Astrofest 2012

Columbia University Department of Astronomy and Astrophysics

September 21, 2012 9:00am - 5:00pm

Breakfast: 9:00-9:30 SMBH mass density by several orders of magnitude. In order to avoid this severe overproduction, BH seed Session 1: 9:30-10:20 formation and growth must become significantly less efficient in less massive protogalaxies, while proceed- ing uninterrupted in the most massive galaxies that Destry Saul formed first. Using Monte-Carlo realizations of the Graduate Student, Columbia University merger and growth history of BHs, we show that X- (Dusty) Pigs in Space! rays from the earliest accreting BHs can provide such a feedback mechanism. In this picture of “cosmic cli- As we followed our brave porcine friends on their in- mate change”, the first miniquasars - among them the tergalactic adventures we discovered that not only do ancestors of the z>6 quasar SMBHs - globally warm they number in the thousands, but that many are in the IGM and suppress the formation and growth of possession of a measurable amount of dust. I will subsequent generations of SMBHs. summarize the current detections with a plot, an image, and a muppets clip. Josh Schroeder Zoltan Haiman Graduate Student, Columbia Astronomy Professor, Columbia Astronomy Millisecond Pulsar Companions I Have Known and Loved Cosmic Climate Change Caused by the Growth of the First Supermassive Black Holes Since the Fermi Space Telescope began observing the Observations of high-redshift quasars at z>6 imply gamma-ray sky, a host of new sources of gamma rays that supermassive black holes (SMBHs) with masses have been discovered including a significant popula- over a billion solar masses were in place less than tion of millisecond pulsars. Some of these objects 1 Gyr after the Big Bang. If these SMBHs assem- have companions that have been observed with op- bled from “seed” BHs left behind by the first stars, tical telescopes. I will show you what these objects then they must have accreted gas at close to the Ed- look like and what they can tell us about millisecond dington limit during a large fraction (>50%) of the pulsars and neutron stars in general. time. A generic problem with this scenario, however, is that the mass density in million-solar-mass Lauren Corlies SMBHs at z=6 already exceeds the locally observed Graduate Student, Columbia Astronomy

1 Better Estimates of Star Formations Rates for diﬀuse stellar cloud in the direction of Triangulum- GASS Galaxies Andromeda.

Star formation rates (SFR) are one of the most fun- David Hendel damental properties of galaxies yet also hard to mea- Graduate Student, Columbia Astronomy sure. In this talk, I’ll briefly explain the benefits of the SED-fitting method of measuring SFRs and why Interpreting Maps of Stellar Clouds this is especially true for the GASS sample of galax- Spectroscopic results from observations of the ies. Triangulum-Andromeda stellar cloud revealed several surprises - the mean radial velocity is sharply peaked Gunes Senturk and nonzero and the feature lacks the strong velocity Graduate Student, Columbia Physics gradient expected from earlier work. Using n-body Gamma-Ray Observational Properties of simulations we model a structure similar to TriAnd TeV-selected Blazars and find that the observed velocity distribution is indeed consistent with being a stellar cloud and we The synergy between the Fermi-LAT and ground- demonstrate how this information can be used to de- based Cherenkov telescope arrays gives us the op- duce its full space motion. portunity for the first time to characterize the high energy emission from blazars over 5 decades in en- Or Graur ergy, from 100 MeV to 10 TeV. In this study, we per- Graduate Student, Tel Aviv University form a Fermi-LAT spectral analysis for TeV- detected Discovering Supernovae in Galaxy Spectra blazars, combine it with archival TeV data and examine the observational properties in the ?-ray band of Using a method to discover and classify supernovae our sample of TeV-selected blazars. (SNe) in galaxy spectra, we find 90 Type Ia SNe (SNe Ia) and 10 Type IIP SNe among the 700,000 galaxy Allyson Sheffield spectra in the Sloan Digital Sky Survey Data Re- Post-doc, Columbia Astronomy lease 7. We use the SN Ia sample to: (1) measure Mapping Stellar Clouds SN Ia rates per unit stellar mass; (2) confirm, at the median redshift of the sample, z = 0.1, the inverse The advent of large-scale photometric surveys, such dependence on galaxy mass of the SN Ia rate per as 2MASS and SDSS, has brought with it a spate of unit mass, previously reported by Li et al. (2011b) discoveries of Galactic substructures. Stellar streams for a local sample; (3) confirm, following Kistler et and diffuse clouds are of particular interest to stud- al. (2011), that this relation can be explained by the ies of Galactic evolution, as these features span huge combination of galaxy “downsizing” and a power-law swathes of sky. Much work over the past decade has delay-time distribution with an index of -1, inherent been devoted to tracing the chemodynamics of stel- to the double-degenerate progenitor scenario; (4) use lar streams but equally detailed studies of individ- the method of Maoz et al. (2011) to directly recover ual stellar clouds are just beginning. I will report the delay-time distribution; and (5) measure the most the first results from spectroscopic work targeting a precise volumetric SN Ia rate at z = 0.1.

