Parity Violation in Cosmology
Parity symmetry is known to be violated in the weak interaction. Do the physical laws behind the unsolved problems of modern cosmology – cosmic inflation, dark matter, and dark energy – also violate parity symmetry? In this talk, we will discuss theoretical and observational possibilities of parity violation in cosmology, a topic that has received much attention in recent years.
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arXiv:2403.03908v1 Announce Type: new
Abstract: We utilize deep JWST NIRCam observations for the first direct constraints on the Galaxy Stellar Mass Function (GSMF) at z>10. Our EPOCHS v1 sample includes 1120 galaxy candidates at 6.5 9 than some studies predict, suggesting a rapid buildup of stellar mass in the early Universe. We find no incompatibility between our results and those of standard cosmological models, as suggested previously, although the most massive galaxies may require a high star formation efficiency. We find that the 'Little Red Dot' galaxies dominate the z=7 GSMF at high-masses, necessitating a better understanding of the relative contributions of AGN and stellar emission. We show that assuming a theoretically motivated top-heavy IMF reduces stellar mass by 0.5 dex without affecting fit quality, but our results remain consistent with existing cosmological models with a standard IMF.
arXiv:2403.03872v1 Announce Type: new
Abstract: Recent observations have found a large number of supermassive black holes already in place in the first few hundred million years after Big Bang. The channels of formation and growth of these early, massive black holes are not clear, with scenarios ranging from heavy seeds to light seeds experiencing bursts of high accretion rate. Here we present the detection, from the JADES survey, of broad Halpha emission in a galaxy at z=6.68, which traces a black hole with mass of ~ 4 * 10^8 Msun and accreting at a rate of only 0.02 times the Eddington limit. The host galaxy has low star formation rate (~ 1 Msun/yr, a factor of 3 below the star forming main sequence). The black hole to stellar mass ratio is ~ 0.4, i.e. about 1,000 times above the local relation, while the system is closer to the local relations in terms of dynamical mass and velocity dispersion of the host galaxy. This object is most likely the tip of the iceberg of a much larger population of dormant black holes around the epoch of reionisation. Its properties are consistent with scenarios in which short bursts of super-Eddington accretion have resulted in black hole overgrowth and massive gas expulsion from the accretion disk; in between bursts, black holes spend most of their life in a dormant state.
arXiv:2403.03379v1 Announce Type: new
Abstract: The ALMA [CII] Resolved Ism in STar-forming gALaxies (CRISTAL) survey is a Cycle 8 ALMA Large Programme that studies the cold gas component of high-redshift galaxies. Its sub-arcsecond resolution observations are key to disentangling physical mechanisms that shape galaxies during cosmic dawn. In this paper, we explore the morphology and kinematics of the cold gas, star-forming, and stellar components in the star-forming main-sequence galaxy CRISTAL-05/HZ3, at z = 5.54. Our analysis includes 0.3" spatial resolution (~2 kpc) ALMA observations of the [CII] line. While CRISTAL-05 was previously classified as a single source, our observations reveal that the system is a close interacting pair surrounded by an extended component of carbon-enriched gas. This is imprinted in the disturbed elongated [CII] morphology and the separation of the two components in the position-velocity diagram (~100 km/s). The central region is composed of two components, named C05-NW and C05-SE, with the former being the dominant one. A significant fraction of the [CII] arises beyond the close pair up to 10 kpc, while the regions forming new massive stars and the stellar component seem compact (r_[CII] ~ 4 r_UV), as traced by rest-frame UV and optical imaging obtained with the Hubble Space Telescope and the James Webb Space Telescope. Our kinematic model, using the DYSMALpy software, yields a minor contribution of dark matter of C05-NW within a radius of ~2x Reff. Finally, we explore the resolved [CII]/FIR ratios as a proxy for shock-heating produced by this merger. We argue that the extended [CII] emission is mainly caused by the merger, which could not be discerned with lower-resolution observations. Our work emphasizes the need for high-resolution observations to fully characterize the dynamic stages of infant galaxies and the physical mechanisms that drive the metal enrichment of the circumgalactic medium.
