August 28: Evan Schneider (Princeton)
Title: The Origin of Multiphase Galaxy Outflows
Star-forming galaxies are often observed to host galactic winds - gas that is flowing out of the galaxy in phases ranging from cold molecular clouds to hot X-ray emitting plasma. While these multiphase outflows are routinely observed, theoretically constraining their origin and evolution has proven difficult. Explaining the prevalence and velocities of the cool ionized phase (T~10^4 K) in particular poses a challenge. In this talk, I will discuss a potential dual origin for this cool gas. Through a series of extremely high-resolution simulations run with the GPU-based Cholla code, I will show that in high star formation surface density systems, dense disk gas can be pushed out by the collective effect of clustered supernovae, explaining the low-velocity material. Subsequent shredding and mixing of these clouds creates gas with intermediate densities and temperatures that is prone to radiative cooling, allowing momentum to transfer between phases and producing high velocity cool gas. In addition to explaining the nature of outflows themselves, these multiphase winds could potentially be a source of the cool photo-ionized gas that is found in abundance in galaxy halos.
September 18: Aklant Bhowmick (UF)
Title: Clustering of quasars and high redshift galaxies: New frontiers for structure formation
Galaxy clustering from large scales (>20 Mpc) to small scales (<1 Mpc) serves as a key probe for the physics of non-linear structure and galaxy formation. At large scales, it enables us to probe the galaxy linear bias, which establishes the connection between galaxy properties with the properties of underlying haloes that correlate with the halo bias. At small scales, we can probe the halo substructure and how galaxies are distributed within it, and also look for possible signatures of hierarchical structure growth. In this talk, I will be presenting the recent results on the clustering statistics of two rare classes of objects in the observable universe, namely, high redshift (z > 7) galaxies and quasars (0 < z < 4) using two state of the art cosmological hydrodynamic simulations, BlueTides and MassiveBlackII. I will discuss how the simulation results compare with existing observational constraints, and prospects of detecting these objects in upcoming surveys.
October 9: Zachary Slepian (UF)
Title: Triangulating the Universe’s Contents, Laws, and Origin with Galaxy Correlation
The Universe is now in an epoch of accelerated expansion of space-time itself, presumed due to dark energy. 3D maps of the distribution of galaxies such as the Sloan Digital Sky Survey (SDSS) have yielded percent-level constraints on dark energy using the imprint of Baryon Acoustic Oscillations (BAO) as a standard ruler to map the Universe's expansion history. Dark Energy Spectroscopic Instrument (DESI; 2019-2024) will map 30 million galaxies (30X SDSS) to improve dark energy constraints by an order of magnitude.
The standard analysis approach for these surveys uses the clustering of galaxy pairs. However, fully exploiting the powerful DESI dataset will demand new ideas. The clustering of galaxy triplets—triangles—measured through the 3-Point Correlation Function (3PCF), offers a powerful new window on cosmic acceleration and dark energy. First, the BAO method can be used in the 3PCF exactly as it is already used with pairs, to sharpen our history of the Universe’s expansion. Second, the 3PCF offers information on the fidelity with which galaxies trace the underlying matter (galaxy biasing), enhancing their utility for cosmology. Third, the direction-dependent 3PCF enables probing modified gravity, another possible explanation for accelerated cosmic expansion. I will present a transformatively fast 3PCF algorithm, and demonstrate its use to make the first application of the BAO method to the 3PCF and place high-precision constraints on galaxy biasing. I will then show how the direction-dependent 3PCF can provide a complementary probe of modified gravity. I will close with further exciting 3PCF cosmology opportunities, such as constraining inflation and the neutrino mass, as well as a novel application to understand the physics of the turbulent interstellar medium as relevant for star formation.
October 23: Jeremiah Murphy (FSU)
Title: How Do Massive Stars Die?
