Luminosity Dependent Evolution of Lyman Break Galaxies from redshift 5 to 3

In this contribution we briefly describe our recent results on the properties of Lyman break galaxies at z~5 obtained from deep and wide blank field surveys using Subaru telescope, and through the comparison with samples at lower redshift ranges we discuss the evolution of star-forming galaxies in the early universe.Comment: 2 pages, 1 figure, for the proceedings of the IAU Symposium 235, Galaxies Across the Hubble Time, J. Palous & F. Combes, ed

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

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

Lyman Break Galaxies at z∼5z\sim5: Rest-Frame UV Spectra

We report initial results for spectroscopic observations of candidates of Lyman Break Galaxies (LBGs) at $z\sim5$ in a region centered on the Hubble Deep Field-North by using the Faint Object Camera and Spectrograph attached to the Subaru Telescope. Eight objects with $I_C\leq25.0$ mag, including one AGN, are confirmed to be at $4.5<z<5.2$. The rest-frame UV spectra of seven LBGs commonly show no or weak Lyalpha emission line (rest-frame equivalent width of 0-10\AA) and relatively strong low-ionization interstellar metal absorption lines of SiII $\lambda$1260, OI+SiII $\lambda$1303, and CII $\lambda$1334 (mean rest-frame equivalent widths of them are $-1.2 \sim -5.1$\AA). These properties are significantly different from those of the mean rest-frame UV spectrum of LBGs at $z\sim3$, but are quite similar to those of subgroups of LBGs at $z\sim3$ with no or weak Lyalpha emission. The weakness of Lyalpha emission and strong low-ionization interstellar metal absorption lines may indicate that these LBGs at $z\sim5$ are chemically evolved to some degree and have a dusty environment. Since the fraction of such LBGs at $z\sim5$ in our sample is larger than that at $z\sim3$, we may witness some sign of evolution of LBGs from $z\sim5$ to $z\sim3$, though the present sample size is very small. It is also possible, however, that the brighter LBGs tend to show no or weak Lyalpha emission, because our spectroscopic sample is bright (brighter than $L^{\ast}$) among LBGs at $z\sim5$. More observations are required to establish spectroscopic nature of LBGs at $z\sim5$.Comment: 16 pages, 3 figures, accepted by Ap

CO(J=6-5) Observations of the Quasar SDSS1044-0125 at z = 5.8

We present a result of the quasar CO(J=6-5) observations of SDSSp J104433.04-012502.2 at z = 5.8. Ten-days observations with the Nobeyama Millimeter Array yielded an rms noise level of ~ 2.1 mJy/beam in a frequency range from 101.28 GHz to 101.99 GHz at a velocity resolution of 120 km/s. No significant clear emission line was detected in the observed field and frequency range. Three sigma upper limit on the CO(J=6-5) luminosity of the object is 2.8 x 10^10 K km/s pc^2, corresponding to a molecular gas mass of 1.2 x 10^11 Solar Mass, if a conversion factor of 4.5 Solar Mass /(K km/s pc^2) is adopted. The obtained upper limit on CO luminosity is slightly smaller than those observed in quasars at z=4-5 toward which CO emissions are detected.Comment: 4 pages, 3 figures, LaTeX2e, to appear in Publication of Astronomical Society of Japan (PASJ), Postscript file available at ftp://ftp.kusastro.kyoto-u.ac.jp/pub/iwata/preprint/sdss1044/sdss.ps.g

Photoabsorption spectra in the continuum of molecules and atomic clusters

We present linear response theories in the continuum capable of describing photoionization spectra and dynamic polarizabilities of finite systems with no spatial symmetry. Our formulations are based on the time-dependent local density approximation with uniform grid representation in the three-dimensional Cartesian coordinate. Effects of the continuum are taken into account either with a Green's function method or with a complex absorbing potential in a real-time method. The two methods are applied to a negatively charged cluster in the spherical jellium model and to some small molecules (silane, acetylene and ethylene).Comment: 13 pages, 9 figure

Star Formation at the Twilight of the Dark Ages: Which Stars Reionized the Universe?

We calculate the global star formation rate density (SFRD) from z ~ 30-3 using a semi-analytic model incorporating the hierarchical assembly of dark matter halos, gas cooling via atomic hydrogen, star formation, supernova feedback, and suppression of gas collapse in small halos due to the presence of a photoionizing background. We compare the results with the predictions of simpler models based on the rate of dark matter halo growth and a fixed ratio of stellar-to-dark mass, and with observational constraints on the SFRD at 3 < z < 6. We also estimate the star formation rate due to very massive, metal-free Pop III stars using a simple model based on the halo formation rate, calibrated against detailed hydrodynamic simulations of Pop III star formation. We find that the total production rate of hydrogen-ionizing photons during the probable epoch of reionization (15 < z < 20) is approximately equally divided between Pop II and Pop III stars, and that if reionization is late (less than about 15, close to the lower limit of the range allowed by the WMAP results), then Pop II stars alone may be able to reionize the Universe.Comment: submitted to ApJ

Nonadiabatic generation of coherent phonons

The time-dependent density functional theory (TDDFT) is the leading computationally feasible theory to treat excitations by strong electromagnetic fields. Here the theory is applied to coherent optical phonon generation produced by intense laser pulses. We examine the process in the crystalline semimetal antimony (Sb), where nonadiabatic coupling is very important. This material is of particular interest because it exhibits strong phonon coupling and optical phonons of different symmetries can be observed. The TDDFT is able to account for a number of qualitative features of the observed coherent phonons, despite its unsatisfactory performance on reproducing the observed dielectric functions of Sb. A simple dielectric model for nonadiabatic coherent phonon generation is also examined and compared with the TDDFT calculations.Comment: 19 pages, 11 figures. This is prepared for a special issue of Journal of Chemical Physics on the topic of nonadiabatic processe