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

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.Comment: 25 pages, 10 figures, accepted MNRA

Effective temperature of ionizing stars of extragalactic HII regions

The effective temperature (Teff) of the radiation field of the ionizing star(s) of a large sample of extragalactic HII regions was estimated using the R = log([O II] (λλ3726 + 29)/[O III] λ5007) index. We used a grid of photoionization models to calibrate the Teff-R relation finding that it has a strong dependence with the ionizing parameter, while it shows a weak direct dependence with the metallicity (variations in Z imply variations in U) of both the stellar atmosphere of the ionizing star and the gas phase of the HII region. Since the R index varies slightly with the Teff for values larger than 40 kK, the R index can be used to derive the Teff in the 30-40 kK range. A large fraction of the ionization parameter variation is due to differences in the temperature of the ionizing stars and then the use of the (relatively) low Teff dependent S2 = [S II] (λλ6717 + 31)/Hα emission-line ratio to derive the ionization parameter is preferable over others in the literature. We propose linear metallicity dependent relationships between S2 and U. Teff and metallicity estimations for a sample of 865 HII regions, whose emission-line intensities were compiled from the literature, do not show any Teff-Z correlation. On the other hand, it seems to be hints of the presence of an anticorrelation between Teff-U.We found that the majority of the studied HII regions (~87 per cent) present Teff values in the range between 37 and 40 kK, with an average value of 38.5(±1) kK. We also studied the variation of Teff as a function of the galactocentric distance for 14 spiral galaxies. Our results are in agreement with the idea of the existence of positive Teff gradients along the disc of spiral galaxies.Instituto de Astrofísica de La Plat

Effective temperature of ionizing stars of extragalactic HII regions

The effective temperature (Teff) of the radiation field of the ionizing star(s) of a large sample of extragalactic HII regions was estimated using the R = log([O II] (λλ3726 + 29)/[O III] λ5007) index. We used a grid of photoionization models to calibrate the Teff-R relation finding that it has a strong dependence with the ionizing parameter, while it shows a weak direct dependence with the metallicity (variations in Z imply variations in U) of both the stellar atmosphere of the ionizing star and the gas phase of the HII region. Since the R index varies slightly with the Teff for values larger than 40 kK, the R index can be used to derive the Teff in the 30-40 kK range. A large fraction of the ionization parameter variation is due to differences in the temperature of the ionizing stars and then the use of the (relatively) low Teff dependent S2 = [S II] (λλ6717 + 31)/Hα emission-line ratio to derive the ionization parameter is preferable over others in the literature. We propose linear metallicity dependent relationships between S2 and U. Teff and metallicity estimations for a sample of 865 HII regions, whose emission-line intensities were compiled from the literature, do not show any Teff-Z correlation. On the other hand, it seems to be hints of the presence of an anticorrelation between Teff-U.We found that the majority of the studied HII regions (~87 per cent) present Teff values in the range between 37 and 40 kK, with an average value of 38.5(±1) kK. We also studied the variation of Teff as a function of the galactocentric distance for 14 spiral galaxies. Our results are in agreement with the idea of the existence of positive Teff gradients along the disc of spiral galaxies.Instituto de Astrofísica de La Plat

Effective temperature of ionizing stars in extragalactic HII regions - II. Nebular parameter relationships based on CALIFA data

We calculate the effective temperature (Teff) of ionizing star(s), the oxygen abundance of the gas phase (O/H), and the ionization parameter U for a sample of HII regions located in the discs of 59 spiral galaxies in the redshift range 0.005 < z < 0.03. We use spectroscopic data taken from the CALIFA data release 3 (DR3) and theoretical (for Teff and U) and empirical (for O/H) calibrations based on strong emission lines. We consider the spatial distribution and radial gradients of these parameters in each galactic disc for the objects in our sample. Most of the galaxies in our sample (∼70 per cent) show positive Teff radial gradients, although some exhibit negative or flat ones. The median value of the Teff radial gradient is 0.762 kK/R25. We find that the radial gradients of both logUand Teff depend on the oxygen abundance gradient, in the sense that the gradient of logU increases as the log(O/H) gradient increases while there is an anti-correlation between the gradient of Teff and the oxygen abundance gradient. Moreover, galaxies with flat oxygen abundance gradients tend to have flat logU and Teff gradients as well. Although our results are in agreement with the idea of the existence of positive Teff gradients along the disc of the majority of spiral galaxies, it seems that this is not a universal property for these objects.Fil: Zinchenko, I. A.. Main Astronomical Observatory of National Academy of Sciences of Ukraine; Ucrania. Zentrum für Astronomie der Universität Heidelberg; AlemaniaFil: Dors, Oli L.. Universidade do Vale do Paraíba; BrasilFil: Hägele, Guillermo Federico. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Cardaci, Monica Viviana. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Krabbe, Angela. Universidade do Vale do Paraíba; Brasi

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

In this work, we used a grid of photoionization models combined with stellar population synthesis models to derive reliable ionization correction factors (ICFs) for the sulphur in star-forming regions. These models cover a large range of nebular parameters and yielding ionic abundances in consonance with those derived through optical and infrared observational data of star-forming regions. From our theoretical ICFs, we suggested an α value of 3.27 ± 0.01 in the classical Stasińska formulae. We compared the total sulphur abundance in the gas phase of a large sample of objects by using our theoretical ICF and other approaches. In average, the differences between the determinations via the use of the different ICFs considered are similar to the uncertainties in the S/H estimations. Nevertheless, we noted that for some objects it could reach up to about 0.3 dex for the low-metallicity regime. Despite of the large scatter of the points, we found a trend of S/O ratio to decrease with the metallicity, independently of the ICF used to compute the sulphur total abundance.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat

Nuclear spirals as feeding channels to the Supermassive Black Hole: the case of the galaxy NGC 6951

We report the discovery of gas streaming motions along nuclear spiral arms towards the LINER nucleus of the galaxy NGC 6951. The observations, obtained using the GMOS integral field spectrograph on the Gemini North telescope, yielded maps of the flux distributions and gas kinematics in the Halpha, [NII]6584 and [SII]6717,31 emission lines of the inner 7x5 arcsec^2 of the galaxy. This region includes a circumnuclear star-forming ring with radius 500pc, a nuclear spiral inside the ring and the LINER nucleus. The kinematics of the ionized gas is dominated by rotation, but subtraction of a kinematic model of a rotating exponential disk reveals deviations from circular rotation within the nuclear ring which can be attributed to (1) streaming motions along the nuclear spiral arms and (2) a bipolar outflow which seems to be associated to a nuclear jet. On the basis of the observed streaming velocities and geometry of the spiral arms we estimate a mass inflow rate of ionized gas of 3x10^(-4) Msun/yr, which is of the order of the accretion rate necessary to power the LINER nucleus of NGC 6951. Similar streaming motions towards the nucleus of another galaxy with LINER nucleus -- NGC 1097 -- have been reported by our group in a previous paper. Taken together, these results support a scenario in which nuclear spirals are channels through which matter is transferred from galactic scales to the nuclear region to feed the supermassive black hole.Comment: 25 pages, 6 eps figures, accepted for publication in Ap

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

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 MNRA