galaxy groups in hicat
DESCRIPTION
Galaxy Groups in HICAT. Jamie Stevens. Outline. Introduction Group-finding in HICAT HIPASS group properties Star formation properties Summary. Introduction. The HIPASS Catalogue (HICAT) contains 4315 galaxies, 4065 of which are certainly real Primarily H I -rich late-type galaxies - PowerPoint PPT PresentationTRANSCRIPT
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Galaxy Groups in HICAT
Jamie Stevens
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Outline
• Introduction
• Group-finding in HICAT
• HIPASS group properties
• Star formation properties
• Summary
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Introduction
• The HIPASS Catalogue (HICAT) contains 4315 galaxies, 4065 of which are certainly real
• Primarily HI-rich late-type galaxies– Can galaxy groups be identified using only
these galaxies?
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HIPASS Catalogue
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Galaxy Groups
• Generally dominated by late-type galaxies• Galaxies can be affected by various processes
– galaxy-galaxy interactions– strangulation– mergers
• How do these processes affect the HI in the group galaxies?
• Compare with– compact groups: same processes, higher density, HI
may be changed/removed, and moved around– clusters: add ram-pressure stripping, HI is rarely
found within cluster cores
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Group-finding in HICAT
• Hierarchical group-finder based on the method of Gourgoulhon (1992)– relied on estimates of the galaxies’ mass– not possible with the information available in
HICAT
• Two mass-independent methods– crossing-time: (4/) (R/v)
– number density: (3/4) (N/R3)
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HIPASS Groups
Crossing-time
groups have crossing-times < 0.30 H0-1
Number density
groups have densities > 3.16 Mpc-3
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Velocity Distribution
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Group Properties
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Group HI Properties
[(2)-1/2vngRg2]-1
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Galaxy Properties
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Galaxy Properties
median field morph = Sd
median group morph = Scd
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Interpretation
• The HIPASS groups are serene– collisions of large galaxies may be very rare
• Higher luminosity galaxies cluster more strongly– observed before (Norberg et al. 2001)
• Early-type fraction increases in denser environments– morphology-density relation (Dressler 1980)
• HI dependence on luminosity isn’t radically affected
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Star Formation
• Can estimate star formation rate (SFR) of the HICAT galaxies with radio continuum luminosity, or far-infrared (FIR) luminosity
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Star Formation – HI Mass
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Star Formation – HI Mass
• surface density of SFR correlates with surface density of gas mass – the Schmidt Law (Kennicutt 1998)
• global SFR – HI mass relation– HI is gas reservoir for SF– young stars disassociate H2 into HI (Allen
2002)– observed relation consistent with
disassociation models (Taylor & Webster 2005)
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SFR Depression
• Star formation rate is depressed in dense environments (Lewis 2002)
• Unlikely to be due to tidal interactions– gas strangulation?
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Summary
• Loose groups found in HICAT using hierarchical group-finder– widely separated galaxies, which rarely interact
• More luminous, earlier-type galaxies cluster more strongly– no great difference between group and field galaxies
• Star formation depressed in group galaxies– may be gas strangulation, but dependence exists on
HI mass