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Journal Club Seminars From 2021 - 2022

Contents


FALL 2021


September 27, 2021

NOTE: Open slot



October 4, 2021

 "Think Like a Nobel Prize Winner"

Brian Keating
Professor of Physics
UCSD-CASS
https://ucsd.zoom.us/j/93716525551


 Meeting ID: 937 1652 5551

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Meeting ID: 937 1652 5551
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ABSTRACT: Think Like a Nobel Prize Winner, a new book by Brian Keating How can you unlock creativity and imagination to inspire, teach and lead? What mental models do the world’s most accomplished scientists use to supercharge their creativity, and strengthen their most precious collaborations?

In this mesmerizing collection of interviews with some of the world’s brightest minds, you’ll discover that achieving greatness doesn’t require genius. Instead, dedication to a simple set of principles—habits and tools -- can boost your creativity, stoke your imagination, and unlock your full potential for out-of-this-universe success.

Through their own words you will discover why Nobel Prize winning scientists credit the often overlooked “soft skills” such as communication, motivation, and introspection as keys to their success. You’ll see why they turn to curiosity, beauty, serendipity, and joy when they need to turn fresh eyes on some of the universe’s most vexing problems...and how you can too no matter what you do!

Within the pages of Into the Impossible: Think Like a Nobel Prize Winner, the wisdom of nine Nobel Laureates has been distilled and compressed into concentrated, actionable data you can use. While each mind is unique, they are united in their emphasis that no one wins alone—and that science, and success itself, belongs to us all.



October 11, 2021

 "Probing Dark Matter through Gaps in Globular Cluster Streems with the Nancy
Grace Roman Telescope"

Christian Aganze
Physics Graduate Student
UCSD-CASS
https://ucsd.zoom.us/j/95370960367


 Meeting ID: 953 7096 0367

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Meeting ID: 953 7096 0367
Find your local number: https://ucsd.zoom.us/u/arUDPBxLj

ABSTRACT: Cosmological models that include cold dark matter (lambda-CDM) predict the existence of substructure at very low masses (subhalos). Low-mass subhalos can perturb thin globular cluster (GC) streams, creating a gap-like feature like those detected in Gaia data (e.g GD-1, Bonaca et al. 2019). The gap morphology offers an avenue for constraining different dark matter models. However, the sample of GC streams in the Galaxy remains small due to their intrinsic low surface brightness. Pearson et al. (2021) have shown that the Nancy Grace Roman Space Telescope (NGRST) will detect thin GC streams with masses above 104 solar masses in external galaxies. We use stream generation algorithms (Fardal et al. 2015) implemented in the Gala package (Price-Whelan et al. 2017) to create gaps in thin globular cluster streams with masses of ~104 Msun orbiting in a Milky-way-like potential. Assuming a Hernquist potential for dark matter subhalos with masses ranging from 105-107 solar masses, we investigate the formation and morphological evolution of gaps created through the interaction between these subhalos and GC streams. We predict detectability thresholds for these gaps by incorporating realistic background stars simulated in the NGRST 0.52 deg2 field of view projected to the distance of Andromeda. This presentation summarizes a project from the Summer School on Galactic Dynamics held this past summer at the Flatiron Institute in New York City.



October 18, 2021

 "The Cosmic Neutrino Background: Helicity, Chirality, Dirac, Majorana,
and All That"

Eric L. Michelsen
Physics Lecturer
UCSD-CASS
https://ucsd.zoom.us/j/94796774154


 Meeting ID: 947 9677 4154

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Meeting ID: 947 9677 4154
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ABSTRACT: Cosmological models and data show that a cosmic neutrino background (CnuB) existed at the time of last scattering, when the cosmic microwave background was formed. However, this CnuB has never been directly detected, because of the weakness of neutrino interactions. Experiments already being built, such as Ptolemy, might reach the sensitivity needed for a direct detection of the CnuB. This would provide valuable validation of cosmological models, aspects of the Standard Model of particles, and possibly new information about the Dirac or Majorana nature of neutrinos, and even their stability as particles. We present some of the physics behind such an intriguing measurement.



