arXiv:2501.08969v2 Announce Type: replace
Abstract: In this work we estimate the explosion and progenitor properties of six Type II supernovae (SNe) at 0.675 <= z <= 3.61 discovered by the James Webb Space Telescope (JWST) Advanced Deep Extragalactic Survey (JADES) transient survey by modeling their light curves. Two Type II SNe are found to have high explosion energies of 3e51 erg, while the other four Type II SNe are estimated to have typical explosion energies found in the local Universe [(0.5-2)e51 erg]. The fraction of Type II SNe with high explosion energies might be higher at high redshifts because of, e.g., lower metallicity, but it is still difficult to draw a firm conclusion because of the small sample size and potential observational biases. We found it difficult to constrain the progenitor masses for Type II SNe in our sample because of the sparse light-curve data. We found two Type II SN light curves can be better reproduced by introducing confined, dense circumstellar matter. Thus, the confined, dense circumstellar matter frequently observed in nearby Type II SNe is likely to exist in Type II SNe at high redshifts as well. Two Type II SNe are estimated to have high host galaxy extinctions, showing the ability of JWST to discover dust-obscured SNe at high redshifts. More high-redshift Type II SNe are required to investigate the differences in the properties of Type II SNe near and far, but here we show the first glimpse into the high-redshift population of Type II SNe.
arXiv:2505.02895v1 Announce Type: new
Abstract: We present a spectroscopic search for broad H$\alpha$ emitters at z~3.7-6.5 in the GOODS-N field, utilizing JWST/NIRCam slitless spectroscopy from FRESCO and CONGRESS, complemented by JADES imaging. We identify 19 broad H$\alpha$ emitters with FWHM > 1000 km/s at z~4-5.5, including 9 new sources. The black hole masses and AGN bolometric luminosities, inferred from the broad H$\alpha$ components, indicate that most sources are accreting at ~10% of the Eddington limit. We derive their host stellar masses via SED fitting and find higher $M_{BH}/M_{*}$ ratios relative to the local $M_{BH}$-$M_{*}$ relations, consistent with previous studies. We find that 42% of the sample do not satisfy the widely-used color selection criteria for Little Red Dots (LRDs), with the majority of these sources lacking the characteristic steep red slope. A comparison of the average SEDs between our sample and LRDs selected in the same field reveals that the steep red slopes observed in some LRDs are likely due to line-boosting effects as previously suggested. Furthermore, we find that 68% of color-selected LRDs with H$\alpha$ detections in the NIRCam/Grism spectra do not exhibit broad-line features. While the limited sensitivity of the grism spectra may hinder the detection of broad-line components in faint sources, our findings still highlight the enigmatic nature of the LRD population.
arXiv:2505.02896v1 Announce Type: new
Abstract: We study the large-scale environments and clustering properties of 28 low-luminosity AGNs at $z=3.9-6$ in the GOODS-N field. Our sample, identified from the JWST NIRCam Imaging and WFSS data in CONGRESS and FRESCO surveys with either broad H$\alpha$ emission lines or V-shape continua, are compared to 782 H$\alpha$ emitters (HAEs) selected from the same data. These AGNs are located in diverse large-scale environments and do not preferentially reside in denser environments compared to HAEs. Their overdensity field, $\delta$, averaged over (15 $h^{-1}$cMpc)$^3$, ranges from $-0.56$ to 10.56, and shows no clear correlation with broad-line luminosity, black hole (BH) masses, or the AGN fraction. It suggests that $> 10$ cMpc structures do not significantly influence BH growth. We measure the two-point cross-correlation function of AGNs with HAEs, finding a comparable amplitude to that of the HAE auto-correlation. This indicates similar bias parameters and host dark matter halo masses for AGNs and HAEs. The correlation length of field AGNs is 4.26 $h^{-1}$cMpc, and 7.66 $h^{-1}$cMpc at $3.9 < z < 5$ and $5 < z < 6$, respectively. We infer a median host dark matter halo mass of $\log (M_h/M_\odot)\approx 11.0-11.2$ and host stellar masses of $\log (M_\star/M_\odot) \approx 8.4-8.6$ by comparing with the UniverseMachine simulation. Our clustering analysis suggests that low-luminosity AGNs at high redshift reside in normal star-forming galaxies with overmassive BHs. They represent an intrinsically distinct population from luminous quasars and could be a common phase in galaxy evolution.