2 Adric Riedel patchy clouds. Atmosphere models have yet to com- Post-doc, AMNH prehensively and consistently reproduce the photometric and spectral features of brown dwarfs with a The Solar Neighborhood’s Nursery physically realistic dust and cloud model. The goal In the last 15 years, a variety of associations and mov- of this project is to combine observations and theory ing groups of young (less than 200 Myr old) stars to make inroads on the process of disentangling the have been discovered in the Solar Neighborhood - observed effects of the clouds. We are using Mie the- closer than the nearest star forming regions. Until ory to find the combination of dust properties that recently, nearly all such young stars have been found best reproduce the effects seen in the spectra of red in the HIPPARCOS and TYCHO-2 astrometric cata- L dwarfs. In particular, we are trying to constrain logs. Those catalogs have magnitude restrictions that the grain size distribution and the grain composition exclude nearly all low-mass stars and brown dwarfs. in red L dwarf clouds. We found that red L dwarfs I will discuss the methods that can be used to locate may have silicate clouds with mean grain size of 0.2 and identify young low-mass stars and brown dwarfs, - 0.3 micron, which is smaller than the previously as- and the results of a new search currently in prepara- sumed value of 10 microns. Our result leads to the tion hypothesis that red L dwarfs have an additional dust haze composed of small particles above the regular Session 2: 10:35-11:25 clouds. Lia Corrales Graduate Student, Columbia University Dan D’Orazio Graduate Student, Columbia Astronomy Interstellar Chemistry with X-rays Black Hole Batteries Light up LIGO Sources X-ray spectroscopy can reveal the presence and abundance of heavy elements in space. Many of these – The merger of a black hole - neutron star binary will including magnesium, silicon, iron, and oxygen – are be detectable in gravitational radiation by Advanced widely suspected to be the main constituents of inter- LIGO. I will show you how these systems could gen- stellar dust. I will describe experiments that directly erate a bright electromagnetic signature just before probe the composition of dust grains along the line merger, without tidally disrupting the NS. of sight to luminous X-ray sources. Jacqueline van Gorkom Kay Hiranaka Professor, Columbia Astronomy Graduate Student, CUNY Graduate Center An HI Deep Field Red L Dwarfs Explained by Dust Haze of Small Particles Why, when and where?

