Wine and Cheese Fall 2021

Wine and Cheese sessions with one speaker will have a 50 minute talk with 10 minutes for questions. Sessions with two speakers will have two 25 minute talks, each with 5 minutes for questions. Sessions in the Graduate Student Series will have three 15 minute talks, each with 5 minutes for questions.

20 September

Yunyang Li (JHU)

The Sunyaev-Zel'dovich Effect, Clusters, and ACT
The Sunyaev-Zel'dovich (SZ) effect introduces a specific distortion of the blackbody spectrum of the cosmic microwave background (CMB) radiation when it scatters off hot gas in clusters of galaxies. The frequency dependence of the distortion is only independent of the cluster redshift when the evolution of the CMB radiation is adiabatic. Using 370 clusters within the redshift range 0.07-1.4 from the largest SZ-selected cluster sample to date from the Atacama Cosmology Telescope, we provide new constraints on the deviation of CMB temperature evolution from the standard model $\alpha=0.017^{+0.029}_{-0.032}$, where $T(z)=T_0(1+z)^{1-\alpha}$. This result is consistent with no deviation from the standard adiabatic model. Attributing deviation from adiabaticity to the decay of dark energy, this result constrains its effective equation of state $w_\mathrm{eff}=-0.998^{+0.008}_{-0.010}$.

Isu Ravi (JHU)

Lyman-alpha Filter Prototype to Enable Astronomical Photometry in the Lyman Ultraviolet
Observations of astronomical objects in the far ultraviolet (FUV wavelengths span 900-1800 A) from earth’s orbit has been impeded due to bright Lyman-α geocoronal emission. The Johns Hopkins Rocket Group is developing a hydrogen absorption cell that would act as a narrow band Lyman-α rejection filter to enable space-based photometric observation in bandpasses that span over the Lyman ultraviolet region shortward of the geocoronal line. While this technology has been applied to various planetary missions with single element photomultiplier detectors it has yet to be used on near earth orbiting satellites with a multi-element detector. We are working to develop a cell that could be easily incorporated into future Lyman ultraviolet missions. The prototype cell is a low-pressure (∼ few torr) chamber sealed between a pair of MgF2 windows allowing transmission down to 1150 ̊A. It is filled with molecular hydrogen that is converted to its neutral atomic form in the presence of a hot tungsten filament, which allows for the absorption of the Lyman-α photons. Molecular hydrogen is stored in a fully saturated non-evaporable getter module (St707TM), which allows the cell pressure to be increased under a modest application of heat (a 20 degree rise from room temperature has produced a rise in pressure from 0.6 to 10 torr). Testing is now underway using a vacuum ultraviolet monochromator to characterize the cell optical depth to Lyman-α photons as functions of pressure and tungsten filament current. We will present these results, along with a discussion of enabled science in broadband photometric applications.

Gabriela Sato-Polito (JHU)

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27 September

Arshia Jacob (JHU)

Small Molecules, Big Impact: Investigating Hydrides in the Interstellar Medium
The nature and distribution of atomic and molecular gas in the interstellar medium (ISM) is of great interest to astrophysicists because it is this gas that provides the raw material for the formation of new stars. My work concentrates on investigating hydride molecules in the ISM and their use as diagnostics of it's different phases. Particular emphasis is given to the central CH radical, a probe of diffuse and translucent molecular clouds, including those not traced by the otherwise common CO. Following which I will detail our search for, and address questions regarding the origin of another molecule, CH2, which despite being chemically associated with the ubiquitous CH, has largely remained elusive. I will also discuss the transition from the diffuse atomic to the diffuse and translucent molecular phases of the ISM by extending our view of the chemistry of argonium, ArH+, a tracer of almost purely atomic gas. And lastly introduce the audience to HyGAL, a SOFIA Legacy Project aimed at characterising the Galactic ISM with observations of hydrides and other small molecules.

