Probing Cosmic Reionization: Observations from Strong Lensing and Beyond

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In summary, the authors discuss recent observations suggesting a decline in star formation rate density over 3 < z < 7 and the challenges this poses in explaining the assembled stellar mass in z ~ 6 galaxies. They propose that this may be due to a period of earlier star formation, which can be studied through strong lensing before the availability of JWST and TMT. The authors also discuss their ongoing spectroscopic and HST/IRAC surveys targeting lensing clusters for 8.5 < z < 10 and their potential to constrain the contribution of early, low luminosity sources to cosmic reionization. They also mention the prospects and challenges of finding galaxies at z ≥ 10 with JWST.
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http://arxiv.org/abs/astro-ph/0508123

Title: Searching for the Sources Responsible for Cosmic Reionization: Probing 7 < z < 10 and Beyond
Authors: Daniel P. Stark, Richard S. Ellis (Caltech)
Comments: 12 pages, 6 figures, to appear in "First Light & Reionization", eds. E. Barton & A. Cooray, New Astronomy Reviews, in press

(Abridged) We review recent observations that suggest the star formation rate density is declining over 3$<z<$7 and illustrate the challenges that this poses in explaining the assembled stellar mass in z$\sim$6 galaxies deduced from Spitzer data. A plausible conclusion is a vigorous period of earlier star formation. Prior to JWST and TMT, strong lensing offers a unique probe of the extent of this earlier activity. We discuss the first results of a blind spectroscopic survey of lensing clusters for 8.5$<z<$10 Ly$\alpha$ emitters using NIRSPEC which is achieving a limiting star formation rate of 0.1 $M_{\odot}$ yr$^{-1}$. A companion HST/IRAC survey is targeting lensed $z$ and $J$-band dropouts and probes a $\simeq$1 arcmin$^2$ region 1 magnitude deeper than the UDF/NICMOS observations. Both surveys will constrain the contribution of early, low luminosity, sources to cosmic reionization.
 
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We also discuss the prospects for finding z$\geq$10 galaxies with JWST and the challenges posed by the faintness of such sources.
 

1. What is cosmic reionisation?

Cosmic reionisation refers to the process in the early universe where the first stars and galaxies formed and emitted enough ultraviolet radiation to ionize the neutral hydrogen gas that filled the universe. This allowed light to travel freely through space, making the universe transparent and visible to us today.

2. When did cosmic reionisation occur?

Cosmic reionisation is estimated to have occurred between 380,000 and 150 million years after the Big Bang, with the most likely timeframe being around 550 million years after the Big Bang. However, more precise measurements are still being made to determine the exact timing.

3. How did cosmic reionisation happen?

Cosmic reionisation happened when the first stars and galaxies, made up of mostly hydrogen and helium, began to form and release intense ultraviolet radiation. This radiation broke apart the neutral hydrogen atoms, freeing the electrons and creating an ionized plasma. Over time, this process spread throughout the universe, making it transparent and visible.

4. What is the significance of cosmic reionisation?

Cosmic reionisation is a crucial event in the history of the universe, as it marks the transition from a dark, opaque universe to one that is transparent and filled with light. It also allowed for the formation of more complex structures, such as galaxies and galaxy clusters, and played a role in shaping the large-scale structure of the universe.

5. How do scientists study cosmic reionisation?

Scientists study cosmic reionisation using a variety of methods, including observations from telescopes and satellites, computer simulations, and theoretical models. They look for signatures of ionized gas and the first galaxies, as well as study the cosmic microwave background radiation, which contains information about the early universe.

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