Observations and Analysis of High-Resolution Magnetic Field Structures in Molecular Clouds

Recent high-angular-resolution (up to 0.7") dust polarization observations toward star forming regions are summarized. With the Sub-Millimeter Array, the emission from the dense structures is traced and resolved. The detected magnetic field morphologies vary from hourglass-like structures to isolated patches depending on the evolutionary stage of the source. These observed features have also served as a testbed to develop new analysis methods, with a particular focus on quantifying the role of the magnetic field in the star formation process.Comment: 4 pages, 2 figures; To appear in Proceedings of Magnetic Fields in the Universe: From Laboratory and Stars to Primordial Structures Aug. 21st - 27th 2011, Zakopane, Poland Eds. M. Soida, K. Otmianowska-Mazur, E.M. de Gouveia Dal Pino & A. Lazaria

UV-finite scalar field theory with unitarity

In this paper we show how to define the UV completion of a scalar field theory such that it is both UV-finite and perturbatively unitary. In the UV completed theory, the propagator is an infinite sum of ordinary propagators. To eliminate the UV divergences, we choose the coefficients and masses in the propagator to satisfy certain algebraic relations, and define the infinite sums involved in Feynman diagram calculation by analytic continuation. Unitarity can be proved relatively easily by Cutkosky's rules. The theory is equivalent to infinitely many particles with specific masses and interactions. We take the $\phi^4$ theory as an example and demonstrate our idea through explicit Feynman diagram computation.Comment: 14 pages, references adde

The circumstellar disk of AB Aurigae: evidence for envelope accretion at late stages of star formation?

The circumstellar disk of AB Aurigae has garnered strong attention owing to the apparent existence of spirals at a relatively young stage and also the asymmetric disk traced in thermal dust emission. However, the physical conditions of the spirals are still not well understood. The origin of the asymmetric thermal emission is unclear. We observed the disk at 230 GHz (1.3 mm) in both the continuum and the spectral line ^12CO J=2-1 with IRAM 30-m, the Plateau de Bure interferometer, and the Submillimeter Array to sample all spatial scales from 0.37" to about 50". To combine the data obtained from these telescopes, several methods and calibration issues were checked and discussed. The 1.3 mm continuum (dust) emission is resolved into inner disk and outer ring. Molecular gas at high velocities traced by the CO line is detected next to the stellar location. The inclination angle of the disk is found to decrease toward the center. On a larger scale, based on the intensity weighted dispersion and the integrated intensity map of ^12CO J=2-1, four spirals are identified, where two of them are also detected in the near infrared. The total gas mass of the 4 spirals (M_spiral) is 10^-7 < M_spiral < 10^-5 M_sun, which is 3 orders of magnitude smaller than the mass of the gas ring. Surprisingly, the CO gas inside the spiral is apparently counter-rotating with respect to the CO disk, and it only exhibits small radial motion. The wide gap, the warped disk, and the asymmetric dust ring suggest that there is an undetected companion with a mass of 0.03 M_sun at a radius of 45 AU. Although an hypothetical fly-by cannot be ruled out, the most likely explanation of the AB Aurigae system may be inhomogeneous accretion well above or below the main disk plane from the remnant envelope, which can explain both the rotation and large-scale motions detected with the 30-m image.Comment: 17 pages, 13 figures, accepted for publication in A&A journal. Typos are correcte

Active Galactic Nuclei Feedback in an Elliptical Galaxy with the Most Updated AGN Physics (I): Low-angular Momentum Case

We investigate the effects of AGN feedback on the cosmological evolution of an isolated elliptical galaxy by performing two-dimensional high-resolution hydrodynamical numerical simulations. The inner boundary of the simulation is chosen so that the Bondi radius is resolved. Compared to previous works, the two accretion modes, namely hot and cold, which correspond to different accretion rates and have different radiation and wind outputs, are carefully discriminated and the feedback effects by radiation and wind in each mode are taken into account. The most updated AGN physics, including the descriptions of radiation and wind from the hot accretion flows and wind from cold accretion disks, are adopted. Physical processes like star formation, Type Ia and Type II supernovae are taken into account. We study the AGN light curve, typical AGN lifetime, growth of the black hole mass, AGN duty-cycle, star formation, and the X-ray surface brightness of the galaxy. We compare our simulation results with observations and find general consistency. Comparisons with previous simulation works find significant differences, indicating the importance of AGN physics. The respective roles of radiation and wind feedbacks are examined and it is found that they are different for different problems of interest such as AGN luminosity and star formation. We find that it is hard to neglect any of them, so we suggest to use the names of "cold feedback mode" and "hot feedback mode" to replace the currently used ones.Comment: 25 pages, 14 figures, accepted for publication to ApJ (Revised to match version published in ApJ

Dust continuum and Polarization from Envelope to Cores in Star Formation: A Case Study in the W51 North region

