The Rest-Frame UV Luminosity Density of Star-Forming Galaxies at Redshifts z>3.5

We have measured the rest--frame lambda~1500 Ang comoving specific luminosity density of star--forming galaxies at redshift 3.5<z<6.5 from deep images taken with the Hubble Space Telescope (HST)and the Advanced Camera for Surveys (ACS), obtained as part of the Great Observatories Origins Deep Survey (GOODS). We used color selection criteria to construct samples of star--forming galaxies at redshifts z~4, 5 and 6, identified by the signature of the 912 Ang Lyman continuum discontinuity and Lyman-alpha forest blanketing in their rest--frame UV colors (Lyman--break galaxies). The ACS samples cover ~0.09 square degree, and are also relatively deep, reaching between 0.2 and 0.5 L_3^*, depending on the redshift, where $L_3^*$ is the characteristic UV luminosity of Lyman--break galaxies at z~3. The specific luminosity density of Lyman--break galaxies appears to be nearly constant with redshift from z~3 to z~6, although the measure at z~6 remains relatively uncertain, because it depends on the accurate estimate of the faint counts of the z~6 sample. If Lyman--break galaxies are fair tracers of the cosmic star formation activity, our results suggest that at z~6 the universe was already producing stars as vigorously as it did near its maximum several Gyr later, at 1<~z<~3. Thus, the onset of large--scale star formation in the universe is to be sought at around z~6 or higher, namely at less than ~7% of the current cosmic age.Comment: AAS LaTeX macros 4.0, 11 pages, 1 postscript figure. Accepted for publication in The Astrophysical Journal, Letter. Minor changes to the figure caption. The data and the GOODS-group papers can be found at http://www.stsci.edu/science/goods

The z ~ 4 Lyman Break Galaxies: Colors and Theoretical Predictions

We investigate several fundamental properties of z ~ 4 Lyman-break galaxies by comparing observations with the predictions of a semi-analytic model based on the Cold Dark Matter theory of hierarchical structure formation. We use a sample of B_{435}-dropouts from the Great Observatories Origins Deep Survey, and complement the ACS optical B_{435}, V_{606}, i_{775}, and z_{850} data with the VLT ISAAC J, H, and K_{s} observations. We extract B_{435}-dropouts from our semi-analytic mock catalog using the same color criteria and magnitude limits that were applied to the observed sample. We find that the i_{775} - K_{s} colors of the model-derived and observed B_{435}-dropouts are in good agreement. However, we find that the i_{775}-z_{850} colors differ significantly, indicating perhaps that either too little dust or an incorrect extinction curve have been used. Motivated by the reasonably good agreement between the model and observed data we present predictions for the stellar masses, star formation rates, and ages for the z ~ 4 Lyman-break sample. We find that according to our model the color selection criteria used to select our z ~ 4 sample surveys 67% of all galaxies at this epoch down to z_{850} < 26.5. We find that our model predicts a roughly 40% mass build-up between the z \~ 4 and z ~ 3 epochs for the UV rest-frame L* galaxies. Furthermore, according to our model, at least 50% of the total stellar mass resides in relatively massive UV-faint objects that fall below our observational detection limit.Comment: 12 pages, including 4 figures; submitted to and accepted by ApJL -- to be published in a special issue of early release GOODS result

Evolution of the Luminosity Function, Star Formation Rate, Morphology and Size of Star-forming Galaxies Selected at Rest-frame 1500A and 2800A

Using the multiwavelength photometric and spectroscopic data covering the CDF-S obtained within the GOODS, we investigate the rest-frame UV properties of galaxies to z~2.2, including the evolution of the luminosity function, the luminosity density, star formation rate (SFR) and galaxy morphology. We find a significant brightening (~ 1 mag) in the rest-frame 2800A characteristic magnitude (M*) over the redshift range 0.3<z<1.7 and no evolution at higher redshifts. The rest-frame 2800A luminosity density shows an increase by a factor ~4 to z~2.2. We estimate the SFR to z~2.2 from the 1500A and 2800A luminosities. The SFR derived from the 2800A luminosity density is almost factor two higher than that derived from the 1500A luminosities. Attributing this to differential dust extinction, we find that an E(B-V)=0.20 results in the same extinction corrected SFR from both 1500A and 2800A luminosities. We investigate the morphological composition of our sample by fitting Sersic profiles to the galaxy images at a fixed rest-frame wavelength of 2800A at 0.5<z<2.2. We find that the fraction of apparently bulge-dominated galaxies (Sersic index n>2.5) increases from ~10% at z~0.5 to ~30% at z~2.2. At the same time, we note that galaxies get bluer at increasing redshift. This suggests a scenario where an increased fraction of the star formation takes place in bulge-dominated systems at high redshift. This could be the evidence that the present day ellipticals are a result of assembly (i.e., mergers) of galaxies at z>1. Finally, we find that galaxy sizes for a luminosity selected sample evolves as (1+z)^{-1.1} between redshifts z=2.2 and z=1.1. This is consistent with previous measurements and suggests a similar evolution over the redshift range 0 < z < 6.Comment: 38 pages with 14 figures. Accepted for publication in Ap

Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution

We examine the evolution of the sizes and number densities of disk galaxies using the high resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). The multiwavelength (B,V,i,z) images allow us to classify galaxies based on their rest-frame B-band morphologies out to redshift z = 1.25. In order to minimize the effect of selection biases, we confine our analysis to galaxies which occupy the region of magnitude-size plane where the survey is almost 90% complete at all redshifts. The observed size distribution is consistent with a log-normal distribution as seen for the disk galaxies in the local Universe and does not show any significant evolution over the redshift range 0.25 < z < 1.25. We find that the number densities of disk galaxies remains fairly constant over this redshift range, although a modest evolution by a factor of four may be possible within the 2-sigma uncertainties.Comment: accepted for publication in ApJL, 4 page

Functional near infrared spectroscopy (fNIRS) to assess cognitive function in infants in rural Africa

Cortical mapping of cognitive function during infancy is poorly understood in low-income countries due to the lack of transportable neuroimaging methods. We have successfully piloted functional near infrared spectroscopy (fNIRS) as a neuroimaging tool in rural Gambia. Four-to-eight month old infants watched videos of Gambian adults perform social movements, while haemodynamic responses were recorded using fNIRS. We found distinct regions of the posterior superior temporal and inferior frontal cortex that evidenced either visual-social activation or vocally selective activation (vocal > non-vocal). The patterns of selective cortical activation in Gambian infants replicated those observed within similar aged infants in the UK. These are the first reported data on the measurement of localized functional brain activity in young infants in Africa and demonstrate the potential that fNIRS offers for field-based neuroimaging research of cognitive function in resource-poor rural communities

Functional near infrared spectroscopy (fNIRS) to assess cognitive function in infants in rural Africa

Cortical mapping of cognitive function during infancy is poorly understood in low-income countries due to the lack of transportable neuroimaging methods. We have successfully piloted functional near infrared spectroscopy (fNIRS) as a neuroimaging tool in rural Gambia. Four-to-eight month old infants watched videos of Gambian adults perform social movements, while haemodynamic responses were recorded using fNIRS. We found distinct regions of the posterior superior temporal and inferior frontal cortex that evidenced either visual-social activation or vocally selective activation (vocal > non-vocal). The patterns of selective cortical activation in Gambian infants replicated those observed within similar aged infants in the UK. These are the first reported data on the measurement of localized functional brain activity in young infants in Africa and demonstrate the potential that fNIRS offers for field-based neuroimaging research of cognitive function in resource-poor rural communities

The Size Evolution of High Redshift Galaxies

Hubble Space Telescope images of high-redshift galaxies selected via color and photometric redshifts are used to examine the size and axial-ratio distribution of galaxies as a function of redshift at lookback times t > 8 Gyr. These parameters are measured at rest-frame UV wavelengths (1200-2000 Angstroms) on images with a rest-frame resolution of less than 0.8 kpc. Galaxy radii are found to scale with redshift approximately as the inverse of the Hubble parameter H(z). This is in accord with the theoretical expectation that the typical sizes of the luminous parts of galaxies should track the expected evolution in the virial radius of dark-matter halos. The mean ratio of semi-major to semi-minor axis for a bright well-resolved sample of galaxies at z ~ 4 is b/a = 0.65, suggesting that these Lyman break galaxies are not drawn from a spheroidal population. However the median concentration index of this sample is C = 3.5, which is closer to the typical concentration indices, C ~ 4, of nearby elliptical galaxies than to the values, C<2 for local disk galaxies of type Sb and later.Comment: 5 pages, including 3 figures; uses emulateapj style; accepted by ApJL for publication in a special issue of early GOODS result

The Hubble Higher-Z Supernova Search: Supernovae to z=1.6 and Constraints on Type Ia Progenitor Models

We present results from the Hubble Higher-z Supernova Search, the first space-based open field survey for supernovae (SNe). In cooperation with the Great Observatories Origins Deep Survey, we have used the Hubble Space Telescope with the Advanced Camera for Surveys to cover 300 square arcmin in the area of the Chandra Deep Field South and the Hubble Deep Field North on five separate search epochs (separated by 45 day intervals) to a limiting magnitude of z'=26. These deep observations have allowed us to discover 42 SNe in the redshift range 0.2 < z < 1.6. As these data span a large range in redshift, they are ideal for testing the validity of Type Ia supernova progenitor models with the distribution of expected ``delay times,'' from progenitor star formation to SN Ia explosion, and the SN rates these models predict. Through a Bayesian maximum likelihood test, we determine which delay-time models best reproduce the redshift distribution of SNe Ia discovered in this survey. We find that models that require a large fraction of ``prompt'' (less than 2 Gyr) SNe Ia poorly reproduce the observed redshift distribution and are rejected at 95% confidence. We find that Gaussian models best fit the observed data for mean delay times in the range of 3 to 4 Gyr.Comment: 32 pages, 15 figures, accepted for publication in the Astrophysical Journa

Sclerostin: Current Knowledge and Future Perspectives

In recent years study of rare human bone disorders has led to the identification of important signaling pathways that regulate bone formation. Such diseases include the bone sclerosing dysplasias sclerosteosis and van Buchem disease, which are due to deficiency of sclerostin, a protein secreted by osteocytes that inhibits bone formation by osteoblasts. The restricted expression pattern of sclerostin in the skeleton and the exclusive bone phenotype of good quality of patients with sclerosteosis and van Buchem disease provide the basis for the design of therapeutics that stimulate bone formation. We review here current knowledge of the regulation of the expression and formation of sclerostin, its mechanism of action, and its potential as a bone-building treatment for patients with osteoporosis