Ayan Acharyya (JHU)

“Mockulus reparo” – to Fix the Effects on Metallicity Gradient Measurements Due to Our Insufficient “Seeing”
Gas-phase metallicity gradients of galaxies are a crucial ingredient for understanding the chemical evolution of galaxies. However, measurements of gradients are often affected by limited spatial resolution. The extent of this effect may be different across observations, making cross-observation comparisons unreliable. We produce mock IFU datacubes from hydrodynamic simulations of an isolated galaxy and use those to quantify the said effect. I will present the application of our models on current IFU surveys — MaNGA, SAMI and CALIFA — by correcting the observed metallicity gradients for the effects of spatial resolution. I will demonstrate that while the mean trend of metallicity gradient versus stellar mass is largely unaffected, individual galaxies can undergo significant corrections. Our proposed method of correcting metallicity gradients by using isolated galaxy simulations already enables meaningful cross-survey comparisons. However, the next goal is to produce mock datacubes of cosmological simulations, in order to sample a broad range of galaxy properties. In this regard, I will briefly highlight some of my current efforts to study the metallicity distributions in the FOGGIE simulations.

11 October

Mi Dai (JHU)

Understanding the Systematics in Type Ia Supernova Modeling for Cosmology
Type Ia supernovae (SNe Ia) are important cosmological probes due to their standardizable nature. In order to obtain distance measurements of SNe Ia, the SN Ia light curves are traditionally fitted to an empirical light curve model. As we gain better knowledge on the various systematics in SN Ia cosmology analysis, the modeling uncertainty will likely become the largest in the near future. I will describe various ways the model training procedure can potentially bias the final cosmological constraints, and discuss improvements we can make to reduce these biases.

Selim Hotinli (JHU)

Fundamental Physics from Velocity Tomography
Next generation cosmic microwave background (CMB) experiments and galaxy surveys will generate a wealth of new data with unprecedented precision on small scales. Correlations between CMB anisotropies and the galaxy density carry valuable cosmological information about the largest scales, creating novel opportunities for inference. In this talk I will discuss the science goals for the kinetic Sunyaev Zel’dovich (kSZ) and the moving-lens effects and describe the method of velocity tomography which allows recovering large-scale cosmological information from the measurements of small scales.

18 October

Yuzo Ishikawa (JHU)

Exploring the Impact of Quasars on Galaxy Evolution and its Environments
Quasars are believed to play an important role in the formation and evolution of galaxies. Their powerful radiation is often invoked to drive quasar feedback, impacting evolution in the galactic to intergalactic scales across cosmic history. I will give an overview of my recent projects exploring the various ways quasars affect these regimes. X-rays probes the radiation from the accretion disk of the central black hole, and deep near-IR imaging probes the earliest quasars at the End of Reionization. Current and future advances in spatially resolved spectroscopy will allow detailed characterization of the quasars' impact.

Christina Lindberg (JHU)

Measuring Massive Star Embeddedness in the Andromeda Galaxy
Massive stars interact with their surrounding interstellar medium (ISM) via dynamically disruptive feedback mechanisms. By studying their relative embeddedness, we can start to constrain the 3D distribution of the ISM, bridging the gap between observation and massive star feedback simulations.

25 October

Elena Murchikova (IAS)

Sagittarius A* in its Natural Habitat
The Milky Way’s Galactic Center black hole Sagittarius A* is the supermassive black hole closest to us and has the largest angular size on the sky. Despite its proximity, the accretion flow onto it is not well understood. At large scales (0.05 pc and beyond), the primary source of information about accretion flow comes from observations of hot X-ray emitting gas. At near horizon scales, the density of the flow is constrained by submm polarization measurements. At intermediate scales, there are too few model-independent probes to reliably determine physical properties of the gas. In 2019, using ALMA observations I discovered a disk of relatively cool (T=10^4K) gas at intermediate distances (0.01 pc) from the black hole. The cool gas can be observed with much higher spatial resolution than the hot X-ray emitting gas, providing new probes of the inner accretion flow of the Sagittarius A*. In this talk I will review what is known about the structure of the accretion flow around Sgr A*, and I will summarize my ongoing research program to determine the origin and the physical conditions of the cool gas and its contribution the accretion onto our local supermassive black hole.

