Wed 21 Feb 13:15: Gaussian Processes for Systematic Mitigation for Global 21-cm Cosmology Experiments
Radio observations of the neutral hydrogen signal from the Cosmic Dawn and Epoch of Reionisation have helped to provide constraints on the properties of the first stars and galaxies. Since this global 21-cm cosmological signal from the Cosmic Dawn is effectively constant on observing timescales and since effects resulting from systematics will vary with time, the effects of these systematics can be mitigated without the need for a model of the systematic. In this talk I will present a method to account for unmodelled time-varying systematics in 21-cm radio cosmology experiments using a Gaussian process method to account for correlations between time bins in a fully Bayesian way. I will finally present a further method using Gaussian process regression to calculate a mean fit to the residuals over time, providing a basis for producing a model of the time-varying systematic.
- Speaker: Christian Kirkham (University of Cambridge)
- Wednesday 21 February 2024, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: Hannah Uebler.
Thu 15 Feb 16:00: Exoplanet adventures the 2020s and beyond
In our quest to find other Earths, we’ve uncovered an extraordinarily diverse set of outcomes of the star-planet formation process, far beyond our imagination, and yet we have still barely scratched the surface of what we can learn about this eclectic zoo of other worlds. While exoplanet hunters continue the search for the nearest Earth twins, our last decade of study has pushed to understand the atmospheres of these new planets, and how their climate physics and chemistry respond to the environment created by their parents stars. In this talk, I will demonstrate how new instrumentation, high in resolution, precision, and contrast is pushing our understanding of exoplanet atmospheres to increasing detail. I’ll discuss studies of gas giants as well as the crucial preparation we are doing to find biosignatures on nearby rocky worlds with the Extremely Large Telescopes. Finally, I will demonstrate our recent work on techniques to map out storms in giant exoplanet atmospheres, and end by discussing the next phase of exoplanet observations that aim to reveal the surface interactions of rocky exoplanets.
- Speaker: Jayne Birkby (University of Oxford)
- Thursday 15 February 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy.
- Series: Institute of Astronomy Colloquia; organiser: eb694.
The ALMaQUEST Survey XIII: Understanding radial trends in star formation quenching via the relative roles of gas availability and star formation efficiency
The SAMI Galaxy Survey: galaxy spin is more strongly correlated with stellar population age than mass or environment
Tue 20 Feb 13:00: Uncovering Long-Period Transiting Exoplanets with TESS and CHEOPS
Long-period transiting exoplanets are incredibly important, allowing us to study planets with temperatures similar to those in our own solar system. However, due to its observing strategy, the Transiting Exoplanet Survey Satellite (TESS) is heavily biased towards the discovery of short-period planets. To increase the yield of long-period planets, I am using TESS “duotransits” – planet candidates with two observed transits separated by a large gap, typically two years. From the two non-consecutive transits, the period of the planet is unknown, but there exists a discrete set of period aliases. As a member of the CHaracterising ExOPlanet Satellite (CHEOPS) Duotransit Program, I perform targeted follow-up of TESS duotransits to recover their true periods. To identify the best targets for CHEOPS follow-up, I developed a specialised pipeline to discover TESS duotransits. In this seminar, I will present my pipeline, its five discoveries and the sample of small, long-period planets being uncovered by TESS and CHEOPS , including the Neptune-mass planet TOI -5678 b and the bright multi-planet system HD 15906 .
- Speaker: Amy Tuson (Cavendish)
- Tuesday 20 February 2024, 13:00-14:00
- Venue: Ryle seminar room + ONLINE - Details to be sent by email.
- Series: Exoplanet Seminars; organiser: Dr Emily Sandford.
