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

On the compact HII galaxy UM 408 as seen by GMOS-IFU: Physical conditions

We present Integral Field Unit GMOS-IFU data of the compact HII galaxy UM408, obtained at Gemini South telescope, in order to derive the spatial distribution of emission lines and line ratios, kinematics, plasma parameters, and oxygen abundances as well the integrated properties over an area of 3"x4".4(~750x1100 pc) located in the central part of the galaxy. The starburst in this area is resolved into two giant regions of ~375 and 250pc diameter, respectively. The ages of these two regions, estimated using Hb equivalent widths, suggest that they are coeval events of ~5Myr with stellar masses of ~10^4M_o. We have also used [OIII]/Hb and [SII]/Ha ratio maps to explore the excitation mechanisms in this galaxy. The Ha emission line was used to measure the radial velocity and velocity dispersion. We derived an integrated oxygen abundance of 12+log(O/H)=7.87 summing over all spaxels in our field of view. An average value of 12+log(O/H)=7.77 and a difference of D(O/H)=0.47 between the minimum and maximum values (7.58+-0.06-8.05+-0.04) were found, considering all data points where the oxygen abundance was measured. The spatial distribution of oxygen abundance does not show any significant gradient across the galaxy. On the other hand, the bulk of data points are lying in a region of +-2sigma dispersion (with sigma=0.1 dex) around the average value, confirming that this compact HII galaxy as other previously studied dwarf irregular galaxies is chemically homogeneous. Therefore, the new metals processed and injected by the current star formation episode are possibly not observed and reside in the hot gas phase, whereas the metals from previous events are well mixed and homogeneously distributed through the whole extent of the galaxy.Comment: 30 pages, 10 figures. AJ accepte

Multiracial versus Collective Black Categories

Current census debates in Brazil surrounding Brazilian race categories center on two contrasting proposals: the adoption of the multiracial moreno term vs. the use of the collective black classification negro. Those proposing the former base their argument on the right to self-classify according to one’s own sense of identity. Proponents of the negro category contend that it would be most efficient for redressing racial discrimination. We examine the meaning and saliency of these categories and explore the possible consequences of their adoption. Using national survey data, we demonstrate how education, age, color, sex and local racial composition structure the choices of moreno and negro over official census terms. Findings include a negative correlation between education and the choice of moreno, while the opposite is true for negro. In addition, an age effect on both categories suggests a popular shift in racial labeling away from official census terms. We note that similar issues structure current census debates in the USA

Stellar Populations Found in the Central kpc of Four Luminous Compact Blue Galaxies at Intermediate Redshift

We investigate the star formation history of the central regions of four Luminous Compact Blue Galaxies (LCBGs). LCBGs are blue (B-V<0.6), compact (MU_B<21.5 mag arcsec^-2) galaxies with absolute magnitudes M_B brighter than -17.5. The LCBGs analyzed here are located at 0.436<z<0.525. They are among the most luminous (M_B < -20.5), blue (B-V < 0.4) and high surface brightness (MU_B < 19.0 mag arcsec^-2) of this population. The observational data used were obtained with the HST/STIS spectrograph, the HST/WF/PC-2 camera and the HST/NICMOS first camera. We find evidence for multiple stellar populations. One of them is identified as the ionizing population, and the other one corresponds to the underlying stellar generation. The estimated masses of the inferred populations are compatible with the dynamical masses, which are typically 2--10x 10^9 M_sun. Our models also indicate that the first episodes of star formation the presented LCBGs underwent happened between 5 and 7 Gyr ago. We compare the stellar populations found in LCBGs with the stellar populations present in bright, local HII galaxies, nearby spheroidal systems and Blue Compact Dwarf Galaxies. It turns out that the underlying stellar populations of LCBGs are similar yet bluer to those of local HII galaxies. It is also the case that the passive color evolution of the LCBGs could convert them into local Spheroidal galaxies if no further episode of star formation takes place. Our results help to impose constraints on evolutionary scenarios for the population of LCBGs found commonly at intermediate redshifts.Comment: 35 pages, 10 Figures. Accepted for publication in AJ. Compile with pdflatex. Contains png figure