arXiv:2306.04536v2 Announce Type: replace
Abstract: We present the properties of 17 faint Ly$\alpha$ emitting galaxies (LAEs) at $z>5.8$ from the JWST Advanced Deep Extragalactic Survey (JADES) in the Hubble Ultra Deep Field/GOODS-S. These LAEs span a redshift range $z\approx5.8-8.0$ and a UV magnitude range $M_{UV}\approx-17$ to $-20.6$, with the Ly$\alpha$ equivalent width (EW) in the range $\approx 25-350$ \AA. The detection of other rest-optical emission lines in the spectra of these LAEs enables the determination of accurate systemic redshifts and Ly{\alpha} velocity offsets, as well as the physical and chemical composition of their stars and interstellar media. These faint LAEs are consistent with metal-poor systems with high ionization parameters, similar to the general galaxy population at $z>6$. We measured an average ionizing photon production efficiency, log($\xi_\rm{ion}$/erg$^{-1}$ Hz) $\approx25.57$ across our LAEs, which does not evolve strongly with redshift. We report an anti-correlation between the Ly$\alpha$ escape fraction (f_\rm{esc}) and the velocity offset from systemic redshift, consistent with model expectations. We further find that the strength and velocity offset of Ly$\alpha$ are neither correlated with galaxy spectroscopic properties nor with $\xi_\rm{ion}$. We find a decrease in $f_\rm{esc}$(Ly$\alpha$) with redshift, indicative of decreasing sizes of ionized bubbles around LAEs at high redshifts. We used a range of galaxy properties to predict Lyman continuum $f_\rm{esc}$ for our LAEs, finding that the ionizing photon output into the intergalactic medium remains roughly constant across the observed Ly$\alpha$ EW, showing a mild increase at fainter M$_{UV}$ and at higher redshifts. We derived correlations between the ionizing photon output from LAEs and $M_{UV}$, Ly$\alpha$ EW and redshifts, which can be used to constrain the ionizing photon contribution of LAEs at $z > 6$ towards cosmic reionization.
Real-time pipelines for SKA — Progress and challenges
The Square Kilometre Array (SKA) will be the largest interferometric radio telescope to date, with unprecedented resolution and sensitivity to study various phenomena of the universe. In data processing pipelines for radio telescopes, real time calibration, such as beam former and pointing offset calibration, are crucial for obtaining high-quality interferometric data from the observations. As an example, I will discuss the design and ongoing implementation of the pointing offset calibration pipeline within SKA ’s data processing software, describing the steps carried out to integrate the pipeline into telescope execution control and data queue system, as well as outlining challenges and greater implications on the data processing algorithm and software within the radio astronomy community.
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arXiv:2402.00930v2 Announce Type: replace
Abstract: We present a simple method for assessing the predictive performance of high-dimensional models directly in data space when only samples are available. Our approach is to compare the quantiles of observables predicted by a model to those of the observables themselves. In cases where the dimensionality of the observables is large (e.g. multiband galaxy photometry), we advocate that the comparison is made after projection onto a set of principal axes to reduce the dimensionality. We demonstrate our method on a series of two-dimensional examples. We then apply it to results from a state-of-the-art generative model for galaxy photometry (pop-cosmos; arXiv:2402.00935) that generates predictions of colors and magnitudes by forward simulating from a 16-dimensional distribution of physical parameters represented by a score-based diffusion model. We validate the predictive performance of this model directly in a space of nine broadband colors. Although motivated by this specific example, the techniques we present will be broadly useful for evaluating the performance of flexible, non-parametric population models of this kind, and can be readily applied to any setting where two sets of samples are to be compared.
