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HEILES CARL The Korean Astronomical Society 1996 Journal of The Korean Astronomical Society Vol.29 No.suppl1
We examine the observations of large-scale magnetic fields in the Universe. We begin at the largest scale with clusters of galaxies and work our way down through galaxies and finally to the Milky Way. on which we concentrate in detail. We examine the observations of the Galactic magnetic field, and their interpretation, under the philosophy that the Galactic magnetic field is like that in other spiral galaxies. We use pulsar data. diffuse Galactic synchrotron emission, and starlight polarization data to discuss the Galaxy's global magnetic configuration and the uniform ($B_u$), random ($B_r$), and total ($B_t$) components of the field strength. We find disagreement among conclusions derived from the various data sets and argue that the pulsar data are not the best indicator for large-scale Galactic field. Near the Solar circle, we find that the azimuthal average of $B_t$ is 4.2$\mu$G and we adopt $B_u\~$2.2 and $B_r\~3.6{\mu}G$. $B_t$ is higher in spiral arms, reaching $\~5.9{\mu}G$. $B_t$ is higher for smaller $R_{Gal}$, reaching $\~8.0{\mu}G$ for $R_{Gal}$ = 4.0 kpc. The pattern of field lines is not concentric circles but spirals. The inclination of the magnetic spiral may be smaller than that of the Galaxy's spiral arms if our sample, which refers primarily to the interarm region near the Sun, is representative. However, it is not inconceivable that the local field lines follow the Galaxy's spiral pattern, as is observed in external galaxies.
LI, DI,XU, DUO,HEILES, CARL,PAN, ZHICHEN,TANG, NINGYU The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
A growing body of evidence has been supporting the existence of so-called "dark molecular gas" (DMG), which is invisible in the most common tracer of molecular gas, i.e., CO rotational emission. DMG is believed to be the main gas component of the intermediate extinction region from Av~0.05-2, roughly corresponding to the self-shielding threshold of $H_2$ and $^{13}CO$. To quantify DMG relative to $H{\small{I}}$ and CO, we are pursuing three observational techniques; $H{\small{I}}$ self-absorption, OH absorption, and THz $C^+$ emission. In this paper, we focus on preliminary results from a CO and OH absorption survey of DMG candidates. Our analysis shows that the OH excitation temperature is close to that of the Galactic continuum background and that OH is a good DMG tracer co-existing with molecular hydrogen in regions without CO. Through systematic "absorption mapping" by the Square Kilometer Array (SKA) and ALMA, we will have unprecedented, comprehensive knowledge of the ISM components including DMG in terms of their temperature and density, which will impact our understanding of galaxy evolution and star formation profoundly.
A 21 cm SPECTRAL AND CONTINUUM STUDY OF IC 443 USING THE VERY LARGE ARRAY AND THE ARECIBO TELESCOPE
Lee, Jae-Joon,Koo, Bon-Chul,Yun, Min S.,Stanimirović,, Snež,ana,Heiles, Carl,Heyer, Mark American Institute of Physics 2008 The Astronomical journal Vol.135 No.3
<P>We report 21 cm spectral-line and continuum observations of the Galactic supernova remnant IC 443 using the Very Large Array (VLA) and the Arecibo telescope. By combining the VLA and Arecibo data, both covering the full extent of IC 443, we have achieved an unprecedented combination of sensitivity and angular resolution, over the continuous range of angular scales from ~40'' to ~1°. Our new radio observations not only reveal previously unknown features of IC 443 but also show the details of the remnant more clearly. The radio morphology of IC 443 consists of two nearly concentric shells. Our 21 cm radio continuum data show that the two shells have distinctly different radial intensity distributions. This morphology supports the scenario whereby the western shell is a breakout portion of the remnant into a rarefied medium. We have developed a dynamical model accounting for the breakout, which provides an estimate for the remnant age of ~2 × 10<SUP>4</SUP> yr. The southeastern boundary of the remnant shows interesting features, seen in our observations for the first time: a faint radio continuum halo and numerous 'spurs.' These features are mainly found in the region where IC 443 overlaps with another remnant, G189.6+3.3. These features most likely originate from the interactions of IC 443 with the surrounding medium. The H <SPAN CLASS='sml'>I</SPAN> emission associated with IC 443 appears over the velocity range between −100 km s<SUP>−1</SUP> and 50 km s<SUP>−1</SUP>. The strongest absorption is seen around v<SUB>LSR</SUB> ~ −5 km s<SUP>−1</SUP>, which corresponds to the systemic velocity of IC 443. We identify a broad, extended lane of H <SPAN CLASS='sml'>I</SPAN> gas near the systemic velocity as preshock gas in the southern part of the remnant. Most of the shocked H <SPAN CLASS='sml'>I</SPAN> gas is located along the southern supernova remnant (SNR) boundary and is blueshifted. We derive an accurate mass of the shocked H <SPAN CLASS='sml'>I</SPAN> gas using template HCO<SUP>+</SUP> (1-0) spectra, which is 493 ± 56 M<SUB>☉</SUB>. Our high-resolution H <SPAN CLASS='sml'>I</SPAN> data enable us to resolve the shocked H <SPAN CLASS='sml'>I</SPAN> in the northeastern region into a few filamentary structures, which are well correlated with radiative filaments, in both position and velocity. This represents the first unambiguous detection of the recombined H <SPAN CLASS='sml'>I</SPAN> in an atomic shock. The characteristics of the filaments are not consistent with a clumpy shock model where the radiative signature is from dense clumps. Instead we propose that the shock has been propagating through a uniform medium of n<SUB>H</SUB> ~ 10 cm<SUP>−3</SUP>.</P>
Park, G.,Koo, B.-C.,Gibson, S. J.,Kang, J.-h.,Lane, D. C.,Douglas, K. A.,Peek, J. E. G.,Korpela, E. J.,Heiles, C.,Newton, J. H. IOP Publishing 2013 The Astrophysical journal Vol.777 No.1
<P>We search for fast-expanding Hi shells associated with Galactic supernova remnants (SNRs) in the longitude range l approximate to 32 degrees to 77 degrees using 21 cm line data from the Inner-Galaxy Arecibo L-band Feed Array (I-GALFA) Hi survey. Among the 39 known Galactic SNRs in this region, we find such Hi shells in 4 SNRs: W44, G54.4-0.3, W51C, and CTB 80. All four were previously identified in low-resolution surveys, and three of those (excluding G54.4-0.3) were previously studied with the Arecibo telescope. A remarkable new result, however, is the detection of Hi emission at both very high positive and negative velocities in W44 from the receding and approaching parts of the Hi expanding shell, respectively. This is the first detection of both sides of an expanding shell associated with an SNR in H I 21 cm emission. The high-resolution I-GALFA survey data also reveal a prominent expanding Hi shell with high circular symmetry associated with G54.4-0.3. We explore the physical characteristics of four SNRs and discuss what differentiates them from other SNRs in the survey area. We conclude that these four SNRs are likely the remnants of core-collapse supernovae interacting with a relatively dense (greater than or similar to 1 cm(-3)) ambient medium, and we discuss the visibility of SNRs in the H I 21 cm line.</P>