Jennifer Lotz

Hubble Science Briefing

Jan. 16, 2014Exploring the Depths of the Universe

Hubble is now observing galaxies97% of the way back to the Big Bang,during the first 500 million years*

Challenge: Can we peer deeper into the Universe than the Hubble Ultra Deep Field before the launch of the James Webb Space Telescope?

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Extragalactic Astronomy 101the speed of light is finite distance = look-back timethe universe is expanding distance = velocityobjects moving away from us look redder redshift = distance = look-back time*

1. distance = time8 minutes3 million years13 billion years13.7 billion yearsthe SunAndromedadistant galaxyecho of the Big BangEarthWe see distant objects as they were in the past because their light takes a long time to reach us*

2. distance = velocity the universe is expanding objects farther away are moving away faster Hubble 1929Distance from our galaxy Velocity away from our galaxy *

3. velocity = redshiftredshift = distance = timeN. Wright / www.astro.ucla.eduvelocityThe light from objects moving away from us is shifted redward.*

Galaxy redshifts are primarily due toexpansion of space, not Doppler shiftExpanding universestretches lightto longer wavelengthsESO animation: http://www.eso.org/public/videos/redshiftv/Redshift z =stretch factorminus one*

(4. Astronomers unit of brightness)Astronomers measure brightness in magnitudes

Larger magnitudes are fainter(backwards!)

Magnitude = -2.5 log10(brightness)

Faintest star the human eye can see is 6th magnitude

Hubble Ultra Deep Field reaches30th magnitude= a factor of 4 billion times fainterthan what we can see with naked eye

Frontier Fields reaches ~10x fainter than Ultra Deep Field= 40 billion times fainter than human eye can see.

Fainter *Figure from http://sci.esa.int/education/35616-stellar-distances/

visible light*

when the universe was young..NASA/WMAP Science teamblue = 0.0 Kgreen = 2.7 Kred = 4.0 K380,000 years after the Big Bangmicrowaves*

When the universe was young...blue = 2.7249 Kgreen = 2.7250 Kred = 2.7251 K380,000 years after the Big BangNASA/WMAP Science team*

from the Big Bang to the Milky Way*

The Hubble Deep Field - 1995*

The Hubble Deep Field South- 1998*

The Hubble Ultra Deep Field -2004new camera on Hubble = new deep field*

*detection of faint galaxies at look-back times < 1 billion years after the Big Bang cosmic star-formation history peaked ~ 10 billion years ago

Galaxies grew in size and mass over this time, and changed their shapes from irregular to smooth

Most distant supernovae used to measure distance, confirm accelerating universe

Accreting supermassive black holes are found in galaxies at look-back times as early as 10-12 billion years ago.

Science Highlights from Deep Fields

Hydrogen atom excitation levelsHow far away are galaxies?Hydrogen atoms absorbs ultraviolet light from distant galaxies; this Lyman break is used to estimate their redshift.*

The Hubble Ultra Deep Field -2009/2012new camera on Hubble = new deep field*

deep infrared images needed to detect the highest redshift galaxiesThe Hubble Ultra Deep Field -2009/2012Cosmic star formation density Redshift/time since Big Bang *

NASA/HST the Ultra Deep Fieldmost distant galaxy candidate*

Challenge: Can we peer deeper into the Universe than the Hubble Ultra Deep Field before the launch of the James Webb Space Telescope?

posed to the Hubble Deep Fields Initiative science working group to develop an ambitious new community deep fields programHUDF ACS (optical) = 416 orbitsWFC3 (IR) = 163 orbits=579 orbits of HST *

Gravitational lensing in action*Credit: Ann Feild (STScI)

Gravitational Lensing*

Wine Glass LensingPhil Marshall*

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Challenge: Can we peer deeper into the Universe than the Hubble Ultra Deep Field before the launch of the James Webb Space Telescope?

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Answer: Use Einsteins theory of general relativity - gravitational lensing - to go intrinsically deeper than the Ultra Deep Field.

The Frontier Fields are being observed by NASAs Great Observatories - Hubble, Spitzer, and Chandra - over the next 3 years.

