Low-ionization Emission-line Regions Research Articles

CAHA/PPAK Integral-field Spectroscopic Observations of M81. II. Testing Photoionization Models in a Spatially Resolved LINER

The origin of the low-ionization nuclear emission-line region (LINER) prevalent in local galaxies and its relationship with supermassive black holes have been debated for decades. We perform a comprehensive evaluation of traditional photoionization models against the circumnuclear ionized gas in M81, for which recent CAHA/PPAK integral-field spectroscopic observations reveal a LINER characteristic out to a galactocentric radius of ∼1 kpc. Constructed with the photoionization code cloudy, the models have the novel aspect of their primary parameters being well constrained by extensive observations of a prototypical low-luminosity active galactic nucleus (LLAGN) and an old stellar bulge in M81. Additionally, these models incorporate a reasonably broad range of uncertain nebular properties. It is found that the integrated photoionization by the LLAGN and hot, low-mass stars distributed in the bulge can roughly reproduce the observed radial intensity distributions of the Hα, Hβ, and [N ii] lines, with the bulge stars dominating the ionizing flux at radii ≳200 pc. However, the models generally fail to reproduce a similarly declining profile of the [O iii] line or an accordingly flat profile of the [O iii]/Hβ ratio. This clearly points to a deficiency of ionizing photons in the outer regions despite an extended photoionization source. The discrepancy might be alleviated if much of the observed [O iii] line arose from a bulge-filling, low-density gas surrounding a denser, Hα-emitting disk, or by a higher AGN luminosity in the recent past. The case of M81 has important implications for the ionization mechanism of LINERs and low-ionization emission-line regions in general.

SDSS-IV MaNGA: Refining Strong Line Diagnostic Classifications Using Spatially Resolved Gas Dynamics

Abstract We use the statistical power of the MaNGA integral-field spectroscopic galaxy survey to improve the definition of strong line diagnostic boundaries used to classify gas ionization properties in galaxies. We detect line emission from 3.6 million spaxels distributed across 7400 individual galaxies spanning a wide range of stellar masses, star formation rates, and morphological types, and find that the gas-phase velocity dispersion σ Hα correlates strongly with traditional optical emission-line ratios such as [S ii]/Hα, [N ii]/Hα, [O i]/Hα, and [O iii]/Hβ. Spaxels whose line ratios are most consistent with ionization by galactic H ii regions exhibit a narrow range of dynamically cold line-of-sight velocity distributions (LOSVDs) peaked around 25 km s−1 corresponding to a galactic thin disk, while those consistent with ionization by active galactic nuclei (AGNs) and low-ionization emission-line regions (LI(N)ERs) have significantly broader LOSVDs extending to 200 km s−1. Star-forming, AGN, and LI(N)ER regions are additionally well separated from each other in terms of their stellar velocity dispersion, stellar population age, Hα equivalent width, and typical radius within a given galaxy. We use our observations to revise the traditional emission-line diagnostic classifications so that they reliably identify distinct dynamical samples both in two-dimensional representations of the diagnostic line ratio space and in a multidimensional space that accounts for the complex folding of the star-forming model surface. By comparing the MaNGA observations to the SDSS single-fiber galaxy sample, we note that the latter is systematically biased against young, low-metallicity star-forming regions that lie outside of the 3″ fiber footprint.

H i galaxies with little star formation: an abundance of LIERs

Abstract We present a sample of 91 H i galaxies with little or no star formation, and discuss the analysis of the integral field unit (IFU) spectra of 28 of these galaxies. We identified H i galaxies from the H i Parkes All-Sky Survey Catalog (HICAT) with Wide-field Infrared Survey Explorer (WISE) colours consistent with low specific star formation (<10−10.4 yr−1), and obtained optical IFU spectra with the Wide-Field Spectrograph (WiFeS). Visual inspection of the PanSTARRS, Dark Energy Survey, and Carnegie-Irvine imaging of 62 galaxies reveals that at least 32 galaxies in the sample have low levels of star formation, primarily in arms/rings. New IFU spectra of 28 of these galaxies reveals 3 galaxies with central star formation, 1 galaxy with low-ionization nuclear emission-line regions (LINERs), 20 with extended low-ionization emission-line regions (LIERs), and 4 with high excitation Seyfert (Sy) emission. From the spectroscopic analysis of H i selected galaxies with little star formation, we conclude that 75 per cent of this population are LINERs/LIERs.

MAPPING SEYFERT AND LINER EXCITATION MODES IN THE INNER KPC OF NGC 3393

ABSTRACT We mapped the extended narrowline region (ENLR) of NGC 3393 on scales of ( kpc) from the nucleus using emission line images of Hα λ6563, [O iii] , and [S ii] , taken with the Hubble Space Telescope as part of the CHandra survey of Extended Emission line Regions in nearby Seyfert galaxies (CHEERS). By mapping these lines onto a spatially resolved Baldwin–Phillips–Terlevich diagram, we investigate the impact of feedback from a Compton-thick active galactic nucleus on its circumnuclear ISM. We find that the expected Seyfert-like emission within the ionization bicone ( 770 pc). We also find a new, figure-8-shaped low ionization emission line region (LINER) cocoon enveloping the bicone and defining a sharp ( pc) transition between higher and lower-ionization zones. These data illustrate the morphological dependence of ionization states of the ENLR relative to bicone and host gas geometries.

