Abstract
We present a case study of HE 0040-1105, an unobscured radio-quiet active galactic nucleus (AGN) at a high accretion rate of
λ
Edd
= 0.19 ± 0.04. This particular AGN hosts an ionized gas ...outflow with the largest spatial offset from its nucleus compared to all other AGNs in the Close AGN Reference Survey. By combining multiwavelength observations from the Very Large Telescope/MUSE, Hubble Space Telescope/Wide Field Camera 3, Very Large Array, and European VLBI Network, we probe the ionization conditions, gas kinematics, and radio emission from host galaxy scales to the central few parsecs. We detect four kinematically distinct components, one of which is a spatially unresolved AGN-driven outflow located within the central 500 pc, where it locally dominates the interstellar medium conditions. Its velocity is too low to escape the host galaxy’s gravitational potential, and may be re-accreted onto the central black hole via chaotic cold accretion. We detect compact radio emission in HE 0040-1105 within the region covered by the outflow, varying on a timescale of ∼20 yr. We show that neither AGN coronal emission nor star formation processes wholly explain the radio morphology/spectrum. The spatial alignment between the outflowing ionized gas and the radio continuum emission on 100 pc scales is consistent with a weak jet morphology rather than diffuse radio emission produced by AGN winds. >90% of the outflowing ionized gas emission originates from the central 100 pc, within which the ionizing luminosity of the outflow is comparable to the mechanical power of the radio jet. Although radio jets might primarily drive the outflow in HE 0040-1105, radiation pressure from the AGN may contribute to this process.
We present the results of high-resolution VLBI (very long baseline interferometry) observations at 1.6 and 4.9 GHz of the radio-loud Seyfert galaxy, Mrk 6. These observations are able to detect a ...compact radio core in this galaxy for the first time. The core has an inverted spectral index ($\alpha ^{1.6}_{4.9}$ = +1.0 ± 0.2) and a brightness temperature of 1 × 108 K. Three distinct radio components, which resemble jet elements and/or hotspots, are also detected. The position angles of these elongated jet elements point not only to a curved jet in Mrk 6, but also towards a connection between the AGN and the kpc-scale radio lobes/bubbles in this galaxy. Firmer constraints on the star formation rate provided by new Herschel observations (SFR < 0.8 M⊙ yr−1) make the starburst-wind-powered bubble scenario implausible. From plasma speeds, obtained via prior Chandra X-ray observations, and ram pressure balance arguments for the interstellar medium and radio bubbles, the north–south bubbles are expected to take 7.5 × 106 yr to form, and the east–west bubbles 1.4 × 106 yr. We suggest that the jet axis has changed at least once in Mrk 6 within the last ≈107 yr. A comparison of the nuclear radio-loudness of Mrk 6 and a small sample of Seyfert galaxies with a subset of low-luminosity FR I radio galaxies reveals a continuum in radio properties.
A global 2‐month comparison is presented between the Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) and the Moderate Resolution Imaging Spectroradiometer (MODIS) for both cloud detection ...and cloud top height (CTH) retrievals. Both CALIOP and MODIS are part of the NASA A‐Train constellation of satellites and provide continuous near‐coincident measurements that result in over 28 million cloud detection comparisons and over 5 million CTH comparisons for the months of August 2006 and February 2007. To facilitate the comparison, a computationally efficient and accurate collocation methodology is developed. With the collocated MODIS and CALIOP retrievals, nearly instantaneous comparisons are compiled regionally and globally. Globally, it is found that the MODIS 1‐km cloud mask and the CALIOP 1‐km averaged layer product agreement is 87% for cloudy conditions for both August 2006 and February 2007. For clear‐sky conditions the agreement is 85% (86%) for August (February). The best agreement is found for nonpolar daytime and the poorest agreement in the polar regions. Differences in cloud top heights depend strongly on cloud type. Globally, MODIS underestimates the CTH relative to CALIOP by 1.4 ± 2.9 km for both August 2006 and February 2007. This value of 1.4 km is obtained using the CALIOP 1 km layer products. When compared to the CALIOP 5‐km products, the differences increase to −2.6 ± 3.9 km as a result of CALIOP's increased sensitivity to optically thin cirrus. When only high clouds above 5 km are considered, the differences are found to be greater than 4 km with individual comparisons having differences larger than 10 km. These large differences (>10 km) represent approximately 16% of the nonpolar high cloud retrievals (>5 km). For high clouds it is found that MODIS retrieves a cloud top height for 90% of the clouds detected by the CALIOP 5‐km layer products. The large MODIS underestimates for optically thin cirrus occur for cases when MODIS reverts to a window brightness temperature retrieval instead of CO2 slicing. A systematic bias is found for marine low‐level stratus clouds, with MODIS overestimating the CTH by over 1 km in dense marine stratocumulus regions. The cause of the bias was identified in the MODIS Collection 5 algorithm; an application of a modified algorithm reduced this bias.
