2012
Links to:
List of colloquium talks given during the summer of 2012
Program of the SAO Summer Intern Symposium, August 15, 2012
2012 Summer Program Calendars for June , July , and August
Abstracts for posters presented at the January, 2013 AAS Meeting
INTERN: Peter Blanchard (University of California - Berkeley)
ADVISOR: Dr. Matt Bayliss (TA Division)
CO-ADVISOR/MENTOR: Dr. Michael McDonald (MIT)
PROJECT TITLE: Searching for Spectroscopic Signatures of Biases in Strong Lensing Selected Clusters
Abstract:
The idea is to test for empirical evidence of astrophysical biases in a sample of galaxy clusters that are selected for their strong lensing efficiency. There is an expectation from simulations that the strong lensing selection should be connected to underlying biases in strong lensing selected clusters vs. the general cluster population, but this expectation has never been tested in real clusters.
Strong lensing galaxy clusters are a small subset of the general cluster population which have anomalously high strong lensing cross-sections. Such high strong lensing cross-sections require that the surface mass density in the cores of these clusters be much higher than typical clusters at the same mass and redshift. We like to think that we have a solid model for the evolution of large scale structure in the universe, but how we end up with strong lensing clusters - the most extremeophile population of massive structures - is still a mystery. The outstanding question here is, what causes the high surface mass density in the cores of these clusters?
There are several possible astrophysical explanations, one of the most reasonable of which is baryonic cooling processes (if baryons cool and contract efficiently in cluster cores, then they can gravitationally drag additional dark matter down into the core and increase the density). Other possible explanations are more exotic (and less likely), and include high rates of major mergers (which would pose a problem for what we think we know about merger rates of halos in simulations) or non-gaussianity in the primordial density field of the universe (which could produce an excess of exceptionally massive and concentrated clusters).
The specific project will involve grabbing SDSS spectra of brightest cluster galaxies (BCGs) for a strong lensing selected sample of clusters, and measuring spectroscopic diagnostics (primarily nebular line emission EWs, which can trace baryonic processes, such as star formation and cool core activity in BCGs) for the strong lensing clusters. This strong lensing selected sample already exists; it is a subset of a complete SDSS optical cluster sample where we have performed a systematic search (with an understood completeness) for giant arcs produced optically selected clusters, and have also performed extensive followup to characterize the purity of the resulting cluster lenses. This sample represents all clusters within a well-defined cosmological volume which are good strong lenses (producing bright giant arcs), includes >~ 200 clusters, and will be published in a paper that should appear on the arxiv by late April. Properties of the strong lensing clusters will be compared to those of the general optical cluster population (e.g. those published in McDonald 2011, ApJL, 742, 35).
INTERN: Philip Cowperthwaite (University of Maryland - College Park)
ADVISOR: Dr. Howard A. Smith (OIR Division)
CO-ADVISOR/MENTOR: Raffaele D'Abrusco (HEA Division)
PROJECT TITLE: The Unique Diagnostic Infrared Colors for Blazars: The WISE Blazar Strip
Abstract:
Blazars are AGN whose powerful relativistic jets are aimed directly towards us, and whose radiation is dominated by nonthermal processes. We have discovered that infrared colors of blazars are a powerful identification tool, and we have used this diagnostic to identify probable new blazars, including some gamma-ray sources, and to begin to address the physical mechanism(s) responsible. We have published 3 papers on this topic in the past year. From a sample of 1365 previously known blazars (from the ROMA BZCAT) observed in the first release of the WISE Preliminary Source catalog we prepared a color-color analysis; we have now added sources from the second WISE release. We find that blazars lie on a narrow strip in infrared colors, distinctly redder on average at the short bands than average stars, starbursts, and bright galaxies. The Spitzer Space Telescope Infrared Spectrometer has observed about 150 blazars as part of many various programs. We propose in this project to reduce and examine these spectra to see if (1) there are any infrared lines that might help to categorize the object; (2) any faint dust features that might help to characterize the dust disk around the throat of the nucleus; (3) model the mid-IR spectra energy shape more precisely by combining the spectral continuum with photometric datasets.
INTERN: Emmet Golden-Marx (Brown University)
ADVISOR: Dr. Matt Ashby (OIR Division)
CO-ADVISOR/MENTOR: Dr. Howard A. Smith (OIR Division)
PROJECT TITLE: Star Formation in Nearby Galaxies Measured by the PACS Instrument Aboard Herschel
Abstract:
tar formation is arguably the most important physical process in the Cosmos. It is the primary driver of galaxy evolution and the mechanism whereby heavy elements are created. Here at the CfA we are leading a project to understand how to best measure the pace and intensity of star formation taking place in nearby galaxies. This is the Star Formation Reference Survey (SFRS).
