arXiv subjects

R. H. Álvarez-Gutiérrez

Publications and source records attributed to R. H. Álvarez-Gutiérrez.

13 recordsLinked to original sources

arXiv2026

Challenges in probing turbulent and magnetic support in cores: the W43-MM1 protocluster case study

Estimating the level of non-thermal support in cores is both challenging and crucial for constraining the earliest stages of star formation. We quantify the kinetic and magnetic support operating within the cores of the high-mass protocluster W43-MM1, and test the assumptions behind the virial theorem used to interpret observations. We used ALMA 12m molecular line observations of DCN (3-2), 13CS (5-4), and CH3CN (5_3-4_3) to estimate kinetic support. The plane-of-sky magnetic field strength (B_POS) was derived from dust-polarization observations using the Davis-Chandrasekhar-Fermi method, obtained at the three-beam scale (~12500 au) and extrapolated to core scales (~2500 au) using the density-field strength relation. We derive kinetic support estimates for 45 cores (21 prestellar and 24 protostellar), of which 21 also have magnetic field estimates. Velocity dispersions range from 0.34 to 4.48 km/s, and B_POS values span 1.1-49.3 mG at core scales. Using the virial theorem, ~70% of cores appear stable against collapse when considering turbulence alone, and ~85% when combining both kinetic and magnetic support (alpha_vir,B > 1). These are unexpectedly high values, particularly for protostellar cores expected to be undergoing collapse. We conclude that contamination of linewidths by organized motions (1-3 km/s, consistent with previous observational studies), together with the omission of surface terms in the observational virial theorem, prevents accurate measurement of non-thermal support in cores. This highlights that simplified virial analyses can introduce significant biases when assessing physical support mechanisms within cores.

astro-ph.GA↗

arXiv2026

ALMA-IMF. XXI.: N$_2$H$^+$ kinematics in the G012.80 protocluster: Evidence for filament rotation and evolution

(abridged) We aim to characterize kinematic processes in the G012.80 protocluster. We principally focus on the N$_2$H$^+$(1$-$0) emission to trace the dense and cold gas. Additionally, we use lines such as DCN(3$-$2), H41$α$, C$^{18}$O(1$-$0), and SiO(5$-$4), as well as continuum maps. We perform a N$_2$H$^+$ hyperfine spectral line fitting to analyze multiple velocity components and spectral parameters. We estimate velocity gradients, column densities, and line-mass profiles for the two main filaments in G012, named R1 and R2. Line-mass profiles follow $λ$($ω$) = 5660 M$_{\odot}$ pc$^{-1}$($ω$/pc)$^{0.30}$ (R1) and $λ$($ω$) = 6943 M$_{\odot}$ pc$^{-1}$($ω$/pc)$^{0.20}$ (R2), which are much larger than those of typical low-mass filaments. R1 and R2 show disparate position-velocity (PV) features. R1 exhibits a transverse velocity gradient of 10.4 kms$^{-1} $pc$^{-1}$ and few dense cores. This gradient is interpreted with a simple rotation toy model, combined with line-mass profile, and corresponds to a rotational timescale of 0.1 Myr. In contrast, R2 exhibits compact velocity structures ($Δ$V < 2 kms$^{-1}$), likely due to collapse, as evidenced by the presence of a comparatively large number of massive cores and protostellar outflows. R2 is forming prestellar and protostellar cores at a rate of 55.3 M$_{\odot}$ Myr$^{-1}$, with an efficiency similar to the Orion Integral Shaped Filament (ISF). The R1 filament, in contrast, lacks protostellar cores and only contains a few prestellar cores, resulting in an estimated SFR of 4.2 M$_{\odot}$ Myr$^{-1}$, more than an order of magnitude below that of R2. Combining these lines of evidence, we suggest that R1 is younger and still rotating, while R2 has evolved to collapse with a higher SFR. G012 thus hosts filaments at different evolutionary stages.