Abstract
We present Chandra X-ray and Very Large Array radio observations of the radio galaxy 3C 305. The X-ray observations reveal the details of the previously known extended X-ray halo around the ...radio galaxy. We show using X-ray spectroscopy that the X-ray emission is consistent with being shock-heated material and can be modelled with standard collisional-ionization models, rather than being photoionized by the active nucleus. On this basis, we can make a self-consistent model in which the X-ray-emitting plasma is responsible for the depolarization of some regions of the radio emission from the jets and hotspots, and to place lower and upper limits on the magnetic field strength in the depolarizing medium. On the assumption that the X-ray-emitting material, together with the previously known extended emission-line region and the outflow in neutral hydrogen, is all being driven out of the centre of the galaxy by an interaction with the jets, we derive a detailed energy budget for the radio galaxy, showing that the X-ray-emitting gas dominates the other phases in terms of its energy content. The power supplied by the jets must be ∼1043 erg s−1.
Abstract
We present a recent Atacama Large Millimeter/submillimeter Array observation of the CO(1−0) line emission in the central galaxy of the Zw 3146 galaxy cluster (
z
= 0.2906). We also present ...updated X-ray cavity measurements from archival Chandra observations. The 5 × 10
10
M
⊙
supply of molecular gas, which is confined to the central 4 kpc, is marginally resolved into three extensions that are reminiscent of the filaments observed in similar systems. No velocity structure that would be indicative of ordered motion is observed. The three molecular extensions all trail X-ray cavities, and are potentially formed from the condensation of intracluster gas lifted in the wakes of the rising bubbles. Many cycles of feedback would be required to account for the entire molecular gas reservoir. The molecular gas and continuum source are mutually offset by 2.6 kpc, with no detected line emission coincident with the continuum source. It is the molecular gas, not the continuum source, that lies at the gravitational center of the brightest cluster galaxy. As the brightest cluster galaxy contains possible tidal features, the displaced continuum source may correspond to the nucleus of a merging galaxy. We also discuss the possibility that a gravitational wave recoil following a black hole merger may account for the displacement.
We present a new Chandra X-ray observation of the off-axis galaxy group merger RX J0751.3+5012. The hot atmospheres of the two colliding groups appear highly distorted by the merger. The images ...reveal arc-like cold fronts around each group core, produced by the motion through the ambient medium, and the first detection of a group merger shock front. We detect a clear density and temperature jump associated with a bow shock of Mach number M = 1.9 ± 0.4 ahead of the northern group. Using galaxy redshifts and the shock velocity of 1100 ± 300 km s−1, we estimate that the merger axis is only ∼10° from the plane of the sky. From the projected group separation of ∼90 kpc, this corresponds to a time since closest approach of ∼0.1 Gyr. The northern group hosts a dense, cool core with a ram pressure stripped tail of gas extending ∼100 kpc. The sheared sides of this tail appear distorted and broadened by Kelvin–Helmholtz instabilities. We use the presence of this substructure to place an upper limit on the magnetic field strength and, for Spitzer-like viscosity, show that the development of these structures is consistent with the critical perturbation length above which instabilities can grow in the intragroup medium. The northern group core also hosts a galaxy pair, UGC 4052, with a surrounding IR and near-UV ring ∼40 kpc in diameter. The ring may have been produced by tidal stripping of a smaller galaxy by UGC 4052 or it may be a collisional ring generated by a close encounter between the two large galaxies.
