Context. Extremely metal-poor (XMP) galaxies are chemically, and possibly dynamically, primordial objects in the local Universe.Aims. Our objective is to characterize the H i content of the XMP galaxies as a class, using as a reference the list of 140 known local XMPs compiled by Morales-Luis et al. (2011). Methods. We have observed 29 XMPs, which had not been observed before at 21 cm, using the Effelsberg radio telescope. This information was complemented with H i data published in literature for a further 53 XMPs. In addition, optical data from the literature provided morphologies, stellar masses, star-formation rates and metallicities. asymmetric (seven sources) or symmetric (one source) single-peak 21 cm line profiles. An asymmetry in the H i line profile is systematically accompanied by an asymmetry in the optical morphology. Typically, the g-band stellar mass-to-light ratios are ∼0.1, whereas the H i gas mass-to-light ratios may be up to two orders of magnitude larger. Moreover, H i gas-to-stellar mass ratios fall typically between 10 and 20, denoting that XMPs are extremely gas-rich. We find an anti-correlation between the H i gas mass-to-light ratio and the luminosity, whereby fainter XMPs are more gas-rich than brighter XMPs, suggesting that brighter sources have converted a larger fraction of their H i gas into stars. The dynamical masses inferred from the H i line widths imply that the stellar mass does not exceed 5% of the dynamical mass, while the H i mass constitutes between 20 and 60% of the dynamical mass. Furthermore, the dark matter mass fraction spans a wide range, but can account, in some cases, for over 65% of the dynamical mass. XMPs are found to be outliers of the mass -and luminosity -metallicity relation, whereby they lack metals for their estimated dynamical mass and luminosity, suggesting the presence of pristine gas. However, they generally follow the luminosity -and baryonic mass Tully-Fisher relation, indicating that the H i gas is partly virialized and contains some rotational support. 60% of the XMP sources show a small velocity offset (10-40 km s −1 ) between the H i gas and the stellar/nebular component, implying that, in these sources, the H i gas is not tightly coupled to the stars and ionized gas. The effective yields provided by oxygen are often larger than the standard theoretical yields, suggesting that the observed H i gas is relatively metal-free. 80% of the XMP sources present asymmetric optical morphology -60 XMPs show cometary structure, 11 show two bright star-forming knots and 18 show multiple star-forming regions. Star-formation rates are found to be similar to those typically found in BCDs. However, specific star-formation rates are high, with timescales to double their stellar mass, at the current rate, of typically less than 1 Gyr.Conclusions. XMP galaxies are among the most gas-rich objects in the local Universe. The observed H i component suggests kinematical disruption and hints at a primordial composition.

-2 -We present Integral Field Unit GMOS-IFU data of the compact HII galaxy UM 408, 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 ′′ ×4 ′′ .4 equivalent with ∼750 × 1100 pc located in the central part of the galaxy. The starburst in this area is resolved into two giant regions of about 1 ′′ .5 and 1 ′′ (∼375 and ∼250 pc) diameter, respectively and separated 1.5-2 ′′ (∼500 pc). The extinction distribution concentrate its highest values close but not coincident with the maxima of Hα emission around each one of the detected regions. This indicates that the dust has been displaced from the exciting clusters by the action of their stellar winds. The ages of these two regions, estimated using Hβ equivalent widths, suggest that they are coeval events of ∼5 Myr with stellar masses of ∼10 4 M ⊙ . We have also used [OIII]/Hβ and [SII]/Hα ratio maps to explore the excitation mechanisms in this galaxy. Comparing the data points with theoretical diagnostic models, we found that all of them are consistent with excitation by photoionization by massive stars. The Hα emission line was used to measure the radial velocity and velocity dispersion. The heliocentric radial velocity shows an apparent systemic motion where the east part of the galaxy is blueshifted, while the west part is redshifted, with a relative motion of ∼ 10 km s −1 . The velocity dispersion map shows supersonic values typical for extragalactic HII regions. Oxygen abundances were calculated from the [OIII]λλ4959,5007/[OIII]λ4363 ratios. 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 ∆(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 ±2σ dispersion (with σ=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.

