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List of
colloquium talks given during the summer of 2014
Links to:
Program of the SAO Summer Intern Symposium, August 13, 2014
2014 Summer Program Calendars for June
, July
, and August
Abstracts for posters presented at the January 2015
AAS Meeting
INTERN: Kirsten Blancato (Wellesley College)
ADVISOR: Igor Chilingarian ( OIR Division CfA)
PROJECT TITLE: Search of Massive Compact Galaxies at Intermediate
Redshifts Using Archival Data from the DEEP2 Survey
Abstract:
Here we propose to bridge the gap between low and high redshifts by
searching for massive compact galaxies in a unique dataset that
consists of high-quality intermediate resolution spectra of
intermediate redshift galaxies (z=0.5-1.1) obtained with the DEIMOS
spectrograph (Keck) as part of the DEEP2 survey. These spectra are
complemented by photometric data obtained with the Hubble Space
Telescope covering a substantial fraction of the DEEP2 survey
footprint and integrated photometry in the optical and near-infrared
bands from ground-based surveys. DEEP2 spectra are now being analyzed
by a group of 3 undergraduate students at the Moscow State University
(advised by I.C.) who will produce by the end of April, 2014 an input
catalogue including measurements of stellar velocity dispersions, mean
ages and metallicities of a few thousands of galaxies from DEEP2
(high signal-to-noise ratio subsample). The preliminary analysis
already showed a couple of dozens of very high velocity dispersion
galaxies to be present in the sample.
For the SAO 2014 student internship program we propose to: (1) select
galaxies having high internal velocity dispersions and no signs of
strong ongoing star formation from the input catalogue; (2) analyze
archival HST images along with the multi-wavelength integrated
photometry for these candidates in order to derive structural
parameters and precise stellar masses using existing software
tools; (3) compare the obtained sample with low- and high-redshift
counterparts and possibly develop the evolutionary scenario for
these objects within the current paradigm of galaxy formation.
INTERN: Christopher Cappiello (Yale University )
ADVISOR: Dr. Paul Nulsen ( HEA Division CfA)
PROJECT TITLE: The Mechanisms of Radio Mode Feedback
Abstract:
The most massive black holes reside in the most massive galaxies,
which are found at the centers of galaxy clusters, surrounded by an
extensive hot, X-ray emitting atmosphere. They often host radio AGN.
Although these galaxies are generally "red and dead," cold gas and
young stars are found in a significant number of of them. In the
radio mode feedback cycle, this gas must have cooled out of the hot
atmospheres. However, although the hot gas emits easily enough
radiation to cool, its energy loss is balanced by the AGN feedback, so
that getting the hot gas to cool to low temperatures requires an
instability. If the gas is turbulent and its viscosity is low enough,
it can be unstable. Furthermore, this instability can account for
cool gas seen in some recent observations. The first project would be
to test a sample of galaxy clusters to see if this mechanism can
explain why some have cold gas, while others do not. It would involve
analysis of X-ray data to determine gas density and temperature
profiles, then using those to test whether or not the gas is thermally
unstable.
Spherical gas flow onto a compact mass, such as a black hole, is
called Bondi flow and this model is used widely to estimate the rate
at which hot gas is accreted by supermassive black holes. However, a
gas can only act as a fluid if the collisional mean free path of the
gas particles is small compared to any scale on which the flow
properties vary. This condition always fails for Bondi flow in the
systems of interest here, causing it to grossly overestimate actual
accretion rates. The second project would be to construct a
theoretical model for spherical accretion flow when the particle mean
free paths are large. In that case, it can shown that a significant
power must emerge outward from the accretion flow and so can play an
important role in the feedback cycle. The main task would be to make
a numerical model of this flow, which involves solving the
Fokker-Planck equation. Solving this problem will provide a much
better estimate of the accretion rate in spherical flows and an
estimate of the power that emerges from the flow, both significant
elements of the feedback cycle.
ADVISOR: Dr. Paul Green (HEA Division CfA)
PROJECT TITLE: Characterizing Celestial Variables with the Time
Domain Spectroscopic Survey
Abstract:
ADVISOR: Dr. Joe Hora (OIR Division CfA)
PROJECT TITLE: A Proper-Motion Search for Galactic Brown Dwarfs
Abstract:
Starting in 2004, the InfraRed Array Camera (IRAC) has surveyed a 10
square degree field in Bootes four times at 3.6, 4.5, 5.8, and
8.0 micron. In January, we were given the green light for a fifth visit
to cover the field with IRAC's two still-operable arrays,
at 3.6 and 4.5 micron. Those observations have been schedule and
will be completed by the end of April. What this means is that we have
four, and soon will have five, independent surveys of this field over
a time interval of 10 years. This will enable an unprecedented
proper-motion survey: by locating sources in the first and last
epochs, and then measuring their apparent motion, we can identify
nearby sources otherwise masquerading as distant galaxies. This is
the so-called 'statistical parallax' method, not to be confused with
trigonometric parallax.
