Abstract
Diffuse ionized gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on star-forming galaxies observed by Mapping Nearby Galaxies at APO, we demonstrate how DIG ...in star-forming galaxies impacts the measurements of emission-line ratios, hence the interpretation of diagnostic diagrams and gas-phase metallicity measurements. At fixed metallicity, DIG-dominated low ΣHα regions display enhanced S ii/Hα, N ii/Hα, O ii/Hβ and O i/Hα. The gradients in these line ratios are determined by metallicity gradients and ΣHα. In line ratio diagnostic diagrams, contamination by DIG moves H ii regions towards composite or low-ionization nuclear emission-line region (LI(N)ER)-like regions. A harder ionizing spectrum is needed to explain DIG line ratios. Leaky H ii region models can only shift line ratios slightly relative to H ii region models, and thus fail to explain the composite/LI(N)ER line ratios displayed by DIG. Our result favours ionization by evolved stars as a major ionization source for DIG with LI(N)ER-like emission. DIG can significantly bias the measurement of gas metallicity and metallicity gradients derived using strong-line methods. Metallicities derived using N2O2 are optimal because they exhibit the smallest bias and error. Using O3N2, R
23, N2 = N ii/Hα and N2S2Hα to derive metallicities introduces bias in the derived metallicity gradients as large as the gradient itself. The strong-line method of Blanc et al. (IZI hereafter) cannot be applied to DIG to get an accurate metallicity because it currently contains only H ii region models that fail to describe the DIG.
We have mapped the stellar and gaseous kinematics, as well as the emission-line flux distributions and ratios, from the inner ≈450 pc radius of the Seyfert 2 galaxy Mrk 1157, using two-dimensional ...near-infrared J- and Kl
-band spectra obtained with the Gemini Near-Infrared Integral-Field Spectrograph instrument at a spatial resolution of ≈35 pc and velocity resolution of ≈40 km s−1.
The stellar velocity field shows a rotation pattern, with a discrete S-shaped zero velocity curve - a signature of a nuclear bar. The presence of a bar is also supported by the residual map between the observed rotation field and a model of circular orbits in a Plummer potential. The stellar velocity dispersion (σ*) map presents a partial ring of low-σ* values (50-60 km s−1) at 250 pc from the nucleus surrounded by higher σ* values from the galaxy bulge. We propose that this ring has origin in kinematically colder regions with recent star formation. The stellar velocity dispersion of the bulge (100 km s−1) implies in a black hole mass of M
BH= 8.3+3.2
− 2.2× 106 M⊙.
Emission-line flux distributions are most extended along the position angle PA = 27°/153°, reaching at least 450 pc from the nucleus and following the orientation observed in previous optical emission-line O iii imaging and radio jets. The molecular hydrogen gas has an excitation temperature T
exc≈ 2300 K and its emission is dominated by thermal processes, mainly due to X-ray heating by the active nucleus, with a possible small contribution from shocks produced by the radio jet. The Fe ii excitation has a larger contribution from shocks produced by the radio jet, as evidenced by the line-ratio maps and velocity dispersion maps, which show spatial correlation with the radio structures. The coronal lines are resolved, extending up to ≈150 pc and are also slightly more extended along PA = 27°/153°.
The gaseous kinematics show two components: one due to the gas located in the galaxy plane, in similar rotation to that of the stars, and another in outflow, which is oriented close to the plane of the sky, thus extending to high latitudes, as the galaxy plane is inclined by ≈45° relative to the plane of the sky. The gas rotating in the plane dominates the H2 and Paβ emission, while the gas in outflow is observed predominantly in Fe ii emission. The Fe ii emission is originated in gas being pushed by the radio jet, which destroys dust grains, releasing Fe. From the outflow velocities and implied geometry, we estimate a mass-outflow rate of
for the ionized gas and a kinetic power for the outflow of
.
