About

Jason Xavier Prochaska is a Professor in the Astronomy & Astrophysics Department within the Physical & Biological Sciences Division at UC Santa Cruz. His primary expertise lies in astrophysics, specifically in spectroscopy, which involves dissecting the light emitted by distant sources such as galaxies, quasars, and transient phenomena to examine the physical properties and processes driving the formation of the universe. His research focuses on the nature of gas within and outside of galaxies during the first few billion years of the universe, utilizing high-resolution spectroscopy of bright, distant sources like quasars and gamma-ray bursts. These observational studies impact our understanding of galaxy formation, cosmology, and fundamental physics. Additionally, he has led follow-up studies of transient and bursting sources, including gamma-ray bursts and fast radio bursts, to gain insights into the gas within galaxies and beyond. Recently, his work with fast radio bursts has contributed to resolving the 'missing baryons problem,' a longstanding challenge in detecting the majority of normal matter in the universe today. Prochaska's background includes a physics degree from Princeton University and a PhD in Physics from the University of California, San Diego. He was a postdoctoral Carnegie+Hubble Fellow at Carnegie Observatories before joining UC Santa Cruz as faculty and an astronomer at the UC Observatories. He became an affiliate of the Ocean Sciences Department at UC Santa Cruz in 2020. His research interests also encompass applying artificial intelligence and machine learning techniques to analyze large and complex datasets in astronomy and oceanography. Recognized for his contributions, he has received numerous awards, including the 2020 AAAS Newcomb Cleveland Prize and the 2023 Simons Pivot Fellowship, and has secured extramural funding from organizations such as the NSF, NASA, and private foundations.

Research topics

• Computer Science
• Physics
• Astronomy
• Astrophysics
• Data Mining
• Optics
• Mathematics
• Programming language

Selected publications

• The Low-mass Dwarf Host Galaxy of Nonrepeating FRB 20230708A

  The Astrophysical Journal · 2026-04-08

  articleOpen access

  Abstract We present Very Large Telescope/X-Shooter spectroscopy for the host galaxies of 12 fast radio bursts (FRBs) detected by the Australian SKA Pathfinder observed through the “Fast and Unbiased FRB Host Galaxy (FURBY)” Large Programme at the European Southern Observatory, which imposes strict selection criteria on the included FRBs and their host galaxies to produce a homogeneous and well-defined sample. We describe the data reduction and analysis of these spectra and report their redshifts, line-emission fluxes, and derived host properties. From the present sample, this paper focuses on the faint host of FRB 20230708A ( m R = 22.53 ± 0.02) identified at low redshift ( z = 0.1050). This indicates an intrinsically very low-luminosity galaxy ( L ≈ 10 8 L ⊙ ), making it the lowest-luminosity nonrepeating FRB host to date by a factor of ∼3 and slightly dimmer than the lowest-luminosity host for repeating FRBs. Our spectral energy distribution fitting analysis reveals a low stellar mass ( M * ≈ 10 8.0 M ⊙ ), low star formation rate (SFR ≈ 0.04 M ⊙ yr −1 ), and very low metallicity( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>12</mml:mn> <mml:mo>+</mml:mo> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mtext>O</mml:mtext> <mml:mspace width="0.1em"/> <mml:mo>/</mml:mo> <mml:mspace width="0.1em"/> <mml:mtext>H</mml:mtext> <mml:mo stretchy="false">)</mml:mo> <mml:mo>∼</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:mn>8.0</mml:mn> <mml:mo>−</mml:mo> <mml:mn>8.3</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:math> ), distinct from the more massive galaxies (log( M / M ⊙ ) ∼ 10) that are commonly identified for nonrepeating FRBs. Its discovery demonstrates that FRBs can arise in the faintest, metal-poor galaxies of the Universe. In turn, this suggests that at least one FRB progenitor channel must include stars (or their remnants) created in very low metallicity environments. This indicates better prospects for detecting FRBs from the high- z Universe where young, low-mass galaxies proliferate.

