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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

We employed observational spectroscopic data of star-forming regions compiled from the literature and photoionization models to analyse the neon ionic abundances obtained using both optical and mid-infrared emission-lines. Comparing Ne++/H+ ionic abundances from distinct methods, we found that, in average, the abundances obtained via IR emission-lines are higher than those obtained via optical lines by a factor of 4. Photoionization models with abundance variations along the radius of the hypothetical nebula provide a possible explanation for a large part of the difference between ionic abundances via optical and infrared emission-lines. Ionization Correction Factor (ICF) for the neon is obtained from direct determinations of ionic fractions using infrared emission-lines. A constant Ne/O ratio (logNe/O \approx -0.70) for a large range of metallicity, independently of the ICF used to compute the neon total abundance is derived., Comment: 17 pages, 14 figures, accepted by MNRAS

[Abbreviated] We review the results of high dispersion spectroscopy of 17 circumnuclear starforming regions (CNSFRs) in 3 nearby early spiral galaxies, NGC2903, NGC3310 and NGC3351. We find that single Gaussian fitting to the H$\beta$ and [OIII]5007A line profiles results in velocity dispersions around 32km/s and 52km/s, respectively, while the IR CaII triplet cross-correlation technique provides stellar velocity dispersion values close to 50km/s. Even though multiple kinematical components are present, the relation between gas velocity dispersion and Balmer emission line luminosity (L-sigma relation) reproduces the correlation for disk giant HII regions albeit with a larger scatter. The scatter in the L-sigma relation is considerably reduced when theoretical evolutionary corrections are applied suggesting that an age range is present in the sample of CNSFRs. To analyse the observed complex profiles, we performed multiple Gaussian component fits to the Hbeta and [OIII]?5007A lines obtaining optimal fits with two Gaussians of different width. These best fits indicate that the narrower component has average velocity dispersion close to 23km/s while the broader component shows average values in the range 50-60km/s for both lines, close to the observed stellar velocity dispersions. The fluxes of the broad and narrow Hbeta components are similar. This is not the case for [OIII]5007A for which the broad components have higher fluxes than the narrow ones, thus producing a clear segregation in their [OIII]/Hbeta ratios. We suggest a possible scenario for understanding the behaviour of CNSFRs in the L-sigma and sigma_gas-sigma_star diagrams involving an inner gaseous disk responsible for the narrow component of the emission lines., Comment: 14 pages, 10 figures, accepted by MNRAS

We present a detailed study of the physical properties of the nebular material in four star-forming knots of the blue compact dwarf galaxy Haro 15. Using long-slit and echelle spectroscopy obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperatures), ionic and total chemical abundances of several atoms, reddening and ionization structure, for the global flux and for the different kinematical components. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the $\eta$ and $\eta$' plots) in different regions of the galaxy. Applying the direct method or empirical relationships for abundance determination, we perform a comparative analysis between these regions. The similarities found in the ionization structure of the different kinematical components implies that the effective temperatures of the ionizing radiation fields are very similar in spite of some small differences in the ionization state of the different elements. Therefore the different gaseous kinematical components identified in each star forming knot are probably ionized by the same star cluster. However, the difference in the ionizing structure of the two knots with knot A showing a lower effective temperature than knot B, suggests a different evolutionary stage for them consistent with the presence of an older and more evolved stellar population in the first., Comment: 21 pages, 6 figures, 8 tables, accepted by MNRAS

We investigate the excitation mechanisms of near-infrared [Fe ii] and H2 emission lines observed in Active Galactic Nuclei (AGNs). We built a photoionization model grid considering a two-component continuum, one accounts for the Big Bump component peaking at 1Ryd and another represents the X-ray source that dominates the continuum emission at high energies. Photoionization models considering as ionizing source a spectral energy distribution obtained from photometric data of the Sy 2 Mrk 1066 taken from the literature were considered. Results of these models were compared with a large sample of observational long-slit and Integral field Unit (IFU) spectroscopy data of the nuclear region for a sample of active objects. We found that the correlation between the observational [Fe ii]{\lambda}1.2570 {\mu}m/Pa{\beta} vs. H2{\lambda}2.1218 {\mu}m/Br{\gamma} is well reproduced by our models as well as the relationships that involve the H2 emission line ratios observed in the spectroscopic data.We conclude that the heating by X-rays produced by active nuclei can be considered a common and very important mechanism of excitation of [Fe ii] and H2., Comment: 10 pages, 9 figures, accepted by MNRAS