Apart from the purely technical advantages of the project, this
undertaking is interesting because the line of sight through this
10 square deg field of Bootes intersects the Milky Way halo. Which
means that the project holds the possibility of identifying the elusive
(faint) brown dwarfs that might be part of the thin disk stellar
population, or the slightly puffier thick disk, or even the halo.
From relative brightness in the two IRAC bands it ought to be
possible to determine which *type* of brown dwarfs are seen. The
coolest and faintest ones ought to be detectable in at least the thin
disk if not the thick disk also.
The student will use archival and planned near-infrared imaging data
from the Spitzer Space Telescope to identify candidate brown dwarfs in
the nearby Milky Way. Specifically, the student will analyze maps of
a 10 square degree field in Bootes that Spitzer imaged with the InfraRed Array
Camera (IRAC) in 2004, 2007, 2008, and 2014 at wavelengths of 3.6
and 4.5 microns. These bands are extremely sensitive to the radiation
from relatively cool, so-called 'failed' stars known as brown dwarfs.
The student will create multi-epoch catalogs and search for moving
sources using the positions measured at each epoch for the millions of
objects seen in the field. Once candidates have been identified, the
student will use other archival data to eliminate imposters and to
'type' the sources that pass identity checks.
ADVISOR: Dr. Guillermo Torres (SSP Division CfA)
PROJECT TITLE: Physical Properties of Low Mass Stars: Testing Models of
Stellar Evolution
Abstract:
The work will involve analyzing high-resolution spectra to determine
the radial velocities of both components of the binary, as well as
the elements of the spectroscopic orbit. This will use sophisticated
two-dimensional cross-correlation techniques. The project will also
require the student to analyze the light curve of the eclipsing binary
(already in hand) with specialized software to derive the geometric
properties of the system, necessary to compute the sizes of the stars
and other characteristics.
ADVISOR: Dr. Suzanne Romaine (HEA Division CfA)
PROJECT TITLE: X-ray optics
Abstract:
The intern will participate in developing and modelling Wolter-I
telescopes for these applications. There is opportunity to be involved
in both modelling/simulations and/or to work with us in the
laboratory on the development and data analysis of these optics.
ADVISOR: Dr. Howard A. Smith (OIR Division CfA)
PROJECT TITLE: Evolving Physical Processes in Late-Stage Interacting
Galaxies as Revealed through Mid-IR Photometry, Spectroscopy, and
Galaxy Simulations
Abstract:
The REU student would work with our group to focus on the mid-infrared
properties of a set of about 40 colliding galaxies in the late stages
of their merger, when the nuclei are closer together in projection
than about one galaxy diameter, and which show tidal distortions.
The basic goal is to determine the relative importance of star
formation versus AGN activity as a function of late-stage merger
details. Late stage mergers are in particular also the sources of
ultra and hyper-luminous galaxies, and a better understanding this
stage will lead to a much enhanced understanding of ultra-luminous
objects in the early universe.
The student would have three related activities: (1) compile and
analyze Spitzer photometric and spectroscopic data from the archival
materials; (2) model these results (with other bands when possible)
using conventional modeling photometric and spectroscopic algorithms
to extract star formation and other key parameters; (3) do a similar
analysis on simulated galaxy interactions to identify and interpolate
intermediate stages of activity not seen in the observations. The
combined work will be a coherent project of its own, and mesh with
the larger program investigating early stage and post- merger systems
(versus late stage systems) and the wider bands from UV to FIR, to
fill in the key gaps.
Our recent graduate Lauranne Lanz completed a multi-band analyses
(UV to FIR ) of set of 31 galaxies in 14 merger groups, quantifying
star formation rates, dust masses and temperatures, and contributions
from black-hole nuclei. We have compared these results with a set of
simulated galaxy interactions to verify and test the models, and shown
for example that star formation rates based solely on luminosity can
be significantly in error. In a third line of research, we have begun
a systematic probe of the mid-infrared band spectra and photometry.
Using a Bayesian analysis of modeled ionized gas in star formation
(HII regions) and nuclear (AGN) activity, we have shown that the
progress of star formation can be measured using this mid-IR band
to compute the compactness of the hot gas, and done so in both
observed and simulated systems.
ADVISOR: Dr. Matthew Ashby (OIR Division CfA)
PROJECT TITLE: Very Distant Galaxies Detected in the HST and
Spitzer-CANDELS Survey
Abstract:
The student will use a combination of HST/WFC3 and Spitzer/IRAC
imaging of up to five extragalactic fields to identify candidate
distant galaxies. In a nutshell, this is a search for
galaxies on the very edge of the known cosmos. Candidates will
be identified on the basis of their colors and morphologies, with a
particular emphasis on the 3.6 and 4.5 micron bands to
which Spitzer's IRAC instrument is sensitive. The student will
also investigate the data with other tools, e.g., the two-point
correlation function to examine galaxy clustering behavior.
