Upcoming and Previous Seminars (Past months or Previous years)

Sep 3, Tuesday
1:10 pm (BCCP/Cosmology seminar)
First meeting, one minute slides
Campbell 131

Sep 10, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Elia Pizzati, Leiden University
Campbell 131
Tracing the Growth and Evolution of Supermassive Black Holes with High-z Quasar Clustering Measurements
Quasar clustering measurements have always been a fundamental ingredient on which we build our understanding of supermassive black holes (SMBHs), their accretion history, and the co-evolution with their host galaxies/halos. Recently, thanks to the advent of the James Webb Space Telescope (JWST), we have pushed the study of quasar clustering well into the era of reionization: several JWST NIRCam-WFSS surveys are measuring the quasar-galaxy cross-correlation and galaxy-galaxy auto-correlation functions at z~6-7, providing a way to constrain the clustering of luminous quasars at these early epochs. Preliminary results from the EIGER surveys suggest that high-z quasars live in moderately strong overdensities, with a large correlation length that agrees well with the trend observed at z~2-4. In this talk, I will present a model that uses these clustering measurements (along with constraints on the luminosity functions) to jointly infer the properties of quasars and galaxies in the early Universe. The model builds on a new large-volume dark-matter-only cosmological simulation, FLAMINGO-10k, and returns key quantities such as the mass distribution of quasar/galaxy-hosting halos, the luminosity-halo mass relation for quasars and galaxies and their duty cycle/occupation fraction. I will discuss how these quantities can provide fundamental constraints to the evolution pathways of early SMBHs and galaxies, and examine the prospects for extending the model to connect results at different redshifts and include different probes of quasar activity. Finally, I will show how these results can help us contextualize the recent discovery of an abundant population of faint and/or obscured broad-line high-z AGN in JWST surveys.

Sep 17, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Avery Meiksin, Institute for Astronomy, Edinburgh
Campbell 131
What does the Lyman-alpha forest tell us about Cosmic Reionization?
While measurements of the Cosmic Microwave Background suggest a redshift range at which intergalactic hydrogen was reionized of about 7 < z < 10, mounting evidence from the Lyman-alpha forest suggests cosmic reionization may have been an extended process lasting to z < 6, and possibly ending as late as z = 5.2. This conclusion, however, depends on the still unknown role Quasi-Stellar Objects play, with growing evidence that their contribution to cosmic reionization and the ultra-violet background after may have been larger than has usually been assumed.

Sep 24, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Tom Crawford, U Chicago
Campbell 131
Cosmology with the South Pole Telescope
The South Pole Telescope (SPT) is a 10-meter-diameter millimeter/submillimeter (mm/submm) telescope located at the National Science Foundation Amundsen-Scott South Pole Station, one of the best sites on Earth for mm/submm observations. The SPT is currently equipped with the SPT-3G camera, the most sensitive CMB camera in active operation. Early SPT-3G results from a small subset of data taken in 2018 have already provided competitive cosmological constraints; in this talk I will preview results (to be released imminently) from a much more powerful data set taken in 2019-2020. The cosmological constraints from 2019-2020 SPT-3G CMB power spectra (TT, TE, and EE) and CMB lensing reconstruction will surpass those of the Planck satellite on certain key parameters (including H0). The aforementioned results all come from deep observations of a 1500-square-degree field; I will also discuss the nearly complete Extended-10k survey totaling 10,000 square degrees, which will improve cosmological constraints by another factor of ~50 (in total LCDM parameter volume) and serve as a pathfinder for upcoming deep-and-wide CMB surveys such as Simons Observatory and CMB-S4.

