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Galaxy-halo connection in current CMB cross-correlation science

In this talk we will review models and constraints on halo occupation distribution (HOD) statistics in Cosmic Microwave Background (CMB) cross-correlation studies. We will focus on CMB lensing and kinetic Sunyavev Zeldovich cross-correlations. As we will see, HOD degeneracies are a limiting aspect of our measurements of the gas distributions around massive halos. We will discuss current constraints on the gas derived from recent ACT data and prospects for SO, as well as the significance of these constraints in the context of hydrodynamical simulations.

• Speaker: Boris Bolliet (Cavendish)
• Friday 31 January 2025, 11:30-12:30
• Venue: Ryle Seminar Room, KICC + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Nature, Published online: 27 January 2025; doi:10.1038/d41586-025-00218-9

Nobel laureate Steven Weinberg’s posthumously published memoir details a swashbuckling life in physics.

arXiv:2408.07749v2 Announce Type: replace Abstract: The spectral energy distribution (SED) of galaxies is essential for deriving fundamental properties like stellar mass and star formation history (SFH). However, conventional methods, including both parametric and non-parametric approaches, often fail to accurately recover the observed cosmic star formation rate (SFR) density due to oversimplified or unrealistic assumptions about SFH and their inability to account for the complex SFH variations across different galaxy populations. To address this issue, we introduce a novel approach that improves galaxy broadband SED analysis by incorporating physical priors derived from hydrodynamical simulations. Tests using IllustrisTNG simulations demonstrate that our method can reliably determine galaxy physical properties from broadband photometry, including stellar mass within 0.05 dex, current SFR within 0.3 dex, and fractional stellar formation time within 0.2 dex, with a negligible fraction of catastrophic failures. When applied to the Sloan Digital Sky Survey (SDSS) main photometric galaxy sample with spectroscopic redshift, our estimates of stellar mass and SFR are consistent with the widely used MPA-JHU and GSWLC catalogs. Notably, using the derived SFHs of individual SDSS galaxies, we estimate the cosmic SFR density and stellar mass density with remarkable consistency to direct observations up to $z \sim 6$. This demonstrates a significant advancement in deriving SFHs from SEDs that closely align with observational data. Consequently, our method can reliably recover observed spectral indices such as $\rm D_{\rm n}(4000)$ and $\rm H\delta_{\rm A}$ by synthesizing the full spectra of galaxies using the estimated SFHs and metal enrichment histories, relying solely on broadband photometry as input. Furthermore, this method is extremely computationally efficient compared to conventional approaches.

arXiv:2407.10845v2 Announce Type: replace Abstract: We propose and implement a novel test to assess deviations from well-established concordance $\Lambda$CDM cosmology while inferring dark energy properties. In contrast to the commonly implemented parametric forms of the dark energy equation-of-state (EoS), we test the validity of the cosmological constant on the more fundamental scale factor [$a(t)$] which determines the expansion rate of the Universe. We constrain our extended `general model' using the late-time observables. The posterior of the dark energy EoS is mainly constrained to be quintessence-like naturally excluding physically unviable regions such as phantom crossings or exponential growth.

The Maxwell equations on the full Kerr black hole family

We discuss a proof of uniform boundedness and decay statements for solutions to the Maxwell equations on Kerr black holes. The proof is unconditional in the full subextremal |a| less than M family, in view of earlier joint work with Yakov Shlapentokh-Rothman. For extremal |a|=M Kerr, it is conditional on a conjecture for the spin ±1 Teukolsky equations motivated by work of Gajic and Casals—Gralla—Zimmerman. This is joint work with Gabriele Benomio (GSSI).

• Speaker: Rita Teixera da Costa
• Friday 31 January 2025, 13:00-14:00
• Venue: Potter Room / https://cam-ac-uk.zoom.us/j/87235967698.
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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Results from the Dark Energy Spectroscopic Instrument (DESI) year-one data release.

DESI represents the culmination of multi-years efforts and advanced spectroscopic techniques. Placed at Mayall 4-meter Telescope, DESI harnesses the power of 5,000 robotic fiber positioners, coupled with state-of-the-art spectrographs, to capture the spectral signatures of millions of galaxies and quasars with unprecedented precision. DESI success is also based on the collaborative spirit of its community, more than 400 scientists over 70 institutions in 5 continents.

This data release (DR1) corresponds to the first year of observations; it holds immense scientific promise across a multitude of fronts: from constraining cosmological parameters, mapping the expansion history of the Universe, to the properties of dark energy, gravity and neutrinos.