Warm, young L dwarfs have think clouds that aﬀect Ximena Fernández emergent spectra. It is thought that redder spectral Graduate Student, Columbia Astronomy energy distribution might indicate thick clouds and bluer spectral energy distribution might be thin or CHILES: COSMOS HI Large Extragalactic Survey

3 We present preliminary results of an HI Deep Field M37’s rich membership, good match to Chandra’s done with the VLA. We observe part of the COSMOS field-of-view, and large number of measured periods field in one pointing from z=0 out to z=0.18. Our tar- ( 700) make it ideal for examining the evolution of get has over 200 galaxies with known spectroscopic coronal X-ray emission. Our X-ray and optical data redshift within the primary beam of the VLA, pro- will provide independent determinations of LX as a viding us with a rich multiwavelength dataset to com- function of rotation and rotation as a function of age; plement our HI detections. I will briefly talk about map out M37’s X-ray luminosity function, with stack- the survey and discuss some of our detections. We de- ing of optically similar sources extending our flux tect galaxies in different redshifts and environments, limits by 10x; test whether magnetic effects pro- from void galaxies at low z to interacting systems at duce anomalous optical colors/luminosities for high z 0.12 that reside in a wall. This study serves as a LX sources; and characterize M37’s interacting bina- pilot for a full survey that will observe out to z=0.5 ries. once the VLA upgrade is completed. Emily Bowsher Miao Li Research Assistant, Columbia Astronomy Graduate Student, Columbia Astronomy The Billion Year Mystery: Rotation and Effect of Streaming Velocities on the Growth of Membership in NGC 752 Supermassive Black Holes at High Redshift Rotation periods are scare for stars older than the 9 Many models that grow 10 M supermassive black Hyades ( 0.6 Gyr), complicating the calibration of an holes (SMBHs) at z>6 from 1st star remnants rely age-rotation relation that can provide reliable age es- 5 on seeds forming in very low mass halos (<10 M ) timates for field stars. I will discuss our work con- at very high redshift (z>30). This is the regime straining the age-rotation relation for the 1-2 Gyr where the recently discovered streaming motion ef- open cluster NGC 752. fect has the largest suppression of gas infall and cooling. We model the BH growth using Monte Carlo Michael Allison merger trees, to investigate how this effect impacts Adjunct Professor, Columbia Astronomy the assembly of 109 M SMBHs. Contemporary Reflections of Newcomb’s “Fictitious Marcel Agüeros Mean Sun” in the NRO, UTC, and MSL Curiosity Clock Time on the Bradbury Landing Professor, Columbia Astronomy

Deep X-ray Imaging of M37, A Better Hyades The fingerprint of Newcomb’s largely forgotten (1895) concept of the “Right Ascension of the Fictitious Recent studies suggest that the standard picture of Mean Sun” can still be seen in the so-called “non- stellar X-ray luminosity (LX) decaying from 10 Myr rotating origin” (NRO) and in the current (17 signifi- to 5 Gyr as a single power-law is overly simplistic. cant figure!) definition of Universal Time in terms M37, a Hyades analog, has been carefully surveyed of the Earth Rotation Angle. Some years ago, a in the optical, and we have obtained complementary Columbia undergrad helped me work up an accu- deep (450 ksec) Chandra data for this open cluster. rate formulation of the Fictitious Mean Sun at Mars

4 (where there is as yet no ICRF) by an elaborate fall we begin our 99-night survey using the Palomar ephemeris calculation (Allison and McEwen, 2000; 200-inch Telescope. The project is the first of its kind Planet. Space Sci.) which now defines Mean Solar and is leading the way for new instruments coming Time for the Curiosity rover. I am currently rework- on-line in the next couple of years. We have a great ing this mathematical expression and related angles head start and are actively seeking a student. The by an entirely different method, revised to match new timing is perfect for a student to learn complex opti- radio tracking measurements of the planet’s spin pole cal/IR instrumentation and conduct ground-breaking precession. science.

Session 3: 11:40-12:30 Doug Brenner Research Scientist, AMNH

Josh Peek Dark Holes Are Nice but Software Still Rides to the Post-doc, Columbia University Rescue

Why HVCs Don’t Matter (and Why They Do) All modern astronomical instruments need some soft- 50 years ago high velocity clouds of neutral gas were ware if only to remove focal plane non-uniformities discovered to be swirling around the galaxy, and they and imperfections. The most complicated instru- have been causing us headaches ever since. I will dis- ments like Kepler and P1640 are useless without soft- pel some persistent myths about the importance of ware for data reduction; In the case of P1640 - an HVCs in the context of our growing, evolving Milky imaging spectrograph (see Ben’s presentation) - soft- Way, and tell a massive secret they’ve been keeping ware must go beyond making the focal plane image from us since their discovery. usable. It has to dig into the resultant speckled image for hidden companions. We are bringing princi- Ryan Joung ple component analysis to bear on the problem. I will Post-doc, Columbia Astronomy discuss the application of PCA to speckle reduction Gas Inﬂows in Galactic Halos in imaging spectrograph images.

