Guillermo F. Hägele

Complex gas kinematics in compact, rapidly assembling star-forming galaxies

Deep, high-resolution spectroscopic observations have been obtained for six compact, strongly star-forming galaxies at redshift z ~ 0.1-0.3, most of them also known as green peas. Remarkably, these galaxies show complex emission-line profiles in the spectral region including H?, [N?II]???6548, 6584, and [S?II]???6717, 6731, consisting of the superposition of different kinematical components on a spatial extent of few kiloparsecs: a very broad line emission underlying more than one narrower component. For at least two of the observed galaxies some of these multiple components are resolved spatially in their two-dimensional spectra, whereas for another one a faint detached H? blob lacking stellar continuum is detected at the same recessional velocity ~7?kpc away from the galaxy. The individual narrower H? components show high intrinsic velocity dispersion (? ~ 30-80?km?s?1), suggesting together with unsharped masking Hubble Space Telescope images that star formation proceeds in an ensemble of several compact and turbulent clumps, with relative velocities of up to ~500?km?s?1. The broad underlying H? components indicate in all cases large expansion velocities (full width zero intensity ?1000?km?s?1) and very high luminosities (up to ~1042 erg s?1), probably showing the imprint of energetic outflows from supernovae. These intriguing results underline the importance of green peas for studying the assembly of low-mass galaxies near and far.

Interaction effects on galaxy pairs with Gemini/GMOS- I : electron density

We present an observational study about the impacts of the interactions in the electron density of ion{H}{ii} regions located in 7 systems of interacting galaxies. The data consist of long-slit spectra in the range 4400-7300 A, obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS). The electron density was determined using the ratio of emission lines [SII]6716/6731. Our results indicate that the electron density estimates obtained of HII regions from our sample of interacting galaxies are systematically higher than those derived for isolated galaxies. The mean electron density values of interacting galaxies are in the range of

Interaction effects on galaxy pairs with Gemini/GMOS - II: oxygen abundance gradients

N_{rm e}=24-532

Metallicity evolution of AGNs from UV emission lines based on a new index

,

Optical and mid-infrared neon abundance determinations in star-forming regions

rm cm^{-3}

G287.84—0.82: an infrared star cluster in the Carina nebula

, while those obtained for isolated galaxies are in the range of

Sulphur abundance determinations in star-forming regions – I. Ionization correction factor

N_{rm e}=40-137: rm cm^{-3}

On the central abundances of active galactic nuclei and star-forming galaxies

. Comparing the observed emission lines with predictions of photoionization models, we verified that almost all the ion{H}{ii} regions of the galaxies AM,1054A, AM,2058B, and AM,2306B, have emission lines excited by shock gas. For the remaining galaxies, only few HII regions has emission lines excited by shocks, such as in AM,2322B (1 point), and AM,2322A (4 points). No correlation is obtained between the presence of shocks and electron densities. Indeed, the highest electron density values found in our sample do not belong to the objects with gas shock excitation. We emphasize the importance of considering theses quantities especially when the metallicity is derived for these types of systems.

High-velocity blueshifted Fe ii absorption in the dwarf star-forming galaxy PHL 293B: evidence for a wind driven supershell?

In this paper we derived oxygen abundance gradients from HII regions located in eleven galaxies in eight systems of close pairs. Long-slit spectra in the range 4400-7300A were obtained with the Gemini Multi-Object Spec- trograph at Gemini South (GMOS). Spatial profiles of oxygen abundance in the gaseous phase along galaxy disks were obtained using calibrations based on strong emission-lines (N2 and O3N2). We found oxygen gradients signifi- cantly flatter for all the studied galaxies than those in typical isolated spiral galaxies. Four objects in our sample, AM1219A, AM1256B, AM 2030A and AM2030B, show a clear break in the oxygen abundance at galactocentric radius R/R25 between 0.2 and 0.5. For AM1219A and AM1256B we found negative slopes for the inner gradients, and for AM2030B we found a positive one. In all these three cases they show a flatter behaviour to the outskirts of the galaxies. For AM2030A, we found a positive-slope outer gradient while the inner one is almost compatible with a flat behaviour. A decrease of star forma- tion efficiency in the zone that corresponds to the oxygen abundance gradient break for AM1219A and AM2030B was found. For the former, a minimum in the estimated metallicities was found very close to the break zone that could be associated with a corotation radius. On the other hand, AM1256B and AM2030A, present a SFR maximum but not an extreme oxygen abundance value. All the four interacting systems that show oxygen gradient breakes the extreme SFR values are located very close to break zones. Hii regions lo- cated in close pairs of galaxies follow the same relation between the ionization parameter and the oxygen abundance as those regions in isolated galaxies.

Nature and chemical abundances of a sample of Lyman-α emitter objects at high redshift

We analyzed the evolution of the metallicity of the gas with the redshift for a sample of AGNs in a very wide redshift range (0<z<4) using ultraviolet emission-lines from the narrow-line regions (NLRs) and photoionization models. The new index C43=log(CIV+CIII])/HeII is suggested as a metallicity indicator for AGNs. Based on this indicator, we confirmed the no metallicity evolution of NLRs with the redshift pointed out by previous works. We found that metallicity of AGNs shows similar evolution than the one predicted by cosmic semi-analytic models of galaxy formation set within the Cold Dark Matter merging hierarchy (for z < 3). Our results predict a mean metallicity for local objects in agreement with the solar value (12+log(O/H)=8.69). This value is about the same that the maximum oxygen abundance value derived for the central parts of local spiral galaxies. Very low metallicity log(Z/Z_{odot})~ -0.8 for some objects in the range 1.5 < z <3 is derived.