Wine and Cheese Fall 2014

This page records the schedule, titles and abstracts of the JHU/STScI CAS Astrophysics Wine & Cheese Series in Fall 2014.

Fall 2014

Date	Speaker	Title
September 8	K.G. Lee (MPIA)	The First z>2 Large-Scale Structure Map with Lyman-Alpha Forest Tomography from LBGs
	Peter Behroozi (STScI)	Close Pairs: Observational Probes for how Halo Accretion Impacts Galaxy Star Formation
September 15	Dheeraj Pasham (Maryland)	A 400 solar mass Black Hole Revealed while Mimicking a Stellar-mass Black Hole
	Alexander Mendez (JHU)	AEGIS+PRIMUS: The Clustering of X-ray, Mid-IR, and Radio-selected AGN
September 22	Yacine Ali-Haïmoud (JHU)	Rotational spectroscopy of Interstellar PAHs
	Jim Green (U. Colorado)	Imaging in the FUSE Band: The Sub-Lyman alpha Explorer
September 29	Remco van den Bosch (MPIA)	Compact Galaxies and Super Massive Black Holes
	Omer Bromberg (Princeton)	Can We Really Trust All That We Know on Short GRBs?
October 6	Matthias Bartelmann (Univ. Heidelberg)	Joint Reconstruction of Galaxy Clusters from all Observables
	Elizabeth Fernandez (KAI)	The Science of Deduction: Interpreting Observations of the Epoch of Reionization
October 13	Amy Reines (U Michigan)	Probing the Origin of Supermassive Black Holes with Dwarf Galaxies
	Nick Stone (Columbia)	Stellar Tidal Disruption: the Role of General Relativity
October 20	Roseanne Cheng (JHU)	Hydrodynamic Circularization of Stellar Tidal Disruption Debris
	Marcio Melendez (Maryland)	Herschel Far-infrared Photometry of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. I. PACS Observations
October 27	Sarah Hoerst (JHU EPS)	Haze Formation in Planetary Atmospheres: Lessons from the Lab
	Cora Uhlemann (LMU Munich)	Large scale structure formation with the Schrödinger method
November 3	Chun Ly (NASA Goddard)	Results from "Direct" Metallicity Studies of Metal-poor, Strongly Star-forming Galaxies
	Jeff Cummings (JHU)	The Initial-Final Mass Relation: Expanding Into Massive White Dwarfs
November 10	Dominika Wylezalek (JHU)	The Large-scale Environments of Radio-loud AGN and Their Evolution across Cosmic Time
	Kevin Lewis (JHU EPS)	Orbital Dynamics and the Martian Rock Record
November 17	Michael Kesden (UT Dallas)	Effective Potentials and Morphological Transitions for Binary Black-hole Spin Precession
	Laura Blecha (Maryland)	The Observability of Recoiling Black Holes as Offset Quasars
November 24	Leonardo Almeida (JHU/São Paulo)	O-type binaries in 30 Doradus: Spectroscopic orbits, fundamental parameters, and distance to this region
	Anastasia Fialkov (ICFP, Paris)	The Rich Complexity of 21-cm Fluctuations Produced by the First Stars
December 1	Hsiang-Yi Karen Yang (Maryland)	The Fermi Bubbles: Possible Nearby Laboratory for AGN Jet Activity
	Sjoert van Velzen (JHU)	Jets from Supermassive Black Holes: from Giants to Newborns
December 8	Richard Anderson (JHU)	Cepheid radial velocity curve modulation impacts Baade-Wesselink distances
	Karrie Gilbert (STScI)	The Global Properties of M31’s Stellar Halo: Results from the SPLASH Survey
December 15	Yicheng Guo (UCSC)	The formation and evolution of clumpy galaxies from z=3 to z=0.5
	Amaya Moro-Martin (STScI)	Herschel studies of extrasolar Kuiper belt-like systems

8 Sept 2014

K.G. Lee

The First z>2 Large-Scale Structure Map with Lyman-Alpha Forest Tomography from LBGs
The hydrogen Lyman-alpha forest is a long-established probe of large-scale structure at z>2, but is typically limited to 1D investigations along individual quasar sightlines. However, by instead targeting LBGs as background sources, the transverse separation between sources is ~Mpc and it becomes possible to do a 3D 'tomographic' reconstruction of the intergalactic medium. I will describe pilot observations using this technique, which has produced the first map of 3D large-scale structure at z~2.3 within the COSMOS field. Comparisons with coeval galaxies and simulations indicate that our map is truly tracing large-scale structure. This motivates the CLAMATO survey, which will map out a volume of (100 Mpc/h)^3 at z~2.3 and allow us to search for galaxy protoclusters, study the effect of environment on galaxy evolution, and constrain cosmological parameters.

