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Star formation in galaxies is regulated by turbulence, outflows, gas heating and cloud dispersal -- processes which depend sensitively on the properties of the interstellar medium (ISM) into which supernovae (SNe) explode. Unfortunately, direct measurements of ISM environments around SNe remain scarce, as SNe are rare and often distant. Here we demonstrate a new approach: mapping the ISM around the massive stars that are soon to explode. This provides a much larger census of explosion sites than possible with only SNe, and allows comparison with sensitive, high-resolution maps of the atomic and molecular gas from the Jansky VLA and ALMA. In the well-resolved Local Group spiral M33, we specifically observe the environments of red supergiants (RSGs, progenitors of Type II SNe), Wolf-Rayet stars (WRs, tracing stars >30 M⊙, and possibly future stripped-envelope SNe), and supernova remnants (SNRs, locations where SNe have exploded). We find that massive stars evolve not only in dense, molecular-dominated gas (with younger stars in denser gas), but also a substantial fraction (∼45\% of WRs; higher for RSGs) evolve in lower-density, atomic-gas-dominated, inter-cloud media. We show that these measurements are consistent with expectations from different stellar-age tracer maps, and can be useful for validating SN feedback models in numerical simulations of galaxies. Along with the discovery of a 20-pc diameter molecular gas cavity around a WR, these findings re-emphasize the importance of pre-SN/correlated-SN feedback evacuating the dense gas around massive stars before explosion, and the need for high-resolution (down to pc-scale) surveys of the multi-phase ISM in nearby galaxies.
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HII Regions and the Warm Ionized Medium
Plasma of temperature 10,000K is created by OB stars and takes the form of discrete HII regions and diffuse gas. It is the key to determining the impact of massive stars on the interstellar medium (ISM) and the lifecycle of ISM gas. We review research this plasma, highlight outstanding questions, and provide recommendations for future facilities.
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- Award ID(s):
- 1714688
- PAR ID:
- 10109626
- Date Published:
- Journal Name:
- Bulletin of the American Astronomical Society
- Volume:
- 51
- Issue:
- 3
- ISSN:
- 2330-9458
- Page Range / eLocation ID:
- 137
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The interstellar medium (ISM) of galaxies like the Milky Way contains low-density diffuse ionized gas (DIG). High-mass stars emit large amounts of ionizing radiation and it is believed that a fraction of this radiation escapes from their HII regions and into the ISM where it is responsible for maintaining the ionization of the DIG. The goal of this dissertation work is to better understand how the radiation produced by high-mass stars is able to leak from the HII regions, how the radiation field changes during this process, and how the radiation affects the ambient ISM. Using Green Bank Telescope (GBT) pointed radio recombination line (RRL) data of a subset of Galactic HII regions and fully-sampled RRL maps from the GBT Diffuse Ionized Gas Survey (GDIGS), we show that the morphology of the photodissociation region surrounding an HII region strongly affects the amount of leaking radiation. We also show that physically large HII regions affect the surrounding ISM out to larger distances from the region. This indicates that giant HII region complexes may have a greater effect on maintaining the ionization of the DIG. We find a correlation between dust temperature and integrated RRL intensity, suggesting that the same radiation field that heats the dust also maintains the ionization of the DIG.more » « less
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ABSTRACT We study gas inflows on to supermassive black holes using hydrodynamics simulations of isolated galaxies and idealized galaxy mergers with an explicit, multiphase interstellar medium (ISM). Our simulations use the recently developed ISM and stellar evolution model called Stars and MUltiphase Gas in GaLaxiEs (SMUGGLE). We implement a novel super-Lagrangian refinement scheme that increases the gas mass resolution in the immediate neighbourhood of the black holes (BHs) to accurately resolve gas accretion. We do not include black hole feedback in our simulations. We find that the complex and turbulent nature of the SMUGGLE ISM leads to highly variable BH accretion. BH growth in SMUGGLE converges at gas mass resolutions ≲3 × 103 M⊙. We show that the low resolution simulations combined with the super-Lagrangian refinement scheme are able to produce central gas dynamics and BH accretion rates very similar to that of the uniform high resolution simulations. We further explore BH fueling by simulating galaxy mergers. The interaction between the galaxies causes an inflow of gas towards the galactic centres and results in elevated and bursty star formation. The peak gas densities near the BHs increase by orders of magnitude resulting in enhanced accretion. Our results support the idea that galaxy mergers can trigger AGN activity, although the instantaneous accretion rate depends strongly on the local ISM. We also show that the level of merger-induced enhancement of BH fueling predicted by the SMUGGLE model is much smaller compared to the predictions by simulations using an effective equation of state model of the ISM.more » « less
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Context.Feedback from stars in the form of radiation, stellar winds, and supernovae is crucial to regulating the star formation activity of galaxies. Dwarf galaxies are especially susceptible to these processes, making them an ideal test bed for studying the effects of stellar feedback in detail. Recent numerical models have aimed to resolve the interstellar medium (ISM) in dwarf galaxies with a very high resolution of several solar masses. However, when it comes to modeling the radiative feedback from stars, many models opt for simplified approaches instead of explicitly solving radiative transfer (RT) because of the computational complexity involved. Aims.We introduce the Realistic ISM modeling in Galaxy Evolution and Lifecycles (RIGEL) model, a novel framework to self-consistently model the effects of stellar feedback in the multiphase ISM of dwarf galaxies with explicit RT on a star-by-star basis. Methods.The RIGEL model integrates detailed implementations of feedback from individual massive stars into the state-of-the-art radiation-hydrodynamics code,AREPO-RT. It forms individual massive stars from the resolved multiphase ISM by sampling the initial mass function and tracks their evolution individually. The lifetimes, photon production rates, mass-loss rates, and wind velocities of these stars are determined by their initial masses and metallicities based on a library that incorporates a variety of stellar models. The RT equations are solved explicitly in seven spectral bins accounting for the infrared to He IIionizing bands, using a moment-base scheme with the M1 closure relation. The thermochemistry model tracks the nonequilibrium H, He chemistry as well as the equilibrium abundance of C I, C II, O I, O II, and CO in the irradiated ISM to capture the thermodynamics of all ISM phases, from cold molecular gas to hot ionized gas. Results.We evaluated the performance of the RIGEL model using 1 M⊙resolution simulations of isolated dwarf galaxies. We found that the star formation rate (SFR) and interstellar radiation field (ISRF) show strong positive correlations with the metallicity of the galaxy. Photoionization and photoheating can reduce the SFR by an order of magnitude by removing the available cold, dense gas fuel for star formation. The presence of ISRF also significantly changes the thermal structure of the ISM. Radiative feedback occurs immediately after the birth of massive stars and rapidly disperses the molecular clouds within 1 Myr. As a consequence, radiative feedback reduces the age spread of star clusters to less than 2 Myr, prohibits the formation of massive star clusters, and shapes the cluster initial mass function to a steep power-law form with a slope of ∼ − 2. The mass-loading factor (measured atz = 1 kpc) of the fiducial galaxy has a median ofηM ∼ 50, while turning off radiative feedback reduces this factor by an order of magnitude. Conclusions.We demonstrate that RIGEL effectively captures the nonlinear coupling of early radiative feedback and supernova feedback in the multiphase ISM of dwarf galaxies. This novel framework enables the utilization of a comprehensive stellar feedback and ISM model in cosmological simulations of dwarf galaxies and various galactic environments spanning a wide dynamic range in both space and time.more » « less
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