Winter Quarter, 2018
The Lowest-Mass Galaxies In the Early Universe: Insights from the Local Group
Thursday January 18
Dan Wiesz
University of California, Berkeley
The Local Group is home to ~100 galaxies less massive than the Small Magellanic Cloud (108 Msun). Such low-mass galaxies have become increasingly relevant to a broad range of astrophysics from cosmic reionization to deciphering the nature of dark matter. Yet, they are simply too faint to be directly detected at any appreciable redshift, compromising our ability to place them into a cosmological context. In this talk, I will describe how observations of resolved stellar populations in Local Group galaxies enable the measurement of detailed star formation histories, which provide the only avenue for tracing the evolution of low-mass galaxies across cosmic time. I will review our current knowledge of low-mass galaxy evolution over 6 decades in stellar mass, with a particular emphasis on the very early Universe. I will illustrate how local and high-redshift galaxy observations can be used in tandem to improve our understanding of cosmic reionization, and will conclude by discussing prospects for increased synergy between near-field and far-field galaxy studies in the JWST era.
Probing the z>3 universe *without* JWST
Thursday January 25
Iary Davidzon
IPAC
I will present some recent result about stellar mass assembly in the early universe (2 < z < 7), in particular the observational measurement of galaxy stellar mass function and the star forming main sequence in the COSMOS field. I will discuss some of the current limitations and open issues in this kind of analyses, especially those concerning massive galaxies. Answering to this question is an example of a goal that JWST will probably not achieve...at least not alone!
Mapping the z~2 Cosmic Web with IGM Tomography with Keck and TMT
Thursday February 1
Khee-Gan Lee
University of California, Berkeley
In recent years, I have been conducting the CLAMATO survey with the Keck telescope, which observed high area densities of z~2-3 star-forming galaxies spectra. This created a closely-spaced grid of sightlines probing the Lyman-alpha forest in the intergalactic medium at z~2.0-2.5. I will discuss the observations which have led to the highest-redshift detection of cosmic voids and preliminary results for the cross-correlation with co-eval galaxies. Future applications include constrained realizations of the observed volume, constraining galaxy-cosmic web intrinsic alignments, and cosmological parameter measurement. In the final 15 minutes of the talk, I will discuss proposed fiber-based spectrograph concepts for Keck (FOBOS) and TMT (Fiber-WFOS).
* Please bring your smartphone to this talk for a virtual reality demonstration *
Dwarf galaxy formation and the nature of dark matter
Thursday February 8
Anna Nierenberg
University of California, Irvine
The abundance of low mass dark matter halos (Mvir < 10 9 Msun) provides key insight into the nature of dark matter, as this abundance depends on the free-streaming length of dark matter at early times and thus its particle properties. Measuring the abundance of low mass halos is difficult as stars become increasingly poor tracers of structure on these scales owing to the complex and not yet well understood physics of star formation in these systems. I will present two complementary approaches to resolving these issues. First I will present measurements of the properties of faint satellite galaxies at a range of redshifts and around a variety of host types and demonstrate how these place new constraints on theoretical models of star formation in low mass halos. Secondly, I will present a novel approach to gravitational lensing which makes it possible directly measure the subhalo mass function to masses well below the mass scale of the missing satellite problem in a much larger sample of systems than previously possible. I will conclude by discussing future prospects for these programs given the next generation of ground and space based facilities.
Galaxy Metallicity Measurements at High Redshift: Probing Galaxy Growth over the past 12 Billion Years
Thursday February 9
Ryan Sanders
University of California, Los Angeles
The emission-line spectrum of a galaxy encodes information about many interesting galaxy properties. Extracting physically-meaningful properties (e.g., star-formation rate, dust reddening, metallicity, gas ionization state, ionizing source) from observed emission-line strengths and line ratios requires the use of diagnostics that are calibrated in the local universe. Observations of high-redshift galaxies suggest that some of these diagnostics evolve with redshift and must be revised in order to provide robust estimates of high-redshift galaxy properties. I will give an overview of the MOSFIRE Deep Evolution Field (MOSDEF) survey, in which we obtained rest-optical emission-line measurements of >1000 galaxies at z~1.5-3.5. Using data from the MOSDEF survey, I will summarize the evolution of galaxy emission-line properties from z~0 to z~3 and discuss the uncertainties affecting the interpretation of emission lines at z>1, particularly focusing on the ability to determine gas-phase metallicity. Despite the remaining uncertainties, progress is being made towards understanding the scaling between metallicity and global galaxy properties such as stellar mass and star-formation rate. The form and evolution of these metallicity scaling relations provide valuable insight into gas accretion, feedback, and galaxy growth throughout cosmic history. Independent metallicity measurements based on temperature-sensitive auroral emission lines present an avenue to reassess metallicity calibrations at high redshift. I will present detections of these temperature-sensitive auroral lines at z>2, and discuss the prospects of obtaining a statistical sample of z>1 galaxies with temperature-based metallicities using current and future facilities. Such measurements can pave the way for robust galaxy metallicities at high redshifts.
Redistributing Stellar Mass: How Environment Influences the Galaxy SMF
Thursday February 15
Adam Tomczak
University of California, Davis
I will be presenting recent measurements and results of the galaxy stellar mass function (SMF) as a function of environment from the ORELSE survey. ORELSE is dedicated spectrophotometric program observing well-known large scale structures at 0.7 < z < 1.3. With these data, we construct galaxy SMFs in several tiers of environment spanning the full range of galaxy densities from the field up to dense cores of massive galaxy clusters. These measurements reveal a strong correlation between environment and the SMF which manifests as a smooth, continual increase in the ratio of high- to low-mass galaxies towards denser environments. A straightforward implication is that environment increases the efficiency of (a) destroying lower-mass galaxies, (b) growth of higher-mass galaxies, or (c) some combination of the two. To attempt to contextualize these measurements we design a simple, semi-empirical model which incorporates prescriptions for star-formation, quenching, and galaxy-galaxy merging. I will finish the talk by discussing results, interpretations, and limitations from this simulation.