Oct 1, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Francisco Maion, Donostia International Physics Center
Campbell 131
Simulation-based modelling of Intrinsic Alignments
Intrinsic-Alignments are one of the main systematic effects hindering the robust interpretation of weak-lensing measurements. In this talk I will describe several works by which my collaborators and I advance the modelling and understanding of IA in the mildly non-linear regime. I will describe HYMALAIA, a model based on a combination of a Lagrangian bias expansion with the non-linear displacements of matter from N-Body simulations, and show how it can correctly describe IA power spectra well into the non-linear regime. I will also describe a newly developed method to measure shape-bias parameters fast and precisely, and our application of it to measure galaxy shape-bias parameters from the MillenniumTNG simulation. Finally, I will describe an innovative simulation suite which will allow us to probe for the first time the relation between IA and baryonic feedback effects.

Oct 8, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Matt McQuinn, U Washington
Campbell 131
Cosmology from the outer Solar System
What will cosmologists do in a couple decades time? LBL scientists will have completed the Stage 5 spectroscopic galaxy surveys, and Aaron Parsons' group will have intensity-mapped the 21cm sky. What's next? I will give one proposal that involves spacecraft with radio dishes in the outer Solar System. I will argue that they could more precisely measure the expansion of the universe (arXiv:2210.07159), the sub-solar mass clumpiness of dark matter (arXiv:2401.08862), and the spectrum of gravitational waves in the unprobed 10^-7-10^-4 Hz band between LISA and pulsar timing arrays. I will especially concentrate on the latter. The low-acceleration environment of the outer Solar System allows one to avoid the sophisticated test mass isolation system of LISA, which we also don't know how to build at these lower frequencies, and still reach sensitivities that are potentially limited by stochastic gravitational wave backgrounds. While you might think this talk sounds too out there, literally, I promise it will also include a lot of interesting physics!

Oct 15, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Hector Cruz, JHU
Campbell 131
The First Billion Years in Seconds: An Effective Model for the 21-cm Signal with Population III Stars
In the next few years, observations of the 21-cm signal will open a window to the cosmic dawn epoch, when the first stars formed. It is conventional to interpret these observations through semi-numerical or hydrodynamical simulations, which are often computationally intensive and inflexible to exotic cosmological or astrophysical effects. I will present a new approach to predict the 21-cm global signal and fluctuations in the presence of PopIII stars in seconds. PopIII stars, residing in low-mass molecular-cooling halos, are highly sensitive to feedback, especially from H2-dissociating Lyman-Werner radiation and dark matter-baryon relative velocities. To bypass expensive numerical simulations, we develop an effective prescription of the star formation rate density in the presence of PopIII stars. Our method recovers the full nonlinear distributions of radiative fields that determine the 21-cm signal including anisotropic feedback. I will show how PopIII stars impact the 21-cm global signal and power spectrum across cosmic time and at different distance scales. I will also highlight how the spatial modulation of the relative velocities induces Velocity Acoustic Oscillations in 21-cm power spectra, providing us with a new and robust cosmological standard ruler. Our public code, Zeus21, can predict 21-cm observables in seconds, presenting a meaningful first step towards rapid precision astrophysics and cosmology in the first billion years.

Oct 17, Thursday
3:30 pm (Astronomy Colloquium)
Boryana Hadzhiyska, UCB
Campbell 131
Solving big-scale problems with small-scale physics
Recent advancements in cosmological observations have provided an unprecedented opportunity to investigate the distribution of gas relative to the underlying dark matter, allowing us to tackle a number of interesting problems in cosmology and also build a complete, multi-scale picture of galaxy formation and evolution. In this talk, I will present pioneering work that uses the photometric survey of the Dark Energy Spectroscopic Instrument (DESI) to probe the stacked kinematic Sunyaev-Zel'dovich (kSZ) effect and infer the distribution of gas in the Universe. Our analysis reveals a surprising amount of baryonic feedback, which significantly exceeds predictions from state-of-the-art hydrodynamical simulations such as IllustrisTNG. As making measurements of the gas at low densities and low temperatures has been challenging until now, our measurement provides an important and viable path towards calibrating large hydrodynamical simulations and bridging the gap between theory and observations. In addition, our finding bears important implications for the effect of baryons on the matter power spectrum and can thus help resolve hotly debated inconsistencies in cosmology such as the "Lensing is low" and the "Low S8" tensions. Our measurement marks a critical step toward comprehending the complex interplay between baryons and the underlying matter.

