High resolution spectroscopy of H II Galaxies: Structure and Supersonic line widths

We present high resolution echelle spectroscopy of a sample of H II galaxies. In all galaxies we identify different H(alpha) emitting knots along the slit crossing the nucleus. All of these have been isolated and separately analyzed through luminosity and size vs diagnosis plots. We find that in all cases, for a particular galaxy, the bulk of emission comes from their main knot and therefore, at least for the compact class galaxies we are dealing with, luminosity and sigma values measured using single aperture observations would provide similar results to what is obtained with spatially resolved spectroscopy. In the size vs plots as expected there is a shift in the correlations depending on whether we are including all emission in a single point or we split it in its different emitting knots. The problem of a proper determination of the size of the emitting region so that it can be used to determine the mass of the system remains open. From the data set gathered, using the highest surface brightness points as recently proposed by Fuentes-Masip et al. (2000), the best luminosity vs correlation turns out to be consistent with a Virial model.Comment: 14 pages, 4 figures, ApJ accepted. Also available from http://www.daf.on.br/~etelles/papers/wht.ps.g

Essay VIII: a key work in the piano output of Christopher Bochmann

Christopher Bochmann's pianistic language is based on a fairly conventional instrumental technique, inherited from the 19th century pianistic tradition, yet encompassing characteristic features developed by authors associated with the 2nd Viennese School and post-serialism, as well as significant experiences in the fields of free forms and aleatoric music. The permeability to a neoclassical sensibility, probably stimulated by contact with Nadia Boulanger in the formative years, has remained over time and manifests itself from time to time, both in the use of techniques, genres and forms of the past, but also, more comprehensively, in a constant search for balance and proportionality, across all of Bochmann’s works. From 1991, the year he composed Essay VIII, for solo piano, Bochmann inaugurated his maturity phase, based on what he calls a “unified technique”. The significant consistency of his instrumental language from then on results, to a large extent, from the synthesis of previously explored elements that Essay VIII operates, as I intend to demonstrate throughout this essay. Furthermore, we shall see how specific traits, not always particularly idiomatic, of Bochmann’s pianistic idiom enhance the aural understanding of the compositional principles that structure the work in analysis, and how a successful performance of the work depends largely on the understanding and highlighting, through specific performance practices, of the composer’s choices

The Local Environment of HII Galaxies

We address the question of whether violent star formation in HII galaxies is induced by low mass companions by describing statistically their local environment as estimated by the correlation function. We argue that even if low mass companions were mainly intergalactic HI clouds, their optical counterparts should be detectable at faint limits of the Automatic Plate Measuring Machine scans. We then cross-correlate a large sample of HII galaxies with the APM faint field galaxy catalogue. The preliminary results are all consistent with HII galaxies being a randomly selected sample of normal faint field galaxy with no extra clustering. This suggests that at least in these dwarf starburst galaxies star formation is not triggered by tidal interactions and may have a different origin.Comment: 4 pages, 2 Postscript figures, uses moriond.sty. To appear in ``Dwarf Galaxies and Cosmology'', Eds. T.X. Thuan, C. Balkowski, V. Cayette, J. Tran Than Van, Editions Frontieres (Gyf-sur-Yvette, France

The environment of HII galaxies

Recent morphological studies (Telles \& Terlevich 1994) of HII galaxies, i.e. dwarf galaxies dominated by a very luminous starburst, have indicated that luminous HII galaxies tend to show distorted morphology suggestive of tidal interactions triggering the present starburst while low luminosity HII galaxies tend to be instead symmetric and regular. To check the tidal origin of the starburst in HII galaxies, we have searched for companions in the neighbourhood of a sample of 51 HII galaxies. We found that only 12 HII galaxies have a neighbour within a projected distance of 1 Mpc and 250 \kmsec~ in velocity difference, and of these 12, only 4 have a luminous (M$_B <$ --19) neighbour. Surprisingly, isolated HII galaxies tend to be of high luminosity and disturbed morphology while HII galaxies with neighbours tend to be low luminosity regular HII galaxies. Furthermore, the metal abundance and the equivalent width of the emission lines in HII galaxies do not depend on the presence of a companion. These results are opposed to simple expectations if interaction with a bright companion is the main mechanism triggering the starbursts. We have also found a loose group of HII galaxies with no luminous companion. For this, there is the additional difficulty of understanding how these starbursts are synchronized on time scales of less than $10^7$ yrs in systems separated by $\sim$ 1-2 Mpc.Comment: 7 pages, uuencoded, compressed, postscript file. (three figures included). Also available via anonymous ftp from ftp://cast0.ast.cam.ac.uk/pub/etelles/environ.ps.

