arXiv subjects

Jack F. Gallimore

Publications and source records attributed to Jack F. Gallimore.

18 recordsLinked to original sources

arXiv2025

A consistent radio to sub-mm pc-scale study of the nucleus of NGC 1068

The origin of radio emission in radio-quiet (RQ) AGN remains a long-standing mystery. We present a detailed study of the cm to sub-mm emission from the nucleus of the nearby prototypical RQ Seyfert 2 galaxy, NGC 1068. We analyse observations between 4.5-706 GHz using $e$-MERLIN, VLA and ALMA. We restricted all data used for imaging to a matching $uv-$range of 15$-$3300 k$λ$, to ensure that all data sampled the same spatial scales. All images were restored with a $\sim$ 0.06$''$ beam. To derive the spectral energy distribution (SED), we fit synchrotron, free-free, dust and coronal component models to these data. We report that the sub-mm excess between $\sim$ 200-700 GHz is consistent with synchrotron emission from a compact and optically thick corona with a radius $R_\mathrm{c}\approx 70\pm5 \,R_\mathrm{g}$, a fraction of $\sim$\,$10\pm2$% of the energy density in the form of non-thermal electrons, and a magnetic field strength $B\approx 148$ G. The luminosity of the corona is roughly consistent with -- though higher than -- the expected from mm--X-ray correlations derived in recent studies of RQ AGN. This difference is likely due to the corona SED peaking at ($\approx$550 GHz). Between 10 and $\sim$ 200 GHz, the SED is dominated by free-free emission. High angular resolution observations at frequencies below 5 GHz are needed to constrain a putative optically thin synchrotron component and the amount of free-free absorption.

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arXiv2024

The Discovery of Polarized Water Vapor Megamaser Emission in a Molecular Accretion Disk

For the first time in an extragalactic source, we detect linearly polarized water maser emission associated with the molecular accretion disk of NGC 1068. The position angles of the electric polarization vectors are perpendicular to the axes of filamentary structures in the molecular accretion disk. The inferred magnetic field threading the molecular disk must lie within approximately 35 degrees of the sky plane. The orientation of the magnetic fields relative to the disk plane implies that the maser region is unstable to hydromagnetically powered outflow; we speculate that the maser region may be the source of the larger scale molecular outflow found in ALMA studies. The new VLBI observations also reveal a compact radio continuum source, NGC 1068*, aligned with the near-systemic maser spots. The molecular accretion disk must be viewed nearly edge-on, and the revised central mass is (16.6 +/- 0.1) million solar masses.

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arXiv2023

Radio jets in NGC 1068 with e-MERLIN and VLA: structure and morphology

We present new high-sensitivity e-MERLIN and VLA radio images of the prototypical Seyfert 2 galaxy NGC 1068 at 5, 10 and 21 GHz. We image the radio jet, from the compact components NE, C, S1 and S2 to the faint double-lobed jet structure of the NE and SW jet lobes. Furthermore, we map the jet between by combining e-MERLIN and VLA data for the first time. Components NE, C and S2 have steep spectra indicative of optically-thin non-thermal emission domination between 5 and 21 GHz. Component S1, which is where the AGN resides, has a flat radio spectrum. We report a new component, S2a, a part of the southern jet. We compare these new data with the MERLIN and VLA data observed in 1983, 1992 and 1995 and report a flux decrease by a factor of 2 in component C, suggesting variability of this jet component. With the high angular resolution e-MERLIN maps, we detect the bow shocks in the NE jet lobe that coincide with the molecular gas outflows observed with ALMA. The NE jet lobe has enough radio power considered to be responsible for driving out the dense molecular gas observed with ALMA around the same region.