We analyze the reliability of oxygen abundances and ionization parameters obtained from different diagnostic diagrams. For this, we compiled from the literature observational emission line intensities and oxygen abundance of 446 star-forming regions whose O/H abundance was determined by direct estimation of electron temperature. The abundances compiled were compared with the values calculated in this work using different diagnostic diagrams in combination with results from a grid of photoionization models. We found that the [\ion{O}{iii}]/[\ion{O}{ii}] vs. [\ion{N}{ii}]/[\ion{O}{ii}], [\ion{O}{iii}]/H$\beta$ vs. [\ion{N}{ii}]/[\ion{O}{ii}], and ([\ion{O}{iii}]/H$\beta$)/([\ion{N}{ii}]/H$\alpha$) vs. [\ion{S}{ii}]/[\ion{S}{iii}] diagnostic diagrams give O/H values close to the $T_{\rm e}$-method, with differences of about 0.04 dex and dispersion of about 0.3 dex. Similar results were obtained by detailed models but with a dispersion of 0.08 dex. The origin of the dispersion found in the use of diagnostic diagrams is probably due to differences between the real N/O-O/H relation of the sample and the one assumed in the models. This is confirmed by the use of detailed models that do not have a fixed N/O-O/H relation. We found no correlation between ionization parameter and the metallicity for the objects of our sample. We conclude that the combination of two line ratio predicted by photoionization models, one sensitive to the metallicity and another sensitive to the ionization parameter, which takes into account the physical conditions of star-forming regions, gives O/H estimates close to the values derived using direct detections of electron temperatures., Comment: 12 pages, 9 figures, accepted by MNRAS

We analyze high signal-to-noise spectrophotometric observations acquired simultaneously with TWIN, a double-arm spectrograph, from 3400 to 10400 \AA of three star-forming regions in the HII galaxy SDSS J165712.75+321141.4. We have measured four line temperatures: Te([OIII]), Te([SIII]), Te([OII]), and Te([SII]), with high precision, rms errors of order 2%, 5%, 6% and 6%, respectively, for the brightest region, and slightly worse for the other two. The temperature measurements allowed the direct derivation of ionic abundances of oxygen, sulphur, nitrogen, neon and argon. We have computed CLOUDY tailor-made models which reproduce the O2+ measured thermal and ionic structures within the errors in the three knots, with deviations of only 0.1 dex in the case of O+ and S2+ ionic abundances. In the case of the electron temperature and the ionic abundances of S+/H+, we find major discrepancies which could be consequence of the presence of colder diffuse gas. The star formation history derived using STARLIGHT shows a similar age distribution of the ionizing population among the three star-forming regions. This fact suggests a similar evolutionary history which is probably related to a process of interaction with a companion galaxy that triggered the star formation in the different regions almost at the same time. The hardness of the radiation field mapped through the use of the softness parameter $\eta$ is the same within the observational errors for all three regions, implying that the equivalent effective temperature of the radiation fields are very similar for all the studied regions of the galaxy, in spite of some small differences in the ionization state of different elements., Comment: 18 pages, 10 figures, accepted by MNRAS

We report sub-arcsecond scale radio continuum observations of a field of 35 by 22 arcmin centred in NGC3351 obtained with the Multi-Element Radio Linked Interferometer Network (MERLIN). We found 23 radio sources in this field, 6 of which are projected within the D$_{25}$ isophote of the galaxy, and 3 are located inside the central 100 arcsec in radius. Two of these three are significantly extended, while the third one is relatively compact. This one is the only source with a previously detected counterpart at other wavelengths and could constitute the radio counterpart of a young supernova remnant. The other two are probably related to jets from a background AGN. We are not able to detect individual supernovae or SNRs in the central region ($r<600$ pc) of the galaxy. This could imply that the ionising populations of the circumnuclear star-forming regions (CNSFRs) are too young (less than a few Myr) to host supernovae. Also the diffusion length of the relativistic electrons in the ISM associated with the SN from previous events of star formation seems to be larger than our maximum resolution of 50 pc in radius. Detecting the thermal bremsstrahlung emission from the circumnuclear HII regions probably requires deeper observations., Comment: 13 pages,5 figures, accepted for publication by MNRAS