In this talk I will focus on the results from the first data release of DESI based on the baryon acoustic oscillations (BAO) and redshift space distortions (RSD) analyses, and their impact in cosmology. On one hand, the BAO signal allows us to trace the expansion history of the universe through the last 11 billion years; and on the other hand the RSD allows us to test GR at cosmological scales over a similar period of time. In addition if baryon density information is added, DESI can also infer the rate of expansion today, the Hubble constant at 1% level (H0=68.56 ± 0.75) km/s/Mpc. All these results seem to be in good agreement with the standard model of cosmology, the LCDM model. When combined with external datasets such as the SuperNovae data and Cosmic Microwave Background anisotropy observations (CMB), we have observed in some cases interesting hints towards evolving dark energy. Furthermore, DESI data in combination with CMB is able to put constraints on the sum of neutrino masses reaching an upper bound of 0.071 eV at 95% confidence level within the LCDM model.

• Speaker: Héctor Gil-Marín (ICC, Barcelona U.)
• Monday 03 February 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

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Geometric Characterizations of Kerr-de Sitter and Related Metrics in All Dimensions

The Kerr-de Sitter metric, originally proposed by Carter in four dimensions and later extended by Gibbons, Lü, Page and Pope to all dimensions, is likely to play a relevant role among Lambda positive vacuum spacetimes. To better understand what makes it special, we calculate the asymptotic data characterizing the metric near conformal infinity. This requires a review of tools in conformal geometry, such as the Fefferman-Graham expansion, and its relation with the asymptotic initial value problem in arbitrary dimensions. The asymptotic data obtained for Kerr-de Sitter admits a straightforward generalization to a broader class of spacetimes that depends on a set of parameters, which we refer to as Kerr-de Sitter-like class. This class of metrics is obtained explicitly as limits or analytic extensions of Kerr-de Sitter and the space of parameters inherits a natural topological structure from the asymptotic data. Furthermore, we discuss additional characterizations within the Kerr-Schild type metrics and the algebraically special metrics that highlight the geometrical significance of the class.

• Speaker: Carlos Peón Nieto (UPM, Madrid)
• Friday 24 January 2025, 13:00-14:00
• Venue: Potter Room / https://cam-ac-uk.zoom.us/j/84511154241?pwd=B778JtHEd8Vb7aTOdsygQhBdXWbybI.1.
• Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.

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• Speaker: Malcolm Druett (Sheffield)
• Monday 17 March 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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• Speaker: Paul Barrere (Geneva)
• Monday 10 March 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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• Speaker: James Rogers (Institute of Astronomy, Cambridge)
• Monday 03 March 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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• Speaker: Serguei Komissarov (Leeds)
• Monday 24 February 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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• Speaker: Tamara Rogers (Newcastle)
• Monday 17 February 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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• Speaker: Adam Ingram (Newcastle)
• Monday 10 February 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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• Speaker: Guiseppe Lodato (Milan)
• Sunday 02 February 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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Formation, Evolution and Radiation of Magnetized Accretion Disks around Black Holes

The role that magnetic fields play in shaping the evolution and the radiative signature of accretion disks around black holes is very uncertain. This uncertainty is mainly due to the scarcity of direct observational constraints on the magnetic field’s geometry or strength in black hole disks. However, even from a theoretical point of viewour understanding of magnetized disks remains relatively poor. Indeed, analytic models of magnetized disks often need inputs from numerical simulations and numerical simulations of magnetized disks are difficult to perform and/or interpret. Because of this lack of magnetized disk models, standard disk models often reduce the magnetic field to a source of turbulence; turbulence through which the accretion can happen. While this simplification may hold for weakly magnetized disks, a large number of numerical simulations have shown that the role of a strong magnetic field goes far beyond producing turbulence. In particular, a strong magnetic field can produce powerful outflows, induce accretion through vertically elevated layers or non-axisymmetric structures, modify the time scales of accretion, enhance dissipation of gravitational energy in the disk and accelerate particles to very high energies. All of these effects will dramatically affect the evolution and the observational signature of accretion disks and open up new and exciting avenues to resolve outstanding problems of the standard accretion disk theory. In this talk, I will present an overview of my recent results on how strongly magnetized disks form, evolve and radiate. I will show in particular how strongly magnetized disks could explain events of very strong variability in AGNs, the flaring behavior of the Galactic center and the hardest emission in X-ray binaries.

• Speaker: Nicolas Scepi (Grenoble)
• Monday 27 January 2025, 14:00-15:00
• Venue: MR14 DAMTP and online.
• Series: DAMTP Astrophysics Seminars; organiser: Loren E. Held.

