Alexander Navarre

Alexander Navarre

Scientifically Rigorous Data Scientist & Astrophysics PhD

Posts by Collection

portfolio

publications

The Cosmic Telescope that Lenses the Sunburst Arc, PSZ1 G311.65-18.48: Strong Gravitational Lensing model and Source Plane Analysis

Published in The Astrophysical Journal, 2022

This paper is a gravitational lensing analysis of the galaxy cluster PSZ1 G311.65-18.48. This cluster lenses the one of the brightest-known lensed galaxies: The Sunburst Arc. The Sunburst Arc, as well as 14 additional lensed galaxies in the field, are identified and characterized to constrain the lensing model. Additionally, the paper argues that an unusual clump of light in the Sunburst Arc is not a transient event.

Recommended citation: Sharon, K., Mahler, G., Rivera-Thorsen, T. E., Dahle, H., Gladders, M. D., Bayliss, M. B., Florian, M. K., Kim, K. J., Khullar, G., Mainali, R., Napier, K. A., Navarre, A., Rigby, J. R., Remolina González, J. D., & Sharma, S. (2022). The Cosmic Telescope That Lenses the Sunburst Arc, PSZ1 G311.65-18.48: Strong Gravitational Lensing Model and Source Plane Analysis. \apj, 941(2), e203. https://doi.org/10.3847/1538-4357/ac927a
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Spatial variations in aromatic hydrocarbon emission in a dust-rich galaxy

Published in Nature, 2023

This paper studies Polycyclic Aromatic Hydrocarbons (PAHs): large orangic molecules that trace the dust that regulares interstellar gas cooling. With the launch of JWST, our ability to resolve infrared galaxy features at high redshift (in the early universe) is highly increased. This paper presents spatially-resolved PAH spectral features. It finds order-of-magnitude variations in the PAH feature strength across the galaxy, suggesting either physical offsets in the PAH distribution or wide variations in the local ultraviolet radiatino field.

Recommended citation: Spilker, J. S., Phadke, K. A., Aravena, M., Archipley, M., Bayliss, M. B., Birkin, J. E., Béthermin, M., Burgoyne, J., Cathey, J., Chapman, S. C., Dahle, H., Gonzalez, A. H., Gururajan, G., Hayward, C. C., Hezaveh, Y. D., Hill, R., Hutchison, T. A., Kim, K. J., Kim, S., … Whitaker, K. E. (2023). Spatial variations in aromatic hydrocarbon emission in a dust-rich galaxy. \nat, 618(7966), 708–711. https://doi.org/10.1038/s41586-023-05998-6
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Small Region, Big Impact: Highly Anisotropic Lyman-continuum Escape from a Compact Starburst Region with Extreme Physical Properties

Published in The Astrophysical Journal Letters, 2023

This paper studies a small region of The Sunburst Arc, one of the brightest-known gravitationally-lensed galaxies. The small region uniquely has high Lyman-Continuum (LyC, ionizing radiation) escape: a critical component to understanding star-formation based Reionization models. Spatially resolved analysis characterizes the region as being consistent with approximately “pure” stellar light. This provides evidence for pencil-beam LyC escape: where anisotropic processes “poke” ionized channels through the surrounding gas, letting radiation escape reletively unimpeded.

Recommended citation: Kim, K. J., Bayliss, M. B., Rigby, J. R., Gladders, M. D., Chisholm, J., Sharon, K., Dahle, H., Rivera-Thorsen, T. E., Florian, M. K., Khullar, G., Mahler, G., Mainali, R., Napier, K. A., Navarre, A., Owens, M. R., & Roberson, J. (2023). Small Region, Big Impact: Highly Anisotropic Lyman-continuum Escape from a Compact Starburst Region with Extreme Physical Properties. \apjl, 955(1), eL17. https://doi.org/10.3847/2041-8213/acf0c5
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Resolving Clumpy versus Extended Lyα in Strongly Lensed, High-redshift Lyα Emitters

Published in The Astrophysical Journal, 2024

This paper studies a set of six strongly-lensed Lyman-Alpha emitting galaxies (LAEs) at redshifts ~ 4-5. Through the analysis of Hubble Space Telescope and Spitzer Space Telescope imaging, this paper calculates esimates of the stellar masses, stellar population ages, and amounts of dust. These properties are consistent with young stellar populations that create Lyman-Alpha. Narrowband Lyman-Alpha imaging indicates these galaxies are non-interacting (not merging galaxies). The paper finds two broad camps of Lyman-Alpha spatial distributions, clumpy and extended. A suggestive trend is found in that the youngest stellar populations in the sample are clumpy while the older populations are extended.

Recommended citation: Navarre, A., Khullar, G., Bayliss, M. B., Dahle, H., Florian, M., Gladders, M., Kim, K. J., Owens, M. R., Rigby, J., Roberson, J., Sharon, K., Shibuya, T., & Walker, R. (2024). Resolving Clumpy versus Extended Ly\ensuremathα in Strongly Lensed, High-redshift Ly\ensuremathα Emitters. \apj, 962(2), e175. https://doi.org/10.3847/1538-4357/ad10ad
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TEMPLATES: Characterization of a Merger in the Dusty Lensing SPT0418–47 System

Published in The Astrophysical Journal, 2024

This paper uses JWST and AMLA to characterize the gravitational-lensing system SPT0418-47, which includes a lensed image of a dusty, star-forming galaxy and an associated companion. The calculated physical separations, redshifts, and evidence of tidal features indicate that these galaxies are interacting. Interestingly, the star-formation rates and stellar masses of both galaxies indicate that their interaction has not noticibly elevated the star-formation level.

