arXiv subjects

A. Rodriguez-Ardila

Publications and source records attributed to A. Rodriguez-Ardila.

25 records · Page 2Linked to original sources

arXiv2004

The continuum and narrow line region of the NLS1 galaxy Mrk 766

We present the first spectroscopic observations in the interval 0.8-4.0 microns, complemented with HST/UV and optical spectroscopy, of the narrow line Seyfert 1 galaxy Mrk766. The NIR spectrum is characterized by permitted lines of HI, HeI, HeII and FeII, and forbidden lines of [SII], [SIII] and [FeII] among others. High ionized species such as [SiIX], [SiX], [SIX] and [MgVII] are also observed. The continuum has a complex shape, with contribution of the central engine, circumnuclear stellar population and dust. This last component is evidenced by the presence of an excess of emission peaking at 2.25 microns, fitted by blackbody function with T_bb=1200K. That temperature is close to the evaporation temperature of graphite grains. As such, it provides strong evidence of hot dust, probably very close to the nucleus. Consistent modeling of the line and broad band continuum spectrum by composite models, which account for the photoionizing flux of the central engine and shocks, shows that the shock velocities are between 100 and 500 km/s, the preshock densities between 100 and 1000 cm^-3 and the radiation fluxes from the active centre between 10^9 and 5x10^12 photons cm^-2 s^-1 eV^-1 at 1 Ryd with spectral indices $α_{UV}$=-1.5 and $α_X$=-0.4. Adopting silicon grains, dust-to-gas ratios are between 10^-{6} and 4x10$^{-4}$ by mass. The emitting clouds are at an average distance of 160 pc from the centre, with high velocity clouds closer and low velocity clouds farther from the centre. The N/H relative abundance could be twice solar. In constrast, Fe is depleted from the gaseous phase by a factor >2. Ratios of calculated to observed line ratios to Hbeta indicate an average contribution of the broad line region to the observed Hbeta of about 40%.

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arXiv2004

Extended Coronal Emission Lines in Active Galactic Nuclei

VLT and NTT spectra are used to examine the nuclear and extended coronal line emission in a sample of well-known Seyfert 1 and 2 galaxies. The excellent spatial resolution obtained with VLT allowed us to map [SiVI] 1.963 $μ$m and [SiVII] 2.48 $μ$m on scales of up to 20 pc. Coronal line emission, extended to distances of $\sim$100 pc, is detected in some of the lines analyzed, particularly in [FeX] 6374Å, [FeXI] 7891Å, and [SiVII] 2.48$μ$m. Most coronal lines are strongly asymmetric towards the blue and broader than low-ionization lines. This result is particularly important for Circinus, where previous observations had failed at detecting larger widths for high-ionization lines. Photoionization models are used to investigate the physical conditions and continuum luminosities necessary to produced the observed coronal emission. We found that an ionization parameter U> 0.10 is necessary to reproduce the observations, although the clouds should be located at distances < 30 pc.

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arXiv2003

Hidden starburst in Seyfert 1 Galaxies

We report the detection of the 3.3 mu Polycyclic Aromatic Hydrocarbon (PAH) feature in two Seyfert 1 galaxies - NGC 3227 and Mrk 766, and one QSO - Mrk 478, observed with SpeX at IRTF at a spectral resolution not previously attained for this type of objects. Except for NGC 3227, this is the first time that the 3.3 mu PAH emission is detected in Mrk 766 and Mrk 478. The widths of the emission, reported also for the first time, are rather similar, ranging from 450 A to 550 A. The luminosity of the 3.3 mu PAH emission measured in the QSO Mrk 478 places it at a level similar of that found in starburst and infrared luminous galaxies and implies that this object is having a vigorous burst of star formation. The spatial resolution of the spectra allows us to constrain the location of the star-forming region to the inner 1 Kpc for the QSO and 150 pc for the Seyferts. Our results support the idea that these objects resides in molecular gas-rich galaxies and that their observed infrared excess is primarily due to star formation, as previously indicated by CO and H_2 observations. We also report, for Mrk 1239, the presence of a broad emission feature centred at 3.43 mu, not previosly detected in an extragalactic object and whose origin is not yet clear.

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arXiv2002

The OI Line Emission in Active Galactic Nuclei Revisited

UV, visible, and near-infrared spectroscopy is used to study the transitions of neutral oxygen leading to the emission of broad OI $λ$8446, $λ$11287 and $λ$1304 in Active Galactic Nuclei. From the strength of the former two lines, contrary to the general belief, we found that in six out of seven galaxies, L-beta fluorescence is not the only mechanism responsible for the formation of these three lines. Because OI $λ$13165 is almost reduced to noise level, continuum fluorescence is ruled out as an additional excitation mechanism, but the presence of OI $λ$7774 in one of the objects suggests that collisional ionization may have an important role in the formation of OI $λ$8446. The usefulness of the OI lines as a reliable reddening indicator for the broad line region is discussed. The values of E(B-V) derived from the OI $λ1304/λ$8446 ratio agree with those obtained using other reddening indicators. The observations point toward a break in the one-to-one photon relation between OI $λ$8446 and OI $λ$1304, attributable to several destruction mechanisms that may affect the latter line.

