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The History of Light: How Stars Formed in Galaxies Kai Noeske European Space Agency/ Space Telescope Science Institute Hubble Science Briefing, 1 Mar 2012
The History of Light: How Stars Formed in Galaxies
Kai Noeske
European Space Agency/ Space Telescope Science Institute
Hubble Science Briefing, 1 Mar 2012
What is a Galaxy?
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The Milky Way
100 Billion Stars like our sun
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Meet the Neighbors.
M51 (“Whirlpool Galaxy”) M104 (“Sombrero Galaxy”)
M31 (“Andromeda Galaxy”), our close neighbor and similar to the Milky Way
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Stars are not evenly distributed in the universe.
Stars are born and live in galaxies.
Most galaxies have billions of stars.
There are billions of galaxies in the known
universe.
Did they always look the same?
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A long time ago in galaxies far, far away: The HST Ultra Deep Field
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A long time ago in galaxies far, far away: The HST Ultra Deep Field
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A long time ago in galaxies far, far away: The HST Ultra Deep Field
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Two immediate results:
I. Galaxies formed at some point in the distant past
II. Galaxies evolved with time
Where do the Stars and Galaxies come from?
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Timeline (very rough)
● Most galaxies have very old stars ● Most galaxies started forming their stars some 10-13 Billion years ago, shortly after the beginning of the Universe
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22%
74%
3.2%
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The Cosmic Microwave Background: a baby photo of the Universe when it was just
300,000 years old
It reveals tiny irregularities; the density of matter varied by parts in a million 14
Dark Matter is more abundant, and dominates gravity.
To understand how gravity created structure (galaxies) from the early
homogeneous Universe, we need to simulate Dark Matter.
Outcome depends strongly on the
structure/geometry of the Universe and the content of Dark Matter
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Supercomputer simulations of Dark Matter: gravity grows the initial density perturbations,
structure forms
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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From
http://cosmicweb.uchicago.edu/filaments.html
choose a “rotating box” version such as
http://cosmicweb.uchicago.edu/images/mov/s02_0.gif
Gravity grows a “Cosmic Web” of Dark Matter - voids, filaments, clusters of clumps that host galaxies
Simulation: A.Kravtsov 17
Gravity grows a “Cosmic Web” of Dark Matter - voids, filaments, clusters of clumps that host galaxies
Simulation: A.Kravtsov
Galaxies form from overdense regions
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Luminous matter, formation of gas disk and stars:
Luminous matter (gas!) is viscous, and heated as it falls into dark matter halos; then heat is radiated away -gas cools - contracts angular momentum is conserved ->spin-up of rotation (“figure skater”) - fast rotating disk energy in turbulent/random motions (perpendicular to disk) is dissipated (viscosity->friction->heating ->heat is radiated away) -> motions perpendicular to ordered rotation disappear ->cold, dense gas disk -> STARS
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Recap: From Dark Matter to Stars
1) The Universe contains mostly Dark Matter 2) Tiny irregularities in the Dark Matter density in the early Universe grew rapidly through gravity 3) Gas fell into the resulting Dark Matter clumps/”halos” (galaxies) and formed cold, dense gas disks 4) Stars are born and live in galaxies because they need cold, dense gas to form
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Hierarchical galaxy formation; disks merge to disk bulges and Ellipticals
Blue: Dark matter Halo; yellow: gas; red: stars
In a “hierarchical” scenario, smaller structures form first, and later merge into bigger ones: -Galaxies merge to form larger ones -Mergers of roughly equal-sized galaxies often (not always) turn Spirals into Ellipticals
Bertola et al.
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Galaxy interactions/mergers: Observations and
Numerical simulations
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http://www.youtube.com/watch?v=agqLEbOFT2A&feature=youtu.be
Credits: Patrik Jonsson, Greg Novak & Joel Primack, University of California, Santa Cruz
QuickTime™ and a decompressor
are needed to see this picture.
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QuickTime™ and a decompressor
are needed to see this picture.
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QuickTime™ and a decompressor
are needed to see this picture.
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QuickTime™ and a decompressor
are needed to see this picture.
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II. How did we learn about galaxy formation?
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New Sky Surveys at many Wavelengths
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Multiwavelength surveys: combined efforts to get the whole picture.
A new era of astronomy:
big collaborations, huge databases
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HST (visual,
near infrared)
GALEX (UV)
star formation
XMM (X-ray)
Dust, star form.,
black holes...
SPITZER
(infrared)
Chandra (X-ray)
VLA (radio)
(gas, mass,
black holes,
star formation)
Redshift, dynamics, ...
DEEP2 (KECK,DEIMOS)
Multiwavelength surveys: combined efforts to get the whole picture.
A new era of astronomy:
big collaborations, huge databases
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time light travels to reach us
Short (millions of years)
Long (billions of years)
Text
even more distant galaxy nearby galaxy
distant galaxy
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Astronomers can look back in time:
light from very distant galaxies took billions of years to reach us.