arXiv:2505.03737v1 Announce Type: new
Abstract: Weak gravitational lensing of the CMB has been established as a robust and powerful observable for precision cosmology. However, the impact of Galactic foregrounds, which has been studied less extensively than many other potential systematics, could in principle pose a problem for CMB lensing measurements. These foregrounds are inherently non-Gaussian and hence might mimic the characteristic signal that lensing estimators are designed to measure. We present an analysis that quantifies the level of contamination from Galactic dust in lensing measurements, focusing particularly on measurements with the Atacama Cosmology Telescope and the Simons Observatory. We employ a whole suite of foreground models and study the contamination of lensing measurements with both individual frequency channels and multifrequency combinations. We test the sensitivity of different estimators to the level of foreground non-Gaussianity, and the dependence on sky fraction and multipole range used. We find that Galactic foregrounds do not present a problem for the Atacama Cosmology Telescope experiment (the bias in the inferred CMB lensing power spectrum amplitude remains below $0.3\sigma$). For Simons Observatory, not all foreground models remain below this threshold. Although our results are conservative upper limits, they suggest that further work on characterizing dust biases and determining the impact of mitigation methods is well motivated, especially for the largest sky fractions.
Physicists are trying to ditch the concept of space-time – the supposed fabric of physical reality. Quantum columnist Karmela Padavic-Callaghan explains why
Deciphering giant planet formation
The multitude of detected exoplanets and their diversity never cease to fascinate us, while the statistical trends emerging from these detections present promising opportunities to delve into the past of planetary systems, all the way back to their formation. In this talk, I will give an overview of my group’s recent observational and theoretical results on the formation of gas giants. Owing to their large gravitational influence these planets cannot be overlooked in the evolution of planetary systems towards a life-harbouring system such as our own. Results of RV and direct imaging surveys in recent years revealed that gas giants are not a common outcome of planet formation, and that their most frequent hosts – the intermediate-mass stars (IMSs) seem to hold the answers to their formation.
We investigate the formation of giant planets using the pebble-accretion driven planet formation simulations, exploring a range of different formation conditions.
In this work, and in contrast to common approaches in the literature, we implement stellar-mass dependent time evolution of luminosity on the pre-main sequence, and find that this makes a significant difference to giant planet formation outcomes. We successfully reproduce the giant planet occurrence rates as a function of stellar mass, found by RV surveys. This work revealed that mass accretion rate is the key parameter in determining whether a star will likely host a giant planet in its future planetary system.
Our large surveys of pre-main sequence star candidates led to the first unbiased sample of such IMSs, and the result that their protoplanetary discs are dispersed faster than discs around low mass stars, a devastating prospect for giant planet formation unless it happens very fast (e.g., via GI). This is in stark contrast with the observational examples of massive discs actively forming planets at 5-6Myr of age. Our work shows that late gas accretion, as seen in some of those sources, must be the dominant mechanism that sustains the mass reservoir of these older protoplanetary discs. Our surveys, and follow-up with ALMA also allowed a unique insight in the elusive transition state from protoplanetary to debris discs and origin of gas in debris discs.
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DESI DR2: Survey overview and cosmological constraints from DR2 Baryon Acoustic Oscillation measurements
The Dark Energy Spectroscopic Instrument (DESI) is undertaking a five-year survey spanning 14,000 square degrees of the sky, with the goal of mapping 40 million extragalactic redshifts. These observations aim to refine our understanding of the universe’s expansion history through Baryon Acoustic Oscillations (BAO) and the growth of cosmic structure via Full Shape analyses. In 2025, the DESI collaboration released BAO cosmology results from the Data Release 2 (DR2) sample, assembled from the first three years of data taking (2021 – 2024).