The distinct flux distributions and kinematics of the H2- and Fe ii-emitting gas, with the former more restricted to the plane of the galaxy and the latter tracing the outflows related to radio jets, are a common characteristic of six Seyfert galaxies (ESO 428-G14, NGC 4051, 7582 and 4151, Mrk 1066, and now Mrk 1157) we have studied so far using similar two-dimensional observations and other two (Circinus and NGC 2110) using long-slit observations. We conclude that the H2 emission surrounding the nucleus in the galaxy plane is a tracer of the gas feeding to the active nucleus, while the Fe ii emission is a tracer of its feedback.
We perform an exploratory study of the physical properties of accretion flows and jets in low-luminosity active galactic nuclei (LLAGNs) by modelling the spectral energy distributions (SEDs) of 12 ...LLAGNs in low-ionization nuclear emission-line regions (LINERs). These SEDs we constructed from high-resolution radio, X-ray and optical/ultraviolet (UV) observations of the immediate vicinity of the black hole. We adopt a coupled accretion-jet model comprising an inner advection-dominated accretion flow (ADAF) and an outer standard thin disc. We present best-fitting models in which either the ADAF or the jet dominates the X-ray emission. Six sources in our sample display an optical-UV excess with respect to ADAF and jet models; this excess can be explained as emission from the truncated disc with transition radii 30-225 R
S
in four of them. In almost all sources the optical emission can also be attributed to unresolved, old stellar clusters with masses ∼107-108 M. We find evidence for a correlation between the accretion rate and jet power and an anticorrelation between the radio loudness and the accretion rate. We confirm previous findings that the radio emission is severely underpredicted by ADAF models and explained by the relativistic jet. We find evidence for a non-linear relation between the X-ray and bolometric luminosities and a slight IR excess in the average model SED compared to that of quasars. We suggest that the hardness of the X-ray spectrum can be used to identify the X-ray emission mechanism and discuss directions for progress in understanding the origin of the X-rays.
We present 2D stellar and gaseous kinematics of the inner ∼130×180 pc2 of the Narrow-Line Seyfert 1 galaxy NGC 4051 at a sampling of 4.5 pc, from near-infrared K-band spectroscopic observations ...obtained with the Gemini's Near-infrared Integral Field Spectrograph (NIFS) operating with the ALTAIR adaptive optics module. We have used the CO absorption band heads around 2.3 μm to obtain the stellar kinematics which show the turnover of the rotation curve at only ≈55 pc from the nucleus, revealing a highly concentrated gravitational potential. The stellar velocity dispersion of the bulge is ≈60 km s−1– implying on a nuclear black hole mass of ≈106M⊙– within which patches of lower velocity dispersion suggest the presence of regions of more recent star formation. From measurements of the emission-line profiles we have constructed 2D maps for the flux distributions, line ratios, radial velocities and gas velocity dispersions for the H2, H ii and Ca viii emitting gas. Each emission-line samples a distinct kinematics. The Brγ emission-line shows no rotation as well as no blueshifts or redshifts in excess of 30 km s−1, and is thus not restricted to the galaxy plane. The Ca viii coronal region is compact but resolved, extending over the inner 75 pc. It shows the highest blueshifts – of up to −250 km s−1, and the highest velocity dispersions, interpreted as due to outflows from the active nucleus, supporting an origin close to the nucleus. Subtraction of the stellar velocity field from the gaseous velocity field has allowed us to isolate non-circular motions observed in the H2 emitting gas. The most conspicuous kinematic structures are two nuclear spiral arms – one observed in blueshift in the far side of the galaxy (to the north-east), and the other observed in redshift in the near side of the galaxy (to the south-west). We interpret these structures as inflows towards the nucleus, a result similar to those of previous studies in which we have found streaming motions along nuclear spirals in ionized gas using optical Integral Filed Unit (IFU) observations. We have calculated the mass inflow rate along the nuclear spiral arms, obtaining , a value ∼100 times smaller than the accretion rate necessary to power the active nucleus. This can be understood as due to the fact that we are only seeing the hot ‘skin’ (the H2 emitting gas) of the total mass inflow rate, which is probably dominated by cold molecular gas. From the H2 emission-line ratios we conclude that X-ray heating can account for the observed emission, but the H2 λ2.1218 μm/Br γ line ratio suggests some contribution from shocks in localized regions close to the compact radio jet.