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arXiv:2412.14023v2 Announce Type: replace Abstract: Due to the large dynamic ranges involved with separating the cosmological 21-cm signal from the Cosmic Dawn from galactic foregrounds, a well-calibrated instrument is essential to avoid biases from instrumental systematics. In this paper we present three methods for calibrating a global 21-cm cosmology experiment using the noise wave parameter formalisation to characterise a low noise amplifier including a careful consideration of how calibrator temperature noise and singularities will bias the result. The first method presented in this paper builds upon the existing conjugate priors method by weighting the calibrators by a physically motivated factor, thereby avoiding singularities and normalising the noise. The second method fits polynomials to the noise wave parameters by marginalising over the polynomial coefficients and sampling the polynomial orders as parameters. The third method introduces a physically motivated noise model to the marginalised polynomial method. Running these methods on a suite of simulated datasets based on the REACH receiver design and a lab dataset, we found that our methods produced a calibration solution which is equally as or more accurate than the existing conjugate priors method when compared with an analytic estimate of the calibrator's noise. We find in the case of the measured lab dataset the conjugate priors method is biased heavily by the large noise on the shorted load calibrator, resulting in incorrect noise wave parameter fits. This is mitigated by the methods introduced in this paper which calibrate the validation source spectra to within 5% of the noise floor.

arXiv:2408.03374v3 Announce Type: replace Abstract: We investigate the spatial extent and structure of the [CII] line emission in a sample of 34 galaxies at $z=4-6$ from the ALMA-CRISTAL Survey. By modeling the [CII] line emission in the interferometric visibility, we derive the effective radius of [CII] line emission assuming an exponential profile. The [CII] line radius ranges from 0.5 to 3.5 kpc with an average value of $\langle R_{e,[CII]}\rangle=1.90$ kpc. We compare the [CII] sizes with the sizes of rest-frame UV and FIR continua, which were measured from the HST F160W images and ALMA Band-7 continuum images, respectively. We confirm that the [CII] line emission is more spatially extended than the continuum emission, with average size ratios of $\langle R_{e,[CII]}/R_{e,UV}\rangle=2.90$ and $\langle R_{e,[CII]}/R_{e,FIR}\rangle=1.54$, although about half of the FIR-detected sample show comparable spatial extent between [CII] line and FIR continuum emission. The residual visibility of the best-fit model do not show statistical evidence of flux excess, indicating that the [CII] line emission in star-forming galaxies can be characterized by an extended exponential profile. Overall, our results suggest that the spatial extent of [CII] line emission can primarily be explained by PDRs associated with star formation activity, while the contribution from diffuse neutral medium (atomic gas) and the effects of past merger events may further expand the [CII] line distributions, causing their variations. Finally, we report the negative correlation between $\Sigma_{[CII]}$ and EW$_{Ly\alpha}$, and possible negative correlation between $R_{e,[CII]}/R_{e,UV}$ and EW$_{Ly\alpha}$, which may be in line with the scenario that atomic gas largely contributes to the extended [CII] line emission. Future 3-D analysis of Ly$\alpha$ and H$\alpha$ lines will shed light on the association of the extended [CII] line emission with atomic gas and outflows.

arXiv:2501.13082v1 Announce Type: new Abstract: Recent observations from JWST have revealed an abundant population of active galactic nuclei (AGN) and so-called ``Little Red Dots'' (LRDs) at $2\lesssim z \lesssim 11$, many of which are characterized by V-shaped UV-to-optical continua with turnovers around the Balmer limit. The physical nature of these LRDs is unclear, and it remains debated whether the peculiar spectral shape originates from AGN, compact galaxies, or both. We present the analysis of new NIRSpec-IFU data from the BlackTHUNDER JWST Large Programme and archival NIRSpec-MSA data of a lensed LRD at $z=7.04$. The spectra confirm the presence of a smooth Balmer break and a broad H$\beta$ tracing the Broad Line Region (BLR) of an AGN. The small velocity dispersion of the H$\beta$ narrow component indicates a small dynamical mass of the host galaxy of $M_{\rm dyn}<4 \times 10^8~M_{\odot}$, which implies that the stellar population cannot contribute more than 10% to the optical continuum. We show that the Balmer break can be well described by an AGN continuum absorbed by very dense ($n_{\rm H}\sim 10^{10}~{\rm cm^{-3}}$) and nearly dust-free gas along our line-of-sight (possibly gas in the BLR or its surrounding). The same gas is expected to produce H$\beta$ absorption, at a level consistent with a tentative detection ($3\sigma$) in the high-resolution spectrum. Such a non-stellar origin of the Balmer break may apply to other LRDs, and would alleviate the issue of extremely high stellar mass surface densities inferred in the case of a stellar interpretation of the Balmer break. We note that this is a rare case of a black hole that is overmassive relative to both the host galaxy stellar and dynamical masses. We finally report indications of variability and the first attempt of AGN reverberation mapping at such an early epoch.

Title to be confirmed

Abstract not available

• Speaker: Etienne Camphuis
• Monday 09 June 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Louis Legrand.

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Title to be confirmed

Abstract not available

• Speaker: Sadra Jazayeri (Imperial College)
• Monday 03 March 2025, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Thomas Colas.

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