The MARVELous Dwarfs meet the Justice League: Constraints on dwarf galaxies using a heroically large simulated sample
Thursday February 22
Ferah Munshi
Vanderbilt University
I will present results from high resolution, fully cosmological simulations of 4 cosmic sheets that contain many (isolated) dwarf galaxies [MARVEL dwarfs] as well as dwarfs drawn from 4 volumes containing a Milky Way analogue [the Justice League]. Together, they create the largest collection of simulated dwarf galaxies to date, with z=0 stellar masses comparable to the LMC or smaller. In total, we have simulated ~100 luminous dwarf galaxies, forming a sample of simulated dwarfs which span a wide range of physical (stellar and halo mass), evolutionary properties (merger history) and environments. I will show how these dwarfs can be calibrated against a wealth of observations of nearby galaxies including star formation histories, HI masses and kinematics, as well as stellar and gas-phase metallicities. I will present preliminary results answering the following key questions: What is the slope of the stellar mass function at extremely low masses? Do halos with HI and no stars exist? What is the scatter in the stellar to halo mass relationship as a function of dwarf mass? What drives the scatter? With this large suite, we can begin to statistically characterize dwarf galaxies and identify the types and numbers of outliers to expect.
Are Type Ia Supernovae in Restframe H-band Brighter in More Massive Galaxies?
Thursday March 1
Kara Ponder
University of California, Berkeley
In the late 1990s, Type Ia Supernovae (SNeIa) were used to discover that the expansion of the universe is accelerating. Since then there have been major efforts to increase the sample size of SNeIa such that the constraints on cosmological parameters are currently limited by systematics. One of the top systematics is the apparent correlation between host galaxy properties, such as global mass or local star formation rates, and the luminosity of SNeIa. This correlation has been shown many times using optical data; however, no tests have been done for SNeIa observed in the near-infrared (NIR). SNeIa have been shown to be more standard in the NIR, so answering this question can give insight into possible astrophysical motivations for the host galaxy correlation.
As the NIR SNeIa data set is an order of magnitude smaller than the optical one, the goal of the SweetSpot Survey is to extend the NIR Hubble diagram out to a redshift of ~0.08 and to further characterize the use of SNeIa as cosmological probes. Using the resulting light curves from SweetSpot along with public data from several other surveys, we explore correlations with different global host galaxy properties calculated from catalog data.
The MOSFIRE Deep Evolution Field (MOSDEF) Survey: A Detailed Census of the Physics of Galaxy Formation in the Early Universe
Thursday March 8
Alice Shapley
University of California, Los Angeles
Understanding the formation and evolution of galaxies remains one of the great challenges of modern cosmology. Key outstanding questions include: What are the physical processes driving the formation of stars in individual galaxies? How do galaxies exchange material with their intergalactic environments? How do the impressive variety of galactic structures that we observe today assemble? How do supermassive black holes affect the evolution of their host galaxies? We present new results from the MOSFIRE Deep Evolution Field (MOSDEF) survey, a comprehensive census of the galaxy population during the peak epoch of activity in the universe ~10 billion years ago. In addition to providing an overview of the MOSDEF survey and its science, we focus on new results regarding the evolving physical conditions in the interstellar medium of star-forming galaxies towards higher redshift.Our new results suggest many exciting future observational directions for untangling the detailed nature of star formation in the early universe.
The Milky Way - evidence for Seyfert activity in the recent past
Thursday March 9
Joss Bland-Hawthorn
University of Sydney
The Galaxy's supermassive black hole is a hundred times closer than any other massive singularity. It is surrounded by a highly unstable gas disk so why is the black hole so peaceful at the present time? This mystery has led to a flurry of models in order to explain why Sgr A* is radiating far below (1 part in 108) the Eddington accretion limit. But has this always been so? Evidence is gathering that Sgr A* has been far more active in the recent past, on timescales of thousands of years and longer. The bipolar wind discovered by MSX, the gamma-ray bubbles discovered by Fermi-LAT, the WMAP haze, the positronium flash confirmed by INTEGRAL, and new UV spectroscopy from HST are suggestive of something truly spectacular in the recent past. We present new evidence that the Galactic Centre was a full blown "active galaxy" just a few million years ago. The echo of this incredible event can be seen today imprinted across the Galaxy.
Observational Signatures of Type Ia Supernova Progenitors and Photometric Redshifts with the Large Synoptic Survey Telescope
Thursday March 15
Melissa Graham
University of Washington
This talk is a "two for the price of one" deal! I will cover two research projects on which I collaborate with members of the UC Davis astronomy department. First, I will discuss recent attempts to observationally constrain the progenitors of Type Ia supernovae. These thermonuclear detonations of carbon-oxygen white dwarf stars are used as impirical standard candles for dark energy cosmology. I will present some observational methods that I use to better understand the type and diversity of their binary companion stars and how they might influence the explosions. Second, I will present my recent evaluation of how the accuracy of photometric redshifts will progress over the lifetime of the LSST survey. Photometric redshifts are a key component in many LSST science goals, and I will also explore how they might be improved with the addition of near-infrared photometry from future space-based wide-field survey telescopes.