astro-ph.GA↗

arXiv2025

ALMA-IMF XIX: C18O (J=2-1): Measurements of turbulence in 15 massive protoclusters

ALMA-IMF is a large program of the Atacama Large Millimeter/submillimeter Array (ALMA) that aims to determine the origin of the core mass function (CMF) of 15 massive Galactic protoclusters (~ 1.0-25.0 x 10^3 solar mass within ~ 2.5 x 2.5 pc^2 ) located towards the Galactic plane. In addition, the objective of the program is to obtain a thorough understanding of their physical and kinematic properties. Here we study the turbulence in these protoclusters with C18O (2-1) emission line using the sonic Mach number analysis (M_s ) and the size-linewidth relation. The probability distribution functions (PDFs) for M_s show a similar pattern, exhibiting no clear trend associated with evolutionary stage, peaking in the range between 4 and 7, and then extending to ~ 25. Such values of M_s indicate that the turbulence in the density regime traced by the C18O line inside the protoclusters is supersonic in nature. In addition, we compare the non-thermal velocity dispersions (sigma_nth, C18O) obtained from the C18O(2-1) line with the non-thermal line widths (sigma_nth, DCN ) of the cores obtained from the DCN (3-2) line. We observe that, on average, the non-thermal linewidth in cores is half that of the gas surrounding them. This suggests that turbulence diminishes at smaller scales or dissipates at the periphery of the cores. Furthermore, we examine the size-linewidth relation for the structures we extracted from the position-position-velocity C18O(2-1) line emission cube with dendrogram algorithm. The power-law index (p) obtained from the size-linewidth relation is between 0.41 and 0.64, steeper than the Kolmogorov law of turbulence, as expected for compressible media. In conclusion, this work is one of the first to carry out such a statistical study of turbulence for embedded massive protoclusters.

astro-ph.GA↗

arXiv2025

ALMA-IMF XVIII: The assembly of a star cluster: Dense N$_2$H$^+$ (1-0) kinematics in the massive G351.77 protocluster

ALMA-IMF observed 15 massive protoclusters capturing multiple spectral lines and the continuum emission. We focus on the G351.77 protocluster ($\sim$ 2500 M$_{\odot}$, estimated from single-dish continuum observations) located at 2 kpc. We trace the dense gas emission and kinematics with N$_2$H$^+$ (1-0) at $\sim$ 4 kau resolution. We estimate an N$_2$H$^+$ relative abundance $\sim (1.7 \pm 0.5) \times 10^{-10}$. We decompose the N$_2$H$^+$ emission into up to two velocity components, highlighting the kinematic complexity in the dense gas. By examining the position-velocity (PV) diagrams on small scales, we observe clear inflow signatures (V-shapes) associated with dense cores. The most prominent V-shape has a mass inflow rate of $\sim 13.5 \times 10^{-4}$ M$_{\odot}$ yr$^{-1}$ and a short timescale of $\sim$ 11.4 kyr. We also observe V-shapes without associated cores. This suggests both that cores or centers of accretion exist below the 1.3 mm detection limit, and that the V-shapes may be viable tracers of very early accretion and star formation on $\sim$ 4 kau scales. The large-scale PV diagram shows that the protocluster is separated into 2 principal velocity structures. Combined with smaller scale DCN and H$_2$CO emission, we propose a scenario of larger scale slow contraction with rotation in the center based on simple toy models. This scenario leads the suggestion of outside-in evolution of the protocluster as it collapses. The gas depletion times implied by the V-shapes are short ($\sim$ 0.3 Myr), requiring either very fast cluster formation, and/or continuous mass feeding of the protocluster. The latter is possible via the Mother Filament G351.77 is forming out of. The similarities in the properties of G351.77 and the recently published work in G353.41 indicate that many of the physical conditions inferred via the ALMA-IMF N$_2$H$^+$ observations may be generic to protoclusters.