Oct 22, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Beatriz Tucci, MPA Garching
Campbell 131
Revealing the information content of galaxy n-point functions with simulation-based inference
Improving cosmological constraints from galaxy clustering presents several challenges, particularly in extracting information beyond the power spectrum due to the complexities involved in higher-order n-point function analysis. In this talk, I will introduce novel inference techniques that allow us to go beyond the state-of-the-art, not only by utilizing the galaxy trispectrum, a task that remains computationally infeasible with traditional methods, but also by accessing the full information encoded in the galaxy density field for the first time in cosmological analysis. I will present simulation-based inference (SBI), a powerful deep learning technique that enables cosmological inference directly from summary statistics in simulations, bypassing the need for explicit analytical likelihoods or covariance matrices. This is achieved using LEFTfield, a Lagrangian forward model based on the Effective Field Theory of Large Scale Structure (EFTofLSS) and the bias expansion, ensuring robustness on large scales. Furthermore, LEFTfield enables field-level Bayesian inference (FBI), where a field-level likelihood is used to analyze the full galaxy density field rather than relying on compressed statistics. I will conclude by exploring the question of how much cosmological information can be extracted at the field level through a comparison of σ8 constraints obtained from FBI, which directly uses the 3D galaxy density field, and those obtained from n-point functions via SBI.

Oct 22, Tuesday
4 pm (RPM)
Julien Carron, UNIGE
LBL 50-5132
Delensing the Cosmic Microwave Background
Gravitational lensing of the Cosmic Microwave Background is a very valuable cosmological signal, detected at very high significance by several experiments. At the same time, it has also become an hindrance to some important science goals of CMB experiments, most notably for best constraints on a primordial background of gravitational waves. After reviewing current lensing estimation techniques and recent results, I’ll discuss how removal of the lensing signal (`delensing’) typically helps measuring small parameters that affects the CMB polarization. Very sensitive experiments must rely on novel more powerful algorithms to optimally extract or remove the lensing signal: I will present the approach developed in our group in Geneva, together with its forecast performance for upcoming experiments, notably CMB-S4.

Oct 24, Thursday
4 pm (LBL RPM)
Kaja Rotermund, LBNL
LBL 50A-5132 and ZOOM
LuSEE-Night – the Dark Ages from the Far Side of the Moon
The “Dark Ages” refers to the cosmic era between the last scattering of the cosmic microwave background and “Cosmic Dawn,” the time when the first stars and galaxies formed. Only cold, non-luminous hydrogen gas existed during the Dark Ages, which emits at 21 cm (f = 1420 MHz). Through the expansion of the universe, this signal has been redshifted to low radio frequencies that are inaccessible from earth due to distortions of our ionosphere and significant terrestrial radio-frequency interference. This era is therefore largely unexplored and remains one of the least constrained frontiers of modern cosmology. LuSEE-Night is a project that aims to make sensitive measurements across two decades in frequency space from the radio-quiet far side of the moon. In doing so, LuSEE-Night will determine the feasibility of conducting radio-frequency astronomy from the lunar surface and acts as a pathfinder for larger missions in the future.

Oct 29, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Caio Bastos de Senna Nascimento, Washington
Campbell 131
The speed of sound in the EFTofLSS
The Effective Field Theory of Large Scale Structure (EFTofLSS) has found tremendous success as a perturbative framework for the evolution of large scale structure, and it is now routinely used to compare theoretical predictions against cosmological observations. The model for the total matter field includes one nuisance parameter at 1-loop order, the effective sound speed, which can be extracted by matching the EFT to full N-body simulations. In this talk we explore two different directions related to the effective sound speed. We first show that its emergence can be understood even without effective field theory ingredients, through a perturbative framework that solves the Vlasov-Poisson system of equations directly in phase space. However, we will argue that the EFT is necessary to ensure self-consistency. We then discuss how one can estimate the effective sound speed, via separate universe techniques, with analytic calculations. The estimate is in good agreement with simulation results, and we show it can be used to extract the cosmology dependence of the effective sound speed and to shed light on what cosmic structures shape its value.

