scholarly journals The census of dense cores in the Serpens region from the Herschel Gould Belt Survey

2020 ◽  
Vol 500 (4) ◽  
pp. 4257-4276
Author(s):  
E Fiorellino ◽  
D Elia ◽  
Ph André ◽  
A Men’shchikov ◽  
S Pezzuto ◽  
...  
Keyword(s):  
Spatial Association ◽  
Mass Function ◽  
Initial Mass Function ◽  
Core Mass ◽  
Filamentary Structure ◽  
Star Forming ◽  
Gould Belt ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Prestellar Cores

ABSTRACT The Herschel Gould Belt survey mapped the nearby (d < 500 pc) star-forming regions to understand better how the prestellar phase influences the star formation process. Here, we report a complete census of dense cores in a ∼15 deg2 area of the Serpens star-forming region located between d ∼ 420 and 484 pc. The PACS and SPIRE cameras imaged this cloud from 70 to 500 μm. With the multiwavelength source extraction algorithm getsources, we extract 833 sources, of which 709 are starless cores and 124 are candidate protostellar cores. We obtain temperatures and masses for all the sample, classifying the starless cores in 604 prestellar cores and 105 unbound cores. Our census of sources is $80{{\ \rm per\ cent}}$ complete for M > 0.8 M⊙ overall. We produce the core mass function (CMF) and compare it with the initial mass function (IMF). The prestellar CMF is consistent with lognormal trend up to ∼2 M⊙, after which it follows a power law with slope of −2.05 ± 0.34. The tail of its CMF is steeper but still compatible with the IMF for the region we studied in this work. We also extract the filaments network of the Serpens region, finding that $81{{\ \rm per\ cent}}$ of prestellar cores lie on filamentary structures. The spatial association between cores and filamentary structure supports the paradigm, suggested by other Herschel observations, that prestellar cores mostly form on filaments. Serpens is confirmed to be a young, low-mass and active star-forming region.

scholarly journals The dense cores and filamentary structure of the molecular cloud in Corona Australis: Herschel SPIRE and PACS observations from the Herschel Gould Belt Survey

2018 ◽  
Vol 615 ◽  
pp. A125 ◽  
Author(s):  
D. Bresnahan ◽  
D. Ward-Thompson ◽  
J. M. Kirk ◽  
K. Pattle ◽  
S. Eyres ◽  
...  
Keyword(s):  
Mass Distribution ◽  
Molecular Cloud ◽  
Evolutionary Stage ◽  
Filamentary Structure ◽  
Star Forming ◽  
Gould Belt ◽  
Star Forming Regions ◽  
Photodetector Array ◽  
Dense Cores ◽  
Prestellar Cores

We present a catalogue of prestellar and starless cores within the Corona Australis molecular cloud using photometric data from the Herschel Space Observatory. At a distance of d ~ 130 pc, Corona Australis is one of the closest star-forming regions. Herschel has taken multi-wavelength data of Corona Australis with both the Spectral and Photometric Imaging Receiver (SPIRE) and the Photodetector Array Camera and Spectrometer (PACS) photometric cameras in a parallel mode with wavelengths in the range 70–500 μm. A complete sample of starless and prestellar cores and embedded protostars is identified. Other results from the Herschel Gould Belt Survey have shown spatial correlation between the distribution of dense cores and the filamentary structure within the molecular clouds. We go further and show correlations between the properties of these cores and their spatial distribution within the clouds, with a particular focus on the mass distribution of the dense cores with respect to their filamentary proximity. We find that only lower-mass starless cores form away from filaments, while all of the higher-mass prestellar cores form in close proximity to or directly on the filamentary structure. This result supports the paradigm that prestellar cores mostly form on filaments. We analyse the mass distribution across the molecular cloud, finding evidence that the region around the Coronet appears to be at a more dynamically advanced evolutionary stage in comparison to the rest of the clumps within the cloud.

scholarly journals A catalogue of dense cores and young stellar objects in the Lupus complex based on Herschel Gould Belt Survey observations

2018 ◽  
Vol 619 ◽  
pp. A52 ◽  
Author(s):  
M. Benedettini ◽  
S. Pezzuto ◽  
E. Schisano ◽  
P. André ◽  
V. Könyves ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Far Infrared ◽  
Mass Function ◽  
Young Stellar Objects ◽  
Spectral Energy ◽  
Core Mass ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Prestellar Cores