arXiv:2403.03243v1 Announce Type: new
Abstract: We present an analysis of the diffuse ionised gas (DIG) in a high-resolution simulation of an isolated Milky Way-like galaxy, incorporating on-the-fly radiative transfer and non-equilibrium thermochemistry. We utilise the Monte-Carlo radiative transfer code COLT to self-consistently obtain ionisation states and line emission in post-processing. We find a clear bimodal distribution in the electron densities of ionised gas ($n_{\rm e}$), allowing us to define a threshold of $n_{\rm e}=10\,\mathrm{cm}^{-3}$ to differentiate DIG from HII regions. The DIG is primarily ionised by stars aged 5-25 Myr, which become exposed directly to low-density gas after HII regions have been cleared. Leakage from recently formed stars ($
The James Webb Space Telescope has revealed that a distant galaxy stopped forming stars extraordinarily fast, making it the furthest dead galaxy ever spotted
arXiv:2403.03192v1 Announce Type: new
Abstract: We present rest-frame optical data of the z~4 sub-millimeter galaxy GN20 obtained with JWST/NIRSpec in integral field spectroscopy (IFS) mode. The H$\alpha$ emission is asymmetric and clumpy and extends over a projected distance of more than 15 kpc. To first order, the large-scale ionised gas kinematics are consistent with a turbulent ($\sigma\sim90$ km/s), rotating disc ($v_{\rm rot}\sim500$ km/s), congruent with previous studies of its molecular and ionised gas kinematics. However, we also find clear evidence for non-circular motions in the H$\alpha$ kinematics. We discuss their possible connection with various scenarios, such as external perturbations, accretion or radial flows. In the centre of GN20, we find broad line emission (FWHM $\sim1000-2000$ km/s) in the H$\alpha$+[N II] complex, suggestive of fast, AGN-driven winds or, alternatively, of the broad-line region of an active black hole. Elevated values of [N II]$\lambda6583$/H$\alpha>0.4$ and EW(H$\alpha)>6$ \r{A}, throughout large parts of GN20 suggest that feedback from the active black hole is able to photo-ionise the interstellar medium. Our data corroborates that GN20 offers a unique opportunity to observe key processes in the evolution of the most massive present-day galaxies acting in concert, over 12 billion years ago.
The Dawn of Galaxy-scale Gravitational Wave Astronomy
For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.
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New Space & the CubeSat Revolution
CubeSats stand at the forefront of the New Space Revolution, a paradigm shift in space exploration characterised by reduced launch costs and increased accessibility to space. These miniature satellites, defined by their standardised dimensions and modular design, have emerged as a pivotal technology with some implications for research in astronomy. With their standardised dimensions and modular design, these Nanosatellites enable a wide range of experiments that were previously the domain of larger, more costly missions. In my talk, I aim to introduce you to valuable opportunities that can emerge by leading a CubeSat project with a special interest in payloads dedicated to astrophysics research. As a cost-effective space instrument, CubeSats unlock observational windows across the ultraviolet, far-infrared, and low-frequency radio spectra, which are inaccessible from Earth’s surface. Beyond their technical capabilities, these satellites enable sustained observations of celestial bodies over extended periods, free from the scheduling constraints of larger telescopes.
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Obscured AGN across cosmic time
The bulk of the growth of supermassive black holes over cosmic time takes place behind heavy obscuration. I will present observational evidence that much, or even most, of these AGN are very heavily obscured (Compton-thick) and thus hidden from many previous multiwavelength surveys. I will discuss the implications for cosmic black hole growth and the populations of AGN now detected in the early Universe with JWST .
