Miriani Griselda Pastoriza

A 0.8-2.4 μm spectral atlas of active galactic nuclei

Aims. We present a near-infrared spectral atlas of 47 active galactic nuclei (AGN) of all degrees of activity in the wavelength interval of 0.8-2.4 � m, including the fluxes of the observed emission lines. We ana lyze the spectroscopic properties of the continuum and emission line spectra of the sources. Methods. In order to exclude aperture and seeing effects we used near-infrared spectroscopy in the short cross-dispersed mode (SXD, 0.8−2.4� m), taking the JHK-bands spectra simultaneously. Results. We present the most extensive NIR spectral atlas of AGN to date. This atlas offers a suitable database for studying the continuum and line emission properties of these objects in a region full of interesting features. The shape of the continuum of QSOs and Sy 1’s are similar, being essentially flat in the H and K bands, while a strong vari ation is found in the J band. In Seyfert 2 galaxies, the contin uum in the Fλ×λ space smoothly decreases in flux from 1.2� m redwards in almost all sources. In J, it smoothly rises bluewards in some sources, while in others a small decrease in flux is observed. The spectra are do minated by strong emission features of Hi, Hei, Heii, [Siii] and by conspicuous forbidden lines of low and high ionization species. Molecular lines of H2 are common features of most objects. The absence of Oi and Feii lines in Seyfert 2 galaxies and the smaller FWHM of these lines relative to that of Hi in the Seyfert 1 give observational support to the fact that they are formed in the outermost portion of the broad-line region. The[Pii] and coronal lines are detected for all degrees of activity. The [Feii] 12570A/16436A line ratio becomes a reliable reddening indicator for the narrow-line region of Seyfert galaxies.

Molecular hydrogen and (Fe II) in Active Galactic Nuclei

Near-infrared spectroscopy is used to study the kinematics and excitation mechanisms of H2 and (Fe ) lines in a sample of mostly Seyfert 1 galaxies. The spectral coverage allows simultaneous observation of the JHK bands, thus eliminating the aperture and seeing effects that have usually plagued previous works. The H2 lines are unresolved in all objects in which they were detected while the (Fe ) lines have widths implying gas velocities of up to 650 km s −1 . This suggests that, very likely, the H2 and (Fe ) emission does not originate from the same parcel of gas. Molecular H2 lines were detected in 90% of the sample, including PG objects, indicating detectable amounts of molecular material even in objects with low levels of circumnuclear starburst activity. Analysis of the observations favors thermal excitation mechanisms for the H2 lines. Indeed, in NGC 3227, Mrk 766, NGC 4051 and NGC 4151, the molecular emission is found to be purely thermal but with heating processes that vary between the objects. Thermal excitation is also confirmed by the rather similar vibrational and rotational temperatures in the objects for which data were available. (Fe ) lines are detected in all of the sample AGN. The (Fe ) 1.254 µm/Paβ ratio is compatible with excitation of the (Fe ) lines by the active nucleus in most Seyfert 1 galaxies, but in Mrk 766 the ratio implies a stellar origin. A correlation between H2/Brγ and (Fe )/Paβ is found for our sample objects supplemented by data from the literature. The correlation of these line ratios is a useful diagnostic tool in the NIR to separate emitting line objects by their level of nuclear activity. X-ray excitation models are able to explain the observed H2 and part of the (Fe ) emission but fail to explain the observations in Seyfert 2 galaxies. Most likely, a combination of X-ray heating, shocks driven by the radio jet and circumnuclear star formation contributes, in different proportions, to the H2 and (Fe ) lines observed. In most of our sample objects, the (Fe ) 1.257 µm/1.644 µm ratio is found to be 30% lower than the intrinsic value based on current atomic data. This implies either that the extinction towards the (Fe )-emitting clouds is very similar in most objects or there are possible inaccuracies in the A-values in the Fe  transitions.

A survey of the interstellar medium in early-type galaxies. III. Stellar and gas kinematics

We present gaseous and stellar kinematics for 14 gas-rich early-type galaxies. Half of the sample exhibit irregular gaseous velocity profiles; gas/star counter-rotation is visible in five galaxies. We also find five counter-rotating stellar cores, while five more galaxies display inner components kinematically decoupled from the main stellar body. We interpret our results as an indication that the ionized gas is of external origin, is generally not in equilibrium, and may have been acquired recently. The merging or accretion events that brought the gas into the galaxy have also affected the stellar kinematics.

