Massimo StiavelliSpace Telescope Science Institute

The Making of the Hubble Ultra Deep Field

Hubble Science BriefingOctober 4, 2012

Bold methods and new technologyBold methods and new technology

- What happens if you point the most powerful camera at the same point in the sky for an unprecedented length of time?

The Wide Field Planetary Camera 2 (WFPC2)

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The Hubble Deep FieldThe Hubble Deep Field

- This is exactly what Bob Williams, then STScI Director, decided to do in 1994.

- The resulting image, known as the Hubble Deep Field, was the deepest picture of the Universe for many years.

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A new instrument…A new instrument…

- A new camera was installed on Hubble in March 2002: the Advanced Camera for Surveys.

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…is a new opportunity…is a new opportunity

- The new STScI Director, Steve Beckwith, decided to use the new, more powerful camera and point it for twice as long as the HDF on a fixed spot in the sky

- The Hubble Ultra The Hubble Ultra Deep Field (HUDF) Deep Field (HUDF) was bornwas born

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More than just fishingMore than just fishing- The HUDF was doing more than just

looking for the unknown- The Sloan Digital Sky Survey (SDSS) had

identified the most distant quasars known, formed about 1 Gyrs after the Big Bang

- Spectra of these objects, taken with Keck and other telescopes, were showing tantalizing clues…

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Reionization of the UniverseReionization of the Universe

- Spectra of the most distant QSOs (quasi-stellar objects) told us that there was some neutral hydrogen in their vicinity

- This is not seen for less distant QSOs

- Galaxies must ionize all hydrogen about 1 Gyrs after the Big Bang

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Could Hubble see them?Could Hubble see them?

- The question then was whether Hubble could see the galaxies responsible for reionization.

- This was the science motivation for the HUDF

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How do you create a deep field?How do you create a deep field?

- Select a carefully chosen random location in the sky

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Field Location OptionsField Location Options

UDFUDF

Hubble Ultra Deep FieldHubble Ultra Deep Field1212

Yes, mostlyYes, mostly

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What about earlier times?What about earlier times?- The galaxies found in the HUDF are the

most distant that can be found in the optical portion of the electromagnetic spectrum; for more distant objects you must search the infrared portion.

- The existing infrared camera (NICMOS) on Hubble gave some hints, but was not powerful enough to do the job.

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- Earlier than 1 Gyrs after the Big Bang, galaxies are faint and relatively rare. We need a sensitive IR instrument: the IR channel of the Wide Field Camera 3 (WFC3).

Need infrared!Need infrared!

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More galaxiesMore galaxies

- WFC3 gave us samples of galaxies all the way to about 650 Myrs after the Big Bang.

- As we go back in time, galaxies become rarer and fainter

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eXtreme Deep Field (XDF)eXtreme Deep Field (XDF)- Galaxies from 650 Myrs to 500 Myrs are

elusive, but possibly within the reach of Hubble.

- To study them one needs very long integrations, on the order of many hundreds of hours

- The XDF is the latest and deepest attempt at studying these objects.

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eXtreme Deep eXtreme Deep FieldField(XDF)(XDF)

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Moon

XDF

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2424Hubble eXtreme Deep FieldHubble eXtreme Deep Field

How XDF lets How XDF lets usus see the early see the early universe universe

Galaxies earlier than 800 Myr after the Big Bang can only be seen in infrared light (“redder” than visible light)

We need We need near-infrared near-infrared

images to images to see them!see them!

observed wavelength [microns]

Galaxy Light

HUDFXDF

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Credit: STScI

previous imageHUDF

new imageXDF

XDF reveals galaxies unseen in XDF reveals galaxies unseen in our deepest visible-light HUDF our deepest visible-light HUDF

imagesimages

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A red galaxy is not necessarily in A red galaxy is not necessarily in the very early universethe very early universe

Red galaxy colors can also be a sign for old stars, or for a lot of dust, which absorbs blue light

These two galaxies are at a distance of about half the age of the universe

This galaxy is about 13 billion light years away

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Even more distant galaxiesEven more distant galaxiesEven more distant galaxiesEven more distant galaxies

- A redshift 10 galaxy

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Why are the early times so important?Why are the early times so important?