Oct 29, Tuesday
1:00 pm (Space Physics seminar)
Raul Monsalve, Berkeley
325 Physics South
Observing the Universe’s Dark Ages and First Stars Through Measurements of Spectral Distortions in the Global Radio Spectrum
Before the first stars formed, the Universe consisted of neutral hydrogen gas and dark matter. This period of the Universe is known as the Dark Ages. The Dark Ages ended about 50 million years after the Big Bang with the appearance of the first stars and galaxies, during the subsequent period known as Cosmic Dawn. Observing the Dark Ages and Cosmic Dawn is one of the main objectives of modern cosmology. The James Webb Space Telescope has made extraordinary progress in the detection of early galaxies. However, the very first stars, which most likely were very massive and short-lived, are too faint and far away to be directly detected. A complementary and exciting technique to observe the early Universe is through the measurement of distortions in the sky-averaged, or global, radio spectrum. The standard model of cosmology predicts two absorption features in the global radio spectrum: a first absorption feature at frequencies < 50 MHz, produced during the Dark Ages, and a second feature at ~50-150 MHz, produced during the Cosmic Dawn. These absorption features have not been detected and confirmed yet. In this talk, I will discuss my work to characterize the global radio spectrum using measurements with the Mapper of the IGM Spin Temperature (MIST) ground-based experiment. Measurements with MIST are complementary to the data that will be provided by the SSL-led LuSEE-Night experiment from the Lunar far side. My talk will focus on our efforts to conduct measurements with MIST from the radio quiet environment of the Canadian High Arctic between 2022 and 2024.

Nov 5, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Cynthia Trendafilova, UIUC
Campbell 131
New Challenges for CMB Experiments: A Case Study in the Dark Sector
Current and next-generation Cosmic Microwave Background (CMB) surveys will measure the anisotropies of the CMB with unprecedented precision. Complementary to other laboratory and astrophysical searches, these measurements provide a probe to search for physics beyond the Standard Model. In this talk, I will discuss some applications of this data to search for signatures of dark sector interactions, such as dark matter-baryon scattering, and dark matter interacting with dark radiation. I will present results leveraging the SPT-3G 2018 temperature and polarization data set to constrain these interactions and discuss the challenges faced by this and future analyses.

Nov 7, Thursday
4 pm (RPM)
Taylor Hoyt, LBL
LBL 50-5132 and ZOOM
Toward a Precision Cosmology Measurement of the Hubble Constant
The local value of the Hubble constant (H0) derived from a Cepheid calibration of nearby supernovae (SNe) continues to disagree with values derived from a Lambda(or w)CDM interpretation of large scale cosmological datasets from, e.g., Planck or DESI. The Cepheid-SN and high-z values of H0 consistently come in close to 73 and 68 km/s/Mpc, respectively, with a latest claim that the Hubble tension has surpassed 5 sigma significance. At the same time, a calibration of the SNe based on the Tip of the Red Giant Branch (TRGB) distance indicator suggests significantly less of a tension, consistently returning values near 69.5 km/s/Mpc. This persistent local Hubble Tension indicates that classical H0 experiments have not yet reached the level of accuracy required of a “precision cosmology” measurement. To this end, I will discuss ongoing efforts aimed at evaluating, and ultimately reducing, the amount that underestimated systematic errors could contribute to SN-derived H0 measurements and subsequently bias the evidence for or against the Hubble Tension. These efforts include: new, higher signal-to-noise distance measurements from JWST, investigations into the differing treatment of nearby SNe, and the calibration of a new methodology for SN distance measurement twice as precise and accurate as the canonical approach. These paths together will ensure a more complete understanding of the Hubble Tension, its significance (e.g., H0 tails), and will prove crucial in ushering the accuracy of local H0 measurements into the regime of precision cosmology.