Steps toward determination of the size and structure of the broad-line region in active galactic nuclei. 6: Variability of NGC 3783 from ground-based data

The Seyfert 1 galaxy NGC 3783 was intensely monitored in several bands between 1991 December and 1992 August. This paper presents the results from the ground-based observations in the optical and near-IR bands, which complement the data set formed by the International Ultraviolet Explorer (IUE) spectra, discussed elsewhere. Spectroscopic and photometric data from several observatories were combined in order to obtain well-sampled light curves of the continuum and of H(beta). During the campaign the source underwent significant variability. The light curves of the optical continuum and of H(beta) display strong similarities to those obtained with the IUE. The near-IR flux did not vary significantly except for a slight increase at the end of the campaign. The cross-correlation analysis shows that the variations of the optical continuum have a lag of 1 day or less with respect to those of the UV continuum, with an uncertainty of is less than or equal to 4 days. The integrated flux of H(beta) varies with a delay of about 8 days. These results confirm that (1) the continuum variations occur simultaneously or with a very small lag across the entire UV-optical range, as in the Seyfert galaxy NGC 5548; and (2) the emission lines of NGC 3783 respond to ionizing continuum variations with less delay than those of NGC 5548. As observed in NGC 5548, the lag of H(beta) with respect to the continuum is greater than those of the high-ionization lines.

Probing the near-infrared stellar population of Seyfert galaxies

We employ Infrared Telescope Facility SpeX near-infrared (NIR; 0.8-2.4 μm) spectra to investigate the stellar population (SP), active galactic nuclei (AGN) featureless continuum (FC) and hot dust properties in nine Sy 1 and 15 Sy 2 galaxies. Both the STARLIGHT code and the hot dust as an additional base element were used for the first time in this spectral range. We found evidence of correlation among the equivalent widths (W λ ) Si I 1.59 μm x Mg I 1.58 μm, equally for both kinds of activity. Part of the W NaI2.21 μm and W CO 2.3 μm strengths may be related to galaxy inclination. Our synthesis shows significant differences between Sy I and Sy 2 galaxies: the hot dust component is required to fit the K-band spectra of ∼90 per cent of the Sy 1 galaxies, and only of ∼25 per cent of the Sy 2; about 50 per cent of the Sy 2 galaxies require an FC component contribution ≳20 per cent, while this fraction increases to about 60 per cent in the Sy 1; also, in about 50 per cent of the Sy2, the combined FC and young components contribute with more than 20 per cent, while this occurs in 90 per cent of the Syl, suggesting recent star formation in the central region. The central few hundred parsec of our galaxy sample contain a substantial fraction of intermediate-age SPs with a mean metallicity near solar. Our SP synthesis confirms that the 1.1 μm CN band can be used as a tracer of intermediate-age SPs. The simultaneous fitting of SP, FC and hot dust components increased in ∼150 per cent the number of AGNs with hot dust detected and the mass estimated. The NIR emerges as an excellent window to study the SP of Sy I galaxies, as opposed to the usually heavily attenuated optical range. Our approach opens a new way to investigate and quantify the individual contribution of the three most important NIR continuum components observed in AGNs.

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 (NLS1s) for which high signal-to-noise ratio spectroscopic observations were available. The resolution is 340 km s-1 (at Hα) over the wavelength interval 3700-9500 A, enabling us to separate the broad and narrow components of the permitted emission lines. Our results show that the flux carried out by the narrow component of Hβ is, on average, 50% of the total line flux. As a result, the [O III] λ5007/Hβ 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 [O III] λ5007/Hβ ratio and the weakness of low-ionization lines of NLS1s. Variation of the relative proportion of these two type of clouds nicely reproduces 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 of galaxies can be explained, to a first approximation, 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 α ~ -2. Flatter spectral indices (α ~ -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 Seyfert 1 galaxies with strong broad optical lines.

