The History of Light: How Stars Formed in Galaxies Kai Noeske European Space Agency/ Space Telescope...

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 sun100 Billion Stars like our sun

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The Milky Way

www.atlasoftheuniverse.com 4

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?7

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

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Fromhttp://cosmicweb.uchicago.edu/filaments.html

choose a “rotating box” version such ashttp://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 toordered rotation disappear

->cold, dense gas disk -> STARS19

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

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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 Multiwavelength surveys: combined efforts to get the whole picture. picture.

A new era of astronomy: A new era of astronomy: big collaborations, big collaborations, huge databaseshuge 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 Multiwavelength surveys: combined efforts to get the whole picture. picture.

A new era of astronomy: A new era of astronomy: big collaborations, big collaborations, huge databaseshuge databases

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time light travels to reach

usShort (millionsof years)

Long (billions of years)

Text

even moredistant 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

usShort (millionsof years)

Long (billions of years)

Text

even moredistant 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

usShort (millionsof years)

Long (billions of years)

Text

even moredistant galaxy

nearby galaxy

distant galaxy

33

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

usShort (millionsof years)

Long (billions of years)

Text

even moredistant 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 telescopeBuilt by Sandra Faber & team, UC Santa Cruz

Can observe spectra of hundreds of distant galaxies at a time

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Overlappingslitmask layout

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120 spectra of distant galaxies

wavelength

emission linesof 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

spect

ral flu

x

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

4141

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 FieldJWST 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

Densi

ty o

f Sta

r Fo

rmati

on

Space

Densi

ty o

f Sta

r Fo

rmati

on 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

Densi

ty o

f Sta

r Fo

rmati

on

Space

Densi

ty o

f Sta

r Fo

rmati

on now 10 Billion yrs ago

Big Galaxies

Small Galaxies

45

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

Densi

ty o

f Sta

r Fo

rmati

on

Space

Densi

ty o

f Sta

r Fo

rmati

on 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 of

years

ago

today

(image: Driver 1998)

big galaxies

small galaxies

rapid star birth & gas consumptio

n

47

bill

ion

s of

years

ago

today

(image: Driver 1998)

big galaxies

small galaxies

rapid star birth & gas consumptio

n

slow star birth & gas consumptio

n

48

bill

ion

s of

years

ago

today

(image: Driver 1998)

big galaxies

small galaxies

rapid star birth & gas consumptio

n

slow star birth & gas consumptio

n

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bill

ion

s of

years

ago

today

(image: Driver 1998)

big galaxies

small galaxies

rapid star birth & gas consumptio

n

slow star birth & gas consumptio

n

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http://hubblesite.org

http://candels.ucolick.org

http://aegis.ucolick.org

http://www.atlasoftheuniverse.com/

noeske@stsci.edu51

Questions?

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