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arXiv2023

High Sensitivity Observations of the Water Megamasers of NGC 1068: Precise Astrometry and Detailed Kinematics

We present High Sensitivity Array observation of the water megamasers of NGC 1068. We obtain absolute astrometry with 0.3 mas precision that confirms the association of the disk masers with the nuclear radio continuum source S1. The new observations reveal two new blueshifted groups of disk masers. We also detect the 22 GHz continuum on short interferometric baselines. The position-velocity diagram of the disk masers shows a curve consistent with a nonaxisymmetric distribution of maser spots. The curve is probably the result of spiral arms with a constant pitch angle of roughly 5 degrees. The disk kinematics are consistent with Keplerian rotation and low turbulent speeds. The inferred central mass is 17 million solar masses. On the basis of disk stability arguments, the mass of the molecular disk is roughly 110 thousand solar masses. The disk masers further resolve into filamentary structures suggesting an ordered magnetic field threading the maser disk. The magnetic field strengths must be greater than 1.6 mG to withstand turbulent motions in the partially ionized molecular gas. We note apparent asymmetries in the molecular disk that might be explained by anisotropic heating by a misaligned inner accretion disk. The new observations also detect the fainter jet masers north of the disk masers. The distribution and kinematics of the jet masers are consistent with an expanding ring of molecular gas.

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arXiv2021

Thermal imaging of dust hiding the black hole in the Active Galaxy NGC 1068

In the widely accepted 'Unified Model' solution of the classification puzzle of Active Galactic Nuclei, the orientation of a dusty accretion torus around the central black hole dominates their appearance. In 'type-1' systems, the bright nucleus is visible at the centre of a face-on torus. In 'type-2' systems the thick, nearly edge-on torus hides the central engine. Later studies suggested evolutionary effects and added dusty clumps and polar winds but left the basic picture intact. However, recent high-resolution images of the archetypal type-2 galaxy NGC 1068 suggested a more radical revision. They displayed a ring-like emission feature which the authors advocated to be hot dust surrounding the black hole at the radius where the radiation from the central engine evaporates the dust. That ring is too thin and too far tilted from edge-on to hide the central engine, and ad hoc foreground extinction is needed to explain the type-2 classification. These images quickly generated reinterpretations of the type 1-2 dichotomy. Here we present new multi-band mid-infrared images of NGC1068 that detail the dust temperature distribution and reaffirm the original model. Combined with radio data, our maps locate the central engine below the previously reported ring and obscured by a thick, nearly edge-on disk, as predicted by the Unified Model. We also identify emission from polar flows and absorbing dust that is mineralogically distinct from that towards the Milky Way centre.

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arXiv2019

Counter-Rotation and High Velocity Outflow in the Parsec-Scale Molecular Torus of NGC 1068

We present 1.4 pc resolution observations of 256 GHz nuclear radio continuum and HCN ($J=3 \to 2$) in the molecular torus of NGC 1068. The integrated radio continuum emission has a flat spectrum consistent with free-free emission and resolves into an X-shaped structure resembling an edge-brightened bicone. HCN is detected in absorption against the continuum, and the absorption spectrum shows a pronounced blue wing that suggests a high-velocity molecular outflow with speeds reaching 450 km/s. Analysis of the off-nucleus emission line kinematics and morphology reveals two nested, rotating disk components. The inner disk, inside $r\sim 1.2$ pc, has kinematics consistent with the nearly edge-on, geometrically thin water megamaser disk in Keplerian rotation around a central mass of $1.66\times 10^7\,\mbox{M}_\odot$. The outer disk, which extends to $\sim 7$~pc radius, counter-rotates relative to the inner disk. The rotation curve of the outer disk is consistent with rotation around the same central mass as the megamaser disk but in the opposite sense. The morphology of the molecular gas is asymmetric around the nuclear continuum source. We speculate that the outer disk formed from more recently introduced molecular gas falling out of the host galaxy or from a captured dwarf satellite galaxy. In NGC 1068, we find direct evidence that the molecular torus consists of counter-rotating and misaligned disks on parsec scales.

