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Journal Club Seminars From 2018 - 2019


FALL 2018

October 5, 2018

NOTE: CASS All-Hands Meet & Greet

 CASS All-Hands Meet & Greet this Friday, October 5, from 12:00 to 1:00 pm in SERF 383. This meeting will be an opportunity for new members of CASS to introduce themselves and present a quick overview of their research. It will also give established members of CASS a chance to summarize their recent work. New graduate students are especially encouraged to attend. Pizza and soda will be provided. Journal Club is an informal environment in which graduate students can give short talks on any subject of interest to them, be it a recent paper, their own research, or any other topic. Talks will resume next week. All are welcome to attend.

October 12, 2018

 "Characterizing bursty star formation and ionizing photon production in dwarf
galaxies through cosmic time"

Najmeh Emami (12:00-1:00)
Finishing Graduate Student
UC Riverside

 Halpha and far-UV luminosities are commonly used as indicators of star formation rates, but they are only accurate if the star formation rate is constant for a long enough period to reach an equilibrium number of stars responsible for the Halpha (~5 Myr) and far-UV (100 Myr) emission. In dwarf galaxies, these tracers of star formation often do not agree, suggesting that star formation rates change significantly, and rapidly. We use the Halpha and far-UV luminosities to determine the stellar masses at which local galaxies become bursty, the time scales of these bursts, and compare our findings to recent hydrodynamical simulations. In the second half of my talk, I will use Halpha and far-UV distributions of high redshift dwarf galaxies to determine the typical efficiency of ionizing photon production (xi_ion), and discuss the implications for reionization.

October 19, 2018

 "Suppressing cooling flows in massive galaxies with cosmic ray injection and turbulent stirring"

Kung-Yi Su (12:00-1:00)
Finishing Graduate Student

 Reading list: <>

Abstract: The quenching "maintenance" and related "cooling flow" problems are important in galaxies from Milky Way mass through clusters. We investigate this in halos with masses ~1e12-1e14 solar mass, using non-cosmological high-resolution hydrodynamic simulations with the FIRE-2 (Feedback In Realistic Environments) stellar feedback model. We first focus on physics present without AGN, and show that various proposed "non-AGN" solution mechanisms in the literature, including Type Ia supernovae, shocked AGB winds, other forms of stellar feedback (e.g. cosmic rays from supernovae), magnetic fields, Spitzer-Braginskii conduction, or "morphological quenching" do not halt or substantially reduce cooling flows nor maintain "quenched" galaxies in this mass range. This all supports the idea that additional physics, e.g., AGN feedback, must be important in massive galaxies. We then test various AGN feedback toy models with different forms of energy input and ranges of coupling, exploring what scenario can possibly quench galaxy and suppress the cooling flows without resulting in halo properties that contradict observations. The test scenarios include momentum injection, turbulent stirring, thermal heating, and cosmic ray injection. We found that turbulent stirring confined within 100 kpc and cosmic ray injection can both maintain a stable, low-SFR halo for extended periods of time, because they provide non-thermal pressure form which can stably lower the core density and cooling rate. This can be much more efficient than heating up the gas thermally. We conclude that the enhancements of turbulence and cosmic ray energy are very important aspects of AGN feedback, and can be the dominant processes that quench the massive ellipticals.

October 26, 2018

NOTE: CASS Annual Sexual Harassment and Discrimination Training
@ Noon in SERF 383

 (In lieu of the CASS Journal Club Seminar)
Pizza & soda provided!

Helen Kaiser from the Office for the Prevention of Harassment & Discrimination (OPHD) will be the featured speaker. Everyone in CASS should attend, if possible.

November 2, 2018

 "Beyond the Two Point Function: Extracting New Information from Cosmological Observations”

David Spergel (12:00-1:00)

November 9, 2018

NOTE: Journal Club Cancelled Today - CMB Workshop

November 16, 2018

NOTE: Journal Club Cancelled Today

November 23, 2018

NOTE: Journal Club Cancelled Today - Thanksgiving Day Holiday

November 30, 2018

Grace's Title: "Spatially Resolved Metal Loss from M31"
Dr. Laha's Title: "The role of ionized and molecular outflows in quasar evolution"

Grace Telford (12:00-12:30)
Graduate Student
University of Washington
Sibasish Laha (12:30-1:00)
Postdoctoral Scholar