Peter Behroozi

Close Pairs: Observational Probes for how Halo Accretion Impacts Galaxy Star Formation

We present a simple observational method for selecting galaxies whose host dark matter haloes have had significantly higher-than-average accretion rates. The method relies on using close pairs of galaxies to preferentially identify major dark matter halo mergers. Applying the method to central L∗ galaxies in the Sloan Digital Sky Survey (SDSS) DR10, we find no evidence for enhanced average or median star formation accompanying as much as an 0.3 dex increase in average halo accretion rates. However, population subsamples do show enhancements. Most interestingly, star-forming L∗ galaxies show a double peak in star formation enhancements as a function of the distance to the close pair. The larger (factor of 2) enhancement occurs for close pairs within 30 kpc, and the smaller (factor of 40%) enhancement occurs for pairs separated by 100-200 kpc (i.e., just within the virial radius of the larger galaxy’s halo). We discuss implications for conditional abundance matching models; while galaxy quenchedness cannot depend only on halo mass and recent accretion, reproducing the full behaviour of star-forming galaxies requires more advanced models than currently exist.

15 Sept 2014

Dheeraj Pasham

A 400 solar mass black hole revealed while mimicking a stellar-mass black hole
The brightest X-ray source in M82 has been thought to be an intermediate-mass black hole (100-10,000 solar masses) because of its extremely high X-ray luminosity and variability characteristics, although some models suggest that its mass may be only of the order of 20 solar masses. The previous mass estimates were based on scaling relations which used low-frequency characteristic timescales which have large intrinsic uncertainties. In stellar-mass black holes we know that the high frequency quasi-periodic oscillations that occur in a 3:2 ratio (100-450 Hz) are stable and scale inversely with black hole mass with a reasonably small dispersion. The discovery of such stable oscillations thus potentially offers an alternative and less ambiguous mass determination for intermediate-mass black holes, but has hitherto not been realized. I will discuss the discovery of stable, twin-peak (3:2 frequency ratio) X-ray quasi-periodic oscillations from M82 X-1 at the frequencies of 3.32 Hz and 5.07 Hz and how this helps overcome the systematic uncertainties present in previous studies. Assuming we can extend the stellar-mass relationship, we estimate its black hole mass to be 428+/-105 solar masses. (See also this paper for more information.)

Alexander Mendez

AEGIS+PRIMUS: The Clustering of X-ray, mid-IR, and radio-selected AGN

We present a clustering study of X-ray, mid-IR, and radio-selected active galactic nuclei (AGN) at 0.2 < z < 1.2 using multi-wavelength imaging and spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys, covering 7 separate fields spanning ~10 square degrees. Using the cross-correlation of AGN with dense galaxy samples, we measure the clustering scale length and slope, as well as the bias, of AGN selected at different wavelengths. We compare the clustering of each AGN sample with galaxy samples with the same stellar mass, star formation rate, and redshift distributions as the AGN host galaxies and find no significant difference in the clustering of AGN with matched galaxy samples. The observed differences in the clustering of AGN selected at different wavelengths can therefore be explained by the clustering differences of their host populations. We further find no significant difference between the clustering of obscured and unobscured AGN, using IRAC or WISE colors or X-ray hardness ratio.

22 Sept 2014

Yacine Ali-Haïmoud

Rotational Spectroscopy of Interstellar PAHs
Polycyclic aromatic hydrocarbons (PAHs) are believed to be ubiquitous in the interstellar medium. Yet, to date no specific PAH molecule has been identified. In this talk I describe a new observational avenue to detect individual PAHs, using their rotational line emission at radio frequencies. Previous PAH searches based on rotational spectroscopy have only targeted the bowl-shaped corannulene molecule, with the underlying assumption that other polar PAHs are triaxial and have a complex and diluted spectrum unusable for identification purposes. I will show that the asymmetry of planar, nitrogen-substituted symmetric PAHs is small enough that their rotational spectrum, when observed with a resolution of about a MHz, has the appearance of a "comb" of evenly spaced stacks of lines. The simple pattern of these "comb" spectra allows for the use of matched-filtering techniques, which can result in a significantly enhanced signal-to-noise ratio. Detection forecasts are discussed for regions harbouring "anomalous microwave emission", believed to originate from the collective PAH rotational emission. A systematic search for PAH lines in various environments is advocated. If detected, PAH "combs" would allow to the conclusive and unambiguous identification of specific, free-floating interstellar PAHs.

