I am a 3rd-year graduate student and NSF GRFP Fellow at Yale University, working with Prof. Pieter van Dokkum. My work focuses primarily on galaxies, and in particular, my thesis is focused on the baryon cycle in galaxies --- how galaxies accrete, proccess, and expel gas. I earned my undergraduate degrees in physics, astrophysics, and (minor) creative writing at UC Berkeley (go bears!) working with Prof. Mariska Kriek.
I also maintain a website with a free Python textbook oriented towards astronomy and astrophysics students. The site also has numerous guides and tutorials you can download and/or use in your classrooms, as well as some advice columns for undergrads about applying to graduate school, the NSF GRFP, and REUs (more on that below).
Finally, I am actively involved in, and committed to, efforts to create a more equitable and inclusive department community and astrophysics field in general. I believe that science is a human endeavor, and that it is critical we all do the work needed to combat systemic and widespread racism, sexism, and ableism in our field. If you want to talk science, grad admissions/NSF apps, Python pedagogy, or DEI work, I am always happy and eager to chat - please don't hesitate to reach out.
Inferring Galaxy Properties via Bayesian Inference
A long-standing goal of extragalactic astronomy is the cataloging of galaxy properties at different epochs and deriving a cohesive picture of how they form and evolve over time. Critical to this effort is the interpretation of a galaxy’s spectral energy distribution (SED), or the light-output at different wavelengths.
This light represents a blend of emission from many physical properties in galaxies, and disentangling these different sources to a galaxy’s light is the purview of SED-fitting, which often involves the simultaneous fitting of many (often-degenerate) parameters. Semi-recent developments in this field include Bayesian inference modeling with MCMC-driven frameworks that allow one to marginalize over these parameters and derive meaningful, physical uncertainties. These new codes feature flexible dust attenuation laws, non-parametric star formation histories, and allow for complex (or simple) priors to be implemented.
One such framework is Prospector, developed by Benjamin Johnson and Joel Leja. Prospector allows you to flexibly fit both photometry and spectra to derive stellar population paremameters in a Bayesian framework. I’ve worked in collaboration with their team, as well as Charlie Conroy, Pieter van Dokkum, and Mariska Kriek, to apply Prospector to meaningful samples of galaxies. In my most recent publication (below), we investigate the star formation rates derived by Prospector by fitting photometry for a sample of nearby galaxies for which we also obtained force-scanned Brackett-gamma spectroscopy, a near-IR emission line less sensitive to dust attenuation.
Mapping the Circumgalactic Medium with Dragonfly Narrowband
3-lens prototype images of continuum and Ha in M81/M82.
The Circumgalactic Medium (CGM) comprises the large reservoir of gas surrounding and ultimately accreting onto galaxies. In some cases, more than half of the baryons bound to a given galaxy are in the CGM, but despite nearly 50 years of active research and numerous indirect arguments demonstrating it must be present, precious little is actually known observationally about the actual morphology and kinematics of the CGM.
For my thesis, I am studying the CGM around local galaxies with a novel method and instrument: extreme narrowband H-alpha imaging using a 120-lens telephoto array. With this instrument, we aim to produce fully resolved maps of direct CGM emission, allowing the first single-object morphological studies capturing the distribution and expected complexity of the CGM.
From Lokhorst+2019: Simulated Dragonfly Narrowband images based on the EAGLE simulation for 10, 100, and 1000 hrs of integration time.
- Brackett-Gamma as a Gold-standard Test of Star Formation Rates Derived from SED-Fitting. Pasha, I., Leja, J., van Dokkum, P., Conroy, C., Johnson, B.D. ApJ, 2020.
- Stellar Metallicities and Elemental Abundance Ratios of z~1.4 Massive Quiescent Galaxies. Kriek, M., Price, S. H., Conroy,C., Suess, K. A., Mowla, L., Pasha, I., Bezanson, R., van Dokkum, P., Barro, G. ApjL, 2019
- The MOSDEF Survey: The Strong Agreement between Hα and UV-to-FIR Star Formation Rates for z~2 Star-forming Galaxies. Shivaei, I., Kriek, M., Reddy, N. A., Shapley, A. E., Barro, G., Conroy, C.,; Coil, A. L., Freeman, W. R., Mobasher, B., Siana, B., Sanders, R., Price, S. H., Azadi, M., Pasha, I., Inami, H. ApjL, 2016
- Discovery and Characterization of Gravitationally Lensed X-ray Sources in the CLASH Sample. Pasha, I., van Weeren, R., Andrade-Santos, F., American Astronomical Society, AAS Meeting #229, id.346.05, (2017).
- Classification of PSN J09254453+3416361 as a Type II Supernova. M.L. Graham, G. Halevi, I. Pasha, I. Shivvers, H. Yuk, A.V. Filippenko (UC Berkeley), Astronomers Telegram ATel 8169, (2016).
- Python for Astronomers: An Introduction to Scientific Computing. Imad Pasha & Christopher Agostino, Publicly Available, (2016).
An Introductory Astro-Python Textbook and Tutorials
I've always had a passion for teaching, and in particular, teaching programming skills that get students up to speed and ready to conduct astronomical research-grade coding in classes, independent research with faculty, or REUs. To that end, I maintain many of the materials I developed teaching Astro 198 (Introduction to Scientific Computing in Python) at UC Berkeley -- including a textbook and interactive tutorials on a variety of topics -- online for free. I also frequently (as I can) add to the growing list of coding/science lessons hosted.