This presentation will introduce the instrument and the survey and review the BAO measurements derived from DR2 . I will discuss the consistency of BAO constraints with other probes—-CMB (including the latest ACT DR6 CMB data) and supernovae—-and present cosmological constraints on dark energy and neutrino masses.
I will conclude by providing an outlook on upcoming DESI analyses.
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Dynamical Formation of Regular Black Holes
I will discuss recent work where it was demonstrated that regular black holes emerge as the unique spherically symmetric solutions to certain gravitational actions that incorporate infinite towers of higher-derivative corrections. I will then illustrate what happens when one considers the collapse of spherical thin shells and dust in these theories, showing that the collapse is generically non-singular. This is based on work with Pablo Bueno, Pablo Cano and Ángel Murcia.
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Testing the HARPS3 Data Reduction Pipeline with Synthetic Spectra to achieve Earth-Twin RV Precision
The High Accuracy Radial velocity Planet Searcher-3 (HARPS3) is being developed for the Terra Hunting Experiment, a 10-year observing campaign to conduct nightly observations of a carefully selected group of solar-like stars to detect long-period, low-mass exoplanets. The goal is to achieve extremely-precise radial velocity (EPRV) measurements at the level of 10 cm/s to enable the detection of an Earth-twin. Attaining this precision requires a deep understanding of all error sources: instrumental systematics, astrophysical noise, and data reduction algorithms.
To address the latter, I have developed a novel method to test the data reduction pipeline (DRP) using synthetic data. Rather than attempting to replicate the instrument’s response exactly, the method is designed to systematically probe the DRP ’s performance, identify potential biases, and validate the reduction algorithms. By injecting known inputs into the DRP and tracing their propagation, I can control all aspects of the data, test specific algorithms, and verify the accuracy of the reduction products. The aim is to use simulated data to identify systematic biases and inaccuracies that could impact EPRV measurements.
In this talk I will present my work, currently in preparation for publication, describing how I simulate the data and discussing the first results of passing the synthetic echellogram through the DRP . This approach provides a framework to assess the performance of HARPS3 during commissioning and early operations – when it comes on-sky in late 2025 – enabling us to identify issues and refine data processing techniques.
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arXiv:2505.02233v1 Announce Type: new
Abstract: We investigate the degeneracy between the effects of ultra-light axion dark matter and baryonic feedback in suppressing the matter power spectrum. We forecast that galaxy shear data from the Rubin Observatory's Legacy Survey of Space and Time (LSST) could limit an axion of mass $m = 10^{-25}\,\mathrm{eV}$ to be $\lesssim 5\%$ of the dark matter, stronger than any current bound, if the interplay between axions and feedback is accurately modelled. Using a halo model emulator to construct power spectra for mixed cold and axion dark matter cosmologies, including baryonic effects, we find that galaxy shear is sensitive to axions from $10^{-27}\,\mathrm{eV}$ to $10^{-21}\,\mathrm{eV}$, with the capacity to set competitive bounds across much of this range. For axions with $m \sim 10^{-25}\,\mathrm{eV}$, the scales at which axions and feedback impact structure formation are similar, introducing a parameter degeneracy. We find that, with an external feedback constraint, we can break the degeneracy and constrain the axion transfer function, such that LSST could detect a $10^{-25}\,\mathrm{eV}$ axion comprising 10\% of the dark matter at $\sim 3 \sigma$ significance. Direct reconstruction of the non-linear matter power spectrum provides an alternative way of analysing weak lensing surveys, with the advantage of identifying the scale-dependent features in the data that the dark matter model imposes. We advocate for dedicated cosmological hydrodynamical simulations with an axion dark matter component so that upcoming galaxy and cosmic microwave background lensing surveys can disentangle the dark matter-baryon transfer function.
