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arXiv:2405.14015v3 Announce Type: replace Abstract: Extragalactic globular clusters (EGCs) are an abundant and powerful tracer of galaxy dynamics and formation, and their own formation and evolution is also a matter of extensive debate. The compact nature of globular clusters means that they are hard to spatially resolve and thus study outside the Local Group. In this work we have examined how well EGCs will be detectable in images from the Euclid telescope, using both simulated pre-launch images and the first early-release observations of the Fornax galaxy cluster. The Euclid Wide Survey will provide high-spatial resolution VIS imaging in the broad IE band as well as near-infrared photometry (YE, JE, and HE). We estimate that the galaxies within 100 Mpc in the footprint of the Euclid survey host around 830 000 EGCs of which about 350 000 are within the survey's detection limits. For about half of these EGCs, three infrared colours will be available as well. For any galaxy within 50Mpc the brighter half of its GC luminosity function will be detectable by the Euclid Wide Survey. The detectability of EGCs is mainly driven by the residual surface brightness of their host galaxy. We find that an automated machine-learning EGC-classification method based on real Euclid data of the Fornax galaxy cluster provides an efficient method to generate high purity and high completeness GC candidate catalogues. We confirm that EGCs are spatially resolved compared to pure point sources in VIS images of Fornax. Our analysis of both simulated and first on-sky data show that Euclid will increase the number of GCs accessible with high-resolution imaging substantially compared to previous surveys, and will permit the study of GCs in the outskirts of their hosts. Euclid is unique in enabling systematic studies of EGCs in a spatially unbiased and homogeneous manner and is primed to improve our understanding of many understudied aspects of GC astrophysics.

arXiv:2406.06678v3 Announce Type: replace Abstract: We use low-amplitude, long period variable (LA-LPV) candidates in \textit{Gaia} DR3 to trace the kinematics and dynamics of the Milky Way bar. LA-LPVs, like other LPVs, are intrinsically bright and follow a tight period-luminosity relation, but unlike e.g. Mira variables, their radial velocity measurements are reliable due to their smaller pulsation amplitudes. We supplement the \textit{Gaia} astrometric and radial velocity measurements with distance moduli assigned using a period-luminosity relation to acquire full 6D phase space information. The assigned distances are validated by comparing to geometric distances and StarHorse distances, which shows biases less than $\sim5\%$. Our sample provides an unprecedented panoramic picture of the inner Galaxy with minimal selection effects. We map the kinematics of the inner Milky Way and find a significant kinematic signature corresponding to the Galactic bar. We measure the pattern speed of the Galactic bar using the continuity equation and find $\Omega_{\rm b}=34.1\pm2.4$ km s$^{-1}$ kpc$^{-1}$. We develop a simple, robust and potential-independent method to measure the dynamical length of the bar using only kinematics and find $R_{\rm b}\sim4.0$ kpc. We validate both measurements using N-body simulations. Assuming knowledge of the gravitational potential of the inner Milky Way, we analyse the orbital structure of the Galactic bar using orbital frequency ratios. The $x_1$ orbits are the dominant bar-supporting orbital family in our sample. Amongst the selected bar stars, the $x_1 v_1$ or "banana" orbits constitute a larger fraction ($\sim 15\%$) than other orbital families in the bar, implying that they are the dominant family contributing to the Galactic X-shape, although contributions from other orbital families are also present.

To be confirmed

Abstract not available

• Speaker: Professor Gary Horowitz - University of California, Santa Barbara
• Wednesday 14 May 2025, 16:00-17:00
• Venue: MR3.
• Series: Theoretical Physics Colloquium; organiser: Amanda Stagg.