Context. How the diffuse medium of molecular clouds condenses in dense cores and how many of these cores will evolve in protostars is still a poorly understood step of the star formation process. Much progress is being made in this field, thanks to the extensive imaging of star-forming regions carried out with the Herschel Space Observatory. Aims. The Herschel Gould Belt Survey key project mapped the bulk of nearby star-forming molecular clouds in five far-infrared bands with the aim of compiling complete census of prestellar cores and young, embedded protostars. From the complete sample of prestellar cores, we aim at defining the core mass function and studying its relationship with the stellar initial mass function. Young stellar objects (YSOs) with a residual circumstellar envelope are also detected. Methods. In this paper, we present the catalogue of the dense cores and YSOs/protostars extracted from the Herschel maps of the Lupus I, III, and IV molecular clouds. The physical properties of the detected objects were derived by fitting their spectral energy distributions. Results. A total of 532 dense cores, out of which 103 are presumably prestellar in nature, and 38 YSOs/protostars have been detected in the three clouds. Almost all the prestellar cores are associated with filaments against only about one third of the unbound cores and YSOs/protostars. Prestellar core candidates are found even in filaments that are on average thermally subcritical and over a background column density lower than that measured in other star-forming regions so far. The core mass function of the prestellar cores peaks between 0.2 and 0.3 M⊙, and it is compatible with the log-normal shape found in other regions. Herschel data reveal several, previously undetected, protostars and new candidates of Class 0 and Class II with transitional disks. We estimate the evolutionary status of the YSOs/protostars using two independent indicators: the α index and the fitting of the spectral energy distribution from near- to far-infrared wavelengths. For 70% of the objects, the evolutionary stages derived with the two methods are in agreement. Conclusions. Lupus is confirmed to be a very low-mass star-forming region, in terms of both the prestellar condensations and the diffuse medium. Noticeably, in the Lupus clouds we have found star formation activity associated with interstellar medium at low column density, usually quiescent in other (more massive) star-forming regions.

scholarly journals The role of molecular filaments in the origin of the prestellar core mass function and stellar initial mass function

2019 ◽  
Vol 629 ◽  
pp. L4 ◽  
Author(s):  
Ph. André ◽  
D. Arzoumanian ◽  
V. Könyves ◽  
Y. Shimajiri ◽  
P. Palmeirim
Keyword(s):  
Power Law ◽  
Molecular Clouds ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Core Mass ◽  
Filamentary Structure ◽  
Star Forming ◽  
Prestellar Cores ◽  
Stellar Initial Mass Function

Context. The origin of the stellar initial mass function (IMF) is one of the most debated issues in astrophysics. Aims. Here we explore the possible link between the quasi-universal filamentary structure of star-forming molecular clouds and the origin of the IMF. Methods. Based on our recent comprehensive study of filament properties from Herschel Gould Belt survey observations, we derive, for the first time, a good estimate of the filament mass function (FMF) and filament line mass function (FLMF) in nearby molecular clouds. We use the observed FLMF to propose a simple toy model for the origin of the prestellar core mass function (CMF), relying on gravitational fragmentation of thermally supercritical but virialized filaments. Results. We find that the FMF and the FLMF have very similar shapes and are both consistent with a Salpeter-like power-law function (dN/dlog Mline ∝ Mline−1.5±0.1) in the regime of thermally supercritical filaments (Mline >  16 M⊙ pc−1). This is a remarkable result since, in contrast, the mass distribution of molecular clouds and clumps is known to be significantly shallower than the Salpeter power-law IMF, with dN/dlog Mcl ∝ Mcl−0.7. Conclusions. Since the vast majority of prestellar cores appear to form in thermally transcritical or supercritical filaments, we suggest that the prestellar CMF and by extension the stellar IMF are at least partly inherited from the FLMF through gravitational fragmentation of individual filaments.

scholarly journals Properties of the dense core population in Orion B as seen by the Herschel Gould Belt survey

2020 ◽  
Vol 635 ◽  
pp. A34 ◽  
Author(s):  
V. Könyves ◽  
Ph. André ◽  
D. Arzoumanian ◽  
N. Schneider ◽  
A. Men’shchikov ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Column Density ◽  
Mass Function ◽  
Smooth Transition ◽  
High Mass ◽  
Core Mass ◽  
Gould Belt ◽  
Dense Cores ◽  
Prestellar Cores ◽  
Consistent Manner