Jim Green

Imaging in the FUSE Band: The Sub-Lyman alpha Explorer
I will present our concept for a Small Explorer that will provide 2 arc second imaging in the 1020 – 1200 angstrom bandpass. Our primary science goals are to directly measure the ionizing escape fraction at low redshift, to quantify the contribution of O stars to galactic energy cycles, and probe the physics of proto-planetary disks. There will be a guest investigator program after the prime science surveys have been completed. The design utilizes dispersive re-construction to create a tunable bandpass below Lyman alpha, so that sub-bandpasses can be created in the 1020 – 1200 angstrom region. I will review the science cases and the optical design. If selected, launch would be in 2020.

29 Sept 2014

Remco van den Bosch

Compact Galaxies and Super Massive Black Holes
Super-massive black holes reside at the center of galaxies. And the masses of these black holes correlate to various properties of their host galaxies. These correlations are the foundation for theories of the (co-)evolution of super-massive black holes and their host galaxies.

However, very few galaxies are nearby enough for direct black hole mass measurements. To find suitable galaxies, we surveyed a thousand galaxies with the Hobby-Eberly Telescope. The first results of this survey was the discovery of a dozen extremely compact, high-dispersion, galaxies, which are candidates to host extraordinary massive black holes. The prototype is NGC1277, which is a small, Re=1kpc, compact, lenticular galaxy which hosts a 10 billion solar mass black hole. Which is a significant fraction of this galaxies mass. These highly compact galaxies appear to be the passively evolved descendants of the red nuggets, sub-mm galaxies, and quasars found at high redshifts.

Omer Bromberg

Can We Really Trust All That We Know on Short GRBs?
The study of short GRBs took a great leap since the arrival of Swift, 10 years ago. However still, a large part of our newly gained knowledge of these events, rely on a relatively small sample of bursts with good enough localization. As there is an overlap with the much more abundant population of long GRBs (with different origin than the short GRBs), there is a risk that contamination by falsely identified long GRBs may alter some of these conclusions. In this talk I will show evidence that such a contamination does exist in the current sample of the short GRBs that are studied (chosen with the criterion of T_90<2 sec). I will then quantify this contamination, based on our knowledge of the nature of long GRBs, and demonstrate how it affects some of our conclusions regarding short GRBs.

6 Oct 2014

Matthias Bartelmann

Joint reconstruction of galaxy clusters from all observables
Galaxy clusters provide five types of observables related to their matter distribution: strong and weak gravitational lensing, X-ray emission, the thermal Sunyaev-Zel'dovich effect, and galaxy kinematics. In the talk, I will show how all these observables can be combined in a non-parametric way into a joint reconstruction of the projected gravitational cluster potential. First examples of cluster potentials reconstructed from X-ray emission, the thermal SZ effect and galaxy kinematics will be given.

Elizabeth Fernandez

The Science of Deduction: Interpreting Observations of the Epoch of Reionization
Up until very recently, the Epoch of Reionization has been largely observationally unexplored . However, with advancements of modern telescopes, we are now able to observe this period of the Universe in multiple ways. While observations are still very challenging due to a host of foreground contaminants, combining observations at multiple wavelengths can lead to a greater understanding of the populations of stars and galaxies at these redshifts. I will describe two of these observables: the Cosmic Infrared Background, which is partially the integrated light from all stars and galaxies at high redshifts, and the 21cm Background, which results from emission from neutral gas. These observables, when paired with theory and simulations, can tell us about some of the first stars and galaxies that formed within our Universe.