The Global Supernova Project
Thursday March 21
Griffin Hosseinzadeh
Las Cumbres Observatory
Many of the remaining uncertainties in stellar evolution can be addressed through immediate and long-term photometry and spectroscopy of transients. The early light curves of thermonuclear supernovae can contain information about the nature of the binary companion to the exploding white dwarf. Spectra of core-collapse supernovae can reveal material lost by massive stars in their final months to years. Thanks to a revolution in technology, we can now routinely discover transients within days of explosion and obtain well-sampled follow-up data for months and years. Here I present several results from the Global Supernova Project at Las Cumbres Observatory that take advantage of these technological advances to catch short-lived phases of transient evolution. These include a Type Ia supernova colliding with a nondegenerate binary companion, a low-luminosity Type IIP supernova interacting with a shell of circumstellar material, a sample of rare Type Ibn supernovae interacting with hydrogen-free circumstellar material, and our high-cadence follow-up of the first kilonova.
Fall Quarter, 2017
New Insights about the Assembly of Massive Galaxies from Hyper Suprime-Cam
Thursday October 5
Song Huang
University of California, Santa Cruz
Predicted by the the promising hierarchical formation model, the extended stellar halos of massive galaxies should keep crucial fossil records regarding their assembly history. However, due to the low surface brightness of these halos, much of these information are yet to be understood. With the help of deep i-band images of a large sample of massive central galaxies at 0.3 < z < 0.5 from the Subaru Hyper Suprime-Cam (HSC) survey, we map their stellar mass distributions out to radius larger than 100 kpc individually. We find that the stellar halos of massive galaxies show a larger intrinsic diversity than their inner structures. Bot the slopes of the surface brightness profiles and the shapes of the stellar halos depend on total stellar mass where more massive galaxies tend to host more extended halos with shallower slope and more elongated shape. Moreover, we also discover subtle, but systematic and robust structural differences that depend on halo mass. Massive central galaxies from more massive halos show very significant excess of mass in the outskirt. Such differences are broadly consistent with richer recent merging history for more massive halos. These results also highlight the importance of deep photometry and the usage of detailed structural information in the study of the assembly history of galaxies.
Simulating galaxies at the epoch of reionization
Friday October 6
Xiangcheng Ma
Caltech
Galaxies at z>5 are thought to be the dominant sources for cosmic reionization, but current knowledge on their abundance, property, and contribution to reionization is still limited. With JWST to be launched next year, it allows us to study high-redshift galaxies in much detail. I will introduce a new suite of high-resolution cosmological zoom-in simulations of z>5 galaxies, taking advantage of the realistic models of the multi-phase ISM, star formation, and stellar feedback from the FIRE project. These simulations provide a more realistic sample of model galaxies, which can be very useful to predict and understand future observations. I will show the predicted galaxy scaling relations, mass functions, and luminosity functions at z>5. I will also discuss some applications using these simulations, including understanding the escape fraction of ionizing photons, high-redshift galaxy morphologies and their implications for the Hubble Frontier Field observations, dust extinction and the bright-end galaxy UV luminosity functions, etc.
ALMA Observations of High Redshift Galaxy Evolution and Arp 220
Thursday October 12
Nick Scoville
Caltech
The new ALMA observatory has factors of 20 increase in both resolution and sensitivity. It is revolutionizing the study of high redshift galaxies and forming planetary systems. I will provide a brief introduction to its capabilities and then describe in detail two projects: 1) observations of 600 galaxies at z = 0.3 to 4 for which we measure the ISM gas contents and observations at 0.1 arcsec resolution of the local ULRIG galaxy Arp 220. In the first project, we analyze the evolution of ISM contents, star formation rates and efficiencies and galaxy accretion rates with cosmic time and galaxy properties for the first time. We also derive the overall cosmic evolution of gas in galaxies for comparison with existing data on the star formation rate density. In the second project, we resolve both nuclei of the late stage merging galaxies and find spectacular properties for the two galactic nuclei.
Galaxy Death and the Role of "Red Geysers"
Thursday October 19
Kevin Bundy
University of California, Santa Cruz
Surveys of the distant universe show that star formation in very massive galaxies begins to die out nearly 10 billion years ago. This mysterious trend continues to the present day, making "red and dead" systems the dominant population among galaxies larger than the Milky Way. Despite the importance of star formation "quenching," its physical origin as well as the mechanisms responsible for preventing star formation at late times is still under debate. Addressing this question is a key goal of MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), a core program in the 4th generation Sloan Digital Sky Survey that is obtaining resolved spectroscopy for 10,000 nearby galaxies. Already the largest integral-field spectroscopic survey ever conducted with over 4500 galaxies observed, MaNGA's rich data set is providing new insight on the physics behind galaxy death. I will present our discovery of surprisingly common "red geysers," elliptical galaxies that harbor large-scale ionized winds, likely driven by low-level accretion onto supermassive black holes. As illustrated by a prototypical example, there is sufficient power in these winds to turbulently heat ambient gas and prevent star formation at late times. Episodes of red geyser activity (we estimate they occur every several 100 Myr) may play a critical role in the final stages of galaxy evolution.
Measuring Neutrino Masses Using Large Scale Structure
Thursday October 26
Arka Banerjee
Stanford University
Neutrino oscillation experiments have shown that the Standard Model neutrinos are massive. The absolute mass scale of neutrinos is not known yet, but bounds from cosmology experiments such as the Planck mission already outperform those from terrestrial experiments, and will continue to improve in the next decade. Massive neutrinos affect the formation of large scale structure in the Universe, and I will start with the prospects of measuring the neutrino mass at the LSST experiment using a combination of galaxy clustering and weak lensing. I will then describe the various challenges and approaches to running fully non-linear simulations of cosmologies with massive neutrinos, and discuss interesting observables which can be studied with these simulations, such as the scale dependent bias of mass-defined voids, and imprints on Redshift Space Distortions (RSD).
