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List of
colloquium talks given during the summer of 2012
Links to:
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 CfA)
PROJECT TITLE: Searching for Spectroscopic Signatures of Biases in
Strong Lensing Selected Clusters
Abstract:
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).
CO-ADVISOR/MENTOR: Dr. Michael McDonald (MIT)
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.
INTERN: Philip Cowperthwaite (University of Maryland - College Park)
ADVISOR: Dr. Howard A. Smith (OIR Division CfA)
PROJECT TITLE: The Unique Diagnostic Infrared Colors for Blazars: The
WISE Blazar Strip
Abstract:
CO-ADVISOR/MENTOR: Raffaele D'Abrusco (HEA Division CfA)
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.
ADVISOR: Dr. Matt Ashby (OIR Division CfA)
PROJECT TITLE: Star Formation in Nearby Galaxies Measured by the
PACS Instrument Aboard Herschel
Abstract:
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:
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.
CO-ADVISOR/MENTOR: Dr. Howard A. Smith (OIR Division CfA)
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).
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
INTERN: Margaret Landis (University of Northern Arizona)
ADVISOR: Dr. Catherine Espaillat (RG Division CfA)
PROJECT TITLE: Exploring The Structure of Young Disks
Abstract:
INTERN: Ryan McKinnon (Yale University)
ADVISOR: Prof. Alicia Soderberg (OIR Division CfA)
PROJECT TITLE: The Ultra-Luminous Pan-STARRS Supernova PS1-11vo
Abstract:
INTERN: Lia Medeiros (University of California - Berkeley)
ADVISOR: Dr. Aneta Siemiginowska (HEA Division CfA)
PROJECT TITLE: X-ray Emission in Luminous Quasars
Abstract:
INTERN: Becky Nevin (Whitman College)
ADVISOR: Dr. Francesca Civano (HEA Division CfA)
PROJECT TITLE: Looking for recoiling SMBHs in Imaging survey
Abstract:
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 CfA)
PROJECT TITLE: Mass Segregation in Dense Cores of Simulated and Observed
Molecular Clouds
Abstract:
Project:
[1] Ridge, N. et al., "The COMPLETE Survey of Star Forming Regions:
Phase 1 Data", 2006, AJ, 131, 2921
INTERN: Bryan Terrazas (Columbia University)
ADVISOR: Dr. Paul Nulsen (HEA Division CfA)
PROJECT TITLE: Particle Leakage and Aging of Radio Lobes
Abstract:
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 CfA)
PROJECT TITLE: Variability of Massive Young Stellar Objects
Abstract:
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.
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.
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.
CO-ADVISOR/MENTOR: Dr. Malgorzata Sobolewska (HEA Division CfA)
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.
CO-ADVISOR/MENTOR: Dr. Andrew Goulding (HEA Division CfA)
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.
CO-ADVISOR: Dr. Stella Offner (TA Division CfA)
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.
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.
[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
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.
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.