Sub-parsec-scale Accleration of the Radio Jet in the Powerful Radio Galaxy NGC 6251

In order to investigate the genesis of powerful radio jet, we have mapped the central 10 pc region of the nearby radio galaxy NGC 6251 with a 0.2 pc resolution using Very Long Baseline Interferometer (VLBI) at two radio frequencies, 5 GHz and 15 GHz, we have found the sub-parsec-scale counterjet for the first time in this radio galaxy. This discovery allows us to investigate the jet acceleration based on the relativistic beaming model.Comment: 7 pages with 7 figures. To appear in PASJ, 52, No. 5, Oct. 25, 200

Observation of weak temperature dependence of spin diffusion length in highly-doped Si by using a non-local 3-terminal method

We conduct an experimental investigation of temperature dependence of spin diffusion length in highly-doped n-type silicon by using a non-local 3-terminal method. Whereas an effect of spin drift is not ignorable to bias- and temperature-dependence of spin signals in non-metallic systems except for the case of a non-local 4-terminal method, it is not fully conclusive how the spin drift affects spin transport properties in highly-doped Si in a non-local 3-terminal method that is often used in Si spintronics. Here, we report on temperature dependence of spin diffusion length in the Si, and it is clarified that the spin transport is less affected by an external electric field.Comment: 13 pages, 3 figure

Possible Detection of Apparent Superluminal inward motion in Markarian 421 after the Giant X-ray flare in February, 2010

We report on the VLBI follow-up observations using the Japanese VLBI Network (JVN) array at 22 GHz for the largest X-ray flare of TeV blazar Mrk 421 that occurred in mid-February, 2010. The total of five epochs of observations were performed at intervals of about 20 days between March 7 and May 31, 2010. No new-born component associated with the flare was seen directly in the total intensity images obtained by our multi-epoch VLBI observations. However, one jet component located at ~1 mas north-west from the core was able to be identified, and its proper motion can be measured as -1.66+/-0.46 mas yr^-1, which corresponds to an apparent velocity of -3.48+/-0.97 c. Here, this negative velocity indicates that the jet component was apparently moving toward the core. As the most plausible explanation, we discuss that the apparent negative velocity was possibly caused by the ejection of a new component, which could not be resolved with our observations. In this case, the obtained Doppler factor of the new component is around 10 to 20, which is consistent with the ones typically estimated by model fittings of spectral energy distribution for this source.Comment: 9 pages, 6 figures, 3 tables, accepted for publication in Ap

A catalogue of damped Lyman alpha absorption systems and radio flux densities of the background quasars

We present a catalogue of the 322 damped Lyman alpha absorbers taken from the literature. All damped Lyman alpha absorbers are included, with no selection on redshift or quasar magnitude. Of these, 123 are candidates and await confirmation using high resolution spectroscopy. For all 322 objects we catalogue the radio properties of the background quasars, where known. Around 60 quasars have radio flux densities above 0.1 Jy and approximately half of these have optical magnitudes brighter than V = 18. This compilation should prove useful in several areas of extragalactic/cosmological research.Comment: 26 Pages, 12 PS tables, 1 embedded table. Accepted by PASA. Continuously updated online catalogue available at http://www.phys.unsw.edu.au/~sjc/dl

Non-Uniform Free-Free Absorption in the GPS Radio Galaxy 0108+388

We have observed the canonical gigahertz-peaked spectrum source 0108+388 with the VLBA at a range of frequencies above and below the spectral peak. The activity that dominates the radio emission from 0108+388, which is also classified as a Compact Symmetric Object, is thought to be less than 1000 years old. We present strong evidence that the spectral turnover in 0108+388 results from free-free absorption by non-uniform gas, possibly in the form of a disk in the central tens of parsecs.Comment: 13 pages, including 8 figures and 3 tables. Accepted for publication in Ap

ALMA Observations of Asteroid 3 Juno at 60 Kilometer Resolution

We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of 0.042 arcseconds (60 km at 1.97 AU). The data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of ten consecutive images reveals continuous changes in the asteroid's profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259pm4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215pm13 K, while the median over the whole surface is 197pm15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas, and lower values beyond the evening terminator. The dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. These results demonstrate ALMA's potential to resolve thermal emission from the surface of main belt asteroids, and to measure accurately their position, geometric shape, rotational period, and soil characteristics.Comment: 8 pages, 3 figures, 2 tables, accepted for publication in the Astrophysical Journal Letter

Discovery of Candidate H2_2O Disk Masers in AGN and Estimations of Centripetal Accelerations