Cosmology Results from the Dark Energy Survey Year 1
Thursday November 2
Elisabeth Krause
Stanford University
This talk presents cosmology constraints from a combined analysis of galaxy clustering and weak gravitational lensing, using 1321 deg2 of griz imaging data from the first year of the Dark Energy Survey (DES Y1). The analysis combines (i) the cosmic shear correlation function of 26 million source galaxies in four redshift bins, (ii) the galaxy angular autocorrelation function of 650,000 luminous red galaxies in five redshift bins, and (iii) the galaxy-shear cross-correlation of luminous red galaxy positions and source galaxy shears. These three measurements yield consistent cosmological results, and provide constraints on the amplitude of density fluctuations (S8 = 0.794+0.029-0.027) and dark energy equation of state (w = -0.80+0.20-0.22) that are competitive with those from Planck cosmic microwave background measurements. I will describe the validation of measurements and modeling from catalogs to cosmology, and highlight cosmology constraints from the combination of DES Y1 with external data sets.
Investigating Quasar Outflows in Absorption and Emission
Thursday November 9
Serena Perrotta
University of California, Riverside
In the last decade, the potential impact of galaxy-scale outflows driven by quasars on their environment has become widely recognized. Quasars not only provide radiative feedback in the form of pressure and photo heating, they also affect the ionization state of the gas in and around the host galaxies. In this talk, I show that there is strong evidence of a different ionization state close to the quasar along and across the line of sight.
I have exploited the spectra of 100 quasars at emission redshift zem = 3.5 - 4.5 to construct a large sample of narrow absorption line (NAL) systems. The observations have been carried out with VLT/X-shooter in the context of the XQ-100 Legacy Survey. I statistically study their physical properties and distribution on different scales. I also present results from stacking Lyman-alpha forest absorbers in the XQ-100 sample to look for metals signal at large velocity separation from the zem.
Finally, I briefly talk about the Extremely Red Quasars, a unique red-quasar population with exotic physical conditions. They are candidates to be young objects in a transition stage between dusty starbursts and unobscured blue quasars: the perfect laboratory where to study powerful outflows through their peculiar emission lines.
Reconstructing the Formation Histories of Massive Galaxies
Thursday November 16
Mariska Kriek
University of California, Berkeley
In past years, large and deep photometric and spectroscopic surveys have significantly advanced our understanding of galaxy growth, from the most active time in the universe (z~2) to the present day. In particular, the evolution in stellar mass, star formation rate, and structure of complete galaxy samples have provided independent and complementary insights into their formation histories. In addition, detailed studies of the properties of individual distant galaxies have lead to a better apprehension of the physical processes which govern galaxy growth. Nonetheless, many outstanding questions remain. In this talk I will give an overview of our current picture of galaxy growth over the past 11 billion years, discuss current challenges and outstanding questions, and introduce new and ongoing efforts to further unravel the formation histories of massive galaxies.
Disk Assembly From z~2 to Now
Thursday November 30
Raymond Simons
Johns Hopkins University
It was once accepted that galaxies form thin disks early: collisional gas with high velocity dispersion should dissipate energy, conserve angular momentum, and develop strong disk-like rotational support in only a few galaxy crossing times (~few hundred Myr). I will present results from our SIGMA survey of star-forming galaxy kinematics at z ~ 2 that challenge this simple picture - well-ordered disks were only just beginning to emerge 3 Gyr after the Big Bang. Combining SIGMA with a similar sample at lower redshift, I will show how rotational-support develops in galaxies from z~2 to now. By the present day, nearly all massive (log M* > 9.5) star-forming galaxies have assembled a rotationally-supported disk. These results tell a story of progressive kinematic assembly of well-ordered disks over the past 10 Gyr.
Why Shear Measurement is Hard, and What to do About it
Thursday December 7
Eric Huff
JPL
Weak lensing is a critical source of information about the nature of the dark sector of the universe, and a centerpiece of the next generation of large cosmological projects. Despite decades of precursor measurements and sustained effort from the community, better data has consistently led to new challenges, frequently requiring us to re-think established solutions to our core measurement and inference problems. In this talk I will discuss some novel approaches taken for the recent Dark Energy Survey (DES) cosmological results, including MetaCalibration, our general solution to the problem of shear calibration. I will offer my own perspective on some of the lessons we can learn from DES for future surveys, and talk briefly about how we might continue to probe the nature of dark energy after the next generation of projects like Euclid, LSST, DESI, and WFIRST.
Spring Quarter, 2017
The Dark Energy Survey: Status and Results
Thursday April 13
Tesla Jeltema
University of California, Santa Cruz
The Dark Energy Survey (DES) is probing the origin of cosmic acceleration and the nature of dark energy with a 5-year, 5-band imaging survey of 5000 square degrees of the southern sky using the Dark Energy Camera on the Blanco 4-meter telescope at the Cerro Tololo Inter-American Observatory. I will present an overview of the survey and the broad range of science results thus far, including cosmological probes, the discovery of new dwarf galaxies, new trans-Neptunian objects, strong lenses, and more. In particular, I will discuss the survey for clusters of galaxies in DES and their follow-up and characterization.
