A Look Back: Galaxies at Cosmic Dawn Revealed in the First Year of the Hubble Frontier Fields Initiative

Transcription

1 A Look Back: Galaxies at Cosmic Dawn Revealed in the First Year of the Hubble Frontier Fields Initiative Dr. Gabriel Brammer (ESA/AURA, STScI) Hubble Science Briefing / November 6,

2 The Early Universe As observed in the Cosmic Microwave Background Radiation (CMBR), structure in the universe 300,000 years after the Big Bang consisted of tiny density fluctuations (1 in 100,000) Graphic credit: Le Figaro 2

3 A universe in a box Start with the initial conditions determined from the cosmic microwave background and let gravity do its thing. z=4 time z=2 z=1 z=0 (today) Dark Matter Gas 3

4 Galaxies today z=4 z=2 z=1 z=0 (today) time Dark Matter Gas 4

5 Galaxies today The local galaxy population: Sloan Digital Sky Survey (SDSS) z=4 z=2 z=1 z=0 (today) time Dark Matter Gas ESA PR

6 Cosmology and galaxy evolution Galaxies in the expanding universe flying apart (E. Hubble) causing the wavelengths of light from distant galaxies to be shifted redward redshift, or z Given the cosmological model supported by the CMBR and many other observations (e.g., supernovae), the measurement of a galaxy s redshift is both a ruler (how far is it from us?) and a clock (what was the age of the universe when the light we observe was emitted?) To build up an understanding of how galaxies form and evolve, we observe and characterize the galaxy population at different redshifts, which correspond to different epochs in the history of the universe 6

7 Relative surface brightness z=0.1 1) Angular size of the Sun s orbit in the Milky Way (8 kpc, in arcseconds) Galaxy evolution A problem: distant galaxies are faint and small! z = 0, today 13.7 Gyr after Big Bang Redshift, z 900 Myr after Big Bang Redshift, z (Gyr: giga/billions, Myr: mega/millions of years) 7

8 Galaxy evolution The Hubble Space Telescope provides the needed sensitivity and image quality to detect distant galaxies

9 Stars formed per year, per unit volume We can measure the total star formation history of the universe in deep Hubble observations! 1995 P. Madau et al. (1996) Redshift, z 9

10 Servicing HST: pushing ever further from cosmic high noon to cosmic dawn Installing Wide-Field Camera 3, 2009 (NASA) 10

11 Stars formed per year, per unit volume Redshift, z 11

12 Stars formed per year, per unit volume P. Oesch et al. (2014) Redshift, z 12

13 Stars formed per year, per unit volume P. Oesch et al. (2014) High noon Dawn Redshift, z 13

14 time 14

15 The next step? How can we use Hubble to efficiently and significantly go beyond the large investments of the existing deep fields today, before the launch of the James Webb Space Telescope in 2018? time 15

16 Natural telescopes: gravitational lenses The Hubble Ultra Deep Field + Massive galaxy cluster (A million-billion times the mass of the sun in stars+gas+dark matter) Illustration by D. Coe, Z. Levay 16

17 Natural telescopes: gravitational lenses = Distortion and magnification of the distant galaxies behind the cluster Illustration by D. Coe, Z. Levay 17

18 The HST Frontier Fields, year

19 19

20 Abell 2744 Cluster 20

21 Abell 2744 Cluster Parallel 21

22 Scientific collaboration The first year of Frontier Fields observations has formed the basis of more than 30 publications with coauthors from 18 countries 22

23 Science highlights 1. Improved determination of the dark matter distribution and total mass of the clusters themselves 2. Ghost light from galaxies torn apart in the Abell 2744 cluster 3. Numerous galaxy candidates at z > 7 4. A robust, multiply-imaged galaxy candidate at z ~ 10 23

24 1. Cluster mass models A reminder: only about 5% of the stuff in the universe (energy density) is composed of matter we know and understand, like stars, gas, and neutrinos. Galaxy clusters are extremely massive (10 14 M in stars, or, > 10 the GDP of the USA, in $) and dominated by dark matter. 24

25 1. Cluster mass models Many multiply imaged lens arcs identified in the deep Frontier Fields imaging of the Abell 2744 and MACS 0416 clusters The arcs put strong constraints on the mass distribution in the clusters (e.g., stars plus dark matter) The total mass of the cluster constrained with a precision of only a few percent! The improved mass model also yields more reliable determination of the magnification map, which is necessary for interpreting the distant background galaxies 25

26 1. Cluster mass models Jauzac et al. (2014) Dozens of multiple image pairs 26

27 1. Cluster mass models Jauzac et al. (2014) Dozens of multiple image pairs Magnification map 27 27

28 2. Ghost light of shredded cluster galaxies Trujillo et al. (2014) Galaxy clusters are a violent environment, with galaxies rushing around at thousands of kilometers per second. Cluster galaxies can get shredded in the process, with the stellar remains strewn about the cluster 28

29 3. Dozens of galaxies at z > 7 Ishikagi et al. (2014) Atek et al. (2014), Zheng et al. (2014) 29

30 3. Dozens of galaxies at z > 7 Ishikagi et al. (2014) Atek et al. (2014), Zheng et al. (2014) 30

31 4. A multiply-imaged galaxy at z~10 a b Zitrin et al. (2010) c a b c Detections only in the reddest HST infrared filters suggest a redshift of z~10. Detecting multiple lensed images greatly increases the likelihood that the object is truly at high redshift and not rather a nearby interloper. 31

32 4. A multiply-imaged galaxy at z~10 Such faint objects can only be detected in the very long full Frontier Fields exposures! An HST orbit 32

33 4. A multiply-imaged galaxy at z~10 Such faint objects can only be detected in the very long full Frontier Fields exposures! a b 1 orbit 2 orbits 8 orbits 24 orbits 33

34 Working as a team NASA s Great Observatories Hubble Space Telescope Spitzer Space Telescope Chandra X-ray Observatory W.M Keck Observatory (Mauna Kea, HI) European Southern Observatory, Very Large Telescope (Cerro Paranal, Chile) Gemini Observatory (Mauna Kea, HI, and Cerro Pachón, Chile) 34

35 Many more exciting results to come! 35