Nov 12, Tuesday
4:00 pm RPM (LBL)
Claire Lamman, Harvard
LBL 50-5132 and ZOOM
Untangling the Cosmic Web: Correlations between small-scale clustering and large-scale structure
Gravitational forces from the largest structures in the Universe leave a detectable imprint on galaxies and their local environment. I will present a new approach to tracing the tidal field using these correlations: the intrinsic alignment of small groups of galaxies, or “multipelts”. Multiplets mostly consist of 2-4 galaxies within 1 Mpc/h of each other, and we measure their orientations relative to the galaxy-traced tidal field. Using spectroscopic redshfits from the DESI Y1 survey, we detect intrinsic alignment out to projected separations of 100 Mpc/h and beyond redshift 1. We find a simillar signal regardless of galaxy luminosity or color, which could make multiplet alignment a useful tool for mapping the direction of the tidal field and any cosmological effects which impact it. Our detection demonstrates that galaxy clustering in the non-linear regime of structure formation preserves an interpretable memory of the large-scale tidal field.

Nov 19, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Andrei Cuceu, LBL
Campbell 131
Mapping the high redshift Universe with DESI Lyman-alpha forests
The Dark Energy Spectroscopic Instrument (DESI) is in the process of building the largest 3D map of the Universe. At high redshifts (z > 2), DESI uses the Lyman-alpha (Lya) forest to map the underlying large-scale structure and constrain cosmology. In the first part of my talk, I will give a brief overview of Lyman-alpha forest cosmology and some of the sources of information accessible through this tracer. I will then present the Lyman-alpha Baryon Acoustic Oscillations (BAO) measurement using the first year of DESI data (DR1), and give an overview of the status of ongoing DESI Lya forest analyses. Finally, I will show preliminary measurements of the Alcock-Paczynski effect and redshift space distortions from the full shape of DESI DR1 Lyman-alpha correlations.

Nov 26, Tuesday

No seminar, Thanksgiving week

Dec 3, Tuesday
1:10 pm (BCCP/Cosmology seminar)
no talk

Dec 4, Wednesday
11 am (special INPA)
Sindhu Satyavolu, IFAE
LBL 5132 and ZOOM
Quasar proximity zones in a partially ionized IGM
Proximity zones of quasars with redshifts z > 5.5 are unique probes of the growth of supermassive black holes, and a nuisance in the direct measurements of the mean free path of the photons that reionize the universe. Interestingly, such proximity zones have been at the centre of two observational puzzles in recent times: 1) about 10% of the measured proximity zone sizes in the quasar Lyman-alpha spectra seem to be too short to explain their black hole masses, and 2) when corrected for the proximity zones, the mean free path of ionizing photons at z ~ 6 appears to be much shorter than theoretical predictions. In this talk, I will present a model of quasar proximity zones that takes into account the patchiness of the ionization and thermal state of the IGM during reionization. I will show that the patchiness of reionization can relieve the tension between the proximity zone sizes and black hole masses to some degree, but not fully. Further, I will show how quasar proximity zones in an inhomogeneously ionized IGM affects mean free path measurements from rest-frame 912 A spectra at z ~ 6. By forward modelling the proximity zones, I will examine the consistency between the direct and indirect redshift-6 mean free path measurements. Finally, I will show that the observed distribution of proximity zone sizes can be explained by a model in which quasars are variable on timescales of ~10^6 yr and have short duty cycles. This conclusion, when combined with the measurements of black hole masses of these quasars, directly leads to a prediction of significant obscuration in high-redshift quasars. I will argue that measurements of this obscuration fraction using JWST can then place constraints on the seed mass and formation redshifts of black holes.