Democratizing Redshifts from Galaxy Clustering
Thursday April 20
Chris Morrison
University of Washington
Current and future wide/deep galaxy surveys rely on redshift estimation from multi-color photometry to produce their science, as complete spectroscopic follow up is impractical for the large numbers of galaxies, given the faint magnitudes these surveys reach. A drawback of these photo-zs is that they require representative spectroscopic samples for calibration/training, which are systematically incomplete at faint magnitudes. Spatial cross-correlations between reference galaxies with known redshifts and samples whose redshifts are unknown is another technique that can be used to estimate the redshift distribution of the unknown sample without the need for a representative training sample. Such cross-correlations techniques have been identified as one of the primary tools for calibrating the redshift distributions for galaxy samples used in cosmological inference. However, clustering-zs can also be used to add value to analyses beyond cosmology. In this talk I will present the-wizz, a clustering redshift code aimed at democratizing clustering-zs in much the same way that photo-zs are widely used an available today. I will present results from using this software on simulations, COSMOS, and the Kilo-Degree Survey (KiDS) and show how clustering-zs can even be used to produce redshifts for single galaxies. Download and try out the software for yourself at
http://github.com/morriscb/the-wizz
Small-scale Intensity Mapping: Extended Halos as a Probe of the Faintest Galaxies and Reionization Physics
Thursday April 27
Lluis Mas-Ribas
University of Oslo
A fundamental question concerning the epoch of cosmic reionization (EoR) is the amount of ionizing photons contributed by primeval galaxies, which is at present dominated by two major unknowns, namely: (i) the contribution of galaxies to reionization depends significantly on the ability of their ionizing radiation to escape the galaxy and its circumgalactic medium (CGM) and ionize the more distant intergalactic medium (IGM). However,the escape fraction of ionizing photons is impossible to measure directly at z > 4. (ii) The presence of a large population of faint (currently unobservable) galaxies which might contribute significantly to the total ionizing photon budget is unclear. I will present and discuss future observations of diffuse Ha and continuum emission around star-forming galaxies with JWST as a new method two address the two above problems. I will demonstrate how these observations can also constrain star formation in the halo of star-forming galaxies when applied to lower redshift, and how the comparison between the Lya, Ha and continuum surface brightness profiles in this case will disentangle the possible mechanisms that give rise to the presence of Lya halos nearly ubiquitously observed around galaxies at z ~2-5. Time-permitting, I will present a distinct approach we are developing to assess the presence of faint (undetectable) galaxies in the IGM, via the cross correlation between the Lya forest and metal absorbers in quasar spectra.
Kinematics of COSMOS Star-forming Galaxies over the last Eight Billion Years
Thursday May 4
Debora Pelliccia
University of California, Davis
Galaxy internal kinematics is one of the most promising tool to study the physical processes that govern the galaxy formation, since it traces the luminous and dark matter distributions and their evolution with time. I will present the new spectroscopic survey HR-COSMOS, with the multi-slit spectrograph ESO-VLT/VIMOS, aimed to obtain the first statistical and representative sample to study the kinematics of star-forming galaxies in the treasury HST/ACS COSMOS field at redshift 0 < z < 1.2. I will present the kinematic analysis performed for two sub-samples at z~0.3 and z~0.9, and the results on constraining the stellar-mass Tully-Fisher relation along with its dependence on cosmic time and environment. I will, moreover, discuss the comparison between the derived dynamical masses and the stellar masses as function of time and galaxy stellar mass. I will conclude with my ongoing work on applying the kinematic analysis to the ORELSE survey.
The Self-Interacting Dark Matter Paradigm: Motivations and Tests
Thursday May 18
Manoj Kaplinghat
University of California, Irvine
I will describe how a simple model where dark matter has large elastic self-interactions can explain the observed diversity of all galactic rotation curves. I will summarize the constraints imposed on model building by observations of clusters of galaxies and end with an outline of tests of this paradigm.
Constraining the Physics of Satellite Quenching
Thursday May 25
Michael Cooper
University of California, Irvine
Despite remarkable success at modeling the evolution of massive galaxies over cosmic time, modern hydrodynamic and semi-analytic models of galaxy formation fail to reproduce the properties of low-mass galaxies. This shortcoming in our theoretical picture is largely driven by an inability to understand the physical mechanisms by which star formation is suppressed (or "quenched") in satellite galaxies. In an effort to address this shortcoming, I will present recent work to measure the efficiency of satellite quenching over more than 6 orders of magnitude in satellite stellar mass at z ~ 0. In particular, our work utilizes observations of galaxy groups identified in the Sloan Digital Sky Survey as well as detailed studies of dwarfs in the Local Volume to constrain the timescale upon which satellite quenching occurs following infall (and thus the physical mechanisms at play). By bringing together multiwavelength data across a broad range in satellite and host mass, our analysis has established a coherent physical picture of satellite quenching that addresses the most glaring deficiencies of current galaxy formation models.
Structures and Masses of Distant Star-Forming Galaxies
Thursday June 1
Sedona Price
University of California, Berkeley
Recent photometric and spectroscopic surveys have paved the way for detailed studies of galaxy evolution from when galaxies were most rapidly forming stars (z~2) to the current epoch. The combination of deep multi-band photometry and spectra has extended our understanding of the structure and masses of early star-forming galaxies. In particular, spectroscopic surveys provide key insights into galaxy masses and structures through their internal kinematics. In this talk, I will present observations of the internal kinematics, and masses of star-forming galaxies at z~1.5-2.3, and how these properties change over time. I will also discuss how mock observations of cosmological simulations let us characterize how accurately we can recover the intrinsic structures, masses, and kinematic properties of distant galaxies from observational data.