October 25, 2021

 "Decaying Sterile Neutrinos in the Early Universe”

Hannah Rasmussen
Post-bac Researcher
University of San Diego
https://ucsd.zoom.us/j/99609802238


 Meeting ID:
996 0980 2238

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Meeting ID: 996 0980 2238
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ABSTRACT: The hot and dense early Universe provides an intriguing opportunity to study Beyond Standard Model physics. We simulate the early Universe to examine the effects of the decay of thermally populated sterile neutrino states into Standard Model products around the time of weak decoupling. These decays deposit a significant amount of entropy into the plasma as well as produce a population of high-energy out-of-equilibrium active neutrinos. As a result, we can constrain these models by their inferred value of N_eff, the effective number of relativistic degrees of freedom. In this talk, I will discuss the results of our recent work (arXiv: https://arxiv.org/abs/2109.11176), where we explore a variety of sterile neutrino decay models with N_eff values consistent with CMB observations, but with vastly different active neutrino spectra which will challenge the standard cosmological model, affect lepton capture rates on free nucleons, and may significantly affect BBN.



November 1, 2021

 "Constraints on low-mass axion dark matter from the CMB and other sources"

Jake Spisak
Physics Graduate Student
UCSD-CASS
https://ucsd.zoom.us/j/99609802238


 Meeting ID: 996 0980 2238

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Meeting ID: 996 0980 2238
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November 8, 2021

 "A new window on star formation history at the Galactic Center"

Zhuo Chen
Graduate Student
UCLA
https://ucsd.zoom.us/j/99609802238


 Meeting ID: 996 0980 2238

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Meeting ID: 996 0980 2238
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ABSTRACT: As the closest galactic nucleus, Milky Way's Nuclear Star Cluster (NSC) provides a unique opportunity to resolve the stellar population and to study its composition and star formation in this extreme environment. The limitation in our current understanding of the NSC star formation history is that previous studies assumed that all stars have solar metallicity. However, age and metallicity are degenerate parameters in star formation histories; by ignoring the effect of metallicities, the age estimates can be biased. Recent spectroscopic surveys showed a significant spread in the metallicity of stars in the NSC, which motivates us to revisit the star formation history and its implications on the formation and evolution of the NSC. In this talk I will present the star formation history of the NSC for the first time with metallicity constraints as obtained from large sample of stellar metallicity measurements from Keck, Gemini and VLT. The analysis shows significantly different star formation history than any previously published works. In addition, we model the initial mass function for the first time simultaneously, and present more accurate estimates on the number of compact objects at the Galactic center.



November 15, 2021

 "Instability and Turbulent Relaxation in a Stochastic Magnetic Field"

Mingyun Cao
Physics Graduate Student
UCSD-CASS
https://ucsd.zoom.us/j/99609802238


 Meeting ID: 996 0980 2238

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Meeting ID: 996 0980 2238
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ABSTRACT: An analysis of instability dynamics in a stochastic magnetic field is presented for the tractable case of the resistive interchange. Externally prescribed static magnetic perturbations convert the eigenmode problem to a stochastic differential equation, which is solved by the method of averaging. The dynamics are rendered multi-scale, due to the size disparity between the test mode and magnetic perturbations. Maintaining quasi-neutrality at all orders requires that small-scale convective cell turbulence be driven by disparate scale interaction. The cells in turn produce turbulent mixing of vorticity and pressure, which is calculated by fluctuation-dissipation type analyses, and are relevant to pump-out phenomena. The development of correlation between the ambient magnetic perturbations and the cells is demonstrated, showing that turbulence will `lock on' to ambient stochasticity. Magnetic perturbations are shown to produce a magnetic braking effect on vorticity generation at large scale. Detailed testable predictions are presented. The relations of these findings to the results of available simulations and recent experiments are discussed.