Observations of SFRS galaxies have already been carried out with a number of star formation tracers from UV to radio wavelengths. However, a significant gap exists in our knowledge of the far-infrared tracers in particular, because no one has yet analyzed the Herschel/PACS photometry for our galaxy sample, forcing us to rely more heavily on IRAS data than we would like. It is important to close this gap, because the far-infrared regime is arguably the 'gold standard' for accurate measurements of star formation rate.
The plan of our proposed project is for the student to:
1. determine which SFRS galaxies have been observed by Herschel/PACS
2. download and reduce the relevant data to measure the fluxes from our sample galaxies at 70, 100, and 160 um with the standard Herschel reduction software package known as HIPE
3. in combination with data already in hand (e.g., redshifts, other photometry), convert the fluxes to luminosities
4. compare the outcome to previous measurements with Spitzer/MIPS and IRAS to identify any deficiencies in any of the involved datasets
5. identify trends in dust temperature and star formation mode (quiescent versus starburst) within the sample so far observed by Herschel
Additionally, it may be possible for the student to compare the outcome to tracers of star formation collected by SFRS team members at other wavelengths, e.g., UV imaging from the GALEX satellite and near-infrared photometry from Spitzer.
INTERN: Margaret Landis (University of Northern Arizona)
ADVISOR: Dr. Catherine Espaillat (RG Division)
PROJECT TITLE: Exploring The Structure of Young Disks
Abstract:
Disks around young stars are known to exhibit infrared variability. However, the physical mechanisms responsible for the observed variability are not yet fully understood. In this project we will detect changes in the structure of the disk, which is relevant to understanding how disks make planets. Many objects in the sample have holes in their disks, possibly formed by planets, and it would be interesting to see how their disk structure changes over time. Using data from infrared ground-based telescopes and the Spitzer Space Telescope, we will look for infrared variability of disks and try to explain the magnitude of the variability with changes in the disk's structure. The project will involve learning basic tools and techniques to analyze infrared data as well as comparing observations to theoretical models.
INTERN: Ryan McKinnon (Yale University)
ADVISOR: Prof. Alicia Soderberg (OIR Division)
PROJECT TITLE: The Ultra-Luminous Pan-STARRS Supernova PS1-11vo
Abstract:
Over the past few years, the field of time domain astronomy has exploded thanks to improvements in technology and instrumentation. The Pan-STARRS optical transient survey has uncovered a diversity in supernovae that has never yet been probed by previous surveys. In particular, the deep sensitivity of Pan-STARRS has enabled rare explosions with extraordinary luminosities to be discovered in rates higher than ever before. Here we report on the analysis of the Type IIn supernova, PS1-11vo, one of the longest lived and most luminous supernova explosions ever documented.
INTERN: Lia Medeiros (University of California - Berkeley)
ADVISOR: Dr. Aneta Siemiginowska (HEA Division)
CO-ADVISOR/MENTOR: Dr. Malgorzata Sobolewska (HEA Division)
PROJECT TITLE: X-ray Emission in Luminous Quasars
Abstract:
This project concerns a sample of quasars observed in the optical and X-ray bands. It will involve a compilation of the spectral energy distributions (SED) for the quasars using SDSS and Chandra (and other if appropriate) archival data and a self-consistent modeling of these data. The "accretion disk + hot corona" emission models have been developed by our group and we will apply them to the quasars in the sample using Sherpa, which is a modern modeling and fitting package in Python. Our sample contains high luminosity quasars with measured black hole masses with high accretion rates. The main goal of this project is to understand the accretion power and a contribution to the X-ray emission given by the hot corona.
INTERN: Becky Nevin (Whitman College)
ADVISOR: Dr. Francesca Civano (HEA Division)
CO-ADVISOR/MENTOR: Dr. Andrew Goulding (HEA Division)
PROJECT TITLE: Looking for recoiling SMBHs in Imaging survey
Abstract:
The existence of quasars misplaced with respect to their host galaxy center has been predicted by models of galaxy formation. When two galaxy merge, also their supermassive black holes (SMBHs) inside will merge. Depending on the initial conditions, the newly formed SMBH can recoil with respect to the center of the host galaxy, due to the asymmetric emission of gravitational waves. If the kick velocity is large enough, it will be possible to observe a misplaced quasar. The search of these objects have been really limited and only 6 candidates have been discovered so far.
I propose to search for misplaced quasars with respect to their host galaxies using imaging data. We will be using the GALFIT software for imaging analysis Galfit and we will look for galaxies showing asymmetries and irregular structures possibly due to a recent merging episode. Then, possible candidates will be studied in detail.