  PublisherDOI

• I can see your halo: Constraining the Milky Way halo DM with FRB population studies

  arXiv (Cornell University) · 2026-01-09

  preprintOpen access

  Fast radio bursts (FRBs) probe the electron column density along the line of sight and hence can be used to probe foreground structures. One such structure is the Galactic halo. In this work, we use a total of 98 high Galactic latitude ($|b| &gt; 20^\circ$) FRBs detected by ASKAP, Parkes, DSA and FAST with 32 associated redshifts to constrain the dispersion measure (DM) contribution from the Galactic halo. We simultaneously fit unknown FRB population parameters, which show correlations with the Galactic halo but are not completely degenerate. We primarily use an isotropic model for the halo, but find no evidence favouring a particular halo model. We find DM$_{\rm MW,halo}$=$68^{+27}_{-24}$pc/cm$^3$, which is in agreement with other results within the literature. Previous constraints on DM$_{\rm MW,halo}$ with FRBs have used a few, low-DM FRBs. However, this is highly subject to fluctuations between different lines of sight, and hence using a larger number of sightlines as we do is more likely to be representative of the true average contribution. Nevertheless, we show that individual FRBs can still skew the data significantly and hence will be important in the future for more precise results.

  PublisherDOI

• High-resolution Giant Metrewave Radio Telescope H <scp>i</scp> 21 cm Imaging of the Host Galaxy of FRB 20250316A

  The Astrophysical Journal · 2026-04-13 · 1 citations

  articleOpen accessSenior author

  Abstract We report Giant Metrewave Radio Telescope (GMRT) H i 21 cm imaging of NGC 4141, the host galaxy of FRB 20250316A at z = 0.0063. Our GMRT H i 21 cm images have spatial resolutions, at z ≈ 0.0063, of ≈0.48–8.0 kpc, and provide evidence for (i) a companion galaxy, LEDA 2582852, to the southwest, (ii) a nearby (27 kpc distant) H i cloud to the southwest, (iii) disturbances in the H i distributions of both NGC 4141 and LEDA 2582852, and (iv) high H i column densities in the southwestern outskirts of NGC 4141. A Sloan Digital Sky Survey spectrum yields a low metallicity and a high star formation rate (SFR) surface density in the southwestern disk of NGC 4141, and an H α -based SFR estimate that is significantly higher than that at the same location from the Galaxy Evolution Explorer near-ultraviolet image, indicating a recent burst of star formation. The total SFR of NGC 4141 is also found to be higher via the H α line than from the 1.4 GHz radio continuum. The above evidence indicates that NGC 4141 has recently (within the last ≈3 Myr) acquired metal-poor gas, via either a merger or accretion, that resulted in the southwestern starburst and that may also have triggered large-scale star-formation activity in NGC 4141, resulting in the formation of the stellar progenitor of FRB 20250316A and the other transients. Our highest-resolution (480 pc) GMRT H i 21 cm image finds no H i 21 cm emission from the location of FRB 20250316A or the nearby star-forming region, suggesting that most of the H i here has been either ionized or converted into the molecular phase. Our nondetection of continuum emission at the location of FRB 20250316A yields the 3 σ upper limit νL 1.38 GHz &lt; 4.4 × 10 34 erg s −1 on the 1.38 GHz radio luminosity of a putative persistent radio source associated with FRB 20250316A, one of the strongest constraints on the radio luminosity of such an associated persistent radio source.

  PublisherDOI

• I can see your halo: Constraining the Milky Way halo DM with FRB population studies

  ArXiv.org · 2026-01-09

  articleOpen access

  Fast radio bursts (FRBs) probe the electron column density along the line of sight and hence can be used to probe foreground structures. One such structure is the Galactic halo. In this work, we use a total of 98 high Galactic latitude ($|b| > 20^\circ$) FRBs detected by ASKAP, Parkes, DSA and FAST with 32 associated redshifts to constrain the dispersion measure (DM) contribution from the Galactic halo. We simultaneously fit unknown FRB population parameters, which show correlations with the Galactic halo but are not completely degenerate. We primarily use an isotropic model for the halo, but find no evidence favouring a particular halo model. We find DM$_{\rm MW,halo}$=$68^{+27}_{-24}$pc/cm$^3$, which is in agreement with other results within the literature. Previous constraints on DM$_{\rm MW,halo}$ with FRBs have used a few, low-DM FRBs. However, this is highly subject to fluctuations between different lines of sight, and hence using a larger number of sightlines as we do is more likely to be representative of the true average contribution. Nevertheless, we show that individual FRBs can still skew the data significantly and hence will be important in the future for more precise results.

