arXiv:2507.14936v1 Announce Type: new
Abstract: A majority of JWST/NIRSpec/IFU studies at high redshifts to date have focused on UV-bright or massive objects, while our understanding of low-mass galaxies at early cosmic times remains limited. In this work, we present NIRSpec/IFS high-resolution observations of two low-mass ($M_* < 10^9 \ M_\odot$), low-metallicity ($[12 + \log(\text{O/H})] < 8$) galaxies at $z \sim 7.66$ with evidence of hosting AGN. Using spatially-resolved maps of rest-frame optical emission lines, we find flat metallicity profiles, indicative of ISM redistribution by outflows or past merging. We identify kinematical components decoupled from galactic rotation with velocities of $\sim 250 - 500 \ \text{km} \ \text{s}^{-1}$. We argue that these components are likely tracing outflows, possibly AGN-driven, for which we infer outflow rates of $\sim 21 - 40 \ M_\odot \ \text{yr}^{-1}$, suggesting they may suppress future star formation. We compare our observational results to those from the new large-volume AESOPICA simulations, which fully incorporate different models of black hole growth and AGN feedback. We find that our observational results of $v_\text{out}/v_\text{esc}$ and $\dot{M}_\text{out}$/SFR are consistent with the AGN population in these simulations, hinting that AGN-driven feedback may contribute to quenching both in our systems and in a wider population of low-mass galaxies in the early Universe. This novel study demonstrates the necessity of deep IFU observations to decompose the complex kinematics and morphology of high-$z$ galaxies, trace outflows, and constrain the effect of feedback in these low-mass systems.
arXiv:2507.14936v1 Announce Type: new
Abstract: A majority of JWST/NIRSpec/IFU studies at high redshifts to date have focused on UV-bright or massive objects, while our understanding of low-mass galaxies at early cosmic times remains limited. In this work, we present NIRSpec/IFS high-resolution observations of two low-mass ($M_* < 10^9 \ M_\odot$), low-metallicity ($[12 + \log(\text{O/H})] < 8$) galaxies at $z \sim 7.66$ with evidence of hosting AGN. Using spatially-resolved maps of rest-frame optical emission lines, we find flat metallicity profiles, indicative of ISM redistribution by outflows or past merging. We identify kinematical components decoupled from galactic rotation with velocities of $\sim 250 - 500 \ \text{km} \ \text{s}^{-1}$. We argue that these components are likely tracing outflows, possibly AGN-driven, for which we infer outflow rates of $\sim 21 - 40 \ M_\odot \ \text{yr}^{-1}$, suggesting they may suppress future star formation. We compare our observational results to those from the new large-volume AESOPICA simulations, which fully incorporate different models of black hole growth and AGN feedback. We find that our observational results of $v_\text{out}/v_\text{esc}$ and $\dot{M}_\text{out}$/SFR are consistent with the AGN population in these simulations, hinting that AGN-driven feedback may contribute to quenching both in our systems and in a wider population of low-mass galaxies in the early Universe. This novel study demonstrates the necessity of deep IFU observations to decompose the complex kinematics and morphology of high-$z$ galaxies, trace outflows, and constrain the effect of feedback in these low-mass systems.
Nature, Published online: 21 July 2025; doi:10.1038/d41586-025-02294-3
Modelling suggests that annihilation of this strange, invisible matter helps stars to retain that youthful glow.
A computer simulation of stars near the centre of our galaxy offers an explanation for their mysteriously young appearance – they may be capturing dark matter for extra fuel
The primary role of jets in exploding all core-collapse supernovae
I will present evidence in core-collapse supernova remnants for the action of jets in the supernova explosion process. Two main types of observations appear in many, but not all, core-collapse supernova remnants: (i) the well-established presence of a pair of opposite `ears’ and (ii) the recently identified point-symmetrical structure in 15 remnants, including SN 1987A , Cassiopeia A, Vela, and the Crab Nebula. The pair of opposite ears suggests that two opposite jets inflate the ears. The point-symmetrical structure results from two or more pairs of jets along different axes, as the jittering jets explosion mechanism (JJEM) predicts. I will compare the JJEM with the neutrino-driven mechanism and conclude that the neutrino-driven mechanism comes short in explaining observations, leaving the JJEM as the primary explosion mechanism of CCS Ne. The JJEM has some unique signatures in addition to its point-symmetric morphology, such as gravitational waves and energetic explosions. I will comment on the overrated popularity of the neutrino-driven mechanism in scientific meetings and literature.