13 Oct 2014

Amy Reines

Probing the Origin of Supermassive Black Holes with Dwarf Galaxies
Supermassive black holes (BHs) live at the heart of essentially all massive galaxies with bulges, power AGN, and are thought to be important agents in the evolution of their hosts. However, the origin of the first supermassive BH "seeds" is far from understood. While direct observations of these distant BHs in the infant Universe are unobtainable with current capabilities, massive BHs in present-day dwarf galaxies offer another avenue to observationally constrain the masses, host galaxies and formation path of supermassive BH seeds. Using optical spectroscopy from the SDSS, we have increased the number of known dwarf galaxies hosting massive BHs by more than an order of magnitude. These dwarf galaxies have stellar masses comparable to the Magellanic Clouds and contain some of the least-massive supermassive BHs known. I will present results from this study, and well as on-going efforts using radio and X-ray observations to reveal massive BHs in star-forming dwarfs that can be missed by optical diagnostics.

Nick Stone

Stellar Tidal Disruption: the Role of General Relativity
In tidal disruption events (TDEs), stars passing too close to supermassive black holes (SMBHs) are violently torn apart. I will discuss several recent findings about the light curves of these events, including the role of orbital pericenter, ways in which the spin of the SMBH can be imprinted into TDE light curves, and possible emission of high frequency gravitational waves. I will also discuss an ongoing project focused on how highly eccentric debris streams from a TDE can circularize into a luminous accretion disk. It appears likely that the circularization process is mediated by general relativistic effects: circularization is aided by apsidal precession and hindered by nodal precession due to Lense-Thirring torques.

20 Oct 2014

Roseanne Cheng

Hydrodynamic Circularization of Stellar Tidal Disruption Debris
Black holes in galaxies are powerful central engines capable of generating accretion flares and jets. A star passing too close to one will tidally disrupt with some of its debris ejected from the system while the rest funnels towards the black hole forming an accretion disk. The emission properties are likely dependent on the mass and spin of the black hole. The process by which debris forms a disk and generates flares and/or jets is not well-understood. We investigate this process by simulating the circularization of stellar tidal disruption debris. We combine a high-resolution relativistic hydrodynamic simulation of the star itself as it is torn apart with a well-resolved relativistic hydrodynamics simulation of the subsequent motion of the stellar debris as it orbits the black hole. With these tools, we track the evolution of such a system long enough for 80% of the stellar mass bound to the black hole to join the accretion flow. We find significant departures from classical expectations for the lightcurve associated with tidal disruptions.

Marcio Melendez

Herschel Far-infrared Photometry of the Swift Burst Alert Telescope Active Galactic Nuclei Sample of the Local Universe. I. PACS Observations
Far-Infrared (FIR) photometry from the Photodetector Array Camera and Spectrometer on the Herschel Space Observatory is presented for 313 nearby, hard X-ray selected galaxies from the 58 month Swift Burst Alert Telescope (BAT) Active Galactic Nuclei catalog. The present data do not distinguish between the FIR luminosity distributions at 70 and 160 um for Seyfert 1 and Seyfert 2 galaxies. This result suggests that if the FIR emission is from the nuclear obscuring material surrounding the accretion disk, then it emits isotropically, independent of orientation. Alternatively, a significant fraction of the 70 and 160 um luminosity could be from star formation, independent of active galactic nucleus (AGN) type. Using a non-parametric test for partial correlation with censored data, we find a statistically significant correlation between the AGN intrinsic power (in the 14-195 keV band) and the FIR emission at 70 and 160 um for Seyfert 1 galaxies. We find no correlation between the 14-195 keV and FIR luminosities in Seyfert 2 galaxies. The observed correlations suggest two possible scenarios: (1) if we assume that the FIR luminosity is a good tracer of star formation, then there is a connection between star formation and the AGN at sub-kiloparsec scales, or (2) dust heated by the AGN has a statistically significant contribution to the FIR emission. Using a Spearman rank-order analysis, the 14-195 keV luminosities for the Seyfert 1 and 2 galaxies are weakly statistically correlated with the F70/F160 ratios.

