2022 Research Projects
Microlensing Parallax for Exoplanets Towards the Bulge
Advisor: S. Calchi Novati
The Spitzer team, in part based at IPAC, is leading a microlensing observational campaign towards the Galactic Bulge following up microlensing events alerted by ground-based surveys. The key feature of this project is the possibility to measure the microlensing parallax thanks to the simultaneous observation of the same microlensing event from two distant (d > 1.5 au) observers (from Earth and from Spitzer). The main scientific driver of the project is to build the Galactic distribution of exoplanets (Calchi Novati et al, 2015a, Zhu et al 2017). Besides six exoplanets (Udalski et al 2015, Street et al 2016, Shvartzvald et al 2017, Ryu et al 2018, Calchi Novati et al 2018 and 2019), several additional interesting events (binary systems, high magnification events, single lens with finite source effects) have also been analyzed based on the first five years (2014-2018) of data, with the sixth season in 2019 expected to be the last one. In addition, relevant work is being done for the analysis of the data (Calchi Novati et al 2015b) and to assess the statistical meaning of the observations (Yee et al 2015b, Zhu et al 2015b). In this framework there are several avenues to pursue, according to the applicant's interests and previous experience: optimizing the photometry of Spitzer data; characterization of microlensing events; evaluation of the detection efficiency.
Prior experience with microlensing is preferred but not required.
Shocked Gas in Compact Groups in the Local Universe
Advisor: Phil Appleton
Understanding the evolution of star formation rates and gas content of galaxies in dense group environments may be important for explaining how massive galaxies are forged over cosmic time. We will study a small sample of Hickson Compact Groups, where galaxies are rapidly evolving through close collisional passes and mergers. We will concentrate on three galaxy groups for which XMM data has been taken (in collaboration with Ewan O’Sullivan at CfA) which shows extended X-ray emission which may be shock excited. We will compare these observations with extensive multi-wavelength data using optical IFUs (diffuse ionized gas), CARMA (cool molecular gas), as well as Herschel and Spitzer (warm neutral gas). This will allow us to explore the multi-phase nature of the gas in these systems, including the shocked IGM. The physical properties of these galaxies will be explored to try to understand how the shocks and turbulence may be influencing their evolution through tidal and collisional heating, gas stripping and eventual merger.
Measuring Accurate Distances to Stellar Streams
Advisor: Carl Grillmair
Our Milky Way Galaxy is enveloped by a network of stellar streams, the presumed remnants of old globular clusters and dwarf galaxies. These streams provide us with potentially powerful new tools for measuring the mass and shape of the Galaxy, as well as the makeup and distribution of dark matter. However, distance estimates to these streams remain one of the largest sources of uncertainty. We have recently obtained Spitzer IRAC time series images of RR Lyra stars found in a number of dynamically cold streams. One objective of this project would be to measure accurate mean infrared magnitudes for these stars and, by using the remarkably tight IR period-luminosity relation for RR Lyrae, to measure stream distances to better than 2%. The goal would be to publish these results towards by end of the fellowship. A second component of this project would be to analyze existing optical spectra of RR Lyrae taken at the Palomar 200 inch telescope. By measuring their radial velocities we can establish whether or not these RR Lyrae are physically associated with known streams. Stream members confirmed in this way will become part of a new target list for future infrared imaging and precise distance estimation.
NEOWISE Light Curves
Advisors: Jessica Krick, Vandana Desai, Dave Shupe
The combined WISE, NEOWISE, and NEOWISE Reactivation catalog is a rich, multiyear, near infrared dataset with which to study variable objects of all varieties from asteroids to stars to AGN. This dataset is important for many fields including galactic structure, cosmological distance scale through the study of cepheids & RR Lyrae, stellar evolution studies, measuring interstellar extinction, and AGN variability to understand the central regions of these sources. We employ the new science platform at the NASA/IPAC Infrared Science Archive (IRSA) to wield the power of machine learning on this very large dataset to a) crossmatch sources with Gaia, b) find these variable objects in the catalog, and c) classify them into groups. The catalog has almost 2 billion sources with light curves from over 130 billion individual detections. Come to IPAC to help us mine this newly formed, classified, light curve database in any field of study! We want you to give you the opportunity to do *your* science with one of the largest currently available infrared datasets. If interested, the successful candidate would also have the opportunity to explore and compare different light curve classification techniques on this very big dataset.