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arXiv:2409.04200v2 Announce Type: replace Abstract: The Zwicky Transient Facility SN Ia Data Release 2 (ZTF SN Ia DR2) contains more than 3,000 Type Ia supernovae (SNe Ia), providing the largest homogeneous low-redshift sample of SNe Ia. Having at least one spectrum per event, this data collection is ideal for large-scale statistical studies of the photometric, spectroscopic and host-galaxy properties of SNe Ia, particularly of the more rare "peculiar" subclasses. In this paper, we first present the method we developed to spectroscopically classify the SNe in the sample, and the techniques we used to model their multi-band light curves and explore their photometric properties. We then show a method to distinguish between the "peculiar" subtypes and the normal SNe Ia. We also explore the properties of their host galaxies and estimate their relative rates, focusing on the "peculiar" subtypes and their connection to the cosmologically useful SNe Ia. Finally, we discuss the implications of our study with respect to the progenitor systems of the "peculiar" SN Ia events.

arXiv:2412.13995v1 Announce Type: new Abstract: Motivated by observed discrepancies between ACT DR4 and Planck 2018 cosmic microwave background (CMB) anisotropy power spectra, particularly in the cross-correlation of temperature and E-mode polarization, we investigate challenges that may be encountered in the comparison of satellite and ground-based CMB data. In particular, we focus on the effects of Fourier-space filtering and masking involving bright point sources. We show that the filtering operation generates bright cross-shaped artifacts in the map, which stretch far outside typical point-source masks. If not corrected, these artifacts can add bias or additional variance to cross-spectra, skewing results. However we find that the effect of this systematic is not large enough to explain the ACT-Planck differences presented with ACT DR4.

arXiv:2404.02303v3 Announce Type: replace Abstract: In this third paper of a series, we study the kinematics of the ionised gas and stars, calculating the dynamical masses of the circumnuclear star-forming regions in the ring of of the face-on spiral NGC 7742. We have used high spectral resolution data from the MEGARA instrument attached to the Gran Telescopio Canarias (GTC) to measure the kinematical components of the nebular emission lines of selected HII regions and the stellar velocity dispersions from the CaT absorption lines that allow the derivation of the associated cluster virialized masses. The emission line profiles show two different kinematical components: a narrow one with velocity dispersion $\sim$ 10 km/s and a broad one with velocity dispersion similar to those found for the stellar absorption lines. The derived star cluster dynamical masses range from 2.5 $\times$ 10$^6$ to 10.0 $\times$ 10$^7$ M$_\odot$. The comparison of gas and stellar velocity dispersions suggests a scenario where the clusters have formed simultaneously in a first star formation episode with a fraction of the stellar evolution feedback remaining trapped in the cluster, subject to the same gravitational potential as the cluster stars. Between 0.15 and 7.07 % of the total dynamical mass of the cluster would have cooled down and formed a new, younger, population of stars, responsible for the ionisation of the gas currently observed.

arXiv:2409.02783v2 Announce Type: replace Abstract: We investigate the level of accuracy and precision of cluster weak-lensing (WL) masses measured with the \Euclid data processing pipeline. We use the DEMNUni-Cov $N$-body simulations to assess how well the WL mass probes the true halo mass, and, then, how well WL masses can be recovered in the presence of measurement uncertainties. We consider different halo mass density models, priors, and mass point estimates. WL mass differs from true mass due to, e.g., the intrinsic ellipticity of sources, correlated or uncorrelated matter and large-scale structure, halo triaxiality and orientation, and merging or irregular morphology. In an ideal scenario without observational or measurement errors, the maximum likelihood estimator is the most accurate, with WL masses biased low by $\langle b_M \rangle = -14.6 \pm 1.7 \, \%$ on average over the full range $M_\text{200c} > 5 \times 10^{13} \, M_\odot$ and $z < 1$. Due to the stabilising effect of the prior, the biweight, mean, and median estimates are more precise. The scatter decreases with increasing mass and informative priors significantly reduce the scatter. Halo mass density profiles with a truncation provide better fits to the lensing signal, while the accuracy and precision are not significantly affected. We further investigate the impact of additional sources of systematic uncertainty on the WL mass, namely the impact of photometric redshift uncertainties and source selection, the expected performance of \Euclid cluster detection algorithms, and the presence of masks. Taken in isolation, we find that the largest effect is induced by non-conservative source selection. This effect can be mostly removed with a robust selection. As a final \Euclid-like test, we combine systematic effects in a realistic observational setting and find results similar to the ideal case, $\langle b_M \rangle = - 15.5 \pm 2.4 \, \%$, under a robust selection.