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arXiv2017

Variability of the Lowest Mass Objects in the AB Doradus Moving Group

We present the detection of [$3.6~μ$m] photometric variability in two young, L/T transition brown dwarfs, WISE J004701.06+680352.1 (W0047) and 2MASS J2244316+204343 (2M2244) using the \textit{Spitzer Space Telescope}. We find a period of $16.4\pm0.2~$hr and a peak-to-peak amplitude of $1.07\pm0.04\%$ for W0047, and a period of $11\pm2~$hr and amplitude of $0.8\pm 0.2\%$ for 2M2244. This period is significantly longer than that measured previously during a shorter observation. {We additionally detect significant $J$-band variability in 2M2244 using the Wide-Field Camera on UKIRT. } We determine the radial and rotational velocities of both objects using Keck NIRSPEC data. We find a radial velocity of $-16.0_{-0.9}^{+0.8}~$km s$^{-1}$ for 2M2244, and confirm it as a bona fide member of the AB Doradus moving group. We find rotational velocities of $v \sin i=9.8\pm0.3~$km s$^{-1}$and $14.3^{+1.4}_{-1.5}~$km s$^{-1}$ for W0047 and 2M2244, respectively. With inclination angles of $85 ^{+5\circ}_{-9}$ and $76 ^{+14\circ}_{-20}$, W0047 and 2M2244 are viewed roughly equator-on. Their remarkably similar colours, spectra and inclinations are consistent with the possibility that viewing angle may influence atmospheric appearance. We additionally present \textit{Spitzer} $[4.5~μ\mathrm{m}]$ monitoring of the young, T5.5 object SDSS111010+011613 (SDSS1110) where we detect no variability. For periods $<18~$hr, we place an upper limit of $1.25\%$ on the peak-to-peak variability amplitude of SDSS1110.

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arXiv2016

High-Velocity Bipolar Molecular Emission from an AGN Torus

We have detected in ALMA observations CO J = 6 - 5 emission from the nucleus of the Seyfert galaxy NGC 1068. The low-velocity (up to +/- 70 km/s relative to systemic) CO emission resolves into a 12x7 pc structure, roughly aligned with the nuclear radio source. Higher-velocity emission (up to +/- 400 km/s) is consistent with a bipolar outflow in a direction nearly perpendicular (roughly 80 degrees) to the nuclear disk. The position-velocity diagram shows that in addition to the outflow, the velocity field may also contain rotation about the disk axis. These observations provide compelling evidence in support of the disk-wind scenario for the AGN obscuring torus.

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arXiv2009

Infrared Diagnostics for the Extended 12 micron Sample of Seyferts

We present an analysis of Spitzer IRS spectroscopy of 83 active galaxies from the extended 12 micron sample. We find rank correlations between several tracers of star formation which suggest that (1) the PAH feature is a reliable tracer of star formation, (2) there is a significant contribution to the heating of the cool dust by stars, (3) the H$_2$ emission is also primarily excited by star formation. The 55-90 vs. 20-30 spectral index plot is also a diagnostic of the relative contribution of Starburst to AGN. We see there is a large change in spectral index across the sample. Thus, the contribution to the IR spectrum from the AGN and starburst components can be comparable in magnitude but the relative contribution also varies widely across the sample. We find rank correlations between several AGN tracers. We search for correlations between AGN and Starburst tracers and we conclude that the AGN and Starburst tracers are not correlated. This is consistent with our conclusion that the relative strength of the AGN and Starburst components varies widely across the sample. Thus, there is no simple link between AGN fueling and Black Hole Growth and star formation in these galaxies. The distribution of Sil 10 micron and 18 micron strengths is consistent with the clumpy torus models of Sirocky et al. We find a rank correlation between the [NeV] 14 micron line and the 6.7 micron continuum which may be due to an extended component of hot dust. The Sy 2s with a Hidden Broad Line Region (HBLR) have a higher ratio of AGN to Starburst contribution to the SED than Sy 2s without an HBLR. This may contribute to the detection of the HBLR in polarized light. The Sy 2s with an HBLR are more similar to the Sy 1s than they are to the Sy 2s without an HBLR.

