ABSTRACT
While intensively studied, it remains unclear how the star formation (SF) in infrared dark clouds (IRDCs) compares to that of nearby clouds. We study G351.77-0.53 (henceforth G351), a ...cluster-forming filamentary IRDC. We begin by characterizing its young stellar object (YSO) content. Based on the average parallax of likely members, we obtain a Gaia distance of $\sim \, 2.0\pm 0.14$ kpc, resolving the literature distance ambiguity. Using our Herschel-derived N(H2) map, we measure a total gas mass of 10 200 M⊙ (within 11 pc2) and the average line-mass profile of the entire filament, which we model as $\lambda =~1660 (w/\rm pc)^{0.62}\, \, {\rm M}_{\odot }\, \rm {pc}^{-1}$. At w < 0.63 pc, our λ profile is higher and has a steeper power-law index than λ profiles extracted in Orion A and most of its substructures. Based on the YSOs inside the filament area, we estimate the SF efficiency (SFE) and SF rate (SFR). We calculate a factor of 5 incompleteness correction for our YSO catalogue relative to Spitzer surveys of Orion A. The G351 SFE is ∼1.8 times lower than that of Orion A and lower than the median value for local clouds. We measure SFR and gas masses to estimate the efficiency per free-fall time, ϵff. We find that ϵff is ∼1.1 dex below the previously proposed mean local relation, and $\sim \, 4.7\times$ below Orion A. These observations indicate that local SF-relations do not capture variations present in the Galaxy. We speculate that cloud youth and/or magnetic fields might account for the G351 inefficiency.
ALMA-IMF Motte, F.; Bontemps, S.; Csengeri, T. ...
Astronomy and astrophysics (Berlin),
06/2022, Letnik:
662
Journal Article
Recenzirano
Odprti dostop
Aims.
Thanks to the high angular resolution, sensitivity, image fidelity, and frequency coverage of ALMA, we aim to improve our understanding of star formation. One of the breakthroughs expected from ...ALMA, which is the basis of our Cycle 5 ALMA-IMF Large Program, is the question of the origin of the initial mass function (IMF) of stars. Here we present the ALMA-IMF protocluster selection, first results, and scientific prospects.
Methods.
ALMA-IMF imaged a total noncontiguous area of ~53 pc
2
, covering extreme, nearby protoclusters of the Milky Way. We observed 15 massive (2.5 −33 × 10
3
M
⊙
), nearby (2−5.5 kpc) protoclusters that were selected to span relevant early protocluster evolutionary stages. Our 1.3 and 3 mm observations provide continuum images that are homogeneously sensitive to point-like cores with masses of ~0.2
M
⊙
and ~0.6
M
⊙
, respectively, with a matched spatial resolution of ~2000 au across the sample at both wavelengths. Moreover, with the broad spectral coverage provided by ALMA, we detect lines that probe the ionized and molecular gas, as well as complex molecules. Taken together, these data probe the protocluster structure, kinematics, chemistry, and feedback over scales from clouds to filaments to cores.
Results.
We classify ALMA-IMF protoclusters as Young (six protoclusters), Intermediate (five protoclusters), or Evolved (four proto-clusters) based on the amount of dense gas in the cloud that has potentially been impacted by H
II
region(s). The ALMA-IMF catalog contains ~700 cores that span a mass range of ~0.15
M
⊙
to ~250
M
⊙
at a typical size of ~2100 au. We show that this core sample has no significant distance bias and can be used to build core mass functions (CMFs) at similar physical scales. Significant gas motions, which we highlight here in the G353.41 region, are traced down to core scales and can be used to look for inflowing gas streamers and to quantify the impact of the possible associated core mass growth on the shape of the CMF with time. Our first analysis does not reveal any significant evolution of the matter concentration from clouds to cores (i.e., from 1 pc to 0.01 pc scales) or from the youngest to more evolved protoclusters, indicating that cloud dynamical evolution and stellar feedback have for the moment only had a slight effect on the structure of high-density gas in our sample. Furthermore, the first-look analysis of the line richness toward bright cores indicates that the survey encompasses several tens of hot cores, of which we highlight the most massive in the G351.77 cloud. Their homogeneous characterization can be used to constrain the emerging molecular complexity in protostars of high to intermediate masses.
Conclusions.
The ALMA-IMF Large Program is uniquely designed to transform our understanding of the IMF origin, taking the effects of cloud characteristics and evolution into account. It will provide the community with an unprecedented database with a high legacy value for protocluster clouds, filaments, cores, hot cores, outflows, inflows, and stellar clusters studies.