Congratulations to Professor George Efstathiou, who has been awarded an honorary degree from Durham University. Honorary graduates exemplify the highest levels of achievement in their spheres of activity. Professor Karen O’Brien, Vice-Chancellor of Durham University, said: "Our honorary graduates are leaders in their...

arXiv:2409.17394v2 Announce Type: replace Abstract: Super-Earths are highly irradiated, small planets with bulk densities approximately consistent with Earth. We construct combined interior-atmosphere models of super-Earths that trace the partitioning of water throughout a planet, including an iron-rich core, silicate-rich mantle, and steam atmosphere. We compare these models with exoplanet observations to infer a $1\sigma$ upper limit on total water mass fraction of $\lesssim 3\%$ at the population level. We consider end-member scenarios that may change this value, including the efficiency of mantle outgassing, escape of high mean-molecular weight atmospheres, and increased iron core mass fractions. Although our constraints are agnostic as to the origin of water, we show that our upper limits are consistent with its production via chemical reactions of primordial hydrogen-dominated atmospheres with magma oceans. This mechanism has also been hypothesised to explain Earth's water content, possibly pointing to a unified channel for the origins of water on small terrestrial planets.

arXiv:2402.18773v2 Announce Type: replace Abstract: Observations with the James Webb Space Telescope (JWST) have revealed active galactic nuclei (AGN) powered by supermassive black holes (SMBHs) with estimated masses of $10^7-10^8$ M$_\odot$ at redshifts $z\sim7-9$. Some reside in overmassive systems with higher AGN to stellar mass ratios than locally. Understanding how massive black holes could form so early in cosmic history and affect their environment to establish the observed relations today are some of the major open questions in astrophysics and cosmology. One model to create these massive objects is through direct collapse black holes (DCBHs) that provide massive seeds ($\sim10^5-10^6$ M$_\odot$), able to reach high masses in the limited time available. We use the cosmological simulation code GIZMO to study the formation and growth of DCBH seeds in the early Universe. To grow the DCBHs, we implement a gas swallowing model set to match the Eddington accretion rate as long as the nearby gaseous environment, affected by stellar and accretion disk feedback, provides sufficient fuel. We find that to create massive AGN in overmassive systems at high redshifts, massive seeds accreting more efficiently than the fiducial Bondi-Hoyle model are needed. We assess whether the conditions for such enhanced accretion rates are realistic by considering limits on plausible transport mechanisms. We also examine various DCBH growth histories and find that mass growth is more sustained in overdense cosmological environments, where high gas densities are achieved locally. We discuss the exciting prospect to directly probe the assembly history of the first SMBHs with upcoming, ultra-deep JWST surveys.

arXiv:2412.10752v1 Announce Type: new Abstract: Using nearly simultaneous radio, near-infrared, optical, and ultraviolet data collected since 2009, we constructed 106 spectral energy distributions (SEDs) of the blazar OJ 287. These SEDs were well-fitted by a log-parabolic model. By classifying the data into `flare' and `quiescent' segments, we found that the median flux at peak frequency of the SEDs during flare segments was 0.37$\pm$0.22 dex higher compared to quiescent segments, while no significant differences were observed in the median values of the curvature parameter $b$ or the peak frequency $\log \nu_{\mathrm{p}}$. A significant bluer-when-brighter trend was confirmed through a relation between $V$ magnitude and $B-V$ color index, with this trend being stronger in the flare segments. Additionally, a significant anti-correlation was detected between $\log \nu_{\mathrm{p}}$ and $b$, with a slope of 5.79 in the relation between $1/b$ and $\log \nu_{\mathrm{p}}$, closer to the prediction from a statistical acceleration model other than a stochastic acceleration interpretation, though a notable discrepancy persists. This discrepancy indicates that additional factors, such as deviations from idealized conditions or radiative contributions-such as thermal emission from the accretion disk in the optical-UV range during quiescent states-may play a role in producing the observed steeper slope. Within the framework of statistical acceleration mechanism, lack of correlation between change in peak intensity and change in peak frequency suggests that change in electron energy distribution is unlikely to be responsible for the time-dependent SED changes. Instead, changes in Doppler boosting or magnetic fields may have a greater influence.