Abstract
Low-excitation radio galaxies (LERGs) are weakly accreting active galactic nuclei (AGNs) believed to be fueled by radiatively inefficient accretion processes. Despite this, recent works have ...shown evidence for ionized and neutral hydrogen gas outflows in these galaxies. To investigate the potential drivers of such outflows, we select a sample of 802 LERGs using the Best & Heckman (2012) catalog of radio galaxies. By modeling the O
iii
λ
5007 profile in Sloan Digital Sky Survey spectra of a sample of 802 LERGs, we determine that the ionized outflows are present in ∼1.5% of the population. Using 1.4 GHz imaging from the Faint Images of the Radio Sky at Twenty Centimeters survey we analyze the radio morphology of LERGs with outflows and find these to be consistent with the parent LERG population. However, we note that unlike the majority of the LERG population, those LERGs showing outflows have Eddington-scaled accretion rates close to 1%. This is indicative that ionized outflows in LERGs are driven by the radiation pressure from the accretion disk of the AGN rather than the radio jets. We report specific star formation rates in the range of 10
−12
< sSFR < 10
−9
yr
−1
. Moreover, we observe higher mass outflow rates, 7–150
M
☉
yr
−1
, for these LERGs than luminous quasars for a given bolometric luminosity, which could possibly be due to the radio source in LERGs boosting the mass loading. This scenario could indicate that these outflows could potentially drive feedback in LERGs.
ABSTRACT
We report the discovery of a secondary pair of radio lobes in the Seyfert galaxy NGC 2639 with polarization-sensitive observations with the Karl G. Jansky Very Large Array (VLA). The ...presence of these lobes, which are aligned nearly perpendicular to the known set of radio lobes observed in the east–west direction, has not been reported previously in the literature. The in-band rotation measure image shows gradients in both the lobes indicative of organized magnetic field structures on kpc-scales. The magnetic field structure is aligned with the jet/lobe direction in both the lobes. Based on the settled optical morphology of the host galaxy, it is likely that a minor merger that did not disrupt the host galaxy structure is responsible for the observed features in NGC 2639. This also explains the near 90° change in the jet direction; the current jet direction being the result of a new accretion disc formed by the minor merger, whose direction was a result of the angular momentum of the inflowing merger gas.
We present results from multifrequency polarization-sensitive Very Large Array observations of the Seyfert-starburst composite galaxy NGC 3079. Our sensitive radio observations reveal a plethora of ...radio "filaments" comprising the radio lobes in this galaxy. We analyze the origin of these radio filaments in the context of existing Chandra X-ray and HST emission-line data. We do not find a one-to-one correlation of the radio filaments with the emission-line filaments. The northeastern lobe is highly polarized with polarization fractions ∼33% at 5 GHz. The magnetic fields are aligned with the linear extents of the optically thin filaments, as observed in our, as well as other, observations in the literature. Our rotation measure images show evidence for rotation measure inversion in the northeastern lobe. Our data best fit a model where the cosmic rays follow the magnetic field lines generated as a result of the dynamo mechanism. There could be additional effects like shock acceleration that might also be playing a role. We speculate that the peculiar radio lobe morphology is a result of an interplay between both the superwinds and the active galactic nucleus jet that are present in the galaxy. The jet, in fact, might be playing a major role in providing the relativistic electron population that is present in the radio lobes.
We have carried out an extensive radio study with the Very Large Array on the Seyfert 1.5 galaxy Mrk 6 and imaged a spectacular radio structure in the source. The radio emission occurs on three ...different spatial scales: 67.5 kpc bubbles, 61.5 kpc bubbles lying nearly orthogonal to them, and a 61 kpc radio jet lying orthogonal to the kiloparsec-scale bubble. To explain the complex morphology, we first consider a scenario in which the radio structures are the result of superwinds ejected by a nuclear starburst. However, recent Spitzer observations of Mrk 6 provide an upper limit to the star formation rate (SFR) of 65.5 M sub( )yr super(-1), an estimate much lower than the SFR of 633 M sub( )yr super(-1) derived assuming that the bubbles are a result of starburst winds energized by supernova explosions. Thus, a starburst alone cannot meet the energy requirements for the creation of the bubbles in Mrk 6. We then present an energetically plausible model wherein the bubbles are a result of energy deposited by the kiloparsec-scale jet as it plows into the interstellar medium. Finally, we consider a model in which the complex radio structure is a result of an episodically powered precessing jet that changes its orientation. This model is the most attractive as it can naturally explain the complex radio morphology and is consistent with the energetics, the spectral index, and the polarization structure. Radio emission in this scenario is a short-lived phenomenon in the lifetime of a Seyfert galaxy, which results from an accretion event.
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