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The primary role of jets in exploding all core-collapse supernovae
I will present evidence in core-collapse supernova remnants for the action of jets in the supernova explosion process. Two main types of observations appear in many, but not all, core-collapse supernova remnants: (i) the well-established presence of a pair of opposite `ears’ and (ii) the recently identified point-symmetrical structure in 15 remnants, including SN 1987A , Cassiopeia A, Vela, and the Crab Nebula. The pair of opposite ears suggests that two opposite jets inflate the ears. The point-symmetrical structure results from two or more pairs of jets along different axes, as the jittering jets explosion mechanism (JJEM) predicts. I will compare the JJEM with the neutrino-driven mechanism and conclude that the neutrino-driven mechanism comes short in explaining observations, leaving the JJEM as the primary explosion mechanism of CCS Ne. The JJEM has some unique signatures in addition to its point-symmetric morphology, such as gravitational waves and energetic explosions. I will comment on the overrated popularity of the neutrino-driven mechanism in scientific meetings and literature.
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arXiv:2507.14136v1 Announce Type: new
Abstract: We present new constraints on the halo masses and matter density profiles of DESI galaxy groups by cross-correlating samples of Luminous Red Galaxies (LRGs) and Bright Galaxy Survey (BGS) galaxies with the publicly available CMB lensing convergence map from ACT DR6. This provides an independent, lensing-based calibration of halo masses, complementary to methods relying on clustering or dynamics. We derive constraints on the mean halo mass for three DESI-selected samples, finding $\log(M_{\rm halo}/(M_\odot/h)) \approx 13.18$, 13.03 and 13.02 for the Main LRG, Extended LRG, and BGS samples, respectively. Using a halo model approach, we also compare the projected galaxy-matter density profiles with previously reported gas profiles inferred from measurements of the kinematic Sunyaev-Zel'dovich (kSZ) effect. This work addresses one of the key uncertainties in interpreting kSZ signals -- the unknown host halo mass distribution -- by providing an independent and consistent mass calibration. The agreement between the gas and total mass profiles at large aperture suggests that sufficiently far from the group center (2--3 virial radii), we recover all the baryons, offering a resolution to the 'missing baryon' problem. We further study the cumulative gas fractions for all galaxies as well as for the most massive galaxy groups in the sample ($\log(M_{\rm halo}/(M_\odot/h)) \approx 13.5$), finding values that are physically sensible and in agreement with previous findings using kSZ and X-ray data: compared to the TNG300 simulation, the observed gas fractions are systematically lower at fixed radius by $\gtrsim$4$\sigma$, providing compelling, independent evidence for stronger baryonic feedback in the real Universe. These findings highlight the power of combining CMB lensing with galaxy surveys to probe the interplay between baryons and dark matter in group-sized halos.
arXiv:2507.14136v1 Announce Type: new
Abstract: We present new constraints on the halo masses and matter density profiles of DESI galaxy groups by cross-correlating samples of Luminous Red Galaxies (LRGs) and Bright Galaxy Survey (BGS) galaxies with the publicly available CMB lensing convergence map from ACT DR6. This provides an independent, lensing-based calibration of halo masses, complementary to methods relying on clustering or dynamics. We derive constraints on the mean halo mass for three DESI-selected samples, finding $\log(M_{\rm halo}/(M_\odot/h)) \approx 13.18$, 13.03 and 13.02 for the Main LRG, Extended LRG, and BGS samples, respectively. Using a halo model approach, we also compare the projected galaxy-matter density profiles with previously reported gas profiles inferred from measurements of the kinematic Sunyaev-Zel'dovich (kSZ) effect. This work addresses one of the key uncertainties in interpreting kSZ signals -- the unknown host halo mass distribution -- by providing an independent and consistent mass calibration. The agreement between the gas and total mass profiles at large aperture suggests that sufficiently far from the group center (2--3 virial radii), we recover all the baryons, offering a resolution to the 'missing baryon' problem. We further study the cumulative gas fractions for all galaxies as well as for the most massive galaxy groups in the sample ($\log(M_{\rm halo}/(M_\odot/h)) \approx 13.5$), finding values that are physically sensible and in agreement with previous findings using kSZ and X-ray data: compared to the TNG300 simulation, the observed gas fractions are systematically lower at fixed radius by $\gtrsim$4$\sigma$, providing compelling, independent evidence for stronger baryonic feedback in the real Universe. These findings highlight the power of combining CMB lensing with galaxy surveys to probe the interplay between baryons and dark matter in group-sized halos.