arXiv:2410.00136v3 Announce Type: replace Abstract: We present JWST/MIRI observations of T~Cha, a highly variable ($\Delta V \sim$3-5\,mag) accreting Sun-like star surrounded by a disk with a large ($\sim 15$\,au) dust gap. We find that the JWST mid-infrared spectrum is signiticantly different from the {\it Spitzer} spectrum obtained 17 years before, where the emission at short wavelengths ($5-10 \mu m$) has decreased by $\sim 2/3$ while at longer wavelengths ($15-25 \mu m$) it increased by up to a factor of $\sim 3$. This 'seesaw' behavior is contemporary with a fairly constant higher optical emission captured by the All Sky Automated Survey. By analyzing and modelling both SEDs, we propose that JWST caught the star during an outburst that destructed the asymmetric inner disk wall responsible for the high optical variability and lower $15-25$\,micron\ emission during the {\it Spitzer} time. The dust mass lost during this outburst is estimated to be comparable ($\sim 1/5$) to the upper limit of the total micron-sized dust mass in the inner disk of T~Cha now. Monitoring this system during possible future outbursts and more observations of its quiescent state will reveal if the inner disk can be replenished or will continue to be depleted and vanish.

arXiv:2410.00136v3 Announce Type: replace Abstract: We present JWST/MIRI observations of T~Cha, a highly variable ($\Delta V \sim$3-5\,mag) accreting Sun-like star surrounded by a disk with a large ($\sim 15$\,au) dust gap. We find that the JWST mid-infrared spectrum is signiticantly different from the {\it Spitzer} spectrum obtained 17 years before, where the emission at short wavelengths ($5-10 \mu m$) has decreased by $\sim 2/3$ while at longer wavelengths ($15-25 \mu m$) it increased by up to a factor of $\sim 3$. This 'seesaw' behavior is contemporary with a fairly constant higher optical emission captured by the All Sky Automated Survey. By analyzing and modelling both SEDs, we propose that JWST caught the star during an outburst that destructed the asymmetric inner disk wall responsible for the high optical variability and lower $15-25$\,micron\ emission during the {\it Spitzer} time. The dust mass lost during this outburst is estimated to be comparable ($\sim 1/5$) to the upper limit of the total micron-sized dust mass in the inner disk of T~Cha now. Monitoring this system during possible future outbursts and more observations of its quiescent state will reveal if the inner disk can be replenished or will continue to be depleted and vanish.

arXiv:2412.08809v1 Announce Type: new Abstract: We use hierarchical Bayesian modelling to calibrate a network of 32 all-sky faint DA white dwarf (DA WD) spectrophotometric standards ($16.5 < V < 19.5$) alongside the three CALSPEC standards, from 912 \r{A} to 32 $\mu$m. The framework is the first of its kind to jointly infer photometric zeropoints and WD parameters ($\log g$, $T_{\text{eff}}$, $A_V$, $R_V$) by simultaneously modelling both photometric and spectroscopic data. We model panchromatic HST/WFC3 UVIS and IR fluxes, HST/STIS UV spectroscopy and ground-based optical spectroscopy to sub-percent precision. Photometric residuals for the sample are the lowest yet yielding $<0.004$ mag RMS on average from the UV to the NIR, achieved by jointly inferring time-dependent changes in system sensitivity and WFC3/IR count-rate nonlinearity. Our GPU-accelerated implementation enables efficient sampling via Hamiltonian Monte Carlo, critical for exploring the high-dimensional posterior space. The hierarchical nature of the model enables population analysis of intrinsic WD and dust parameters. Inferred SEDs from this model will be essential for calibrating the James Webb Space Telescope as well as next-generation surveys, including Vera Rubin Observatory's Legacy Survey of Space and Time, and the Nancy Grace Roman Space Telescope.