We present a self-consistent study of the stellar populations and the ionized gas in a sample of 10 HII galaxies with, at least, four measured electron temperatures and a precise determination of ionic abundances following the "direct method". We fitted the spectral energy distribution of the galaxies using the program STARLIGHT in order to quantify the contribution of the underlying stellar population to EW(Hbeta), which amounts to about 10% for most of the objects. We then studied the Wolf-Rayet stellar populations detected in seven of the galaxies. The presence of these populations and the corrected EW(Hbeta) values indicate that the ionizing stellar populations were created following a continuous star formation episode of 10 Myr duration, hence WR stars may be present in all of objects even if they are not detected in some of them. The derived stellar features, the number of ionizing photons and the relative intensities of the strongest emission lines were used as input parameters to compute tailored models with the photoionization code CLOUDY. Our models are able to y reproduce their thermal and ionization structure as deduced from their collisionally excited emission lines and, hence, no abundance discrepancy factors are implied for this kind of objects. Only the electron temperature of S+ is overestimated by the models, pointing to the possible presence of outer shells of diffuse gas in these objects. This kind of geometrical effects can affect the determination of the equivalent effective temperature of the ionizing cluster using calibrators which depend on low-excitation emission lines., Comment: 20 pages, 12 figures, MNRAS (in press)

Gas and star velocity dispersions have been derived for eight circumnuclear star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC3310 using high resolution spectroscopy in the blue and far red. Stellar velocity dispersions have been obtained from the CaII triplet in the near-IR, using cross-correlation techniques, while gas velocity dispersions have been measured by Gaussian fits to the Hb 4861A and [OIII]5007A emission lines. The CNSFRs stellar velocity dispersions range from 31 to 73 km/s. These values, together with the sizes measured on archival HST images, yield upper limits to the dynamical masses for the individual star clusters between 1.8 and 7.1 x 10$^6$ M$_\odot$, for the whole CNSFR between 2 x 10$^7$ and 1.4 x 10$^8$ M$_\odot$, and 5.3 x 10$^7$ M$_\odot$ for the nucleus inside the inner 14.2 pc. The masses of the ionizing stellar population responsible for the HII region gaseous emission have been derived from their published Ha luminosities and are found to be between 8.7 x 10$^5$ and 2.1 x 10$^6$ M$_\odot$ for the star-forming regions, and 2.1 x 10$^5$ M$_\odot$ for the galaxy nucleus; they therefore constitute between 1 and 7 per cent of the total dynamical mass. The ionized gas kinematics is complex; two different kinematical components seem to be present as evidenced by different line widths and Doppler shifts., Comment: 24 pages, accepted by MNRAS

In this thesis we have identified two star formation sites for star formation in galaxies which differ widely in metal content. We conclude that `massive' star formation that occurs in a high density, high metallicity environment, like that encountered in circumnuclear star-forming regions, takes place in systems that comply to the definition of super stellar clusters and that are arranged in star forming complexes. These complexes have Halpha luminosities, and therefore masses of ionizing stars, that overlap at the lower end with those found in HII galaxies, which have a much lower metallicity. The fact that their ionization structure and the temperature of their ionizing radiation field are very similar, point to stellar clusters in these two environments which have the same equivalent effective temperature. This is contrary to what is expected from stellar evolution models which predict lower stellar effective temperatures in high metallicity regions., Comment: PhD Thesis at Universidad Autonoma de Madrid, Sept. 2008

(Abridged) Gas and star velocity dispersions have been derived for four circumnuclear star-forming regions (CNSFRs) and the nucleus of the spiral galaxy NGC2903 using high resolution spectroscopy in the blue and far red. Stellar velocity dispersions have been obtained from the CaII triplet (CaT) lines at 8494, 8542, 8662A, using cross-correlation techniques while gas velocity dispersions have been measured by Gaussian fits to the Hbeta line. The CNSFRs, with sizes of about 100 to 150pc in diameter, show a complex structure at the Hubble Space Telescope resolution, with a good number of subclusters with linear diameters between 3 and 8pc. Their stellar velocity dispersions range from 39 to 67 km/s. These values, together with the sizes measured on archival HST images yield upper limits to the dynamical masses for the individual star clusters between 1.8 and 8.7 x 10$^6$ M$_\odot$ and upper limits to the masses for the whole CNSFR between 4.9 x 10$^6$ and 4.3 x 10$^7$ M$_\odot$. ..., Comment: 20 pages, 12 figures, 6 tables. Accepted for publication in MNRAS