November 22, 2021

 "Resolving Temperature and Metallicity Variations In Nearby Galaxies with Integral Field Spectroscopy"

Ryan Rickards Vaught
PhD Candidate
UCSD-CASS
https://ucsd.zoom.us/j/99609802238


 Meeting ID: 996 0980 2238

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Meeting ID: 996 0980 2238
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ABSTRACT: Characterizing the sub-kpc variation of metal abundance (or metallicity) in the Interstellar Medium (ISM) is the next step towards understanding the chemical enrichment history of galaxies. There are a number of astrophysical phenomena that could potentially mix and redistribute metals throughout the ISM. Despite many studies performed towards this goal there remain significant hurdles 1) the faintness of requisite diagnostic lines that most accurately trace metallicity 2) systematic uncertainty is calibrated diagnostics and 3) biased statistics due to sparse sampling. We present here preliminary results from our Keck Cosmic Web Imager analysis of nearby, star-forming, disk galaxies.



November 29, 2021

 "Exploring Fifth Forces and Ultralight Dark Matter with Planetary/Asteroidal
Dynamics and Space Quantum Technology"

Dr. Yu-Dai Tsai
https://ucsd.zoom.us/j/99609802238


 Meeting ID: 996 0980 2238

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Meeting ID: 996 0980 2238
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ABSTRACT: We use planetary astrometric data and space Quantum technology to study ultralight dark matter. Using the orbital data collected for asteroids and other minor planets, one can set leading bounds for ultralight dark matter, which mediate long-range forces and induce precessions of the celestial objects. One can also extend this method to study modified gravity theories. With NASA's new Deep Space Atomic Clocks, one can study the ultralight dark matter in unexplored parameter space. I am looking to provide new connections between astrophysics, planetary observations, quantum technology, and fundamental physics.


WINTER 2022


January 3, 2022

NOTE: No Journal Club today



January 10, 2022

 "Directly Measuring the Mass of Microlensing Exoplanets with the Roman Space
Telescope"

Sean Terry
Postdoctoral Scholar
UC Berkeley
https://ucsd.zoom.us/j/91007750006


 Meeting ID: 910 0775 0006

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Meeting ID: 910 0775 0006
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ABSTRACT: The Gravitational Microlensing technique has now discovered over 100 exoplanets, with thousands expected to be detected by the upcoming Roman Galactic Exoplanet Survey (RGES). In most microlensing events, the planet-star mass ratio is measured and a galactic model is used to infer other physical properties of the lens system. I will show a new technique for directly measuring the planet and host star masses through high-resolution follow-up imaging with Keck (and in the future with Roman). This has led to some interesting implications about the assumptions made in galactic models, as well as the “mass-gap” for wide-orbiting gas giant planets in the core-accretion theory of planet formation.



January 17, 2022

NOTE: No Journal Club today - MLK, Jr. Holiday



January 24, 2022

NOTE: No Journal Club today



February 7, 2022

NOTE: UCSD-SDSU Astrophysics Seminar in lieu of Journal Club
 "Planets are Places: Characterization of Other Worlds in the 2020s and Beyond"

Dr. Laura Kreidberg
Director, APEx Department
Max Planck Institute for Astronomy (MPIA), Heidelberg
https://ucsd.zoom.us/j/92145268589?pwd=R1Mzc1lpa21hQ0poTTRmMVpNektVUT09


 Meeting ID: 921 4526 8589
Password: 945763

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Meeting ID: 921 4526 8589
Find your local number: https://ucsd.zoom.us/u/abVtGkr0G

ABSTRACT: The past 25 years have revealed a diversity of exoplanets far beyond what was imagined from the limited sample in the Solar System. With new and upcoming observing facilities and a rapidly growing number of nearby planets, we are poised to bring this diversity into focus, with detailed follow-up characterization of the planets’ atmospheres. In this talk, I will discuss two frontier topics in exoplanet atmosphere studies: (1) what can we learn about giant planets' origins from their present-day atmospheres? and (2) what can we learn about habitability from “Earth cousins”, planets that are a little bigger or a little hotter than the Earth? Finally, I will conclude with my outlook on the search for biosignatures in the atmospheres of potentially inhabited planets.



