When did the initial mass function become bottom-heavy?

Abstract

The characteristic mass that sets the peak of the stellar initial mass function (IMF) is closely linked to the thermodynamic behaviour of interstellar gas, which controls how gas fragments as it collapses under gravity. As the Universe has grown in metal abundance over cosmic time, this thermodynamic behaviour has evolved from a primordial regime dominated by the competition between compressional heating and molecular hydrogen cooling to a modern regime where the dominant process in dense gas is protostellar radiation feedback, transmitted to the gas by dust-gas collisions. In this paper we map out the primordial-to-modern transition by constructing a model for the thermodynamics of collapsing, dusty gas clouds at a wide range of metallicities. We show the transition from the primordial regime to the modern regime begins at metallicity $Z\sim 10^{-4}{\mathrm{Z}}_{\odot }$, passes through an intermediate stage where metal line cooling is dominant at $Z\sim 10^{-3}{\mathrm{Z}}_{\odot }$, and then transitions to the modern dust- and feedback-dominated regime at $Z\sim 10^{-2}{\mathrm{Z}}_{\odot }$. In low pressure environments like the Milky Way, this transition is accompanied by a dramatic change in the characteristic stellar mass, from $\sim 50{\mathrm{M}}_{\odot }$ at $Z\sim 10^{-6}{\mathrm{Z}}_{\odot }$ to $\sim 0.3{\mathrm{M}}_{\odot }$ once radiation feedback begins to dominate, which marks the appearance of the modern bottom-heavy Milky Way IMF. In the high pressure environments typical of massive elliptical galaxies, the characteristic mass for the modern, dust-dominated regime falls to $\sim 0.1{\mathrm{M}}_{\odot }$, thus providing an explanation for the more bottom-heavy IMF observed in these galaxies. We conclude that metallicity is a key driver of variations in the characteristic stellar mass, and by extension, the IMF.

26 pages (main result in figures 7 and 8). MNRAS in press

References in corpus (86)