Gravitational lensing magnifies and stretches light from distant galaxies behind massive clusters, making them appear brighter and larger. Six very massive clusters of galaxies chosen as the best zoom lenses, with input from community. *

Frontier Fields will also observe 6 fields in parallel with the clusters, the second deepest observations of blank fields ever obtained.

Simultaneous images are taken with Hubbles infrared camera WFC3/IR and the optical camera ACS; cameras will swap positions ~6 months later.*

Deep observations of the Frontier Fields will:

probe galaxies 10-20x intrinsically fainter than any seen before, particularly those in the first billion years of the Universe

study the early formation histories of galaxies intrinsically faint enough to be the early progenitors of the Milky Way

study internal properties of highly-magnified galaxies at high spatial resolutions

provide a statistical picture of galaxy formation at early times*

Deep observations of the Frontier Fields will:

+ map out dark matter, substructure in clusters

+ use 100s of multiple images as probe of distance, DE

+ search for (lensed) SN, transients in distant universe

+ deep and high-spatial resolution studies of z~1-4 galaxies, (UV escape fraction, sub-kpc structures and star-formation)

+ search for trans-Neptunian objects in solar system

+ give parallaxes of Milky Way stars

+ ???

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Spitzer Frontier FieldsInfrared Spitzer Space Telescope will look at Frontier Fields in 2 filters redder than Hubble can see to depths of ~26.5 magnitude Spitzer crucial for confirming the distant galaxies, measuring their total stellar masses

http://irsa.ipac.caltech.edu/data/SPITZER/Frontier/ *

Chandra Frontier FieldsX-ray detect hot cluster gas cluster massand background accreting black holes

archival Chandra data available for all of Frontier Fields;Chandra FOV encompasses both cluster + parallel fields

new observations began this fallMACS0717.5+3745C. Jones-FormanMACS0416.1-2403S. Murray*

HST Frontier Fields: ClustersAvoid dusty, bright regions of sky; visible from south (ALMA) and north (Mauna Kea)*

HST Frontier Fields

Abell 2744MACSJ0416.1-2403MACSJ0717.5+3745MACSJ1149.5+2223.Abell370Abell S1063Hubble will observe 2 cluster per year, over 3 years140 orbits per cluster*

Cluster Parallel Blank FieldAbell 2744 - HST Epoch 1 completed November 2013

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Parallel Blank FieldCluster Abell 2744 - HST Epoch 1 completed November 2013

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Abell 2744Parallel Blank Field*

Abell 2744Cluster *

Abell 2744Cluster *

Abell 2744Cluster *

Abell 2744Cluster a model of the clusters optics gives us the magnification powermodel credit: J. Richard, CATS team*

background galaxies are magnified by factors up to ~10-20, providing the deepest yet view of the universe*

background galaxies are magnified by factors up to ~10-20, providing the deepest yet view of the universelensed galaxies*

Abell 2744 + parallels are very very deepOptical ACS images (blue, green, yellow) reach ~29th magnitude (dashed line)

Infrared WFC3/IR images (orange, pink, red, dark-red) >~28.7 magnitude(observed magnitudes, not intrinsic magnitudes)*Fainter Fainter Number of galaxiesNumber of galaxies

Take observed fluxes x lensing magnifications (average ~1.8x, max ~80x)

intrinsically faintest Frontier Fields galaxies ~2.5 magnitudes (10x) fainter than Ultra Deep Field (blue dashed line)Deepest view yet into the distant universe:HUDF12HUDF12*Intrinsically Fainter Observed Fainter Number of galaxies

The Frontier Fields is combining the power of natures telescopes - massive clusters of galaxies - with HST to provide the intrinsically deepest view of the universe yet. Parallel imaging is providing the second deepest observations of blank fields, and improve our statistical understanding of most distant and faint galaxies.

NASAs Great Observatories -- Hubble, Spitzer, and Chandra - will observe the Frontier Field clusters and parallel fields over the next 3 years.