February 14, 2022

 "Probing Particle Physics Models from Astrophysical Experiments"

Tanmay Kumar Poddar
Researcher at Physical Research Laboratory
in India
https://urldefense.proofpoint.com/v2/url?u=https-3A__ucsd.zoom.us_j_94872962266&d=DwIFaQ&c=-35OiAkTchMrZOngvJPOeA&r=dAPpfnpYhWbY44YHDe0KeA&m=t_tg0NPh6kQvFpRr-2_TuMpdVx5_MaZYl4cs1cGCuidFTx9Q7G57RufmLRdj4Ky0&s=1IOQ7LmL31q3UyUnwYCTXa97HQpmxKxxtGDnN04Ssw4&e=


 Meeting ID: 948 7296 2266

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Meeting ID: 948 7296 2266
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ABSTRACT: The orbital period loss of compact binary systems which is the indirect evidence of gravitational waves and the perihelion precession of planets agree quite well with Einstein's general theory of relativity to a very good accuracy with the experiments. However, a small mismatch from the observational data allows us to think of the emission of ultralight particles from those systems. These particles are well motivated from particle physics models and can be a good candidate for dark matter. In this talk, I will discuss how to probe those ultralight particles from those observations and possible bounds on coupling and mass.



February 21, 2022

NOTE: No Journal Club today (Presidents' Day)



February 28, 2022

NOTE: No Journal Club today



March 7, 2022

 "The Galactic Dust-Up: Modeling Dust Evolution in FIRE"

Caleb Choban
Physics Graduate Student
UCSD-CASS
https://ucsd.zoom.us/j/95841943699


 Meeting ID: 958 4194 3699

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Meeting ID: 958 4194 3699
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ABSTRACT: Dust is integral to the physics within the ISM, providing a surface for complex astrochemistry, reducing the abundance of gas phase coolants, affects ISM radiation pressure, and redistributes galactic SEDs. Observations find diverse dust scaling relations which suggest a complex dust system depending heavily on local gas properties, but many galaxy formation models do not capture this, treating dust in post-processing or assume a constant dust-to-metals ratio (D/Z). Recent strides have been made developing dust evolution models for galaxy formation simulations but these approaches vary in their assumptions and degree of complexity.

In this talk, I will present two separate dust evolution models (labeled 'Elemental' and 'Species') I have developed and coupled with FIRE. The 'Elemental' model tracks the evolution of individual elements locked in generalized dust species and utilizes a simple, `tunable' dust growth routine, while the 'Species' model tracks the evolution of specific dust species with set chemical compositions and incorporates a physically motivated dust growth routine. I compare these models in an idealized Milky Way-mass galaxy and find that while both can produce reasonable galaxy-integrated dust-to-metals (D/Z) ratios, a chemically motivated model is needed to reproduce the observed scaling relation between individual element depletions and D/Z with column density and local gas density as seen in the Milky Way. I also find the inclusion of theoretical metallic iron and O-bearing dust species and integration of a sub-resolution dense molecular gas/CO scheme are needed in the case of specific dust species in order to match observed O, Fe, and C depletions respectively. Beyond the Milky Way, spatially resolved extragalactic observations of D/Z coupled with local gas properties are the next best benchmark and are roughly consistent with both models, but current observations are limited.



March 14, 2022

NOTE: No Journal Club today



March 21, 2022

NOTE: No Journal Club today


SPRING 2022


March 28, 2022

 "Unveiling Supermassive Black Hole Growth & Feeding Using X-rays”

Lynnie Saade
PhD student
UCLA
https://ucsd.zoom.us/j/91705682170


 Meeting ID: 917 0568 2170

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Meeting ID: 917 0568 2170
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ABSTRACT: Supermassive black holes (SMBHs) and the active galactic nuclei (AGN) they power are considered important players on the stage of galaxy evolution. To better understand how SMBHs impact their host galaxies, we need to provide constraints on how they grow. The two main ways that SMBHs are thought to have grown is through mergers with other black holes in a binary system and AGN accretion. I will present my most recent research on binary supermassive black holes and recently faded AGN”.