27 Oct 2014

Sarah Hoerst

Haze Formation in Planetary Atmospheres: Lessons from the Lab
For more than 50 years, haze formation in planetary atmospheres has been simulated in the laboratory. Of particular interest are simulations of haze formation in the atmosphere of Titan, the largest moon of Saturn. These simulation experiments have provided a wealth of knowledge about the possible composition and optical properties of haze particles, informed efforts to understand the transition between gas phase and particle chemistry, and provide “analogue” materials to aid in the selection and testing of the next generation of spacecraft based analytical techniques. In this talk I will review the current state of knowledge from Titan atmosphere simulation experiments, discuss difficulties that have arisen from knowledge gained from the Cassini-Huygens mission to the Saturn system, and present particular areas where laboratory studies could provide much needed guidance for the observation and modeling communities studying atmospheres in our solar system and beyond. I'm not sure what you are looking for in a bio but the short version is that I have a BS in Planetary Science and a BS in Literature from Caltech. I got my PhD in Planetary Science at the University of Arizona. I was an NSF Astronomy and Astrophysics Postdoctoral Fellow at the University of Colorado-Boulder and I am now an Assistant Professor in the Department of Earth and Planetary Sciences at JHU.

Cora Uhlemann

Large scale structure formation with the Schrödinger method
When describing large-scale structure formation of collisionless dark matter one is interested in the dynamics of a large collection of identical point particles that interact only gravitationally. Via gravitational instability initially small density perturbations evolve into eventually bound structures, like dark matter halos that are distributed along the cosmic web. Even though this problem seems quite simple from a conceptual point of view, no sufficiently general solution of the underlying equation, the collisionless Boltzmann equation coupled to the Poisson equation, is known. Therefore one usually has to resort to N-body simulations which tackle the problem numerically. Analytical methods to describe structure formation are in general based on the dust model which describes cold dark matter as a pressureless fluid characterized by density and velocity. This model works quite well up to the quasi-linear regime but eventually fails when multiple streams form that are especially important for halo formation but lead to singularities in the model. We employ the so-called Schrödinger method, originally proposed by Widrow & Kaiser (1993) as a numerical tool, to develop a model which is able to describe multi-streaming and therefore can serve as theoretical N-body double. As a first application we study the coarse-grained dust model, which is a limiting case of the Schrödinger method, within Eulerian and Lagrangian perturbation theory.

3 Nov 2014

Chun Ly

Results from "Direct" Metallicity Studies of Metal-poor, Strongly Star-forming Galaxies
The chemical enrichment of galaxies, driven by star formation and regulated by gas flows from supernova and cosmic accretion, is a key process in galaxy formation that remains to be understood. The most reliable metallicity determination is made possible by detecting [OIII]4363. The technique is often called the "direct" method for its ability to determine the electron temperature of the ionized gas, and hence the gas-phase metallicity. However, this nebular emission line is intrinsically weak, and thus have not been detected for large samples of galaxies, especially at higher redshift. In this talk, I will present new results from the detection of [OIII]4363 in two complementary samples of 20--30 metal-poor, strongly star-forming galaxies at z~0.8. The samples are selected from the Subaru Deep Field and the DEEP2 Galaxy Redshift Survey. Together, they represent the largest intermediate redshift sample (N ~ 50) with direct metallicities.

Combining optical spectroscopy with multi-wavelength imaging, I explore the relationship between stellar mass, dust-corrected star formation rate (SFR), and temperature-based gas metallicity. I find that these galaxies are undergoing rapid evolution with stellar mass doubling times of about 100 Myr, a factor of 10 faster than typical z~1 star-forming galaxies on the star-formation "main sequence." I also find that these galaxies deviate toward lower metallicity on the mass--metallicity relation. Finally, I will discuss these galaxies in context to the mass--metallicity--SFR relation (i.e., the "fundamental metallicity relation"). I will argue that stochastic star formation in these dwarf galaxies results in significant dispersion and the lack of a correlation between stellar mass, metallicity, and SFR.

Jeff Cummings

The Initial-Final Mass Relation: Expanding Into Massive White Dwarfs
Spectroscopic analysis of white dwarfs is a proven technique to establish their log g, Teff, mass, and cooling age. For white dwarfs in star clusters, a comparison of its cooling age to the cluster turnoff age provides the lifetime and initial mass of the white dwarf's progenitor. This creates the initial-final mass relation (IFMR), which gives a direct measurement of total mass loss for stars and can illustrate its dependence on mass and metallicity. In our project we have first analyzed a broad white dwarf sample (0.7 to 0.95 Msun) from a single solar metallicity cluster, NGC 2099, which greatly limits systematic effects. Comparison to results from the metal-rich Hyades and Praesepe indicates that there is little metallicity dependence in the IFMR at this parameter range. This data also reliably helps to illustrate the nonlinearity of the IFMR, which has important consequences in the interpretation of the poorly understood high-mass white dwarfs (> 1 Msun) of the IFMR. Therefore, our photometric survey of young, rich, and nearby clusters is searching for massive white dwarfs, which are needed to fully understand their progenitor evolution but also to help constrain the lower-mass limit of Type II SNe.