Recommended citation: Cathey, J., Gonzalez, A. H., Lower, S., Phadke, K. A., Spilker, J., Aravena, M., Bayliss, M., Birkin, J. E., Birrer, S., Chapman, S., Dahle, H., Hayward, C. C., Hezaveh, Y., Hill, R., Hutchison, T. A., Kim, K. J., Mahler, G., Marrone, D. P., Narayanan, D., … Vizgan, D. (2024). TEMPLATES: Characterization of a Merger in the Dusty Lensing SPT0418–47 System. \apj, 967(1), e11. https://doi.org/10.3847/1538-4357/ad33c9
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Connecting Lyα and Ionizing Photon Escape in the Sunburst Arc

Published in The Astrophysical Journal, 2024

This paper is a study of the Lyman-Continuum (LyC) and Lyman-Alpha (Lya) emission of the Sunburst Arc: one of the brightest-known gravitationally-lensed galaxies. Strong correlations are found between the LyC escape fraction and mulitple Lya measures such as peak separation and equivalent width. A possible complex geometry of neutral hydrogen is proposed to explain the differences in the Lya/LyC spectra across the sunburst arc. The study underscores the importance of resolving small physical scales to reliably explain Lya and LyC escape.

Recommended citation: Owens, M. R., Kim, K. J., Bayliss, M. B., Rivera-Thorsen, T. E., Sharon, K., Rigby, J. R., Navarre, A., Florian, M., Gladders, M. D., Burns, J. G., Khullar, G., Chisholm, J., Mahler, G., Dahle, H., Malhas, C. M., Welch, B., Hutchison, T. A., Gassis, R., Choe, S., & Adhikari, P. (2024). Connecting Ly\ensuremathα and Ionizing Photon Escape in the Sunburst Arc. \apj, 977(2), e234. https://doi.org/10.3847/1538-4357/ad9247
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talks

Characterizing Strongly Lensed Lyman-Alpha Emitting Galaxies at z > 4

Published:

Lyman-Alpha emission is a valuable tool for identifying star-forming galaxies, as large quantities are emitted from neutral HII regions around young, massive stars. Lyman-Alpha is Hydrogen’s brightest recombination line, making it an excellent tracer for star formation, as well as being able to precisely identify redshifts. However, Lyman-Alpha is scattered by neutral Hydrogen through non-trivial processes, making spatial measurements difficult to use. While Lyman-Alpha is useful at all redshifts, high redshift Lyman-Alpha Emitters (LAEs) are often too faint and/or have very small angular sizes, making them difficult to study individually. We analyze six strongly gravitationally lensed LAEs at 4.1 < z < 5.2, taking advantage of the magnification to perform a high spatial resolution study of young galaxies in the distant universe. We examine their morphologies in Lyman-Alpha and the UV continuum, and compare them to local universe analogues. Broadband data from Hubble (rest-frame UV) and Spitzer (rest-frame optical) is combined with narrowband data isolating Lyman-Alpha to gain photometric measurements. Additionally, models of the lenses allow creation of source plane images, which are used to measure intrinsic properties of the LAEs such as size and brightness. The LAEs fall into two broad categories: extended Lyman-Alpha emission concentric with the UV continuum, and clumpy Lyman-Alpha emission dispersed among the UV continuum. The bimodality of this sample suggests that LAEs in the distant universe are not a homogeneous class of objects.

teaching

Introductory Mechanics: Discussion

Undergraduate Course, University of Cincinnati, Physics Department, 2018

From August 2018 to January 2020, I was a teaching assistant for multiple introductory physics courses. As part of these courses, students would also have to attend weekly “Discussion Sections” in groups of 20-30, led by a TA (me). I would present the students with problems related to the most recent lecture, and task them to finding the answer in small groups. I would monitor the students and provide help when stuck. Additionally, I would try and build a professional relationship with the students to raise their engagement level with the course. From my own experience, discussion sections with personable and friendly TAs motivated me to remain engaged.

Introductory Mechanics: Lab

Undergraduate Course, University of Cincinnati, Physics Department, 2018

From August 2018 to January 2020, I was a teaching assistant for multiple introductory physics courses. As part of these courses, students would also have to attend weekly laboratory sessions in groups of ~20, led by a TA (me). I would present a physical experiment setup that showcased a principle recently covered in the associated lecture. I would guide the students through the lab worksheets, teaching them proper measuring and recording practices. I also ensured that the students understood the connection between the week’s activity and what was taught in lecture. Three to four times per semester, the lab would require a graded writeup. In addition to teaching the labs, I would teach proper formatting techniques, data visualization techniques, and basic scientific writing. Once graded, I would also provide class-wide feedback.

Introductory Mechanics: Lecture

Undergraduate Course, University of Cincinnati, Physics Department, 2018

From August 2018 to January 2020, I was a teaching assistant for multiple introductory physics lectures on mechanics. The course was set up so that 2-3x per lecture, the students would solve a short problem related to what they just learned. This was done either in small groups or alone, and asking the TAs for help (me) was encouraged. I would answer 10-20 student questions on average per lecture, guiding the students towards the correct answer without outright telling them. Additionally, I observed students during tests/quizzes to ensure the absence of cheating. I also graded many of the test/quizzes and assignments. On occasion, at the teaching professor’s request, I would lead the lecture in their place.