We present a stellar population study of three H ii galaxies (Mrk 36, UM 408, and UM 461) based on the analysis of new ground-based high-resolution near-infrared J, H, and K p broadband and Brγ narrowband images obtained with Gemini/NIRI. We identify and determine the relative ages and masses of the elementary star clusters and/or star cluster complexes of the starburst regions in each of these galaxies by comparing the colors with evolutionary synthesis models that include the contribution of stellar continuum, nebular continuum, and emission lines. We found that the current star cluster formation efficiency in our sample of low-luminosity H ii galaxies is ∼10%. Therefore, most of the recent star formation is not in massive clusters. Our findings seem to indicate that the star formation mode in our sample of galaxies is clumpy, and that these complexes are formed by a few massive star clusters with masses 10 4 M . The age distribution of these star cluster complexes shows that the current burst started recently and likely simultaneously over short timescales in their host galaxies, triggered by some internal mechanism. Finally, the fraction of the total cluster mass with respect to the low surface brightness (or host galaxy) mass, considering our complete range in ages, is less than 1%.

Aims. Create a catalog of images of HII galaxies and their individual star-formation regions in order to study the distribution of the gas emission and their underlying stellar continuum. Methods. We have used Hβ narrow-band images of 43 selected HII galaxies obtained at ESO NTT 3.58 m telescope using the SUSI2 camera. Results. Surface photometric Hβ fluxes and equivalent widths for all objects and star-formation regions are presented in this catalog. A myriad of filamentary structure were found in the pure Hβ emission-line or continuum-subtracted images, probably attributed to expanding shells as a consequence of the star-formation activity. Our results indicate that the number of regions with high Hβ equivalent width or young regions increase with the instrumental resolution, showing that the instrumental resolution is a bias to determine the cluster ages. Therefore, we showed that some of the observed giant HII regions may have been formed by ensembles of unresolved star forming regions or candidates to host Super Star Clusters. Pure Hβ emission-line images, continuum contours and EW(Hβ) maps showing the morphology of the gaseous and stellar emission in HII galaxies and their individual star-formation regions were obtained. All calibrated continuum and Hβ emission line fluxes and the derived Hβ equivalent width images are available in fits format from http://www.on.br/astro/etelles/HIIgalaxies/Hbeta/.

Aims. Previous studies have found that the coefficients and intrinsic dispersions of both the Kormendy relation and the Fundamental Plane depend on the magnitude range within which the galaxies are contained. We study whether this type of behaviour is also present for the Faber-Jackson relation. Methods. We take a sample of early-type galaxies from the Sloan Digital Sky Survey (SDSS-DR7, ∼90 000 galaxies) spanning a range of approximately 7 mag in both g and r filters and analyse the behaviour of the Faber-Jackson relation parameters as functions of the magnitude range. We calculate the parameters in two ways: i) we consider the faintest (brightest) galaxies in each sample and we progressively increase the width of the magnitude interval by inclusion of the brighter (fainter) galaxies (increasing-magnitudeintervals); and ii) we consider narrow-magnitude intervals of the same width (ΔM = 1.0 mag) over the whole magnitude range available (narrow-magnitude-intervals). Results. Our main results are that: i) in both increasing and narrow-magnitude-intervals the Faber-Jackson relation parameters change systematically, ii) non-parametric tests show that the fluctuations in the values of the slope of the Faber-Jackson relation are not products of chance variations. Conclusions. We conclude that the values of the Faber-Jackson relation parameters depend on the width of the magnitude range and the luminosity of galaxies within the magnitude range. This dependence is caused, to a great extent by the selection effects and because the geometrical shape of the distribution of galaxies on the M − log(σ 0 ) plane depends on luminosity. We therefore emphasize that if the luminosity of galaxies or the width of the magnitude range or both are not taken into consideration when comparing the structural relations of galaxy samples for different wavelengths, environments, redshifts and luminosities, any differences found may be misinterpreted.