10 Nov 2014

Dominika Wylezalek

The Large-scale Environments of Radio-loud AGN and Their Evolution across Cosmic Time

Powerful high redshift radio-loud AGN (RLAGN), are known to preferentially lie in overdense fields and are promising beacons for identifiying large-scale structure and galaxy (proto)-clusters. However, due to the relatively small number of confirmed high-z clusters, it is still challenging to draw a clear picture of their formation and evolution. I will present results of our large Spitzer program, CARLA (Clusters Around Radio-Loud AGN), that has targetd 420 RLAGN at 1.3<z<3.2 for a total of more than 300 hours of Spitzer/IRAC time and that for the first time allows to systematically study the fields of a large sample of powerful RLAGN over a wide redshift range. Studying the density of red color-selected sources shows that ∼200 CARLA fields are rich and compact structures with overdensities established within cells of 0.5 Mpc. The surface density proves that indeed most of the excess sources are associated with the targeted RLAGN. Two CARLA protoclusters have already been spectroscopically confirmed and more observations with KMOS/MUSE/HST are under way. This large (proto-)cluster sample also allows us for the first time at these redshifts, to systematically measure the luminosity function of clusters around RLAGN. Our measurements for m∗ are consistent with passive evolution models and high formation redshifts (z_f ∼ 3). We find a slight trend toward fainter m∗ for the richest clusters, implying that the most massive clusters in our sample could contain older stellar populations. The results are consistent with cosmic downsizing, as the clusters studied here were all found in the vicinity of RLAGNs—which have proven to be preferentially located in massive dark matter halos in the richest environments at high redshift—and they may therefore be older and more evolved systems than the general protocluster population.

Kevin Lewis

Orbital Dynamics and the Martian Rock Record

Aside from the Earth, Mars is the only object in our solar system known to host an extensive sedimentary rock record. Study of the terrestrial sedimentary record largely drives our understanding of the planet's biological, climatic, and geophysical evolution over time. Likewise, the sedimentary record of Mars has begun to yield clues to that planet's early history, via both remote sensing and in situ analysis from robotic missions. A central objective of the Curiosity rover mission is the search for evidence of past habitable environments at the Martian surface. This talk will highlight recent results and future goals of the Curiosity mission, along with a parallel question: how can we tell time in the Martian rock record? Recent results suggest the widespread preservation in the Martian rock record of repetitive environmental changes induced by cyclic variations in the planet's orbital configuration. These patterns may finally provide a yardstick with which to determine the duration of more habitable climate conditions on early Mars.

17 Nov 2014

Michael Kesden

Effective Potentials and Morphological Transitions for Binary Black-hole Spin Precession

Generic binary black holes have spins that are misaligned with their orbital angular momentum. When the binary separation between the black holes is large compared to their gravitational radii, the timescale on which the spins precess is much shorter than the radiation-reaction time on which the orbital angular momentum decreases due to gravitational-wave emission. We use conservation of the total angular momentum and the projected effective spin on the precession time to derive an effective potential for BBH spin precession. This effective potential allows us to solve the orbit-averaged spin-precession equations analytically for arbitrary mass ratios and spins. These solutions are quasiperiodic functions of time: after a precessional period the spins return to their initial relative orientations. We classify black-hole spin precession into three distinct morphologies between which the black holes can transition during their inspiral. Our new solutions constitute fundamental progress in our understanding of black-hole spin precession and also have important applications to astrophysical black holes. We derive a precession-averaged evolution equation that can be numerically integrated on the radiation-reaction time, allowing us to statistically track black-hole spins from formation to merger. This will greatly help us predict the signatures of black-hole formation in the gravitational waves emitted near merger and the distributions of final spins and gravitational recoils.

