About this Article

The JWST Cycle 4 Call for Proposals (CfP) is scheduled to be issued August 1, 2024. The CfP contains several changes that are new this year and will directly impact how JWST proposers write and submit their General Observer (GO) and Archival (AR) proposals. This Newsletter article is meant to serve as a supplementary guide to the Cycle 4 CfP to explain the motivation for and implementation of the upcoming changes at a high level. The changes aim to improve the proposal review process by addressing key challenges that were noted by the JWST Users Committee (JSTUC). 

Several members of the JSTUC served on the Cycle 3 Telescope Allocation Committee (TAC) including the TAC Chair, Emily Levesque. Fresh from the review at their March 2024 meeting, the JSTUC discussed some of the challenges that the Telescope Allocation Committee (TAC) encountered. At the highest level, the scale of the review process is straining the system and causing problems. Indeed, the number of proposals submitted by the astronomical community in response to the JWST CfP has grown from 1,173 proposals in Cycles 1 to 1,931 proposals in Cycle 3, breaking STScI records in both Cycles 2 and 3. This  has led to very high workloads for the TAC Executive Committee members and the Discussion panelists. Second, the JSTUC noted that the Science Categories, drawn from Hubble and Spitzer heritage and defining how proposals are grouped, are less well matched to JWST proposals and need to be updated. In Cycles 1–3, the majority of proposals (~60%) were submitted to two of the seven Science Categories: “Exoplanets and Exoplanet Formation” and “Galaxies and the Intergalactic Medium.” The topics covered by those Science Categories are very broad and reviewers are increasingly looking for proposals that are aligned more closely with their scientific expertise. 

To address these issues of overall workload and matching expertise, we are revising the Page Limits, Size Categories, and Science Categories for the JWST Cycle 4 Call for Proposals.

Page Limits

The time that reviewers spend evaluating proposers is directly related to proposal length. The JSTUC noted that the page limits for proposals in Cycles 1–3 were substantially longer than that of other US and international observatories. As a result, they have recommended that the JWST limits be reduced. The meat of a proposal is the Scientific Justification and the Technical Description (for GO programs) or Analysis Plan (for AR proposals). Table 1 shows a comparison of Cycle 1–3 page limits against those of other observatories, along with the updated Cycle 4 page limits for those two sections. In most cases, the page limits are being reduced by approximately a factor of two. As a specific example, the page limit for those sections in Small GO proposals is being reduced from 8 pages to 4 pages including figures and tables but excluding references. One additional page is available for all proposals to describe Special Requirements, Justify Coordinated Parallel Observations, Justify Duplications, and Justify Coordinated Observations with Other Facilities sections. Proposals that violate the page limits and/or fail to use 12-point font throughout will be disqualified as non-compliant.

 
*Other observatories include ALMA, Chandra, Fermi, NOIRLab, Swift, and TESS

Size Categories

The TAC comprises four different groups of reviewers that are assigned proposals by proposal size and scientific expertise. 

• External Panelists grade Very Small and most Archival proposals asynchronously and do not meet. Each proposal receives at least five independent reviews.
• Small and Medium proposals and Survey proposals are reviewed by Discussion panelists. Discussion Panelists submit preliminary grades for Small and Medium proposals before their panel meets to determine which proposals will be discussed at the panel meetings. During the meeting, Discussion Panelists regrade proposals based on their consensus opinion and recommend a ranked list of proposals for acceptance to the STScI Director.
• The Executive Committee, comprised of the Panel Chairs (and Vice Chairs for Cycle 4) evaluate the Large, Treasury, and Archival Legacy proposals. Like the Discussion Panelists, EC members grade proposals before the EC meets to determine which proposals will be discussed at the EC that convenes after the Discussion Panel meetings. During the meeting, EC members examine the overall scientific portfolio recommended by the TAC and adjudicate duplications in addition to creating a ranked list of Large, Treasury, and Archive Legacy proposals.
• Finally, Expert Reviewers provide a handful of reviews of EC proposals that the EC members take into account during their grading.

The Cycle 1–3 Size Categories were defined prior to launch, before the community had an opportunity to scope out projects that could be carried out with JWST. During the first three review cycles, observers have learned JWST capabilities, imagined JWST science, and learned how much telescope time their projects take. For HST, the External and Discussion Panelists allocate ~50% of the available telescope time to Very Small and Small proposals; the Discussion Panelists allocate ~30% to Medium proposals; and the EC allocates ~20% to Large proposals. For JWST Cycle 3, the External and Discussion Panelists allocated ~38% of the available telescope time (2050 hours out of 5500 hours) to Very Small and Small proposals; the Discussion Panelists allocated ~38% (2100 hours) to Medium proposals; and the EC allocated ~25% (1350 hours) to Large proposals. Consequently, the JWST Discussion Panelists and Executive Committee communities were performing a disproportionately large fraction of work. For Cycle 4, the JWST Science Policies Group (SPG) is rebalancing the workload by adjusting the boundaries between Very Small, Small, Medium, and Large Size Categories as listed in Table 2.

Science Categories

Science Categories are critical to the assignment of proposals to reviewers during the JWST review.