I will report on some of the interesting ﬁndings that Mary Putman we made in the past year regarding the shape, ther- Professor, Columbia Astronomy mal and kinematic properties of gas inﬂows in galactic Is the Milky Way Weird? halos, based on high-resolution cosmological simulations. The Milky Way does not show large amounts of baryons in warm and warm-hot gas in its halo com- Ben Oppenheimer pared to what has been found for other galaxies. Is it Associated Curator and Professor, AMNH weird, or is the gas hiding due to our internal view? Project 1640: Come Find Some Planets! Gray Kanarek Project 1640, the world’s most advanced set of instru- Graduate Student, Columbia Astronomy mentation designed to image and take spectra of planets orbiting nearby stars, is fully operational, and this An NIR Photometric Search for Galactic WR Stars

5 A massive NIR survey for WR stars in the Galactic trade-oﬀ between a large survey footprint and irregu- plane has already contributed 25% of the currently lar sampling when searching for microlensing events, known Milky Way WR stars. Continued use of this and to examine the feasibility of detecting such events tremendous resource has led to new photometric se- in these data. This work will help inform predictions lection techniques using the survey’s NB photome- about the expected microlensing event rates in future try along with 2MASS and WISE broadband magni- wide-ﬁeld time-domain surveys such as LSST. tudes. Lam Hui Gurtina Besla Professor, Columbia Physics Post-doc, Columbia Astronomy Pulsars as Resonance Detectors for Gravitational Interactions between Dwarf Galaxies Waves

Dwarf galaxies are traditionally thought to evolve via Lunch and Poster Session: interactions with more massive hosts, like our Milky 12:30-2:00 Way. However, isolated starbursting dwarfs show ob- vious signs of tidal interactions and are thought to be The poster titles and participants are listed in the the product of dwarf mergers. Such observations lead back of this program. us to conclude that interactions between dwarf galaxies may play an important role in understanding the Session 4: 2:00-2:50 modes of star formation and the baryon cycle in low mass, metal poor galaxies. However, to date, the fre- Matt Turk quency and properties of such interactions have never Post-doc, Columbia Astronomy been quantified... I’ll describe ongoing work to tackle Chemistry, Cooling, and Astrophysical Simulations this problem. Large, multi-physics astrophysical simulations of- Adrian Price-Whelan ten require following the chemical state of multiple Graduate Student, Columbia Astronomy species of atoms and molecules. For instance, in pri- Identifying Microlensing Events in Large, mordial gas, typically up to 12 species are followed: Non-uniformly Sampled Surveys H, H+, He, He+, He++, e-, H2, H2-, H-, D, D+, HD. In addition to these species, the thermal state Many current photometric, time-domain surveys are of the gas must also be evolved self-consistently. For driven by specific goals, such as supernova searches, metal-enriched gas, the situation is far more dire: ion- transiting exoplanet discoveries, or stellar variability ization and molecular states must be followed up to studies, which set the cadence with which individual relatively high atomic number, particularly at low- fields get re-imaged. In the case of the Palomar Tran- metallicities near the so-called “critical density.” I sient Factory (PTF), several such sub-surveys are be- present on a new method and package (“Dengo”) for ing conducted in parallel, leading to an extremely self-consistently constructing chemical networks for non-uniform sampling gradient over the survey foot- use in astrophysical simulations, such that next gen- print. We use the existing PTF data to study the eration calculations can follow to high-precision a