X-ray and multiwavelength view of NGC 4278

(Abridged) Based on UV to X-ray and radio to UV flux ratios, some argue that low ionization emission line regions (LINERs) and low luminosity AGN (LLAGN) are a scaled-down version of their more luminous predecessors Seyfert galaxies. Others, based on the lack of X-ray short (hours) time-scale variability, the non-detection of an iron line at 6.4 keV, and the faint UV emission, suggest the truncation of the classical thin accretion disk in the inner regions of the AGN where a radiatively inefficient accretion flow (RIAF) structure forms. We investigate the LINER-Seyfert connection by studying the unabsorbed, AGN powered, LINER galaxy NGC 4278. We analyzed one XMM-Newton and seven Chandra X-ray observations of NGC 4278 spread over a three year period. We detected a flux increase by a factor of ~3 on a ~3 months time-scale and by a factor of 5 between the faintest and the brightest observation separated by ~3 years. During only the XMM-Newton observation, where the highest flux level is detected, we found a 10% flux increase on a ~1 hour time-scale. A combination of an absorbed power law (N(H)~10^20 cm^-2, Gamma~2.2) plus a thermal component (kT~0.6 keV) were able to fit the Chandra spectra. The XMM-Newton spectra, where the highest X-ray flux is detected, are well fitted with a single absorbed power-law. No Fe K(alpha) emission line is detected at 6.4 keV. We constructed SEDs based on simultaneous or quasi simultaneous observations and compared them to LINER, radio-loud, and radio-quiet quasar SEDs. We find that at a low X-ray flux the NGC 4278 SED resembles that of typical LINER sources where the radio to X-ray emission can be considered as originating from a jet and/or RIAF, whereas at a high X-ray flux, NGC 4278 SED is more like a low luminosity Seyfert SED. Consequently, NGC 4278 could exhibit both LINER and Seyfert nuclear activity depending on the strength of its X-ray emission.

High-Ionization Nuclear Emission-Line Region in the Seyfert Galaxy Tololo 0109−383

We present a detailed optical spectroscopic analysis of the high-ionization Seyfert galaxy Tololo 0109-383, which was classified originally as a type 2 Seyfert nucleus. The high-ionization nuclear emission-line region (HINER) (traced by e.g., [Fe X] λ6374) of this galaxy is found to be spatially extended. Although the total radial extent of the HINER amounts to ~1.1 kpc, ~70% of the HINER emission is concentrated in the inner 220 pc in radius. The inner HINER in Tololo 0109-383 can be interpreted by the photoionization model of Ferguson, Korista, & Ferland, while the extended HINER suggests that low-density interstellar medium is also photoionized by high-energy continuum emission as described by Korista & Ferland. We find an extended low-ionization emission line region traced by Hα, [N II], and [S II] emission lines with very narrow widths (<200 km s-1) at ~2.2 kpc east of the nucleus. This region is characterized by (1) the observed [N II]/Hα ratio, which is ~0.8; (2) no measurable [O III] emission; and (3) a low ionization parameter, U ~ 6 × 10-5. These properties can also be interpreted in terms of a photoionization model. As well as confirmation of the presence of broad emission in both Hα and Hβ lines, we also find optical Fe II emission features in our spectra. Since the optical Fe II emission is one of the important characteristics of type 1 active galactic nuclei, it is shown that Tololo 0109-383 harbors a type 1 central engine in its nucleus. Since the soft X-ray–to–infrared (60 μm) luminosity ratio of Tololo 0109-383 is higher than those of typical type 2 Seyfert nuclei, we consider that blocking by a dusty torus may be incomplete and thus we are able to observe the type 1 nature of Tololo 0109-383.

THE CONTINUUM INFRARED EMISSION OF AGN

ABSTRACT Far-infrared observations, obtained with the Infrared Astronomical Satellite, have shown intense IR emission in AGNs. Analyzing a sample composed of Seyfert 2 galaxies, narrow-line radio galaxies and LINERs (Low Ionization Emission-line Region), we show that the IR continua of these objects are not significantly contaminated by the emission lines, in contrast with planetary nebulae and H II regions. Studying the IR continua of Sy 2, and determining their thermal and non-thermal components, we conclude that the IR emission is mainly due to thermal reradiation by dust heated by the central source, and distributed in the narrow line region (NLR) with an estimated mass of the order of 20 to 80 solar mass. Furthermore, comparing the relative IRAS fluxes of these AGN, including starburst galaxies (SBG), we found that Sy 2 have the most luminous IR nuclei, followed by NLRG, SBG and LINERs. This sequence can be understood on the basis of the importance of the dust contribution to the IR-continuum of each object.

A redshift difference between high and low ionization emission-line regions in QSOs - Evidence for radial motions

The discovery of a systematic difference between the redshifts of the emission lines arising from the different ionization zones of broad-line quasar clouds is reported. The C UFscmcapsiv, N UFscmcapsv, C UFscmcapsiii), (Fe,UFscmcapsx), (Fe UFscmcapsxi), and possibly Lyman-..cap alpha.. lines are at a lower redshift than the O UFscmcapsi, Mg UFscmcapsii, and Balmer lines. Comparison with the redshifts of the narrow emission lines shows that it is the high-ionization broad emission lines that are systematically blueshifted by 600 km s/sup -1/. This blueshift together with the high degree of symmetry of the high-ionization lines strongly constrains models of the broad emission line region. The blueshifting of the strongest emission lines readily observable in high-redshift quasars will affect the number of absorption-line systems which appear to have z/sub a/bs> or =z/sub e/m.