Early Reionization: HUDF-JD2 Examined

[wolram]

http://arxiv.org/abs/astro-ph/0509605

Authors: N. Panagia (1), S.M. Fall (2), B. Mobasher (1), M. Dickinson (3), H.C. Ferguson (2), M. Giavalisco (2), D. Stern (4), T. Wiklind (1) ((1) ESA/STScI, (2) STScI, (3) NOAO/Tucson, (4) JPL)
Categories: astro-ph
Comments: 6 pages, 2 figures. Accepted for publication in ApJ Letters

We examine the possible reionization of the intergalactic medium (IGM) by the source UDF033238.7-274839.8 (hereafter HUDF-JD2), which was discovered in deep {\it HST}/VLT/{\it Spitzer} images obtained as part of the Great Observatory Origins Deep Survey and {\it Hubble} Ultra-Deep Field projects. Mobasher et al (2005) have identified HUDF-JD2 as a massive ($\sim6\times10^{11}M_\odot$) post-starburst galaxy at redshift z$\gtrsim6.5$. We find that HUDF-JD2 may be capable of reionizing its surrounding region of the Universe, starting the process at a redshift as high as z$\approx 15 \pm5$.

 

[wolram]

http://arxiv.org/abs/astro-ph/0509616

Spectroscopic Studies of z~5.7 and z~6.5 Galaxies: Implications for Reionization
Authors: Esther M. Hu (1), Lennox L. Cowie (1), Peter Capak (1,2), Yuko Kakazu (1) ((1) IfA, Univ. of Hawaii, (2) Presently at Caltech)
Categories: astro-ph
Comments: 6 pages, 6 figures, to appear in IAU 199 Conf. Proc.: "Probing Galaxies through Quasar Absorption Lines," eds. Williams, Shu, Menard

The recent development of large, complete samples which identify high-redshift galaxies at z~5.7 and z~6.5 from deep, wide-field surveys provides detailed information on the earliest galaxies, their numbers, spatial and kinematic distributions, and implications for early reionization of the IGM. In this contribution we present results of spectroscopic studies of z~5.7 and z~6.5 galaxies identified from our deep, Lyman alpha narrowband and multicolor surveys conducted with the SuprimeCam mosaic CCD camera on the 8.3-m Subaru telescope and observed with the DEIMOS multi-object spectrograph on Keck. The luminosity function of the z~6.5 galaxies is shown to be similar to the luminosity function of the z~5.7 galaxy samples, suggesting that a substantial star-forming population is already in place at z~6.5. Comparisons of both individual and stacked spectra of galaxies in these two samples show that the Lyman alpha emission profiles, equivalent widths, and continuum break strengths do not substantially change over this redshift interval. The wide-field nature of the surveys also permits mapping the large-scale distribution of the high-redshift galaxies in spatial structures extending across individual SuprimeCam fields (~60 Mpc). Field-to-field variations in the number of objects at z~6.5 may shortly be able to place constraints on the porosity of the reionization boundary.

 

[Garth]

Interesting, a 6 x 10¹¹M_solar galaxy at z = 6.5, when the universe was 860 Myrs old, (age given by Ned Wright's calculator allowing for DE). Substantial re-ionisation - Pop III stars and substantial star formation even in the presence of such re-ionisation.

Does this all fit?

Garth

 

[Chronos]

The most important recent paper on early reionization might be:

Outshining the quasars at reionisation: The X-ray spectrum and lightcurve of the redshift 6.29 Gamma-Ray Burst GRB050904
http://arxiv.org/abs/astro-ph/0509640

 

[SpaceTiger]

http://arxiv.org/abs/astro-ph/0509605

Yeah, we discussed this one at coffee the other day. They make a lot of assumptions (as one must at z=6.5), but most of them seem to be conservative. The galaxy is showing the signature of A stars, indicating that the youngest population (O and B stars, which would normally dominate the light) had already died off by z=6.5. Fitting their star formation models to the light, they estimate the age of the population and determine that the O and B stars could have reionized a region about the size of the Hubble Ultradeep Field.

Things to consider:

- The star formation models they use include a locally determined initial mass function (IMF). Since stars at high-redshift are expected to have much lower metallicities, we can't be sure that their IMF would be even close to the same. Most models indicate, however, that low-metallicity populations should have a "top-heavy" IMF, meaning that there should be more massive stars than locally. This would actually strengthen their argument about reionization.
- There may be more galaxies (with lower surface brightness) at these redshifts in the HUDF field. If so, this also strengthens their arguments.
- Small-number statistics. In fact, one object is as small a number of galaxies as you can get in a sample. This means that any generalizations to reionization as a whole will have extremely large error bars.

All in all, though, I think it looks promising. The discrepancy between the WMAP reionization estimates and the optical ones is becoming less significant.

 

[Chronos]

There has been a flood of reionization papers - some recent entries

The sources of the Cosmic Infrared Background
http://www.arxiv.org/abs/astro-ph/0509556

Outshining the quasars at reionisation: The X-ray spectrum and lightcurve of the redshift 6.29 Gamma-Ray Burst GRB050904
http://arxiv.org/abs/astro-ph/0509640

Spectroscopic Studies of z~5.7 and z~6.5 Galaxies: Implications for Reionization
http://arxiv.org/abs/astro-ph/0509616

A large population of galaxies 9 to 12 billion years back in the history of the Universe
http://arxiv.org/abs/astro-ph/0509628

 

[Garth]

Another paper about the galaxy HUDF-JD2: Evidence for a Massive Post-Starburst Galaxy at z ~ 6.5

If the high-redshift interpretation is correct, this object would be an example of a galaxy that formed by a process strongly resembling traditional models of monolithic collapse, in a way which a very large mass of stars formed within a remarkably short period of time, at very high redshift.

As I asked above - "Does it all fit with the mainstream model timing?"

Garth