6 ﬂexible number and selection of chemical and cool- Jia Liu ing processes. Graduate Student, Columbia Astronomy

Probing the Center of Neutron Stars with Astro-H Brian Farras SXS Post-doc, Columbia Astronomy

Binary Black Holes and Circumgalactic Disks 40 years after their discovery, the internal structure of neutron stars is still a puzzle. Understanding the Binary black hole mergers in circumbinary gaseous equation of state (EOS) of the matters at the core accretion disks are prime candidates for simultaneous of neutron stars is the key to probing interactions of observations of both gravitational and electromag- matters in extremely dense environments, and two netic waves. We study such systems using our fully key quantities to be measured are the masses and general relativistic magnetohydrodynamics code. We radii of the neutron stars. One way to constrain sketch recent developments in our study, which fo- the mass and radius relation is through measuring cuses on the ﬁnal stages of binary black hole merger the gravitational redshift of absorption lines from the and the dynamical response of the disk, highlighting neutron star surface. I will discuss the possibility accretion onto the black holes during their late inspi- of observing such features during X-ray bursts using ral and merger. the Soft X-ray Spectrometer (SXS) onboard Astro-H, Japan Aerospace Exploration Agency (JAXA)’s next Joo Heon Yoon X-ray telescope scheduled for launch in 2014. Graduate Student, Columbia Astronomy Jenna Lemonias Circumgalactic Medium in Cluster and Filament Graduate Student, Columbia Astronomy Environments The Bivariate HI Mass Function for Massive It is known that galaxies are surrounded by large Galaxies amount of gas. This circumgalactic medium is stud- 10 ied in a cluster and ﬁlament environment with obser- I used a sample of ∼500 massive (M∗ > 10 vations of QSO absorption lines. I will discuss how M ) galaxies with homogeneously measured stellar much gas is around galaxies in a cluster and the re- masses, star formation rates, and HI masses ob- lation of gas to galaxy properties. served as part of the GALEX Arecibo SDSS Sur- vey (GASS) to derive the bivariate HI mass function, Kathryn Johnston φ(MHI ,M∗). I will discuss the methodology, results, Professor, Columbia Astronomy implications and why it is useful.

Spitzer, Gaia, and the Potential of the Milky Way Duane Lee Graduate Student, Columbia Astronomy In this talk I will show how a new sample of Spitzer data can potentially be combined with future Gaia Reconstructing The Accretion History Of Stellar measurements to probe the mass distribution in the Halos Using The Expectation-Maximization outer Galaxy. Algorithm

