cosmology and extragalactic astronomy mat page mullard space science lab, ucl 2. galaxies
TRANSCRIPT
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Cosmology and extragalactic astronomy
Mat Page
Mullard Space Science Lab, UCL
2. Galaxies
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1. Galaxies
• This lecture:• Classification of galaxies
– Spirals– Ellipticals– Irregulars
• Characteristics of the different types
Slide 2
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Hubble’s tuning fork
• Basic set of galaxy types.
Slide 3
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• Ellipticals• Spirals
– barred– normal
• Irregulars
3 groups:Slide 4
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• Classified as E0-E7
• En
• n=10(1-b/a)
Ellipticals
M87: Giant elliptical (E1) Classified according to view from Earth!
Slide 5
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Most of the galaxies in the local group are dwarf ellipticals!
M 110: dwarf elliptical (E6)
EllipticalsSlide 6
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Elliptical characteristics
• Random star motions
• Little dust, little gas– gas is hot, can be X-ray sources
• no star formation
• no hot, young bright stars
• old, red stars
• no spiral structure
• Large range of sizes: 105-1013 Mo.
Slide 7
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Spirals
• Like the Milky Way– central bulge– flattened disc– spiral pattern– sometimes a bar
• Classified as • S (for spiral) or • SB (barred spiral)• plus a,b,c,(d)
NGC 1365 SBbc
Slide 8
Credit: Marco Iacobelli (XMM SOC) & ESA
XMM-Newton Optical Monitor
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NGC 2997: Sc
This one has no ‘B’ because it has no bar
Slide 9
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Spiral classification
• Sa and SBa have:• large central bulges• Tightly-wound spiral
arms
• Sc and SBc have:• small central bulges• Loosely-wound spiral
arms
M81(Sab) NGC4321(Sc)
Slide 10
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M81 UV (XMM))
Slide 11
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M81 21cm
Slide 12
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M100 (AAT))
Slide 13
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M51 (HST))
Slide 14
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Characteristics of spirals
• Consistent rotational motion in the disc• Lots of gas and dust in the disc• Star formation in disc, especially in the arms• Young, bright blue stars in the arms• Spiral structure
• 109 - 4x1011 Mo
Slide 15
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Lenticular galaxies
• Lenticular -- ‘lens-like’• Like a spiral, but without spiral structure• Designated S0 or SB0• I think difficult to tell from ellipticals by eye.
Slide 16
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Irregulars
• No definite structure– Everything that
doesn’t fit on the tuning fork
• Mostly small, faint• May have strong star
formation• May have lots of gas
and dust– e.g. LMC and SMC
Slide 17
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LMC in the UV (Swift UVOT))
Slide 18
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Back to Hubble’s tuning fork
• Hubble thought that galaxies evolved from ellipticals to spirals
• This is very unlikely!
Slide 19
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Some key points about galaxies:
• Ellipticals– no overall rotation– old stars, little gas.
• Spirals– rotating disc– old stars in the bulge– young stars in the disc and in bulge
• Lenticulars– bulge and disc without spiral structure
• Irregulars– often lots of gas– sometimes strong star formation
Slide 20