arXiv:2409.11464v3 Announce Type: replace
Abstract: For the first time, we present a systematic search for galaxies with extended emission line and potential outflow features using \textit{JWST} medium-band images in the GOODS-S field. This is done by comparing the morphology in medium-band images to adjacent continuum and UV bands. We look for galaxies that have a maximum extent 50\% larger, an excess area 30\% greater, or an axis ratio difference of more than 0.3 in the medium band compared to the reference bands. After visual inspection, we find 326 candidate galaxies at $1.4 < z < 8.4$, with a peak in the population near cosmic noon, benefiting from the good coverage of the medium-band filters. By fitting their SEDs, we find that the candidate galaxies are at least 20\% more bursty in their star-forming activity and have 50\% more young stellar populations compared to a control sample selected based on the continuum band flux. Additionally, these candidates exhibit a significantly higher production rate of ionizing photons. We further find that candidates hosting known AGN produce extended emission that is more anisotropic compared to non-AGN candidates. A few of our candidates have been spectroscopically confirmed to have prominent outflow signatures through NIRSpec observations, showcasing the robustness of the photometric selection. Future spectroscopic follow-up will better help verify and characterize the kinematics and chemical properties of these systems.
arXiv:2505.01512v1 Announce Type: new
Abstract: The discovery of inhabited exoplanets hinges on identifying biosignature gases. JWST is revealing potential biosignatures in exoplanet atmospheres, though their presence is yet to provide strong evidence for life. The central challenge is attribution: how to confidently identify biogenic sources while ruling out, or deeming unlikely, abiotic explanations? Attribution is particularly difficult for individual planets, especially regarding system-scale stochastic processes that could set atmospheric conditions. To address this, we here propose a comparative multi-planet approach: comparing atmospheric compositions across multiple planets within a system to empirically define the 'abiotic baseline'. This baseline serves as a reference point for biosignatures, and enables marginalisation over inaccessible, shared abiotic parameters. This is possible because planets within a system are linked by their birth in the same natal disk, having been irradiated by the same evolving star, and having a related dynamical history. Observations aligning with the abiotic baseline, where the locally informed abiotic models demonstrate high out-of-sample predictive accuracy, are likely non-biological. Deviations from the baseline -- potentially biotic anomalies -- suggest an alternative origin. We present the application of Bayesian leave-one-out cross-validation to evaluate the performance of geochemical- and biogeochemical-climate models in explaining these anomalies, using the expected log pointwise predictive density as a diagnostic. When biogeochemical models outperform their abiotic counterparts, the anomaly may be shaped by life, and constitutes a comparative biosignature. If both models perform poorly, the anomaly is flagged as an "unknown unknown" -- a signature of either unrecognised abiotic chemistry, or life as we don't yet know it.
The Oxygen Valve on Hydrogen Escape Since the Great Oxidation Event
The Great Oxidation Event (GOE) was a 200 Myr transition circa 2.4 billion years ago that converted the Earth’s anoxic atmosphere to one where molecular oxygen (O2) was abundant. This rise in O2 is thought to have substantially throttled hydrogen (H) escape and the associated water (H2O) loss. In this study we use WACCM6 , a three-dimensional Earth System Model to simulate Earth’s atmosphere and predict the diffusion-limited escape rate of hydrogen due to varying O2 concentrations based on atmospheric estimations from the GOE onward, ranging between 0.1 PAL to 150 PAL , where PAL is the present atmospheric level of 21 % by volume. O2 indirectly acts as a control valve on the amount of hydrogen atoms reaching the homopause in the simulations: less O2 leads to decreased O3 densities, reducing local temperatures by up to 5 K, which increases H2O freeze-drying. For the considered scenarios, the maximum difference in the total H mixing ratio at the homopause and calculated diffusion-limited escape rates is a factor of 3.2 and 4.7, respectively, with the prescribed CH4 mixing ratio setting a minimum diffusion escape rate of ≈ 2 × 10^10 mol H/yr. These numerical predictions support geological evidence that the majority of Earth’s hydrogen escape occurred prior to the GOE .
