Observable and ionizing properties of star-forming galaxies with very massive stars and different IMFs

Abstract

The presence of very massive stars (VMS, masses $>100$ M${}_{\odot }$) is now firmly established in the local group, nearby galaxies, and out to cosmological distances. If present, these stars could boost the UV luminosity and ionizing photon production of galaxies, helping thus to alleviate the overabundance of UV-bright galaxies found with the JWST at high-redshift. Combing consistent stellar evolution and atmosphere models tailored to VMS we compute spectral energy distributions (SEDs) for a large set of models. We find that VMS contribute significantly to the UV luminosity and Lyman continuum of young stellar populations, and they are characterized by strong stellar HeII1640 emission, with EW(HeII) up to 4-8 Ang at young ages or $\sim 2.5-4$ Ang for constant SFR. For IMFs with a Salpeter slope, the boost of the UV luminosity is relatively modest. However, small changes in the IMF slope (e.g.~from ${\alpha }_2=-2.35$ to $-2$) lead to large increases in $L_{UV}$ and the ionizing photon production $Q$. Emission line strengths and the ionizing photon efficiency ${\xi }_{\mathrm{ion}}$ are also increased with VMS. Interestingly, SEDs including VMS show smaller Lyman breaks, and the shape of the ionizing spectra remain unaltered up to $\sim 35$ eV, but becomes softer at higher energies. We derive and discuss the maximum values quantities such as $L_{UV}$ per stellar mass or unit SFR, and ${\xi }_{\mathrm{ion}}$, $Q$ can reach when VMS are included, and we show that these values become essentially independent of the IMF. We propose observational methods to test for VMS and constrain the IMF. Finally, using JWST observations, we examine if high-redshift galaxies show some evidence of the presence of VMS and signs of non-standard IMFs. Very top-heavy IMFs can be excluded on average, but the IMF could well extend into the regime of VMS and be flatter than Salpeter in the bulk of high-$z$ galaxies. (abridged)

16 pages, 11 figures. Astronomy & Astrophysics, in press

References in corpus (42)

• Cosmic Star Formation History
• Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
• The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit
• A Comprehensive Study on Galaxies at z~9-16 Found in the Early JWST Data: UV Luminosity Functions and Cosmic Star-Formation History at the Pre-Reionization Epoch
• CEERS Key Paper I: An Early Look into the First 500 Myr of Galaxy Formation with JWST
• Efficient Formation of Massive Galaxies at Cosmic Dawn by Feedback-Free Starbursts
• The chemical enrichment in the early Universe as probed by JWST via direct metallicity measurements at z~8
• An excess of massive stars in the local 30 Doradus starburst
• Spectroscopic confirmation of two luminous galaxies at $z\sim 14$
• Mass loss from late-type WN stars and its Z-dependence: very massive stars approaching the Eddington limit
• A massive quiescent galaxy at redshift 4.658
• On the stunning abundance of super-early, massive galaxies revealed by JWST
• The brightest galaxies at Cosmic Dawn
• New Constraints on the Lyman Continuum Escape Fraction at z~1.3
• Wolf-Rayet stars in the Small Magellanic Cloud: I. Analysis of the single WN stars
• New Insights into the Evolution of Massive Stars and Their Effects on Our Understanding of Early Galaxies
• The JWST-PRIMAL Legacy Survey. A JWST/NIRSpec reference sample for the physical properties and Lyman-$\alpha$ absorption and emission of $\sim 500$ galaxies at $z=5.5-13.4$
• The Star Formation Burstiness and Ionizing Efficiency of Low-mass Galaxies
• Low-redshift compact star-forming galaxies as analogues of high-redshift star-forming galaxies
• An extreme blue nugget, UV-bright starburst at z=3.613 with ninety per cent of Lyman continuum photon escape
• The production of ionizing photons in UV-faint z~3-7 galaxies
• The impact of an evolving stellar initial mass function on early galaxies and reionisation
• How extreme are the Wolf-Rayet clusters in NGC3125?
• The UV-brightest Lyman continuum emitting star-forming galaxy
• Mass loss and the Eddington parameter: a new mass-loss recipe for hot and massive stars
• Very Massive Stars and Pair-Instability Supernovae: Mass-loss Framework for low Metallicity
• Resolving the core of R136 in the optical
• Spectroscopic evolution of very massive stars at Z = 1/2.5 Zsun
• Clues on the presence and segregation of very massive stars in the Sunburst Lyman-continuum cluster at z=2.37
• The Sunburst Arc with JWST: I. Detection of Wolf-Rayet stars injecting nitrogen into a low-metallicity, $z=2.37$ proto-globular cluster leaking ionizing photons
• A strong He II $\lambda$1640 emitter with extremely blue UV spectral slope at $z=8.16$: presence of Pop III stars?
• Physics and evolution of the most massive stars in 30 Dor. Mass loss, envelope inflation, and a variable upper stellar mass limit
• WO-Type Wolf-Rayet Stars: the Last Hurrah of Massive Star Evolution
• Implications of a Temperature Dependent IMF I: Photometric Template Fitting
• Inferring the presence of very massive stars in local star-forming regions
• Evidence for Very Massive Stars in extremely UV-bright star-forming galaxies at $z\sim 2.2-3.6$
• Extreme broad He\2 emission at high and low redshifts: the dominant role of VMS in NGC 3125-A1 and CDFS131717
• Spectral properties and detectability of supermassive stars in protoglobular clusters at high redshift
• Very Massive Star Models: I. Impact of Rotation and Metallicity and Comparisons with Observations
• Implications of a Temperature Dependent IMF II: An Updated View of the Star-Forming Main Sequence
• Detection of He++ ion in the star-forming ring of the Cartwheel using MUSE data and ionizing mechanisms
• Non-Universal Stellar Initial Mass Functions: Large Uncertainties in Star Formation Rates at $z\approx 2-4$ and Other Astrophysical Probes

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