arXiv:2507.13495v1 Announce Type: new
Abstract: Simulation-Based Inference (SBI) offers a principled and flexible framework for conducting Bayesian inference in any situation where forward simulations are feasible. However, validating the accuracy and reliability of the inferred posteriors remains a persistent challenge. In this work, we point out a simple diagnostic approach rooted in ensemble learning methods to assess the internal consistency of SBI outputs that does not require access to the true posterior. By training multiple neural estimators under identical conditions and evaluating their pairwise Kullback-Leibler (KL) divergences, we define a consistency criterion that quantifies agreement across the ensemble. We highlight two core use cases for this framework: a) for generating a robust estimate of the systematic uncertainty in parameter reconstruction associated with the training procedure, and b) for detecting possible model misspecification when using trained estimators on real data. We also demonstrate the relationship between significant KL divergences and issues such as insufficient convergence due to, e.g., too low a simulation budget, or intrinsic variance in the training process. Overall, this ensemble-based diagnostic framework provides a lightweight, scalable, and model-agnostic tool for enhancing the trustworthiness of SBI in scientific applications.
arXiv:2507.13495v1 Announce Type: new
Abstract: Simulation-Based Inference (SBI) offers a principled and flexible framework for conducting Bayesian inference in any situation where forward simulations are feasible. However, validating the accuracy and reliability of the inferred posteriors remains a persistent challenge. In this work, we point out a simple diagnostic approach rooted in ensemble learning methods to assess the internal consistency of SBI outputs that does not require access to the true posterior. By training multiple neural estimators under identical conditions and evaluating their pairwise Kullback-Leibler (KL) divergences, we define a consistency criterion that quantifies agreement across the ensemble. We highlight two core use cases for this framework: a) for generating a robust estimate of the systematic uncertainty in parameter reconstruction associated with the training procedure, and b) for detecting possible model misspecification when using trained estimators on real data. We also demonstrate the relationship between significant KL divergences and issues such as insufficient convergence due to, e.g., too low a simulation budget, or intrinsic variance in the training process. Overall, this ensemble-based diagnostic framework provides a lightweight, scalable, and model-agnostic tool for enhancing the trustworthiness of SBI in scientific applications.
arXiv:2507.13495v1 Announce Type: new
Abstract: Simulation-Based Inference (SBI) offers a principled and flexible framework for conducting Bayesian inference in any situation where forward simulations are feasible. However, validating the accuracy and reliability of the inferred posteriors remains a persistent challenge. In this work, we point out a simple diagnostic approach rooted in ensemble learning methods to assess the internal consistency of SBI outputs that does not require access to the true posterior. By training multiple neural estimators under identical conditions and evaluating their pairwise Kullback-Leibler (KL) divergences, we define a consistency criterion that quantifies agreement across the ensemble. We highlight two core use cases for this framework: a) for generating a robust estimate of the systematic uncertainty in parameter reconstruction associated with the training procedure, and b) for detecting possible model misspecification when using trained estimators on real data. We also demonstrate the relationship between significant KL divergences and issues such as insufficient convergence due to, e.g., too low a simulation budget, or intrinsic variance in the training process. Overall, this ensemble-based diagnostic framework provides a lightweight, scalable, and model-agnostic tool for enhancing the trustworthiness of SBI in scientific applications.
arXiv:2507.14094v1 Announce Type: new
Abstract: Our understanding of the chemical evolution of galaxies has advanced through measurements from both distant galaxies across redshift, and our own Milky Way (MW). To form a comprehensive picture, it is essential to unify these constraints, placing them on a common scale and parlance and to understand their systematic differences. In this study, we homogenize oxygen and iron measurements from star-forming galaxies at Cosmic Noon ($z{\sim}2-3$) with resolved stellar abundances from the Local Group. The MW is divided into four components, assuming the outer halo is dominated by debris from the Gaia-Sausage-Enceladus (GSE) progenitor. After converting all abundances to a common Solar scale, we identify clear $\alpha$- and iron-enhancement trends with mass in the $z{\sim}2-3$ galaxies and find good agreement between these galaxies and the MW high-$\alpha$ disc in [O/Fe] vs. [Fe/H]. We also find excellent agreement between the [O/Fe] trends seen in the MW high- and low-$\alpha$ discs with O-abundances seen in old and young planetary nebulae in M~31 respectively, supporting the existence of $\alpha$-bimodality in the inner regions of M~31. Finally, we use globular cluster ages to project the MW and GSE back in time to $z{\sim}3$ and find that their estimated mass, oxygen and iron abundances are strikingly consistent with the mass-metallicity relation of star-forming galaxies at $z{\sim}3$. In the future, increased transparency around the choice of Solar scale and abundance methodology will make combining chemical abundances easier -- contributing to a complete picture of the chemical evolution of all galaxies.
