ABSTRACT
We employ MUSE/VLT data to study the ionized and highly ionized gas phases of the feedback in Circinus, the closest Seyfert 2 galaxy to us. The analysis of the nebular emission allowed us to ...detect a remarkable high-ionization gas outflow beyond the galaxy plane traced by the coronal lines Fe vii λ6089 and Fe x λ6374, extending up to 700 and 350 pc NW from the nucleus, respectively. This is the first time that the Fe x emission is observed at such distances from the central engine in an active galactic nucleus (AGN). The gas kinematics reveals expanding gas shells with velocities of a few hundred km s−1, spatially coincident with prominent hard X-ray emission detected by Chandra. Density and temperature sensitive line ratios show that the extended high-ionization gas is characterized by a temperature reaching 25 000 K and an electron density >102 cm−3. We found that local gas excitation by shocks produced by the passage of a radio jet leads to the spectacular high-ionization emission in this object. This hypothesis is fully supported by photoionization models that account for the combined effects of the central engine and shocks. They reproduce the observed emission line spectrum at different locations inside and outside of the NW ionization cone. The energetic outflow produced by the radio jet is spatially located close to an extended molecular outflow recently reported using ALMA which suggests that they both represent different phases of the same feedback process acting on the AGN.
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 (Wλ) Si i 1.59 μm × Mg i 1.58 μm, equally for both kinds of activity. Part of the WNa I 2.21 μm and WCO 2.3 μm strengths may be related to galaxy inclination. Our synthesis shows significant differences between Sy 1 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 Sy1, 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 1 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.
Abstract
Low-luminosity active galactic nuclei, i.e.
$L_{\rm b{\rm ol}}$
/L
edd ∼ 10−6–10−3, constitute the bulk population of active galactic nuclei (AGNs). Powerful jets, common in these objects, ...are a crucial source of feedback energy-driving mass outflows into the host galaxy and the intergalactic medium. This paper reports the first direct measurement of powerful mass outflows traced by the forbidden high-ionization gas in the low-luminosity AGN NGC 1386 at scales of a few parsecs from the central engine. The high-angular resolution of the data allows us to directly measure the location, morphology and kinematic of the outflow. This has the form of two symmetrical expanding hot gas shells moving in opposite directions along the line of sight. The co-spatiality of the gas shells with radio emission seen at the same parsec scales and with X-rays indicates that this is a shock-driven outflow presumably induced by an incipient core jet. With a minimum number of assumptions, we derive a mass outflow rate of 11 M⊙ yr−1, comparable to those of powerful AGN. The result has strong implications in the global accounting of feedback mass and energy driven by a low-luminosity AGN into the medium and the corresponding galaxy evolution.
The relationship between the emission of coronal lines (CLs) and nuclear activity in 36 Type 1 and 18 Type 2 active galactic nuclei (AGNs) is analyzed, for the first time, based on near-infrared ...(0.8-2.4 Delta *mm) spectra. The eight CLs studied, of Si, S, Fe, Al, and Ca elements and corresponding to ionization potentials (IPs) in the range 125-450 eV, are detected (3 Delta *s) in 67% (36 AGNs) of the sample. Our analysis shows that the four most frequent CLs Si VI 1.963 Delta *mm, S VIII 0.9913 Delta *mm, S IX 1.252 Delta *mm, and Si X 1.430 Delta *mm display a narrow range in luminosity, with most lines located in the interval log L 39-40 erg s--1. We found that the non-detection is largely associated with either loss of spatial resolution or increasing object distance: CLs are essentially nuclear and easily lose contrast in the continuum stellar light for nearby sources or get diluted by the strong AGN continuum as the redshift increases. Yet, there are AGNs where the lack of coronal emission, i.e., lines with IP >= 100 eV, may be genuine. The absence of these lines reflects a non-standard AGN ionizing continuum, namely, a very hard spectrum lacking photons below a few Kev. The analysis of the line profiles points out a trend of increasing FWHM with increasing IPs up to energies around 300 eV, where a maximum in the FWHM is reached. For higher IP lines, the FWHM remains nearly constant or decreases with increasing IPs. We ascribe this effect to an increasing density environment as we approach the innermost regions of these AGNs, where densities above the critical density of the CLs with IPs larger than 300 eV are reached. This sets a strict range limit for the density in the boundary region between the narrow and the broad region of 108-109 cm--3. A relationship between the luminosity of the CLs and that of the soft and hard X-ray emission and the soft X-ray photon index is observed: the coronal emission becomes stronger with both increasing X-ray emission (soft and hard) and steeper X-ray photon index, i.e., softer X-ray spectra. Thus, photoionization appears as the dominant excitation mechanism. These trends hold when considering Type 1 sources only; they get weaker or vanish when including Type 2 sources, very likely because the X-ray emission measured in the latter is not the intrinsic ionizing continuum.