Building Big Mosaics of the Sky: Studying the Low Surface Brightness Universe with TESS, and more!
Advisor: Bruce Berriman
The images delivered by the Transiting Exoplanet Sky Survey (TESS) offer a unique opportunity probe the low surface brightness Universe, primarily due to the exceptionally deep coverage at the ecliptic poles that is most likely limited only by zodiacal light. Thus, TESS images will enable studies such as derivation of the halo profiles mass of nearby galaxies, tests of Lambda-CDM galaxy formation scenarios, derivation of stellar halo fractions for different mass and morphology galaxies and identification of local stellar streams that cross over sectors and other galaxy cannibalism leftovers. The student will join a small team of scientists and computer scientists analyzing the TESS images to address the science cases just described. The work will have a substantial technological component, and will involve using the Montage image mosaic engine to create analysis-ready mosaics of the sky as observed by TESS, and to understand the impact of background radiation on the science content of the images. The work will very likely provide the opportunity to perform computations on the Amazon Elastic Cloud. In addition, the student will have the opportunity to create images delivered by TESS (and other missions) for consumption by the World Wide Telescope, an immersive E/PO environment used world wide.
Probing the Atmospheres of the HotTESSt Jupiters
Advisor: Jessie Christiansen
The discovery of the first exoplanets completely changed our views of how planets form, specifically Jupiter-sized planets orbiting very close to their host star. Signs of the history and evolution of these planets are trapped in the chemical composition of the planetary atmospheres. For planets that form farther out and migrate in, we expect the amount of refractory material to be lower than the stellar abundance, but if the planet formed closer in, we might expect the refractory abundances to be higher than the stellar values. However, even in our own Solar System, it is not clear how the giant planets formed and acquired their abundances. Our team is conducting a large survey program with the SOAR Telescope to obtain optical (~380-680 nm) transmission spectra of ~20 hot Jupiters above 1700 K which were observed or discovered by TESS in order to constrain atmospheric oxygen and metal abundance through measurement of titanium oxide, vanadium oxide, and sodium features. A visiting graduate student fellow will work with our team to refine our data processing pipeline, combine our new data with archival photometric and spectroscopic measurements, and constrain atmospheric properties (e.g. abundances, Rayleigh scattering, clouds/hazes) of these hot Jupiters via atmospheric retrievals. Familiarity with Python is strongly recommended.
A Spitzer-based Companion Search around the Nearest Stars
Advisors: J. Davy Kirkpatrick, Chris Gelino, Federico Marocco
One complication in accurately determining the single-object mass function at the lowest stellar masses is knowing the extent to which higher mass stars have lower mass companions of their own. Specifically, within a 20-pc radius around the Sun there are ~550 solivagant L, T and Y dwarfs known, but there are roughly 2,500 K and M dwarfs. If only a relatively small fraction of these K and M stars have faint companions, those companions could add appreciably to the sum of L, T, and Y dwarfs within the volume and therefore impact significantly on our understanding of the low-mass end of the mass function.
Data from the Infrared Array Camera (IRAC) in the Spitzer Heritage Archive (SHA) afford an exciting opportunity to look for widely separated faint companions around the Sun's closest neighbors, using both the 3.6-4.5 micron colors and, for fields with good epochal coverage, common proper motions. This will be the first opportunity to search through the *entirety* of the SHA for companions, as all Spitzer data are now beyond their proprietary periods. Fields to be searched will include not only those from programs specifically targeting the host star, but also fields observed serendipitously around the 0.1-pc tidal radius for any of those potential hosts. Note that Spitzer data complement Gaia data because these coldest companions are not observable at the shorter wavelengths of Gaia.