7 Galactic halos provide a unique record of hierarchi- development activities of the VERITAS/CTA group cal merging that reveals a lot about a galaxy’s evo- at Columbia University and Barnard College. These lution via its accretion history. The record of an activities include studies of very high energy gamma- halo’s recent accretion history can constructed by ob- ray emission from blazars, pulsars, pulsar wind neb- serving and analyzing the spacial substructure in the ulae, unidentiﬁed TeV sources, and indirect detection halo. Unfortunately, this analysis has it’s limits since of dark matter with VERITAS, with a close synergy phase-mixing of these features washes out any infor- with Fermi-LAT, as well as technical contributions to mation concerning the early buildup of the host halo. CTA. However, since stars retain, in large part, a signature of their galactic origin in their stellar chemical abun- Arlin Crotts dances, we can exploit this information to recount the Professor, Columbia Astronomy broad nature of galactic halo accretion from its birth. Recurrent Nova T Pyx: A Flash in the Pain In our study, we apply mixture theory to our simu- Sometimes Illuminates the Pan lated halos using the expectation-maximization algorithm to construct an accretion history from analysis The recurrent nova T Pyxidis exploded in April 2011 of stellar chemical abundance distributions. as part of a sequence of eruptions every few decades over roughly the past century. This time we were able Daniel Nieto to follow the outburst with Hubble Space Telescope Research Scientist, VERITAS/CTAA imaging and spectroscopy, and in the process reveal Very High Energy Gamma-ray Astrophysics with a number of previously unknown phenomena associ- VERITAS/CTA ated with the central source, the surrounding ejecta from previous outbursts, and details of the current Abstract TextColumbia University and Barnard Col- event. lege participate in the present and future of the very high energy astrophysics thanks to their contribution to the Very Energetic Radiation Imaging Telescope Session 5: 3:05-3:55 Array System (VERITAS) and the Cherenkov Tele- scope Array (CTA) observatories respectively. VER- Christine Simpson Graduate Student, Columbia Astronomy ITAS is a recently upgraded array of four imaging at- mospheric Cherenkov telescopes currently operating Feedback and Stellar Metallicity in dSph Galaxies at the Fred Lawrence Whipple Observatory in south- ern Arizona, sensitive to very high energy gamma- I will discuss what we know about the metallicity of rays of energies from 100 GeV to 30 TeV. CTA is stars in dSph galaxies of the Local Group and how an international project for a next-generation instru- this observable is a signature of the eﬀectiveness of ment conceived as an array of few tens of imaging at- supernova feedback in these systems. I will show re- mospheric Cherenkov telescopes, aiming to improve cent metallicity results from my own simulations of on the current generation sensitivity by an order of low-mass dwarf halos and will discuss their implica- magnitude, with an energy coverage from a few tens tions for feedback models as implemented in high- of GeV to 100 TeV. We will describe the research and resolution hydrodynamical simulations.

8 Kerstin Perez non-equilibrium time-evolution of the disk and the Post-doc, Columbia Astrophysics Laboratory orbital decay of the BBH.

General Antiparticle Spectrometer Steven Mohammed The General Antiparticle Spectrometer (GAPS) ex- Post-bac, Columbia Astronomy periment aims to detect low-energy antideuterons Neutral Hydrogen in Nearby Massive Galaxies that result from dark matter interactions in the galactic halo. This signature, which has essentially zero As a part of the GALEX Arecibo SDSS Survey conventional astrophysical background, is predicted (GASS), we assembled a homogenized catalog of by many models of both supersymmetry and extra- physical properties of 504 nearby massive galaxies dimensional theories. I will report on our in-house (redshifts 0.025 < z < 0.05; M? >108) from various fabrication of the Si(Li) tracking detectors for GAPS existing surveys to examine their neutral hydrogen , as well as show some pretty pictures from our suc- (HI) gas content. By comparing our catalog with the cessful launch of the prototype GAPS (pGAPS) bal- GASS scaling relations of atomic gas fraction versus loon experiment, ﬂown from Hokkaido, Japan in June stellar mass and NUV-r color versus surface density, 2012. we hope to gain insight into the transition between blue star-forming gas rich galaxies to red, gas deﬁ- Munier Salem cient galaxies. Graduate Student, Columbia Astronomy

Black Hole Tango Michael Shara Adjunct Professor, AMNH Binary black hole (BBH) mergers release an enor- mous burst of energy as gravitational radiation which The Novae of M87 future devices like LISA hope to detect as standard 60 HST orbits’ of images of the giant elliptical galaxy probes of cosmology. While this black hole tango were obtained almost daily over a 3 month period. 57 is increasingly well understood in a vacuum, basic erupting classical novae were found, yielding the best questions regarding the gas surrounding these holes light curves and luminosity function ever determined have yet to be answered: How much gas is present for novae in any galaxy. The nova rate is at least 3x during the late time inspiral? Will the dynamics of higher than previously determined in other surveys. this gas produce a strong E&M radiation signature? I’ll show our latest results, and suggest a research Can we use this signature to corroborate LISA’s find- project for a first or second-year student. ings? Will the gas alter the BBH dynamics itself? To answer these questions, I have been developing a David Schiminovich simple numerical model to follow the coupled time- Professor, Columbia Astronomy evolution of a BBH and a circumbinary gas accretion disk. The model includes the gravitational torque Imaging the Ionized Circumgalactic Medium exchange between the BBH and the disk, as well as heating, cooling and viscous mechanisms in the disk. I will briefly discuss several instrument projects to This model allows us to follow, simultaneously, the image the ionized circumgalactic and intergalactic

9 medium in the nearby and moderate redshift uni- instability grows when AGN is on and cold ﬁlaments verse, both from space-based and ground-based ob- form mostly along the jet propagation direction, ex- servatories. tending up to 10kpc.