ADVISOR: Dr. Hans Moritz Guenther (HEA Division CfA)
PROJECT TITLE: X-ray Coronal Cycles in Solar to Late Type Stars in
the Chandra Deep Field South
Abstract:
ADVISOR: Dr. Cara Battersby (RG Division CfA)
PROJECT TITLE: The Bones of the Milky Way
Abstract:
The student will work with large surveys (radio-IR) of the the Milky
Way to perform one of the first searches for the "Bones of the Milky
Way." These surveys will then be used to determine basic physical
properties of the filaments, as well as studying their kinematics.
The "Bones of the Milky Way" and their properties can then be compared
with those in nearby galaxies or with star-forming activity in their
vicinity.
ADVISOR: Dr. Christine Jones (HEA Division CfA)
PROJECT TITLE: Chandra X-ray Observations of Planck Clusters
Abstract:
In this project the student will analyze Chandra observations of the
luminous, nearby Planck-detected cluster RXC J0528.9-3927
that is forming from two merging sub-clusters. The student will use surface
brightness images to identify features of interest related to the
merger, and perform imaging and spectral analyses to measure the
density, temperature, pressure and entropy in/across these
features. The student will use these data to determine the masses,
luminosities, and velocities of the sub-clusters, constrain the stage
and orbital parameters of the merger, and model the hydrodynamic state
of the diffuse cluster gas.
CO-ADVISORS/MENTORS: Dr. Ivana Damjanov, Dr. Sean Moran (OIR Division CfA)
Massive compact quiescent galaxies (a.k.a. "red nuggets") were
discovered about a decade ago at high redshifts (z ~ 1.5-2) in
high-resolution images obtained by the Hubble Space Telescope and
since then attracted a lot of attention. These systems, characterized
by a lack of ongoing star formation, regular morphology, small extent
on the sky, and high stellar velocity dispersions (suggesting
extremely high stellar densities), looked to be a unique class of
a galaxy observed only at high redshifts and having no low redshift
counterparts. Numerous scenarios were proposed to explain how they can
be transformed into galaxies observed in the local Universe. Recently,
we discovered a number of "red nuggets" at low redshifts by analysing
the archival spectral data from the Sloan Digital Sky Survey and
Hubble Space Telescope images (Damjanov et al. 2013 ApJL 775 L48),
that suggested that representatives of this galaxy class exist at low
redshifts as well.
An extragalactic radio source is formed when the supermassive black
hole in the nucleus of a galaxy undergoes an outburst, dumping energy
into surrounding gas through a pair of opposed jets. Outbursts like
this from "active galactic nuclei" (AGN) have significant impacts. By
stirring and heating the gas, they can reduce the rate at which it
cools and forms new stars. They can also reduce the supply of gas that
power future outbursts, creating a feedback cycle between AGN activity
and gas cooling. There is a strong case that this "radio mode AGN
feedback" is what suppresses star formation almost completely in the
most massive galaxies, keeping them "red and dead." Despite its
importance for galaxy formation, we do not understand how the radio
mode feedback cycle works. Here we offer two possible projects aimed
at understanding how the gas cools and feeds the AGN in the feedback
cycle. The choice of project will depend on the interests of the
student.
INTERN: Virginia Cunningham (West Virginia University)
CO-ADVISOR/MENTOR: Dr. Eric Morganson (HEA Division CfA)
Our Time Domain Spectroscopic Survey (TDSS)
of 100,000 variables is just starting, and the sky is our oyster,
or, umm, playground. TDSS will analyze SDSS/BOSS spectra of variable
point sources detected in the PanSTARRS
survey to characterize the strongest celestial variables across 7500
square degrees of sky, over 6 years beginning in 2014.
The student will participate in visual inspection, classification, and
measurement of spectra of variable objects from brown dwarfs to
quasars. We will build up the statistics of our sample, contrast the
efficacy of variability/color/X-ray target selection techniques,
and in all probability encounter several extreme or unusual objects
worthy of anecdotal publication.
INTERN: Zequn Li (Swarthmore College )
CO-ADVISOR: Dr. Matthew Ashby (OIR Division CfA)
Brown dwarfs are the so-called 'failed' stars that, because of their
low masses, never initiated hydrogen fusion and are therefore
relatively cool and underluminous, compared to ordinary stars.
They are best observed in the infrared, and new infrared instruments
are making it possible to understand for the first time some of the
basic facts about these objects: that they are abundant, that there
are distinct classes with different traits, and moreover that new
ypes are being discovered often.