Third Generation Disadvantage among Mexican Americans

Among Mexican Americans, generational differences in education do not fit with assimilation theory’s predictions of significant improvement from the second to third generation; instead, education for third generation remains similar to the second generation and falls behind that of non-Hispanic whites. Scholars have not examined this educational gap for recent cohorts, nor have they considered a wide range of economic outcomes by generation. Using a nationally representative sample of young adults from the National Educational Longitudinal Survey, we examine various educational and economic outcomes among second- and third-generation Mexican Americans and compare it to whites and blacks. We find that third-generation Mexican Americans have similar outcomes to the second generation and lower education and economic levels than whites and blacks, even when controlling for key factors. Our findings reveal limitations to assimilation theory and suggest that the persistent low status of third-generation Mexican Americans may be largely due to their racialization. These findings coupled with prior research on Mexican Americans point to a consistent pattern of third generation disadvantage, which stands in contrast to second generation advantage

The Internal Kinematics of the HII Galaxy II Zw 40

We present a study of the kinematic properties of the ionized gas in the dominant giant HII region of the well known HII galaxy: II Zw 40. High spatial and spectral resolution spectroscopy has been obtained using IFU mode on the GMOS instrument at Gemini-North telescope. We have used a set of kinematics diagnostic diagrams, such as the intensity vs. velocity dispersion intensity vs. radial velocity, for global and individual analysis in sub-regions of the nebula. We aim to separate the main line broadening mechanisms responsible for producing a smooth supersonic integrated line profile for the giant HII region. The brightest central region (R ~ 50 pc) is responsible for sigma derived from a single fit to the integrated line profile. The dominant action of gravity, and possibly unresolved winds of young (<10 Myr) massive stars, in this small region should be responsible for the characteristic Halpha velocity profile of the starburst region as a whole. Our observations show that the complex structure of the interstellar medium of this galactic scale star-forming region is very similar to that of nearby extragalactic giant HII regions in the Local Group galaxies.Comment: 40 pages, 13 figures. Accepted for publication in The Astrophysical Journa

How old are the HII Galaxies?

Using a novel approach we have reanalized the question of whether the extreme star forming galaxies known as HII galaxies are truly young or rejuvenated old systems. We first present a method of inversion that applies to any monotonic function of time describing the evolution of independent events. We show that, apart from a normalization constant, the ``true'' time dependence can be recovered from the inversion of its probability density function. We applied the inversion method to the observed equivalent width of Hbeta (EW(Hbeta)) distribution for objects in the Terlevich and collaborators Spectrophotometric Catalogue of HII galaxies and found that their global history of star formation behaves much closer to the expectations of a continuos star formation model than to an instantaneous one. On the other hand, when the inversion method is applied to samples within a restricted metallicity range we find that their history of star formation behaves much closer to what the instantaneous model predicts. Our main conclusion is that, globally, the evolution of HII galaxies seems consistent with a succession of short starbursts separated by quiescent periods and that, while the emission lines trace the properties of the present burst, the underlying stellar continuum traces the whole star formation history of the galaxy. Thus, observables like the EW(Hbeta) that combine an emission line flux, i.e. a parameter pertaining to the present burst, with the continuum flux, i.e. a parameter that traces the whole history of star formation, should not be used alone to characterize the present burst.Comment: Accepted for publication in MNRA