The ALMA-IMF Large Program provides multi-tracer observations of 15 Galactic massive protoclusters at a matched sensitivity and spatial resolution. We focus on the dense gas kinematics of the G353.41 ...protocluster traced by N$_2$H$^+$ (1$-$0), with a spatial resolution of sim \,0.02 pc. G353.41, at a distance of sim 2\,kpc, is embedded in a larger-scale ($ filament and has a mass of odot within $1.3 pc$^2$. We extracted the N$_2$H$^+$ (1$-$0) isolated line component and decomposed it by fitting up to three Gaussian velocity components. This allows us to identify velocity structures that are either muddled or impossible to identify in the traditional position-velocity diagram. We identify multiple velocity gradients on large (sim 1\,pc) and small scales (sim 0.2\,pc). We find good agreement between the N$_2$H$^+$ velocities and the previously reported DCN core velocities, suggesting that cores are kinematically coupled with the dense gas in which they form. We have measured nine converging ``V-shaped'' velocity gradients (VGs) ($ $) that are well resolved (sizes $ mostly located in filaments, which are sometimes associated with cores near their point of convergence. We interpret these V-shapes as inflowing gas feeding the regions near cores (the immediate sites of star formation). We estimated the timescales associated with V-shapes as $, and we interpret them as inflow timescales. The average inflow timescale is $ kyr, or about twice the free-fall time of cores in the same area ($ but substantially shorter than protostar lifetime estimates ($ Myr). We derived mass accretion rates in the range of $(0.35-8.77)\ $ M$_ odot $ yr$^ $. This feeding might lead to further filament collapse and the formation of new cores. We suggest that the protocluster is collapsing on large scales, but the velocity signature of collapse is slow compared to pure free-fall. Thus, these data are consistent with a comparatively slow global protocluster contraction under gravity, and faster core formation within, suggesting the formation of multiple generations of stars over the protocluster's lifetime.
ALMA-IMF Ginsburg, A.; Csengeri, T.; Galván-Madrid, R. ...
Astronomy and astrophysics (Berlin),
06/2022, Letnik:
662
Journal Article
Recenzirano
Odprti dostop
We present the first data release of the ALMA-IMF Large Program, which covers the 12m-array continuum calibration and imaging. The ALMA-IMF Large Program is a survey of fifteen dense molecular cloud ...regions spanning a range of evolutionary stages that aims to measure the core mass function. We describe the data acquisition and calibration done by the Atacama Large Millimeter/submillimeter Array (ALMA) observatory and the subsequent calibration and imaging we performed. The image products are combinations of multiple 12 m array configurations created from a selection of the observed bandwidth using multi-term, multi-frequency synthesis imaging and deconvolution. The data products are self-calibrated and exhibit substantial noise improvements over the images produced from the delivered data. We compare different choices of continuum selection, calibration parameters, and image weighting parameters, demonstrating the utility and necessity of our additional processing work. Two variants of continuum selection are used and will be distributed: the “best-sensitivity” (
bsens
) data, which include the full bandwidth, including bright emission lines that contaminate the continuum, and “cleanest” (
cleanest
), which select portions of the spectrum that are unaffected by line emission. We present a preliminary analysis of the spectral indices of the continuum data, showing that the ALMA products are able to clearly distinguish free-free emission from dust emission, and that in some cases we are able to identify optically thick emission sources. The data products are made public with this release.
ALMA-IMF Cunningham, N.; Ginsburg, A.; Galván-Madrid, R. ...