All three mentors have extensive experience with Spitzer data. Our plan is to have the student spend the Fellowship examining data in the SHA for previously hidden companions, while placing constraints on the percentage of the 0.1-pc physical radius covered by the data and the depths to which low-mass companions could be found. The student will start with those stars closest to the Sun and proceed outward in distance until the two-thirds point in the Fellowship is reached (with a stretch goal of completing the work for the entire 20-pc sample). In the final third of the Fellowship, the student will begin writing, as lead author, a publishable paper summarizing the results over that completed search volume.
Characterizing High-Redshift Galaxies with ALPINE
Advisor: Andreas Faisst
The ALPINE project is a 70h large ALMA program aimed at characterizing the far infrared (FIR) and [CII] (158um) properties of 4<z<6 galaxies. We seek students to work on combining the extensive existing multi-wavelength imaging and spectroscopy with the ALMA data to conduct a range of studies. A possible project could focus on studying the internal dust attenuation distribution and external environment of some of these galaxies by using newly acquired data from the Hubble Space Telescope (some technical tasks would include extraction of kpc-resolved photometry and photometric redshift fitting). The findings can then be related to the evolution of galaxies on the z ~ 5 main sequence and their far-infrared and [CII] properties and dynamics. The student would have access to all ALPINE data and ideas for other projects are welcome.
Title: CLU: A Galaxy Survey as Part of the Search for Gravitational Waves
Advisor: David Cook
The Census of the Local Universe (CLU) is a survey that aims to find new galaxies in the nearby Universe (out to a distance of 200~Mpc; z~0.05). We utilize four wavelength-adjacent narrow-band filters to search for Halpha emission-line sources across 3pi (~26,470 deg^2) of the sky; roughly the footprint of Pan-STARRS. A preliminary analysis of the data has yielded thousands of nearby galaxy candidates that are being used to augment lists of known galaxy inside the LIGO/Virgo gravitational waves (GW) sensitivity distance limit (See paper: https://ui.adsabs.harvard.edu/abs/2019ApJ...880....7C/abstract). However, we expect find many 10s of thousands more with refinements to the data processing and analysis. These additional candidates will increase the completeness of galaxies in the local volume and further narrow down the search for counterparts to GW events.
The prospective student's main focus in the project would be to devise and implement an "uber" photometric calibration of the 4 narrow-band filters. However, there are many opportunities to be involved in several aspects of the project including: galaxy finding algorithms, applying photo-z methods (both SED fitting and machine learning) to test distance estimates, vetting galaxy candidates, interacting with a large GW follow-up group here at Caltech/IPAC, analysis of extreme local star-forming galaxies (blue compact dwarfs and green peas), and getting first-hand observing experience at Palomar Observatory. We are looking for a student with experience in data reduction and calibration; python and PSQL/SQL data languages are a plus.
Challenging Planet Formation Theories with the Lowest Metallicity TESS Targets
Advisor: Jessie Christiansen
Previous studies of exoplanet demographics have shown that planet occurrence rates depend on the bulk metallicity of the host star. This is a natural outcome of the core accretion model of planet formation. This model also predicts that below a certain protoplanetary disk metallicity, the surface density of solid material is too low to form planets. Due to the target selection process of previous large surveys, the lower metallicity bound probed by the results in the literature ([Fe/H] ~ -0.5) is still higher than that predicted to be too low to support planet formation ([Fe/H] < -1). Our team received a Director’s Discretionary Time allocation on the NASA TESS mission to observe several thousand of the brightest, lowest metallicity ([Fe/H] < -1) stars in the sky at high cadence, in order to provide a fundamental observational test of these theoretical predictions. A visiting graduate student fellow would be expected to examine this sample for planet candidates, using code that the team has already developed and tested on TESS data. Any confirmed planets from the sample would already challenge existing models, and a null result would produce strong upper limits. The fellow would gain experience in planet detection and characterization, as well as occurrence rate modeling using Bayesian methods.