ABSTRACT
Coronal-line forest (CLiF) active galactic nuclei (AGNs) are characterized by strong high-ionization lines, which contrasts with what is found in most AGNs. Here, we carry out a ...multiwavelength analysis aimed at understanding the physical processes in the narrow-line region (NLR) of these objects, and at discovering whether they are indeed a special class of AGNs. By comparing coronal emission-line ratios we conclude that there are no differences between CLiF and non-CLiF AGNs. We derive physical conditions of the NLR gas and we find electron densities in the range of 3.6 × 102 to 1.7 × 104 cm−3 and temperatures of 3.7 × 103 to 6.3 × 104 K, suggesting that the ionization mechanism is associated primarily with photoionization by the AGN. We suggest an NLR dominated by matter-bounded clouds to explain the high-ionization line spectrum observed. The mass of the central black hole, derived from the stellar velocity dispersion, shows that most of the objects have values in the interval 107–108 M⊙. Our results imply that CLiF AGNs are not in a separate category of AGNs. In all optical/near-infrared emission-line properties analysed, they represent an extension to the low/high ends of the distribution within the AGN class.
ABSTRACT
Coronal-Line Forest Active Galactic Nuclei (CLiF AGN) are characterized by strong, high-ionization lines, which are in contrast to what is found in typical AGNs. Here, we carry out an ...infrared analysis aimed at understanding the spectral energy distribution (SED) of six sources from this group. In this work, the properties of the dusty torus for these objects are analysed. To this purpose, we infer the physical and geometrical properties of the dust structure that surrounds the central region by fitting with models, the SED of CLiF AGNs in the infrared. For this analysis, we compare the results of three models: clumpy, skirtor, and cat3d-wind. Using the Bayesian information criterion, skirtor was found to have the most robust fit to the SEDs in five out of six galaxies. The remaining object was best fitted with clumpy. The results indicate that these objects are preferentially Type I sources, supporting the detection of broad components in the permitted lines, likely associated with the broad-line region in the near-infrared spectra. The best SED fitting indicates that the line of sight gives access to the view of the central source for these objects, but the amount of dusty clouds in the same direction is high, suggesting the hypothesis that they obscure the emission of the continuum produced by the central source and that the obscuration makes the coronal lines to not overlap with the continuum.
ABSTRACT
We study the ionized and highly ionized gas phases in the Seyfert 2 galaxy IC 5063 by means of the Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) integral field ...spectroscopy. Our analysis allowed us to detect a high-ionization gas outflow traced by the coronal lines Fe vii λ6087 and Fe x λ6375. Both emissions are found to be extended. The former up to 1.2 kpc and 700 pc north-west (NW) and south-east (SE) from the nucleus, respectively. The latter reaches 700 pc NW of the nucleus. This is the first time that Fe x emission is observed at such distances from the central engine in an active galactic nucleus. The Fe vii λ6087 emission peaks at the nucleus, with two secondary peaks at the position of the NW and SE radio lobes. The gas kinematics is complex, with the coronal emission displaying split line profiles along the radio jet and line widths of several hundred km s−1. Velocity shifts of up to 600 km s−1 in excess of the systemic velocity of the galaxy are found very close to the radio lobes and along the jet propagation. The extended coronal gas is characterized by temperatures reaching 20 000 K and electron densities >102 cm−3, with the larger values associated with the regions of larger turbulence, likely due to the passage of the radio jet. This hypothesis is supported by photoionization models that combine the effects of the central engine and shocks. Our work highlights the strong relationship between extended coronal emission and the radio jet, with the former suitably tracing the latter, which in the case of IC 5063, propagates very close to the galaxy disc.
