La mascletada cósmica

La mascletada cósmic

Andròmeda, la nostra Galàxia Veïna

Andròmeda, la nostra Galàxia Veïn

Els secrets de la nebulosa

Els secrets de la nebulos

The Ultraviolet Luminosity Density of the Universe from Photometric Redshifts of Galaxies in the Hubble Deep Field

Studies of the Hubble Deep Field (HDF) and other deep surveys have revealed an apparent peak in the ultraviolet (UV) luminosity density, and therefore the star-formation rate density, of the Universe at redshifts 1<z<2. We use photometric redshifts of galaxies in the HDF to determine the comoving UV luminosity density and find that, when errors (in particular, sampling error) are properly accounted for, a flat distribution is statistically indistinguishable from a distribution peaked at z~1.5. Furthermore, we examine the effects of cosmological surface brightness (SB) dimming on these measurements by applying a uniform SB cut to all galaxy fluxes after correcting them to redshift z=5. We find that, comparing all galaxies at the same intrinsic surface brightness sensitivity, the UV luminosity density contributed by high intrinsic SB regions increases by almost two orders of magnitude from z~0 to z~5. This suggests that there exists a population of objects with very high star formation rates at high redshifts that apparently do not exist at low redshifts. The peak of star formation, then, may occur somewhere beyond a redshift z~>5.Comment: 4 pages total, including 3 embedded figures, to appear in the proceedings of the Xth Rencontres de Blois, "The Birth of Galaxies." LaTeX style file include

Recovering the real-space correlation function from photometric redshift surveys

Measurements of clustering in large-scale imaging surveys that make use of photometric redshifts depend on the uncertainties in the redshift determination. We have used light-cone simulations to show how the deprojection method successfully recovers the real space correlation function when applied to mock photometric redshift surveys. We study how the errors in the redshift determination affect the quality of the recovered two-point correlation function. Considering the expected errors associated to the planned photometric redshift surveys, we conclude that this method provides information on the clustering of matter useful for the estimation of cosmological parameters that depend on the large scale distribution of galaxies.Comment: 11 pages, 8 figures. Accepted for publication in MNRA

La cara fosca de l'Univers

La cara fosca de l'Univer