Decoding the Galaxy Population Space with Variational Autoencoders
Advisor: Shoubaneh Hemmati
Galaxies are studied through their images at a range of wavelengths. The higher the spatial and spectral resolution, wavelength coverage, and depth of these images, the more information they entail. Galaxy surveys have been pushing in one or more of these avenues to improve the characterization of galaxies. Given the wealth of the galaxy data today and advancements in image processing with deep learning, further improvements can come about using data-driven approaches. We will explore the extent of spatial/spectral resolution boosting and denoising of images for future large galaxy surveys (e.g., by LSST, Roman, Euclid, SPHEREx) by training autoencoders on existing CANDELS data. We will quantify the gain in the estimation of various physical properties given the enhanced data products.
Determination of the Galactic metallicity with Herschel/PACS and SPIRE spectroscopic measurements
Advisor: Roberta Paladini
The metallicity of gas and stars is one of the most powerful tools to distinguish among galaxy evolutionary scenarios, as metals are the results of the cumulative star-formation activity of a galaxy and of its gas inflow/outflow history. The gas metallicity is in most cases much easier to measure than stellar metallicity, and the most favorable environment where to perform this kind of measurement is the interior of HII regions, i.e. ionized pockets of material surrounding massive OB stars, which are largely understood and tested.
The tool commonly used to estimate gas metallicity is atomic fine-structure emission lines radiated by various ions on various excitation levels. In particular, the use of mid-infrared to sub-millimeter emission lines allows one to overcome the extinction problem that plagues optical measurements.
In this project, we propose to use Herschel PACS and SPIRE spectroscopic data for a sample of Galactic HII regions in order to determine the Galactic gas metallicity as well as the HII regions ionization state and its variation as a function of Galactocentric distance. This study will provide the calibration at redshift zero for the metallicity - reshift relation and will inform galactic evolutionary models in view of future space mission such as SPICA.
Looking for Ionizing Photons Escaping from Dwarf Galaxies at High Redshifts
Advisor: Anahita Alavi
The epoch of reionization (EoR) is a crucial benchmark in the history of the universe and a primary science driver for major observing facilities planned for the near future, including JWST and the 30m telescopes. Hundreds of hours of observations have been devoted to understanding when and how EoR occurred. Ionizing radiation (Lyman continuum) from young massive stars in star-forming galaxies is now believed to be the primary source of EoR’s total ionizing budget. However, it is not yet known which type of galaxy these stars belong to. These Lyman continuum photons must escape absorption within the interstellar medium and reach the intergalactic medium. Recently, studies of UV luminosity functions at high redshifts have revealed that the faint-end is steep, possibly increasing with redshift, indicating that a large number of faint star-forming galaxies (dwarf galaxies) exist at these redshifts. Dwarf galaxies may play a significant role at EoR depending on 1) the intrinsic luminosity they produce and 2) the fraction of this luminosity that escapes. Studies of local dwarf star-forming galaxies indicate that they emit copious amounts of ionizing radiation. Nevertheless, the escape fraction of photons from these objects still needs to be constrained. One powerful way to explore these faint dwarf galaxies is to exploit the magnification of strong gravitational lensing offered by foreground massive clusters.
Our team was granted Hubble Space Telescope time to obtain UV images of six lensing galaxy clusters from the Hubble Frontier Fields survey to search for escaping Lyman Continuum photons from high-redshift dwarf galaxies. A visiting graduate student fellow would be expected to work with these UV HST data and catalogs to identify any possible detection of ionizing radiation from lensed dwarf galaxies. Our team has extensive experience on this topic and can assist the visiting student through a variety of resources including catalogs, ground-based spectroscopic data, as well as analysis tools.