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arXiv2006

Spitzer IRS spectra of a large sample of Seyfert galaxies: a variety of infrared SEDs in the local AGN population

We are conducting a large observing program with the Spitzer Space Telescope to determine the mid-to-far infrared spectral energy distributions of a well-defined sample of 87 nearby, 12 micron-selected Seyfert galaxies. In this paper we present the results of IRS low-resolution spectroscopy of a statistically representative subsample of 51 of the galaxies (59%), with an analysis of the continuum shapes and a comparison of the Seyfert types. We find that the spectra clearly divide into groups based on their continuum shapes and spectral features. Some spectral features are clearly related to a starburst contribution to the IR spectrum, while the mechanisms producing observed power-law continuum shapes, attributed to an AGN component, may be dust or non-thermal emission. The infrared spectral types appear to be related to the Seyfert types. Principal component analysis results suggest that the relative contribution of starburst emission may be the dominant cause of variance in the observed spectra. We find that Sy 1's have higher ratios of IR/radio emission than Sy 2's, as predicted by the unified model if the torus is optically thick in the mid-IR. However, smooth-density torus models predict a much larger difference between type 1's and 2's than observed in our sample. Our observations may be consistent with clumpy torus models containing a steep radial distribution of optically thick dense clumps. (Abridged)

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arXiv2006

Infrared SEDs of Seyfert Galaxies: Starbursts and the Nature of the Obscuring Medium

We present the results of IRS low-resolution spectroscopy of 51 Seyfert galaxies, part of a large Spitzer observing program to determine the mid-to-far infrared spectral energy distributions of a well-defined sample of 87 nearby, 12 micron-selected Seyferts. We find that the spectra clearly divide into groups based on their continuum shapes and spectral features. The infrared spectral types appear to be related to the Seyfert types. Some features are clearly related to a starburst contribution to the IR spectrum, while the observed power-law continuum shapes, attributed to the AGN, may be dust or non-thermal emission. Principal component analysis results suggest that the relative contribution of starburst emission is the dominant cause of variance in the spectra. We find that the Sy 2's show on average stronger starburst contributions than the Sy 1's.

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arXiv2005

VLBA Identification of the Milliarcsecond Active Nucleus in the Seyfert Galaxy NGC 4151

The Seyfert galaxy NGC 4151 has been imaged at resolution better than 0.1 pc using a VLBI array consisting of the VLBA and three 100m-class telescopes. A flat-spectrum 3-mJy source with a monochromatic radio power of ~10^{37} ergs/s has been detected, apparently at the location of the active galactic nucleus (AGN) and its central black hole. The radio source has a minimum brightness temperature of 2.1 x 10^8 K and a size upper limit of 0.035 pc, about 10 times the diameter of the broad-line region and 15,000 times the diameter of the black hole's event horizon. An additional flat-spectrum component located within a parsec of the apparent nucleus is likely to be a knot in the inner radio jet. The presence of some steep-spectrum radio emission within 0.1 pc of the galaxy nucleus limits the emission measure of a possible ionized torus to a maximum value of 10^8 cm^{-6}pc. If the hard X-ray source in NGC 4151 is associated with the radio AGN, its radio to X-ray ratio is less than 10^{-5}, putting NGC 4151 securely in the radio-quiet class of AGNs. The radio image reveals a 0.2 pc two-sided base to the well-known arcsecond radio jet. Apparent speeds of jet components relative to the radio AGN are <0.050c and <0.028c at respective nuclear distances of 0.16 pc and 6.8 pc. These are the lowest speed limits yet found for a Seyfert galaxy, and indicate non-relativistic jet motions, possibly due to thermal plasma, on a scale only an order of magnitude larger than the broad-line region.

