Halo White Dwarfs and the Hot Intergalactic Medium

Abstract

We present a schematic model for the formation of baryonic galactic halos and hot gas in the Local Group and the intergalactic medium. We follow the dynamics, chemical evolution, heat flow and gas flows of a hierarchy of scales, including: protogalactic clouds, galactic halos, and the Local Group itself. Within this hierarchy, the Galaxy is built via mergers of protogalactic fragments. We find that early bursts of star formation lead to a large population of remnants (mostly white dwarfs), which would reside presently in the halo and contribute to the dark component observed in the microlensing experiments. The hot, metal-rich gas from early starbursts and merging evaporates from the clouds and is eventually incorporated into the intergalactic medium. The model thus suggests that most microlensing objects could be white dwarfs ($m \sim 0.5 \msol$), which comprise a significant fraction of the halo mass. Furthermore, the Local Group could have a component of metal-rich hot gas similar to, although less than, that observed in larger clusters. We discuss the known constraints on such a scenario and show that all local observations can be satisfied with present data in this model. The best-fit model has a halo that is 40% baryonic, with an upper limit of 77%.

15 pages, LaTex, uses aas2pp4.sty, 7 postscript figures. Substantially revised and enlarged to a full-length article. Somewhat different quantitative results, but qualitative conclusions unchanged

References in corpus (12)

• A Theory of the IMF for Star Formation in Molecular Clouds
• A ROSAT survey of Hickson's compact galaxy groups
• Contribution of brown dwarfs and white dwarfs to recent microlensing observations and to the halo mass budget
• Hubble Deep Field Constraint on Baryonic Dark Matter
• Implications of White Dwarf Galactic Halos
• The Chemical Residue of a White Dwarf-Dominated Galactic Halo
• Model Independent Predictions of Big Bang Nucleosynthesis from \he4 and \li7: Consistency and Implications
• On the Effects of Bursts of Massive Star Formation During the Evolution of Elliptical Galaxies
• The Mass-Function of Low Mass Halo Stars: Limits on Baryonic Halo Dark Matter
• Limits on the Halo White Dwarf Component of Baryonic Dark Matter from the {\em Hubble Deep Field}
• The X-ray halo of the Local Group and its implications for microwave and soft X-ray background
• Properties of Simulated Compact Groups of Galaxies

Cited by in corpus (22)

• X-ray Properties of Groups of Galaxies
• Cooling Models for Old White Dwarfs
• Black Hole Binary Formation in the Expanding Universe --- Three Body Problem Approximation ---
• Pure hydrogen atmosphere for very cool white dwarfs
• Observational evidence for a different IMF in the early Galaxy
• The halo white dwarf population
• The LMC Microlensing Events: Evidence for a Warped and Flaring Milky Way Disk?
• The Chemical Evolution of Mg Isotopes vs. the Time Variation of the Fine Structure Constant
• Chemical Abundance Constraints on White Dwarfs as Halo Dark Matter
• Low frequency gravitational waves from black hole MACHO binaries
• The Fine-structure Constant as a Probe of Chemical Evolution and AGB Nucleosynthesis in Damped Lyman-alpha Systems
• Further constraints on white dwarf galactic halos
• No Need for MACHOS in the Halo
• On the Nature and Location of the Microlenses
• Halo dark clusters of brown dwarfs and molecular clouds
• Non-Nucleosynthetic Constraints on the Baryon Density and Other Cosmological Parameters
• Kepler Rotation Effects on the Binary-Lens Microlensing Events
• Magellanic Cloud Gravitational Microlensing Results: What Do They Mean?
• Dynamical limits on galactic winds, halo machos and intergalactic globular clusters
• Red Clump Stars as a Tracer of Microlensing Optical Depth
• Brown Dwarfs, White Knights and Demons
• Neutron Stars and Black Holes as MACHOs