1 November

Alaina Henry (STScI)

Unlocking the Reionization: Keys from Low Redshift Analog Galaxies
Presently, little is known about the detailed history of the IGM reionization. While JWST is expected to uncover unprecedented populations of galaxies in the early universe, there are key questions that it will not address--namely, how do UV Lyman Continuum (LyC) photons escape galaxies to ionize the IGM? In recent years, populations of low redshift objects with stellar and nebular properties similar to galaxies at high-redshifts have been identified in the SDSS. Spectroscopic followup observations with HST/COS have opened up a new window into their absorbing ISM: strong Lyman Alpha emission is common, and ionizing radiation has been found to escape in some cases. In this talk, I will review recent results from the Low Redshift Lyman Continuum Survey and other HST programs. Armed with a statistical sample, for the first time we are able to explore the physical conditions that lead to LyC escape in low-redshift galaxies. I will discuss the numerous indicators for LyC escape that are accessible through UV and optical spectroscopy, and show the successes that are now uncovered by our HST/COS observations.

8 November

Abhishek Maniyar (NYU)

Weak lensing: Globally Optimal Estimator and a New Probe of the High-Redshift Universe
In recent years, weak lensing of the cosmic microwave background (CMB) has emerged as a powerful tool to probe fundamental physics. The prime target of CMB lensing surveys is the lensing potential, which is reconstructed from observed CMB temperature T and polarization E and B fields. In this talk, I will show that the classic Hu-Okamoto (HO02) estimator used for the lensing potential reconstruction is not the absolute optimal lensing estimator that can be constructed out of quadratic combinations of T, E and B fields. Instead, I will derive the global-minimum-variance (GMV) lensing quadratic estimator and show explicitly that the HO02 estimator is suboptimal to the GMV estimator. The rapidly expanding field of the line intensity mapping (LIM) promises to revolutionise our understanding of the galaxy formation and evolution. Although primarily a tool for galaxy astrophysics, LIM technique can be used as a cosmological probe and I will point out one such application in rest of the talk. I will show that a linear combination of lensing maps from the cosmic microwave background (CMB) and from line intensity maps (LIMs) allows to exactly null the low-redshift contribution to CMB lensing, and extract only the contribution from the Universe from/beyond reionization. This would provide a unique probe of the Dark Ages, complementary with 21 cm. I will quantify the interloper bias (which is a key hurdle to LIM techniques) to LIM lensing for the first time, and derive a "LIM-pair" estimator which nulls it exactly. In the end, I will show some results for prospects of observing the Doppler boosted CIB emission and its applications.

15 November

Yuanze Luo (JHU)

A Multiwavelength view of IC 860: What Is in Action inside Quenching Galaxies
Observations of the galaxy population throughout the cosmic time have suggested an evolution scenario where galaxies evolve from blue and star-forming, to red and quiescent as star formation is quenched and gas is consumed in stars or becomes unavailable for stellar synthesis. The absence of a significant population falling in the intermediate region implies that these transitions must occur quite rapidly. Though multiple mechanisms have been shown to be able to quench galaxies in different ways, the interplay and relative importance of these mechanisms are still not fully understood. In this work, we study a particular quenching galaxy: IC 860, for which we have exquisite multiwavelength data to probe different activities such as outflows and AGN in the galaxy. IC 860 is a quenching galaxy at a very early stage and is therefore an ideal case study for understanding the triggers of quenching. Our analysis has confirmed the existence of multiphase outflows (in neutral and molecular gas), revealed evidence for a recent merger and the presence of a buried AGN, and supports the quenching picture where outflows help suppress star formation by disturbing rather than expelling all of the gas.

Rui Shi (JHU)

SMICA and its Application on CLASS-like Data
The Cosmology Large Angular Scale Surveyor (CLASS) is a ground-based telescope array in the Atacama Desert, aiming at measuring the largest scales of the cosmic microwave background (CMB) polarization to study early universe physics. CLASS has been observing the 75% of the sky since 2016, and now data from all of the four bands (40, 90, 150, 220 GHz) are being processed. One of the final steps in the analysis is component separation, by which the microwave frequency maps, contaminated by Galactic emission, are filtered and combined to separate out the pure CMB information. I will talk about my ongoing project to apply the Spectral Matching Independent Component Analysis (SMICA, a specific type of component separation method) to CLASS-like data.