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arXiv2005

An Atlas of Warm AGN and Starbursts from the IRAS Deep Fields

We present 180 AGN candidates based on color selection from the IRAS slow-scan deep observations, with color criteria broadened from the initial Point-Source Catalog samples to include similar objects with redshifts up to z=1 and allowing for two-band detections. Spectroscopic identifications have been obtained for 80 (44%); some additional ones are secure based on radio detections or optical morphology, although yet unobserved spectroscopically. These spectroscopic identifications include 13 Sy 1 galaxies, 17 Sy 2 Seyferts, 29 starbursts, 7 LINER systems, and 13 emission-line galaxies so heavily reddened as to remain of ambiguous classification. The optical magnitudes range from R=12.0-20.5; counts suggest that incompleteness is important fainter than R=15.5. Redshifts extend to z=0.51, with a significant part of the sample at z>0.2. The sample includes slightly more AGN than star-forming systems among those where the spectra contain enough diagnostic feature to make the distinction. The active nuclei include several broad-line objects with strong Fe II emission, and composite objects with the absorption-line signatures of fading starbursts. These AGN with warm far-IR colors have little overlap with the "red AGN" identified with 2MASS; only a single Sy 1 was detected by 2MASS with J-K > 2. Some reliable IRAS detections have either very faint optical counterparts or only absorption-line galaxies, potentially being deeply obscured AGN. The IRAS detections include a newly identified symbiotic star, and several possible examples of the "Vega phenomenon", including dwarfs as cool as type K. Appendices detail these candidate stars, and the optical-identification content of a particularly deep set of high-latitude IRAS scans (probing the limits of optical identification from IRAS data alone).

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arXiv2004

The Parsec-scale Radio Structure of NGC 1068 and the Nature of the Nuclear Radio Source

We present sensitive, multifrequency Very Long Baseline Array (VLBA) images of the nuclear radio sources of NGC 1068. At 5 GHz and 8.4 GHz, the radio continuum source S1, argued to mark the location of the hidden active nucleus, resolves into an elongated, ~ 0.8 pc source oriented nearly at right angles to the radio jet axis but more closely aligned to the distribution of the nuclear H2O maser spots. S1 is detected at 5 GHz but not at 1.4 GHz, indicating strong free-free absorption below 5 GHz, and it has a flat spectrum between 5 GHz and 8.4 GHz. A 5/8.4 GHz spectral index map reveals an unresolved, inverted spectrum source at the center of the S1 structure which may mark the AGN proper. The average brightness temperature is too low for synchrotron self-absorption to impact the integrated spectrum significantly. In addition, a careful registration with the nuclear H2O masers argues that the S1 continuum source arises from the inner regions of the maser disk rather than a radio jet. The emission mechanism may be direct, thermal free-free emission from an X-ray-heated corona or wind arising from the molecular disk. We demonstrate that the hidden active nucleus is sufficiently luminous, to within the current estimates, to provide the requisite heating.

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arXiv2003

Parsec-Scale Radio Structure of the Double Active Nucleus of NGC 6240

NGC 6240 is a luminous infrared galaxy that, based on recent MERLIN and CHANDRA observations, appears to host a pair of active galactic nuclei. We present new, multiepoch and multifrequency radio observations of NGC 6240 obtained using the Very Long Baseline Array (VLBA). These observations resolve out all of the diffuse radio continuum emission related to starburst activity to reveal three compact sources, two associated with the infrared and X-ray nuclei: components N1, the northern nucleus, and S, the southern nucleus; and component S1, a weak point source lying northeast of component S. The radio continuum properties of N1 and S both resemble those of compact radio sources in Seyfert nuclei, including an inverted spectrum at low frequencies and high brightness temperatures. Component N1 further resolves into a 9 pc linear source, again resembling compact jets in some well-studied Seyfert nuclei. The inverted radio spectrum is most likely caused by free-free absorption through foreground plasma with emission measures of order 1E7 cm^(-6) pc, consistent with the X-ray spectroscopy which infers the presence of a foreground, Compton thick absorber. Synchrotron self-absorption may also contribute to the flat spectrum of component S. Component S1 better resembles a luminous radio supernova such as those detected in Arp 220, although we cannot specifically rule out the possibility that S1 may be ejected material from the southern active nucleus. We demonstrate that the light curve of S1 is at least consistent with current radio supernova models, and, given the high star-formation rate in the nuclear region and the (possible) proclivity of infrared merger galaxies to produce luminous RSNe, it is not surprising that one such supernova is detected serendipitously in the VLBA observations.