(Abbr.) We present high resolution (R~20000) spectra in the blue and the far red of cicumnuclear star-forming regions (CNSFRs) in three early type spirals (NGC3351, NGC2903 and NGC3310) which have allowed the study of the kinematics of stars and ionized gas in these structures and, for the first time, the derivation of their dynamical masses for the first two. In some cases these regions, about 100 to 150 pc in size, are seen to be composed of several individual star clusters with sizes between 1.5 and 4.9 pc estimated from Hubble Space Telescope (HST) images. The stellar dispersions have been obtained from the Calcium triplet (CaT) lines at $\lambda\lambda$ 8494,8542,8662 \AA, while the gas velocity dispersions have been measured by Gaussian fits to the H$\beta$ and [OIII] $\lambda\lambda$ 5007 \AA lines on the high dispersion spectra. Values of the stellar velocity dispersions are between 30 and 68 km/s. We apply the virial theorem to estimate dynamical masses of the clusters, assuming that systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 10$^7$ to 10$^8$ solar masses for the whole CNSFRs. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km/s with the H$\beta$ emission lines being narrower than both the stellar lines and the [OIII] $\lambda\lambda$ 5007 \AA lines. The twice ionized oxygen, on the other hand, shows velocity dispersions comparable to those shown by stars, in some cases, even larger. We have found indications of the presence of two different kinematical components in the ionized gas of the regions..., Comment: 4 pages, proceeding of the meeting "Young massive star clusters - Initial conditions and environments", Granada, Spain, 2007

(Abbr.) A study of cicumnuclear star-forming regions (CNSFRs) in several early type spirals has been made in order to investigate their main properties: stellar and gas kinematics, dynamical masses, ionising stellar masses, chemical abundances and other properties of the ionised gas. Both high resolution (R$ \sim $20000) and moderate resolution (R ~ 5000) have been used. In some cases these regions, about 100 to 150 pc in size, are seen to be composed of several individual star clusters with sizes between 1.5 and 4.9 pc estimated from Hubble Space Telescope (HST) images. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km/s with the H$\beta$ emission lines being narrower than both the stellar lines and the [OIII] $\lambda$ 5007 \AA lines. The twice ionized oxygen, on the other hand, shows velocity dispersions comparable to those shown by stars. We have applied the virial theorem to estimate dynamical masses of the clusters, assuming that systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 10$^7$ to 10$^8$ solar masses for the whole CNSFRs. ..., Comment: 7 pages, 8 figures, proceeding of the meeting "Young massive star clusters - Initial conditions and environments", Granada, Spain, 2007

Circumnuclear star forming regions, also called hotspots, are often found in the inner regions of some spiral galaxies where intense processes of star formation are taking place. In the UV, massive stars dominate the observed circumnuclear emission even in the presence of an active nucleus, contributing between 30 and 50% to the H$\beta$ total emission of the nuclear zone. Spectrophotometric data of moderate resolution (3000 < R < 11000) are presented from which the physical properties of the ionized gas: electron density, oxygen abundances, ionization structure etc. have been derived., Comment: 4 pages, 2 figures, proceeding of the meeting "Pathways Through an Eclectic Universe", Tenerife, 2007

We present high signal-to-noise spectrophotometric observations of seven luminous HII galaxies. The observations have been made with the use of a double-arm spectrograph which provides spectra with a wide wavelength coverage, from 3400 to 10400\AA free of second order effects, of exactly the same region of a given galaxy. These observations are analysed applying a methodology designed to obtain accurate elemental abundances of oxygen, sulphur, nitrogen, neon, argon and iron in the ionized gas. Four electron temperatures and one electron density are derived from the observed forbidden line ratios using the five-level atom approximation. For our best objects errors of 1% in t_e([OIII]), 3% in t_e([OII]) and 5% in t_e([SIII]) are achieved with a resulting accuracy of 7% in total oxygen abundances, O/H. The ionisation structure of the nebulae can be mapped by the theoretical oxygen and sulphur ionic ratios, on the one side, and the corresponding observed emission line ratios, on the other -- the \eta and \eta' plots --. The combination of both is shown to provide a means to test photo-ionisation model sequences currently applied to derive elemental abundances in HII galaxies., Comment: 24 pages, 8 figures, accepted by MNRAS