INTERN: Kayla Redmond (University of North Carolina at Asheville)
ADVISOR: Dr. Helen Kirk (RG Division)
CO-ADVISOR: Dr. Stella Offner (TA Division)
PROJECT TITLE: Mass Segregation in Dense Cores of Simulated and Observed Molecular Clouds
Abstract:
Background:
Within our close galactic neighborhood (a few hundred parsecs or lightyears), many molecular clouds have been detected where star formation is ongoing. Many puzzles remain in understanding star formation, including the influence of the large-scale cloud properties on the formation and evolution of the embedded forming stars. To better understand these processes, large surveys are underway at several telescopes focussing on nearby molecular clouds, and an unprecedented amount of data is becoming available. One of the precursors to these multi-telescope, multi-cloud surveys was COMPLETE (led by Dr. Goodman, [1]), which focussed on star formation in several molecular clouds, particularly the Perseus molecular cloud. Most stars appear to form in clusters, where interactions between dense star-forming cores may play an important role in subsequent evolution. Observations from the COMPLETE survey have shown that dense cores in Perseus tend to have very small motions relative to their immediate surroundings, and that the motions between cores within a clustered region are a factor of two smaller then the large-scale gas motions [2]. Interpretation of these results is challenging without knowledge of the 3D structure and dynamics of the cloud.
Project:
There is currently much debate over whether clusters found in star forming regions are born mass-segregated, or if the segregation is a result of dynamic evolution over in the first few million years. The student will examine this question with numerical simulations of star-formation, where the intial environmental conditions and the 3D cloud structure is known.
[1] Ridge, N. et al., "The COMPLETE Survey of Star Forming Regions: Phase 1 Data", 2006, AJ, 131, 2921
[2] Kirk, H., Pineda, J., Johnstone, D., & Goodman, A. "The Dynamics of Dense Cores in the Perseus Molecular Cloud. II. The Relationship Between Dense Cores and the Cloud," 2010, ApJ, 723, 457
INTERN: Bryan Terrazas (Columbia University)
ADVISOR: Dr. Paul Nulsen (HEA Division)
PROJECT TITLE: Particle Leakage and Aging of Radio Lobes
Abstract:
An extragalactic radio source is formed when a "supermassive" black hole at the center of a galaxy spews enormous amounts of energy into its surroundings through a pair of narrow, opposed jets. The jets inflate lobes with relativistic electrons and magnetic field. We see the radio source because relativistic electrons in a magnetic field produce synchrotron radiation.
Energy released in these outbursts can heat surrounding gas enough to affect the amount of gas supplied to the black hole, which creates a feedback loop linking the rate of gas cooling to the rate and size of outbursts. By limiting gas cooling, this "AGN feedback" can also limit star formation and there is mounting evidence that this is why the most luminous galaxies are not nearly as bright as predicted by simple galaxy formation models. As a result, there is great interest in understanding how radio sources work in detail.
In addition to the relativistic electrons and magnetic field, radio lobes probably contain other relativistic particles (cosmic rays) and thermal material that are largely undetectable. We want to relate the composition of radio lobes to their observable properties in order to study AGN feedback. The aim of this project is to investigate how the composition of radio lobes changes with time. By making a model for the aging of radio lobes, we hope to be able to use their radio properties alone to estimate key properties like their ages and how much energy was required to produce them.
The aims of the project will be to make models for aging radio lobes and to see if they can explain the X-ray and radio properties of a sample of observed radio sources. The project will involve both theory and data analysis, depending on the interests of the student.
INTERN: Nancy Thomas (University of Washington)
ADVISOR: Dr. Joe Hora (OIR Division)
PROJECT TITLE: Variability of Massive Young Stellar Objects
Abstract:
Young Stellar Objects (YSOs) are stars in the process of formation. They are surrounded by disks and are actively accreting material onto their surface. The disks also provide the material from which planets will form around these stars. Several recent investigations have shown a high rate of photometric variability in YSOs at near- and mid-infrared wavelengths. Theoretical models for the formation of stars remain highly idealized, and little is known about the mechanisms that produce the variability. There are many possible scenarios, such as rotation of the star and disk where hot spots are present, variability of accretion rates, and changes in the temperature of hot spots.
Even less is known about the variability of massive YSOs, which form under different conditions than most of the nearby low-mass stars. We have an ongoing Spitzer Space Telescope program to study massive star formation in the Cygnus-X region. We were recently awarded additional Spitzer time to monitor two fields in Cygnus-X to find the YSOs and characterize their variability. In conjunction with the Spitzer observations, over the past couple years we have conducted a ground-based near-infrared observing program of these fields using PAIRITEL, the automated infrared telescope at the Whipple Observatory. The near-IR and Spitzer observations will allow us to distinguish between different models to explain the origin of the variability. The summer project will involve extracting the near-IR photometry from the PAIRITEL images using a data reduction pipeline that we have developed at SAO, assembling the time-series data for each YSO in the field from the individual epochs, and correlating the data with the existing Spitzer observations. We will then characterize the variability of each of the YSOs, and determine periods and other properties of the variability which will help constrain models of star and planet formation.