Amanda White Maureen Teyssier Research Scientist, AMNH Graduate Student, Columbia Astronomy

Three-Dimensional Image Analysis of NASA Identifying Local Group Field Galaxies That Have Stardust Tracks Interacted with the Milky Way

The NASA Stardust mission to comet Wild 2 re- We distinguish between Local Group field galaxies turned to Earth in 2006 with cometary material that may have passed through the virial volume of trapped in aerogel. The cometary particles were the Milky Way, and those that have not, via a statis- captured at a relative velocity of 6.1 km/s, creat- tical comparison against populations of dark matter ing three-dimensional tracks containing void space, haloes in the Via Lactea II (VLII) simulation with compressed aerogel, melted aerogel, and fragmented known orbital histories. Analysis of VLII provides cometary material. Each track represents a unique expectations for this escaped population: they con- hypervelocity impact event. The nature of each tribute 13 per cent of the galactic population between track-forming event, including the original state of 300 and 1500 kpc from the Milky Way, and hence the impactor, is recorded in the track morphol- we anticipate that about 7 of the 54 known Local ogy and material distribution. Using a Zeiss LSM Group galaxies in that distance range are likely to 710 laser scanning confocal microscope (LSCM), we be Milky Way escapees. These objects can be of any have obtained non-destructive, high resolution (< 80 mass below that of the Milky Way, and they are ex- nm/pixel), three-dimensional images of these tracks. pected to have positive radial velocities with respect Here, we report significant progress in understanding to the Milky Way. Comparison of the radius-velocity and perfecting LSCM image processing to maximize distributions of VLII populations and measurements recovered information from whole cometary tracks of Local Group galaxies presents a strong likelihood and first steps in using the LSCM spectroscopic ca- that Tucana, Cetus, NGC3109, SextansA, SextansB, pabilities to distinguish between deposited cometary Antlia, NGC6822, Phoenix, LeoT, and NGC185 have material and melted silica aerogel as well as identify passed through the Milky Way. Most of these dwarfs cometary material. have a lower HI mass fraction than the majority of dwarfs lying at similar distances to either the Milky Yuan Li Way or M31. Indeed, several of these galaxies – espe- Graduate Student, Columbia Astronomy cially those with lower masses – contain signatures in Simulating AGN Feedback in Cool Core Clusters their morphology, star formation history and/or gas content indicative of evolution seen in simulations of We perform three-dimensional high-resolution adap- satellite/parent galactic interactions. Our results of- tive mesh refinement simulations of the interaction fer strong support for scenarios in which dwarfs of between AGN jets and the intracluster medium in a different types form a sequence in morphology and cool core galaxy cluster. We find that local thermal gas content, with evolution along the sequence being

10 driven by interaction history. Ricardo Fernández Graduate Student, Columbia Astronomy