We have obtained long-slit observations in the optical and near infrared of 12 circumnuclear HII regions (CNSFR) in the early type spiral galaxies NGC 2903, NGC 3351 and NGC 3504 with the aim of deriving their chemical abundances. Only for one of the regions, the [SIII] $\lambda$ 6312 \AA was detected providing, together with the nebular [SIII] lines at $\lambda\lambda$ 9069, 9532 \AA, a value of the electron temperature of T$_e$([SIII])= 8400$^{+ 4650}_{-1250}$K. A semi-empirical method for the derivation of abundances in the high metallicity regime is presented. We obtain abundances which are comparable to those found in high metallicity disc HII regions from direct measurements of electron temperatures and consistent with solar values within the errors. The region with the highest oxygen abundance is R3+R4 in NGC 3504, 12+log(O/H) = 8.85, about 1.5 solar if the solar oxygen abundance is set at the value derived by Asplund et al. (2005), 12+log(O/H)$_{\odot}$ = 8.66$\pm$0.05. Region R7 in NGC 3351 has the lowest oxygen abundance of the sample, about 0.6 times solar. In all the observed CNSFR the O/H abundance is dominated by the O$^+$/H$^+$ contribution, as is also the case for high metallicity disc HII regions. For our observed regions, however, also the S$^+$/S$^{2+}$ ratio is larger than one, contrary to what is found in high metallicity disc HII regions for which, in general, the sulphur abundances are dominated by S$^{2+}$/H$^+$..., Comment: 24 pages, 19 figures, accepted by MNRAS

In this work we present a study of the strong optical collisional emission lines of Ne and Ar in an heterogeneous sample of ionized gaseous nebulae for which it is possible to derive directly the electron temperature and hence the chemical abundances of neon and argon. We calculate using a grid of photoionization models new ionization correction factors for these two elements and we study the behaviour of Ne/O and Ar/O abundance ratios with metallicity. We find a constant value for Ne/O, while there seems to be some evidence for the existence of negative radial gradients of Ar/O over the disks of some nearby spirals. We study the relation between the intensities of the emission lines of [NeIII] at 3869 \AA and [OIII] at 4959 \AA and 5007 \AA. This relation can be used in empirical calibrations and diagnostic ratios extending their applicability to bluer wavelengths and therefore to samples of objects at higher redshifts. Finally, we propose a new diagnostic using [OII], [NeIII] and Hdelta emission lines to derive metallicities for galaxies at high z., Comment: 12 pages, 12 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

We have measured gas and stellar velocity dispersions in 5 circumnuclear starforming regions (CNSFRs) and the nucleus of the barred spiral galaxy NGC 3351. The stellar dispersions have been obtained from high resolution spectra of the CaT lines at $\lambda\lambda$ 8494, 8542, 8662 \AA, while the gas velocity dispersions have been measured by Gaussian fits to the H$\beta$ $\lambda$ 4861 \AA line on high dispersion spectra. The CNSFRs, with sizes of about 100 to 150 pc in diameter, are seen to be composed of several individual star clusters with sizes between 1.7 and 4.9 pc on an HST image. Using the stellar velocity dispersions, we have derived dynamical masses for the entire starforming complexes and for the individual star clusters. Values of the stellar velocity dispersions are between 39 and 67 km s$^{-1}$. Dynamical masses for the whole CNSFRs are between 4.9 $\times$ 10$^6$ and 4.3 $\times$ 10$^7$ M$_\odot$ and between 1.8 and 8.7 $\times$ 10$^6$ M$_\odot$ for the individual star clusters. Stellar and gas velocity dispersions are found to differ by about 20 km s$^{-1}$ with the H$\beta$ lines being narrower than both the stellar lines and the [O{\sc iii}] $\lambda$ 5007 \AA lines. We have found indications for the presence of two different kinematical components in the ionised gas of the regions. The radial velocity curve shows deviation from circular motions for the ionised hydrogen consistent with its infall towards the central regions of the galaxy at a velocity of about 25 km s$^{-1}$. To disentangle the origin of these two components it will be necessary to map these regions with high spectral and spatial resolution and much better S/N in particular for the O$^{2+}$ lines., Comment: 17 pages, 13 figures, 7 tables - Accepted by MNRAS