Fragmentation of Massive Dense Cores Down to ≲ 1000 Au: Relation Between Fragmentation and Density Structure

Palau, Aina; Estalella, R.; Girart, J. M.; Fuente, A.; Fontani, F.; Commerçon, B.; Busquet, G.; Bontemps, Sylvain; Sánchez-Monge, Á.; Zapata, Luis A.; Zhang, Qizhou; Hennebelle, P.; Francesco, James Di

doi:10.1088/0004-637x/785/1/42

Cited by 87 publications

(159 citation statements)

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“…As in M 16, these α values have to be taken with caution since they mix different structures. Nevertheless, the high alpha value observed in regions close to the ionizing sources has already been seen in other regions such as the central, dense, high-mass starforming ridge in the cloud NGC 6334 (Russeil et al 2013) and more recently in Palau et al (2014) for the massive dense cores DR21-OH, AFGL 5142 and CB3. The transition from high values to low values typical of other clouds seems to indicate that the compression from ionization is also playing a role at high column densities where structures are expected to be gravitationally collapsing.…”

Section: Rosette Nebulamentioning

confidence: 76%

Ionization compression impact on dense gas distribution and star formation

Tremblin

Schneider

Minier

et al. 2014

A&A

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Aims. Ionization feedback should impact the probability distribution function (PDF) of the column density of cold dust around the ionized gas. We aim to quantify this effect and discuss its potential link to the core and initial mass function (CMF/IMF). Methods. We used Herschel column density maps of several regions observed within the HOBYS key program in a systematic way: M 16, the Rosette and Vela C molecular clouds, and the RCW 120 H ii region. We computed the PDFs in concentric disks around the main ionizing sources, determined their properties, and discuss the effect of ionization pressure on the distribution of the column density. Results. We fitted the column density PDFs of all clouds with two lognormal distributions, since they present a "double-peak" or an enlarged shape in the PDF. Our interpretation is that the lowest part of the column density distribution describes the turbulent molecular gas, while the second peak corresponds to a compression zone induced by the expansion of the ionized gas into the turbulent molecular cloud. Such a double peak is not visible for all clouds associated with ionization fronts, but it depends on the relative importance of ionization pressure and turbulent ram pressure. A power-law tail is present for higher column densities, which are generally ascribed to the effect of gravity. The condensations at the edge of the ionized gas have a steep compressed radial profile, sometimes recognizable in the flattening of the power-law tail. This could lead to an unambiguous criterion that is able to disentangle triggered star formation from pre-existing star formation. Conclusions. In the context of the gravo-turbulent scenario for the origin of the CMF/IMF, the double-peaked or enlarged shape of the PDF may affect the formation of objects at both the low-mass and the high-mass ends of the CMF/IMF. In particular, a broader PDF is required by the gravo-turbulent scenario to fit the IMF properly with a reasonable initial Mach number for the molecular cloud. Since other physical processes (e.g., the equation of state and the variations among the core properties) have already been said to broaden the PDF, the relative importance of the different effects remains an open question.

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Section: Rosette Nebulamentioning

confidence: 76%

Ionization compression impact on dense gas distribution and star formation

Tremblin

Schneider

Minier

et al. 2014

A&A

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“…In the following, we investigate the effects of turbulent and thermal pressure in regulating the fragmentation of the clusters in NGC 6334, by determining the Jeans mass and comparing with the measured mass of the fragments (see e.g. Palau et al 2015Palau et al , 2014.…”