The Stellar Halos of Galaxies
Thursday June 8
Raja GuhaThakurta
University of California, Santa Cruz
I will present results from a few ongoing surveys of the structure/substructure, dynamics, and chemical abundance of the stellar halos and disk-halo interfaces of galaxies. The surveys include: (1) the HALO7D survey of the outer halo of the Milky Way, which combines HST based proper motions with Keck/DEIMOS radial velocities to obtain 3D stellar kinematics; (2) the HST based PHAT survey and Keck/DEIMOS based SPLASH survey of M31's halo and disk; (3) the Magellan/MegaCam and Keck/DEIMOS based PISCeS survey of NGC 253, M81, and Centaurus A in nearby galaxy groups; and (4) the CHFT/MegaCam and Keck/DEIMOS based NGVS project, with a specific focus on dwarf early type galaxies and the remote outskirts of M87.
Winter Quarter, 2017
Free-floating Evaporating Gaseous Globules (frEGGS)
Thursday January 19
Raghvendra Sahai
NASA JPL
Understanding the early origins and formation of stars and solar systems like our own, and how the evolutionary details of the star formation process depend on the local environment, is a major enterprise in astrophysics. Massive stars have a strong feedback effect on their environment and can alter the likelihood for the formation of stars in nearby clouds and limit the accretion process of nearby protostars. The formation of the Sun in the pre-solar dense cloud core was likely affected by the debris, and possibly the dynamical impact, of a nearby supernova.
We have recently discovered a new class of stellar nurseries embedded within the large HII bubbles of nearby massive star formation regions (dubbed free-floating Evaporating Gaseous Globules or frEGGs), which are possible analogs of the pre-solar cloud core. Because of their relative isolation from surrounding molecular clouds, frEGGs are the best astrophysical laboratories for robust, quantitative testing of cloud collapse models. In this talk, we describe our discovery survey of frEGGs using Spitzer data, and ongoing multiwavelength observational efforts to study their properties.
H0LiCOW: H0 Lenses in COSMOGRAIL's Wellspring
Thursday January 26
Edi Rusu
University of California, Davis
Gravitationally lensed quasars with measured time delays between the multiple images are a powerful probe of cosmology. In particular, the time-delay distances from such systems are primarily sensitive to the Hubble constant H0, and completely independent of the local distance ladder measurements. H0LiCOW is a program aimed at measuring H0 from five such systems with high quality data such as: deep HST imaging as well as spectroscopy for the lens mass modeling, wide-field imaging and spectroscopy to characterize the lens environment, as well as time delays inferred from about a decade of monitoring. The analysis is currently complete for 3/5 systems, resulting in a 3.8% precision on H_0 in a flat Lambda-CDM cosmology. I will present the recent series of papers detailing the H0LiCOW technique, as well as its power to break degeneracies when compared to other cosmological probes, in more general cosmological models.
The BlackGEM synoptic survey project
Thursday February 2
Paul Groot
Radbound University
The BlackGEM array will consists of, initially, three, wide-field 65cm telescopes, each with a 2.7 square degree field-of-view at 0.56"/pix. Installation will be at ESO La Silla in mid-2018. The prototype system MeerLICHT will be installed at SAAO Sutherland (ZA) in spring 2017. Sensitivity of BlackGEM will be g=23 at S/N=5 in five minutes in dark conditions. The telescope design has been optimized for image quality to take advantage of the excellent site. The primary objective of the BlackGEM project is to detect optical counterparts to gravitational wave events. To achieve this the project will also perform: a) a Southern All Sky Survey (in the u,g,r,i,z and broad-band q filters) down to 23rd mag over 30 000 square degrees, b) a Fast Synoptic Survey to characterize fast variability (minutes - days) down to 23rd magnitude on a 1-minute cadence in multiple filters over hundreds of square degrees, c) a Twilight program to monitor bright galaxies out to 30 Mpc on a daily basis. As part of the All Sky Survey a regular bi-weekly scan of the available sky (10000 sqd) will be performed in the broad-band (420-720) q-band filter.
BlackGEM will be a "Southern PTF" or an "LSST-lite", taking full advantage of its Southern location and the excellent conditions at the La Silla site. BlackGEM is developed by a consortium consisting of NOVA, Radboud University and KU Leuven. The consortium is open for new partners and/or collaborations.
Dwarf Galaxy Formation in a Universe with Self-Interacting Dark-Matter
Thursday February 23
Peter Creasey
University of California, Riverside
The Lambda Cold Dark Matter theory has condensed as the central paradigm of cosmology, providing an evolutionary description that is tractable to numerical simulation. The self-similarity of the dark matter halos that emerge from this - in terms of their (i) mass function, (ii) satellite mass function and (iii) inner density slopes - appear difficult to simultaneously reconcile with low mass galaxies, even with the invocation of baryonic effects. One mechanism that can alleviate the tension between these and observed dwarfs is the inclusion of self-interaction channels for cold dark matter.
The redshift evolution of strong emission line ratios reflects a link between N/O ratio and galaxy stellar mass
Thursday February 16
Dan Masters
Caltech
The offset of high redshift star-forming galaxies in the [OIII]/H-beta vs. [NII]/H-alpha BPT diagnostic diagram in comparison with the local star-forming galaxy sequence is now well established. The physical origin of the shift is the subject of some debate, with potentially important implications for metallicity estimation at all redshifts. I will present results from an investigation of the BPT shift using a sample of roughly 100,000 star-forming galaxies from SDSS DR12. This sample (which includes numerous high-redshift "analogs") lets us determine how galaxy physical properties - in particular, star formation rate density, ionization parameter, N/O ratio, and stellar mass - drive position in key emission line diagnostic diagrams. I will present evidence that a relation between the nitrogen-to-oxygen (N/O) ratio and galaxy stellar mass underlies the observed BPT offset, and is more fundamental than the well-studied relation between N/O and O/H. The relation between N/O ratio and stellar mass induces a mass-dependence in the BPT diagram, such that the BPT shift observed in high redshift galaxies reflects the evolution of the mass-metallicity (MZ) relation. I will discuss implications of this result for metallicity measurements based on strong lines at high redshift, as well as for the proposed fundamental metallicity relation (FMR) between metallicity, star - formation rate, and stellar mass.