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arXiv2002

Multicolor photometry of ten Seyfert 1 galaxies

We present BVI photometry of ten Seyfert 1 galaxies and narrow band H-alpha images for six of these objects as well. The results indicate that the luminosity sample distribution has an amplitude of almost 4 magnitudes with an average of M_B=-20.7. The observed morphologies are confined to early type galaxies. A barred structure is found in only 2 objects. Despite that early morphological types are dominant in this sample, integrated (B-V) colors are very blue. For instance, the SO galaxies show, on average, a (B-V)=0.78. This effect seems to be caused by the luminosity contribution of the active nucleus and/or the disk to the total luminosity of the galaxy. In the B band, the contribution of the active galactic nucleus to the total luminosity of the galaxy varies from 3% to almost 60% and the bulge to disk luminosity ratio (L_bulge/L_disk) ranges from 0.6 to 22. Signs of tidal interactions seems to be a common characteristic since they are observed in 6 of the objects and one of them seems to be located in a poor cluster not yet identified in the literature. H_alpha extended emission is rare, with only 1 galaxy showing clear evidence of it. Luminosity profile decomposition shows that the model Gauss + bulge + disk properly reproduces the surface brightness of the galaxies. However, in order to account for the luminosity profile, most of the disk galaxies needs the inner truncated exponential form with a central cutoff radius ranging from 3 to 10 kpc. This is interpreted in terms of reddened regions that are well identified in the B-V color maps. These regions present very similar colors among them, with (B-V)~1.2. This fact could be associated to the presence of dust confined in the inner regions of the galaxies.

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arXiv2001

Infrared FeII Emission in Narrow-Line Seyfert 1 Galaxies

We obtained 0.8-2.4 micron spectra at a resolution of 320 km/s of four narrow-line Seyfert 1 galaxies in order to study the near-infrared properties of these objects. We focus on the analysis of the FeII emission in that region and the kinematics of the low-ionization broad lines. We found that the 1 micron FeII lines (9997 A, 10501 A, 10863 A and 11126 A) are the strongest FeII lines in the observed interval. For the first time, primary cascade lines of FeII arising from the decay of upper levels pumped by Ly-alpha fluorescence are resolved and identified in active galactic nuclei. Excitation mechanisms leading to the emission of the 1 micron FeII features are discussed. A combination of Ly-alpha fluorescence and collisional excitation are found to be the main contributors. The flux ratio between near-IR FeII lines varies from object to object, in contrast to what is observed in the optical region. A good correlation between the 1 micron and optical FeII emission is found. This suggests that the upper z4Fo and z4Do levels from which the bulk of the optical lines descend are mainly populated by the transitions leading to the 1 micron lines. The width and profile shape of FeII 11127, CaII 8642 and OI 8446 are very similar but significantly narrower than Pa-beta, giving strong observational support to the hypothesis that the region where FeII, CaII and OI are produced are co-spatial, interrelated kinematically and most probably located in the outermost portion of the BLR.

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arXiv2000

The Narrow Line Region of Narrow-Line Seyfert 1 Galaxies

This work studies the optical emission line properties and physical conditions of the narrow line region (NLR) of seven narrow-line Seyfert 1 galaxies (NLS1). Our results show that the flux carried out by the narrow component of H-beta is, on average, 50% of the total line flux. As a result, the [OIII] 5007/H-beta ratio emitted in the NLR varies from 1 to 5, instead of the universally adopted value of 10. This has strong implications for the required spectral energy distribution that ionizes the NLR gas. Photoionization models that consider a NLR composed of a combination of matter-bounded and ionization-bounded clouds are successful at explaining the low [OIII] 5007/H-beta ratio and the weakness of low-ionization lines of NLS1s. Variation of the relative proportion of these two type of clouds nicely reproduce the dispersion of narrow line ratios found among the NLS1 sample. Assuming similar physical model parameters of both NLS1s and the normal Seyfert 1 galaxy NGC 5548, we show that the observed differences of emission line ratios between these two groups can be explained in terms of the shape of the input ionizing continuum. Narrow emission line ratios of NLS1s are better reproduced by a steep power-law continuum in the EUV -- soft X-ray region, with spectral index alpha ~ -2. Flatter spectral indices (alpha ~ -1.5) match the observed line ratios of NGC 5548 but are unable to provide a good match to the NLS1 ratios. This result is consistent with ROSAT observations of NLS1s, which show that these objects are characterized by steeper power-law indices than those of Sy1 galaxies with strong broad optical lines.

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