arXiv:2306.07316v2 Announce Type: replace
Abstract: In this work, we use hydrodynamical simulations to explore the effects of kinetic AGN jet feedback on the progression and outcome of the major merger of two isolated, gas-rich galaxies. We present simulations that use the moving-mesh code AREPO to follow the progression of the merger through first passage and up to the final coalescence, modelling the black holes at the centres of both of the merging galaxies using our prescription for black hole accretion via an $\alpha$-disc and feedback in the form of a spin-driven jet. We find that the jets drive large-scale, multiphase outflows which launch large quantities of cold gas out to distances greater than 100 kpc and with velocities that reach $\sim 2500 \, {\rm km \, s^{-1}}$. Gas in the outflows that decelerates, cools and falls back on the galaxies can provide a rich source of fuel for the black hole, leading to intense episodes of jet activity in which the jet can become significantly misaligned. The presence of AGN jets affects the growth of the stellar component: star formation is moderately suppressed at all times during the merger and the peak of the star formation rate, attained during the final coalescence of the galaxies, is reduced by a factor of $\sim 2$. Analysis of simulations such as these will play a central role in making precise predictions for multimessenger investigations of dual radio-AGN, which next-generation observational facilities such as LISA, Athena and SKA will make possible.
arXiv:2402.10697v1 Announce Type: new
Abstract: In this paper we present and validate the galaxy sample used for the analysis of the baryon acoustic oscillation (BAO) signal in the Dark Energy Survey (DES) Y6 data. The definition is based on a color and redshift-dependent magnitude cut optimized to select galaxies at redshifts higher than 0.6, while ensuring a high-quality photo-$z$ determination. The optimization is performed using a Fisher forecast algorithm, finding the optimal $i$-magnitude cut to be given by $i$
arXiv:2402.10696v1 Announce Type: new
Abstract: We present the angular diameter distance measurement obtained with the Baryonic Acoustic Oscillation feature from galaxy clustering in the completed Dark Energy Survey, consisting of six years (Y6) of observations. We use the Y6 BAO galaxy sample, optimized for BAO science in the redshift range 0.60.75 from any survey and the most precise measurement at any redshift from photometric surveys. The analysis was performed blinded to the BAO position and it is shown to be robust against analysis choices, data removal, redshift calibrations and observational systematics.
On the physical spectra of primordial perturbations from inflation
It has been suggested that the effects of renormalization significantly reduce the amplitude of the inflationary spectra at scales measurable in the cosmic microwave background. Via a gauge-invariant analysis, we compute the renormalized scalar and tensor power spectra and follow their evolution in an inflating universe that undergoes a transition to an FRW phase with a growing horizon. For perturbations originating from Minkowski vacuum fluctuations, we show that the standard prediction for the spectrum on superhorizon scales is a late-time attractor, while it is UV finite at all times. Our result is independent of the equation of state after inflation, showing that the standard prediction is fully robust.
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Emergent gauge fields, fractionalised quasiparticles and dynamical fractals
Field theoretic descriptions are a powerful tool to capture the emergent, collective behaviour of strongly correlated many body systems on large scales. Gauge field theories in particular are of special interest in modern physics, due to their connection to topological behaviour and fractionalisation. Through this modelling, the original dense system of strongly interacting degrees of freedom can be interpreted as an emergent vacuum with quasiparticle excitations whose properties are closely related to the nature of the emergent gauge fields. This change in perspective affords us an unprecedented insight into the properties of these systems and in predicting new behaviour. We will review some of these concepts in a model and material that has become a paradigmatic case in point: spin ice. We shall further discuss how microscopic details can lead to surprisingly important effects in the cooperative dynamics of these systems, which becomes underpinned by near-fractal structures.
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arXiv:2312.08828v2 Announce Type: replace
Abstract: Constraints on the potential properties of superconducting cosmic strings provide an indirect probe of physics beyond the standard model at energies inaccessible to terrestrial particle colliders. In this study, we perform the first joint Bayesian analysis to extract constraints on superconducting cosmic strings from current 21-cm signal measurements while accounting rigorously for the uncertainties in foregrounds and high redshift astrophysics. We include the latest publicly available 21-cm power spectrum upper limits from HERA, 21-cm global signal data from SARAS 3, and the synergistic probe of the unresolved X-ray background in our final analysis. This paper thus constitutes the first attempt to use 21-cm power spectrum data to probe cosmic strings. In contrast to previous works, we find no strong constraints can be placed on superconducting cosmic strings from current 21-cm measurements. This is because of uncertainties in the X-ray emission efficiency of the first galaxies, with X-ray emissivities greater than $3 \times 10^{40}$erg s$^{-1}$ M$_{\odot}^{-1}$ yr able to mask the presence of cosmic strings in the 21-cm signal. We conclude by discussing the prospects for future constraints from definitive 21-cm signal measurements and argue that the recently proposed soft photon heating should be cause for optimism due to its potential to break degeneracies that would have otherwise made the signatures of cosmic strings difficult to distinguish from those of astrophysical origin.
