Galaxies at redshift 10
A Search for Galaxies just 500 Million Years After the Big Bang
Using the deepest near-IR observations ever obtained with the Hubble Space Telescope, we conducted a search for galaxies to fainter limits and further back in time than had been possible before. Specifically, we conducted a search for galaxies at z~10, when the universe was just 480 million years old. Amazingly enough, we were able to find one source that is consistent with existing back at these early times. While there is a considerable 'wow'-factor that goes along with the existence of such a source, the search also teaches us an important lesson about early evolution of the star formation history and about galaxy growth. Compared to slightly later epochs, the star formation rate density at these early times appears to be 10x and 20x smaller than it is just 150 and 250 million years later respectively. This shows us that the universe is changing very rapidly at these young times!
In our letter to Nature we report the direct detection of a probable redshift z~10 galaxy. This galaxy lies in the heart of the reionization epoch, when the universe was just 4% of its present age. Our z~10 candidate, just 500 million years after the Big Bang, pushes back the timescale for early galaxy buildup to z>10, thereby increasing the likely role of galaxies in providing the UV flux needed to reionize the universe, and bringing us closer to the time of the first stars and the birth of galaxies just 200-300 million years earlier.
This image is the result of nearly 8 days of exposures using the new WFC3/IR instrument on the Hubble. Taken in the summer of 2009 and fall of 2011 using 111 orbits of Hubble time the HUDF09 is the deepest image ever taken of the universe in the infrared. It has enabled astronomers to look back in time and find the earliest galaxies yet - including a plausible galaxy just 500 million years from the Big Bang.
Telescope: Hubble Space Telescope
Instrument: Wide Field Camera 3 Infrared Channel (WFC3/IR)
Filters: F105W(Y), F125W(J), and F160W(H)
Exposure Dates: August 2009 - September 2010
Total Exposure Time: 87.2 hours
Exposure Time by Filter:
F105W: 18.6 hours, 48 exposures
F125W: 27.8 hours, 68 exposures
F160W: 40.8 hours, 106 exposures
HST Proposal ID: 11563
HUDF09 Team: G. Illingworth (UCO/Lick Observatory and the University of California, Santa Cruz), R. Bouwens (UCO/Lick Observatory and Leiden University), M. Carollo (Swiss Federal Institute of Technology, Zurich), M. Franx (Leiden University), I. Labbe (Carnegie Institution of Washington), D. Magee (University of California, Santa Cruz), P. Oesch (Swiss Federal Institute of Technology, Zurich), M. Stiavelli (STScI), M. Trenti (University of Colorado, Boulder), and P. van Dokkum (Yale University).
A candidate redshift z ~ 10 galaxy and rapid changes in that population at an age of 500 Myr
Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6,000 galaxies existing just 900-2,000 million years (Myr) after the Big Bang (redshifts 6 > z > 3). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z ~ 8 galaxies that, together with reports of a gamma-ray burst at z ~ 8.2, constitute the earliest objects reliably reported to date. Observations of z ~ 7-8 galaxies suggest substantial star formation at z > 9-10. Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z ~ 10 galaxies in the heart of the reionization epoch, only 500 Myr after the Big Bang. Not only do we find one possible z ~ 10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (~10%) at this time than it is just ~200 Myr later at z ~ 8. This demonstrates how rapid galaxy build-up was at z ~ 10, as galaxies increased in both luminosity density and volume density from z ~ 8 to z ~ 10. The 100-200 Myr before z ~ 10 is clearly a crucial phase in the assembly of the earliest galaxies.
Expanded Search for z~10 Galaxies from HUDF09, ERS, and CANDELS Data: Evidence for Accelerated Evolution at z>8?
We search for z~10 galaxies over ~160 arcmin^2 of WFC3/IR data in the Chandra Deep Field South, using the public HUDF09, ERS, and CANDELS surveys, that reach to 5sigma depths ranging from 26.9 to 29.4 in H_160 AB mag. z>~9.5 galaxy candidates are identified via J_125-H_160>1.2 colors and non-detections in any band blueward of J_125. Spitzer IRAC photometry is key for separating the genuine high-z candidates from intermediate redshift (z~2-4) galaxies with evolved or heavily dust obscured stellar populations. After removing 16 sources of intermediate brightness (H_160~24-26 mag) with strong IRAC detections, we only find one plausible z~10 galaxy candidate in the whole data set, previously reported in Bouwens et al. (2011). The newer data cover a 3x larger area and provide much stronger constraints on the evolution of the UV luminosity function (LF). If the evolution of the z~4-8 LFs is extrapolated to z~10, six z~10 galaxies are expected in our data. The detection of only one source suggests that the UV LF evolves at an accelerated rate before z~8. The luminosity density is found to increase by more than an order of magnitude in only 170 Myr from z~10 to z~8. This increase is >=4x larger than expected from the lower redshift extrapolation of the UV LF. We are thus likely witnessing the first rapid build-up of galaxies in the heart of cosmic reionization. Future deep HST WFC3/IR data, reaching to well beyond 29 mag, can enable a more robust quantification of the accelerated evolution around z~10.
Redshift 10 Galaxy Candidate
Zoom-in of z~10 galaxy candidate UDFj-39546284
Color close-up of z~10 galaxy candidate UDFj-39546284
Hubble Ultra Deep Field 2009-2010 and UDFj-39546284
HUDF09 WFC3/IR Image - The Deepest IR image ever taken
NASA's Hubble Space Telescope has made the deepest image of the universe ever taken in near-infrared light.
The Early Universe
Probing the Early Universe
Star Birth Rate in the Early Universe
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