Session 6: 4:10-5:00 Shocking Inflows: A Pathway in Forming a Jeno Sokoloski Supermassive Black Hole Research Scientist, Columbia Astronomy The discovery of quasars at redshifts greater than 6 A Swift View of Accretion by the Digital Sky Survey signals the existence of su- per massive black holes (SMBHs) as massive as few In symbiotic binary stars, a white dwarf accretes from 9 times 10 M at an epoch when the Universe was the wind of a red-giant companion star. These stars less than a billion years old. The formation scenario experience a newly recognized mode of mass trans- for these first SMBHs lies in mystery. To answer this fer that lies somewhere between Roche-lobe overflow mystery we have conducted large numerical cosmo- and Bondi-Hoyle capture of the donor star’s wind. logical simulations, investigating the possible massive But since the light from the red giant dominates in black hole seed formation by colliding cold accretion the optical, this accretion has been difficult to ob- flows in the center of the first galaxies. serve. A recent survey of symbiotic stars with the Swift satellite has revealed that in many symbiotics, Morgan May the accretion disk produces moderately hard X-ray Adjunct Professor, Columbia Physics emission as well as rapidly variable UV emission – both of which can be used to investigate the nature of Lensing Peaks, Dark Energy, and LSST accretion through the large, wind-fed accretion disks Abstract TextLensing peaks, local maxima of the in these binaries. Swift data from a second survey shear field, have their origin in single or multiple of symbiotic stars, which is currently under way, are galaxy clusters along the line of sight. Unlike CMB available to a student interested in a first- or second- maps, lensing maps are highly non-gaussian and thus year project on this topic. contain much information beyond the power spec- Maria Charisi trum. We are studying the improvement in LSST Graduate Student, Columbia Astronomy (Large Synoptic Survey Telescope) sensitivity to dark energy when lensing peaks are included in the analy- Relativistic Response of a Circumbinary Disk to sis and the biases induced by baryon rearrangement. SMBH Recoil

When SMBHs merge, they emit gravitational waves. Greg Bryan If the final BH recoils after the merger, Newtonian Professor, Columbia Astronomy and hydrodynamic simulations have shown that a spi- Simple Models of Warm Filamentary Accretion in ral shock wave propagates through the gaseous cir- Galactic Hot Halos cumbinary disk and brightens it. The detection of such an afterglow could provide the EM signature of Numerical simulations show that much of the gas ac- GWs. This study is extended by examining the region cretion on to galactic halos is in the form of filamen- closer to the BH and taking into account relativistic tary flows. For low halo masses, radiative cooling is effects. very efficient and these filaments can directly fall in

11 without shocking. For higher mass halos, a roughly tiple populations with different carbon abundances. spherical shock forms, resulting in a hot gas halo. To understand the origin of the spreads in carbon However, much of the gas accretion is still filamentary abundance, we propose to study other key chemical in these larger halos, and is not fully shock-heated, elements. Such a study will help in understanding resulting in a warm accretion mode. We investigate the first generation of stars that have polluted the the thermal history of these filaments as they form clusters. and pass through the accretion shock using simple analytic models inspired by numerical simulations. Jennifer Weston Graduate Student, Columbia Astronomy Stephanie Fiorenza In Search of “Normal" Novae Graduate Student, CUNY Graduate Student Center As observations of stellar novae improve, new data The Search for the Primordial Population in is putting our past assumptions into question. From Galactic Globular Clusters gaps between observation and theory to the recently Globular clusters are compact, massive, and oldest discovered gamma-ray novae, unexpected discoveries stellar systems of the Galaxy. They were thought to make it difficult to classify what a “normal" novae be homogeneous systems with a single stellar popu- should look like, or if such a thing even exists. lation. However, recent results based on precise pho- tometry from HST suggests the presence of more than Jeff Andrews one stellar population among globular cluster stars. Graduate Student, Columbia Astronomy These stars have a different abundance pattern com- Constraining the IFMR pared to halo stars of similar metallicities. To understand globular cluster formation, in the context of hi- The relation between the zero age main sequence stel- erarchical Galaxy formation models, it is necessary to lar mass and the mass of its white dwarf progeny is understand the origin of their abundance pattern. We dubbed the initial to final mass relation (IFMR). De- have used the SDSS spectra from Data Release 8 to spite its importance to stellar astrophysics, the IFMR estimate the carbon abundances for 5 globular clus- remains poorly understood. In this talk, I will dis- ters. We find large spreads in the carbon abundances cuss a new technique that could potentially provide throughout the CMDs of the clusters, indicating mul- improved constraints.