Ultra Deep Field Galaxies at z ~ 6-5: From HST to Spitzer

[wolram]

http://arxiv.org/abs/astro-ph/0507673

Title: Rest-frame Ultraviolet-to-Optical Properties of Galaxies at z ~ 6 and 5 in the Hubble Ultra Deep Field: from Hubble to Spitzer
Authors: Haojing Yan (SSC, Caltech), Mark Dickinson (NOAO), Daniel Stern (JPL), Peter R. M. Eisenhardt (JPL), Ranga-Ram Chary (SSC, Caltech), Mauro Giavalisco (STScI), Henry C. Ferguson (STScI), Stefano Casertano (STScI), Christopher J. Conselice (Caltech), Casey Papovich (Steward), William T. Reach (SSC, Caltech), Norman Grogin (STScI), Leonidas A. Moustakas (JPL), Masami Ouchi (STScI)
Comments: Accepted for publication in ApJ

We use data from the first epoch of observations with the IRAC/Spitzer for the GOODS to detect and study a collection of LBGs at z ~ 6 to 5 in the HUDF, six of which have spectroscopic confirmation. At these redshifts, IRAC samples rest-frame optical light in the range 0.5 to 0.8 um, where the effects of dust extinction are smaller and the sensitivity to light from evolved stars is greater than at shorter, rest-frame UV observable from the ground or with the HST. As such, it provides useful constraints on the ages and masses of these galaxies' stellar populations. We find that the SEDs for many of these galaxies are best fitted by models of stellar populations with masses of a few x 1e10 M_sun, and with ages of a few hundred Myrs, values quite similar to those derived for typical LBGs at z ~ 3. When the universe was only 1 Gyr old, some galaxies had already formed a mass of stars approaching that of the present-day Milky Way, and that they started forming those stars at z > 7, and in some cases much earlier. We find that the lower limits to the space density for galaxies in this mass range are consistent with predictions from recent hydrodynamic simulations of structure formation in a LCDM universe. All objects in our samples are consistent with having solar metallicity, suggesting that they might have already been significantly polluted by metals. The values for dust reddening derived from the model fitting are low or zero, and we find that some of the galaxies have rest-frame UV colors that are even bluer than those predicted by the stellar population models to which we compare them. These colors might be attributed to the presence of very massive stars (> 100 M_sun), or by weaker intergalactic HI absorption than what is commonly assumed.

 

[AndyW]

Dear author,

Thank you for sharing your research on the rest-frame ultraviolet-to-optical properties of galaxies at z ~ 6 and 5 in the Hubble Ultra Deep Field. Your study provides valuable insights into the formation and evolution of galaxies in the early universe. The use of IRAC/Spitzer data to study these galaxies at rest-frame optical wavelengths is a novel approach and has yielded interesting results.

It is intriguing to see that the stellar populations of these galaxies have masses and ages similar to those of typical LBGs at z ~ 3. This suggests that the formation of these galaxies may have followed a similar path as galaxies at lower redshifts. The fact that some of these galaxies have already formed a mass of stars approaching that of the present-day Milky Way when the universe was only 1 Gyr old is also remarkable. This highlights the rapid pace of galaxy formation in the early universe.

Furthermore, your findings are consistent with predictions from hydrodynamic simulations of structure formation in a LCDM universe. The agreement between observational data and theoretical predictions is always a reassuring confirmation of our understanding of the universe.

The low or zero dust reddening values derived from your model fitting are also noteworthy. This suggests that these galaxies may have already been significantly polluted by metals, which is surprising given their young ages. The possibility of very massive stars (> 100 M_sun) or weaker intergalactic HI absorption contributing to the observed UV colors is intriguing and warrants further investigation.

Overall, your study provides valuable insights into the early stages of galaxy formation and adds to our understanding of the evolution of galaxies in the early universe. Thank you for sharing your research and I look forward to seeing future developments in this field.