does the fornax dwarf spheroidal have a central cusp or core? · detectability in absorption:...
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Cold streams: synthesised observations and characteristics
Collaborators: Andi Burkert, Daniel Ceverino, Avishai Dekel, Romain Teyssier
Tobias Goerdt
University of Vienna
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Cold streams
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Central geometry
• Observes central galaxy through its own circum galactic medium
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Detectability in absorption: Computed sky covering fraction
• Very low sky covering fraction
• Low metallicity in streams
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Stacked line profile:• Averaging over all available example line
profiles (3 galaxies, all directions)
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Statistics• Mg II: inflow > 150 km s−1 with an EW > 0.2 Å in
1.3 % of all observations
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Emission: Lyman alpha blobs• First observed by Steidel et al. 2000• Redshift range z = 2 – 6.5• Observation by Matsuda et al. 2004
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Emission: Lyman alpha blobs
• Cold streams loose potential energy released as Ly alpha photons.
• Computed vs. Observed Surface brightness maps
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Ly α blob luminosity function
• Mass luminosity scaling relation correlated with Sheth Tormen mass function
• Observational data from Matsuda et al. (2004, 2009)
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Relation to structure:• Ibata et al: Andromeda: thin disk of satellites• Cold streams carry clumps
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Assumptions:• Majority of incoming satellite galaxies enter the
host halo through cold streams
• Orientation of cold streams does NOT change during period of accretion
• Subhaloes stay on planar orbits defined by stream and impact parameter
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Consequence: Coplanar satellite structure!
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Inflow velocity• In units of virial velocity• Constant with radius → • Power law with redshift ↓• “Parabula-like” with mass ↓
• Emerging equation:
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Inflow distribution• Double Gaussian• Represents mergers and smooth infall• Observationally found by Sargent et al. (2012):
star formation: main sequence | starburst activity
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• Detectability in absorption:– Difficult (low sky covering fraction / metallicity)
• Cold stream emission: Lyα blobs– Simulation maps very similar to observations in
extent, shape, luminosity– Luminosity function fits data
• Relation to structure:– Thin satellite disks: natural consequence of streams
• Characteristics:– Velocity vs. radius: constant– Velocity vs. redshift: power law– Velocity vs. mass: “parabola-like”– Inflow distribution: double Gaussian (like Sargent et
al's star formation observations)