Research Interests

Resolving the Baryon Cycle within Nearby Galaxies

Emmy Noether Research Project, funded by the DFG

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. My research 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.


Funded by the European Research Council (ERC) Starting Grant

The introduction of heavy elements (metals) into the interstellar medium (ISM) via stellar feedback processes is crucial for the regulation of star formation and thus galaxy evolution. Metals set the heating and cooling balance in star-forming regions, and establish the carbon chemistry that is necessary for life on our planet. The gas-phase metal abundance (metallicity) is the most accessible measure of the build-up of chemical enrichment over cosmic time. However, there are large systematic uncertainties in our metallicity measurements, to the extent that we do not know if most galaxies are metal-rich or metal-poor compared to the Milky Way. These long-standing uncertainties plague our understanding of metal variations, but can now be addressed by vast new homogeneous data sets resolving tens of thousands of individual HII regions across nearby galaxies. This ambitious ERC starting grant tackles this problem by applying a data-driven approach to emission line measurements in our own Milky Way, Local Group galaxies (SDSS-V/LVM) and more distant Local Volume galaxies (PHANGS-MUSE). This project aims to resolve long-standing discrepancies in absolute metallicity calibrations and develop new and robust prescriptions that directly address electron temperature uncertainties. We will apply our methods to map out metallicity variations across more than 50 galaxies, providing quantitative constraints on the mixing scale and correlations with local physical conditions in the ISM. By establishing a new homogeneous local benchmark for absolute metallicity measurements, the ISM-METALS project will build a foundation for future studies of galaxy metallicities, enabling the robust interpretation of metallicity variations soon to be measured across cosmic time with upcoming new facilities (JWST, ELT).

Ongoing projects and projects and project leads within the 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)
  • A pilot project for LVM, we use the SDSS-IV instrument MaNGA to survey 10 x 10 kpc in the disk of IC 342 (Kreckel)

Recently published results

  • Kreckel, Egorov, et al 2022, A physically motivated `charge-exchange method' for measuring electron temperatures within HII regions [ADS]
  • Scheuermann, Kreckel et al. 2022, Planetary Nebula Luminosity Function distances for 19 galaxies observed by PHANGS-MUSE [ADS]
  • Williams, Kreckel et al. 2022, The 2D metallicity distribution and mixing scales of nearby galaxies [ADS]
  • Barnes, Chandar, Kreckel et al. 2022 Linking stellar populations to HII regions across nearby galaxies: I. Constraining pre-supernova feedback from young clusters in NGC1672 [ADS]
  • Santoro, Kreckel, et al. 2022 PHANGS-MUSE: The H II region luminosity function of local star-forming galaxies [ADS]
  • Lamarche, Smith, Kreckel et al. 2022 Direct Far-infrared Metal Abundances (FIRA). I. M101 [ADS]
  • Egorov et al. 2021, Star formation in the nearby dwarf galaxy DDO 53: interplay between gas accretion and stellar feedback [ADS]
  • Barnes, Glover, Kreckel et al. 2021 Comparing the pre-SNe feedback and environmental pressures for 6000 H II regions across 19 nearby spiral galaxies [ADS]
  • Kreckel et al. 2020, Measuring the mixing scale of the ISM within nearby spiral galaxies [ADS]
  • Kreckel et al. 2019, Mapping metallicity variations across nearby galaxy disks [ADS]
  • 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.

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    SDSS-V: The Local Volume Mapper

    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.

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    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. Within the Baryon Cycle group, our 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.

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    Other ongoing projects:

    FISHPPAK (Far-Inrared Selection of Herschel Pointings, PPAK Accessible)

    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.

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    CHILES: A 1000 hour HI deep field survey with the VLA

    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

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    The Void Galaxy Survey (VGS)

    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. Curent work aims to obtain a full IFU view of galaxies that inhabit voids through the CAVITY project.

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    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.

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