Is it possible to reconcile extragalactic IMF variations with a universal Milky Way IMF?

Abstract

One of the most robust observations of the stellar initial mass function (IMF) is its near-universality in the Milky Way and neighboring galaxies. But recent observations of early-type galaxies can be interpreted to imply a bottom-heavy IMF, while others of ultra-faint dwarfs could imply a top-heavy IMF. This would impose powerful constraints on star formation models. We explore what sort of cloud-scale IMF models could possibly satisfy these constraints. We utilize simulated galaxies which reproduce (broadly) the observed galaxy properties, while they also provide the detailed star formation history and properties of each progenitor star-forming cloud. We then consider generic models where the characteristic mass of the IMF is some arbitrary power-law function of progenitor cloud properties, along with well-known literature IMF models, which scale with Jeans mass, turbulent Bonnor-Ebert mass, temperature, the opacity limit, metallicity, or the protostellar heating mass. We show that no IMF models currently in the literature - nor any model where the turnover mass is an arbitrary power-law function of a combination of cloud temperature/density/size/metallicity/velocity dispersion/magnetic field - can reproduce the claimed IMF variation in ellipticals or dwarfs without severely violating observational constraints in the Milky Way. Specifically, they predict too much variation in the extreme environments of the Galaxy, compared to that observed. Either the IMF varies in a more complicated manner, or alternative interpretations of the extragalactic observations must be explored.

12 pages, 8 figures, 4 tables

References in corpus (23)

• The effect of photo-ionization on the cooling rates of enriched, astrophysical plasmas
• A systematic variation of the stellar initial mass function in early-type galaxies
• Analytical theory for the initial mass function: CO clumps and prestellar cores
• The 2013 Release of Cloudy
• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• The Stellar Population of the Chamaeleon I Star-Forming Region
• The Importance of Radiative Feedback for the Stellar Initial Mass Function
• Black Holes on FIRE: Stellar Feedback Limits Early Feeding of Galactic Nuclei
• Radial variations in the stellar initial mass function of early-type galaxies
• The SL2S Galaxy-scale Lens Sample. V. Dark Matter Halos and Stellar IMF of Massive Early-type Galaxies out to Redshift 0.8
• 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
• Evidence for primordial mass segregation in globular clusters
• Variations in the initial mass function in early-type galaxies: A critical comparison between dynamical and spectroscopic results
• The stellar initial mass function of early type galaxies from low to high stellar velocity dispersion: homogeneous analysis of ATLAS${}^{3D}$ and Sloan Lens ACS galaxies
• The initial mass function of a massive relic galaxy
• Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses
• 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
• The Complete Initial Mass Function Down to the Sub-Solar Regime in the Large Magellanic Cloud with Hubble Space Telescope ACS Observations
• The low-mass Initial Mass Function in the young cluster NGC 6611
• Initial Mass Function Variability (or not) Among \\ Low-Velocity Dispersion, Compact Stellar Systems
• Stellar dynamics in the strong-lensing central galaxy of Abell 1201: A low stellar mass-to-light ratio, a large central compact mass, and a standard dark matter halo
• Improved mass constraints for two nearby strong-lensing elliptical galaxies from Hubble Space Telescope Imaging
• Low-mass pre--main-sequence stars in the Magellanic Clouds

Cited by in corpus (7)

• Unveiling the time evolution of chemical abundances across the Milky Way disk with APOGEE
• Evolution of giant molecular clouds across cosmic time
• On the origin of the peak of the stellar initial mass function: exploring the tidal screening theory
• The statistical properties of stars at redshift, z=5, compared with the present epoch
• Stellar initial mass function variation in massive early-type galaxies: the potential role of the deuterium abundance
• When did the initial mass function become bottom-heavy?
• Fornax 3D project: assessing the diversity of IMF and stellar population maps within the Fornax Cluster