Keck Deep Fields. II. The UV Galaxy Luminosity Function at z~4, 3, and 2

We use very deep UGRI multi-field imaging obtained at the Keck telescope to study the evolution of the rest-frame 1700A galaxy luminosity function as the Universe doubles its age from z~4 to z~2. The depth of our imaging allows us to constrain the faint end of the luminosity function reaching M_1700A ~ -18.5 at z~3 (equivalent to ~1M_sun/yr) accounting for both N^1/2 uncertainty in the number of galaxies and for cosmic variance. We carefully examine many potential sources of systematic bias in our LF measurements before drawing the following conclusions. We find that the luminosity function of Lyman Break Galaxies evolves with time and that this evolution is likely differential with luminosity. The result is best constrained between the epochs at z~4 and z~3, where we find that the number density of sub-L* galaxies increases with time by at least a factor of 2.3 (11sigma statistical confidence); while the faint end of the LF evolves, the bright end appears to remain virtually unchanged, indicating that there may be differential, luminosity-dependent evolution significant at the 97% level. Potential systematic biases restric our ability to draw strong conclusions about continued evolution of the luminosity function to lower redshifts, z~2.2 and z~1.7, but, nevertheless, it appears certain that the number density of z~2.2 galaxies at all luminosities we studied, -22<M_1700A<-18, is at least as high as that of their counterparts at z~3. While it is not yet clear what mechanism underlies the observed evolution, the fact that this evolution is differential with luminosity opens up new avenues of improving our understanding of how galaxies form and evolve at high redshift.Comment: Accepted for publication in ApJ. Updated preprint to reflect this final versio

Heisenberg chains cannot mirror a state

Faithful exchange of quantum information can in future become a key part of many computational algorithms. Some Authors suggest to use chains of mutually coupled spins as channels for quantum communication. One can divide these proposals into the groups of assisted protocols, which require some additional action from the users, and natural ones, based on the concept of state mirroring. We show that mirror is fundamentally not the feature chains of spins-1/2 coupled by the Heisenberg interaction, but without local magnetic fields. This fact has certain consequences in terms of the natural state transfer

A multi-wavelength view on the dusty Wolf-Rayet star WR 48a

We present results from the first attempts to derive various physical characteristics of the dusty Wolf-Rayet star WR 48a based on a multi-wavelength view of its observational properties. This is done on the basis of new optical and near-infrared spectral observations and on data from various archives in the optical, radio and X-rays. The optical spectrum of WR 48a is acceptably well represented by a sum of two spectra: of a WR star of the WC8 type and of a WR star of the WN8h type. The strength of the interstellar absorption features in the optical spectra of WR 48a and the near-by stars D2-3 and D2-7 (both members of the open cluster Danks 2) indicates that WR 48a is located at a distance of ~4 kpc from us. WR 48a is very likely a thermal radio source and for such a case and smooth (no clumps) wind its radio emission suggests a relatively high mass-loss rate of this dusty WR star (dM/dt = a few x 10^(-4) solar masses per year). Long timescale (years) variability of WR 48a is established in the optical, radio and X-rays. Colliding stellar winds likely play a very important role in the physics of this object. However, some LBV-like (luminous blue variable) activity could not be excluded as well.Comment: Accepted for publication in MNRAS; 16 pages, 16 figures, 6 table

N-enlarged Galilei Hopf algebra and its twist deformations

The N-enlarged Galilei Hopf algebra is constructed. Its twist deformations are considered and the corresponding twisted space-times are derived.Comment: 8 pages, no figure

Keck Deep Fields. III. Luminosity-dependent Evolution of the Ultraviolet Luminosity and Star Formation Rate Densities at z~4, 3, and 2

We use the Keck Deep Fields UGRI catalog of z~4, 3, and 2 UV-selected galaxies to study the evolution of the rest-frame 1700A luminosity density at high redshift. The ability to reliably constrain the contribution of faint galaxies is critical and our data do so as they reach to M*+2 even at z~4 and deeper still at lower redshifts. We find that the luminosity density at high redshift is dominated by the hitherto poorly studied galaxies fainter than L*, and, indeed, the the bulk of the UV light in the high-z Universe comes from galaxies in the luminosity range L=0.1-1L*. It is these faint galaxies that govern the behavior of the total UV luminosity density. Overall, there is a gradual rise in luminosity density starting at z~4 or earlier, followed by a shallow peak or a plateau within z~3--1, and then followed by the well-know plunge at lower redshifts. Within this total picture, luminosity density in sub-L* galaxies evolves more rapidly at high redshift, z>~2, than that in more luminous objects. However, this is reversed at lower redshifts, z<~1, a reversal that is reminiscent of galaxy downsizing. Within the context of the models commonly used in the observational literature, there seemingly aren't enough faint or bright LBGs to maintain ionization of intergalactic gas even as late as z~4. This is particularly true at earlier epochs and even more so if the faint-end evolutionary trends we observe at z~3 and 4 continue to higher redshifts. Apparently the Universe must be easier to reionize than some recent studies have assumed. Nevertheless, sub-L* galaxies do dominate the total UV luminosity density at z>~2 and this dominance further highlights the need for follow-up studies that will teach us more about these very numerous but thus far largely unexplored systems.Comment: Accepted for publication in the Astrophysical Journal. Abstract abridge