Spectro-Morphology of Galaxies

We present a quantitative method to classify galaxies, based on multi-wavelength data and elaborated from the properties of nearby galaxies. Our objective is to define an evolutionary method that can be used for low and high redshift objects. We estimate the concentration of light (C) at the galaxy center and the 180 degree-rotational asymmetry (A), computed at several wavelengths, from ultraviolet (UV) to I-band. The variation of the indices of concentration and asymmetry with the wavelength reflects the proportion and the distribution of young and old stellar populations in galaxies. In general C is found to decrease from optical to UV, and A is found to increase from optical to UV: the patchy appearance of galaxies in UV with no bulge is often very different from their counterpart at optical wavelengths, with prominent bulges and more regular disks. The variation of C and A with the wavelength is quantified. By this way, we are able to distinguish five types of galaxies that we call spectro-morphological types: compact, ringed, spiral, irregular and central-starburst galaxies, which can be differentiated by the repartition of their stellar populations. We discuss in detail the morphology of galaxies of the sample, and describe the morphological characteristics of each spectro-morphological type. We apply spectro-morphology to three objects at a redshift z=1 in the Hubble Deep Field North, that gives encouraging results for applications to large samples of high-redshift galaxies. This method of morphological classification could be used to study the evolution of the morphology with the redshift and is expected to bring observational constraints on scenarios of galaxy evolution.Comment: Accepted for publication in Astronomy & Astrophysic

The "Twin Jet" Planetary Nebula M2-9

We present a model for the structure, temporal behavior, and evolutionary status of the bipolar nebula M2-9. According to this model the system consists of an AGB or post-AGB star and a hot white dwarf companion, with an orbital period of about 120 years. The white dwarf has undergone a symbiotic nova eruption about 1200 years ago, followed by a supersoft x-ray source phase. The positional shift of the bright knots in the inner nebular lobes is explained in terms of a revolving ionizing source. We show that the interaction between the slow, AGB star's wind, and a collimated fast wind from the white dwarf clears a path for the ionizing radiation in one direction, while the radiation is attenuated in others. This results in the mirror-symmetric (as opposed to the more common point-symmetric) shift in the knots. We show that M2-9 provides an important evolutionary link among planetary nebulae with binary central stars, symbiotic systems, and supersoft x-ray sources.Comment: 13 pages + 2 figures. Submitted to Ap

HST Imaging of Globular Clusters in the Edge--on Spiral Galaxies NGC 4565 and NGC 5907

We present a study of the globular cluster systems of two edge-on spiral galaxies, NGC4565 and NGC5907, from WFPC2 images in the F450W and F814W filters. The globular cluster systems of both galaxies appear to be similar to the Galactic globular cluster system. In particular, we derive total numbers of globular clusters of N_{GC}(4565)= 204+/-38 {+87}{-53} and N_{GC}(5907)=170+/-41 {+47}{-72} (where the first are statistical, the second potential systematic errors) for NGC4565 and NGC5907, respectively. This determination is based on a comparison to the Milky Way system, for which we adopt a total number of globular clusters of 180+/-20. The specific frequency of both galaxies is S_N~0.6: indistinguishable from the value for the Milky Way. The similarity in the globular cluster systems of the two galaxies is noteworthy since they have significantly different thick disks and bulge-to-disk ratios. This would suggest that these two components do not play a major role in the building up of a globular cluster system around late-type galaxies.Comment: Accepted for publication in the Astronomical Journal, 17 pages incl 5 figures, AAS style two columns. Also available at http://www.eso.org/~mkissler, Color version of figure 1 only available at http://www.eso.org/~mkissler (B/W version included

Ideally embedded space-times

Due to the growing interest in embeddings of space-time in higher-dimensional spaces we consider a specific type of embedding. After proving an inequality between intrinsically defined curvature invariants and the squared mean curvature, we extend the notion of ideal embeddings from Riemannian geometry to the indefinite case. Ideal embeddings are such that the embedded manifold receives the least amount of tension from the surrounding space. Then it is shown that the de Sitter spaces, a Robertson-Walker space-time and some anisotropic perfect fluid metrics can be ideally embedded in a five-dimensional pseudo-Euclidean space.Comment: layout changed and typos corrected; uses revtex