Spectroscopic monitoring of active Galactic nuclei from CTIO. 1: NGC 3227

The results of a five-month monitoring campaign on the Seyfert 1.5 galaxy NGC 3227 are presented. Variability was detected in the continuum and in the broad emission lines. Cross correlations of the 4200 A continuum light curve with the H beta and He II wavelength 4686 emission-line light curves indicate delays of 18 +/- 5 and 16 +/- 2 days, respectively, between the continuum variations and the response of the lines. We apply a maximum entropy method to solve for the transfer function that relates the H beta and He II wavelength 4686 lines and 4200 A continuum variability and the result of this analysis suggests that there is a deficit of emission-line response due to gas along the line of sight to the continuum source for both lines. Using a composite off-nuclear spectrum, we synthesize the bulge stellar population, which is found to be mainly old (77% with age greater than 10 Gyr) with a metallicity twice the solar value. The synthesis also yields an internal color excess E(B - V) approximately equal 0.04. The mean contribution of the stellar population to the inner 5 sec x 10 sec spectra during the campaign was approximately equal 40%.

Optical Spectroscopic Properties of a Sample of Interacting Galaxies

We present spectroscopic observations of 83 galaxies from a sample of 49 pairs of optically selected interacting galaxies, most of them previously unobserved. These pairs consist of a main galaxy (component A) and a companion (component B) that has about half or less the diameter of component A. From our spectra we determine that 27 galaxies form truly physical pairs and seven are apparent pairs, for the remaining pairs we could only extract the spectra of the A components. The spectra of the physical pairs were classified into four groups according to the emission-line spectra observed in each component. These classifications were made because the sample exhibits a very large range of spectral properties, ranging from well-evolved stellar populations (older than 200 Myr) to emission-line-dominated starburst systems (80 Myr or younger). In general terms, these spectral types are well correlated with the morphological types of the galaxies. However, we find no evidence of correlation of the equivalent width of Hα + [N II] emission lines with the degree of the interaction or with the blue absolute magnitude of the components. From the data it is also determined that the average EW(Hα + [N II]) for the physical pairs is 37 A for the A components and 54 A for the B components. For the galaxies that form apparent pairs we obtain EW(Hα + [N II]) = 27 A, confirming that physical pairs have higher mean star formation rates than isolated galaxies. This enhancement of the star formation activity is more likely to take place in both galaxies, but the strength of the activity seems to be higher in the B components. The mean observed values of EW(Hα + [N II]) are comparable with those observed in a sample of strongly interacting or merging galaxies. On the other hand, we do not find the excess of Seyfert-type nuclei previously reported in studies of similar samples of galaxies.

The first detection of near-infrared CN bands in active galactic nuclei:signature of star formation

We present the first detection of the near-infrared CN absorption band in the nuclear spectra of active galactic nuclei (AGNs). This feature is a recent star formation tracer, being particularly strong in carbon stars. The equivalent width of the CN line correlates with that of the CO at 2.3 μm as expected in stellar populations (SPs) with ages between ~0.2 and ~2 Gyr. The presence of the 1.1 μm CN band in the spectra of the sources is taken as unambiguous evidence of the presence of young/intermediate SPs close to the central source of the AGNs. Near-infrared bands can be powerful age indicators for star formation connected to AGNs, the understanding of which is crucial in the context of galaxy formation and AGN feedback.

Infrared Fe II emission in narrow-line Seyfert 1 galaxies

We obtained 0.8-2.4 μm spectra at a resolution of 320 km s-1 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 Fe II emission in that region and the kinematics of the low-ionization broad lines. We show that the 1 μm Fe II lines (λ9997, λ10501, λ10863, and λ11126) are the strongest Fe II lines in the observed interval. For the first time, primary cascade lines of Fe II arising from the decay of upper levels pumped by Lyα fluorescence are resolved and identified in active galactic nuclei. Excitation mechanisms leading to the emission of the 1 μm Fe II features are discussed. A combination of Lyα fluorescence and collisional excitation is found to be the main contributor. The flux ratio between near-IR Fe II lines varies from object to object, in contrast to what is observed in the optical region. A good correlation between the 1 μm and optical Fe II emission is found. This suggests that the upper z4F0 and z4D0 levels from which the bulk of the optical Fe II lines descend are mainly populated by the transitions leading to the 1 μm lines. The width and profile shape of Fe II λ11127, Ca II λ8642, and O I λ8446 are very similar but significantly narrower than Paβ, giving strong observational support to the hypothesis that the regions where Fe II, Ca II, and O I are produced are cospatial, interrelated kinematically, and most probably located in the outermost portion of the broad-line region.