We present stellar and gaseous kinematics of the inner ≈350-pc radius of the Seyfert galaxy Mrk 1066 derived from J and K
l bands data obtained with the Gemini's Near-Infrared Integral Field ...Spectrograph (NIFS) at a spatial resolution of ≈35 pc. The stellar velocity field is dominated by rotation in the galaxy plane but shows an S-shape distortion along the galaxy minor axis which seems to be due to an oval structure seen in an optical continuum image. Along this oval, between 170 and 280 pc from the nucleus we find a partial ring of low σ* (≈50 km s−1) attributed to an intermediate-age stellar population. The velocity dispersion of the stellar bulge (σ*≈ 90 km s−1) implies a supermassive black hole mass of ≈5.4 × 106 M⊙. From measurements of the emission-line fluxes and profiles (P iiλ 1.1886 μm, Fe iiλ 1.2570 μm, Paβ and H2λ 2.1218 μm), we have constructed maps for the gas centroid velocity, velocity dispersion as well as channel maps. The velocity fields for all emission lines are dominated by a similar rotation pattern to that observed for the stars, but are distorted by the presence of two structures: (i) a compact rotating disc with radius r≈ 70 pc; (ii) outflows along the radio jet which is oriented approximately along the galaxy major axis. The compact rotating disc is more conspicuous in the H2 emitting gas, which presents the smallest σ values (≤70 km s−1) and most clear rotation pattern, supporting a location in the galaxy plane. We estimate a gas mass for the disc of ∼107 M⊙. The H2 kinematics further suggests that the nuclear disc is being fed by gas coming from the outer regions. The outflow is more conspicuous in the Fe ii emitting gas, which presents the highest σ values (up to 150 km s−1) and the highest blue and redshifts of up to 500 km s−1, while the highest stellar rotation velocity is only ≈130 km s−1. We estimate a mass-outflow rate in ionized gas of ≈6 × 10−2 M⊙ yr−1. The derived kinematics for the emitting gas is similar to that observed in previous studies supporting that the H2 is a tracer of the active galactic nucleus feeding and the Fe ii of its feedback.
We present integral field spectroscopy of the inner 700 × 700 pc2 of the Seyfert galaxy Mrk 1066 obtained with Gemini's Near-Infrared Integral Field Spectrograph (NIFS) at a spatial resolution of ≈35 ...pc. This high spatial resolution allowed us to observe, for the first time in this galaxy, an unresolved dust concentration with mass ∼1.4 × 10−2 M⊙. This unresolved concentration, with emission well reproduced by a blackbody with temperature ∼830 K, is possibly part of the nuclear dusty torus. We compared maps of emission-line flux distributions and ratios with a 3.6 cm radio-continuum image and O iii image in order to investigate the origin of the near-infrared emission. The emission-line fluxes are elongated in PA = 135°/315° in agreement with the O iii and radio images and, except for the H lines, are brighter to the north-west than to the south-east. This close association with the radio hot spot implies that at least part of the emitting gas is co-spatial with the radio outflow. The H emission is stronger to the south-east, where we find a large region of star-formation. The strong correlation between the radio emission and the highest emission-line fluxes indicates that the radio jet plays a fundamental role at these intensity levels. At lower emission-line fluxes this correlation disappears suggesting a contribution from the plane of the galaxy to the observed emission. The H2 flux is more uniformly distributed and has an excitation temperature of ≈2100 K. Its origin appears to be circum-nuclear gas heated by X-rays from the central active nucleus. The Fe ii emission also is consistent with X-ray heating, but its spatial correlation with the radio jet and O iii emission indicates additional emission due to excitation and/or abundance changes caused by shocks in the radio jet. The coronal-line emission of Ca viii and S ix is unresolved by our observations indicating a distribution within 18 pc from the nucleus. The reddening map obtained via the Paβ/Brγ line ratio ranges from E(B−V) ≈ 0 to 1.7 with the highest values defining a S-shaped structure along PA ≈ 135°/315°. The emission-line ratios are Seyfert-like within the ionization cone indicating that the line emission is powered by the central active nucleus in these locations. Low ionization regions are observed away from the ionization cone, and may be powered by the diffuse radiation field which filters through the ionization cone walls. Two regions at 0.5 arcsec south-east and at 1 arcsec north-west of the nucleus show starburst-like line ratios, co-spatial with an enhancement in the emission of the H lines. We attribute this change to additional emission from star-forming regions. The mass of ionized gas is MH II≈ 1.7 × 107 M⊙ and that of hot molecular gas is .