arXiv:2507.14094v1 Announce Type: new
Abstract: Our understanding of the chemical evolution of galaxies has advanced through measurements from both distant galaxies across redshift, and our own Milky Way (MW). To form a comprehensive picture, it is essential to unify these constraints, placing them on a common scale and parlance and to understand their systematic differences. In this study, we homogenize oxygen and iron measurements from star-forming galaxies at Cosmic Noon ($z{\sim}2-3$) with resolved stellar abundances from the Local Group. The MW is divided into four components, assuming the outer halo is dominated by debris from the Gaia-Sausage-Enceladus (GSE) progenitor. After converting all abundances to a common Solar scale, we identify clear $\alpha$- and iron-enhancement trends with mass in the $z{\sim}2-3$ galaxies and find good agreement between these galaxies and the MW high-$\alpha$ disc in [O/Fe] vs. [Fe/H]. We also find excellent agreement between the [O/Fe] trends seen in the MW high- and low-$\alpha$ discs with O-abundances seen in old and young planetary nebulae in M~31 respectively, supporting the existence of $\alpha$-bimodality in the inner regions of M~31. Finally, we use globular cluster ages to project the MW and GSE back in time to $z{\sim}3$ and find that their estimated mass, oxygen and iron abundances are strikingly consistent with the mass-metallicity relation of star-forming galaxies at $z{\sim}3$. In the future, increased transparency around the choice of Solar scale and abundance methodology will make combining chemical abundances easier -- contributing to a complete picture of the chemical evolution of all galaxies.
arXiv:2507.14094v1 Announce Type: new
Abstract: Our understanding of the chemical evolution of galaxies has advanced through measurements from both distant galaxies across redshift, and our own Milky Way (MW). To form a comprehensive picture, it is essential to unify these constraints, placing them on a common scale and parlance and to understand their systematic differences. In this study, we homogenize oxygen and iron measurements from star-forming galaxies at Cosmic Noon ($z{\sim}2-3$) with resolved stellar abundances from the Local Group. The MW is divided into four components, assuming the outer halo is dominated by debris from the Gaia-Sausage-Enceladus (GSE) progenitor. After converting all abundances to a common Solar scale, we identify clear $\alpha$- and iron-enhancement trends with mass in the $z{\sim}2-3$ galaxies and find good agreement between these galaxies and the MW high-$\alpha$ disc in [O/Fe] vs. [Fe/H]. We also find excellent agreement between the [O/Fe] trends seen in the MW high- and low-$\alpha$ discs with O-abundances seen in old and young planetary nebulae in M~31 respectively, supporting the existence of $\alpha$-bimodality in the inner regions of M~31. Finally, we use globular cluster ages to project the MW and GSE back in time to $z{\sim}3$ and find that their estimated mass, oxygen and iron abundances are strikingly consistent with the mass-metallicity relation of star-forming galaxies at $z{\sim}3$. In the future, increased transparency around the choice of Solar scale and abundance methodology will make combining chemical abundances easier -- contributing to a complete picture of the chemical evolution of all galaxies.
This NASA/ESA Hubble Space Telescope image features the galaxy cluster Abell 209.ESA/Hubble & NASA, M. Postman, P. Kelly
A massive, spacetime-warping cluster of galaxies is the setting of today’s NASA/ESA Hubble Space Telescope image. The galaxy cluster in question is Abell 209, located 2.8 billion light-years away in the constellation Cetus (the Whale).
This Hubble image of Abell 209 shows more than a hundred galaxies, but there’s more to this cluster than even Hubble’s discerning eye can see. Abell 209’s galaxies are separated by millions of light-years, and the seemingly empty space between the galaxies is filled with hot, diffuse gas that is visible only at X-ray wavelengths. An even more elusive occupant of this galaxy cluster is dark matter: a form of matter that does not interact with light. Dark matter does not absorb, reflect, or emit light, effectively making it invisible to us. Astronomers detect dark matter by its gravitational influence on normal matter. Astronomers surmise that the universe is comprised of 5% normal matter, 25% dark matter, and 70% dark energy.
Hubble observations, like the ones used to create this image, can help astronomers answer fundamental questions about our universe, including mysteries surrounding dark matter and dark energy. These investigations leverage the immense mass of a galaxy cluster, which can bend the fabric of spacetime itself and create warped and magnified images of background galaxies and stars in a process called gravitational lensing.