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On the Road to the Radius Valley
Twenty years after their initial discovery, the nature of super-Earths and sub-Neptunes remains largely unknown. In this talk, I will discuss recent work addressing their interior compositions and formation pathways. In particular, I will show how the detection of young transiting exoplanets may provide a route to revealing their interior compositions.
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‘Shocking’ results from a major astronomical study have raised doubts about the standard model of cosmology, forcing scientists to consider new ways of understanding dark energy and gravity
arXiv:2410.19905v2 Announce Type: replace
Abstract: Energetic feedback processes associated with accreting supermassive black holes can expel gas from massive haloes and significantly alter various measures of clustering on ~Mpc scales, potentially biasing the values of cosmological parameters inferred from analyses of large-scale structure (LSS) if not modelled accurately. Here we use the state-of-the-art FLAMINGO suite of cosmological hydrodynamical simulations to gauge the impact of feedback on large-scale structure by comparing to Planck + ACT stacking measurements of the kinetic Sunyaev-Zel'dovich (kSZ) effect of SDSS BOSS galaxies. We make careful like-with-like comparisons to the observations, aided by high precision KiDS and DES galaxy-galaxy lensing measurements of the BOSS galaxies to inform the selection of the simulated galaxies. In qualitative agreement with several recent studies using dark matter only simulations corrected for baryonic effects, we find that the kSZ effect measurements prefer stronger feedback than predicted by simulations which have been calibrated to reproduce the gas fractions of low redshift X-ray-selected groups and clusters. We find that the increased feedback can help to reduce the so-called S8 tension between the observed and CMB-predicted clustering on small scales as probed by cosmic shear (although at the expense of agreement with the X-ray group measurements). However, the increased feedback is only marginally effective at reducing the reported offsets between the predicted and observed clustering as probed by the thermal SZ (tSZ) effect power spectrum and tSZ effect--weak lensing cross-spectrum, both of which are sensitive to higher halo masses than cosmic shear.
arXiv:2505.00095v1 Announce Type: new
Abstract: Metallicity ($Z$) estimates based on ultraviolet (UV) emission lines from the narrow-line regions (NLRs) of active galactic nuclei (AGNs) have been found to differ from those derived from optical lines. However, the origin of this discrepancy ($ZR$) remains poorly understood. To investigate the source of $ZR$, we compiled from the literature the fluxes of narrow near-UV ($1000 < \lambda(\angstrom) < 2000)$ and optical ($3000 < \lambda(\angstrom) < 7000)$ emission line measurements for a sample of 11 AGNs (9 at $z<0.4$ and 2 at $z\sim2.4$). Metallicity values for our sample were derived using a semi-empirical calibration based on the $C43$=log[(\ion{C{iv}$\lambda$1549+\ion{C{iii}]$\lambda$1909)/\ion{He}{ii}$\lambda$1640] emission-line ratio and compared with those obtained via direct measurement of the electron temperature ($T_{\rm e}$-method) and via calibrations based on optical emission-lines. The source of the discrepancy was investigated in terms of the ionization parameter ($U$), electron density ($N_{\rm e}$), and carbon abundance (C/H). We found a weak correlation between $ZR$, $U$ and $N_{\rm e}$. However, a moderate correlation was observed between $ZR$ and direct estimates of C/H, suggesting that the previously assumed (C/O)-$Z$ relations in photoionization models used to derive UV carbon-line calibrations may not be valid for AGNs. By combining a large set of abundance estimates for local star-forming regions with those of our AGN sample, we derived a new (C/O)-$Z$ relation. Comparisons between the results of photoionization models that assume this new abundance relation and the UV observational data of our sample produce $Z$ values derived from the $C43$ index that are consistent with those obtained using the $T_{\rm e}$-method.
