THE PROPERTIES OF MASSIVE, DENSE CLUMPS: MAPPING SURVEYS OF HCN AND CS

By Jingwen Wu, N. Evans II, Y. Shirley, C. Knez. 2010

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We have mapped over 50 massive, dense clumps with four dense gas tracers: HCN J = 1–0 and 3–2; and CS J = 2–1 and 7–6 transitions. Spectral lines of optically thin H13CN 3–2 and C34S 5–4 were also obtained toward the map centers. These maps usually demonstrate single well-peaked distributions at our resolution, even with higher J transitions. The size, virial mass, surface density, and mean volume density within a well-defined angular size (FWHM) were calculated from the contour maps for each transition. We found that transitions with higher effective density usually trace the more compact, inner part of the clumps but have larger linewidths, leading to an inverse linewidth–size relation using different tracers. The mean surface densities are 0.29, 0.33, 0.78, 1.09 g cm−2 within FWHM contours of CS 2–1, HCN 1–0, HCN 3–2, and CS 7–6, respectively. We find no correlation of LIR with surface density and a possible inverse correlation with mean volume density, contrary to some theoretical expectations. Molecular line luminosities L′mol were derived for each transition. We see no evidence in the data for the relation between L′mol and mean density posited by modelers. The correlation between L′mol and the virial mass is roughly linear for each dense gas tracer. No obvious correlation was found between the line luminosity ratio and infrared luminosity, bolometric temperature, or the LIR/MVir ratio. A nearly linear correlation was found between the infrared luminosity and the line luminosity of all dense gas tracers for these massive, dense clumps, with a lower cutoff in luminosity at LIR = 104.5 L☉. The LIR–L′HCN1–0 correlation agrees well with the one found in galaxies. These correlations indicate a constant star formation rate per unit mass from the scale of dense clumps to that of distant galaxies when the mass is measured for dense gas. These results support the suggestion that starburst galaxies may be understood as having a large fraction of gas in dense clumps.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/5052e725dff1fe5ae50d62685052fa34a5e1e36c

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Citations in the corpus

Gravity or turbulence? II. Evolving column density PDFs in molecular clouds (2011, background): “…et al. (2011), based on observations of massive dense cores (Caselli & Myers 1995; Plume et al. 1997; Shirley et al. 2003; Gibson et al. 2009; Wu et al. 2010), showed that the Larson (1981) relationship between velocity dispersion and size arises naturally if turbulent motions are the result…”
THE STAR FORMATION RATE AND GAS SURFACE DENSITY RELATION IN THE MILKY WAY: IMPLICATIONS FOR EXTRAGALACTIC STUDIES (2010, methodology): “Uncertainties in the ΣHCN are computed by adding in quadrature the errors in the FWHM size and the mass as discussed in Wu et al. (2010).”
MAXIMALLY STAR-FORMING GALACTIC DISKS. I. STARBURST REGULATION VIA FEEDBACK-DRIVEN TURBULENCE (2011, background): “Motivated by observations showing a linear relation between very dense gas and star formation (e.g. Gao & Solomon 2004; Wu et al. 2005, 2010), we assume that star formation takes place in gas above a density threshold ρthr = µnthr at a fixed efficiency per free-fall time εff(nthr); we also assume…”
Dusty Star Forming Galaxies at High Redshift (2014, methodology): “When Wu et al. (2010) examined the robust fits between the SFR and a variety of dense gas tracers, a number of tracers exhibited sub-linear slopes; on the other hand, the least squares fits were typically consistent with slopes of unity.”
THE STAR FORMATION RATE OF TURBULENT MAGNETIZED CLOUDS: COMPARING THEORY, SIMULATIONS, AND OBSERVATIONS (2012, methodology): “The observational data are from Galactic observations of clouds and YSOs identified in the Spitzer Cores-to-Disks (C2D) and GB surveys (Evans et al. 2009) of massive dense clumps (Wu et al. 2010), and of the Taurus molecular cloud (Pineda et al. 2010; Rebull et al. 2010).”
Star Formation in the Milky Way and Nearby Galaxies (2012, methodology): “The line luminosities of other dense gas tracers also show strong correlations with both virial mass (Wu et al. 2010a) and the mass derived from dust continuum observations (Reiter et al. 2011b).”
STAR FORMATION RELATIONS IN NEARBY MOLECULAR CLOUDS (2014, methodology): “We plot these SFRs in red using the mass from the maps of HCN J = 1 → 0 from Wu et al. (2010), where both measurements exist.”
A UNIVERSAL, LOCAL STAR FORMATION LAW IN GALACTIC CLOUDS, NEARBY GALAXIES, HIGH-REDSHIFT DISKS, AND STARBURSTS (2011, unknown): “For this reason, we do not consider published estimates of the SFR for objects with dynamical times ≪ 1 Myr (e.g. the compact regions surveyed by Wu et al. 2010 or the high density sample of Heiderman et al. 2010, which have crossing times ∼ 0.1 Myr).”
ON THE STAR FORMATION RATES IN MOLECULAR CLOUDS (2010, methodology): “At higher gas surface densities their measurements appear to connect smoothly to those of Wu et al. (2005, 2010).”
Gravity or turbulence? Velocity dispersion–size relation (2010, methodology): “6), implies that massive, compact cores should develop larger velocity dispersions for larger column densities (N ∼ 1023–1025 cm−2, Shirley et al. 2003; Gibson et al. 2009; Wu et al. 2010).”
Collapse, outflows and fragmentation of massive, turbulent and magnetized prestellar barotropic cores (2011, background): “In the context of massive cores (Beuther et al. 2002a, Motte et al. 2007, Wu et al. 2010, Csengeri et al. 2010), the influence of the magnetic field is not extensively explored yet because only few studies have been performed (e.g. Banerjee & Pudritz 2007) in spite of the measurement which suggest…”
The big problems in star formation: The star formation rate, stellar clustering, and the initial mass function (2014, background): “In the latter category, there have been a number of surveys of extragalactic star formation using HCN, HCO+, higher rotational transitions CO, and other molecules that have critical densities ranging from nH2 ∼ 104 − 108 cm−3 (Gao & Solomon 2004a,b; Narayanan et al. 2005; Graciá-Carpio et al. 2006;”