  PublisherOA PDF

• Constraining Gas Mass Fractions in Galaxy Groups and Clusters with the First CHIME/FRB Outrigger

  The Astrophysical Journal · 2026-05-11

  preprintOpen access

  Abstract In recent years, localized fast radio bursts (FRBs) have emerged as a powerful tool to study the structure of the baryonic matter in the Universe. Their dispersion measures (DMs) scale linearly with electron density independent of gas temperature, making them particularly well suited to studying the intragroup medium (IGrM), where traditional probes such as X-ray emission and the Sunyaev–Zeldovich effect are weak. Evidence suggests that the gas in group mass halos ( M 500 ∼ 10 13 –10 14 M ⊙ ) is strongly affected by galactic feedback, causing deviations from cluster scaling relations. Three FRBs from the first CHIME/FRB Outrigger sample come from host galaxies found within or behind galaxy clusters and groups. We estimate the DM contribution of each ICM/IGrM by integrating different halo density profiles, accounting for uncertainties in halo mass and the host galaxy line-of-sight distance. For the more massive halos, predicted cluster DMs agree with the extragalactic DM budget. One burst, FRB 20230703A, intersects three groups yet has a low extragalactic DM. By comparing model predictions with the measured DM, we constrain the gas mass fraction f g ( R ) in these halos. Comparing with published M – f g relations, we find consistency with recent eROSITA results at R 500 and mild tension at R 200 and with earlier X-ray–based relations. As CHIME/FRB Outriggers build a large catalog of localized FRBs, many additional sightlines through groups and clusters will be obtained. These will enable systematic tests of intragroup and intracluster gas properties and sharpen constraints on the distribution of baryons in massive halos.

  PublisherDOI

• Data from: The low-mass dwarf host galaxy of nonrepeating FRB 20230708A

  DRYAD · 2026-03-29

  datasetOpen access1st authorCorresponding

  We present Very Large Telescope/X-Shooter spectroscopy for the host galaxies of 12 fast radio bursts (FRBs) detected by the Australian SKA Pathfinder (ASKAP), observed through the ESO Large Programme "FURBY", which imposes strict selection criteria on the included FRBs and their host galaxies to produce a homogeneous and well-defined sample. We describe the data reduction and analysis of these spectra and report their redshifts, line-emission fluxes, and derived host properties. From the present sample, this paper focuses on the faint host of FRB (mR = 22.53 +/- 0.02) identified at low redshift (z = 0.1050). This indicates an intrinsically very low-luminosity galaxy (L ~ 108 L_Sun), making it the lowest-luminosity non-repeating FRB host to date by a factor of ~3, and slightly dimmer than the lowest-luminosity host for repeating FRBs. Our SED fitting analysis reveals a low stellar mass (M* ~ 108 MSun), low star formation rate (SFR ~ 0.04 MSun/yr), and very low metallicity (12 + log(O/H) ~ 8.0-8.3), distinct from the more massive galaxies (log(M/M_Sun) ~ 10) that are commonly identified for non-repeating FRBs. Its discovery demonstrates that FRBs can arise in among the faintest, metal-poor galaxies of the universe. In turn, this suggests that at least one FRB progenitor channel must include stars (or their remnants) created in very low metallicity environments. This indicates better prospects for detecting FRBs from the high-z Universe where young, low-mass galaxies proliferate.