April 4, 2022

NOTE: Journal Club will be held in-person in SERF 383 and via Zoom
 "To Merge or Not to Merge: Stellar Mass Binary Black Holes in AGN Disks"

Hui Li
Scientist
Los Alamos National Laboratory
https://ucsd.zoom.us/j/92683845714


 Meeting ID: 926 8384 5714

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Meeting ID: 926 8384 5714
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ABSTRACT: The recent GW190521 event – an 85 an 85 Msun and a 66 Msun black hole (BH) coalescing to a 142 Msun BH – the heaviest binary black hole (BBH) merger to date has opened up more discussions on the formation channels of BBHs. In this talk, we focus on the scenario where BBHs are embedded inside an AGN disk and study its orbital evolution, in particular under which conditions the BBH will tighten its orbit or expand. We perform a series of high-resolution 2D and 3D hydrodynamical simulations of equal-mass BBHs embedded in an AGN accretion disk to study whether these binaries can be driven to merger by the surrounding gas. We demonstrate that there is a hierarchy of disk structures in such an embedded BBH, including the circum-single disk (CSD) and the circum-binary disk (CBD), both of which play an essential role in regulating the angular momentum evolution. We determine through detailed analysis of the binary torque that the spiral structure in the CSDs orbiting each black hole is important and properly resolving these spirals—both with high resolution and small gravitational potential softening—is essential. We discuss the parameter spaces that will cause the BBH to contract or expand. Implications for possible observational signatures and several other related processes will be discussed as well.



April 11, 2022

NOTE: Journal Club will be held in-person in SERF 383 and via Zoom.
**A pizza lunch will follow the talk @ 1pm on the 4th floor balcony**
 "Galaxy Evolution with Space-based Spectroscopy: from Hubble to JWST
(and Beyond)"

Casey Papovich
Professor of Physics and Astronomy
Texas A&M University
https://ucsd.zoom.us/j/99496300275


 Meeting ID: 994 9630 0275

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Meeting ID: 994 9630 0275
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ABSTRACT: Infrared slitless spectroscopy from the Hubble Space Telescope (HST) has become a mainstream method to study distant galaxies. This observing mode provides detailed information of galaxies with high angular resolution (spatially resolved) and at wavelengths unobstructed by the Earth's atmosphere. I will discuss constraints using such data to study distant galaxies based on a large HST program (from the CLEAR [CANDELS Lyman-alpha Emission At Reionization] survey). CLEAR targets roughly 100 square arcminutes in the GOODS-North and -South fields using slitless spectroscopy covering 0.85 to 1.65 micron. CLEAR was designed to study the evolution of Lyman-alpha emission in galaxies at z > 6, but the data also cover important spectral features of galaxies, including rest-frame optical absorption and emission lines for galaxies at redshifts z~1-3. I will discuss results from CLEAR, including (1) the implications for Lyman-alpha emission from galaxies into the epoch of reionization, (2) star-formation histories and chemical evolution of quenched galaxies at z > 1, (2) the evolution of gas metallicity and ionization of galaxies at z ~ 1-3, and (3) results from spatially resolved metallicities and star-formation of galaxies as a constraint on gas accretion and feedback processes. The results from HST/CLEAR bode well for future, and I will discuss forthcoming programs from JWST (in Cycle 1) and beyond (e.g., NGRST) that will employ both deep and/or wide-area space-based infrared slitless spectroscopy to study galaxy properties.



