High-resolution [C II] imaging of HDF850.1 reveals a merging galaxy at z=5.185

New high-resolution maps with the IRAM Interferometer of the redshifted [C II] 158 micron line and the 0.98mm dust continuum of HDF850.1 at z = 5.185 show the source to have a blueshifted northern component and a redshifted southern component, with a projected separation of 0.3 arcsec, or 2 kpc. We interpret these components as primordial galaxies that are merging to form a larger galaxy. We think it is the resulting merger-driven starburst that makes HDF850.1 an ultraluminous infrared galaxy, with an L(IR) of 1E13 Lsun. The observed line and continuum brightness temperatures and the constant line-to-continuum ratio across the source imply (1) high [C II] line optical depth, (2) a [C II] excitation temperature of the same order as the dust temperature, and (3) dust continuum emission that is nearly optically thick at 158 microns. These conclusions for HDF850.1 probably also apply to other high-redshift submillimeter galaxies and quasar hosts in which the [C II] 158 micron line has been detected, as indicated by their roughly constant [C II]-to-158 micron continuum ratios, in sharp contrast to the large dispersion in their [C II]-to-FIR luminosity ratios. In brightness temperature units, the [C II] line luminosity is about the same as the predicted CO(1-0) luminosity, implying that the [C II] line can also be used to estimate the molecular gas mass, with the same assumptions as for CO.Comment: Accepted by Astronomy and Astrophysic

Extraordinary nonlinear plasmonics in graphene nanoislands

Nonlinear optical processes rely on the intrinsically weak interactions between photons enabled by their coupling with matter. Unfortunately, many applications in nonlinear optics are severely hindered by the small response of conventional materials. Metallic nanostructures partially alleviate this situation, as the large light enhancement associated with their localized plasmons amplifies their nonlinear response to record high levels. Graphene hosts long-lived, electrically tunable plasmons that also interact strongly with light. Here we show that the nonlinear polarizabilities of graphene nanoislands can be electrically tuned to surpass by several orders of magnitude those of metal nanoparticles of similar size. This extraordinary behavior extends over the visible and near-infrared for islands consisting of hundreds of carbon atoms doped with moderate carrier densities. Our quantum-mechanical simulations of the plasmon-enhanced optical response of nanographene reveal this material as an ideal platform for the development of electrically tunable nonlinear optical nanodevices.Comment: 16 pages, 12 figures, 54 reference

Studying the small scale ISM structure with supernovae

AIMS. In this work we explore the possibility of using the fast expansion of a Type Ia supernova photosphere to detect extra-galactic ISM column density variations on spatial scales of ~100 AU on time scales of a few months. METHODS. We constructed a simple model which describes the expansion of the photodisk and the effects of a patchy interstellar cloud on the observed equivalent width of Na I D lines. Using this model we derived the behavior of the equivalent width as a function of time, spatial scale and amplitude of the column density fluctuations. RESULTS. The calculations show that isolated, small (<100 AU) clouds with Na I column densities exceeding a few 10^11 cm^-2 would be easily detected. In contrast, the effects of a more realistic, patchy ISM become measurable in a fraction of cases, and for peak-to-peak variations larger than ~10^12 cm^-2 on a scale of 1000 AU. CONCLUSIONS. The proposed technique provides a unique way to probe the extra-galactic small scale structure, which is out of reach for any of the methods used so far. The same tool can also be applied to study the sub-AU Galactic ISM structure.Comment: 6 pages, 3 figures. Accepted for publication in Astronomy & Astrophysic

TEACHING STATISTICAL METHODS TO GRADUATE STUDENTS IN COLLEGES OF AGRICULTURE

One method of judging the effectiveness of the teaching of statistical methods is to rate the quality of their use in the research journals of the agricultural sciences. A conclusion that improvement is possible is easily supported by such a review. Basic concepts such as the meaning of replication, the definition of an experimental unit and the nature of experimental error are misunderstood, and this leads to faulty analyses and incorrect conclusions. Changes in teaching that would improve the product are not specified easily because research on the topic is difficult. Perhaps more emphasis on the basic concepts of experimental science could lead to more complete understanding of the nature of statistical thinking and, consequently, more effective and correct use of the methods available

New method for critical failure prediction of complex systems

Rigorous analytical technique, called criticality determination methodology /or CD technique/ determines the probability that a given complex system will successfully achieve stated objectives. The CD technique identifies critical elements of the system by a failure mode and effects analysis