astro-ph.GA↗

arXiv2025

ALMA-IMF XVII -- Census and lifetime of high-mass prestellar cores in 14 massive protoclusters

High-mass prestellar cores are extremely rare. The search for such objects has long been hindered by small sample sizes, leading to large uncertainties in their lifetimes and the conditions in which high-mass stars ($> 8\,M_{\odot}$) form. We leverage the large sample ($\sim 580$ cores) detected in the ALMA-IMF survey to identify both protostellar and prestellar cores and estimate their relative lifetimes. We use CO and SiO outflows to identify protostellar cores and introduce a new automated method based on aperture line emission and background subtraction to systematically detect outflows associated with each of the 141 most massive cores. Massive cores that do not drive an outflow in either tracer are classified as prestellar. Our method enables efficient outflow detection with performance comparable to more traditional techniques. We identify 30 likely prestellar cores with $M > 8\,M_{\odot}$, including 12 with $M > 16\,M_{\odot}$, the best candidates for high-mass star precursors. Most of these 12 cores reside in the crowded central regions of protoclusters, where high-mass stars are expected to form. Using prestellar-to-protostellar core ratios and a 300 kyr protostellar lifetime, we estimate prestellar lifetimes of 120 to 240 kyr for $8\,M_{\odot} < M < 16\,M_{\odot}$ and 50 to 100 kyr for $30\,M_{\odot} < M < 55\,M_{\odot}$. These timescales, which depend on different mass reservoir evolution scenarios, significantly exceed the 4 to 15 kyr free-fall time of the cores, suggesting that high-mass cores persist for 10 to 30 free-fall times. This indicates that collapse is slowed by turbulence, magnetic fields, or rotation at or below the observed scale.

astro-ph.GA↗

arXiv2024

ALMA-IMF XVI: Mass-averaged temperature of cores and protostellar luminosities in the ALMA-IMF protoclusters

ALMA-IMF imaged 15 massive protoclusters down to a resolution of of 2 kau scales, identifying about 1000 star-forming cores. The mass and luminosity of these cores, which are fundamental physical characteristics, are difficult to determine, a problem greatly exacerbated at the distances >2 kpc of ALMA-IMF protoclusters. We combined new datasets and radiative transfer modeling to characterize these cores. We estimated their mass-averaged temperature and the masses these estimates imply. For 1/6 of the sample, we measured the bolometric luminosities, implementing deblending corrections when necessary. We used spectral energy distribution (SED) analysis obtained with the PPMAP Bayesian procedure, which aims to preserve the best angular resolution of the input data. We extrapolated the luminosity and dust temperature images provided by PPMAP at 2.5" resolution to estimate those of individual cores, which were identified at higher angular resolution. To do this, we applied approximate radiative transfer relationships between the luminosity of a protostar and the temperature of its surrounding envelope and between the external heating of prestellar cores and their temperatures. For the first time, we provide data-informed estimates of dust temperatures for 883 cores identified with ALMA-IMF: 17-31 K and 28-79 K (5th and 95th percentiles, up to 127 K) for the 617 prestellar and 266 protostellar cores, respectively. We also measured protostellar luminosities spanning 20-80 000 Lsun. For hot cores, we estimated systematically lower temperatures than studies based on complex organic molecules. We established a mass-luminosity evolutionary diagram, for the first time at the core spatial resolution and for a large sample of high-mass protostellar cores. The ALMA-IMF data favor a scenario in which protostars accrete their mass from a larger mass reservoir than their host cores.

astro-ph.GA↗

arXiv2024

ALMA-IMF XIII: N$_2$H$^+$ kinematic analysis on the intermediate protocluster G353.41

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.

astro-ph.GA↗

arXiv2024

Benchmarking the IRDC G351.77-0.53: Gaia DR3 distance, mass distribution, and star formation content

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 $λ=~1660 (w/\rm pc )^{0.62}\,\,M_{\odot}\,\rm{pc}^{-1}$. 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 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, $ε_{\rm ff}$. We find that $ε_{\rm ff}$ 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.