arXiv:2309.04533v2 Announce Type: replace
Abstract: This study introduces novel constraints on the free-streaming of thermal relic warm dark matter (WDM) from Lyman-$\alpha$ forest flux power spectra. Our analysis utilises a high-resolution, high-redshift sample of quasar spectra observed using the HIRES and UVES spectrographs ($z=4.2-5.0$). We employ a Bayesian inference framework and a simulation-based likelihood that encompasses various parameters including the free-streaming of dark matter, cosmological parameters, the thermal history of the intergalactic medium, and inhomogeneous reionization, to establish lower limits on the mass of a thermal relic WDM particle of $5.7\;\mathrm{keV}$ (at 95\% C.L.). This result surpasses previous limits from the Lyman-$\alpha$ forest through reduction of the measured uncertainties due to a larger statistical sample and by measuring clustering to smaller scales ($k_{\rm max}=0.2\;\mathrm{km^{-1}\,s}$). The approximately two-fold improvement due to the expanded statistical sample suggests that the effectiveness of Lyman-$\alpha$ forest constraints on WDM models at high redshifts are limited by the availability of high-quality quasar spectra. Restricting the analysis to comparable scales and thermal history priors as in prior studies ($k_{\rm max}
arXiv:2306.02469v3 Announce Type: replace
Abstract: We use SEDz* -- a code designed to chart star formation histories (SFHs) of 6
Stellar Mass Assembly of Galaxy Populations up to z = 4 with pop-cosmos
In a recent paper we presented pop-cosmos, a state-of-the-art stellar population synthesis (SPS) framework. We described the details of how we fitted this framework to a large, deep, flux-limited (r < 25) sample of galaxies from the Cosmic Evolution Survey (COSMOS), enabling investigation of the full web of dependencies between different galaxy properties for the first time. In this talk I will present my recent work investigating the star formation histories (SFHs) of galaxy populations up to z=4 utilising the pop-cosmos model. I will begin by summarizing the details of our model and the SFH prescription employed in it. I will then present key galaxy evolution results such as the mean stellar mass assembly histories of galaxy populations through cosmic time. Further, by defining star-forming and quiescent subpopulations based on recent star formation activity (i.e. last 100 Myr), these relations will highlight how these subpopulations build up their stellar mass.
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arXiv:2402.08717v1 Announce Type: new
Abstract: We investigate galaxy sizes at redshift $z\gtrsim 6$ with the cosmological radiation-magneto-hydrodynamic simulation suite THESAN(-HR). These simulations simultaneously capture the reionization of the large-scale intergalactic medium and resolved galaxy properties. The intrinsic size ($r^{\ast}_{1/2}$) of simulated galaxies increases moderately with stellar mass at $M_{\ast} \lesssim 10^{8}\,{\rm M}_{\odot}$ and decreases fast at larger masses, resulting in a hump feature at $M_{\ast}\sim 10^{8}\,{\rm M}_{\odot}$ that is insensitive to redshift. Low-mass galaxies are in the initial phase of size growth and are better described by a spherical shell model with feedback-driven gas outflows competing with the cold inflows. In contrast, massive galaxies fit better with the disk formation model. They generally experience a phase of rapid compaction and gas depletion, likely driven by internal disk instability rather than external processes. We identify four compact quenched galaxies in the $(95.5\,{\rm cMpc})^{3}$ volume of THESAN-1 at $z\simeq 6$, and their quenching follows reaching a characteristic stellar surface density akin to the massive compact galaxies at cosmic noon. Compared to observations, we find that the median UV effective radius ($R^{\rm UV}_{\rm eff}$) of simulated galaxies is at least three times larger than the observed ones at $M_{\ast}\lesssim 10^{9}\,{\rm M}_{\odot}$ or $M_{\rm UV}\gtrsim -20$ at $6 \lesssim z \lesssim 10$. This inconsistency, related to the hump feature of the intrinsic size--mass relation, persists across many other cosmological simulations with different galaxy formation models and numerical resolutions, demonstrating the potential of using galaxy morphology to constrain galaxy formation models at high redshifts.