We present a detailed study of the Orion B molecular cloud complex (d ~ 400 pc), which was imaged with the PACS and SPIRE photometric cameras at wavelengths from 70 to 500 μm as part of the Herschel Gould Belt survey (HGBS). We release new high-resolution maps of column density and dust temperature for the whole complex, derived in the same consistent manner as for other HGBS regions. In the filamentary subregions NGC 2023 and 2024, NGC 2068 and 2071, and L1622, a total of 1768 starless dense cores were identified based on Herschel data, 490–804 (~28−45%) of which are self-gravitating prestellar cores that will likely form stars in the future. A total of 76 protostellar dense cores were also found. The typical lifetime of the prestellar cores was estimated to be tpreOrionB = 1.7−0.6+0.8Myr. The prestellar core mass function (CMF) derived for the whole sample of prestellar cores peaks at ~0.5 M⊙ (in dN/dlogM format) and is consistent with a power-law with logarithmic slope −1.27 ± 0.24 at the high-mass end, compared to the Salpeter slope of − 1.35. In the Orion B region, we confirm the existence of a transition in prestellar core formation efficiency (CFE) around a fiducial value AVbg ~ 7 mag in background visual extinction, which is similar to the trend observed with Herschel in other regions, such as the Aquila cloud. This is not a sharp threshold, however, but a smooth transition between a regime with very low prestellar CFE at AVbg < 5 and a regime with higher, roughly constant CFE at AVbg ≳ 10. The total mass in the form of prestellar cores represents only a modest fraction (~20%) of the dense molecular cloud gas above AVbg ≳ 7 mag. About 60–80% of the prestellar cores are closely associated with filaments, and this fraction increases up to >90% when a more complete sample of filamentary structures is considered. Interestingly, the median separation observed between nearest core neighbors corresponds to the typical inner filament width of ~0.1 pc, which is commonly observed in nearby molecular clouds, including Orion B. Analysis of the CMF observed as a function of background cloud column density shows that the most massive prestellar cores are spatially segregated in the highest column density areas, and suggests that both higher- and lower-mass prestellar cores may form in denser filaments.

scholarly journals The highly variable time evolution of star-forming cores identified with dendrograms

2020 ◽  
Vol 497 (4) ◽  
pp. 4517-4534
Author(s):  
Rachel A Smullen ◽  
Kaitlin M Kratter ◽  
Stella S R Offner ◽  
Aaron T Lee ◽  
Hope How-Huan Chen
Keyword(s):  
Time Evolution ◽  
Mass Function ◽  
Density Field ◽  
Initial Mass Function ◽  
Stellar Content ◽  
Core Mass ◽  
Structure Variation ◽  
Star Forming ◽  
The Core ◽  
Dense Cores

ABSTRACT We investigate the time evolution of dense cores identified in molecular cloud simulations using dendrograms, which are a common tool to identify hierarchical structure in simulations and observations of star formation. We develop an algorithm to link dendrogram structures through time using the three-dimensional density field from magnetohydrodynamical simulations, thus creating histories for all dense cores in the domain. We find that the population-wide distributions of core properties are relatively invariant in time, and quantities like the core mass function match with observations. Despite this consistency, an individual core may undergo large (&gt;40 per cent), stochastic variations due to the redefinition of the dendrogram structure between time-steps. This variation occurs independent of environment and stellar content. We identify a population of short-lived (&lt;200 kyr) overdensities masquerading as dense cores that may comprise $\sim\!20$ per cent of any time snapshot. Finally, we note the importance of considering the full history of cores when interpreting the origin of the initial mass function; we find that, especially for systems containing multiple stars, the core mass defined by a dendrogram leaf in a snapshot is typically less than the final system stellar mass. This work reinforces that there is no time-stable density contour that defines a star-forming core. The dendrogram itself can induce significant structure variation between time-steps due to small changes in the density field. Thus, one must use caution when comparing dendrograms of regions with different ages or environment properties because differences in dendrogram structure may not come solely from the physical evolution of dense cores.

scholarly journals Very Low-Luminosity Objects in Star-Forming Regions

1998 ◽  
Vol 11 (1) ◽  
pp. 423-424
Author(s):  
Motohide Tamura ◽  
Yoichi Itoh ◽  
Yumiko Oasa ◽  
Alan Tokunaga ◽  
Koji Sugitani
Keyword(s):  
Brown Dwarfs ◽  
Mass Function ◽  
T Tauri Stars ◽  
Initial Mass Function ◽  
Formation Mechanisms ◽  
Star Forming ◽  
Star Forming Regions ◽  
T Tauri ◽  
Low Mass ◽  
Stellar Sources

Abstract In order to tackle the problems of low-mass end of the initial mass function (IMF) in star-forming regions and the formation mechanisms of brown dwarfs, we have conducted deep infrared surveys of nearby molecular clouds. We have found a significant population of very low-luminosity sources with IR excesses in the Taurus cloud and the Chamaeleon cloud core regions whose extinction corrected J magnitudes are 3 to 8 mag fainter than those of typical T Tauri stars in the same cloud. Some of them are associated with even fainter companions. Follow-up IR spectroscopy has confirmed for the selected sources that their photospheric temperature is around 2000 to 3000 K. Thus, these very low-luminosity young stellar sources are most likely very low-mass T Tauri stars, and some of them might even be young brown dwarfs.

