0 Assigned ID: 379 ----- Attempting Submission 1 (Fri Mar 06 03:17:53 GMT 2020) ----- We propose a project to identify and analyze archival HST imaging of ~200 ultra-luminous X-ray source (ULX) candidates out to intermediate redshifts (z~0.25). ULXs are luminous (LX>10^39 erg/s), off-nuclear X-ray sources in galaxies, and at intermediate redshifts they are expected to contribute significantly to the cosmic X-ray background. They are also unique laboratories for studying the physics of super-Eddington accretion or accretion onto massive stars and stellar remnants. Some ULXs may also represent accretion onto intermediate-mass black holes (IMBHs) that have been deposited into the host galaxy following a merger and may be the seed masses of supermassive black holes. HST is the only observational resource with the imaging resolution and sensitivity to detect intermediate redshift ULX stellar counterparts and to resolve their galactic environments. This project will yield the largest sample of ULXs out to intermediate redshifts studied with HST, and we will use it to conduct four tests designed to elucidate their nature: A) test for likely contaminants (background or foreground sources) based on association with external galaxies; B) test the stellar mass origin or IMBH scenarios by measuring stellar counterpart masses or upper limits; C) test if the ULXs reside in galaxies with enhanced star-formation rates; and D) test if the ULXs reside in locally star-forming environments. The results of these tests will enable, for the first time, a comprehensive view of how ULX properties evolve out to intermediate redshifts. The archival approach of this project will eliminate the burden on HST time while maximizing its contribution to the science of ULXs. PI Barrows: Dr. Scott Barrows has significant experience working with multi-wavelength data of spatially offset X-ray sources (offset AGN, ultra-luminous X-ray sources, and hyper-luminous X-ray sources), including NIR and optical imaging, both of which will be analyzed in this project. PI Barrows also has extensive experience modeling and analyzing the morphologies of galaxies imaged by HST, which will be the primary component of this project. PI Barrows will be responsible for the overall direction and success of the project. PI Barrows will be responsible for completing all analysis steps. This consists of assembling the dataset of HST imaging, the image modeling, and the overall scientific analysis. Co-I Comerford: Prof. Julia Comerford is an expert on studies of galaxy evolution and galaxy properties, both of which are vital to understanding the environments of ULX candidates. Dr. Comerford also has significant experience working with HST imaging of galaxies. Co-I Comerford will assist in the overall direction of the project, and in the analysis and interpretation of the results. Co-I Prato: Dr. Lisa Prato is an expert on observational and theoretical properties of young stars, including the physics of stellar accretion which is a key scientific component of this project. Co-I Prato will assist in the overall direction of the project, and in the analysis and interpretation of the results. Co-I Llama: Dr. Joe Llama is an expert on multi-wavelength observations of stars, including the optical, UV, and X-ray properties of stars pertinent to this project. Co-I Llama will assist in the overall direction of the project, and in the analysis and interpretation of the results. PI Barrows and Co-I Comerford have institutional access (through CU Boulder) to the Apache Point Observatory 3.5m telescope. This will be the facility used to obtain the spectroscopic redshifts of the sample created through this project. Stellar Populations and the Interstellar Medium Stellar Physics and Stellar Types 0 Regular false false false false false SUPPORTED