Based on spectroscopic signatures, about one-third of known H$_2$O maser sources in active galactic nuclei (AGN) are believed to arise in highly inclined accretion disks around central engines. These "disk maser candidates" are of interest primarily because angular structure and rotation curves can be resolved with interferometers, enabling dynamical study. We identify five new disk maser candidates in studies with the Green Bank Telescope, bringing the total number published to 30. We discovered two (NGC1320, NGC17) in a survey of 40 inclined active galaxies (v_{sys}< 20000 kms^{-1}). The remaining three disk maser candidates were identified in monitoring of known sources: NGC449, NGC2979, NGC3735. We also confirm a previously marginal case in UGC4203. For the disk maser candidates reported here, inferred rotation speeds are 130-500 kms^{-1}. Monitoring of three more rapidly rotating candidate disks (CG211, NGC6264, VV340A) has enabled measurement of likely orbital centripetal acceleration, and estimation of central masses (2-7x10^7 M_\odot) and mean disk radii (0.2-0.4pc). Accelerations may ultimately permit estimation of distances when combined with interferometer data. This is notable because the three AGN are relatively distant (10000<v_{sys}<15000 kms^{-1}). As signposts of highly inclined geometries at galactocentric radii of \sim0.1-1pc, disk masers also provide robust orientation references that allow analysis of (mis)alignment between AGN and surrounding galactic stellar disks, even without interferometric mapping. We find no preference among published disk maser candidates to lie in high-inclination galaxies, providing independent support for conclusions that central engines and galactic plane orientations are not correlated. (ABRIDGED)Comment: 7 figures, accepted for publication in ApJ, Dec. 10, 200

Spitzer mid-infrared spectroscopy of compact symmetric objects: What powers radio-loud active galactic nuclei?

We present low- and high-resolution mid-infrared (mid-IR) spectra and photometry for eight compact symmetric objects (CSOs) taken with the Infrared Spectrograph on the Spitzer Space Telescope. The hosts of these young, powerful radio galaxies show significant diversity in their mid-IR spectra. This includes multiple atomic fine-structure lines, H2 gas, polycyclic aromatic hydrocarbon (PAH) emission, warm dust from T = 50 to 150 K, and silicate features in both emission and absorption. There is no evidence in the mid-IR of a single template for CSO hosts, but 5/8 galaxies show similar moderate levels of star formation (<10 M_sun/yr from PAH emission) and silicate dust in a clumpy torus. The total amount of extinction ranges from A_V ~ 10 to 30, and the high-ionization [Ne V] 14.3 and 24.3 um transitions are not detected for any galaxy in the sample. Almost all CSOs show contributions both from star formation and active galactic nuclei (AGNs), suggesting that they occupy a continuum between pure starbursts and AGNs. This is consistent with the hypothesis that radio galaxies are created following a galactic merger; the timing of the radio activity onset means that contributions to the IR luminosity from both merger-induced star formation and the central AGN are likely. Bondi accretion is capable of powering the radio jets for almost all CSOs in the sample; the lack of [Ne V] emission suggests an advection-dominated accretion flow mode as a possible candidate. Merging black holes (BHs) with M_BH > 10^8 M_sun likely exist in all of the CSOs in the sample; however, there is no direct evidence from these data that BH spin energy is being tapped as an alternative mode for powering the radio jets.Comment: 22 pages, 14 figures; published in Ap

ALMA Long Baseline Observations of the Strongly Lensed Submillimeter Galaxy HATLAS J090311.6+003906 at z=3.042

We present initial results of very high resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $z$=3.042 gravitationally lensed galaxy HATLAS J090311.6+003906 (SDP.81). These observations were carried out using a very extended configuration as part of Science Verification for the 2014 ALMA Long Baseline Campaign, with baselines of up to 15 km. We present continuum imaging at 151, 236 and 290 GHz, at unprecedented angular resolutions as fine as 23 milliarcseconds (mas), corresponding to an un-magnified spatial scale of ~180 pc at z=3.042. The ALMA images clearly show two main gravitational arc components of an Einstein ring, with emission tracing a radius of ~1.5". We also present imaging of CO(10-9), CO(8-7), CO(5-4) and H2O line emission. The CO emission, at an angular resolution of ~170 mas, is found to broadly trace the gravitational arc structures but with differing morphologies between the CO transitions and compared to the dust continuum. Our detection of H2O line emission, using only the shortest baselines, provides the most resolved detection to date of thermal H2O emission in an extragalactic source. The ALMA continuum and spectral line fluxes are consistent with previous Plateau de Bure Interferometer and Submillimeter Array observations despite the impressive increase in angular resolution. Finally, we detect weak unresolved continuum emission from a position that is spatially coincident with the center of the lens, with a spectral index that is consistent with emission from the core of the foreground lensing galaxy.Comment: 9 pages, 5 figures and 3 tables, accepted for publication in the Astrophysical Journal Letter