Large Silicon Abundance in Photodissociation Regions

Kawada

Murakami

et al. 2010

A&A

Aims. We investigate the structure of the interstellar medium (ISM) and identify the location of possible embedded excitation sources from far-infrared (FIR) line and mid-infrared continuum emission maps. Methods. We carried out imaging spectroscopic observations of four giant Galactic star-forming regions with the Fourier transform spectrometer (FTS) onboard AKARI. We obtained [O III] 88 μm and [C II] 158 μm line intensity maps of all the regions: G3.270-0.101, G333.6-0.2, NGC 3603, and M 17. Results. For G3.270-0.101, we obtained high-spatial-resolution [O III] 88 μm line-emission maps and a FIR continuum map for the first time, which imply that [O III] 88 μm emission identifies the excitation sources more clearly than the radio continuum emission. In G333.6-0.2, we found a local [O III] 88 μm emission peak, which is indicative of an excitation source. This is supported by the 18 μm continuum emission, which is considered to trace the hot dust distribution. For all regions, the [C II] 158 μm emission is distributed widely as suggested by previous observations of star-forming regions. Conclusions. We conclude that [O III] 88 μm emission traces the excitation sources more accurately than the radio continuum emission, especially where there is a high density and/or column density gradient. The FIR spectroscopy provides a promising means of understanding the nature of star-forming regions.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Properties of active galactic star-forming regions probed by imaging spectroscopy with the Fourier transform spectrometer (FTS) onboard AKARI

Kawada

Murakami

et al. 2010

A&A

“…In S171 and σ Sco region, the PDR contribution to the [C ii] emission is estimated by the PDR modeling, and the ionized gas contribution shows a spatial distribution with about 80% at positions closer to the exciting stars, but only 20% or 30% at positions farther away (Okada et al 2006(Okada et al , 2003. Similarly 10-30% contribution of the ionized gas is re- ported in several star-forming regions in nearby galaxies with almost solar metallicity (Contursi et al 2013;Kramer et al 2005).…”

Section: Estimate Of the [C Ii] Emission Coming From Ionized Gasmentioning

confidence: 98%

Velocity resolved [C ii], [C i], and CO observations of the N159 star-forming region in the Large Magellanic Cloud: a complex velocity structure and variation of the column densities

Requeña-Torres

Güsten

et al. 2015

A&A

Self Cite

Context. The [C ii] 158 µm fine structure line is one of the dominant cooling lines in star-forming active regions. Together with models of photon-dominated regions, the data is used to constrain the physical properties of the emitting regions, such as the density and the radiation field strength. According to the modeling, the [C ii] 158 µm line integrated intensity compared to the CO emission is expected to be stronger in lower metallicity environments owing to lower dust shielding of the UV radiation, a trend that is also shown by spectral-unresolved observations. In the commonly assumed clumpy UV-penetrated cloud scenario, the models predict a [C ii] line profile similar to that of CO. However, recent spectral-resolved observations by Herschel/HIFI and SOFIA/GREAT (as well as the observations presented here) show that the velocity resolved line profile of the [C ii] emission is often very different from that of CO lines, indicating a more complex origin of the line emission including the dynamics of the source region. Aims. The Large Magellanic Cloud (LMC) provides an excellent opportunity to study in great detail the physics of the interstellar medium (ISM) in a low-metallicity environment by spatially resolving individual star-forming regions. The aim of our study is to investigate the physical properties of the star-forming ISM in the LMC by separating the origin of the emission lines spatially and spectrally. In this paper, we focus on the spectral characteristics and the origin of the emission lines, and the phases of carbon-bearing species in the N159 star-forming region in the LMC. Methods. We mapped a 4 ′ ×(3 ′ -4 ′ ) region in N159 in [C ii] 158 µm and [N ii] 205 µm with the GREAT instrument on board SOFIA. We also observed CO(3-2), (4-3), (6-5), 13 CO(3-2), and [C i] 3 P 1 -3 P 0 and 3 P 2 -3 P 1 with APEX. All spectra are velocity resolved. Results. The emission of all transitions observed shows a large variation in the line profiles across the map and in particular between the different species. At most positions the [C ii] emission line profile is substantially wider than that of CO and [C i]. We estimated the fraction of the [C ii] integrated line emission that cannot be fitted by the CO line profile to be 20% around the CO cores, and up to 50% at the area between the cores, indicating a gas component that has a much larger velocity dispersion than the ones probed by the CO and [C i] emission. We derived the relative contribution from C + , C, and CO to the column density in each velocity bin. The result clearly shows that the contribution from C + dominates the velocity range far from the the velocities traced by the dense molecular gas. Spatially, the region located between the CO cores of N159 W and E has a higher fraction of C + over the whole velocity range. We estimate the contribution of the ionized gas to the [C ii] emission using the ratio to the [N ii] emission, and find that the ionized gas contributes ≤ 19% to the [C ii] emission at its peak position, and ≤ 15% over the whol...

“…Previous studies show that over 10% of Si atoms are in the gas-phase in star-forming regions (Okada et al 2008(Okada et al , 2006(Okada et al , 2003Mizutani et al 2004;Fuente et al 2000;Colgan et al 1993), whereas the gas-phase abundance of Si in the cool ISM is ∼ 5% (Savage & Sembach 1996). On the other hand, the gas-phase Fe abundance is below 1% or a few % of the solar abundance (Okada et al 2008;Lebouteiller et al 2008;van den Ancker et al 2000;Timmermann et al 1996).…”

Section: Previous Studies and Its Limitationsmentioning

confidence: 96%

Depletion Study of Si And Fe with Mid- and Far-Infrared Imaging Spectroscopy with SPICA

SPICA Joint European/Japanese Workshop

Onaka

Kaneda

et al. 2009

Ionic emission lines, such as [Si II] 35 μm, [Fe II] 26 μm, and [Fe III] 23 μm, can be used to investigate the gas-phase abundance of Si and Fe, which are key elements of the constituents of interstellar dust grains. The depletion study of Si and Fe provides crucial information on the chemical composition of dust. The investigation of the spatial distribution and the correlation with the physical properties of the environment in active regions is important for the understanding of the evolution of the interstellar matter. Previous studies showed that the gas-phase Si abundance is much larger than that in cool interstellar clouds and much less depleted than Fe. However, the depletion of these metals in active regions still has large uncertainties due to the varying physical properties in the large aperture as well as the insufficient sensitivity. We explore the strategy to estimate the physical properties using midand far-infrared emission lines that SPICA can observe.