display coherently rotating satellite planes, posing tensions with cosmological simulations. NGC 2750 has emerged as an additional candidate system hosting a co-rotating group of galaxies. We aim to assess the presence of a coherent satellite plane around NGC 2750 by identifying new candidate dwarf galaxies and low surface brightness features. We conducted deep, wide-field photometric observations of NGC 2750 using the Large Binocular Telescope in the g- and r-bands. Standard data reduction techniques were applied to enhance the detection of low-surface-brightness features down to about 31 mag/arcsec^2 in r. Our observations led to the discovery of six new candidate dwarf galaxies, including one with properties consistent with an ultra-diffuse galaxy. We also identified tidal features around NGC 2750, indicating past interactions with nearby satellites. The spatial distribution of satellites suggests a moderate flattening, further supported by the newly identified candidates. Follow-up spectroscopic measurements will be critical in confirming or challenging the strong kinematic coherence observed previously. The luminosity function of NGC 2750 reveals an excess of bright satellites compared to similar systems, adding to the growing tension between observed satellite populations and cosmological simulations.

The Atacama Cosmology Telescope: DR6 Constraints on Extended Cosmological Models

Recent IoA Publications - Wed, 25/06/2025 - 10:00
arXiv:2503.14454v2 Announce Type: replace Abstract: We use new cosmic microwave background (CMB) primary temperature and polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) to test foundational assumptions of the standard cosmological model and set constraints on extensions to it. We derive constraints from the ACT DR6 power spectra alone, as well as in combination with legacy data from Planck. To break geometric degeneracies, we include ACT and Planck CMB lensing data and baryon acoustic oscillation data from DESI Year-1, and further add supernovae measurements from Pantheon+ for models that affect the late-time expansion history. We verify the near-scale-invariance (running of the spectral index $d n_s/d\ln k = 0.0062 \pm 0.0052$) and adiabaticity of the primordial perturbations. Neutrino properties are consistent with Standard Model predictions: we find no evidence for new light, relativistic species that are free-streaming ($N_{\rm eff} = 2.86 \pm 0.13$, which combined with external BBN data becomes $N_{\rm eff} = 2.89 \pm 0.11$), for non-zero neutrino masses ($\sum m_\nu < 0.082$ eV at 95% CL), or for neutrino self-interactions. We also find no evidence for self-interacting dark radiation ($N_{\rm idr} < 0.134$), early-universe variation of fundamental constants, early dark energy, primordial magnetic fields, or modified recombination. Our data are consistent with standard BBN, the FIRAS-inferred CMB temperature, a dark matter component that is collisionless and with only a small fraction allowed as axion-like particles, a cosmological constant, and the late-time growth rate predicted by general relativity. We find no statistically significant preference for a departure from the baseline $\Lambda$CDM model. In general, models introduced to increase the Hubble constant or to decrease the amplitude of density fluctuations inferred from the primary CMB are not favored by our data.

The Atacama Cosmology Telescope: DR6 Constraints on Extended Cosmological Models

Cosmology and Fundamental physics - Wed, 25/06/2025 - 10:00
arXiv:2503.14454v2 Announce Type: replace Abstract: We use new cosmic microwave background (CMB) primary temperature and polarization anisotropy measurements from the Atacama Cosmology Telescope (ACT) Data Release 6 (DR6) to test foundational assumptions of the standard cosmological model and set constraints on extensions to it. We derive constraints from the ACT DR6 power spectra alone, as well as in combination with legacy data from Planck. To break geometric degeneracies, we include ACT and Planck CMB lensing data and baryon acoustic oscillation data from DESI Year-1, and further add supernovae measurements from Pantheon+ for models that affect the late-time expansion history. We verify the near-scale-invariance (running of the spectral index $d n_s/d\ln k = 0.0062 \pm 0.0052$) and adiabaticity of the primordial perturbations. Neutrino properties are consistent with Standard Model predictions: we find no evidence for new light, relativistic species that are free-streaming ($N_{\rm eff} = 2.86 \pm 0.13$, which combined with external BBN data becomes $N_{\rm eff} = 2.89 \pm 0.11$), for non-zero neutrino masses ($\sum m_\nu < 0.082$ eV at 95% CL), or for neutrino self-interactions. We also find no evidence for self-interacting dark radiation ($N_{\rm idr} < 0.134$), early-universe variation of fundamental constants, early dark energy, primordial magnetic fields, or modified recombination. Our data are consistent with standard BBN, the FIRAS-inferred CMB temperature, a dark matter component that is collisionless and with only a small fraction allowed as axion-like particles, a cosmological constant, and the late-time growth rate predicted by general relativity. We find no statistically significant preference for a departure from the baseline $\Lambda$CDM model. In general, models introduced to increase the Hubble constant or to decrease the amplitude of density fluctuations inferred from the primary CMB are not favored by our data.