An Early Universe Cosmologist Explores the Implications of Variable Stars for the Current Rate of Cosmic Expansion
Thursday February 23
Brent Follin
University of California, Davis
Local measurements of the rate of cosmic expansion today from Cepheid variable stars (Riess et. al. 2016) are in ~3 sigma tension with Cosmic Microwave Background-derived inferences of the same quantity under the standard cosmological concordance model. This tension, if unexplained by systematic effects in either dataset, is evidence for new physics. In this talk, I will discuss my attempts to make sense of the variable star analysis and its assumptions, particularly in its inference of Cepheid brightness. In this talk, framed by a Jupyter Notebook available in advance by email request, I will highlight the toolbox I used for data exploration, which may be of general interest to students interested in learning how to approach academic research with an eye to a future career in industrial data science or data analysis.
Ten Billion Years of Galaxy Alignments in Clusters
Thursday March 2
Michael West
Lowell Observatory
A galaxy's orientation is one of its most basic observable properties. Because the universe is homogeneous and isotropic on large scales, astronomers long assumed that galaxies should be randomly oriented in space. Instead, the most massive galaxies today show a marked tendency to share the same orientation as the surrounding matter distribution on larger scales, a remarkable coherence of structures over many millions of light years. A better understanding of the origin of these alignments may yield insights into the processes that have shaped the most massive galaxies over the history of the universe. Using Hubble Space Telescope observations of 38 distant galaxy clusters, we have shown for the first time that similar alignments are seen at much earlier epochs when the universe was only one-third its current age. These results suggest that the brightest galaxies in clusters are the product of a special formation history, one influenced by development of the cosmic web over billions of years.
The Intergalactic Medium Near Reionization
Thursday March 9
George Becker
University of California, Riverside
When and how the intergalactic medium (IGM) became reionized carries fundamental implications for the formation of the first galaxies. Several lines of evidence now suggest that hydrogen reionization ended just before z=6. Though not yet conclusive, part of the argument relates to rapid changes and surprisingly large-scale fluctuations in the properties of the z<6 IGM. I will present what we know about the evolution of the IGM up to z=7, and discuss how this evolution may (or may not) be driven by late reionization. I will also describe new experiments now underway to probe the physics of the IGM and the connection between galaxies and their large-scale environments near this critical epoch.
Gas Flows: from Black Holes to Galaxies
Thursday March 16
Vivan U
University of California, Riverside/Irvine
The tight correlations between black hole mass and the bulge properties of its host galaxy suggest that black holes and their hosts coevolve. However, the drastically different size and mass scales of these two structures make a physical explanation of the correlation challenging. Gas plays a prominent role in galaxy evolution by fueling supermassive black holes and star formation; feedback processes quench activity by heating or removing the gas. Tracing nuclear gas kinematics at small scales presents the most direct way to examine the feeding and feedback associated with massive black holes, particularly in the luminous regime where mass accretion is happening most rapidly. In this talk, I will present our ongoing efforts to explore the broad line region structure and dynamics in luminous Seyfert galaxies using reverberation mapping in a new campaign of the Lick AGN Monitoring Project. I will also discuss results from the Keck OSIRIS AO LIRGs Analysis (KOALA) Survey that highlight the properties of molecular outflows driven by AGN and starbursts at the heart of nearby luminous infrared galaxies. I will demonstrate the power of near-infrared diagnostics of shocks associated with nuclear winds that will become indispensable for understanding the interstellar medium as we enter an exciting era of astronomy with the imminence of JWST, 30-meter class telescopes, and beyond.
Constraining Cosmic Reionization with Hubble, James Webb, and WFIRST
Thursday March 23
Brant Robertson
University of California, Santa Cruz
Understanding cosmic reionization requires the identification and characterization of early sources of hydrogen-ionizing photons. Through a series of intense observational campaigns with Wide Field Camera 3 aboard Hubble Space Telescope we have now systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicate reionization was underway. High-redshift observations with HST including UDF12, CANDELS, and the Frontier Fields provide the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize results from these HST campaigns and the most recent constraints from Planck CMB observations to infer redshift-dependent ultraviolet luminosity densities, reionization histories, and the electron scattering optical depth evolution consistent with the available data. We preview how JWST, scheduled to launch in 2018, and eventually WFIRST will provide a new window into the reionization epoch and teach us about the physics of galaxy formation in the early universe.
Fall Quarter, 2016
The Role of Dwarf Galaxies in Cosmic Reionization
Friday October 7
Aparna Venkatesan
University of San Fransisco
Dwarf galaxies are predicted to dominate the universe by number at early times, with many having large star formation rates per unit mass. Measurements of the escape fraction of ionizing radiation, f_esc, from dwarf galaxies are an important input to cosmological simulations but are largely unconstrained by observations. I will present recent theoretical calculations of f_esc in low-mass galaxies, and discuss the important role of factors such as early X-rays and the correlations between the escape fractions in Ly-alpha versus Ly-continuum radiation from early galaxies. These results imply that UV-faint galaxies contribute more to the ionizing background than implied by the faint-end slope of the UV luminosity function, and have a potentially strong impact on cosmic reionization. Gas-rich low-mass systems in the local universe that have survived reionization are more accessible observationally, and provide an important cross-check with models of first-light ionizing sources. Using ongoing 21 cm studies from the Arecibo ALFALFA survey, as well as HST and archival GALEX data, I will share new limits on f_esc of low-mass star-forming galaxies in the local volume, providing much-needed observational constraints on their role in reionization. Last, I will discuss the tantalizing similarities in element abundance patterns between local ultra-faint dwarf spheroidal galaxies and the extremely metal-poor stars in the Galactic halo.