Vacuum spacetimes of embedding class two

Doubt is cast on the much quoted results of Yakupov that the torsion vector in embedding class two vacuum space-times is necessarily a gradient vector and that class 2 vacua of Petrov type III do not exist. The rst result is equivalent to the fact that the two second fundamental forms associated with the embedding necessarily commute and has been assumed in most later investigations of class 2 vacuum space-times. Yakupov stated the result without proof, but hinted that it followed purely algebraically from his identity: Rijkl Ckl = 0 where Cij is the commutator of the two second fundamental forms of the embedding.From Yakupov's identity, it is shown that the only class two vacua with non-zero commutator Cij must necessarily be of Petrov type III or N. Several examples are presented of non-commuting second fundamental forms that satisfy Yakupovs identity and the vacuum condition following from the Gauss equation; both Petrov type N and type III examples occur. Thus it appears unlikely that his results could follow purely algebraically. The results obtained so far do not constitute denite counter-examples to Yakupov's results as the non-commuting examples could turn out to be incompatible with the Codazzi and Ricci embedding equations. This question is currently being investigated

Teaching argumentative synthesis writing through deliberative dialogues: instructional practices in secondary education

Dialogical argumentation practice contributes positively to argumentative writing skills. Specifically, deliberative dialogues are effective in promoting argument and counterargument integration in students' essays. However, the potential of dialogic activities may be increased if they are combined with instructional practices. The primary objective of this research is to compare the impact of four intervention programs, aimed at improving argumentative synthesis writing from conflicting sources. The four programs resulted from the combination of two instructional components (Explicit Instruction through video modelling—EI, or a Procedural Guideline—G), while Deliberative Dialogues—DD—were a constant element. We conducted a pre-post quasi-experimental study in which 186 Spanish third grade secondary school students (aged 14–15) participated. We evaluated the quality of the syntheses by examining the level of argumentative coverage (the total number of arguments included in the synthesis) and the level of integration (the type and frequency of the argumentative strategies used in the syntheses). The results showed that the effectiveness of the instructional methods varies according to the synthesis quality indicator. Explicit instruction, in combination with deliberative dialogues, was especially helpful in improving the level of integration of syntheses. The procedural guideline, in combination with deliberative dialogues, contributed significantly to the coverage of arguments. The combination of these two elements did not favor the writing of synthesis as expected, probably due to the conditions in which the intervention was carried out. The findings of this study revealed that the coverage of arguments and integration processes are of different nature, follow different learning paths and require different instructional processes.pre-print875 K

Light Element Evolution and Cosmic Ray Energetics

Using cosmic-ray energetics as a discriminator, we investigate evolutionary models of LiBeB. We employ a Monte Carlo code which incorporates the delayed mixing into the ISM both of the synthesized Fe, due to its incorporation into high velocity dust grains, and of the cosmic-ray produced LiBeB, due to the transport of the cosmic rays. We normalize the LiBeB production to the integral energy imparted to cosmic rays per supernova. Models in which the cosmic rays are accelerated mainly out of the average ISM significantly under predict the measured Be abundance of the early Galaxy, the increase in [O/Fe] with decreasing [Fe/H] notwithstanding. We suggest that this increase could be due to the delayed mixing of the Fe. But, if the cosmic-ray metals are accelerated out of supernova ejecta enriched superbubbles, the measured Be abundances are consistent with a cosmic-ray acceleration efficiency that is in very good agreement with the current epoch data. We also find that neither the above cosmic-ray origin models nor a model employing low energy cosmic rays originating from the supernovae of only very massive progenitors can account for the $^6$Li data at values of [Fe/H] below $-$2.Comment: latex 19 pages, 2 tables, 10 eps figures, uses aastex.cls natbib.sty Submitted to the Astrophysical Journa

Constraints from 26^{26}Al Measurements on the Galaxy's Recent Global Star Formation Rate and Core Collapse Supernovae Rate

Gamma-rays from the decay of $^{26}$Al offer a stringent constraint on the Galaxy's global star formation rate over the past million years, supplementing other methods for quantifying the recent Galactic star formation rate, such as equivalent widths of H$\alpha$ emission. Advantages and disadvantages of using $^{26}$Al gamma-ray measurements as a tracer of the massive star formation rate are analyzed. Estimates of the Galactic $^{26}$Al mass derived from COMPTEL measurements are coupled with a simple, analytical model of the $^{26}$Al injection rate from massive stars and restrict the Galaxy's recent star formation rate to \hbox{5 $\pm$ 4 M\sun yr$^{-1}$}. In addition, we show that the derived $^{26}$Al mass implies a present day \hbox{Type II + Ib} supernovae rate of 3.4 $\pm$ 2.8 per century, which seems consistent with other independent estimates of the Galactic core collapse supernova rate. If some independent measure of the massive star initial mass function or star formation rate or \hbox{Type II + Ib} supernovae rate were to become available (perhaps through estimates of the Galactic $^{60}$Fe mass), then a convenient way to restrain, or possibly determine, the other parameters is presented.Comment: 11 pages including 1 figure, ApJ in pres