The first set of Hubble observations of Abell 2744 are complete, and images have been publicly released. These reveal thousands of distant galaxies, many at intrinsic luminosities ~10 times fainter than ever seen before.

http://www.stsci.edu/hst/campaigns/frontier-fieldshttp://frontierfields.wordpress.com/https://www.facebook.com/FrontierFields

Exploring the Depths of the Universe*

Jennifer Lotz, Matt Mountain, & the Frontier Fields TeamSpace Telescope Science Institute,Spitzer Science Centerwww.stsci.edu/hst/campaigns/frontier-fields

contact: lotz@stsci.edu

Exploring the Depths of the Universe*

Now that we have some understanding of our galaxy, were almost ready to go out and try to understand othergalaxies. But there are a few things about the universe we need to know first.1) The speed of light is finite. It is really really fast but it is not infinitely fast. This means that as we look fartheraway from the Earth, the light reaching us has travelled for a longer time. Therefore we see distant objectsas they were in the past.2) The universe is expanding. Distant galaxies are moving away from us more quickly than nearby ones.3) The light coming from distant objects is shifted redwards... measuring this red-shifts gives us an estimate of the distancefrom us, and hence the look-back time.1) The speed of light is finite -- we dont notice this when we call Tokyo using fiber-optic cables on Earth because the Earth is so small. The distance of the Sun is much larger than the circumference of the Earth -- the light we see from the Sun left the Sun 8 minutes earlier -- therefore we see the Sun as it was 8 minutes ago. The nearest big galaxies to us is Andromeda. It take 3 million years from Andromedas light to reach us therefore we see Andromeda as it was 3 million years ago. The most distant galaxies we can see are at a look-back time of 13 billion years ago. Finally, the most distant thing we can see is light radiated from ionized hydrogen a few 100,000 years after the Big Bang -- this light was emitted 13.7 billion years ago. Therefore, by looking farther away, astronomers are essentially looking back in time and can see how the universe has evolved and changed with time.2) The universe is expanding. Using the apparent brightness of well-understood variablestars to estimate the distance to galaxies, Edwin Hubble discovered that most distant galaxieswere moving away from us, and that their velocities were proportional to their distance from us. This means that by measuring a galaxys velocity away from us, we can get an estimate of its distance 3) Objects moving away from us appear to be redder. The bottom of this figure shows the light from a nearby star spread out by prism. The cool hydrogen at the surface of the star absorbs the stars light at very particular colors, making a recognizable pattern. Now, if we take the light from a nearby galaxy and put it through a prism, we would see this pattern shifted to the red. A more distant galaxy would have the hydrogen line pattern shifted even further redward. Therefore by measuring this redshift we can estimate the galaxys velocity away from us and, using Hubbles law, its distance from us. However, this redshift effect is true for the all the light from the galaxy, not just the hydrogen lines.Intrinsically blue stars will appear redder in very distant galaxies; observing galaxies at different distances in the same color will pick up red stars for nearby galaxies but blue stars for distant galaxies.What does the universe look like after the Big Bang? When we point the Hubble Space Telescope at one small patch of sky and use it to detect the light from stars, we see something very different.Okay, now we are ready to look into the distant universe -- and we are going to look as far as we possibly can. This image is a picture of the cosmic microwave background -- the light emitted by ionized hydrogen when the universe was only 380,00 years old. The image is in false color, with a stretch such that any regions of the sky glowing at 4 degrees would appear red and regions of the sky at 0 degree would appear to be blue. Except for gas from our Milky Way galaxy, the sky is remarkably uniform. This is the same image, this time with the Milky Way subtracted out and the stretch changed such that blue is now 0.0001 degrees colder than the average temperature and red is 0.0001 degrees hotter than the average temperatures. The average variations in the light from the ionized hydrogen at the early universe are very small. In our local universe, we see large galaxies like the Milky Way. With the Hubble Space Telescope, we can see galaxies as they were 1 billion years after the Big Bang. But beyond this point, we are not able to observe galaxies or stars. Sometime between the Big Bang and a billion years later, the first galaxies formed out of the initial small density fluctuations. This is an image of the Ultra Deep Field, the deepest image ever taken of the sky. There are thousands of galaxies in this very small region of the sky. In fact there are many more galaxies in the universe than there are stars in our galaxy. Most of the galaxies we see here are at look-back times 5-10 billion years after the Big Bang.