Fri 16 Feb 13:00: Numerical-relativity-informed effective-one-body model for black-hole–neutron-star mergers with higher modes and spin precession
We present the first effective-one-body model for generic-spins quasicircular black-hole–neutron-star (BHNS) inspiral-merger-ringdown gravitational waveforms (GWs). Our model is based on a new numerical-relativity (NR) informed expression of the BH remnant and its ringdown. It reproduces the NR (ℓ, m ) = ( 2, 2 ) waveform with typical phase agreement of ≲0.5 rad ( ≲1 rad) to merger (ringdown). The maximum (minimum) mismatch between the (2, 2) and the NR data is 4% (0.6%). Higher modes (HMs) (2, 1), (3, 2), (3, 3), (4, 4), and (5, 5) are included, and their mismatch with the available NR waveforms are up to (down to) a 60% (1%) depending on the inclination. Phase comparison with a 16 orbit precessing simulation shows differences within the NR uncertainties. We demonstrate the applicability of the model in GW parameter estimation by performing the first BHNS Bayesian analysis with HMs (and nonprecessing spins) of the event GW190814 , together with new (2, 2)-mode analysis of GW200105 and GW200115 . For the GW190814 study, the inclusion of HMs gives tighter parameter posteriors. The Bayes factors of our analyses on this event show decisive evidence for the presence of HMs, but no clear preference for a BHNS or a binary black hole source. Similarly, we confirm GW200105 and GW200115 show no evidence for tidal effects.
- Speaker: Alejandra González (FSU Jena)
- Friday 16 February 2024, 13:00-14:00
- Venue: Potter room/Zoom.
- Series: DAMTP Friday GR Seminar; organiser: Daniela Cors.
Multiple Beads-on-a-string: Dark Matter-Deficient Galaxy Formation in a Mini-bullet Satellite-satellite Galaxy Collision
Ly$\alpha$ emission in galaxies at $z\simeq5-6$: new insight from JWST into the statistical distributions of Ly$\alpha$ properties at the end of reionization
Wed 14 Feb 13:15: Correcting for Malmquist Bias in Type Ia Supernova Cosmology
Type Ia supernovae (SNe Ia) can be standardised to provide distance estimates to put constraints on cosmological parameters. When building a sample for this, astrophysical selection effects mean that we are biased towards detecting SNe Ia with certain characteristics. The most famous example is Malmquist bias, meaning surveys are more likely to detect brighter SNe towards the edge of their limiting magnitudes. This disproportionally bright sample at high redshifts leads to an underestimation of distances on the Hubble diagram. If we fit for cosmological parameters naively without accounting for this effect, we will bias our constraints on fundamental parameters. In this presentation I will cover some of the existing methods to correct for Malmquist bias. I will then outline our own method that combines simulation-based inference and hierarchical Bayesian modelling. Simple simulations will be used to demonstrate our method can match analytical solutions. I will conclude by discussing plans to show the generalisation of our flexible method to real survey selection effects where analytical solutions are intractable.
- Speaker: Ben Boyd
- Wednesday 14 February 2024, 13:15-13:40
- Venue: The Hoyle Lecture Theatre + Zoom .
- Series: Institute of Astronomy Seminars; organiser: .
In a new era of astronomy, we're feeling for vibrations in space-time
Einstein may be wrong about how mirrors travelling at light speed work
Mon 26 Feb 13:00: Title to be confirmed
Abstract not available
- Speaker: Silvia Pla Garcia (King's College London)
- Monday 26 February 2024, 13:00-14:00
- Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
- Series: Cosmology Lunch; organiser: Thomas Colas.
A catalogue of dual-field interferometric binary calibrators
Tue 13 Feb 11:15: Interferometric measurements of the 21-cm signal with the SKA
The Cosmic Dawn marks the first star formations and preceded the Epoch-of-Reionization, when the Universe underwent a fundamental transformation propelled by the radiation from these first stars and galaxies. Interferometric 21-cm experiments aim to probe redshifted neutral hydrogen signals from these periods, constraining the conditions of the early Universe. The SKA -LOW instrument of the Square Kilometre Array telescope is envisaged to be the largest and most sensitive radio telescope at m and cm wavelengths. In this talk we present a data analysis pipeline that was used in the SKA Science Data Challenge 3a: Epoch of Reionisation (SKA SDC3a) to process the novel data products expected from the SKA . To determine whether a successful 21-cm detection is possible with the envisaged SKA , we implement predictive foreground and Bayesian Gaussian Process Regression models alongside a foreground avoidance strategy to isolate the 21-cm signal from that of the astrophysical radio frequency (RF) foregrounds.
