Thessaloniki, Oct 3rd 2009

Cool dusty galaxies: the impact of the Herschel mission

Michael Rowan-RobinsonImperial College London

Thessaloniki, Oct 3rd 2009

Cool dusty galaxies: the impact of the Herschel mission

To set the scene for the Herschel far infrared and submillimetre mission, I’m going to talk first about some of the key discoveries from the IRAS and Spitzer missions

Thessaloniki, Oct 3rd 2009

1983 saw the launch ofIRAS, the Infrared Astronomical Satellite, which made the first all-sky survey at infrared wavelengths, from 10-100 microns

IRAS

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IRAS - the infrared ‘cirrus’

south celestial pole

emission from clouds of interstellar dust in our Galaxy, the infrared ‘cirrus’

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IRAS - star forming regions

constellation OrionLMC, the Large Magellanic Cloud

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IRAS discovered ultraluminous infrared galaxies, forming stars 100-1000 times faster than our Galaxy, probably caused by mergers between two galaxies

this is an HST image of Arp 220

Uultraluminous infrared galaxies

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IRAS - dust debris disks

IRAS also discovered dust debris disks around stars, confirmed by imaging with the Hubble Space Telescope, evidence for planetary systems in formation. Today over 300 exoplanets are known.

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IRAS

the IRAS all-sky survey of infrared point-sources: white: star-forming regions, blue: red giant stars, green: galaxies. IRAS detected 60,000 dusty, star-forming glaxies over the whole sky.

Thessaloniki, Oct 3rd 2009SPITZER, 2003

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LMC

star formation in our nearest neighbour, the Large Magellanic Cloud, seen at infrared wavelengths

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IC1396, the Elephant’s Trunk

- a dark globule inside an emission nebula

- a pair of newly formed stars have created a cavity

- the animation shows how the appearance changes from the optical, where dust absorbs light to the infrared where the dust radiates

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QuickTime™ and aMPEG-4 Video decompressor

are needed to see this picture.

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infrared emission from debris along a comet orbit

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SINGS - Spitzer Nearby Galaxy Survey

• 75 nearby galaxies

• detailed studies of their gas, dust, and star-formation rate

M81

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visible (HST) and infrared (Spitzer) images of M51, the ‘Whirlpool’ galaxy

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Sombrero galaxy

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Two interacting galaxies

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Visible and infrared images of the star-forming galaxy Messier 82

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High-redshift galaxies with Spitzer

• Egami et al 2005: z ~ 6.7

lensed galaxy with M = 109 Mo,

stellar age at least 50 Myr

Spitzer is only an 85-cm telescope, but it can detect the most distant galaxies known

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SWIRE (Spitzer Wide-Area IR Extragalactic Survey)

I’ve been mainly involved with SWIRE, a survey of ~50 square degrees of the sky at 3.6-160 microns.

We found 1.5 million galaxies and have used their optical and near infrared colours to estimate their distances, and hence their luminosities, star-formation rates, stellar masses and dust masses

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optical templates for photometric redshifts

t

These are the galaxy templates we use for estimating the redshift of the galaxies

(Rowan-Robinson et al 2008)

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Over 1 million photometric redshifts

This shows the kind of performance we achieve, a comparison of our photometric redshifts with spectroscopic redshifts

5 optical bands, + 3.6, 4.5 m

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SPITZER-IRS spectra of ULIRGs

• detailed infrared spectra of some ultraluminous infrared galaxies (ULIRGs), and our models for these

• we need Herschel to test the

behaviourof these galaxies at

submillimetre wavelengths

(Farrah et al, 2008)

our infrared templates

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star-formation rate v. redshift

• whole SWIREcatalogue

• strong selection effects

• consistent with strong rise to z = 1.5

(RR et al 2008)

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star formation history as a function of redshift

• The Infrared Space Observatory (1996-9) showed a steep rise in the star-formation rate to z = 1

• submm surveys and surveys with Spitzer show flat behaviour from z = 1 - 2.5

• very uncertain at z > 2-3

• Herschel surveyswill detect thousands of high-redshift star-forming galaxies

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SOURCE COUNTS AT 24 microns

• to understand the numbers of sources as a function of brightness, different tyes of galaxy need to undergo different evolutionary histories

M82cirrus

dust tori

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COUNTS AT 8-1100 m, ir background

Predicted counts from 8

1100 microns, comparison

with observed counts at

160, 850 and 1100

microns, and with

integrated background

spectrum

(Rowan-Robinson 2009)

Integrated background spectrum

160 m

850 m

1100 m

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HERSCHEL SPACE OBSERVATORY

Herschel launch May 14th 2009, now in orbit at L2

Science demonstration phase started two weeks ago

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HERSCHEL SPACE OBSERVATORY

Composite of M51 with PACS array

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HERSCHEL SPACE OBSERVATORY

SPIRE images of M66 and M74

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HERSCHEL SPACE OBSERVATORY

SPIRE images of M74 (and high redshift galaxies ?) at 250, 350, 500m

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Messier83

background galaxies very clear on latest image,of M83

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Herschel view of the Milky Way

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European-ELT: 2017

Proposed 43-m, segmented mirror, working at 0.6-23 microns.

Will allow us to image exoplanets, take their spectra, and to see the very first galaxies in the universe, at redshift > 10