Laura Blecha

The Observability of Recoiling Black Holes as Offset Quasars

The merger of two supermassive black holes (SMBHs) imparts a gravitational-wave (GW) recoil kick to the remnant SMBH, and in extreme cases SMBHs may be ejected from their host galaxies. An accreting, recoiling SMBH may be observable as a spatially or kinematically offset quasar. Prior to the advent of a space-based GW observatory, offset quasars may offer the best evidence of recent SMBH mergers. Indeed, promising candidates have already been identified. However, systematic searches for recoils are hampered by large uncertainties, including how often and in which host galaxies offset quasars should be observable, and whether BH spin alignment prior to merger is efficient at suppressing large recoils. Motivated by this, we have developed a model for recoiling quasars in a cosmological framework, utilizing information about the progenitor galaxies from cosmological hydrodynamic simulations. Varying degrees of BH spin alignment are considered. We find that the observability of offset quasars, and their preferred host galaxies, depend strongly on the efficiency of pre-merger spin alignment, with promising indications that discoveries of recoils could distinguish between at least the extreme limits of spin alignment models. These findings will inform the design of dedicated searches for recoiling quasars.

24 Nov 2014

Leonardo Almeida

O-type binaries in 30 Doradus: Spectroscopic orbits, fundamental parameters, and distance to this region
A key ingredient missing from current formation and evolution theories of massive stars, and of cluster evolution, is a robust binary fraction and the intrinsic distributions of orbital parameters. The VLT-FLAMES Tarantula Survey (VFTS), which targeted 800 O- and B- stars in 30 Dor, was designed to detect most massive binaries with orbital periods < 200 d: the observed O-type binary fraction is 27% (100 binaries). To characterize these binaries, in 2012, Hugues et al. started an observational campaign, Tarantula massive binary monitoring, using the GIRAFFE/VLT/ESO spectrograph. 32 spectra of the sample were collected between 2012 and 2014. Using the radial velocity curves we characterized the orbits of these systems, with the aim of obtaining the first measurements of the orbital period, mass-ratio and eccentricity distributions. For 12 binaries that show ellipsoidal variation and/or eclipse, we derived their fundamental properties, e.g., masses, radii, temperature, etc, and the distance to this region, which is dense and dynamically complex closer to those in super-star-clusters observed beyond the Local Group.

Anastasia Fialkov

The Rich Complexity of 21-cm Fluctuations Produced by the First Stars
The 21-cm signal of neutral hydrogen is expected to be the richest three-dimensional probe of the early Universe at the epochs of Reionization and Cosmic Dawn. In this talk I will discuss the latest theoretical predictions for the 21-cm signal from redshifts 7-40. This redshift range includes various epochs of cosmic evolution related to primordial star formation, and should be accessible to existing or planned low-frequency radio telescopes.

1 Dec 2014

Hsiang-Yi Karen Yang

The Fermi Bubbles: Possible Nearby Laboratory for AGN Jet Activity
One of the most important discoveries of the Fermi Gamma-ray Space Telescope is the detection of two giant bubbles extending 50 degrees above and below the Galactic center (GC). The symmetry about the GC of the Fermi bubbles suggests some episode of energy injection from the GC, possibly related to past jet activity of the central active galactic nuclei (AGN). Thanks to the proximity to the GC, the Fermi Bubbles are excellent laboratories for studying cosmic rays (CRs), Galactic magnetic field, and AGN feedback in general. Using three-dimensional magnetohydrodynamic simulations that include relevant CR physics, I will show how leptonic AGN jets can explain the key characteristics of the Fermi bubbles and the spatially correlated features observed in the X-ray, microwave, and radio wavelengths. I will also discuss how we use our simulations in combination with the multi-wavelength data to obtain constraints on the composition of the Fermi bubbles.

Sjoert van Velzen

Jets from Supermassive Black Holes: from Giants to Newborns

Why do only 10% of quasar show powerful radio jets? The answer to this question is currently unknown but should involve at least one fundamental property of supermassive black holes (eg, spin or mass) as well as the evolution of their host galaxies. This talk, I will approach the questions of radio loudness from two different angles. First, using the lobes of radio galaxies to study jets on long (> million year) timescales. Second, using the tidal disruption of stars by massive black holes to probe jets on human timescales.