Using GMOS–IFU spectroscopic observations of the compact H ii/blue compact dwarf galaxies Tol 0104−388 and Tol 2146−391, we study the spatial distribution of emission lines, equivalent width EW(Hβ), extinction c(Hβ), ionization ratios ([O iii] λ5007/Hβ, [S ii] λλ6717, 6731/Hα and [N ii] λ6584/Hα), kinematics and the chemical pattern (O/H, N/H and N/O) of the warm interstellar medium in these galaxies. We also investigate a possible dependence of these properties on the I(He ii λ4686)/I(Hβ) ratio and find no significant correlation between these variables. In fact, the oxygen abundances appear to be uniform in the regions where the He ii λ4686 emission line was measured. It can be interpreted in the sense that these correlations are related to global properties of the galaxies and not with small patches of the interstellar medium. Although a possible weak N/H gradient is observed in Tol 2146−391, the available data suggest that the metals from previous star formation events are well mixed and homogeneously distributed through the optical extent of these galaxies. The spatial constancy of the N/O ratio might be attributed to efficient transport and mixing of metals by starburst‐driven supershells, powered by a plethora of unresolved star cluster in the inner part of the galaxies. This scenario agrees with the idea that most of the observed He ii λ4686 emission line is produced by radiative shocks, although other sources such as Wolf Rayet stars, high mass X‐ray Binaries and O stars cannot be excluded.

We present a detailed study of the kinematic, chemical and excitation properties of the giant Lyα emitting nebula and the giant H i absorber associated with the z = 2.92 radio galaxy MRC 0943-242, using spectroscopic observations from VLT/MUSE, VLT/X-SHOOTER and other instruments. Together, these data provide a wide range of restframe wavelength (765Å -6378Å at z = 2.92) and 2D spatial information. We find clear evidence for jet gas interactions affecting the kinematic properties of the nebula, with evidence for both outflows and inflows being induced by radio-mode feedback. We suggest that the regions of relatively lower ionization level, spatially correlated with the radio hotspots, may be due to localised compression of photoionized gas by the expanding radio source, thereby lowering the ionization parameter, or due to a contribution from shock-heating. We find that photoionization of super-solar metallicity gas (Z/Z = 2.1) by an AGN-like continuum (α=-1.0) at a moderate ionization parameter (U = 0.018) gives the best overall fit to the complete X-SHOOTER emission line spectrum. We identify a strong degeneracy between column density and Doppler parameter such that it is possible to obtain a reasonable fit to the H i absorption feature across the range log N(H i/cm −2 ) = 15.20 and 19.63, with the two best-fitting occurring near the extreme ends of this range. The extended H i absorber is blueshifted relative to the emission line gas, but shows a systematic decrease in blueshift towards larger radii, consistent with a large scale expanding shell.

Using VIMOS-IFU observations, we study the interstellar medium (ISM) of two star-forming dwarf galaxies, UM 461 and Mrk 600. Our aim was to search for the existence of metallicity inhomogeneities that might arise from infall of nearly pristine gas feeding ongoing localized star-formation. The IFU data allowed us to study the impact of external gas accretion on the chemical evolution as well as the ionised gas kinematics and morphologies of these galaxies. Both systems show signs of morphological distortions, including cometary-like morphologies. We analysed the spatial variation of 12 + log(O/H) abundances within both galaxies using the direct method (T e ), the widely applied HII-CHI-mistry code, as well as by employing different standard calibrations. For UM 461 our results show that the ISM is fairly well mixed, at large scales, however we find an off-centre and low-metallicity region with 12 + log(O/H) < 7.6 in the SW part of the brightest H ii region, using the direct method. This result is consistent with the recent infall of a low mass metal-poor dwarf or H i cloud into the region now exhibiting the lowest metallicity, which also displays localized perturbed neutral and ionized gas kinematics. Mrk 600 in contrast, appears to be chemically homogeneous on both large and small scales. The intrinsic differences in the spatially resolved properties of the ISM in our analysed galaxies are consistent with these systems being at different evolutionary stages.