Red Halos of Galaxies - Reservoirs of Baryonic Dark Matter?

Abstract

Deep optical/near-IR surface photometry of galaxies outside the Local Group have revealed faint and very red halos around objects as diverse as disk galaxies and starbursting dwarf galaxies. The colours of these structures are too extreme to be reconciled with stellar populations similar to those seen in the stellar halos of the Milky Way or M31, and alternative explanations like dust reddening, high metallicities or nebular emission are also disfavoured. A stellar population obeying an extremely bottom-heavy initial mass function (IMF), is on the other hand consistent with all available data. Because of its high mass-to-light ratio, such a population would effectively behave as baryonic dark matter and could account for some of the baryons still missing in the low-redshift Universe. Here, we give an overview of current red halo detections, alternative explanations for the origin of the red colours and ongoing searches for red halos around types of galaxies for which this phenomenon has not yet been reported. A number of potential tests of the bottom-heavy IMF hypothesis are also discussed.

arXiv comment9 pages, proceedings of IAU Symposium 244, Dark Galaxies & Lost Baryons

References in corpus (27)

• Wilkinson Microwave Anisotropy Probe (WMAP) Three Year Results: Implications for Cosmology
• Dark Matter Substructure in Galactic Halos
• Where are the missing galactic satellites?
• Evolutionary population synthesis: models, analysis of the ingredients and application to high-z galaxies
• Tracing Galaxy Formation with Stellar Halos I: Methods
• The MACHO Project: Microlensing Results from 5.7 Years of LMC Observations
• LCDM-based models for the Milky Way and M31 I: Dynamical Models
• The Cosmic Energy Inventory
• A UBVR CCD Survey of the Magellanic Clouds
• Stars beyond Galaxies: The Origin of Extended Luminous Halos around Galaxies
• Formation of Disk Galaxies: Warm Dark Matter and the Angular Momentum problem
• Squelched Galaxies and Dark Halos
• The baryon fraction of LambdaCDM haloes
• Ring structure and warp of NGC5907 -- Interaction with dwarf galaxies
• The Spheroid Luminosity and Mass Functions From HST Star Counts
• Halos around edge-on disk galaxies in the SDSS
• A Faint Luminous Halo that May Trace the Dark Matter around Spiral Galaxy NGC~5907
• The abundance of dark galaxies
• The Spatial Distribution of the Galactic First Stars I: High-Resolution N-body Approach
• The Subdwarf Luminosity Function
• A faint red stellar halo around an edge-on disc galaxy in the Hubble Ultra Deep Field
• Formation of Low Mass Stars in Elliptical Galaxy Cooling Flows
• The Stellar Content of the Halo of NGC 5907 from Deep HST NICMOS Imaging
• The Red Halo Phenomenon
• The low-mass initial mass function of the field population in the Large Magellanic Cloud with Hubble Space Telescope WFPC2 Observations
• A Search for Near-Infrared Emission From the Halo of NGC 5907 at Radii of 10 kpc to 30 kpc
• Massive (?) starburst hosts of blue compact galaxies (BCGs)

Cited by in corpus (1)

• Are the red halos of galaxies made of low-mass stars? Constraints from subdwarf star counts in the Milky Way halo