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The Local Universe
Ann Martin2010 Undergraduate ALFALFA Workshop(with thanks to Brian Kent!)
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What is a Galaxy?
The Wikipedia Definition: “A galaxy is a massive, gravitationally bound system consisting of stars, an interstellar medium of gas and dust, and dark matter.”
M31, from Hubble
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What do Galaxies Look Like?
M81: X-Ray, UV, Visible, Visible, NIR, MIR, FIR, Radio
From the IPAC Multiwavelength Museum
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Types of Galaxies
From dwarfs to giants, from spirals to ellipticals
Andromeda, a spiral galaxy, with a nearby dwarf elliptical
M31, from Hubble
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Types of Galaxies: SpiralsThin disksMost have some form of a bar – arms will emanate from the ends of the barsOther classification:
Relative importance of central luminous bulge and disk in overall light from the galaxyThe tightness of the winding of the
spiral armsBarred or not?
M33
M51
NGC 1365
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Types of Galaxies: Ellipticals
Ellipticals: look like smooth, featureless “blobs”Older (redder) stellar populationsTend to have little neutral gas (HI) – so ALFALFA doesn’t see these!More rare in the early Universe
M87 in the Virgo Cluster
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Types of Galaxies: Irregulars
Irregulars: Many different properties, often because of interactions or other unusual events nearby.
NGC 1427A
HST Image of Sagittarius Dwarf Irregular Galaxy (SagDIG)
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Types of Galaxies: Irregulars
LMC and SMC are satellite galaxies of our own –disrupted by gravitational interaction with the Milky Way
LMC and SMC
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Dwarf Galaxies
Smaller size than giant galaxiesLower surface brightnessMost common galaxies!
M32Sagittarius Dwarf
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Dwarf Galaxies: SDSS Ultra-Faint Galaxies
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The Hubble Tuning Fork
Early TypeEarly Type Late TypeLate Type
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Our Galaxy: The Milky Way
An Sbc galaxy that is 30 kpc in diameter
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The Hubble Tuning Fork
Early TypeEarly Type Late TypeLate Type
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Anatomy of the Milky Way
•R0 ~ 8 kpc
•200 billion stars
•Mtot 5 x 1011 M
•SFR ~ 3 M /yr
•Bulge ~ 3 kpc in diameter
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Our Neighborhood: The Local Group
The Local group has 43 + 5? members (and growing), ranging from large spiral galaxies to small dwarf irregulars. Most galaxies are dwarf spheroidals…
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Our Neighborhood: The Local Group
The Local group has 43 + 5? members (and growing), ranging from large spiral galaxies to small dwarf irregulars. Most galaxies are dwarf spheroidals…
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The Andromeda GalaxySb galaxy 770 kpcfrom the Milky Way.Larger, more luminous, with a larger disk scale length than the Milky Way – it even rotates faster at 260 km/s!At least 9 known satellite galaxies –dwarf elliptical and spheroidals!
cz = -300 km/s
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Another Contribution from Hubble . . .
The Universe is expanding!
dHcz 0=
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A simple calculation: Redshift
Measure the shift in a spectral line – f0 is the rest frequency (λ0 the rest wavelength)Extragalactic objects often identified by their czmeasurement. ALFALFA covers cz = –2000 to 17000 km/s (out to ~ 250 Mpc)
obs
obsobs
fffz −
=−
= 0
0
0
λλλ
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Another Contribution from Hubble . . .
The Universe is expanding!dHcz 0=
However, there are other factors to take into account in the local Universe –peculiar velocities! Deviations can be quite large depending on the galaxy, and whether it is part of a group or a field galaxy.
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Distances to nearby galaxies
Tonry, et al. 2000
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Distribution of Galaxies
~450,000 galaxies(SDSS, with more
than 800,000 today!)
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Distribution of Galaxies
Structures in the Universe: The best place to find a galaxy is next to another one!
GroupsClustersSuperclustersFilaments and Voids
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Distribution of Galaxies
Structures in the Universe: The best place to find a galaxy is next to another one!
GroupsClustersSuperclustersFilaments and Voids
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Groups of galaxies
Galaxies can be gravitationally bound to each other, and undergo interactions and collisions.Separations across intergalactic distances range from 50 kpc up to 1 Mpc.ALFALFA science goals include studying the effects within the group environment –
What is HI mass function?How do unseen HI clouds/starless galaxies effect dynamics?Are there unseen tidal remnants or debris?What are sizes of HI disks?
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Groups of galaxies
cz = -34 km/s
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M66 Group: The Leo Triplet
cz = 5917 km/s
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M66 Group: The Leo Triplet
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Colliding Galaxies: The Antennae
cz = 1706 km/s
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Colliding Galaxies: The Antennae
cz = 1706 km/s
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Distribution of Galaxies
Structures in the Universe: The best place to find a galaxy is next to another one!
Groups
ClustersSuperclustersFilaments and Voids
The Virgo Cluster is the closest
nearby cluster, at about 17 Mpc. It contains about 1500 member
galaxies!
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Clusters of Galaxies
Around half the galaxies in the Universe are found in clusters or groups.Clusters have a higher density than “loose” groups – brightest galaxies are S0s and ellipticals instead of spiralsAbell Catalog contains 4073 rich clustersGravity binds the members, as well as hot intracluster gas (seen in the X-ray)
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Virgo Cluster
cz ~ 1035 km/s∆v ~ 1000 km/s 1300 catalogued membersMost galaxies are dwarf elliptical type
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Fornax cluster
cz ~ 1400 km/s
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Local Supercluster
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Distribution of Galaxies
Structures in the Universe: The best place to find a galaxy is next to another one!
GroupsClusters
SuperclustersFilaments and Voids
Superclusters are “clusters of
clusters” and can extend for
hundreds of millions of light
years.
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Distribution of Galaxies
Structures in the Universe: The best place to find a galaxy is next to another one!
GroupsClustersSuperclusters
Filaments and Voids
This simulation contains more than 10 billion particles, and
attempts to trace galaxy, cluster &
superclusterformation.
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ALFALFA View of the Local Universe
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ALFALFA View of the Local Universe
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ALFALFA View of the Local Universe
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ALFALFA View of the Local Universe