Years: 0.3 8 16 32

For both humans and galaxies the pace of development is not uniform: more things happen early on 2929

Changing how astronomy is doneChanging how astronomy is done

- The HDF image and the source catalogs were made public.

- Astronomers started using other telescopes to study specific objects, measure redshifts, obtain radio or X-ray data.

- Most of these data were also made public.

From American Physical Society Newsletter May 1997 3030

PapersPapers- The HDF and HUDF surveys led to 1,584 research

papers, of which only 89 were published by the team.

• The vast majority (94%) of these science papers were published by other scientists

- The HDF was the first case in astronomy of highly valuable data made public, and it encouraged open cooperation.

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CDF-S* region is rich in data (HST, Spitzer, Chandra, etc)[*Chandra Deep Field South]

CDF-S* region is rich in data (HST, Spitzer, Chandra, etc)[*Chandra Deep Field South]

1999-2000 Chandra CDF-S 2002-2003 ACS GOODS2003 ACS HUDF2003 NICMOS HUDF 2004 Spitzer GOODS 2003-2007 NICMOS2005 HUDF05 2009 ERS2009-2010 HUDF092010-2011 Chandra 4Ms 2010-2012 CANDELS2012-2013 Ellis

All these data were available within 3 months.

CDF-South

~22’ x 22’3232

Garth D. Illingworth STScI May 2010 Workshop

No more lonely hearts of the cosmosNo more lonely hearts of the cosmos

- The old-style way of doing research in small research group is being replaced by participation in large groups.

- In the past astronomers tended to focus on a few specific objects Now we focus on large samples

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Non-hierarchical scienceNon-hierarchical science

- In a large collaboration working on a large sample, the difference between team members and non-team members starts to fade.

- This opens up possibilities for unaffiliated astronomers, and also for the interested public.

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Galaxy Zoo: HubbleGalaxy Zoo: Hubble

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JWSTJWST

Ultimately, in order to see more and fainter objects at these redshifts we need a telescope designed for infrared imaging:

the James Webb Space Telescope

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6.5m James Webb Space Telescope6.5m James Webb Space Telescope3838

Full-scale modelFull-scale model

The Hubble UDF (F105W, F105W, F160W)

Simulated JWST

JWST improvements over Hubble’s resolution

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JWST improvements over Hubble’s resolution

The Hubble UDF (F105W, F105W, F160W)

Simulated JWST

4103/07/2010

HST/ACSViz

HST/NICMOS J H

JWST/NIRCamViz

(simulated)

JWST/NIRCamJ H

(simulated)

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JWST-Spitzer image comparisonJWST-Spitzer image comparison

Spitzer, 1500 min. per band

(GOODS collaboration)

1’x1’ region in the HUDF – 3.5 to 5.8 m

JWST, 16 min. per band (simulated)(simulation by S. Casertano)

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Hubble & James Webb to same scaleHubble & James Webb to same scaleHubble & James Webb to same scaleHubble & James Webb to same scale

JWST is 7 tons and fits inside an Ariane V shroudThis is made possible by:

• Ultra-lightweight optics (~20 kg/m2)• Deployed, segmented primary mirror• Multi-layered, deployed sunshade• L2 Orbit allowing open design/passive cooling

Astronaut

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JWST Launch ConfigurationJWST Launch Configuration

LongFairing17m

Upper stage

H155 Core stage

P230 SolidPropellantbooster

Stowed Configuration

JWST is folded into stowed position to fit into the payload fairing of the Ariane V launch vehicle

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ConclusionsConclusions

WFC3-IR has allowed us to begin studying galaxies up to 650 million years from the Big Bang.

Progress on these objects is going to be slow because they are too faint for any existing telescope, save for major efforts like the XDF.

The James Webb Space Telescope has the sensitivity required to study these objects and even earlier ones.

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