8 Dec 2014

Richard Anderson

Cepheid radial velocity curve modulation impacts Baade-Wesselink distances
Classical Cepheids are crucial Galactic and extragalactic distance tracers thanks to the famous period-luminosity relation and carry high weight in the determination of the Hubble parameter. Precise individual Cepheid distances are required to accurately calibrate this relation and in particular its zero-point. The Baade-Wesselink technique enables the determination of precise distances to individual Cepheids in both the Milky Way and the Magellanic Clouds and is thus essential for investigating how metallicity affects the famous Cepheid period-luminosity relation. Here, I will present the recent discovery of modulation in Cepheid radial velocity curves and show that modulation leads to a new, previously ignored, systematic uncertainty for Baade-Wesselink distances. In the worst case, modulation can lead to systematic distance errors as high as 15%. However, modulation may also be the key for improving the precision of Baade-Wesselink distances.

Karrie Gilbert

The Global Properties of M31’s Stellar Halo: Results from the SPLASH Survey
Large surveys of Andromeda's resolved stellar populations have revolutionized our view of this galaxy over the past decade. The combination of large-scale, contiguous photometric surveys and pointed spectroscopic surveys has been particularly powerful for discovering and following up new substructures and disentangling the structural components of Andromeda. The SPLASH survey has now amassed spectra of nearly ten thousand of red giant branch stars in Andromeda's halo, disk, and dwarf galaxies. I will present recent results from the SPLASH survey, focusing on the spatial structure and metallicity gradient of M31’s halo.

15 Dec 2014

Yicheng Guo

The formation and evolution of clumpy galaxies from z=3 to z=0.5

A common feature of star-forming galaxies at z>1 is the existence of giantstar-forming clumps,which are fundamental to our understanding of the accretionhistory of galaxies, formation of bulges, and evolution of gas-rich disks. Inthis talk, I will present our work on linking high-redshift clumpy galaxies andlow-redshift settled (rotation dominated) disks in three aspects: (1) thephysical properties of high-redshift clumps; (2) the evolution of the fractionof clumpy galaxies from z=3 to z=0.5; and (3) the connection between the clumpyappearance and the kinematics of settled and unsettled disks at z~0.5. Thethree aspects provide important clues of tracing the physical mechanisms thatare responsible for transferring distant clumpy galaxies into disk galaxies seen in the local universe.

Amaya Moro-Martin

Herschel studies of extrasolar Kuiper belt-like systems

Planetesimals are the building blocks of planets. They can be traced by the dust they produce in collisions or sublimation that forms a debris disk. In the solar system, such a dust disk is produced by the asteroids, comets and Kuiper Belt objects, with a dust production rate that has changed significantly with time, being higher in the past when the planetesimal belts were more densely populated. The Herschel DEBRIS, DUNES, and GT programs observed 37 extrasolar planetary systems within 25 pc. With a sensitivity to detect far-infrared excess emission at flux density levels only an order of magnitude greater than that of the current solar system’s Kuiper belt, these surveys identified 11 debris disks, indicating the presence of planetesimals. We discuss the general characteristics of these Kuiper belt-like disks and the correlations between the stellar, planetary, and debris components. We also present results from an unbiased subsample of the Herschel surveys consisting of 204 FGK stars, located at distances <20 pc, with ages > 100 Myr, and with no binary companions at <100 AU, and discuss whether the presence of planets affect the frequency and properties of extrasolar Kuiper belts. Is there evidence that debris disks are more common, or more dusty, or have a different characteristic temperature around stars harboring high-mass or low-mass planets compared to a control sample without identified planets? Are debris disks more or less common, or more or less dusty, around stars harboring multiple planets compared to single-planet systems? The study of extrasolar Kuiper belt-like disks can shed light on planet formation and migration scenarios. It can also help assess whether terrestrial planet detection might be feasible in these systems. The debris dust can cause an important observational issue for direct detection, with the level of zodiacal light being one of the parameters that defines the design of future telescopes like ATLAST, that have a goal of detecting biosignatures. From our unbiased subsample, we find that 14% of solar-type stars harbor dust-producing planetesimals at 10s of AU from the star with a distribution of fractional luminosity (L_dust/L_star) that can be reproduced by a Gaussian centered at the solar-system’s level. A Gaussian distribution centered at 10× the solar-system’s value can be ruled out. Because this dust would drift into the terrestrial planet region under PR drag, this indicates that there are good prospects for finding a large number of debris-disk systems—with evidence of harboring planetesimals—with zodi emission low enough to be appropriate targets for terrestrial-planet searches.