Astrophysical signatures on the LISA data stream from Massive Black Hole Binaries
European Space Agency recently adopted the Laser interferometry space antenna (LISA) to launch it in the 2030s to observe Gravitational waves (GWs) in the millihz frequency band. LISA ’s primary sources are massive black hole binaries (MBHBs) of 104-108 solar masses due to the merger of galaxies, stellar-mass BHs coalescence into their galactic central MBH , and numerous white dwarf binaries that exist in the Milky Way. I focus on MBH Bs that usually require an environment consisting mainly of gas and stars to merge within the Universe’s lifetime. I primarily consider the effects of a gas accretion disc for a sub-pc separation as it can significantly torque the binary to affect the initial binary parameters in the LISA band, especially orbital eccentricity. While gas perturbations become sub-dominant to GWs a few years before the merger of MBH Bs, they can still cause detectable phase shifts and excite observable eccentricities for reasonable disc properties that hint toward their history before reaching the millihz band. I will use analytical and numerical techniques to show the minimum measurable eccentricity of an MBHB that LISA will measure in a vacuum and gas. To be robust, I consider a high-order post-Newtonian gravitational waveform model, LISA ’s motion in its orbit around the Sun, and the time delay interferometery to enhance astrophysical signal over the dominant laser noise. I also explore if a weak gas effect can be mimicked by a small eccentricity and vice versa to motivate synergies between LISA and electromagnetic observations to unlock mysteries of the MBHB evolution.
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Nature, Published online: 14 February 2024; doi:10.1038/d41586-024-00489-8
The eROSITA telescope’s detailed pictures are among the most precise cosmological measurements ever made.
Quantifying the impact of baryons on large scale structure with the FLAMINGO simulations
Measurements of the clustering of large scale structure can place strong constraints on our understanding of cosmology. However, many of our predictions of non-linear structure formation are based on gravity only (i.e. dark matter only) N-body simulations because the simultaneous modelling of lengths scales from a few parsecs for star formation to 100s of megaparsecs for the cosmic web is a prohibitively expensive process. In order to address any potential systematics arising from the neglect of baryons, we have performed a suite of cosmological, fully hydrodynamic simulations called the FLAMINGO simulations. Using these simulations, we have created realistic mock catalogues for the SDSS DR12 CMASS galaxy sample, a sample that is often used to derive cosmological constraints. From these catalogues we measure the projected correlation function, monopole and quadrupole correlation functions and compare these to observations to provide a bound on the impact of baryons on large scale structure cosmology. We further investigate the effect of assuming different models for AGN
feedback and star formation.
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The predicted present-day amplitude of matter fluctuations based on cosmic microwave background (CMB) anisotropy data has sometimes been found discrepant with more direct measurements of late-time structure. This has motivated many extensions to the standard cosmological model, including kinetic interactions between dark matter and dark energy that introduce a drag force slowing the growth of structure at late times. Exploring this scenario, we develop a model for quasi-linear scales in the matter power spectrum by calculating the critical overdensity in the presence of this interaction and a varying dark energy equation of state. We explicitly avoid modeling or interpretation of data on non-linear scales in this model (such as use of $\Lambda$CDM-calibrated priors), which would require numerical simulations. We find that the presence of the drag force hinders halo formation, thus increasing the deviation from $\Lambda$CDM in the mildly non-linear regime. We use CMB lensing observations from the sixth data release of the Atacama Cosmology Telescope up to $L=1250$ (in combination with Planck, Sloan Digital Sky Survey, and 6dFGS data) to derive the strongest constraints to date on the amplitude of the drag term, finding the dimensionless interaction strength $\Gamma_\mathrm{DMDE}/(H_0\rho_\mathrm{c})