• Array Programming with NumPy
• Theory of Star Formation
• A systematic variation of the stellar initial mass function in early-type galaxies
• The Resolved Properties of Extragalactic Giant Molecular Clouds
• The Atomic to Molecular Transition in Galaxies. II: HI and H_2 Column Densities
• On the Star Formation Efficiency of Turbulent Magnetized Clouds
• Physical properties of molecular clouds for the entire Milky Way disk
• An extremely primitive halo star
• The Mass Distribution and Lifetime of Prestellar Cores in Perseus, Serpens, and Ophiuchus
• The Effects of Radiative Transfer on Low-Mass Star Formation
• The Mass Spectrum of the First Stars
• Fragmentation of star-forming clouds enriched with the first dust
• The Importance of Radiative Feedback for the Stellar Initial Mass Function
• Uncertainties in H2 and HD Chemistry and Cooling and their Role in Early Structure Formation
• An excess of massive stars in the local 30 Doradus starburst
• HI-to-H2 Transitions and H I Column Densities in Galaxy Star-Forming Regions
• N-body modeling of globular clusters: Masses, mass-to-light ratios and intermediate-mass black holes
• Radial variations in the stellar initial mass function of early-type galaxies
• Fragmentation of Massive Protostellar Disks
• Modeling jet and outflow feedback during star cluster formation
• The chemistry of population III supernova ejecta: II - The nucleation of molecular clusters as a diagnostic for dust in the early universe
• Disentangling the Galactic Halo with APOGEE: I. Chemical and Kinematical Investigation of Distinct Metal-Poor Populations
• Effective destruction of CO by cosmic rays: implications for tracing H${}_2$ gas in the Universe
• Variations of the stellar initial mass function in the progenitors of massive early-type galaxies and in extreme starburst environments
• On the Evolutionary History of Stars and their Fossil Mass and Light
• Very high redshift quasars and the rapid emergence of super-massive black holes
• Diverging UV and Halpha fluxes of star forming galaxies predicted by the IGIMF theory
• The SINFONI Nearby Elliptical Lens Locator Survey: Discovery of two new low-redshift strong lenses and implications for the initial mass function in giant early-type galaxies
• The statistical properties of stars and their dependence on metallicity
• The statistical properties of stars and their dependence on metallicity: the effects of opacity
• Variations in the initial mass function in early-type galaxies: A critical comparison between dynamical and spectroscopic results
• On the Constancy of the Characteristic Mass of Young Stars
• When did Population III star formation end?
• Physical Properties of Molecular Clouds at 2 parsec Resolution in the Low-Metallicity Dwarf Galaxy NGC 6822 and the Milky Way
• Tidally induced brown dwarf and planet formation in circumstellar discs
• Understanding star formation in molecular clouds II. Signatures of gravitational collapse of IRDCs
• Merge or survive: Number of Population III stars per minihalo
• HD and H2 formation in low-metallicity dusty gas clouds at high redshift
• The possible role of stellar mergers for the formation of multiple stellar populations in globular clusters
• The lowest detected stellar Fe abundance: The halo star SMSS J160540.18-144323.1
• R-Process elements from magnetorotational hypernovae
• The physics of gas phase metallicity gradients in galaxies
• Evidence for an aspherical Population III supernova explosion inferred from the hyper metal-poor star HE1327-2326
• Cosmic-Ray Heating of Molecular Gas in the Nuclear Disk: Low Star Formation Efficiency
• The Stellar Initial Mass Function in Early-Type Galaxies From Absorption Line Spectroscopy. IV. A Super-Salpeter IMF in the center of NGC 1407 from Non-Parametric Models
• CO-dark molecular gas at high redshift: very large H${}_2$ content and high pressure in a low metallicity damped Lyman-alpha system
• Is the dust-to-gas ratio constant in molecular clouds?
• The Pristine survey VIII: The metallicity distribution function of the Milky Way halo down to the extremely metal-poor regime
• Characterizing the Brown Dwarf Formation Channels from the Initial Mass Function and Binary-star Dynamics
• Zero-metallicity hypernova uncovered by an ultra metal-poor star in the Sculptor dwarf spheroidal galaxy
• The Pristine Inner Galaxy Survey (PIGS) II: Uncovering the most metal-poor populations in the inner Milky Way
• Further evidence for a time-dependent initial mass function in massive early-type galaxies
• Ultra-faint dwarf galaxies: unveiling the minimum mass of the first stars
• Carbon monoxide in an extremely metal-poor galaxy
• Connection between dynamically derived IMF normalisation and stellar population parameters
• Galaxy structure from multiple tracers: III. Radial variations in M87's IMF
• Chemodynamics of a Simulated Disc Galaxy: Initial Mass Functions and SNIa Progenitors
• Supernova dust formation and the grain growth in the early universe: The critical metallicity for low-mass star formation
• Impact of Cosmic Rays on Population III Star Formation
• The Astrochemical Impact of Cosmic Rays in Protoclusters I: Molecular Cloud Chemistry
• The Origin of the Stellar Mass Distribution and Multiplicity
• Metallicity and the Universality of the IMF
• On the dynamics of dust during protostellar collapse
• Accretion Phase of Star Formation in Clouds with Different Metallicities
• Formation of Wide Binaries by Turbulent Fragmentation
• The IMF and multiplicity of stars from gravity, turbulence, magnetic fields, radiation and outflow feedback
• The CO-dark molecular gas mass in 30 Doradus
• Dynamical evolution of Population III stellar systems and the resulting binary statistics
• Combining radiative transfer and diffuse interstellar medium physics to model star formation
• The DUVET Survey: Direct $T_e$-based metallicity mapping of metal-enriched outflows and metal-poor inflows in Mrk 1486
• High resolution spectroscopic follow-up of the most metal-poor candidates from SkyMapper DR1.1
• Extreme CO Isotopologue Line Ratios in ULIRGS: Evidence for a top-heavy IMF
• Disk fragmentation and the formation of population III stars
• Big Fish in Small Ponds: Massive Stars in the Low Mass Clusters of M83
• Testing Star Formation Laws on Spatially Resolved Regions in a $z\approx 4.3$ Starburst Galaxy
• Spatially resolved carbon and oxygen isotopic ratios in NGC 253 using optically thin tracers
• Sampling methods for stellar masses and the mmax-Mecl relation in the starburst dwarf galaxy NGC 4214
• Quantifying the Universality of the Stellar Initial Mass Function in Old Star Clusters
• Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF?
• A new approach to determine optically thick H2 cooling and its effect on primordial star formation
• New ultra metal-poor stars from SDSS: follow-up GTC medium-resolution spectroscopy
• Evidence for Two Distinct Stellar Initial Mass Functions : Probing for Clues to the Dichotomy
• Implementation of stellar heating feedback in simulations of star cluster formation: effects on the initial mass function
• Modelling the Observed Stellar Mass Function and its Radial Variation in Galactic Globular Clusters
• On the origin of the peak of the stellar initial mass function: exploring the tidal screening theory
• Far-Infrared Spectral Energy Distributions and Photometric Redshifts of Dusty Galaxies