  PublisherDOI

• Extremes of Dissolved Oxygen in the California Current System

  Journal of Physical Oceanography · 2025-07-25

  article1st authorCorresponding

  Abstract Dissolved oxygen (DO) is a nonconservative tracer of interactions at the air–sea interface, respiration and photosynthesis, and advection. In this manuscript, we study extremes in the degree of oxygen saturation (SO), the ratio of DO to the maximum concentration given the water’s temperature, salinity, and depth with SO = 1 critically saturated. We perform the analysis with the California Underwater Glider Network (CUGN), which operates gliders on four lines that extend from the California coast to several hundred kilometers offshore, profiling to 500-m depth every 3 km. Since ∼2017, the gliders have been equipped with a Sea-Bird 63 optode sensor to measure the DO content. We find that parcels with SO &gt; 1.1, hyperoxic extrema, occur primarily nearshore in the upper 50 m of the water column and during nonwinter months. Along Line 90 which originates in San Diego, these hyperoxic events occur primarily in stratified waters with shallow mixed layers. We hypothesize that photosynthesis elevates DO in subsurface water that cannot rapidly ventilate with the surface. Along the three other lines, hyperoxic extrema occur almost exclusively closest to the surface and are correlated with elevated Chl-a fluorescence suggesting they are primarily driven by blooms of photosynthesis. We also examine hypoxic extrema, finding that parcels with SO &lt; 0.9 and z &lt; 50 m occur most frequently along the northernmost line where upwelling has the greatest impact.

  PublisherDOI

• Estimation of intrinsic fast radio burst width and scattering distributions from CRAFT data

  ArXiv.org · 2025-10-07

  preprintOpen access

  The intrinsic width and scattering distributions of fast radio bursts (FRBs) inform on their emission mechanism and local environment, and act as a source of detection bias and, hence, an obfuscating factor when performing FRB population and cosmological studies. Here, we utilise a sample of 29 FRBs with measured high-time-resolution properties and known redshift, which were detected using the Australian Square Kilometre Array Pathfinder (ASKAP) by the Commensal Real-time ASKAP Fast Transients Survey (CRAFT), to model these distributions. Using this sample, we estimate the completeness bias of intrinsic width and scattering measurements, and fit the underlying, de-biased distributions in the host rest-frame. In no case do our model fits prefer a down-turn at high values of the intrinsic distributions of either parameter in the 0.01-40 ms range probed by the data. Rather, when assuming a spectral scattering index of $α= -4$, we find that the intrinsic scattering distribution at 1\,GHz is consistent with a log-uniform distribution above 0.04 ms, and that this functional form is strongly favoured over the lognormal descriptions used by previous works. We also find that the intrinsic width distribution rises as a Gaussian in log-space in the 0.03-0.3 ms range, with a log-uniform distribution above that slightly preferred to a lognormal distribution. This confirms previous works suggesting that FRB observations are currently strongly width- and scattering-limited, and we encourage FRB searches to be extended to higher values of time-width. It also implies a bias in FRB host galaxy studies, although the form of that bias is uncertain. Finally, we find that our updated width and scattering models - when implemented in the zDM code - produce $\sim$10% more FRBs at redshift z=1 than at z=0 when compared to alternative width/scattering models.

  PublisherOA PDFDOI

• A Comprehensive Characterization of Galaxy-cool CGM Connections at <i>z</i>  &lt; 0.4 with DESI Year 1 Data

  The Astrophysical Journal · 2025-10-28 · 1 citations

  articleOpen access

  Abstract We investigate the relationships between the cool circumgalactic medium (CGM), traced by Ca ii absorption lines, and galaxy properties at z &lt; 0.4 using ∼900,000 galaxy–quasar pairs within 200 kpc from the Year 1 data of the Dark Energy Spectroscopic Instrument (DESI). This large data set enables us to obtain composite spectra with sensitivity reaching to the mÅ level and to explore the Ca ii absorption as a function of stellar mass, star formation rate (SFR), redshift, and galaxy types, including active galactic nuclei (AGNs). Our results show a positive correlation between the absorption strength and stellar mass of star-forming galaxies with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">〈</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>W</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">Ca</mml:mi> </mml:mrow> <mml:mspace width="0.25em"/> <mml:mrow> <mml:mi mathvariant="normal">II</mml:mi> </mml:mrow> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">〉</mml:mo> <mml:mo>∝</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>∗</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> over 3 orders of magnitude in stellar mass from ∼10 8 to 10 11 M ⊙ , while such a mass dependence is weaker for quiescent galaxies. At a fixed mass, Ca ii absorption is stronger around star-forming galaxies than quiescent ones especially within impact parameters &lt;30 kpc. Among star-forming galaxies, the Ca ii absorption further correlates with SFR, following ∝SFR 0.3 . However, in contrast to the results at higher redshifts, stronger absorption is not preferentially observed along the minor axis of star-forming galaxies, indicating a possible redshift evolution of CGM dynamics resulting from galactic feedback. Moreover, no significant difference between the properties of the cool gas around AGNs and galaxies is detected. Finally, we measure the absorption profiles with respect to the virial radius of dark matter halos and show that the total Ca ii mass in the CGM is comparable to the Ca mass in the ISM of galaxies.

