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تسجيل مستخدم جديدA Virialized Filamentary Infrared Dark Cloud
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Audra K. Hernandez
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The initial conditions of massive star and star cluster formation are expected to be cold, dense and high column density regions of the interstellar medium, which can reveal themselves via near, mid and even far-infrared absorption as Infrared Dark Clouds (IRDCs). Elucidating the dynamical state of IRDCs thus constrains theoretical models of these complex processes. In particular, it is important to assess whether IRDCs have reached virial equilibrium, where the internal pressure balances that due to the self-gravitating weight of the cloud plus the pressure of the external environmental. We study this question for the filamentary IRDC G035.39-00.33 by deriving mass from combined NIR & MIR extinction maps and velocity dispersion from C18O (1-0) & (2-1) line emission. In contrast to our previous moderately super-virial results based on 13CO emission and MIR-only extinction mapping, with improved mass measurements we now find that the filament is consistent with being in virial equilibrium, at least in its central parsec-wide region where ~1000 M_Sun snakes along several parsecs. This equilibrium state does not require large-scale net support or confinement by magnetic fields.
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Infrared Dark Clouds (IRDCs) are cold, high mass surface density and high density structures, likely to be representative of the initial conditions for massive star and star cluster formation. CO emission from IRDCs has the potential to be useful for
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We present molecular line observations, made with angular resolutions of ~20, toward the filamentary infrared dark cloud G34.43+0.24 using the APEX [CO(3-2), 13CO(3-2), C18O(3-2) and CS(7-6) transitions], Nobeyama 45 m [CS(2-1), SiO(2-1), C34S(2-1),
HCO+(1-0), H13CO+(1-0) and CH3OH(2-1) transitions], and SEST [CS(2-1) and C18O(2-1) transitions] telescopes. We find that the spatial distribution of the molecular emission is similar to that of the dust continuum emission observed with 11 resolution showing a filamentary structure and four cores. The cores have local thermodynamic equilibrium masses ranging from 3.3x10^2 - 1.5x10^3 solar masses and virial masses from 1.1x10^3 - 1.5x10^3 solar masses, molecular hydrogen densities between 1.8x10^4 and 3.9x10^5 cm^{-3}, and column densities >2.0x10^{22} cm^{-2}; values characteristics of massive star forming cores. The 13CO(3-2) profile observed toward the most massive core reveals a blue profile indicating that the core is undergoing large-scale inward motion with an average infall velocity of 1.3 km/s and a mass infall rate of 1.8x10^{-3} solar masses per year. We report the discovery of a molecular outflow toward the northernmost core thought to be in a very early stage of evolution. We also detect the presence of high velocity gas toward each of the other three cores, giving support to the hypothesis that the excess 4.5 $mu$ emission (green fuzzies) detected toward these cores is due to shocked gas. The molecular outflows are massive and energetic, with masses ranging from 25 -- 80 solar masses, momentum 2.3 - 6.9x10^2 Msun km/s, and kinetic energies 1.1 - 3.6x10^3 Msun km^2 s^{-2}; indicating that they are driven by luminous, high-mass young stellar objects.
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We present results of a high resolution study of the filamentary infrared dark cloud G192.76+00.10 in the S254-S258 OB complex in several molecular species tracing different physical conditions. These include three isotopologues of carbon monoxide (C
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Infrared dark clouds (IRDCs) are thought to be potential hosts of the elusive early phases of high-mass star formation. Here we conduct an in-depth kinematic analysis of one such IRDC, G034.43+00.24 (Cloud F), using high sensitivity and high spectral
resolution IRAM-30m N$_2$H$^+$ ($1-0$) and C$^{18}$O ($1-0$) observations. To disentangle the complex velocity structure within this cloud we use Gaussian decomposition and hierarchical clustering algorithms. We find that four distinct coherent velocity components are present within Cloud F. The properties of these components are compared to those found in a similar IRDC, G035.39-00.33 (Cloud H). We find that the components in both clouds have: high densities (inferred by their identification in N$_2$H$^+$), trans-to-supersonic non-thermal velocity dispersions with Mach numbers of $sim$ $1.5-4$, a separation in velocity of $sim$3 km s$^{-1}$, and a mean red-shift of $sim$ 0.3 km s$^{-1}$ between the N$_2$H$^+$ (dense gas) and C$^{18}$O emission (envelope gas). The latter of these could suggest that these clouds share a common formation scenario. We investigate the kinematics of the larger-scale Cloud F structures, using lower-density-tracing $^{13}$CO ($1-0$) observations. A good correspondence is found between the components identified in the IRAM-30m observations and the most prominent component in the$^{13}$CO data. We find that the IRDC Cloud F is only a small part of a much larger structure, which appears to be an inter-arm filament of the Milky Way.
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