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arXiv2000

Discovery of a very luminous megamaser during a radio flare in the Seyfert 2 galaxy Mrk 348

We report the detection of a new H_2O megamaser in the Seyfert 2 galaxy Mrk 348 with the MPIfR 100 m telescope in Effelsberg. With an apparent isotropic luminosity of L_H2O ~ 420 L_sun the maser is the third most luminous maser discovered so far. The detected line is unusually broad (Delta v ~ 130 km/s), is redshifted by ~130 km/s from the systemic velocity, and is asymmetric with a pronounced blue wing. While evidence for obscuring material towards the nucleus of this galaxy was found earlier, this detection is the first direct observation of molecular material in the vicinity of the AGN. We also searched for absorption from ammonia (NH_3) and cyclopropenylidene (C_3H_2) against the bright radio nucleus. The H_2O line was only marginally detected in archival data indicating that the maser flared recently in conjunction with a huge radio continuum flare. Continuum and line flux density increased by a factor of three, suggesting an unsaturated maser. The radio continuum flare has made Mrk 348 the most radio luminous megamaser galaxy known. It is pointed out that megamaser galaxies contain a rather large fraction of galaxies with prominent radio cores and it is speculated that the flare in the maser emission in Mrk 348 is related to the flare in the nuclear jet.

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arXiv1999

Radio Structures of Seyfert Galaxies. VIII. A Distance and Magnitude Limited Sample of Early-Type Galaxies

The VLA has been used at 3.6 and 20 cm to image a sample of about 50 early-type Seyfert galaxies with recessional velocities less than 7,000 km/s and total visual magnitude less than 14.5. The nuclear radio structures of Seyfert 2.0's in the early-type sample tend to be aligned with the [OIII] and Halpha+[NII] structures even though the radio extents are smaller than the [OIII] and Halpha+[NII] extents by a factor of ~2->5. This alignment, previously known for individual Seyferts with `linear' radio sources, is here shown to be characteristic of early-type Seyfert galaxies as a class. Seyfert 2.0's in the early-type sample also show a significant alignment between the emission-line ([OIII] and Halpha+[NII]) axes and the major axis of the host galaxy. These alignments are consistent with a picture in which the ionized gas represents ambient gas predominantly co-planar with the galaxy stellar disk. This ambient gas is ionized by nuclear radiation that may escape preferentially along and around the radio axis, and is compressed in shocks driven by the radio ejecta. We use this alignment to constrain the product of the velocity of the radio ejecta and the period of any large angle precession of the inner accretion disk and jet : V_ejecta x P >= 2 kpc. An investigation of a larger sample of Seyferts reveals the unexpected result that the Seyfert 1's with the largest radio extent (>= 1.5 kpc) are all of type Seyfert 1.2. It appears that classification as this type of intermediate Seyfert depends on some factor other than the relative orientation of the nuclear obscuring torus to the line of sight.

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arXiv1997

A direct image of the obscuring disk surrounding an active galactic nucleus

Active galactic nuclei (AGN) are generally accepted to be powered by the release of gravitational energy in a compact accretion disk surrounding a massive black hole. Such disks are also necessary to collimate powerful radio jets seen in some AGN. The unifying classification schemes for AGN further propose that differences in their appearance can be attributed to the opacity of the accreting material, which may obstruct our view of the central region of some systems. The popular model for the obscuring medium is a parsec-scale disk of dense molecular gas, although evidence for such disks has been mostly indirect, as their angular size is much smaller than the resolution of conventional telescopes. Here we report the first direct images of a pc-scale disk of ionised gas within the nucleus of NGC 1068, the archetype of obscured AGN. The disk is viewed nearly edge-on, and individual clouds within the ionised disk are opaque to high-energy radiation, consistent with the unifying classification scheme. In projection, the disk and AGN axes align, from which we infer that the ionised gas disk traces the outer regions of the long-sought inner accretion disk.

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