Dr. Oleg V. Egorov

Research

I study how feedback from massive stars regulates the interstellar medium (ISM), star formation, and chemical evolution of nearby galaxies, with a particular interest in the Local Volume dwarf galaxies. I am also interested in how external gas inflows, resulting from accretion, tidal interactions, and mergers, regulate star formation and galaxy evolution. My work relies largely on optical integral-field spectroscopy, which I use alongside other multiwavelength data to analyse the morphology, kinematics, physical conditions, and chemical abundances of gas and dust on scales from small H II regions to kiloparsec-sized star-forming complexes, superbubbles and outflows.

Stellar feedback and the multi-phase ISM

Radiation, winds, from massive stars, and subsequent supernovae heat, ionize, enrich, and stir up the ISM, from individual H II regions to kiloparsec-scale star-forming complexes and superbubbles, thereby regulating how efficiently galaxies form stars. Which feedback mechanisms dominate, how their energy couples to the different phases of the ISM, and how this changes with environment are key open questions.

My approach I compare the kinematics and energetics of the different gas phases with the young stars and star clusters that power it, across samples of nearby galaxies.

Superbubbles and turbulent ionized gas in PHANGS-MUSE galaxies, and the energy balance with the young stars that drive them (Egorov et al. 2023).
Superbubbles and turbulent ionized gas in PHANGS-MUSE galaxies, and the energy balance with the young stars that drive them (Egorov et al. 2023).

Highlight papers

Ionized gas as a diagnostic tool

Emission lines are the main source of information on the physical conditions, chemical composition, and dynamics of ionized gas in star-forming regions. Interpreting them correctly requires knowing how density, temperature, ionization, and metallicity vary within H II regions and the diffuse ionized gas, and what information is lost when a nebula is observed unresolved, as is the case for distant galaxies.

My approach I map these properties from sub-parsec to kiloparsec scales using optical spectroscopy: SDSS-V LVM in the Milky Way and the Magellanic Clouds, and MUSE and other instruments in nearby galaxies.

SDSS-V LVM observations of the Galactic WR nebula S 308 reveal strong variations in electron temperature, chemical abundances, and ionisation state. (Egorov et al., submitted).
SDSS-V LVM observations of the Galactic WR nebula S 308 reveal strong variations in electron temperature, chemical abundances, and ionisation state. (Egorov et al., submitted).

Highlight papers

Dwarf galaxies and low-metallicity environments

Dwarf galaxies are the most common type of galaxy and the closest local analogues of the young, metal-poor galaxies of the early Universe. Their shallow potential wells, low metallicities, and large gas reservoirs alter how stars form and how strongly massive stars affect the surrounding gas, driving expanding superbubbles and outflows and, in some cases, enriching the environment through unusual massive stars.

My approach I study how the ISM and massive stars are connected in Local Volume dwarf galaxies, combining high-resolution 3D spectroscopy of the ionized gas with data on the neutral gas and resolved stellar populations.

Ionized superbubbles in the metal-poor Local Group dwarf galaxy Sextans B (Gerasimov, Egorov et al. 2024).
Ionized superbubbles in the metal-poor Local Group dwarf galaxy Sextans B (Gerasimov, Egorov et al. 2024).

Highlight papers

Dust and PAHs in star-forming regions

Dust grains and polycyclic aromatic hydrocarbons (PAHs) reprocess a large fraction of the starlight in galaxies and regulate the heating and cooling of the ISM. PAHs are destroyed in star-forming regions and are scarce at low metallicity, while the depletion of metals onto dust grains alters the gas-phase abundances we measure. Understanding both is therefore essential for using essential for using dust and gas as reliable tracers of star formation and chemical evolution.

My approach I combine mid-infrared imaging with spectroscopy of the ionized gas to relate the dust and PAH content of the ISM to the local radiation field, metallicity and the young stars, for large samples of star-forming regions.

PHANGS-JWST view of NGC 628 and the anti-correlation between the PAH fraction and the ionization parameter of H II regions (Egorov et al. 2023).
PHANGS-JWST view of NGC 628 and the anti-correlation between the PAH fraction and the ionization parameter of H II regions (Egorov et al. 2023).

