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Baryonic Cycle Research Group

Resolving the Baryon Cycle within Nearby Galaxies
To understand galaxies, we must understand the physical processes and local conditions that drive their buildup of stellar mass through star formation. This evolution is regulated through the baryon cycle, the transformation of gas into stars and eventual ejection and recycling of that material to form the next generation of stars. The relevant physics occurs on the 50 pc scales of individual molecular clouds, star forming HII regions and supernova remnants, only now accessible in a diverse sample of external galaxies. This group works within the PHANGS collaboration to use ALMA and VLT observations to identify and characterize the physical conditions in and around HII regions and ask: How does metal enrichment proceed within the disk? Does the injection of energy and momentum from stellar winds and supernovae trigger or suppress star formation? What is the source of ionization in the diffuse ionized gas? Addressing these topics ultimately requires us to map the internal ionization structure of star-forming regions, which will be undertaken in an ambitious new Local Volume Mapper (LVM/SDSS-V) spectroscopic survey of the Milky Way and Local Group galaxies.

This Emmy Noether research group is funded by the German Science Foundation (DFG) and established starting in 2019.

Current Group Members:
  • Kathryn Kreckel (group leader)
  • Fabian Scheuermann (PhD student)
  • Jing Li (PhD student)
  • Elizabeth Watkins (postdoc)
  • Oleg Egorov (postdoc)



Current projects/collaborations:
  • Physics at High Angular resolution in Nearby GalaxieS (PHANGS): The PHANGS survey is making high resolution observations of nearby galaxies with several telescope, including ALMA, HST, and MUSE/VLT. We aim to understand the interplay of the small-scale physics of gas and star formation with galactic structure and galaxy evolution. Ongoing projects and projects leads within the Baryon Cycle group:
    • Within the PHANGS-MUSE survey of 19 nearby galaxies at 50pc resolution, we are able to isolate more than 20,000 individual HII regions. With this sample, we explore differences in their HII region luminosity function and changes in physical conditions (metallicity, pressure, temperature). By mapping these samples across the full star-forming disk, we can explore trends with galaxy environment and other local conditions (e.g. stellar mass and molecular gas surface density). (Kreckel)
    • Using their strong [OIII] emission, we identify ~1000 planetary nebulae within the PHANGS-MUSE sample. Using these as standard candels we are able to measure the distances to each galaxies with ~5% accuracy, and place constraints on the metallicity dependence of the planetary nebula luminosity function (Scheuermann)
    • Examining the morphological and kinematic features of the molecular gas distribution mapped by PHANGS-ALMA in relation to the ionizing clusters seen by PHANGS-HST, we can place quantitative constraints on feedback processes as the young star clusters blow superbubbles into the molecular ISM (Watkins)
    • A search for more evolved superbubbles, identified by their turbulent ionized ISM via PHANGS-MUSE, can be compared with the stellar clusters identified in PHANGS-HST. We quantify the energy associated with the clusters and measured in the ionized gas superbubbles to constrain what drives their growth and sustains their turbulent nature (Egorov)
    • Joining PHANGS-MUSE with PHANGS-HST, we can directly connect the ionizing stellar sources with their impact on the surrounding ISM, and match individual HII regions and individual ionizing clusters. Using the age information from SED modeling of the HST data allows us to trace an evolutionary sequence across a statistical sample of HII regions (Scheuermann)
    • Combining multi-wavelength observations, this project will identify supernova remnants and Wolf-Rayet star clusters within nearby galaxies. Using optical spectroscopy, we will then directly measure the radiative and mechanical input of stellar winds into the ISM. With statistical samples, we will spatially correlate supernova remnants and Wolf-Rayet star positions with the locations of current massive star formation to understand if this feedback serves to trigger or suppress star formation (Li)
    • Recently published results:
      • Measuring the mixing scale of the ISM within nearby spiral galaxies [ADS]
      • Mapping metallicity variations across nearby galaxy disks [ADS]
      • A 50 pc Scale View of Star Formation Efficiency across NGC 628 [ADS]

  • SDSS-V: The Local Volume Mapper (Survey planned 2022-2025)
    • The Local Volume Mapper (LVM) is an optical, integral-field spectroscopic survey that will target the Milky Way, Small and Large Magellanic Clouds, and other Local Volume galaxies at unprecidented spatial resolution (1-10pc). LVM will make use of new telescopes and newly built spectrographs that cover a wavelength range of 3600-10000 A, with spectral resolution R~4000 (based on the DESI spectrograph design). This new LVM instrument will collect roughly 20 million contiguous spectra over 2,500 square degrees of sky, including the midplane of the Milky Way, Orion, and the Magellanic Clouds from Las Campanas Observatory, Chile in SDSS-V.
    • White Paper [ADS]
    • A pilot study: IC 342 with MaNGA

  • SFB "The Milky Way System" - Quantifying the Impact of Feedback in the Milky Way Star-Forming Regions
    • LVM will resolve the internal structure of star forming regions and ionized nebulae, enabling us to observe the "energy injection scale" and quantify the impact of feedback. This subproject aims to compile catalogs of essential ancillary data and optimize the survey strategy, in order to ensure that SDSS-V/LVM data can be exploited as soon as it become available (Kreckel, Watkins)


Other ongoing projects:
  • FISHPPAK (Far-Inrared Selection of Herschel Pointings, PPAK Accessible) (PI: Kreckel)
    • A multi-wavelength view of the ISM provides critical insights into the varying physical conditions (temperature, density, metallicity) and gas phases (ionized, atomic, molecular). Dithered observations with the PMAS/PPAK instrument, with its combination of wide field of view and high resolution, provides a wealth of optical emission line information with the flexibility to spatially convolve and match lower resolution images for a variety of different instruments and different science goals. Pointing positions are selected based on the exisitng KINGFISH Herschel PACS fields for 21 galaxies.
    • Initial results compare dust in emission and absorption, quantify the multi-phase feedback from a starburst driven superwind, and identify star formation fueled through gas accretion.
    • Key project: Mapping the metallicity variations within M101 and their effect on the ISM (14 nights PMAS-PPAK project)

  • A 1000 hour HI deep field survey with the VLA - CHILES
    • Neutral hydrogen plays a central role in both driving and regulating star formation over cosmic time. We will produce the first HI deep field, to be carried out with the VLA in B array and covering a redshift range from z=0 to z=0.45

  • The Void Galaxy Survey (VGS): Star formation history and gas content of void galaxies
    • Void galaxies, residing within the deepest underdensities of the Cosmic Web, present an ideal population for the study of galaxy formation and evolution in an environment undisturbed by the complex processes modifying galaxies in clusters and groups, as well as provide an observational test for theories of cosmological structure formation.
    • A full IFU view of galaxies that inhabit voids: CAVITY



Completed projects:
  • The Reach of Stars: Connecting physical processes in the ISM with galaxy evolution
    • Using privileged access to KINGFISH, a legacy dataset of 61 galaxies, and data from our neighbour, the Andromeda galaxy (M31), we aimed to measure the "The Reach of Stars". We studied; a) the cooling mechanisms of the ISM using molecular and atomic emission lines, and b) ISM heating from the scales of molecular clouds and up, respectively, and reconcile these with the observed distribution of stars.
    • This project was funded through the DFG priority program 1573 "Physics of the Interstellar Medium", and ran from 2012-2018. A list of project-related publications is available here.