Looking far is looking back
time light travels to reach us
Short (millions of years)
Long (billions of years)
Text
even more distant galaxy nearby galaxy
distant galaxy
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Astronomers can look back in time:
light from very distant galaxies took billions of years to reach us.
Looking far is looking back
time light travels to reach us
Short (millions of years)
Long (billions of years)
Text
even more distant galaxy nearby galaxy
distant galaxy
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Astronomers can look back in time:
light from very distant galaxies took billions of years to reach us.
Looking far is looking back
Astronomers can look back in time:
light from very distant galaxies took billions of years to reach us.
Looking far is looking back
time light travels to reach us
Short (millions of years)
Long (billions of years)
Text
even more distant galaxy nearby galaxy
distant galaxy
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Large telescopes on the ground: Spectroscopy gives each galaxy a “time stamp”
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DEIMOS spectrograph on the Keck II telescope Built by Sandra Faber & team, UC Santa Cruz
Can observe spectra of hundreds of distant galaxies
at a time 36
Overlapping
slitmask layout
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120 spectra of distant galaxies
wavelength
emission lines of ionized gas
The emission lines are at longer wavelengths than measured in the lab: They are “redshifted”.
This is because distant galaxies move away from us (“Doppler effect”, expansion of the Universe).
The redshift (=velocity) measures the distance and how far we look back in time
wavelength
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For galaxies in the early universe, the infrared matters:
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For distant galaxies, light from young stars (UV) and older stars (visible) is redshifted to long wavelengths (Infrared)
wavelength
spectr
al flux
young stars
(starbirth)
older stars
young stars
(starbirth)
older stars
UV Visible Light Infrared
Nearby Galaxy (not redshifted)
Distant Galaxy (redshifted)
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Spitzer Extended Deep Survey
Reduction: M. Ashby
The Spitzer Space Telescope provided infrared data: pierce through the dust,
measure star formation rates
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Hubble & JWST Probe the Early Universe
HST: currently the most sensitive telescope in the short-wavelength infrared (near-infrared): Can observe redshifted UV (star formation) from the most distant galaxies
JWST (launch: 2018) will be more sensitive, and reach longer infrared wavelengths: will reach even further back in time, and observe redshifted visible & infrared light in
earliest galaxies 42
HST Ultra Deep Field JWST Ultra Deep Field
Simulation
JWST will have much improved sensitivity to faint distant galaxies:
First Stars & Galaxies
Small galaxies across cosmic time
...
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Star formation in galaxies over the last 10 billion years
Heavens et al. 2004 Hopkins & Beacom 2006
now 10 Billion yrs ago
Space D
ensity o
f S
tar
Form
ation
Spa
ce D
ensity o
f S
tar
Form
ation now 10 Billion yrs ago
Big Galaxies
Small Galaxies
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Co-moving star formation rate (SFR) density declined by ~x10
Galaxy star formation histories are mass-dependent:
massive galaxies formed bulk of stars quickly and early, less massive galaxies formed on longer timescales (“Downsizing”)
Star formation in galaxies over the last 10 billion years
Heavens et al. 2004 Hopkins & Beacom 2006
now 10 Billion yrs ago
Space D
ensity o
f S
tar
Form
ation
Spa
ce D
ensity o
f S
tar
Form
ation now 10 Billion yrs ago
Big Galaxies
Small Galaxies
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Co-moving star formation rate (SFR) density declined by ~x10
Galaxy star formation histories are mass-dependent:
massive galaxies formed bulk of stars quickly and early, less massive galaxies formed on longer timescales (“Downsizing”)
Star formation in galaxies over the last 10 billion years
Heavens et al. 2004 Hopkins & Beacom 2006
now 10 Billion yrs ago
Space D
ensity o
f S
tar
Form
ation
Spa
ce D
ensity o
f S
tar
Form
ation now 10 Billion yrs ago
Big Galaxies
Small Galaxies
Reason for declining star formation:
Galaxies run out of gas!
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bill
ion
s o
f years
ago
to
day
(image: Driver 1998) big galaxies small galaxies
rapid star
birth & gas
consumption
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bill
ion
s o
f years
ago
to
day
(image: Driver 1998) big galaxies small galaxies
rapid star
birth & gas
consumption
slow star birth
& gas
consumption
48
bill
ion
s o
f years
ago
to
day
(image: Driver 1998) big galaxies small galaxies
rapid star
birth & gas
consumption
slow star birth
& gas
consumption
49
bill
ion
s o
f years
ago
to
day
(image: Driver 1998) big galaxies small galaxies
rapid star
birth & gas
consumption
slow star birth
& gas
consumption
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http://hubblesite.org
http://candels.ucolick.org
http://aegis.ucolick.org
http://www.atlasoftheuniverse.com/
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Questions?
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