We present near-infrared emission-line flux distributions, excitation and kinematics, as well as stellar kinematics, of the inner 520 × 520 pc2 of the Seyfert 2 galaxy NGC 5929. The observations were ...performed with Gemini's Near-Infrared Integral Field Spectrograph (NIFS) at a spatial resolution of ∼20 pc and spectral resolution of 40 km s− 1 in the J and K
l bands. The flux distributions of H2, Fe ii, P ii and H recombination lines are extended over most of the field of view, with the highest intensity levels observed along PA = 60/240°, and well correlated with the radio emission. The H2 and Fe ii line emission originated in thermal processes, mainly due to heating of the gas by X-rays from the central active galactic nucleus (AGN). The contribution of shocks due to the radio jet is observed at locations co-spatial with the radio hotspots at 0.50 arcsec north-east and 0.60 arcsec south-west of the nucleus, as evidenced by the emission-line ratio and gas kinematics. The stellar kinematics shows rotation with an amplitude at 250 pc from the nucleus of ∼200 km s− 1 after correcting for the inferred inclination of 18.3°. The stellar velocity dispersion obtained from the integrated K-band spectrum is σ* = 133 ± 8 km s− 1, which implies a mass for the supermassive black hole of
$M_\bullet = 5.2^{1.6}_{-1.2} \times 10^7\,{\rm M_{{\odot }}}$
, using the M
•–σ* relation. The gas kinematics present three components: (1) gas in the plane of the galaxy in counter-rotation relative to the stars; (2) an outflow perpendicular to the radio jet that seems to be due to an equatorial AGN outflow; and (3) turbulence of the gas observed in association with the radio hotspots, supporting an interaction of the radio jet with the gas of the disc. We estimated the masses of ionized gas and warm molecular gas to be ∼1.3 × 106 M⊙ and ∼470 M⊙, respectively.
We have conducted an archival Spitzer study of 38 early-type galaxies in order to determine the origin of the dust in approximately half of this population. Our sample galaxies generally have good ...wavelength coverage from 3.6 mu m to 160 mu m, as well as visible-wavelength Hubble Space Telescope (HST) images. We use the Spitzer data to estimate dust masses, or establish upper limits, and find that all of the early-type galaxies with dust lanes in the HST data are detected in all of the Spitzer bands and have dust masses of ~105-106.5 M, while galaxies without dust lanes are not detected at 70 mu m and 160 mu m and typically have <105 M of dust. We propose that dust in early-type galaxies is seeded by external accretion, yet the accreted dust is maintained by continued growth in externally accreted cold gas beyond the nominal lifetime of individual grains. As the majority of dusty early-type galaxies are also low-luminosity active galactic nuclei and likely fueled by this cold gas, their lifetime should similarly be several Gyr.
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