April 18, 2022

NOTE: No Journal Club today



April 25, 2022

NOTE: Journal Club will be held in-person in SERF 383 and via Zoom.
**A pizza lunch will follow the talk @ 1pm on the 4th floor balcony**
 "Revealing how Galaxy Growth, Star Formation and Quenching proceed in High Redshift Galaxies with Spatially Resolved Space-based Slitless Spectroscopy"

Jasleen Matharu
Postdoc
Texas A&M University
https://ucsd.zoom.us/j/91953018206


 Meeting ID: 919 5301 8206

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Meeting ID: 919 5301 8206
Find your local number: https://ucsd.zoom.us/u/ab9ixavEMZ

ABSTRACT: Space-based slitless spectroscopy capabilities on-board the Hubble Space Telescope have made it possible for us to conduct spatially-resolved studies of star formation in high redshift galaxies for the first time. The future is truly slitless, with the James Webb Space Telescope and the Nancy Grace Roman Space Telescope vastly improving and capitalizing on the scientific gains we will make with this mode of observation. I will begin by demonstrating how spatially resolved studies with the Hubble Space Telescope have allowed us to determine which galaxy size growth mechanisms dominate and how the quiescent (not forming stars) population of galaxies builds up with redshift. Subsequently, I will unveil the first spatially resolved H-Alpha emission line maps of cluster galaxies at z~1 from the GCLASS survey, made possible with the Wide Field Camera 3 G141 grism on-board the Hubble Space Telescope, revealing what they have taught us about the shutdown of star formation in galaxy clusters at this crucial epoch in the history of cosmic star formation. I will end by presenting deep spatially resolved H-Alpha emission line maps of CANDELS galaxies at z~0.5 from the CLEAR survey, made possible with the Wide Field Camera 3 G102 grism on-board the Hubble Space Telescope, and what these have unveiled on galaxy size growth via star formation at intermediate redshifts. By synthesizing the few existing spatially-resolved studies of High-Redshift Galaxies between 0.5<z<1.7 we now have, I will provide the first results on how star formation propagates spatially in galaxies over time.



May 2, 2022

NOTE: No Journal Club today



May 9, 2022

NOTE: Journal Club will be held in-person in SERF 383 and via Zoom.
**A pizza lunch will follow the talk @ 1pm on the 4th floor balcony**
 "JWST/MIRI Imaging: Insights into Obscured Star-Formation and AGN for Distant
Galaxies in Deep Surveys"

Guang Yang
Casey P. Postdoc
TAM
https://ucsd.zoom.us/j/91810747749


 Meeting ID: 918 1074 7749

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Meeting ID: 918 1074 7749
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ABSTRACT: The JWST MIRI instrument, covering 5-28 μm, will soon revolutionize extragalactic astronomy by providing unprecedented sensitivity to the emission from polycyclic-aromatic-hydrocarbon (PAH) and AGN-heated dust in distant galaxies.

I will talk about our recent paper that simulates realistic MIRI imaging. In this work, we assess the potential of MIRI photometry to constrain properties of galaxies in the Cosmic Evolution Early Release Science (CEERS) survey. We extract PSF-matched photometry from the simulated data, and fit the source SEDs with CIGALE, simultaneously modeling the photometric redshift and other physical properties. Adding the MIRI data, the accuracy of both the redshift and frac_AGN (fractional AGN contribution to total IR) is significantly improved for sources at z<~3. The simulated CEERS MIRI data are slightly more sensitive to AGN detections than the deepest X-ray survey, based on the empirical L_X-L_6μm relation. Like X-ray observations, MIRI can also be used to constrain the AGN accretion power (accuracy ≈ 0.3 dex).

I will also talk about some potential science with MIRI imaging. This includes Compton-thick AGNs (especially at z>3), a new potential SFR estimator based on MIRI imaging, and spatially resolved obscured versus unobscured star formation. These projects will be immediately feasible based on the planned MIRI imaging surveys such as CEERS and MIRI-HUDF. Finally, I will mention MIRI medium-resolution spectrometer (MRS), which will provide unprecedented mid-IR spectral data. The MRS observations will also simultaneously provide “free” MIRI images, further enlarging the archival MIRI database and enabling statistical analyses with large samples.



May 16, 2022

NOTE: No Journal Club today



May 23, 2022

NOTE: No Journal Club today