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Research Result Report
ICRR Inter-University Research Program 2023
Research Subject: Investigating the gamma-ray signatures of feedback microphysics
in star-forming environments
Principal Investigator: Dr. Ellis R. Owen (Department of Earth and Space Science,Osaka University)
Participating Researchers: Prof. Marcel Strzys (ICRR, University of Tokyo); Prof.
Yoshiyuki Inoue (Department of Earth and Space Science, Osaka University).
Summary of Research Result: This project aimed to investigate the origin of cosmic
rays in and around star-forming environments and construct new tests of cosmic rayinteractions and acceleration in and around (1) supernova remnants, (2) star-forming
clusters/regions, and (2) galaxy scale systems. During the FY2023 fiscal year, thisproject was in an initial, exploratory stage. Three specific objectives were planned:(1) Modeling gamma-ray emission from selected clouds near supernova remnants up
to TeV energies under different CR propagation and composition scenarios.

Achievement: Models were constructed. It was identified that sub-mm data wasrequired, and proposals were submitted to ALMA and JCMT. Discussion with the hostgroup at ICRR led this aspect of the project to be expanded, towards an investigationof star-forming regions as cosmic ray sources. These would seem to be more promisingtargets for new scientific developments, as our understanding of how cosmic rays areaccelerated in detail within these complex environments is incomplete – yet they havebeen identified as potentially important source of the Galactic cosmic ray flux
(possibly comparable to supernova remnants). Increasing gamma-ray data isavailable to allow for substantial progress to be made in modelling the detailed
configurations of these regions, and their individual capability to accelerate cosmicrays through (i) wind interactions, (ii) wind termination shocks, (iii) 2nd order Fermi
processes, (iv) bow shocks from escaping O/B stars. During FY2023, preliminary
follow-up Fermi analysis was conducted for promising source young massive stellar
cluster and other star-forming region candidates (based on their age, O/B stellar
population and stellar mass). The properties of these objects were carefully analyzed
in conjunction with Gaia DR3 data sets, and initial steps have been made towards
constructing physical models of cosmic ray acceleration in winds, bespoke for eachtarget star-forming region. A final determination of selected targets is yet to be made,as more detailed investigations of some star-forming regions to understand why they
are gamma-ray bright or dark in the Fermi data is still ongoing. This work willcontinue as an ongoing collaborative effort in FY2024, although budget for dedicatedForm 8

additional visits to ICRR is not required (project P.I. will move to the Tokyo area for
a new position, so this project can freely continue without specific support).
(2) Population study of starburst galaxies showing indications of an outflow inexisting gamma-ray data. Use of their gamma-ray luminosities to set cosmic ray
spectral normalizations for specific hydrodynamical flow models to create complete
models of circum-galactic flow dynamics suitable for use as feedback testbeds.

Achievement: A search for extended emission from starburst and main-sequence
galaxies detected in gamma-rays was conducted, with follow-up detailed Fermi data
analysis. Few sources showed clear evidence of extended gamma-ray emission that
could be indicative of emission from an outflow. A preliminary study is instead being
conducted first with archival eROSITA data to identify nearby gamma-ray detectedgalaxies that show X-ray emission signatures from their hot baryons suggestive ofcosmic ray dynamical activity. From these, follow-up detailed Fermi analysis will bepossible using a more informed morphological model based on the X-ray data. It now
appears that this approach will provide a clearer starting point for tests of feedback
models, with gamma-ray follow up studies or non-detection limits being useful for
additional insights and model constraints. This project objective will therefore be
revisited when the eROSITA archival study has been completed.
(3) Preparation of observational proposals for Galactic star-forming regions inJanuary 2024 for CTA observations at TeV energies to obtain data for model inputs.

Achievement: Based on estimated fluxes at TeV energies with preliminary models
and information at GeV energies with existing Fermi detections of promising targets,it was found that existing archival TeV data obtained with H.E.S.S. would be superior
to any observations currently possible with CTA-LST1 alone, for the identified targets
worthy of study. A target list and model predictions have been prepared for future
observational cycles when more LSTs are online and better data quality can beachieved. This project objective will therefore also be revisited in future, based on theoperational status of CTA.
Current status & immediate next steps in FY2024: Overall, this project is now
developing from an exploratory stage towards a point where novel scientific returns
can soon be achieved. In the next FY2024, the primary focus will be placed theanalysis and modeling of star-forming regions in the GeV band to properly
understand their currently observed gamma-ray emission properties and theimplications for cosmic-ray acceleration depending on the exact configuration of eachtarget object. Dedicated funding for these continuing efforts is not required.
No. F29