2023 Spring Postdoc Symposium

1:00–4:00 pm ERC 401

We are excited to announce that the second KICP Postdoc Symposium of the year will be held on May 5th from 1pm - 3:45 pm as an in-person event in ERC 501.

Everyone in KICP and A&A is welcome and encouraged to attend! The goal of the event will be to bring together the community, let postdocs share what we have been working on this past year, and hopefully create collaborations with our colleagues, students and faculty members.

The event will start after Funch (during which lunch will be served), and will involve a series of science talks by postdocs (15min + 5min for questions) with a coffee break and time to mingle afterwards in the Hubble lounge (ERC 501).

12:00	Funch
1:00	Introduction
1:05	Erin Healy "Probing new physics with a precision polarization calibration for CMB telescopes" The polarization of the cosmic microwave background (CMB) contains rich information about the origins and evolution of the universe. Its precision measurement could reveal a signature of gravitational waves generated during inflation via their interaction with the CMB. Evidence of such primordial gravitational waves would provide insights into the quantum mechanical nature of gravity, but no such signal has been detected. Measurements of CMB polarization also probe cosmic birefringence, in which a birefringent material in the universe asymmetrically rotates linear orthogonal polarizations. Such an effect has been hinted at by the satellite telescope Planck, potentially indicating new fundamental fields, but the measurement limited by systematics. Detecting evidence of primordial gravitational waves or cosmic birefringence will require significant advancements to the polarization calibration of CMB telescopes. I will describe a novel calibration plan for the Simons Observatory, which will use a small aperture telescope, its cryogenic rotating half-wave plate, and an external polarizing plate to characterize the instruments.
1:25	TK Chan "Minihalos in the epoch of reionization" Minihalos are dark matter halos that can retain gas but the gas cannot cool through atomic cooling. These halos are numerous, so they could impede reionization through self-shielding and recombination. To study the impact of minihalos on reionization, we perform high resolution cosmological simulation with radiation hydrodynamics. The simulation volume is large enough to sample the minihalo population, whereas the resolution is high enough to model photo-evaporation of small minihalos. We found that the recombination rate can be enhanced by a factor of 10-20 because of the density inhomogeneity. But photo-evaporation reduces the inhomogeneity in ~100 Myr. Overall, minihalos boost the reionization photon budget by 20-100% depending on the redshift of reionization and photo-ionization rate.
1:45	Gabriela Marques "Cosmology with Weak Lensing: 1, 2, and Beyond 2-Point Statistics" According to the current favored cosmological model, the matter density of the Universe is mostly dominated by non-luminous dark matter and consequently is not directly observable. However, the matter density can be probed by studying the deflections of the photon’s path caused by the weak gravitational lensing effect (WL). While the traditional analysis using two-point statistics is sufficient to describe Gaussian fields such as the Cosmic Microwave Background, the large-scale structure that sources the weak lensing signal has undergone nonlinear growth and is thus far from Gaussian. In this talk, I will present the potential of constraining Cosmology by studying the non-Gaussian information contained in the weak lensing data. In particular, I will discuss our recent analysis using the Hyper Suprime-Cam Subaru weak lensing data and different high-order statistics.
2:05	Coffee break
2:40	Ariane Dekker "Searching for dark matter signals in the Galactic halo" The nature of dark matter remains unknown and its most studied candidate is cold dark matter (CDM) with GeV-TeV mass. Its non-detection with direct detection experiments motivates to search for particles beyond that, such as lighter candidates with keV to MeV mass. These particles would leave an imprint on the Galactic dark matter halo which are distinguishable from CDM. In particular, warm dark matter (WDM) with keV mass suppresses the formation of structure at small scales due to free-streaming effects. The abundance of structure therefore provides a valuable probe to distinguish between dark matter candidates. Semi-analytical models for dark matter substructure offer a fast and flexible way to predict the abundance. I will present such a model and apply it to the Milky-Way satellites. By comparing with observations we set constraints on WDM candidates. Moreover, warm and light dark matter can decay into photons and produce a diffuse emission in the Galactic halo, detectable with X-ray and soft gamma-rays. I will discuss indirect searches with future (eROSITA) and current (INTEGRAL) data that set stringent constraints on two well-motivated candidates; sterile neutrinos and axion-like particles.
3:00	Mike Zevin "Formation Channels of Binary Black Holes & Eccentric Mergers" Eccentricity in binary black hole mergers is a clear sign that some kind of dynamical processes were responsible for the coalescence of the binary. In this talk, I will overview eccentricity predictions from various dynamical formation channels, and what an eccentric gravitational-wave detection would imply for binary black hole formation channels. Given the robust predictions for the eccentricity distribution in dense star clusters, I will show how a single confident eccentric detection (or lack thereof) in the upcoming observing run of the LIGO—Virgo—KAGRA network will allow for stringent constraints on the fraction of merging systems that have a dynamical origin. I will also discuss the redshift evolution of the eccentricity distribution, which will be apparent with next-generation gravitational-wave detectors, and the astrophysical quandaries the quantification of this effect will answer.
3:20	Rafael Luque "Six sub-Neptunes in sync around HD 110067" HD 110067 is a nearby K2V star bright in both the visible and the IR. TESS observations in Sectors 23 and 49 revealed two periodic small planets and six further transits from four additional planets (two duo-transit candidates and two mono-transits). Targeted CHEOPS GTO observations of the star were able to reveal the orbital period of planet d, as well as ruling out many possible orbital periods for the other long-period planets. A dynamical study of the innermost planet triplet, which is trapped in a tight Laplace resonant chain, allowed the prediction and later confirmation of the orbits of the three transiting outer planets. The six planets are found to be of sub-Neptune size with radii ranging from 1.94 to 2.85 Re. Three of the planets have measured masses, yielding low bulk densities that suggest the presence of large hydrogen-dominated atmospheres. At present, HD 110067 stands as the most amenable multi-planet system for the characterization of sub-Neptune atmospheres and a rare fossil from planet formation.

Event Type

Meetings