Euclid: An emulator for baryonic effects on the matter bispectrum

Cosmology and Fundamental physics - Wed, 25/06/2025 - 09:49
arXiv:2506.18974v1 Announce Type: new Abstract: The Euclid mission and other next-generation large-scale structure surveys will enable high-precision measurements of the cosmic matter distribution. Understanding the impact of baryonic processes such as star formation and AGN feedback on matter clustering is crucial to ensure precise and unbiased cosmological inference. Most theoretical models of baryonic effects to date focus on two-point statistics, neglecting higher-order contributions. This work develops a fast and accurate emulator for baryonic effects on the matter bispectrum, a key non-Gaussian statistic in the nonlinear regime. We employ high-resolution $N$-body simulations from the BACCO suite and apply a combination of cutting-edge techniques such as cosmology scaling and baryonification to efficiently span a large cosmological and astrophysical parameter space. A deep neural network is trained to emulate baryonic effects on the matter bispectrum measured in simulations, capturing modifications across various scales and redshifts relevant to Euclid. We validate the emulator accuracy and robustness using an analysis of \Euclid mock data, employing predictions from the state-of-the-art FLAMINGO hydrodynamical simulations. The emulator reproduces baryonic suppression in the bispectrum to better than 2$\%$ for the $68\%$ percentile across most triangle configurations for $k \in [0.01, 20]\,h^{-1}\mathrm{Mpc}$ and ensures consistency between cosmological posteriors inferred from second- and third-order weak lensing statistics.

Euclid: An emulator for baryonic effects on the matter bispectrum

Recent IoA Publications - Wed, 25/06/2025 - 09:49
arXiv:2506.18974v1 Announce Type: new Abstract: The Euclid mission and other next-generation large-scale structure surveys will enable high-precision measurements of the cosmic matter distribution. Understanding the impact of baryonic processes such as star formation and AGN feedback on matter clustering is crucial to ensure precise and unbiased cosmological inference. Most theoretical models of baryonic effects to date focus on two-point statistics, neglecting higher-order contributions. This work develops a fast and accurate emulator for baryonic effects on the matter bispectrum, a key non-Gaussian statistic in the nonlinear regime. We employ high-resolution $N$-body simulations from the BACCO suite and apply a combination of cutting-edge techniques such as cosmology scaling and baryonification to efficiently span a large cosmological and astrophysical parameter space. A deep neural network is trained to emulate baryonic effects on the matter bispectrum measured in simulations, capturing modifications across various scales and redshifts relevant to Euclid. We validate the emulator accuracy and robustness using an analysis of \Euclid mock data, employing predictions from the state-of-the-art FLAMINGO hydrodynamical simulations. The emulator reproduces baryonic suppression in the bispectrum to better than 2$\%$ for the $68\%$ percentile across most triangle configurations for $k \in [0.01, 20]\,h^{-1}\mathrm{Mpc}$ and ensures consistency between cosmological posteriors inferred from second- and third-order weak lensing statistics.

Weird line of galaxies may have been created by a cosmic bullet

Astronomy News - Wed, 25/06/2025 - 09:45

A high-speed crash between two dwarf galaxies might explain a unique feature in space – and provide useful information on dark matter

Earth is more sensitive to greenhouse gases than we thought

Astronomy News - Wed, 25/06/2025 - 09:45

Our climate seems to be more sensitive to greenhouse gas emissions than some researchers had hoped, meaning the world will have to up its decarbonisation efforts

Enigmatic lizards somehow survived near Chicxulub asteroid impact

Astronomy News - Wed, 25/06/2025 - 09:44

The night lizards may have been the only terrestrial vertebrates that survived in the region of the asteroid impact 66 million years ago, which led to the extinction of non-avian dinosaurs

Tue 24 Jun 13:15: Earth, a Cosmic Spectacle

IoA Institute of Astronomy Talk Lists - Tue, 24/06/2025 - 13:28
Earth, a Cosmic Spectacle

Louise Beer, IoA Artist in Residence, will share a presentation that considers the philosophical impacts of dark skies, and how having access to them can help us to understand better loss and grief, our individual connection to the deep time history of Earth and the Universe, and the cosmic significance of the climate crisis. Louise will share her 2024 British Council-funded project, Earth, a Cosmic Spectacle which was developed in collaboration with astronomer Dr Ian Griffin and Tūhura Otago Museum in Aotearoa New Zealand. In this project, the artist invited astronomers, biologists, and geologists to gaze into the dark skies of New Zealand and anonymously write a letter exploring how their knowledge of Earth’s long and gradual development, starting from the dawn of the Universe, shapes their understanding of the cosmic significance of the climate crisis.