Section: Fragmentation Statusmentioning

confidence: 99%

Physical properties of the star-forming clusters in NGC 6334

Sadaghiani

Sánchez-Monge

Schilke

et al. 2020

A&A

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Aims. We aim to characterise certain physical properties of high-mass star-forming sites in the NGC 6334 molecular cloud, such as the core mass function (CMF), spatial distribution of cores, and mass segregation. Methods. We used the Atacama Large Millimetre/sub-millimetre Array (ALMA) to image the embedded clusters NGC 6334-I and NGC 6334-I(N) in the continuum emission at 87.6 GHz. We achieved a spatial resolution of 1300 au, enough to resolve different compact cores and fragments, and to study the properties of the clusters. Results. We detected 142 compact sources distributed over the whole surveyed area. The ALMA compact sources are clustered in different regions. We used different machine-learning algorithms to identify four main clusters: NGC 6334-I, NGC 6334-I(N), NGC 6334-I(NW), and NGC 6334-E. The typical separations between cluster members range from 4 000 au to 12 000 au. These separations, together with the core masses (0.1-100 M ), are in agreement with the fragmentation being controlled by turbulence at scales of 0.1 pc. We find that the CMFs show an apparent excess of high-mass cores compared to the stellar Initial Mass Function. We evaluated the effects of temperature and unresolved multiplicity on the derived slope of the CMF. Based on this, we conclude that the excess of high-mass cores might be spurious and due to inaccurate temperature determinations and/or resolution limitations. We searched for evidence of mass segregation in the clusters and we find that clusters NGC 6334-I and NGC 6334-I(N) show hints of segregation with the most massive cores located in the centre of the clusters. Conclusions. We searched for correlations between the physical properties of the four embedded clusters and their evolutionary stage (based on the presence of H ii regions and infrared sources). NGC 6334-E appears as the most evolved cluster, already harboring a well-developed H ii region. NGC 6334-I is the second-most evolved cluster with an ultra-compact H ii region. NGC 6334-I(N) contains the largest population of dust cores distributed in two filamentary structures and no dominant H ii region. Finally, NGC 6334-I(NW) is a cluster of mainly low-mass dust cores with no clear signs of massive cores or H ii regions. We find a larger separation between cluster members in the more evolved clusters favoring the role of gas expulsion and stellar ejection with evolution. The mass segregation, seen in the NGC 6334-I and NGC 6334-I(N) clusters, suggests a primordial origin for NGC 6334-I(N). In contrast, the segregation in NGC 6334-I might be due to dynamical effects. Finally, the lack of massive cores in the most evolved cluster suggests that the gas reservoir is already exhausted, while the less evolved clusters still have a large gas reservoir along with the presence of massive cores. In general, the fragmentation process of NGC 6334 at large scales (from filament to clump, i.e. at about 1 pc) is likely governed by turbulent pressure, while at smaller scales (scale of cores and sub-fragments, i.e. a few hundred au) ...

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“…Furthermore, these simulations suggest that the initial density profile of star-forming clumps/cores could be the most important factor for fragmentation and evolution of HMSF regions. Palau et al (2014) observed a number of massive dense cores to study the relation between fragmentation and density structure of massive cores and they find that steeper density profiles tend to show lower fragmentation. These results probably indicate that AS more easily form massive stars by limiting fragmentation.…”

Section: Massive Star Formationmentioning

confidence: 99%

H II regions and high-mass starless clump candidates

Zhang

Zavagno

Yuan

et al. 2020

A&A

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Context. The role of ionization feedback on high-mass (> 8 M ) star formation is still highly debated. Questions remain concerning the presence of nearby H ii regions changes the properties of early high-mass star formation and whether H ii regions promote or inhibit the formation of high-mass stars. Aims. To characterize the role of H ii regions on the formation of high-mass stars, we study the properties of a sample of candidates high-mass starless clumps (HMSCs), of which about 90% have masses larger than 100 M . These high-mass objects probably represent the earliest stages of high-mass star formation; we search if (and how) their properties are modified by the presence of an H ii region. Methods. We took advantage of the recently published catalog of HMSC candidates. By cross matching the HMSCs and H ii regions, we classified HMSCs into three categories: 1) The HMSCs associated with H ii regions both in the position in the projected plane of the sky and in velocity; 2) HMSCs associated in the plane of the sky, but not in velocity; and 3) HMSCs far away from any H ii regions in the projected sky plane. We carried out comparisons between associated and nonassociated HMSCs based on statistical analyses of multiwavelength data from infrared to radio. Results. We show that there are systematic differences of the properties of HMSCs in different environments. Statistical analyses suggest that HMSCs associated with H ii regions are warmer, more luminous, more centrally-peaked and turbulent. We also clearly show, for the first time, that the ratio of bolometric luminosity to envelope mass of HMSCs (L/M) could not be a reliable evolutionary probe for early massive star formation due to the external heating effects of the H ii regions. Conclusions. We show HMSCs associated with H ii regions present statistically significant differences from HMSCs far away from H ii regions, especially for dust temperature and L/M. More centrally peaked and turbulent properties of HMSCs associated with H ii regions may promote the formation of high-mass stars by limiting fragmentation. High-resolution interferometric surveys toward HMSCs are crucial to reveal how H ii regions impact the star formation process inside HMSCs.

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Fragmentation of Massive Dense Cores Down to ≲ 1000 Au: Relation Between Fragmentation and Density Structure

Cited by 87 publications

References 100 publications

Ionization compression impact on dense gas distribution and star formation

Ionization compression impact on dense gas distribution and star formation

Physical properties of the star-forming clusters in NGC 6334

H II regions and high-mass starless clump candidates

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Fragmentation of Massive Dense Cores Down to ≲ 1000 Au: Relation Between Fragmentation and Density Structure

Cited by 87 publications

References 100 publications

Ionization compression impact on dense gas distribution and star formation

Ionization compression impact on dense gas distribution and star formation

Physical properties of the star-forming clusters in NGC 6334

H II regions and high-mass starless clump candidates

Contact Info

Product

Resources

About

H II regions and high-mass starless clump candidates