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The Fate of Matter Fields in Metric-Affine Gravity
General relativity (GR) exists in different formulations. They are equivalent in pure gravity but generically lead to distinct predictions once matter is included. After a brief overview of various versions of GR, I will focus on metric-affine gravity, which avoids any assumption about the vanishing of curvature, torsion, or nonmetricity. With a view toward the Standard Model, we can construct a generic model of (complex) scalar, fermionic, and gauge fields coupled to GR and derive an equivalent metric theory, which features numerous new interaction terms. There are multiple phenomenological consequences, which I will detail: an improved setting for Higgs inflation, a new (purely gravitational) production channel for fermionic dark matter, and an outlook on axion inflation.
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Relative contribution from comets and carbonaceous asteroids to the Earth's volatile budget
Recent models of solar system formation suggest that a dynamical instability among the giant planets happened within the first 100 Myr after disk dispersal, perhaps before the Moon-forming impact. As a direct consequence, a bombardment of volatile-rich impactors may have taken place on Earth before internal and atmospheric reservoirs were decoupled. However, such a timing has been interpreted to potentially be at odds with the disparate inventories of Xe isotopes in Earth’s mantle compared to its atmosphere. In this seminar, I will talk about the dynamical effects of an Early Instability on the delivery of carbonaceous asteroids and comets to Earth, and address the implications for the Earth’s volatile budget.
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arXiv:2309.05713v2 Announce Type: replace
Abstract: Dust-obscured galaxies are thought to represent an early evolutionary phase of massive galaxies in which the active galactic nucleus (AGN) is still deeply buried in significant amounts of dusty material and its emission is strongly suppressed. The unprecedented sensitivity of the James Webb Space Telescope enables us for the first time to detect the rest-frame optical emission of heavily obscured AGN and unveil the properties of the hidden accreting super-massive black holes (BHs). In this work, we present the JWST/NIRSpec IFS data of ALESS073.1, a massive, dusty, star-forming galaxy at $z = 4.76$ hosting an AGN at its center. The detection of a very broad $H_\alpha$ emission associated with the Broad Line Region (BLR) confirms the presence of a BH ($\log(M_{BH}/M_\odot)>8.7$) accreting at less than 15\% of its Eddington limit and classifies the target as a Type 1 AGN. The rest-frame optical emission lines also reveal a fast ionized gas outflow marginally resolved in the galaxy center. The high sensitivity of NIRSpec allows us to perform the kinematic analysis of the narrow H$\alpha$ component which indicates that the warm ionized gas velocity field is consistent with disk rotation. We also find that, in the innermost nuclear regions ($
arXiv:2306.09142v2 Announce Type: replace
Abstract: Recent observations with the \textit{James Webb} Space Telescope (JWST) have further refined the spectroscopic redshift of GN-z11, one of the most distant galaxies identified with the \textit{Hubble} Space Telescope (HST) at $z=10.603$. The presence of extremely dense gas ($>10^{10}$ cm$^{-3}$), the detection of high-ionisation lines and of CII*1335 emission, as well as the presence of an ionisation cone, indicate that GN-z11 also hosts an Active Galactic Nucleus (AGN). Further photometric and spectroscopic follow-up demonstrates that it lies in a large-scale, overdense structure with possible signatures of Population III (PopIII) stars in its halo. Surprisingly, Ly$\alpha$ has also been detected despite the expected largely neutral inter-galactic medium at such a redshift. We exploit recent JWST/NIRSpec IFU observations to demonstrate that the Ly$\alpha$ emission in GN-z11 is part of an extended halo with a minimum size of 0.8--3.2 kpc, depending on the definition used to derive the halo size. The surface brightness of the Ly$\alpha$ halo around GN-z11 appears consistent with Ly$\alpha$ halos observed around $z\sim6$ quasars. At the wavelength of Ly$\alpha$ at $z\sim$10.6, we identify three other emission line candidates within the IFU Field-of-View with no UV rest-frame counterpart visible in deep images from the JWST/NIRCam. If confirmed, this could be the first evidence that the local region of GN-z11 represents a candidate protocluster core, forming just 400 Myr after the Big Bang. We give a first estimate of the dark matter halo mass of this structure ($M_h$=2.96$^{+0.44}_{-0.39} \times$10$^{10}$ M$_{\odot}$), consistent with a Coma-like cluster progenitor.