The title of this talk remains an important fundamental question in theoretical astrophysics. The explosive deaths of massive stars, core-collapse supernovae, are
some of the most energetic events in the Universe; they herald the
birth of neutron stars and black holes, are a major site for
nucleosynthesis, influence galactic hydrodynamics, trigger further
star formation, and are prodigious emitters of neutrinos and
gravitational waves. Though these explosions play an important and
multifaceted role in many cosmic phenomena, the details of the
explosion mechanism have remained elusive for many decades. The
fundamental challenge of core-collapse theory is to understand what makes the difference between a fizzled result (black hole formation) and
successful explosions. Ultimately, answering this question will
require both theory and observational constraints.
In this talk, I will present recent progress in theory and observations that constrain the theory.
November 6: Dan D'Orazio (CfA)
Title: Hunting for Black Hole Binaries with Gravitational Lensing
The merger of two galaxies, each with a supermassive black hole (SBH) at its heart, results in the formation of a supermassive black hole binary (SBHB) at the center of the new galaxy. The eventual inspiral and merger of SBHBs generates gravitational waves that will be detectable by the space interferometer gravitational wave observatory LISA, and the Pulsar Timing Arrays. However, the steps between galactic merger and black hole merger are poorly understood. It is not even clear if most SBHBs will merge. To address this outstanding issue, commonly referred to as the “final parsec problem,” we must find SBHBs during the compact, sub-parsec-separation stage of their lives. While identification of such a population is notoriously difficult, it would open the field of SBHB demography, elucidating the processes at play in galactic nuclei that facilitate (or hinder) SBHB mergers. Here I discuss techniques for identifying sub-parsec separation SBHBs, and highlight a novel signature that arises via periodic gravitational lensing of an accretion disk around one SBH in the binary by the other SBH. I will present a recently discovered self-lensing binary candidate and discuss further applications of this technique to the stellar-mass black hole binaries that merge in LIGO/VIRGO.
November 27: [Thanksgiving Week: No Seminar]
Dec 4: Chiara Mingarelli (Flatiron Institute)
Title: Probing supermassive black hole mergers with pulsar timing
Galaxy mergers are a standard aspect of galaxy formation and evolution, and most (likely all) large galaxies contain supermassive black holes. As part of the merging process, the supermassive black holes should in-spiral together and eventually merge, generating a background of gravitational radiation in the nanohertz regime. An array of precisely timed pulsars spread across the sky can form a galactic-scale gravitational wave detector in this band. I describe the current efforts to develop and extend the pulsar timing array concept, together with recent limits which have emerged from international efforts to constrain astrophysical phenomena at the heart of supermassive black hole mergers.
Dec 11: Pedro Capelo (University of Zurich)
Title: Dual active galactic nuclei and the pairing of supermassive black holes
in the LISA era
Pairs of accreting supermassive black holes (SMBHs), known as dual
active galactic nuclei (AGN), and the generation of gravitational waves
(GWs) from the inspiral and coalescence of SMBHs are two faces of the
same coin. The SMBHs that, by coalescing, generate GWs detectable by the
Laser Interferometer Space Antenna (LISA) are the same systems which,
millions or billions of years earlier, were potentially both accreting
gas at the centre of a galactic merger remnant and producing a dual AGN,
akin to the few systems we currently observe via electromagnetic (EM)
Connecting these two physical events is paramount to understanding (i)
how the large scale structure of the Universe evolved, (ii) how SMBHs
and their host galaxies co-evolve, and (iii) how SMBH accretion and AGN
feedback work. To do so, we need to perform high-resolution numerical
simulations that model a huge variety of astrophysical systems and
processes, compare our results to current EM observations, and be ready
to interpret the signals that will come from evolved EM probes (e.g.
ATHENA) and, soon, from LISA.
In this talk, I will show that both SMBH pairing and dual AGN activity
can depend significantly on a wide assortment of astrophysical
parameters, including the mass ratio between two merging galaxies, the
occurrence of gas instabilities, and the dark matter content of the
interacting systems, to name a few, making the field of multi-messenger
astrophysics both challenging and exciting.