We analyse Near-Infrared Integral Field Spectrograph (NIFS) observations of the type-2 quasar (QSO2) SDSS J094521.33+173753.2 to investigate its warm molecular and ionized gas kinematics. This QSO2 ...has a bolometric luminosity of 10
45.7
erg s
−1
and a redshift of
z
= 0.128. The
K
-band spectra provided by NIFS cover a range of 1.99–2.40 μm where low ionization (Pa
α
and Br
δ
), high ionization (S XI
λ
1.920 μm and Si VI
λ
1.963 μm), and warm molecular lines (from H
2
1-0S(5) to 1-0S(1)) are detected, allowing us to study the multi-phase gas kinematics. Our analysis reveals gas in ordinary rotation in all the emission lines detected and also outflowing gas in the case of the low and high ionization emission lines. In the case of the nuclear spectrum, which corresponds to a circular aperture of 0.3″ (686 pc) in diameter, the warm molecular lines can be characterized using a single Gaussian component of full width at half maximum (
FWHM
) = 350 − 400 km s
−1
, while Pa
α
, Br
δ
, and Si VI are best fitted with two blue-shifted Gaussian components of
FWHM
∼ 800 and 1700 km s
−1
, in addition to a narrow component of ∼300 km s
−1
. We interpret the blue-shifted broad components as outflowing gas, which reaches the highest velocities, of up to −840 km s
−1
, in the south-east direction (PA ∼ 125°), extending up to a distance of ∼3.4 kpc from the nucleus. The ionized outflow has a maximum mass outflow rate of
Ṁ
out,max
= 42–51
M
⊙
yr
−1
, and its kinetic power represents 0.1% of the quasar bolometric luminosity. Very Large Array (VLA) data of J0945 show extended radio emission (PA ∼ 100°) that is aligned with the clumpy emission traced by the narrow component of the ionized lines up to scales of several kiloparsecs, and with the innermost part of the outflow (central ∼0.4″ = 915 pc). Beyond that radius, at the edge of the radio jet, the high velocity gas shows a different PA of ∼125°. This might be an indication that the line-emitting gas is being compressed and accelerated by the shocks generated by the radio jet.
Context.
NGC 1232 is a face-on spiral galaxy that serves as an excellent laboratory for the study of star formation due to its proximity. Recent studies have revealed interesting features about this ...galaxy: X-ray observations suggest that it recently collided with a dwarf galaxy, however, no apparent remnant is observed.
Aims.
In this study, we search for evidence of this possible collision.
Methods.
We used long-slit optical spectra of the galaxy in two different positions obtained with the Goodman spectrograph at the SOAR telescope.
Results.
We detected 18 HII regions in the north-south direction and 22 HII regions in the east-west direction and a background galaxy, NGC 1232B, for which we present the first redshift measurement and spectral analysis. We used the stellar population fitting technique to study the underlying stellar population of NGC 1232 and NGC 1232B and to subtract it from the spectra to measure the emission lines. The emission lines were used to determine the extinction, electron density, chemical abundance, and the star-formation rate gradient of NGC 1232.
Conclusions.
As is common in spiral galaxies, we found a stellar population gradient with older populations at the central regions and younger ones towards the outskirts, along with a negative oxygen abundance gradient of −0.16 dex/r
e
. Due to the difficulty of measuring important emission lines, the number of objects for the abundance gradient is small, but there is a hint that this galaxy has a broken gradient profile, with a drop towards the center. Some authors have explained this effect as the result of a satellite collision, but observations of a large sample of spiral galaxies shows evidence that goes against such a mechanism. If the collision caused any disturbance in the galaxy, we believe it would be small and hard to detect with a limited number of objects. From all the other measurements, we found no deviations from a typical spiral galaxy and no significant difference between different directions in the galaxy. The stellar population and emission line analysis of NGC 1232B suggest that it is a starburst galaxy.
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 μm, including the fluxes of the observed emission ...lines. We analyze 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 μm), 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 variation is found in the J band. In Seyfert 2 galaxies, the continuum in the $F\lambda\, \times\, \lambda$ space smoothly decreases in flux from 1.2 μm 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 dominated by strong emission features of $\ion{H}{i}$, $\ion{He}{i}$, $\ion{He}{ii}$, $\ion{S}{iii}$ and by conspicuous forbidden lines of low and high ionization species. Molecular lines of H2 are common features of most objects. The absence of $\ion{O}{i}$ and $\ion{Fe}{ii}$ lines in Seyfert 2 galaxies and the smaller FWHM of these lines relative to that of $\ion{H}{i}$ in the Seyfert 1 give observational support to the fact that they are formed in the outermost portion of the broad-line region. The$\ion{P}{ii}$ and coronal lines are detected for all degrees of activity. The $\ion{Fe}{ii}$ 12 570 Å/16 436 Å line ratio becomes a reliable reddening indicator for the narrow-line region of Seyfert galaxies.
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