2014

Links to:

    List of colloquium talks given during the summer of 2014 
    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) 
CO-ADVISORS/MENTORS: Dr. Ivana Damjanov, Dr. Sean Moran (OIR Division)

PROJECT TITLE: Search of Massive Compact Galaxies at Intermediate Redshifts Using Archival Data from the DEEP2 Survey

Abstract: 
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.

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)

PROJECT TITLE: The Mechanisms of Radio Mode Feedback

Abstract: 
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.

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) 
CO-ADVISOR/MENTOR: Dr. Eric Morganson (HEA Division)

PROJECT TITLE: Characterizing Celestial Variables with the Time Domain Spectroscopic Survey

Abstract: 
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.

ADVISOR: Dr. Joe Hora (OIR Division) 
CO-ADVISOR: Dr. Matthew Ashby (OIR Division)

PROJECT TITLE: A Proper-Motion Search for Galactic Brown Dwarfs

Abstract: 
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.

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)

PROJECT TITLE: Physical Properties of Low Mass Stars: Testing Models of Stellar Evolution

Abstract: 
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.

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) 
CO-ADVISOR/MENTOR: Dr. Jaesub Hong (HEA Division

PROJECT TITLE: X-ray optics

Abstract: 
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.

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) 
CO-ADVISORS/MENTORS: Matt Ashby (OIR Division), Andreas Zezas (HEA Division ), Rafael Martinez-Galarza, Lauranne Lanz, Chris Hayward, Chao-Ling Hung (OIR and HEA Divisions CfA)

PROJECT TITLE: Evolving Physical Processes in Late-Stage Interacting Galaxies as Revealed through Mid-IR Photometry, Spectroscopy, and Galaxy Simulations

Abstract: 
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.

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) 
CO-ADVISOR/MENTOR: Dr. Joe Hora (OIR Division)

PROJECT TITLE: Very Distant Galaxies Detected in the HST and Spitzer-CANDELS Survey

Abstract: 
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.

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) 
CO-ADVISOR/MENTOR: Katie Auchettl (HEA Division)

PROJECT TITLE: X-ray Coronal Cycles in Solar to Late Type Stars in the Chandra Deep Field South

Abstract: 
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.

ADVISOR: Dr. Cara Battersby (RG Division) 
CO-ADVISOR: Professor Alyssa Goodman (RG Division)

PROJECT TITLE: The Bones of the Milky Way

Abstract: 
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?

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) 
CO-ADVISOR: Dr. Marie Machacek (HEA Division)

PROJECT TITLE: Chandra X-ray Observations of Planck Clusters

Abstract: 
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.

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.