Highlight papers

Gas accretion onto galaxies

Galaxies need a continuous supply of gas to keep forming stars. Accretion from the intergalactic medium, as well as tidal interactions and mergers, brings in fresh fuel, alters the chemical composition of the gas, and reshapes galaxies, producing polar rings, kinematically decoupled gas, and tidal structures. Linking resolved observations to cosmological simulations is key to understanding how gas inflows drive galaxy assembly.

My approach I look for kinematic and chemical signatures of external gas — motions decoupled from the stellar disc, or gas that is more metal-poor than expected — combining 3D spectroscopy of the ionized gas with multiwavelength data on the stars and the neutral gas.

The void galaxy Ark 18: optical image and the ionized-gas velocity field from the scanning Fabry–Pérot interferometer at the 6-m telescope, the basis of its interpretation as a dwarf–dwarf merger remnant (Egorova, Egorov et al. 2021).
The void galaxy Ark 18: optical image and the ionized-gas velocity field from the scanning Fabry–Pérot interferometer at the 6-m telescope, the basis of its interpretation as a dwarf–dwarf merger remnant (Egorova, Egorov et al. 2021).

Highlight papers

Methods and instruments

Integral-field spectroscopy (IFS) provides a spectrum for every point of an extended object. Scanning Fabry-Pérot interferometers combine high spectral resolution with a wide field of view, which is ideal for studying the kinematics of ionised gas, while classical integral-field units (IFUs) offer broad spectral coverage. Novel ultra-wide-field IFUs, such as SDSS-V LVM and SDSS-VI LVM2, map large areas of the sky. Imaging data and photoionisation models connect these spectra to the physical properties of the gas, dust, and stars. All these techniques demand substantial effort in data processing and analysis to turn raw observations into final data products and physical properties.

My approach I work on developing or improving the software behind these data, and on releasing the data products to the community.

Initial 101 SDSS-V LVM survey tiles covering the H II region IC 434 within Orion. Continuum-subtracted [S III]9532 (magenta), [S II]6717+6731 (blue), and Hα (orange) trace high-ionisation, low-ionisation, and average nebular emission, respectively, at <0.1 pc scales. (Drory et al. 2024).
Initial 101 SDSS-V LVM survey tiles covering the H II region IC 434 within Orion. Continuum-subtracted [S III]9532 (magenta), [S II]6717+6731 (blue), and Hα (orange) trace high-ionisation, low-ionisation, and average nebular emission, respectively, at <0.1 pc scales. (Drory et al. 2024).

Highlight papers

Surveys and collaborations

  • PHANGS

    Physics at High Angular resolution in Nearby GalaxieS — a multi-wavelength survey of nearby star-forming galaxies with ALMA, VLT/MUSE, HST, JWST, MeerKAT and more. I am a lead of the Ionized ISM & Stellar Feedback working group.

  • SDSS-V · Local Volume Mapper (LVM)

    A wide-field integral-field spectroscopic survey mapping the ionized gas and stellar population of the Milky Way plane and the Magellanic Clouds. I am SDSS-V Architect and Lead of the LVM Data QA efforts.

  • After-Sloan-5 (SDSS-VI) · LVM2

    The next-generation wide-field IFU survey within SDSS-VI that will map M31, M33 and northern nearby dwarf galaxies (LVM2-North), and perform deep observations of the Galactic plane to systematically map faint emission lines (LVM2-South). I am a Survey Scientist.

  • SIGMA-FPI

    Supersonic Ionized Gas Motions Analysis performed with Fabry–Pérot Interferometer — a public archive of high-resolution (R ≈ 8000–16 000) scanning Fabry–Pérot observations (data cubes and maps) of ~90 nearby, mostly dwarf galaxies obtained at the 6-m BTA telescope since 2001. I am the lead author of the archive.

Software

Developing or contributions to the data reduction and analysis pipelines:

SDSS-V Local Volume Mapper
  • lvmdatasimulator LVM data simulator; co-developer
  • lvmqa LVM QA pipeline (currently not public), developer
  • lvmdrp LVM data reduction; contributor
PHANGS
Other pipelines
  • ifured SCORPIO-2/IFU data reduction (IDL); developer
  • longred long-slit data reduction with a 'one-interpolation' approach; developer
  • kinescope A tool for Fabry–Pérot data cube analysis (IDL); developer