• Principal Investigators (PIs) initially designate their preferred Science Category for each proposal based on the Science Keywords selected. The  Astronomer’s Proposal Tool (APT) provides an option to designate not only a primary but also a secondary Science Category for proposals that may straddle boundaries. Proposers also identify Science Keywords for each proposal,
• JWST Science Policy Group (SPG) members at STScI recruit reviewers to match anticipated programs within a Science Category. Occasionally, reviewers request to be assigned to a different Science Category and are reassigned. All reviewers are recruited before the proposal deadline and each reviewer provides their own, self-identified Science Keywords.
• During the week immediately following the deadline, SPG members read the abstracts for all of the submitted proposals to determine whether the submitted Science Category matches the range of reviewer expertise in that category. The SPG may reassign a proposal to a different Science Category to better match the reviewer expertise.
• Once proposals and reviewers are sorted into the final Science Categories, then SPG members assign individual reviewers to proposals using the Science Keywords. This includes both assignments of external panelists for Very Small proposals, and assignments of the discussion panelists who will provide preliminary reviews for proposals to be discussed at the TAC meeting.

The Cycle 1–3 Science Categories were also originally defined before launch, based on the HST and Spitzer Science Categories. HST has eight Science Categories: Solar System, Exoplanets and Exoplanet Formation, Stellar Physics, Stellar Populations and the Interstellar Medium (ISM), Galaxies, the Intergalactic Medium (IGM) and the Circumgalactic Medium (CGM), Supermassive Black Holes, and Large Scale Structure. For JWST, “Galaxies” and “IGM and CGM” were combined into a single Science Category with a shortened title, “Galaxies and the IGM.” As an infrared telescope rather than a primarily UV/visual telescope, the science topics requested in JWST proposals have proven to be demographically different than with HST (see Table 3). For example, JWST allocates a substantially larger proportion of telescope time to Exoplanets and Exoplanet Formation than HST. For HST, the science category Stellar Populations and the ISM is dominated by proposals studying stellar clusters and galactic archaeology. For JWST, Stellar Populations and the ISM, is dominated by proposals studying the diffuse ISM, notably PAHs, and star formation in the Milky Way and the Local Group. As a result, the number of reviewers needed for the traditional stellar populations proposals is much smaller and those reviewers tend to be more closely aligned with the Stellar Physics reviewers than the ISM and star formation reviewers on their panels. Galaxies and the Intergalactic Medium is large for both HST and JWST (see Table 3).

 
*For HST, this area is divided into two separate Science Categories that together total 34.5%: Galaxies (26.7%) and the Intergalactic Medium and Circumgalactic Medium (9.6%).

For JWST Cycle 4, the JWST SPG is adjusting the Science Categories to better balance the fraction of proposals across Science Categories and better align the Science Categories with distinct scientific communities. “Exoplanets and Exoplanet Formation” will be split into “Exoplanet Atmospheres and Habitability” and “Planetary System Formation and Dynamics”. “Galaxies and the IGM” and “Large Scale Structure” will be combined and split into “Nearby Galaxies to Cosmic Noon” and “High-Redshift Galaxies and the Distant Universe”. “Stellar Physics” and “Stellar Populations” will be combined and split into “Stars and Stellar Populations” and “Gas and Dust”. “Solar System” and “Supermassive Black Holes” will remain the same.

Thus, the JWST Cycle 4 Science Categories that will be offered are the following:

• Solar System (no change) — Studies of objects within the Solar System, including planets and their moons and rings, minor bodies, and the zodiacal dust.
• Exoplanet Atmospheres and Habitability — Studies of individual exoplanets, focusing on their atmosphere and/or surface properties. Studies may include host stars and isolated planetary-mass objects to better understand exoplanet atmospheres and habitability more generally.
• Planetary System Formation and Dynamics — Studies of exoplanetary systems including more than one exoplanet (e.g. comparative studies of more than one exoplanet orbiting the same host star) and isolated planetary-mass objects; protoplanetary, debris, and white dwarf disks.
• Stars and Stellar Populations — Studies of individual protostars, stars, and/or stellar remnants and clusters of these objects, focusing on the objects themselves.
• Gas and Dust — Studies of resolved gas and dust in the ISM and star formation in the Milky Way and nearby galaxies. Studies focusing on gas and dust diagnostics to understand host stars should be submitted to Stars and Stellar Populations. Those focusing on larger scale structure should be submitted to Gas and Dust.
• High-Redshift Galaxies and the Distant Universe — Studies of galaxies at redshifts beyond the peak of star formation through the end of the epoch of cosmic reionization to the early universe, including the first galaxies.
• Nearby Galaxies to Cosmic Noon — Studies of galaxy kinematics, star formation, ionized gases (including H II), etc. in nearby galaxies up to the peak of star formation at redshifts of z~2-3.
• Supermassive Black Holes (no change) — Studies of supermassive black holes at the centers of galaxies, including understanding the impact of the black hole on the host galaxy’s properties.

More details, including the Science Keywords within each Science Category, will be available in the JWST Cycle 4 Call for Proposals. As always, the JWST SPG is mindful that science is continuously evolving and that today’s science demographics is just a snapshot in time showing that evolution. The SPG will review the outcome of Cycle 4 proposal selection and make adjustments as necessary for Cycle 5 and beyond.