Add to your calendar or Include in your list

Tue 24 Jun 13:15: Earth, a Cosmic Spectacle

Next Wednesday Seminars - Tue, 24/06/2025 - 13:28
Earth, a Cosmic Spectacle

Louise Beer, IoA Artist in Residence, will share a presentation that considers the philosophical impacts of dark skies, and how having access to them can help us to understand better loss and grief, our individual connection to the deep time history of Earth and the Universe, and the cosmic significance of the climate crisis. Louise will share her 2024 British Council-funded project, Earth, a Cosmic Spectacle which was developed in collaboration with astronomer Dr Ian Griffin and Tūhura Otago Museum in Aotearoa New Zealand. In this project, the artist invited astronomers, biologists, and geologists to gaze into the dark skies of New Zealand and anonymously write a letter exploring how their knowledge of Earth’s long and gradual development, starting from the dawn of the Universe, shapes their understanding of the cosmic significance of the climate crisis.

Add to your calendar or Include in your list

Categories: Talks

The Simons Observatory: Validation of reconstructed power spectra from simulated filtered maps for the Small Aperture Telescope survey

Instrumentation and Surveys - Tue, 24/06/2025 - 11:01
arXiv:2502.00946v2 Announce Type: replace Abstract: We present a transfer function-based method to estimate angular power spectra from filtered maps for cosmic microwave background (CMB) surveys. This is especially relevant for experiments targeting the faint primordial gravitational wave signatures in CMB polarisation at large scales, such as the Simons Observatory (SO) small aperture telescopes. While timestreams can be filtered to mitigate the contamination from low-frequency noise, usual methods that calculate the mode coupling at individual multipoles can be challenging for experiments covering large sky areas or reaching few-arcminute resolution. The method we present here, although approximate, is more practical and faster for larger data volumes. We validate it through the use of simulated observations approximating the first year of SO data, going from half-wave plate-modulated timestreams to maps, and using simulations to estimate the mixing of polarisation modes induced by an example of time-domain filtering. We show its performance through an example null test and with an end-to-end pipeline that performs inference on cosmological parameters, including the tensor-to-scalar ratio $r$. The performance demonstration uses simulated observations at multiple frequency bands. We find that the method can recover unbiased parameters for our simulated noise levels.

The Simons Observatory: Validation of reconstructed power spectra from simulated filtered maps for the Small Aperture Telescope survey

Cosmology and Fundamental physics - Tue, 24/06/2025 - 11:01
arXiv:2502.00946v2 Announce Type: replace Abstract: We present a transfer function-based method to estimate angular power spectra from filtered maps for cosmic microwave background (CMB) surveys. This is especially relevant for experiments targeting the faint primordial gravitational wave signatures in CMB polarisation at large scales, such as the Simons Observatory (SO) small aperture telescopes. While timestreams can be filtered to mitigate the contamination from low-frequency noise, usual methods that calculate the mode coupling at individual multipoles can be challenging for experiments covering large sky areas or reaching few-arcminute resolution. The method we present here, although approximate, is more practical and faster for larger data volumes. We validate it through the use of simulated observations approximating the first year of SO data, going from half-wave plate-modulated timestreams to maps, and using simulations to estimate the mixing of polarisation modes induced by an example of time-domain filtering. We show its performance through an example null test and with an end-to-end pipeline that performs inference on cosmological parameters, including the tensor-to-scalar ratio $r$. The performance demonstration uses simulated observations at multiple frequency bands. We find that the method can recover unbiased parameters for our simulated noise levels.

The Simons Observatory: Validation of reconstructed power spectra from simulated filtered maps for the Small Aperture Telescope survey

Recent IoA Publications - Tue, 24/06/2025 - 11:01
arXiv:2502.00946v2 Announce Type: replace Abstract: We present a transfer function-based method to estimate angular power spectra from filtered maps for cosmic microwave background (CMB) surveys. This is especially relevant for experiments targeting the faint primordial gravitational wave signatures in CMB polarisation at large scales, such as the Simons Observatory (SO) small aperture telescopes. While timestreams can be filtered to mitigate the contamination from low-frequency noise, usual methods that calculate the mode coupling at individual multipoles can be challenging for experiments covering large sky areas or reaching few-arcminute resolution. The method we present here, although approximate, is more practical and faster for larger data volumes. We validate it through the use of simulated observations approximating the first year of SO data, going from half-wave plate-modulated timestreams to maps, and using simulations to estimate the mixing of polarisation modes induced by an example of time-domain filtering. We show its performance through an example null test and with an end-to-end pipeline that performs inference on cosmological parameters, including the tensor-to-scalar ratio $r$. The performance demonstration uses simulated observations at multiple frequency bands. We find that the method can recover unbiased parameters for our simulated noise levels.