Dec 6, Friday
12 noon (INPA)
Alina Sabyr, Columbia
LBL 5132 and ZOOM
Future Cosmology with CMB Spectral Distortions and Secondaries
Spectral distortions–small deviations of the cosmic microwave background (CMB) energy spectrum from that of a perfect blackbody--probe the physical processes that occur in the primordial Universe (\mu-distortion) and at late times (y-distortion). In this talk, I will present a new instrument concept, SPECTER, that we forecast to observe the \mu-distortion at high significance while marginalizing over astrophysical foregrounds. Within the standard cosmological model, the \mu-distortion is sourced primarily by the energy injected via Silk damping and is thus sensitive to the primordial power spectrum at very small scales. Next, I will present a new constraint on the y-distortion from the re-analysis of the COBE/FIRAS archival data. The known source of the y-distortion is the thermal Sunyaev-Zeldovich (tSZ) effect – inverse-Compton scattering of CMB photons off of energetic electrons primarily located in galaxy groups and clusters. Therefore, y-distortion can give tight constraints on the mean ionized gas properties. Finally, upcoming CMB anisotropy experiments will provide high-resolution and low-noise component-separated tSZ maps. I will discuss the cosmological constraining power of several tSZ higher-order statistics. Using a large suite of halo-model-based simulations, we show that there is substantial non-Gaussian information in the tSZ maps that can be extracted in future analyses.

Jan 21, Tuesday
1:10 pm (BCCP/Cosmology seminar)
,
Campbell 131

Jan 28, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Jahmour Givans, CCA
Campbell 131

Feb 4, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Alex van Engelen , ASU
Campbell 131

Feb 11, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Susanna Azzoni, Princeton
Campbell 131

Feb 18, Tuesday
1:10 pm (BCCP/Cosmology seminar)
,
Campbell 131

Feb 25, Tuesday
1:10 pm (BCCP/Cosmology seminar)
held,
Campbell 131

Mar 4, Tuesday
1:10 pm (BCCP/Cosmology seminar)
,
Campbell 131

Mar 11, Tuesday
1:10 pm (BCCP/Cosmology seminar)
,
Campbell 131

Mar 18, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Richard Ellis, UCL
Campbell 131

Mar 25, Tuesday
Spring break, no talk

Apr 1, Tuesday
no 1:10 pm BCCP/Cosmology seminar; instead an RPM 4:00 pm
Jason Rhodes, JPL
LBL 50-5132

Apr 3, Thursday
3:30 pm (Astronomy Colloquium)
Jason Rhodes, JPL
Campbell 131

Apr 8, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Johannes Lange, American University
Campbell 131

Apr 14, Monday
4:15 pm (Physics Colloquium)
Nathalie Palanque-Delabrouille, LBL
1 Physics North
DESI shakes up the dark Universe
The Dark Energy Spectroscopic Instrument (DESI) is building the largest 3D map of our universe to measure its expansion history over the past 11 billion years, and thereby, study the biggest mystery in cosmology: dark energy. The DESI first-year BAO results find tantalizing hints of time-varying dark energy. Combining BAO and clustering at all scales, DESI also sheds light on other outstanding questions in cosmology relative to neutrino masses or modified gravity. In this colloquium, I will give an overview of the DESI experiment, describe the year-1 cosmology results and their implication, and present the most recent updates using BAO information from the year-3 DESI data.

Apr 15, Tuesday
1:10 pm (BCCP/Cosmology seminar)
,
Campbell 131

Apr 15, Tuesday
1:10 pm (BCCP/Cosmology seminar)
,
Campbell 131

Apr 22, Tuesday
1:10 pm (BCCP/Cosmology seminar)
,
Campbell 131

Apr 29, Tuesday
1:10 pm (BCCP/Cosmology seminar)
Julien Lesgourgues, Aachen
Campbell 131