Grace's Abstract: As galaxies evolve, they must enrich and exchange gas with the intergalactic medium, but the mechanisms driving these processes remain poorly understood. In this work, we leverage missing metals as tracers of past gas flows to constrain the history of metal ejection and redistribution in M31. This nearby, roughly L∗ galaxy is a unique case where spatially resolved measurements of the gas-phase and stellar metallicity, dust extinction, and neutral ISM gas content are available, enabling a census of the metal mass present in stars, gas, and dust. We combine spatially resolved star formation histories from the Panchromatic Hubble Andromeda Treasury survey with a model of metal production by Type II SNe, Type Ia SNe, and AGB stars to calculate the history of metal production in M31. We find that 62% of the metals formed in the M31 disk are missing in our fiducial model. For any reasonable modeling choices, the missing metals from M31’s disk far exceed the metal mass that has been detected in M31’s circumgalactic medium. We then use the metal production histories to place constraints on the timing of this metal loss and on the required redistribution of newly produced metals within the disk in the last 1.5 Gyr.

Dr. Laha's Abstract: The reason for cosmic down sizing of quasars is still a big puzzle in astronomy and it is commonly believed that the central active galactic nucleus (AGN) must have played a significant role in quenching itself, in a self-regulatory mechanism popularly termed “AGN feedback” . The AGN feedback also plays a crucial role in black hole and host galaxy coevolution across cosmic time. In this talk I will discuss the nature and impact of pc scale outflows from AGN, detected in X-rays, popularly known as warm absorbers (WAX sample study, Laha et al. 2014, 2016), as well as kpc scale outflows detected in IR and sub-mm, popularly known as Molecular outflows (MOX sample study, Laha et al. 2018). These different types of outflows are believed to be strong contenders for removing gas and dust from the vicinity of the super massive black hole and thereby starving it to death (quenching). However, the exact nature of the interaction of these outflows with that of the host galaxy gas and dust is still highly debated. Although we largely believe that feedback is an important mechanism by which the quenching happens, it brings us to an interesting question: Is there any fundamental difference between the central engines of the local AGN compared to their high redshift counterparts? Are they simply scaled down (lower black hole mass) versions of their higher redshift counterparts, or are different in some other way? I will present results from a sample study of low luminosity quasars (LLQSO study, Laha et al. 2018) in the local Universe to address this issue.


January 11, 2019

OPEN TIME SLOT (12:00-12:30)
OPEN TIME SLOT (12:30-1:00)

January 18, 2019

 "Goodbye Kepler, Hello TESS"

Sanchit Sabhlok (12:00-12:30)
Physics Graduate Student
OPEN TIME SLOT (12:30-1:00)

January 25, 2019

 "Observations to Origins: Disentangling Gas Flows in the Circumgalactic Medium"

Zach Hafen (12:00-1:00)
Graduate Student
Northwestern University

 As much as half of the gas mass in our galaxy's dark matter halo may reside not in the galaxy itself, but in the surrounding area, the circumgalactic medium (CGM). The vast gas content of the CGM, loosely defined as the volume immediately outside the galaxy but inside the dark matter halo, can be broadly classified as originating either in accretion from the intergalactic medium (IGM) or winds from galaxies. Both of these are crucial to the process of galaxy formation: IGM accretion provides the material necessary for observed star formation rates, while galactic winds are linked closely to the regulation of star formation through feedback. Despite their individual importance, differentiating these gas flows in observations is an outstanding problem in studies of the CGM. I will discuss our efforts to address this problem through the use of hydrodynamic galaxy formation simulations on two fronts: mock observations of CGM quasar absorption lines and "particle-tracking" analyses that reconstruct the full history of CGM gas.

February 1, 2019

 "Weighing the giants with CMB lensing"

Sanjay Patil (12:00-1:00)
Graduate Student
University of Melbourne

 Galaxy clusters are the largest virialized objects in the Universe, and are powerful probes of cosmology. Their abundance as a function of mass and redshift is extremely sensitive to how structures grow and the properties of dark energy. Though they are powerful probes of cosmology, they are currently limited by mass uncertainty which is ~ 15%. One way to measure cluster mass is through lensing of the cosmic microwave background (CMB). CMB-cluster lensing offers a robust and accurate way to constrain galaxy cluster masses, especially at high redshift (z > 1) where optical lensing measurements are challenging. With CMB lensing we expect to improve mass uncertainty to 3% for upcoming experiments such as AdVACT, SPT-3G etc., and to 1% for next-generation CMB experiments. In this talk, I will report on a demonstration of this technique using CMB data from the South Pole Telescope (SPT) to constrain masses of the Dark Energy Survey (DES) galaxy cluster catalog.