Astronomy and astrophysics (Berlin),
10/2023, Letnik:
678
Journal Article
Recenzirano
Odprti dostop
ALMA-IMF is an Atacama Large Millimeter/submillimeter Array (ALMA) Large Program designed to measure the core mass function (CMF) of 15 protoclusters chosen to span their early evolutionary stages. ...It further aims to understand their kinematics, chemistry, and the impact of gas inflow, accretion, and dynamics on the CMF. We present here the first release of the ALMA-IMF line data cubes (DR1), produced from the combination of two ALMA 12 m-array configurations. The data include 12 spectral windows, with eight at 1.3 mm and four at 3 mm. The broad spectral coverage of ALMA-IMF (∼6.7 GHz bandwidth coverage per field) hosts a wealth of simple atomic, molecular, ionised, and complex organic molecular lines. We describe the line cube calibration done by ALMA and the subsequent calibration and imaging we performed. We discuss our choice of calibration parameters and optimisation of the cleaning parameters, and we demonstrate the utility and necessity of additional processing compared to the ALMA archive pipeline. As a demonstration of the scientific potential of these data, we present a first analysis of the DCN (3–2) line. We find that DCN (3–2) traces a diversity of morphologies and complex velocity structures, which tend to be more filamentary and widespread in evolved regions and are more compact in the young and intermediate-stage protoclusters. Furthermore, we used the DCN (3–2) emission as a tracer of the gas associated with 595 continuum cores across the 15 protoclusters, providing the first estimates of the core systemic velocities and linewidths within the sample. We find that DCN (3–2) is detected towards a higher percentage of cores in evolved regions than the young and intermediate-stage protoclusters and is likely a more complete tracer of the core population in more evolved protoclusters. The full ALMA 12m-array cubes for the ALMA-IMF Large Program are provided with this DR1 release.
ALMA-IMF is an Atacama Large Millimeter/submillimeter Array (ALMA) Large Program designed to measure the core mass function (CMF) of 15 protoclusters chosen to span their early evolutionary stages. ...It further aims to understand their kinematics, chemistry, and the impact of gas inflow, accretion, and dynamics on the CMF. We present here the first release of the ALMA-IMF line data cubes (DR1), produced from the combination of two ALMA 12m-array configurations. The data include 12 spectral windows, with eight at 1.3mm and four at 3mm. The broad spectral coverage of ALMA-IMF (~6.7 GHz bandwidth coverage per field) hosts a wealth of simple atomic, molecular, ionised, and complex organic molecular lines. We describe the line cube calibration done by ALMA and the subsequent calibration and imaging we performed. We discuss our choice of calibration parameters and optimisation of the cleaning parameters, and we demonstrate the utility and necessity of additional processing compared to the ALMA archive pipeline. As a demonstration of the scientific potential of these data, we present a first analysis of the DCN (3-2) line. We find that DCN traces a diversity of morphologies and complex velocity structures, which tend to be more filamentary and widespread in evolved regions and are more compact in the young and intermediate-stage protoclusters. Furthermore, we used the DCN (3-2) emission as a tracer of the gas associated with 595 continuum cores across the 15 protoclusters, providing the first estimates of the core systemic velocities and linewidths within the sample. We find that DCN (3-2) is detected towards a higher percentage of cores in evolved regions than the young and intermediate-stage protoclusters and is likely a more complete tracer of the core population in more evolved protoclusters. The full ALMA 12m-array cubes for the ALMA-IMF Large Program are provided with this DR1 release.
We present the first data release of the ALMA-IMF Large Program, which covers the 12m-array continuum calibration and imaging. The ALMA-IMF Large Program is a survey of fifteen dense molecular cloud ...regions spanning a range of evolutionary stages that aims to measure the core mass function (CMF). We describe the data acquisition and calibration done by the Atacama Large Millimeter/submillimeter Array (ALMA) observatory and the subsequent calibration and imaging we performed. The image products are combinations of multiple 12m array configurations created from a selection of the observed bandwidth using multi-term, multi-frequency synthesis imaging and deconvolution. The data products are self-calibrated and exhibit substantial noise improvements over the images produced from the delivered data. We compare different choices of continuum selection, calibration parameters, and image weighting parameters, demonstrating the utility and necessity of our additional processing work. Two variants of continuum selection are used and will be distributed: the "best-sensitivity" data, which include the full bandwidth, including bright emission lines that contaminate the continuum, and "cleanest", which select portions of the spectrum that are unaffected by line emission. We present a preliminary analysis of the spectral indices of the continuum data, showing that the ALMA products are able to clearly distinguish free-free emission from dust emission, and that in some cases we are able to identify optically thick emission sources. The data products are made public with this release.