- Speaker: Yuchen Liu & Oscar O'Hara (Cavendish Astrophysics)
- Tuesday 13 February 2024, 11:15-12:00
- Venue: Coffee area, Battcock Centre.
- Series: Hills Coffee Talks; organiser: Charles Walker.
Tue 12 Mar 16:00: Star Formation, Feedback, and Cosmic Evolution: A Modern Primer
The cosmic history of galaxy formation is the history of star formation writ large. While the contents of the universe are mostly invisible and interact with baryons only weakly, a wide array of physical processes affect evolution of the observable baryons. Some of the most important processes involve coupling between stellar and gaseous components, since massive stars are the primary energy source in the interstellar medium (ISM), circumgalactic medium (CGM), and intergalactic medium (IGM). The majority of stellar energy — including UV radiation, winds, and supernovae — is returned rapidly after a given population of stars forms, and is therefore collectively termed “star formation feedback.” Because the state of the ISM determines the star formation rate, and stellar feedback determines the ISM state, quantifying how this co-regulation works is crucial to theoretical modeling. The need to quantify feedback responses also extends to galaxy formation theory on larger scales, where galactic winds driven by feedback heat and add metals to the CGM , thereby regulating the accretion that replenishes the ISM , and where escaping stellar UV ionizes the IGM . Because the observational characterization of galaxies — both near and far — relies on emission lines and infrared continuum from gas and dust subject to photoheating and photochemistry from starlight, quantitative interpretation of observations also relies on calibration using physical models that accurately represent radiative transfer in complex environments. In this lecture, I will review current theory of the physics of feedback, showcasing results from state-of-the-art, high-resolution numerical radiation-magnetohydrodynamic simulations that directly follow multiphase ISM evolution including the effects of UV radiation, stellar winds, and supernovae. These simulations, on both scales of individual star-forming molecular clouds, and scales of galactic disks, show star formation efficiencies and rates that are consistent with detailed observations in the nearby universe, and also indicate strong sensitivity to environment. At high densities and where dust and metal abundances are high, stellar radiation does not propagate as far, and cooling rates are enhanced. As a result of the reduced effectiveness of feedback in maintaining the ISM pressure (turbulent, thermal, and magnetic), star formation rates and efficiencies are expected to increase in high-density environments. Results from suites of resolved star-forming ISM simulations have been used to calibrate new subgrid models, and incorporation of these new results in galaxy formation models may potentially significantly change predictions for star formation at high redshift.
- Speaker: Eve Ostriker (Princeton University)
- Tuesday 12 March 2024, 16:00-17:00
- Venue: Hoyle Lecture Theatre, Institute of Astronomy (and online - details to be sent by e-mail).
- Series: The Kavli Lectures; organiser: Steven Brereton.
Mon 17 Jun 14:00: Title to be confirmed
Abstract not available
- Speaker: Claudio Zanni (INAF Turin)
- Monday 17 June 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 10 Jun 14:00: Title to be confirmed
Abstract not available
- Speaker: Chris Osborne (Glasgow)
- Monday 10 June 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 03 Jun 14:00: Title to be confirmed
Abstract not available
- Speaker: Ugo Lebreuilly (CEA Saclay)
- Monday 03 June 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Tue 28 May 14:00: Title to be confirmed
Abstract not available
- Speaker: Thomas Berlok (Niels Bohr Institute)
- Tuesday 28 May 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.
Mon 20 May 14:00: Title to be confirmed
Abstract not available
- Speaker: Kenta Kiuchi (Max Planck)
- Monday 20 May 2024, 14:00-15:00
- Venue: MR14 DAMTP and online.
- Series: DAMTP Astrophysics Seminars; organiser: Roger Dufresne.