Some fun stats for learnastropython.com
- Pageviews (Mar-July 2020): 5,267
- Unique Visitors (Mar-July 2020): 2,291
- Textbook Downloads (Mar-July 2020): 406
How to grad school
Over time and through various mentoring roles, I've compiled some advice on, more or less, the process of applying to the NSF GRFP and/or graduate school.
Teaching ExperienceBelow, you can find my teaching experience. All listed below are TA/TF/GSI positions (e.g., running sections, developing worksheets and other course content, grading), with the exception of Astronomy 198 for which I was the lead instructor and developed the sylabus, textbook, and course structure myself.
- Astronomy 210: Stars and their Evolution. Prof. Bob Zinn. Fall 2020.
- Astronomy 155: Intro to Astronomical Observing. Dr. Michael Faison. Fall 2019.
- Yale Summer Program in Astrophysics (YSPA) - Dr. Michael Faison. Summer 2019.
- Astronomy 255: Research Methods in Astronomy - Prof. Marla Geha. Spring 2019.
- Astronomy 150: Earth in its Cosmic Context. Prof. Gregory Laughlin. Fall 2018.
University of California, Berkeley
- Astronomy 198: Astronomical Python. Lead instructor. Spring 2015,2016,2017
- Astronomy 120: Optical and Infrared Astronomy Lab. Dr. Gaspard Duchene. Fall 2016.
- Astronomy C10: Introduction to General Astronomy. Prof. Alex Filippenko. Spring 2016.
Service & Outreach
I am an organizing member or participant in several service groups within the Astronomy Department. I currently servce as the Vice-Chair of the Yale Astronomy Climate and Diversity Committee, and am co-chair of its subcommitee on undergraduate affairs. I am also currently co-organizing (along with some fantastic folks) our departments first Equity and Inclusion Journal Club.
Below, you can find the departmental service groups I participate in and my affiliation with them. I am always happy to talk about the work we are trying to do in our department to build an equitable and just community, and I stand in full solidarity with Black Lives Matter. You can read more about our department's efforts here, and here.
- Astronomy Climate and Diversity Committee (ACDC). Vice Chair.
- Subcommittee on Undergraduate Affairs. Co-Chair.
- Astronomy Equity and Inclusion Journal Club. Organizing Committee Member.
- Astro Big-Sibs program. Organizing Member.
- Astronomy on Tap: New Haven. Organizer.
University of California, Berkeley
- Undergraduate Astronomy Society. Organizing Committee Member.
Astronomy on Tap New Haven
Astronomy on Tap is an organization of science communicators around the country, generally based within physics and astronomy departments, who organize and host public science talks at bars and pubs on a variety of interesting astronomy topics.
I am one of the organizers of this event's New Haven iteration, and have also MC'd and spoken at different AoT events. You can read more about AoT and find out about upcoming events at our Facebook and Twitter pages.
If you've made it this far down my page, I figured I'd share a little bit about myself - we can't all be academics all the time, right?
The first joke all my (current) fiends make about me is that I'm constantly talking about my time at Cal. In particular, I spent 3 years as an Arts & Entertainment reporter, concert photographer and later section editor at the Daily Californian, the newspaper of record for the city of Berkeley, CA. You can find a full listing of the articles (mostly film/concert reviews and interviews) here (be warned they're a struggling local newsroom so... ads galore). If you're curious, you can check out a portfolio of my concert phography here.
I also have a personal, perhaps unsurprising love of astrophotography, and while I'm no expert, I enjoy it, and am pretty proud of a few of the shots I've managed!
One of the best shots I've gotten of the Milky Way was in Bar Harbor, Maine (technically at the top of Mt. Cadillac), on a trip I took with my REU-mates at the SAO REU at the CfA. Other shots here include the Milky Way over SWAT Valley in Northern Pakistan, my attempt at catching the 2018 solar eclipse, and a good old fasioned moon shot.
I love all kinds of music, grew up playing in symphonies (viola), then bands (guitar/bass), and now... well, mostly I just listen to a lot of music. My college roommate was a film major, so we really had the whole thing going.
A very non inclusive, spur of the moment list of music I currently enjoy includes: The National, Glass Animals, Bon Iver, Taylor Swift, OK Go, Electric Guest, Queen, The Dear Hunter, Slothrust, Arctic Monkeys, The Strokes, Sylvan Esso, Rise Against, Explosions in the Sky, All American Rejects, alt-j, The Black Keys, Hippo Campus, Hozier, La Dispute, M83, Hippo Campus, Kendrick Lamar, Pink Floyd, [etc.?]
I'm also a huge Dungeons and Dragons (D&D) nerd; I watch people play it online, I play as a character in a few campaigns, and I DM (run) a few campaigns myself. I love worldbuilding and creating shared stories with my friends -- when I got to Yale, I started up and DM'd a D&D group that at one point contained first-, second-, third-, fifth-, and sixth0-year astronomy students.
To round out the stereotype nicely, I also very much enjoy bouldering and top roping, and a small contingent in the department hits up our local climbing gym ~3 times a week.