The ALMA-IMF Large Program imaged a total noncontiguous area of 53pc2, covering 15 extreme, nearby protoclusters of the Milky Way. They were selected to span relevant early protocluster evolutionary ...stages. Our 1.3mm and 3mm observations provide continuum images that are homogeneously sensitive to point-like cores with masses of 0.2 and 0.6Msun, respectively, with a matched spatial resolution of 2000au. We also detect lines that probe the protocluster structure, kinematics, chemistry, and feedback over scales from clouds to filaments to cores. We classify ALMA-IMF protoclusters as Young, Intermediate, or Evolved based on the amount of dense gas in the cloud that has potentially been impacted by HII regions. The ALMA-IMF catalog contains 700 cores that span a mass range of 0.15-250Msun at a typical size of 2100au. We show that this core sample has no significant distance bias and can be used to build core mass functions at similar physical scales. Significant gas motions, which we highlight here in the G353.41 region, are traced down to core scales and can be used to look for inflowing gas streamers and to quantify the impact of the possible associated core mass growth on the shape of the CMF with time. Our first analysis does not reveal any significant evolution of the matter concentration from clouds to cores or from the youngest to more evolved protoclusters, indicating that cloud dynamical evolution and stellar feedback have for the moment only had a slight effect on the structure of high-density gas in our sample. Furthermore, the first-look analysis of the line richness toward bright cores indicates that the survey encompasses several tens of hot cores, of which we highlight the most massive in the G351.77 cloud. Their homogeneous characterization can be used to constrain the emerging molecular complexity in protostars of high to intermediate masses.
While intensively studied, it remains unclear how the star formation (SF) in Infrared Dark Clouds (IRDCs) compares to that of nearby clouds. We study G351.77-0.53 (henceforth G351), a cluster-forming ...filamentary IRDC. We begin by characterizing its young stellar object (YSO) content. Based on the average parallax of likely members, we obtain a Gaia distance of \(\sim\,2.0\pm0.14\) kpc, resolving the literature distance ambiguity. Using our Herschel-derived N(H\(_2\)) map, we measure a total gas mass of 10200 M\(_{\odot}\) (within 11 pc\(^2\)) and the average line-mass profile of the entire filament, which we model as \(\lambda =~1660 (w/\rm pc )^{0.62}\,\,M_{\odot}\,\rm{pc}^{-1}\). At \(w < 0.63\) pc, our \(\lambda\) profile is higher and has a steeper power-law index than \(\lambda\) profiles extracted in Orion A and most of its substructures. Based on the YSOs inside the filament area, we estimate the SF efficiency (SFE) and SF rate (SFR). We calculate a factor of 5 incompleteness correction for our YSO catalog relative to Spitzer surveys of Orion A. The G351 SFE is \(\sim 1.8\) times lower than that of Orion A and lower than the median value for local clouds. We measure SFR and gas masses to estimate the efficiency per free-fall time, \(\epsilon _{\rm ff}\). We find that \(\epsilon_{\rm ff}\) is \(\sim\) 1.1 dex below the previously proposed mean local relation, and \(\sim\,4.7\times\) below Orion A. These observations indicate that local SF-relations do not capture variations present in the Galaxy. We speculate that cloud youth and/or magnetic fields might account for the G351 inefficiency.
The ALMA-IMF Large Program provides multi-tracer observations of 15 Galactic
massive protoclusters at matched sensitivity and spatial resolution. We focus
on the dense gas kinematics of the G353.41 ...protocluster traced by N$_2$H$^+$
(1$-$0), with an spatial resolution $\sim$0.02 pc. G353.41, at a distance of
$\sim$2 kpc, has a mass of $\sim$2500 M$_{\odot}$ within $1.3\times1.3$ pc$^2$.
We extract the N$_2$H$^+$ isolated line component and we decompose it by
fitting up to 3 Gaussian velocity components. This allows us to identify
velocity structures that are impossible to identify in the traditional
position-velocity diagram. We identify multiple velocity gradients on large
($\sim$1 pc) and small scales ($\sim$0.2 pc). We find good agreement between
the N$_2$H$^+$ velocities and the previously reported DCN core velocities,
suggesting that cores are kinematically coupled to the dense gas in which they
form. We measure 9 converging ``V-shaped'' velocity gradients ($\sim20$
km/s/pc), located in filaments, which are sometimes associated with cores near
their point of convergence. The average inflow timescale is $\sim67$ kyr, or
about twice the free-fall time of cores in the same area ($\sim33$ kyr) but
substantially shorter than protostar lifetime estimates ($\sim$0.5 Myr). We
derive mass accretion rates in the range of $(0.35-8.77)\,\times\,10^{-4}$
M$_{\odot}$/yr. This feeding might lead to further filament collapse and
formation of new cores. We suggest that the protocluster is collapsing on large
scales, but the velocity signature of collapse is slow compared to pure
free-fall. These data are consistent with a comparatively slow global
protocluster contraction under gravity, and faster core formation within,
suggesting the formation of multiple generations of stars over the protocluster
lifetime.
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