arXiv subjects

Il-Gyo Jeong

Publications and source records attributed to Il-Gyo Jeong.

24 records · Page 2Linked to original sources

arXiv2017

First results from BISTRO -- a SCUBA-2 polarimeter survey of the Gould Belt

We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array 2 (SCUBA-2) camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope (JCMT) in Hawaii. We discuss the survey's aims and objectives. We describe the rationale behind the survey, and the questions which the survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC 1 region. We see that the magnetic field lies approximately perpendicular to the famous 'integral filament' in the densest regions of that filament. Furthermore, we see an 'hour-glass' magnetic field morphology extending beyond the densest region of the integral filament into the less-dense surrounding material, and discuss possible causes for this. We also discuss the more complex morphology seen along the Orion Bar region. We examine the morphology of the field along the lower-density north-eastern filament. We find consistency with previous theoretical models that predict magnetic fields lying parallel to low-density, non-self-gravitating filaments, and perpendicular to higher-density, self-gravitating filaments.

astro-ph.GA↗

arXiv2016

Infrared Supernova Remnants and their Infrared to X-ray Flux Ratios

Recent high-resolution infrared space missions have revealed supernova remnants (SNRs) of diverse morphology in infrared (IR) dust emission that is often very different from their X-ray appearance. The observed range of infrared-to-X-ray (IRX) flux ratios of SNRs are also wide. For a sample of 20 Galactic SNRs, we obtain their IR and X-ray properties and investigate the physical causes for such large differences. We find that the observed IRX flux ratios ($R_{IRX.obs}$) are related to the IRX morphology, with SNRs with the largest $R_{IRX,obs}$ showing anticorrelated IRX morphology. By analyzing the relation of $R_{IRX,obs}$ to X-ray and IR parameters, we show that the $R_{IRX,obs}$ of some SNRs agree with theoretical ratios of SNR shocks in which dust grains are heated and destroyed by collisions with plasma particles. For the majority of SNRs, however, $R_{IRX,obs}$ values are either significantly smaller or significantly larger than the theoretical ratios. The latter SNRs have relatively low dust temperatures. We discuss how the natural and/or environmental properties of SNRs could have affected the IRX flux ratios and the IRX morphology of these SNRs. We conclude that the SNRs with largest $R_{IRX,obs}$ are probably located in dense environment and that their IR emission is from dust heated by shock radiation rather than by collisions. Our result suggests that the IRX flux ratio, together with dust temperature, can be used to infer the nature of unresolved SNRs in external galaxies.

astro-ph.GA↗

arXiv2013

CO J=1-0 and J=2-1 Line Observations of the Molecular Cloud - Blocked Supernova Remnant 3C434.1

We present the results of CO emission line observations toward the semicircular Galactic supernova remnant (SNR) 3C434.1 (G94.0+1.0). We mapped an area covering the whole SNR in the 12CO J=1-0 emission line using the Seoul Radio Astronomy Observatory (SRAO) 6-m telescope, and found a large molecular cloud superposed on the faint western part of the SNR. The cloud was elongated along the north-south direction and showed a very good spatial correlation with the radio features of the SNR. We carried out 12CO J=2-1 line observations of this cloud using the Kölner Observatorium für Sub-Millimeter Astronomie (KOSMA) 3-m telescope and found a region in which the 12CO J=2-1 to J=1-0 ratio was high (~ 1.6). This higher excitation, together with the morphological relation, strongly suggested that the molecular cloud was interacting with the SNR. The systemic velocity of the molecular cloud (-13 km/s) gave a kinematic distance of 3.0 kpc to the SNR-molecular cloud system. We derived the physical parameters of the SNR based on this new distance. We examined the variation of the radio spectral index over the remnant and found that it was flatter in the western part, wherein the SNR was interacting with the molecular cloud. We therefore propose that 3C434.1 is the remnant of a supernova explosion that occurred just outside the boundary of a relatively thin, sheetlike molecular cloud. We present a hydrodynamic model showing that its asymmetric radio morphology can result from its interaction with this blocking molecular cloud.