arXiv:2412.07970v1 Announce Type: new Abstract: The visibility of the Lyman-$\alpha$ (Ly$\alpha$) emission from reionization-epoch galaxies depends sensitively on the extent of the intrinsic \lya emission redwards of 1215.67~\AA. The prominent red peak resulting from resonant radiative transfer in the interstellar medium is often modelled as a single Gaussian. We use the \textsc{Azahar} simulation suite of a massive-reionization epoch galaxy to show that a significantly larger fraction of the \lya emission extends to $400$-$800$~km~s$^{-1}$, and thus significantly further to the red than predicted by a Gaussian line profile. A cycle of frequent galaxy mergers strongly modulates the \lya luminosity, the red peak velocity and its extended red wing emerging from the galaxy, which all also strongly vary with viewing angle. The \lya emission also depends sensitively on the implemented feedback, dust and star formation physics. Our simulations including cosmic rays reproduce the observed spectral properties of reionization epoch \lya emitters (LAEs) well if we assume that the \lya emission is affected by very little dust. The visibility of LAEs can be strongly underestimated if the extended red wings of the intrinsic \lya emission are not accounted for. We discuss implications for using the visibility of LAEs to constrain the evolution of the volume-averaged neutral fraction during reionization.

arXiv:2412.08557v1 Announce Type: new Abstract: Aims: We aim to observe the transits and occultations of WASP-33b, which orbits a rapidly-rotating $\delta$ Scuti pulsator, with the goal of measuring the orbital obliquity via the gravity-darkening effect, and constraining the geometric albedo via the occultation depth. Methods: We observed four transits and four occultations with CHEOPS, and employ a variety of techniques to remove the effects of the stellar pulsations from the light curves, as well as the usual CHEOPS systematic effects. We also performed a comprehensive analysis of low-resolution spectral and Gaia data to re-determine the stellar properties of WASP-33. Results: We measure an orbital obliquity 111.3 +0.2 -0.7 degrees, which is consistent with previous measurements made via Doppler tomography. We also measure the planetary impact parameter, and confirm that this parameter is undergoing rapid secular evolution as a result of nodal precession of the planetary orbit. This precession allows us to determine the second-order fluid Love number of the star, which we find agrees well with the predictions of theoretical stellar models. We are unable to robustly measure a unique value of the occultation depth, and emphasise the need for long-baseline observations to better measure the pulsation periods.

arXiv:2412.08557v1 Announce Type: new Abstract: Aims: We aim to observe the transits and occultations of WASP-33b, which orbits a rapidly-rotating $\delta$ Scuti pulsator, with the goal of measuring the orbital obliquity via the gravity-darkening effect, and constraining the geometric albedo via the occultation depth. Methods: We observed four transits and four occultations with CHEOPS, and employ a variety of techniques to remove the effects of the stellar pulsations from the light curves, as well as the usual CHEOPS systematic effects. We also performed a comprehensive analysis of low-resolution spectral and Gaia data to re-determine the stellar properties of WASP-33. Results: We measure an orbital obliquity 111.3 +0.2 -0.7 degrees, which is consistent with previous measurements made via Doppler tomography. We also measure the planetary impact parameter, and confirm that this parameter is undergoing rapid secular evolution as a result of nodal precession of the planetary orbit. This precession allows us to determine the second-order fluid Love number of the star, which we find agrees well with the predictions of theoretical stellar models. We are unable to robustly measure a unique value of the occultation depth, and emphasise the need for long-baseline observations to better measure the pulsation periods.