We present the first high-angular resolution (up to 0.7", ~5000 AU) polarization and thermal dust continuum images toward the massive star-forming region W51 North. The observations were carried out with the Submillimeter Array (SMA) in both the subcompact (SMA-SubC) and extended (SMA-Ext) configurations at a wavelength of 870 micron. W51 North is resolved into four cores (SMA1 to SMA4) in the 870 micron continuum image. The associated dust polarization exhibits more complex structures than seen at lower angular resolution. We analyze the inferred morphologies of the plane-of-sky magnetic field (B_bot) in the SMA1 to SMA4 cores and in the envelope using the SMA-Ext and SMA-SubC data. These results are compared with the B_bot archive images obtained from the CSO and JCMT. A correlation between dust intensity gradient position angles (phi_{nabla I}) and magnetic field position angles (phi_B) is found in the CSO, JCMT and both SMA data sets. This correlation is further analyzed quantitatively. A systematically tighter correlation between phi_{nabla I} and phi_B is found in the cores, whereas the correlation decreases in outside-core regions. Magnetic field-to-gravity force ratio (Sigma_B) maps are derived using the newly developed polarization - intensity gradient method by Koch, Tang & Ho 2012. We find that the force ratios tend to be small (Sigma_B <= 0.5) in the cores in all 4 data sets. In regions outside of the cores, the ratios increase or the field is even dominating gravity (Sigma_B > 1). This possibly provides a physical explanation of the tightening correlation between phi_{nabla I} and phi_B in the cores: the more the B field lines are dragged and aligned by gravity, the tighter the correlation is. Finally, we propose a schematic scenario for the magnetic field in W51 North to interpret the four polarization observations at different physical scales.Comment: Accepted for publication in ApJ. 10 pages. 7 figure

High-Angular Resolution Dust Polarization Measurements: Shaped B-field Lines in the Massive Star Forming Region Orion BN/KL

We present observational results of the thermal dust continuum emission and its linear polarization in one of the nearest massive star-forming sites Orion BN/KL in Orion Molecular Cloud-1. The observations were carried out with the Submillimeter Array. With an angular resolution of 1" (~2 mpc; 480 AU), we have detected and resolved the densest cores near the BN/KL region. At a wavelength of ~870 micron, the polarized dust emission can be used to trace the structure of the magnetic field in this star-forming core. The dust continuum appears to arise from a V-shaped region, with a cavity nearly coincident with the center of the explosive outflows observed on larger scales. The position angles (P.A.s) of the observed polarization vary significantly by a total of about 90 degree but smoothly, i.e., curl-like, across the dust ridges. Such a polarization pattern can be explained with dust grains being magnetically aligned instead of mechanically with outflows, since the latter mechanism would cause the P.A.s to be parallel to the direction of the outflow, i.e., radial-like. The magnetic field projected in the plane of sky is therefore derived by rotating the P.A.s of the polarization by 90 degree. We find an azimuthally symmetric structure in the overall magnetic field morphology, with the field directions pointing toward 2.5" west to the center of the explosive outflows. We also find a preferred symmetry plane at a P.A. of 36 degree, which is perpendicular to the mean magnetic field direction (120 degree) of the 0.5 pc dust ridge. Two possible interpretations of the origin of the observed magnetic field structure are discussed.Comment: 27 pages, 7 figures; ApJ in pres

The relation of optical/UV and X-ray emission in low-luminosity active galactic nuclei

We study the relation of optical/UV and X-ray emission in the low luminosity active galactic nuclei (LLAGNs), using a sample of 49 sources including 28 local Seyfert galaxies and 21 low-ionization nuclear emission-line regions (LINERs) with the optical/UV spectral luminosity at the wavelength \lambda=2500\AA, 23.0\leq \log L_{\nu(2500\AA)(erg/s/Hz)\leq 27.7, and the X-ray spectral luminosity at 2 keV, 20.5\leq \log L_{\nu(2 keV)}\leq 25.3. The strong correlations are found between the X-ray luminosity and the optical/UV to X-ray index, \alpha_{ox}, with the optical/UV luminosity, with the slopes very similar to the findings for the luminous AGNs in the previous works. The correlation between \alpha_{ox} and L_{\nu(2 keV) is very weak as that found for the luminous AGNs in the majority of previous similar works. We also study the relation between $\alpha_{\rm ox} and the Eddington ratio L_{bol}/L_{Edd} for our sample and find a significant anti-correlation for the sources with L_{bol}/L_{Edd}\lesssim 10^{-3}, which is opposite to the correlation between the two variables for the luminous AGNs. Using the advection dominated accretion flow (ADAF) model, we roughly reproduce this anti-correlationship for the two variables for the LLAGNs. This result strongly supports the ADAF as a candidate accretion mode in LLAGNs.Comment: 21 pages, 1 table, 5 figures. Accepted for publication in Ap