astro-ph.HE↗

arXiv2012

SRAO CO Observation of 11 Supernova Remnants in l = 70 to 190 deg

We present the results of 12CO J = 1-0 line observations of eleven Galactic supernova remnants (SNRs) obtained using the Seoul Radio Astronomy Observatory (SRAO) 6-m radio telescope. The observation was made as a part of the SRAO CO survey of SNRs between l = 70 and 190 deg, which is intended to identify SNRs interacting with molecular clouds. The mapping areas for the individual SNRs are determined to cover their full extent in the radio continuum. We used halfbeam grid spacing (60") for 9 SNRs and full-beam grid spacing (120") for the rest. We detected CO emission towards most of the remnants. In six SNRs, molecular clouds showed a good spatial relation with their radio morphology, although no direct evidence for the interaction was detected. Two SNRs are particularly interesting: G85.4+0.7, where there is a filamentary molecular cloud along the radio shell, and 3C434.1, where a large molecular cloud appears to block the western half of the remnant. We briefly summarize the results obtained for individual SNRs.

astro-ph.GA↗

arXiv2010

Molecular environment and thermal X-ray spectroscopy of the semicircular young composite supernova remnant 3C 396

We have investigated the molecular environment of the semicircular composite supernova remnant (SNR) 3C396 and performed a Chandra spatially resolved thermal X-ray spectroscopic study of this young SNR. With our CO millimeter observations, we find that the molecular clouds (MCs) at V(LSR)~84km/s can better explain the multiwavelength properties of the remnant than the V(LSR)=67-72km/s MCs that are suggested by Lee et al. (2009). At around 84km/s, the western boundary of the SNR is perfectly confined by the western molecular wall. The CO emission fades out from west to east, indicating that the eastern region is of low gas density. In particular, an intruding finger/pillar-like MC, which may be shocked at the tip, can well explain the X-ray and radio enhancement in the southwest and some infrared filaments there. The SNR-MC interaction is also favored by the relatively elevated 12CO J=2-1/J=1-0 line ratios in the southwestern "pillar tip" and the molecular patch on the northwestern boundary. The redshifted 12CO (J=1-0 and J=2-1) wings (86-90km/s) of an eastern 81km/s molecular patch may be the kinematic evidence for shock-MC interaction. We suggest that the 69km/s MCs are in the foreground based on HI self-absorption while the 84km/s MCs at a distance of 6.2 kpc (the tangent point) are in physical contact with SNR 3C396. The X-ray spectral analysis suggests an SNR age of ~3kyr. The metal enrichment of the X-ray emitting gas in the north and south implies a 13-15Msun B1-B2 progenitor star.

astro-ph.GA↗

arXiv2008

Discovery of molecular shells associated with supernova remnants. (II) Kesteven 75

The young composite supernova remnant (SNR) Kesteven 75, with a pulsar wind nebula at its center, has an unusual morphology with a bright southern half-shell structure in multiwavelengths. The distance to Kes 75 has long been uncertain. Aiming to address these issues, we have made millimeter spectroscopic observations of the molecular gas toward the remnant. The V_{LSR}~83--96 km/s molecular clouds (MCs) are found to overlap a large north-western region of the remnant and are suggested to be located in front of the SNR along the line of sight. Also in the remnant area, the V_{LSR}= 45--58 km/s MC shows a blue-shifted broadening in the 12CO (J=1-0) line profile and a perturbed position-velocity structure near the edge of the remnant, with the intensity centroid sitting in the northern area of the remnant. In particular, a cavity surrounded by a molecular shell is unveiled in the intensity map in the broadened blue wing (45--51 km/s), and the southern molecular shell follows the bright partial SNR shell seen in X-rays, mid-infrared, and radio continuum. These observational features provide effective evidences for the association of Kes 75 with the adjacent 54 km/s MC. This association leads to a determination of the kinematic distance at ~10.6 kpc to the remnant, which agrees with a location at the far side of the Sagittarius arm. The morphological coincidence of the shell seen in multiwavelengths is consistent with a scenario in which the SNR shock hits a pre-existing dense shell. This dense molecular shell is suggested to likely represent the debris of the cooled, clumpy shell of the progenitor's wind bubble proximately behind the 54 km/s cloud. The discovery of the association with MC provides a possible explanation for the gamma-ray excess of the remnant.

astro-ph↗