astro-ph.GA↗

arXiv2024

ALMA-IMF XI: The sample of hot core candidates A rich population of young high-mass proto-stars unveiled by the emission of methyl formate

Sites associated with high-mass star and cluster formation exhibit a so-called hot core phase, characterized by high temperatures and column densities of complex organic molecules. We built a comprehensive census of hot core candidates towards the ALMA-IMF protoclusters based on the detection of two CH3OCHO emission lines at 216.1 GHz. We used the source extraction algorithm GExt2D to identify peaks of methyl formate (CH3OCHO) emission that is a complex species commonly observed towards sites of star formation. We built up a catalog of 76 hot core candidates with masses ranging from about 0.2 to 80 Msun , of which 56 are new detections. A large majority of these objects are compact, rather circular, with deconvolved FWHM sizes of about 2300 au on average. About 30% of our sample of methyl formate sources have core masses above 8 Msun within sizes ranging from about 1000 au to 13400 au, which well correspond to archetypical hot cores. The origin of the CH3OCHO emission toward the lower-mass cores can be explained by a mixture of contribution from shocks, or may correspond to objects in a more evolved state, i.e. beyond the hot core stage. We find that the fraction of hot core candidates increases with the core mass. The large fraction of hot core candidates towards the most massive cores suggests that they rapidly enter the hot core phase and feedback effects from the forming protostar(s) impact their environment on short time-scales.

astro-ph.GA↗

arXiv2023

ALMA-IMF IX: Catalog and Physical Properties of 315 SiO Outflow Candidates in 15 Massive Protoclusters

We present a catalog of 315 protostellar outflow candidates detected in SiO J=5-4 in the ALMA-IMF Large Program, observed with ~2000 au spatial resolution, 0.339 km/s velocity resolution, and 2-12 mJy/beam (0.18-0.8 K) sensitivity. We find median outflow masses, momenta, and kinetic energies of ~0.3 M$_{\odot}$, 4 M$_{\odot}$ km/s, and 10$^{45}$ erg, respectively. Median outflow lifetimes are 6,000 years, yielding median mass, momentum, and energy rates of $\dot{M}$ = 10$^{-4.4}$ M$_{\odot}$ yr$^{-1}$, $\dot{P}$ = 10$^{-3.2}$ M$_{\odot}$ km/s yr$^{-1}$, and $\dot{E}$ = 1 L$_{\odot}$. We analyze these outflow properties in the aggregate in each field. We find correlations between field-aggregated SiO outflow properties and total mass in cores (~3$-$5$σ$), and no correlations above 3$σ$ with clump mass, clump luminosity, or clump luminosity-to-mass ratio. We perform a linear regression analysis and find that the correlation between field-aggregated outflow mass and total clump mass - which has been previously described in the literature - may actually be mediated by the relationship between outflow mass and total mass in cores. We also find that the most massive SiO outflow in each field is typically responsible for only 15-30% of the total outflow mass (60% upper limit). Our data agree well with the established mechanical force-bolometric luminosity relationship in the literature, and our data extend this relationship up to L $\geq$ 10$^6$ L$_{\odot}$ and $\dot{P}$ $\geq$ 1 M$_{\odot}$ km/s yr$^{-1}$. Our lack of correlation with clump L/M is inconsistent with models of protocluster formation in which all protostars start forming at the same time.

astro-ph.GA↗

arXiv2023

ALMA-IMF. VII. First release of the full spectral line cubes: Core kinematics traced by DCN J=(3-2)

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.

astro-ph.GA↗

arXiv2023

ALMA-IMF II -- investigating the origin of stellar masses: Continuum Images and Data Processing

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.

astro-ph.GA↗

arXiv2021

ALMA-IMF I -- Investigating the origin of stellar masses: Introduction to the Large Program and first results

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.

astro-ph.GA↗