February 8, 2019

 Reviewing "What FIREs up star formation: the emergence of the Kennicutt-
Schmidt law from feedback"

Cameron Trapp (12:00-12:30)
Physics Graduate Student

 Cameron will be reviewing this paper:

February 15, 2019

 "Radial and Rotational Velocities of Ultracool Dwarfs From High-Resolution

Dino Chih-Chun Hsu (12:00-12:30)
Physics Graduate Student
OPEN TIME SLOT (12:30-1:00)

 Precise measurements of radial (RV) and rotational (vsini) velocities of stars are essential for studying stellar kinematics (space velocities and dispersions), binary orbits, and rotational dynamics (angular momentum evolution). However, the high-resolution spectroscopic observations necessary to make these measurements is challenging for the intrinsically faint ultracool dwarfs (UCDs), stellar or sub-stellar objects with effective temperatures less than 3,000 K, and velocity samples of these objects are correspondingly small. I will discuss the current understanding of the ultracool dwarfs, specifically focusing on and the key questions that can be addressed by measuring the precise RVs and vsinis in the era of Gaia. I will present the preliminary results of analysis of the archival Keck/NIRSPEC high-resolution spectroscopic data of the UCDs spanning 20 years, reduced and analyzed by the NIRSPEC Data Reduction Pipeline and our Markov Chain Monte Carlo forward-modeling pipeline. I will conclude by reviewing other spectroscopic datasets that can be analyzed in a similar manner.

February 22, 2019

 Revewing "AGN wind scaling relations and the co-evolution of black holes and

Gene Leung (12:00-12:30)
Physics Graduate Student
OPEN TIME SLOT (12:30-1:00)

March 1, 2019

 "The Variation of the Dust-to-Metals Ratio in Nearby Galaxies"

I-Da Chiang (12:00-12:30)
Physics Graduate Student
OPEN TIME SLOT (12:30-1:00)

March 8, 2019

 "Paleolithic Astronomy"

Bernie Taylor (12:00-1:00)

 Naturalist and author Bernie Taylor will present an origin to modern astronomy in European Paleolithic caves from 34,000 years ago that connects with global myths of hunter-gatherers and the ancients in the Mediterranean region. Taylor proposes that astronomy was developed to pass on timeless myths and cultural traditions among prehistoric hunter-gathers. He will explore deep sources to Ptolemy's Almagest and the hero's journey monomyth as popularized by Joseph Campbell, and test precession against the Paleolithic record.

Bernie Taylor is an independent naturalist and author whose research explores the mythological connections and biological knowledge among prehistoric, indigenous and ancient peoples. His works in these areas include Biological Time (2004) and Before Orion: Finding the Face of the Hero (2017). Before Orion is premised on Joseph’s Campbell’s hero's journey monomyth that is at the core of stories worldwide among indigenous peoples, the ancients, and our modern society. Before Orion explores a deeper root for this monomyth by looking at how hunter-gatherers viewed themselves within the natural and spiritual worlds through Paleolithic cave art from 40,000 years ago. Taylor proposes that select cave paintings are fundamental pieces in the human journey to self-realization, the foundation of written language, and a record of biological knowledge that irrevocably impacted some of the artistic styles, religious practices, and stories that are still with us. Taylor addresses a profound archaeological elephant in the room by opening up an uncharted place in our history, which points to the cultural ancestors of mankind in western North Africa. Before Orion will change the idea of who you think you are.

March 15, 2019

Logan Howe (12:00-12:30)
Physics Graduate Student
OPEN TIME SLOT (12:30-1:00)


April 19, 2019

NOTE: CASS All-Hands Meeting @ Noon in SERF 383

 (In lieu of the CASS Journal Club Seminar)
Pizza & soda provided!

This will be a presentation from the RESEARCH COMMUNICATION PROGRAM OFFICE about Research Communications, and the UCSD resources available to graduate students and faculty to help with communicating and presenting their work to colleagues and the public. Slated presenters are: Sherry Seethaler, Director of Education Initiaties, Division of Physical Sciences; Mario Aguilera, Director of Communication-Bio Sci, University Communications; and possibly Cynthia Dillon, Director of Communications-Phys Sci, University Communications. Everyone in CASS is encouraged to attend.

April 26, 2019

Tucker Elleflot (12:00-12:30)
Physics Graduate Student
OPEN TIME SLOT (12:30-1:00)