The JWST/AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. I. A Diversity of Nebular Attenuation Curves and Evidence for Non-Unity Dust Covering Fractions

Galaxy Evolution and AGN - Tue, 24/06/2025 - 10:26
arXiv:2506.17396v1 Announce Type: new Abstract: We present the nebular attenuation curves and dust covering fractions for 24 redshift z=1.5-4.4 star-forming galaxies using multiple Balmer and Paschen lines from the JWST/AURORA survey. Nebular reddening derived from Paschen lines exceeds that from Balmer lines for at least half the galaxies in the sample when assuming the commonly-adopted Galactic extinction curve, implying the presence of optically-thick star formation. The nebular attenuation curves exhibit a broad range of normalizations (Rv ~ 3.2-16.4). Motivated by the offsets in reddening deduced from the Balmer and Paschen lines, and the high Rv values for the individual nebular attenuation curves, both of which suggest variations in the dust-stars geometry, we propose a model with a subunity dust covering fraction (fcov). Fitting such a model to the HI recombination line ratios indicates fcov ~ 0.6-1.0. The normalizations of the nebular attenuation curves, Rv, are driven primarily by fcov and the mix of optically-thick and thin OB associations. Thus, the diversity of nebular attenuation curves can be accommodated by assuming dust grain properties similar to that of Milky Way sightlines but with a subunity covering fraction of dust. Integrated measurements of multiple Balmer and Paschen lines can be used to place novel constraints on the dust covering fraction towards OB associations. These, in turn, provide new avenues for exploring the role of dust and gas covering fraction in a number of relevant aspects of high-redshift galaxies, including the impact of stellar feedback on ISM porosity and the escape of Ly-alpha and Lyman continuum radiation.

The JWST/AURORA Survey: Multiple Balmer and Paschen Emission Lines for Individual Star-forming Galaxies at z=1.5-4.4. I. A Diversity of Nebular Attenuation Curves and Evidence for Non-Unity Dust Covering Fractions

Recent IoA Publications - Tue, 24/06/2025 - 10:26
arXiv:2506.17396v1 Announce Type: new Abstract: We present the nebular attenuation curves and dust covering fractions for 24 redshift z=1.5-4.4 star-forming galaxies using multiple Balmer and Paschen lines from the JWST/AURORA survey. Nebular reddening derived from Paschen lines exceeds that from Balmer lines for at least half the galaxies in the sample when assuming the commonly-adopted Galactic extinction curve, implying the presence of optically-thick star formation. The nebular attenuation curves exhibit a broad range of normalizations (Rv ~ 3.2-16.4). Motivated by the offsets in reddening deduced from the Balmer and Paschen lines, and the high Rv values for the individual nebular attenuation curves, both of which suggest variations in the dust-stars geometry, we propose a model with a subunity dust covering fraction (fcov). Fitting such a model to the HI recombination line ratios indicates fcov ~ 0.6-1.0. The normalizations of the nebular attenuation curves, Rv, are driven primarily by fcov and the mix of optically-thick and thin OB associations. Thus, the diversity of nebular attenuation curves can be accommodated by assuming dust grain properties similar to that of Milky Way sightlines but with a subunity covering fraction of dust. Integrated measurements of multiple Balmer and Paschen lines can be used to place novel constraints on the dust covering fraction towards OB associations. These, in turn, provide new avenues for exploring the role of dust and gas covering fraction in a number of relevant aspects of high-redshift galaxies, including the impact of stellar feedback on ISM porosity and the escape of Ly-alpha and Lyman continuum radiation.

A Martian Volcano in the Mist

Astronomy News - Tue, 24/06/2025 - 10:16
NASA/JPL-Caltech/ASU

Arsia Mons, one of the Red Planet’s largest volcanoes, peeks through a blanket of water ice clouds in this image captured by NASA’s 2001 Mars Odyssey orbiter on May 2, 2025. Odyssey used a camera called the Thermal Emission Imaging System (THEMIS) to capture this view while studying the Martian atmosphere, which appears here as a greenish haze above the scene. A large crater known as a caldera, produced by massive volcanic explosions and collapse, is located at the summit. At 72 miles (120 kilometers) wide, the Arsia Mons summit caldera is larger than many volcanoes on Earth.

Learn more about Arsia Mons and Mars Odyssey.

Image Credit: NASA/JPL-Caltech/ASU

First images from world’s largest digital camera leave astronomers in awe

Astronomy News - Tue, 24/06/2025 - 10:15

Nature, Published online: 23 June 2025; doi:10.1038/d41586-025-01973-5

The new observatory in Chile will map the entire southern sky every 3–4 nights.