arXiv subjects

Wanggi Lim

Publications and source records attributed to Wanggi Lim.

23 records · Page 2Linked to original sources

arXiv2017

Temperature structure and kinematics of the IRDC G035.39-00.33

Aims. Infrared dark clouds represent the earliest stages of high-mass star formation. Detailed observations of their physical conditions on all physical scales are required to improve our understanding of their role in fueling star formation. Methods. We investigate the large-scale structure of the IRDC G035.39-00.33, probing the dense gas with the classical ammonia thermometer. This allows us to put reliable constraints on the temperature of the extended, pc-scale dense gas reservoir and to probe the magnitude of its non-thermal motions. Available far-infrared observations can be used in tandem with the observed ammonia emission to estimate the total gas mass contained in G035.39-00.33. Results. We identify a main velocity component as a prominent filament, manifested as an ammonia emission intensity ridge spanning more than 6 pc, consistent with the previous studies on the Northern part of the cloud. A number of additional line-of-sight components are found, and a large scale, linear velocity gradient of ~0.2 km s$^{-1}$ pc$^{-1}$ is found along the ridge of the IRDC. In contrast to the dust temperature map, an ammonia-derived kinetic temperature map, presented for the entirety of the cloud, reveals local temperature enhancements towards the massive protostellar cores. We show that without properly accounting for the line of sight contamination, the dust temperature is 2-3 K larger than the gas temperature measured with NH$_3$. Conclusions. While both the large scale kinematics and temperature structure are consistent with that of starless dark filaments, the kinetic gas temperature profile on smaller scales is suggestive of tracing the heating mechanism coincident with the locations of massive protostellar cores.

astro-ph.GA↗

arXiv2016

The Distribution of Mass Surface Densities in a High-Mass Protocluster

We study the probability distribution function (PDF) of mass surface densities, $Σ$, of infrared dark cloud (IRDC) G028.37+00.07 and its surrounding giant molecular cloud. This PDF constrains the physical processes, such as turbulence, magnetic fields and self-gravity, that are expected to be controlling cloud structure and star formation activity. The chosen IRDC is of particular interest since it has almost 100,000 solar masses within a radius of 8 parsecs, making it one of the most massive, dense molecular structures known and is thus a potential site for the formation of a "super star cluster." We study $Σ$ in two ways. First, we use a combination of NIR and MIR extinction maps that are able to probe the bulk of the cloud structure up to $Σ\sim1\:{\rm{g\:cm}^{-2}}\:$($A_V\simeq200$ mag). Second, we study the FIR and sub-mm dust continuum emission from the cloud utilizing Herschel PACS and SPIRE images and paying careful attention to the effects of foreground and background contamination. We find that the PDFs from both methods, applied over a $\sim20^\prime$(30 pc)-sized region that contains $\simeq1.5\times10^5\:M_\odot$ and encloses a minimum closed contour with $Σ\simeq0.013\:{\rm{g\:cm}^{-2}}\:$($A_V\simeq3$ mag), shows a log-normal shape with the peak measured at $Σ\simeq0.021\:{\rm{g\:cm}^{-2}}\:$($A_V\simeq4.7$ mag). There is tentative evidence for the presence of a high-$Σ$ power law tail that contains from $\sim3\%$ to 8\% of the mass of the cloud material. We discuss the implications of these results for the physical processes occurring in this cloud.

astro-ph.GA↗

arXiv2015

Spectroscopic infrared extinction mapping as a probe of grain growth in IRDCs

We present spectroscopic tests of MIR to FIR extinction laws in IRDC G028.36+00.07, a potential site of massive star and star cluster formation. Lim & Tan (2014) developed methods of FIR extinction mapping of this source using ${\it Spitzer}$-MIPS ${\rm 24μm}$ and ${\it Herschel}$-PACS ${\rm 70μm}$ images, and by comparing to MIR ${\it Spitzer}$-IRAC $3$--${\rm 8μm}$ extinction maps, found tentative evidence for grain growth in the highest mass surface density regions. Here we present results of spectroscopic infrared extinction (SIREX) mapping using ${\it Spitzer}$-IRS (14 to ${\rm 38μm}$) data of the same IRDC. These methods allow us to first measure the SED of the diffuse Galactic ISM that is in the foreground of the IRDC. We then carry out our primary investigation of measuring the MIR to FIR opacity law and searching for potential variations as a function of mass surface density within the IRDC. We find relatively flat, featureless MIR-FIR opacity laws that lack the $\sim{\rm 12μm}$ and $\sim{\rm 35μm}$ features associated with the thick water ice mantle models of Ossenkopf & Henning (1994). Their thin ice mantle models and the coagulating aggregate dust models of Ormel et al. (2011) are a generally better match to the observed opacity laws. We also find evidence for generally flatter MIR to FIR extinction laws as mass surface density increases, strengthening the evidence for grain and ice mantle growth in higher density regions.

astro-ph.GA↗

arXiv2013

Far-infrared extinction mapping of infrared dark clouds

Progress in understanding star formation requires detailed observational constraints on the initial conditions, i.e. dense clumps and cores in giant molecular clouds that are on the verge of gravitational instability. Such structures have been studied by their extinction of Near-Infrared (NIR) and, more recently, Mid-Infrared (MIR) background light. It has been somewhat more of a surprise to find that there are regions that appear as dark shadows at Far-Infrared (FIR) wavelengths as long as $\sim$100$μm$. Here we develop analysis methods of FIR images from Spitzer-MIPS and Herschel-PACS that allow quantitative measurements of cloud mass surface density, $Σ$. The method builds upon that developed for MIR extinction mapping (MIREX) (Butler and Tan 2012), in particular involving a search for independent saturated, i.e. very opaque, regions that allow measurement of the foreground intensity. We focus on three massive starless core/clumps in IRDC G028.37+00.07, deriving mass surface density maps from 3.5 to 70$μm$. A by-product of this analysis is measurement of the spectral energy distribution of the diffuse foreground emission. The lower opacity at 70$μm$ allows us to probe to higher $Σ$ values, up to $\sim1\:{\rm{g\:cm}^{-2}}$ in the densest parts of the core/clumps. Comparison of the $Σ$ maps at different wavelengths constrains the shape of the MIR-FIR dust opacity law in IRDCs. We find it is most consistent with the thick ice mantle models of Ossenkopf and Henning (1994). There is tentative evidence for grain ice mantle growth as one goes from lower to higher $Σ$ regions.

astro-ph.SR↗

arXiv2012

Trends of Papers Published from 2006 to 2010 in Journals Nature and Science

We present an analysis of the papers published in the journals Nature and Science in the years from 2006 to 2010. During this period, a total of 7788 papers were published in the two journals. This includes 544 astronomy papers that comprise 7.0% of the papers in `all' research fields and 18.9% of those in the fields of `physical sciences'. The sub-fields of research of the astronomy papers are distributed, in descending order of number of papers, in Solar System, stellar astronomy, galaxies and the universe, the Milky Way Galaxy, and exoplanets. The observational facilities used for the studies are mainly ground-based telescopes (31.1%), spacecrafts (27.0%), and space telescopes (22.8%), while 16.0% of papers did not use any noticeable facilities and 1.7% used other facilities. Korean scientists have published 86 papers (33 in Nature and 53 in Science), which is 1.10% of all the papers (N=7788) in the two journals. The share of papers by Korean astronomers among the scientific papers by Koreans is 8.14%, slightly higher than the contribution of astronomy papers (7.0%) in both journals.

astro-ph.IM↗