scholarly journals Origin of the prestellar core mass function and link to the IMF – Herschel first results

2010 ◽  
Vol 6 (S270) ◽  
pp. 255-262 ◽  
Author(s):  
Ph. André ◽  
A. Men'shchikov ◽  
V. Könyves ◽  
D. Arzoumanian
Keyword(s):  
Gravitational Instability ◽  
Mass Function ◽  
Initial Mass Function ◽  
Mhd Turbulence ◽  
Core Mass ◽  
Thin Filaments ◽  
Close Relationship ◽  
Prestellar Cores ◽  
First Results ◽  
The Imf

AbstractWe briefly review ground-based (sub)millimeter dust continuum observations of the prestellar core mass function (CMF) and its connection to the stellar initial mass function (IMF). We also summarize the first results obtained on this topic from the Herschel Gould Belt survey, one of the largest key projects with the Herschel Space Observatory. Our early findings with Herschel confirm the existence of a close relationship between the CMF and the IMF. Furthermore, they suggest a scenario according to which the formation of prestellar cores occurs in two main steps: 1) complex networks of long, thin filaments form first, probably as a result of interstellar MHD turbulence; 2) the densest filaments then fragment and develop prestellar cores via gravitational instability.

scholarly journals Massive Stars at High Redshifts

2007 ◽  
Vol 3 (S250) ◽  
pp. 415-428
Author(s):  
Max Pettini
Keyword(s):  
Massive Stars ◽  
High Redshift ◽  
Mass Function ◽  
Initial Mass Function ◽  
Stellar Spectra ◽  
Star Forming ◽  
Star Forming Regions ◽  
Look Ahead ◽  
Low Metallicity ◽  
High Redshift Universe

AbstractThe five years that have passed since the last IAU Symposium devoted to massive stars have seen a veritable explosion of data on the high redshift universe. The tools developed to study massive stars in nearby galaxies are finding increasing application to the analysis of the spectra of star-forming regions at redshifts as high as z = 7. In this brief review, I consider three topics of relevance to this symposium: the determination of the metallicities of galaxies at high redshifts from consideration of their ultraviolet stellar spectra; constraints on the initial mass function of massive stars in galaxies at z = 2 − 3; and new clues to the nucleosynthesis of carbon and nitrogen in massive stars of low metallicity. The review concludes with a look ahead at some of the questions that may occupy us for the next five years (at least!).

Prestellar Core Collisions - Impact on the formation of the CMF? A case study on FeSt 1-457

2018 ◽  
Vol 14 (S345) ◽  
pp. 328-329
Author(s):  
Gabor I. Herbst-Kiss ◽  
Joao Alves
Keyword(s):  
Molecular Cloud ◽  
Mass Function ◽  
Initial Mass Function ◽  
Initial Mass ◽  
Core Mass ◽  
Preliminary Results ◽  
The Core ◽  
Prestellar Cores

AbstractThe initial mass function (IMF) is a profoundly studied subject, however its origin is still unclear and heavily disputed. The Core Mass Function (CMF) has a remarkable resemblance to a shifted IMF along the mass axis of a factor of 3. This CMF has been observed amongst others in the Pipe Nebula, a calm molecular cloud at approximately 130 pc. We study the origin of the CMF under the assumption that collisions and merging of prestellar cores shape the CMF. We present our preliminary results of core collisions for the well known FeSt 1-457.

scholarly journals Modes of star formation from Herschel

2012 ◽  
Vol 8 (S292) ◽  
pp. 87-90
Author(s):  
L. Testi ◽  
E. Bressert ◽  
S. Longmore
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Mass Function ◽  
Initial Mass Function ◽  
Dense Gas ◽  
Nearby Star ◽  
Star Forming ◽  
Star Forming Regions ◽  
Massive Cluster

AbstractWe summarize some of the results obtained from Herschel surveys of nearby star forming regions and the Galactic plane. We show that in the nearby star forming regions the starless core spatial surface density distribution is very similar to that of the young stellar objects. This, taken together with the similarity between the core mass function and the initial mass function for stars and the relationship between the amount of dense gas and star formation rate, suggest that the cloud fragmentation process defines the global outcome of star formation. This “simple” view of star formation may not hold on all scales. In particular dynamical interactions are expected to become important at the conditions required to form young massive clusters. We describe the successes of a simple criterion to identify young massive cluster precursors in our Galaxy based on (sub-)millimeter wide area surveys. We further show that in the location of our Galaxy where the best candidate for a precursor of a young massive cluster is found, the “simple” scaling relationship between dense gas and star formation rate appear to break down. We suggest that in regions where the conditions approach those of the central molecular zone of our Galaxy it may be necessary to revise the scaling laws for star formation.

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