INTERN: Allison Matthews (Lafayette College )
The goal of the project is to derive accurate parameters for the
components of an eclipsing binary (masses, radii, temperatures,
luminosities, etc.) for the purpose of testing predictions from models
of how low-mass stars evolve. These models have shown some
disagreements with observations for similar stars, which are still not
well understood but may have something to do with stellar activity and
magnetic fields. One possible target for study is the eclipsing binary
V530 Ori, for which the stellar parameters have never been determined before.
INTERN: Nicole Melso (Penn State University )
CO-ADVISOR/MENTOR: Dr. Jaesub Hong (HEA Division CfA
We are involved in developing light weight X-ray optics for several
applications including optics for future X-ray astronomy missions and
also optics for X-ray observations of planetary objects.
The optics for these two applications are similar, but involve quite
different specifications to meet the demands of the specific missions.
INTERN: Lee Rosenthal (Haverford College )
CO-ADVISORS/MENTORS: Matt Ashby (OIR Division CfA), Andreas Zezas (HEA
Division CfA ), Rafael Martinez-Galarza, Lauranne Lanz, Chris Hayward,
Chao-Ling Hung (OIR and HEA Divisions CfA)
Mergers and interactions have profound effects on the evolution of
galaxies and on the various physical processes associated with star
formation and the fueling of active nuclei (AGN). There remains,
however, an incomplete understanding of how interactions affect such
processes or how important they are in controlling the appearance of
today's universe.
INTERN: Peter Senchyna (Washington University )
CO-ADVISOR/MENTOR: Dr. Joe Hora (OIR Division CfA)
The Spitzer Space Telescope recently completed the Spitzer Extended
Deep Survey (SEDS; Ashby et al 2013). SEDS made use of the
largest-ever allocation of Spitzer observing time to cover five small
extragalactic fields to unprecedented depths. The idea was to detect
the most distant galaxies in infrared light with Spitzer's Infrared
Array Camera (IRAC). Two aspects of SEDS make it unique. First, it
is among the deepest surveys ever carried out in the infrared, so it
will pick up the faintest, most distant galaxies -- and indeed,
publications describing SEDS detections of distant galaxies are
starting to appear in the literature. Second, SEDS uses infrared
light to detect these distant objects in their rest-frame visible
light -- making it possible to estimate their masses. This is a
significant opportunity to better understand how galaxies form in the
early Universe.
INTERN: Maurice Wilson (Embry-Riddle Aeronautical University )
CO-ADVISOR/MENTOR: Katie Auchettl (HEA Division CfA)
The aim of this proposal is to identify long-term X-ray coronal cycles
in low-activity old-disk starsin the Chandra Deep Field South. The
unprecedented depth and long baseline of the observations will allow
both short- and long-term variations in the coronal X-ray emission of solar-
and late-type stars to be studied, allowing analogues of the 11 year
solar cycle to be identified.Long-term X-ray variations have been identified
in only five stars other than the Sun, and only two of those show
clear cyclic behavior. This proposal can greatly increase this number,
producing a significant sample of main-sequence stars with identified
X-ray activity cycles. This will provide important constraints on the form of
stellar dynamos and the level and variability of stellar activity,
which is important for theories of the evolution of planetary systems
and the X-ray variability of the Sun over time.
INTERN: Catherine Zucker (University of Virginia)
CO-ADVISOR: Professor Alyssa Goodman (RG Division CfA)
We are searching for a summer intern to investigate the role of
massive filamentary gas clouds in the Milky Way. The "Bones of
the Milky Way" may have an important dynamic role in the formation
of massive star clusters throughout our Galaxy. Such objects have
only recently been discovered through large-scale surveys and their
physical properties and dynamics have yet to be uncovered. How many
are there and what are their properties? How do they form and what
is their role in the star formation process? Are there large-scale
flows of material onto the filaments?
INTERN: Zhoujian Zhang (Nanjing University)
CO-ADVISOR: Dr. Marie Machacek (HEA Division CfA)
Galaxy clusters are the most massive, virialized structures known.
Their evolution across cosmic time places significant constraints on
the nature of dark matter and dark energy. In the current hierarchical
cosmological models massive galaxy clusters grow through mergers
between less massive sub-clusters and galaxy groups. Signatures of
these interactions, i.e. merger and sloshing cold fronts, shocks,
extended tails and sweeping spirals in temperature, density and
entropy, are imprinted on the hot X-ray emitting gas (ICM) that
dominates the clusters' baryon distributions. Simulations show
these X-ray signatures are often long lasting on the order of
gigayears. Deep, high spatial resolution X-ray observations of
luminous galaxy clusters taken with the Chandra X-ray Observatory
provide an ideal laboratory to probe how clusters grow, and how
mergers affect the measured properties of the cluster and the ICM.