arXiv:2412.06982v1 Announce Type: new Abstract: Precision radial velocity (RV) spectrographs that use adaptive optics (AO) show promise to advance telescope observing capabilities beyond those of seeing-limited designs. We are building a spectrograph for the Large Binocular Telescope (LBT) named iLocater that uses AO to inject starlight directly into single mode fibers (SMF). iLocater's first acquisition camera system (the `SX' camera), which receives light from one of the 8.4m diameter primary mirrors of the LBT, was initially installed in summer 2019 and has since been used for several commissioning runs. We present results from first-light observations that include on-sky measurements as part of commissioning activities. Imaging measurements of the bright B3IV star 2 Cygni ($V=4.98$) resulted in the direct detection of a candidate companion star at an angular separation of only $\theta = 70$ mas. Follow-up AO measurements using Keck/NIRC2 recover the candidate companion in multiple filters. An $R\approx1500$ miniature spectrograph recently installed at the LBT named ``Lili'' provides spatially resolved spectra of each binary component, indicating similar spectral types and strengthening the case for companionship. Studying the multiplicity of young runaway star systems like 2 Cygni ($36.6 \pm 0.5$ Myr) can help to understand formation mechanisms for stars that exhibit anomalous velocities through the galaxy. This on-sky demonstration illustrates the spatial resolution of the iLocater SX acquisition camera working in tandem with the LBT AO system; it further derisks a number of technical hurdles involved in combining AO with Doppler spectroscopy.

arXiv:2412.06896v1 Announce Type: new Abstract: The Sagittarius dwarf spheroidal galaxy (Sgr dSph) is a satellite orbiting the Milky Way that has experienced multiple stripping events due to tidal interactions with our Galaxy. Its accretion history has led to a distinct stellar overdensity, which is the remnant of the core of the progenitor. We present a complete chemical analysis of 111 giant stars in the core of Sgr dSph to investigate the chemical evolution and enrichment history of this satellite. Employing the metallicity-sensitive Ca H&K photometry from the Pristine Inner Galaxy Survey, we selected stars spanning a wide metallicity range and obtained high-resolution spectra with the ESO FLAMES/GIRAFFE multi-object spectrograph. For the stellar sample covering $-2.13 < \rm{[Fe/H] < -0.35}$, we derived abundances for up to 14 chemical elements with average uncertainties of $\sim 0.09$ dex and a set of stellar ages which allowed us to build an age-metallicity relation (AMR) for the entire sample. With the most comprehensive set of chemical species measured for the core of Sgr, we studied several [X/Fe] ratios. Most trends align closely with Galactic chemical trends, but notable differences emerge in the heavy $n$-capture elements, which offer independent insights into the star formation history of a stellar population. The deficiency in the $\alpha$-elements with respect the Milky Way suggests a slower, less efficient early star formation history, similar to other massive satellites. $S$-process element patterns indicate significant enrichment from AGB stars over time. The AMR and chemical ratios point to an extended star formation history, with a rapid early phase in the first Gyr, followed by declining activity and later star-forming episodes. These findings are consistent with Sgr hosting multiple stellar populations, from young ($\sim 4$ Gyr) to old, metal-poor stars ($\sim 10$ Gyr)

arXiv:2408.13314v2 Announce Type: replace Abstract: Enhanced emission in the months to years preceding explosion has been detected for several core-collapse supernovae (SNe). Though the physical mechanisms driving the emission remain hotly debated, the light curves of detected events show long-lived ($\geq$50 days), plateau-like behavior, suggesting hydrogen recombination may significantly contribute to the total energy budget. The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will provide a decade-long photometric baseline to search for this emission, both in binned pre-explosion observations after an SN is detected and in single-visit observations prior to the SN explosion. In anticipation of these searches, we simulate a range of eruptive precursor models to core-collapse SNe and forecast the discovery rates of these phenomena in LSST data. We find a detection rate of ~40-130 yr$^{-1}$ for SN IIP/IIL precursors and ~110 yr$^{-1}$ for SN IIn precursors in single-epoch photometry. Considering the first three years of observations with the effects of rolling and observing triplets included, this number grows to a total of 150-400 in binned photometry, with the highest number recovered when binning in 100-day bins for 2020tlf-like precursors and in 20-day bins for other recombination-driven models from the literature. We quantify the impact of using templates contaminated by residual light (from either long-lived or separate precursor emission) on these detection rates, and explore strategies for estimating baseline flux to mitigate these issues. Spectroscopic follow-up of the eruptions preceding core-collapse SNe and detected with LSST will offer important clues to the underlying drivers of terminal-stage mass loss in massive stars.