Ammonia in infrared dark clouds

By T. Pillai, F. Wyrowski, S. Carey, K. M. M. M. F. Radioastronomie, Bonn Spitzer Science Center, C. I. O. Technology.. 2006

204 citations recorded by the source corpus.

Context. While low mass clouds have been relatively well studied, our picture of high-mass star formation remains unclear. Infrared Dark Clouds appear to be the long sought population of cold and dense aggregations with the potential of harbouring the earliest stages of massive star formation. Up to now there has been no systematic study on the temperature distribution, velocity fields, chemical and physical state toward this new cloud population. Aims. Knowing these properties is crucial for understanding the presence, absence and the very potential of star formation. The present paper aims at addressing these questions. We analyse temperature structures and velocity fields and gain information on their chemical evolution. Methods. We mapped the $(J,K) = (1,~1)$ and (2, 2) inversion transitions of ammonia in 9 infrared dark clouds. Our observations allow the most reliable determination of gas temperatures in IRDCs to date. Results. The gas emission is remarkably coextensive with the extinction seen at infrared wavelengths and with the submillimeter dust emission. Our results show that IRDCs are on average cold ($T 100 ~$${M}_\odot$), highly turbulent (1–3 $ \rm km~s^{-1}$) and exhibit significant velocity structure (variations around 1–2 $\rm km~s^{-1}$ over the cloud). Conclusions. We find an increasing trend in temperature from IRDCs with high ammonia column density to high mass protostellar objects and Ultracompact Hii regions, stages of early warm high-mass star formation. The linewidths of IRDCs are smaller than those observed in high mass protostellar objects and hot core/Ultracompact Hii regions. On basis of this sample, and by comparison of the ammonia gas properties within a cloud and between different clouds, we infer that while active star formation is not yet pervasive in most IRDCs, local condensations might collapse in the future or have already begun forming stars.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/2125ce08fbac3b92f6c33d9c5228cafd319041a7

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Citations in the corpus

The ATLASGAL survey: a catalog of dust condensations in the Galactic plane (2013, background): “Their physical properties have also been extensively studied since then (e.g. Pillai et al. 2006; Vasyunina et al. 2009; Ragan et al. 2012).”
Dense gas in the Galactic central molecular zone is warm and heated by turbulence (2015, background): “Dust and NH3 derived temperatures are usually assumed and often observed to agree in Galactic disk clouds (Pillai et al. 2006; Dunham et al. 2010; Juvela et al. 2012; Battersby et al. 1 Assuming the IAU-recommended d = 8.5 kpc (Ghez et al. 2008; Gillessen et al. 2009; Reid et al. 2009; Gillessen et…”
CHEMISTRY IN INFRARED DARK CLOUD CLUMPS: A MOLECULAR LINE SURVEY AT 3 mm (2011, background): “Temperatures derived using NH3 observations are lower than dust temperatures and range from ∼10–20 K (Pillai et al. 2006; Sakai et al. 2008; Devine et al. 2011; Ragan et al. 2011).”
FRAGMENTATION AT THE EARLIEST PHASE OF MASSIVE STAR FORMATION (2009, methodology): “Systematic studies found that many IRDCs contain over 103M of dense molecular gas (Simon et al. 2006a; Rathborne et al. 2006; Pillai et al. 2006).”
Hierarchical fragmentation and differential star formation in the Galactic ‘Snake’: infrared dark cloud G11.11−0.12 (2014, methodology): “As far as we see with current data, our results combined with Pillai et al. (2006b) supports the disc scenario.”
Cold Dark Clouds: The Initial Conditions for Star Formation (2007, background): “From observations of CO, NH3, CH3C2H, and H2CO temperatures are estimated to be below 20 K with densities in excess of 105 cm−3 (Carey et al. 1998; Teyssier et al. 2002; Pillai et al. 2006).”
The RMS Survey: Ammonia and water maser analysis of massive star forming regions. ⋆ (2011, methodology): “We derive minimum and maximum beam filling factors of 0.1 and 0.6 respectively, with a mean value of∼0.3; this compare well to the values reported by Pillai et al. (2006) (ηff ∼0.3–0.5) from ammonia mapping observations of a small sample of infrared dark clouds (IRDCs) and Rosolowsky et al. (2008)…”
Fragmentation and mass segregation in the massive dense cores of Cygnus X (2009, background): “…2002, Faúndez et al. 2004), and more recently inside the dark filaments seen in the infrared surveys of the Galactic plane, the so-called IRDCs (e.g. Simon et al. 2006, and references therein), have found a number of candidates to host such precursors (Rathborne et al. 2006, Pillai et al. 2006).”
Ammonia from cold high-mass clumps discovered in the inner Galactic disk by the ATLASGAL survey (2012, background): “Moreover, Pillai et al. (2006) obtained NH3 abundances from 10−8 to 10−7 for a sample of IRDCs, their χNH3 range is narrower compared to our values and similar to our higher abundances.”