While this image lacks the dramatic rings that gravitational lensing can sometimes create, Abell 209 still shows subtle signs of lensing at work, in the form of streaky, slightly curved galaxies within the cluster’s golden glow. By measuring the distortion of these galaxies, astronomers can map the distribution of mass within the cluster, illuminating the underlying cloud of dark matter. This information, which Hubble’s fine resolution and sensitive instruments help to provide, is critical for testing theories of how our universe evolved.
Text Credit: ESA/Hubble
Image credit: ESA/Hubble & NASA, M. Postman, P. Kelly
Instead of the big bang, some physicists have suggested that our universe may have come from a big bounce following another universe contracting – but quantum theory could rule this out
From a silhouetted space station to glowing comet tails and swirling stars, this year's ZWO Astronomy Photographer of the Year contest inspires us to see the cosmos in a new light
Small, compact galaxies seen in the early universe have puzzled astronomers – finding these unusual objects closer to home could provide hints about how they form
arXiv:2507.12622v1 Announce Type: new
Abstract: Temperate sub-Neptunes are compelling targets for detecting liquid-water oceans beyond the Solar System. If water-rich and lacking massive hydrogen-helium envelopes, these planets could sustain liquid layers beneath their atmospheres despite sizes larger than Earth. Previous observations of the temperate sub-Neptune K2-18 b revealed an H2-dominated atmosphere rich in CH4, with moderate evidence for CO2 and tentative signs of dimethyl sulfide (DMS). Here we present four new JWST/NIRSpec transit observations of K2-18 b. The resulting high-precision transmission spectrum robustly detects both CH4 and CO2, precisely measuring their abundances and firmly establishing the planet's water-rich nature: either a thick envelope with >10% H2O by volume or a thin atmosphere above a liquid-water ocean. The spectrum reveals no detectable H2O, NH3, or CO. The absence of atmospheric water vapor suggests an efficient cold trap, while the nondetections of NH3 and CO support the scenario of a small H2-rich atmosphere overlying a liquid reservoir. However, alternative models that include these gases can also reproduce the spectrum within uncertainties, highlighting the need for deeper observations. The spectrum only contains marginal signals of DMS, methyl mercaptan (CH3SH), and nitrous oxide (N2O), with none exceeding 3 sigma in model preference and all falling below ~2 sigma without imposing a strong super-Rayleigh haze. Meanwhile, our self-consistent photochemical models show that DMS and CH3SH may form abiotically in massive H2-rich atmospheres of high metallicity, making it important to consider additional indicators for their potential use as biosignatures. K2-18 b, a cool, water-rich world, stands out as one of the most promising temperate sub-Neptunes for exploring the emergence of liquid-water environments in non-Earth-like planets, motivating further characterization of its atmosphere and interior.
arXiv:2507.12622v1 Announce Type: new
Abstract: Temperate sub-Neptunes are compelling targets for detecting liquid-water oceans beyond the Solar System. If water-rich and lacking massive hydrogen-helium envelopes, these planets could sustain liquid layers beneath their atmospheres despite sizes larger than Earth. Previous observations of the temperate sub-Neptune K2-18 b revealed an H2-dominated atmosphere rich in CH4, with moderate evidence for CO2 and tentative signs of dimethyl sulfide (DMS). Here we present four new JWST/NIRSpec transit observations of K2-18 b. The resulting high-precision transmission spectrum robustly detects both CH4 and CO2, precisely measuring their abundances and firmly establishing the planet's water-rich nature: either a thick envelope with >10% H2O by volume or a thin atmosphere above a liquid-water ocean. The spectrum reveals no detectable H2O, NH3, or CO. The absence of atmospheric water vapor suggests an efficient cold trap, while the nondetections of NH3 and CO support the scenario of a small H2-rich atmosphere overlying a liquid reservoir. However, alternative models that include these gases can also reproduce the spectrum within uncertainties, highlighting the need for deeper observations. The spectrum only contains marginal signals of DMS, methyl mercaptan (CH3SH), and nitrous oxide (N2O), with none exceeding 3 sigma in model preference and all falling below ~2 sigma without imposing a strong super-Rayleigh haze. Meanwhile, our self-consistent photochemical models show that DMS and CH3SH may form abiotically in massive H2-rich atmospheres of high metallicity, making it important to consider additional indicators for their potential use as biosignatures. K2-18 b, a cool, water-rich world, stands out as one of the most promising temperate sub-Neptunes for exploring the emergence of liquid-water environments in non-Earth-like planets, motivating further characterization of its atmosphere and interior.