  PublisherDOI

• The Multi-Phase Circumgalactic Medium of DESI Emission-Line Galaxies at z~1.5

  ArXiv.org · 2025-11-05

  preprintOpen access

  We study the multi-phase circumgalactic medium (CGM) of emission line galaxies (ELGs) at $z\sim1.5$, traced by MgII$\lambda2796$, $\lambda2803$ and CIV$\lambda1548$, $\lambda1550$ absorption lines, using approximately 7,000 ELG-quasar pairs from the Dark Energy Spectroscopic Instrument. Our results show that both the mean rest equivalent width ($W_{0}$) profiles and covering fractions of MgII and CIV increase with ELG stellar mass at similar impact parameters, but show similar distributions when normalized by the virial radius. Moreover, warm CIV gas has a more extended distribution than cool MgII gas. The dispersion of MgII and CIV gas velocity offsets relative to the galaxy redshifts rises from $\sim100 \, \rm km \, s^{-1}$ within halos to $\sim 200 \, \rm km \, s^{-1}$ beyond. We explore the relationships between MgII and CIV $W_{0}$ and show that the two are not tightly coupled: at a fixed absorption strength of one species, the other varies by several-fold, indicating distinct kinematics between the gas phases traced by each. We measure the line ratios, FeII/MgII and CIV/MgII, of strong MgII absorbers and find that at $&lt;0.2$ virial radius, the FeII/MgII ratio is elevated, while the CIV/MgII ratio is suppressed compared with the measurements on larger scales, both with $\sim4-5\, σ$ significance. We argue that multiphase gas that is not co-spatial is required to explain the observational results. Finally, by combining with measurements from the literature, we investigate the redshift evolution of CGM properties and estimate the neutral hydrogen, metal, and dust masses in the CGM of DESI ELGs -- found to be comparable to those in the ISM.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Disentangling the Cosmic Web with Fast Radio Bursts

  NSF · $320k · 2019–2023

• CAREER: Enriching the Universe -- Investigating Nucleosynthesis and Galaxy Formation in the First Few Billion Years

  NSF · $475k · 2006–2012

• Lyman Limit Systems: Probing the Protogalactic/IGM Interface

  NSF · $275k · 2003–2007

• Collaborative Research: The Definitive Follow-up Campaign for Fast Radio Bursts

  NSF · $680k · 2022–2026

• Quasars Probing Quasars

  NSF · $391k · 2014–2018

Frequent coauthors

• J. S. Bloom

  New York University

  471 shared

• E. Ramirez‐Ruiz

  University of California, Santa Cruz

  340 shared

• Arthur M. Wolfe

  University of California, San Diego

  331 shared

• N. Butler

  Arizona State University

  328 shared

• A. Kutyrev

  Goddard Space Flight Center

  308 shared

• M. G. Richer

  308 shared

• A. M. Watson

  297 shared

• E. Troja

  University of Rome Tor Vergata

  297 shared

Education

• Ph.D., Astronomy

  University of California, Santa Cruz

  2002

• M.S., Astronomy

  University of California, Santa Cruz

  1998

• B.S., Astronomy

  University of California, Santa Cruz

  1996

Awards & honors

• Simons Pivot Fellowship (2023)
• AAAS Newcomb Cleveland Prize (2020)
• Distinguished Professor (UCSC) (2020)
• Outstanding Faculty Award (Division of Physical and Biologic…
• Humboldt Fellow Grants (2010)