arXiv:2211.02038v2 Announce Type: replace
Abstract: We utilise theoretical models of Population III stellar+nebular spectra to investigate the prospects of observing and accurately identifying Population III galaxies with JWST using both deep imaging and spectroscopy. We investigate a series of different colour cuts, finding that a combination of NIRCam and MIRI photometry through the F444W-F560W, F560W-F770W colours offers the most robust identifier of potential $z=8$ Pop III candidates. We calculate that NIRCam will have to reach $\sim$28.5-30.0 AB mag depths (1-20 h), and MIRI F560W must reach $\sim$27.5-29.0 AB mag depths (10-100 h) to achieve $5\sigma$ continuum detections of $M_* = 10^6~\mathrm{M}_\odot$ Pop III galaxies at $z=8$. We also discuss the prospects of identifying Pop III candidates through slitless and NIRSpec spectroscopic surveys that target Ly$\alpha$, H$\beta$ and/or He II $\lambda 1640$. We find small differences in the H$\beta$ rest-frame equivalent width (EW) between Pop III and non-Pop III galaxies, rendering this diagnostic likely impractical. Instead, we find that the detection of high EW He II $\lambda 1640$ emission will serve as the definitive Pop III identifier, requiring (ultra-)deep integrations (10-250 h) with NIRSpec/G140M for $M_*=10^6~\mathrm{M}_\odot$ Pop III galaxies at $z=8$. However, MIRI F770W detections of Pop III galaxies will require substantial gravitational lensing ($\mu=10$) and/or fortuitous imaging of exceptionally massive ($M_* = 10^7~\mathrm{M}_\odot$) Pop III galaxies. Thus, NIRCam medium-band imaging surveys that can search for high EW He II $\lambda 1640$ emitters in photometry may perhaps be a viable alternative for finding Pop III candidates.
arXiv:2403.00490v1 Announce Type: new
Abstract: We apply a suite of different estimators to the Quijote-PNG halo catalogues to find the best approach to constrain Primordial non-Gaussianity (PNG) at non-linear cosmological scales, up to $k_{\rm max} = 0.5 \, h\,{\rm Mpc}^{-1}$. The set of summary statistics considered in our analysis includes the power spectrum, bispectrum, halo mass function, marked power spectrum, and marked modal bispectrum. Marked statistics are used here for the first time in the context of PNG study. We perform a Fisher analysis to estimate their cosmological information content, showing substantial improvements when marked observables are added to the analysis. Starting from these summaries, we train deep neural networks (NN) to perform likelihood-free inference of cosmological and PNG parameters. We assess the performance of different subsets of summary statistics; in the case of $f_\mathrm{NL}^\mathrm{equil}$, we find that a combination of the power spectrum and a suitable marked power spectrum outperforms the combination of power spectrum and bispectrum, the baseline statistics usually employed in PNG analysis. A minimal pipeline to analyse the statistics we identified can be implemented either with our ML algorithm or via more traditional estimators, if these are deemed more reliable.
The Nature of Dark Matter with Lyman-Alpha Forest
The existence of dark matter, which constitutes 85% of the matter density and 26% of the total energy density, is clearly demonstrated by cosmological observations of the Universe. And yet, very little is known about the nature of dark matter. The observations support the ‘cold dark matter’ (CDM) paradigm, in which the dark matter is a heavy particle, with little to no interactions through fundamental forces other than gravity. The cosmological and astrophysical observations of dark matter’s gravitational interaction currently provide the only robust evidence of dark matter. These observations typically rely on characterising the distribution of matter in the Universe. A dark matter particle that is lighter than the standard CDM paradigm predicts imprints a suppression of structure in the matter distribution. The exact scale where this happens is most often linked to the mass of the dark matter particle. I will present new results on the thermal relic warm dark matter constraints using the high-redshift cosmic web as traced by the Lyman-alpha forest.
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