arXiv subjects

Massimo Stiavelli

Publications and source records attributed to Massimo Stiavelli.

75 records · Page 5Linked to original sources

arXiv2000

WFPC2 Observations of the Hubble Deep Field-South

The Hubble Deep Field-South observations targeted a high-galactic-latitude field near QSO J2233-606. We present WFPC2 observations of the field in four wide bandpasses centered at roughly 300, 450, 606, and 814 nm. Observations, data reduction procedures, and noise properties of the final images are discussed in detail. A catalog of sources is presented, and the number counts and color distributions of the galaxies are compared to a new catalog of the HDF-N that has been constructed in an identical manner. The two fields are qualitatively similar, with the galaxy number counts for the two fields agreeing to within 20%. The HDF-S has more candidate Lyman-break galaxies at z > 2 than the HDF-N. The star-formation rate per unit volume computed from the HDF-S, based on the UV luminosity of high-redshift candidates, is a factor of 1.9 higher than from the HDF-N at z ~ 2.7, and a factor of 1.3 higher at z ~ 4.

astro-ph↗

arXiv1999

A NICMOS search for high redshift elliptical galaxy candidates

We have collected optical follow-up observations from the ground and the Hubble Space Telescope (HST) for 13.74 square ' of archival images taken with the Near Infrared Camera and Multi Object Spectrograph (NICMOS). We use two criteria to select E/S0 galaxy candidates at z>~1 and z>~1.5 (HizECs) based on colors and infrared morphology. The observed surface density of HizECs is significantly smaller than what is predicted assuming the local luminosity function (LF) of E/S0, constant comoving density, and pure passive evolution with a high redshift of formation of the stellar populations (z>~ 5). On the other hand, assuming a low redshift (z<~2) of formation, not enough HizECs are predicted. The data are very well matched assuming that a substantial fraction of present-day E/S0s (10-66%, depending on cosmology and on the local LF of E/S0s) formed at z = 3 or higher and then evolved passively. The rest of the current E/S0 population may have formed at lower redshift, or may have been rejected by the selection criteria because of interactions or more recent episodes of star-formation (disturbed morphology and/or bluer colors).

astro-ph↗

arXiv1998

Does the Fine Structure Constant Really Vary in Time?

We discuss how laboratory experiments can be used to place constraints on possible variations of the fine structure constant alpha in the observationally relevant redshift interval z ~= 0 - 5, within a rather general theoretical framework. We find a worst case upper limit for Delta alpha / alpha of 8 x 10^-6 for z <= 5 and Delta alpha / alpha of 0.9 x 10^-6 for z <= 1.6. The derived limits are at variance with the recent findings by Webb et al. (1998), who claim an observed variation of Delta alpha/alpha = -2.6 +- 0.4 x 10^-5 at 1<z<1.6.

astro-ph↗