John Soltis (JHU)

Predicting Follow-Up Observations of Galaxy Clusters Using Machine Learning
The eROSITA X-ray telescope, launched in 2019, is predicted to observe roughly 100,000 galaxy clusters. Our ability to follow up these observations with longer, higher resolution observations is expensive and limited, and objects for follow-up must be chosen with care. To aid in the evaluation of potential follow ups, we have developed a proof-of-concept algorithm for predicting longer, higher quality, observations based on mock eROSITA observations. We do so making use of the hydrodynamic cosmological simulation Magneticum, simulated eROSITA instrument conditions using SIXTE, and a novel convolutional neural network. We are able to closely predict radial luminosity profiles, remove noise, and capture substructure.

29 November

Nicholas Kern (MIT)

First Results from HERA Phase I: New Limits on the EoR 21 cm Power Spectrum
Cosmic Dawn and the Epoch of Reionization (EoR) are crucial milestones in the growth of luminous structure and in the global picture of star and galaxy formation. Yet, to-date we currently have few direct constraints on exactly when and how these events took place. Hydrogen intensity mapping experiments hope to present a new picture of these processes by directly mapping the density, temperature, and ionization state of the intergalactic medium (IGM) from redshifts 6 < z < 30. However, significant technical challenges stand in the way of these measurements. Current experiments are addressing this with novel techniques for calibration, interference identification, and foreground and systematic modeling, leading to improved power spectrum upper limits. In this talk, I will discuss new limits set by the HERA experiment that improve upon existing limits at z=8 by over an order of magnitude in sensitivity. I will discuss key steps in the analysis that made this possible, the scientific impact of the limits, and future directions as HERA construction is completed and full-science observations commence.​

6 December

Leslie Rogers (Chicago)

Glimpsing the Compositions of Sub-Neptune-Size Worlds
Sub-Neptune and super-Earth-size planets are a new category of astrophysical objects. Though absent from the Solar System, exoplanet surveys have revealed that they are a dominant outcome of planet formation found in abundance around other stars. The nature of these planets is not well understood. In the sub-Neptune size range a large variety of planet bulk compositions are a priori possible, including terrestrial super-Earths, mini-Neptunes with hydrogen-helium envelopes, and water-worlds with several tens of percent water by mass. In this talk, I will present recent results from my group aimed at understanding the nature and origin of these enigmatic sub-Neptune-size worlds and disentangling the relative contributions from various compositional scenarios to the observed population of planets.

13 December

Duncan Watts (UiO)

BeyondPlanck and Cosmoglobe: An End-to-End Bayesian Analysis of CMB Data
BeyondPlanck is a Bayesian reanalysis of the Planck Low Frequency Instrument (LFI) data. The framework performs Gibbs sampling for each stage of the data analysis pipeline, from raw diode data to maps of the galaxy and the Cosmic Microwave Background (CMB). BeyondPlanck is the first CMB analysis pipeline that explores the full posterior distribution of all parameters, including the properties of the instrument including gain, correlated noise, and bandpasses, to the astrophysical components and cosmological parameters. This allows for a proper error propagation and handling of correlations between various parameters along the analysis pipeline. I will present the results of the BeyondPlanck analysis, highlighting the improvements over the official Planck analysis pipeline, and pay special attention to the novel goodness-of-fit tests that we are able to perform in this framework.

After summarizing the BeyondPlanck results, I will discuss the application of this framework to the WMAP data set, with particular emphasis on the Q-band data. I will show this as an example of the extendability of the Bayesian end-to-end formalism to external datasets beyond just the Planck LFI. This is the first step in the Cosmoglobe project, which will perform joint analysis of multiple datasets at once at the rawest level possible. I will close by describing the benefits of joint multi-experiment analyses in this form, and present the path of the Cosmoglobe project going forward.