Hidden Sector Hydrogen as Dark Matter: Predictions for Small-scale Structure
Thursday October 13
Anna Kwa
University of California, Irvine
I will discuss the atomic physics and the astrophysical implications of a model in which the dark matter is the analog of hydrogen in a secluded sector. The self interactions between dark matter particles include both elastic scatterings as well as inelastic processes due to a hyperfine transition. The self-interaction cross sections are computed by numerically solving the coupled Schrodinger equations for this system. The velocity-dependence of the self-interaction cross sections produces the low dark matter density cores seen in spiral galaxies while maintaining consistency with constraints from observations of galaxy clusters. Significant cooling losses may occur due to inelastic excitations to the hyperfine state and subsequent decays (up to about 10% of the collisional heating rate) in this region of parameter space, with implications for the evolution of low mass halos and early growth of black holes. Finally, the minimum halo mass is in the range of 10^3 to 10^7 solar masses for viable regions of parameter space, which is significantly larger than the typical predictions for weakly-interacting dark matter models.
Reverberation mapping as a probe of black hole masses and AGN structure: new results from intensive monitoring campaigns
Thursday October 20
Aaron Barth
University of California, Irvine
The method of reverberation mapping uses the time delay between continuum and emission-line variations in active galactic nuclei to probe the structure of the broad-line region and to derive estimates of black hole masses. Reverberation mapping results provide a fundamental low-redshift calibration for the methods used to trace the cosmological evolution of supermassive black holes. I will present recent developments in reverberation mapping based on observations from the Lick AGN Monitoring Project and from the AGN-STORM project, which carried out a 6-month intensive program of monitoring the nearby Seyfert 1 galaxy NGC 5548 in 2014.
A First Characterization of the Surprising Properties of Tidal Disruption Events
Thursday October 27
Iair Arcavi
University of California, Santa Barbara
The search for the tidal disruption of stars by supermassive black holes is now yielding exciting results. Recently, we tied several of these tidal disruption events (TDEs) together into a coherent class of outbursts. This picture immediately offers two new insights. First, TDE emission properties are not as expected - our set of objects all peak in the near UV rather than the x-ray, show lower than expected velocities and span a continuum of spectral classes from H-rich to H-poor. These observations sparked a flurry of theoretical work to try and understand the emission mechanisms. The second insight relates to the host galaxies - TDEs show a strong (200x!) preference for rare post-starburst galaxies. The reason for this is still unknown but it has launched many investigations into the special history and dynamics of these galaxies. We are collecting more and more observations of TDEs as they are discovered by wide field transient surveys and by our own first-ever specialized survey for TDEs. Understanding TDE emission properties and their peculiar host galaxy preference has far reaching implications for studying quiescent massive black holes, accretion physics and galaxy dynamics.
The Hubble Constant from Time Delays of Gravitationally Lensed Images
Thursday November 3
Curtis McCully
Las Cumbres Observatory
Gravitational lensing has been instrumental in probing the dark matter and the Hubble constant. In rare cases, close alignment between foreground galaxies and background sources can yield multiple images of the background source. These strong gravitational lens systems have been used to map galaxy mass distributions and constrain the Hubble Constant. As data and models improve, people look to achieve percent-level precision on the Hubble constant with strong lensing. To reach that goal on the theoretical side, we need to understand and control systematic uncertainties in lens models. One key systematic arises because matter near a gravitational lens galaxy or projected along the line of sight can affect strong lensing observables by more than contemporary measurement errors. I will present our new framework for multi-plane lensing (which now self-consistently includes effects due to underdense regions, e.g. voids), and show that we can recover lens model parameters without bias and to a precision limited only by the lens profile degeneracy and measurement noise. On the observational side, Las Cumbres Observatory represents a new technology to measure short time delays of strongly lensed systems as we can continuously monitor the lensed sources for 24 hours a day. I will present the early results from three extensive continuous-monitoring campaigns on the well-studied lens HE 0435-1223. I will conclude by discussing the exciting prospects of using recently discovered strongly lensed supernovae to constrain the Hubble constant.
The Zwicky Transient Facility
Thursday November 10
Eric Bellm
Caltech
The Zwicky Transient Facility (ZTF) is a next-generation optical time-domain survey that will survey more than an order of magnitude faster than its predecessor, the Palomar Transient Factory. First light is expected in 2017. I will provide an overview of the survey design, science goals, and technical progress to date. Thanks to support from the NSF MSIP program, ZTF will include several public components. I will detail our plans for the public surveys and the associated transient alerts and data releases.
Insights into Galaxy Assembly from Star Formation in Luminous Quasars at z>1
Thursday November 17
Duncan Farrah
Virginia Tech
There exist multiple lines of evidence for a deep connection between star formation and AGN activity, at all redshifts. This connection has a profound impact on the mass assembly history of galaxies. The nature of the connection however remains controversial, due to, for example, strong evolution effects in the AGN duty cycle and the obscuring effect of dust. The luminous type 1 quasars are an insightful population to study in this context; accretion rates can be estimated from the UV/optical continuum shape, black hole masses can be estimated from rest-frame UV line properties, and star formation rates can be cleanly estimated from far-infrared imaging from Herschel. Our group has been studying the relationships between star formation, black hole masses and accretion rates in luminous type 1 quasars over 0.5<z<3, using data from Herschel and the SDSS. In this talk I will present some of our latest results, and discuss some implications from them for galaxy assembly at z>1.