Search for: All records

Purpose: Mathematics instructors seek to address the well-being of students who are Indigenous, Black and Students of Color who have experienced mathematics classrooms as harmful spaces. Lesson study (LS), which engages multiple instructors at once, is a viable tool for enacting institutional change. This study investigates one US university mathematics and statistics department implementing a rehumanizing mathematics (RM) framework and especially how one AfroLatina member experienced the work. Changes in their instruction sought to better support Latine students in Science, Technology, Engineering and Mathematics (STEM). The study sought to understand what meaning faculty members made of their work. Design/methodology/approach: This is a case study of one university mathematics and statistics department that engaged in several cycles of LS to learn and implement the concept of RM in their classrooms. Data draw from faculty member responses to a Google Form and a 60–90 min interview. Inductive and deductive coding (Saldaña, 2012) were used to generate findings. Findings: Findings indicate mathematics and statistics department members found LS made the RM framework more tangible and actionable. Zarai found the work both exciting and scary, as she grappled with what it meant to question mathematics and center the most vulnerable students, do the work as a woman of color and feel exhausted from the work. As a case study (Yin, 2017), the findings are not generalizable. Rather, they describe the phenomenon and what were salient features for the participants (faculty members). Research limitations/implications: Limitations include that participants were surveyed and interviewed one year after receiving RM professional development and 8 months after their first LS cycle; relied upon Google survey forms and interviews where participants self-reported their experiences, and all but the first author are members of the department. To address memory issues, we returned to Padlet responses offered during the RM workshop and, during interviews, prompted participants with documents they had created in the LS cycle to jog their memories. We ameliorated department member biases by having the first author conduct interviews and lead analyses. This study raises several issues for researchers studying RM/STEM in other spaces (e.g. departments with less expertise/commitment to equity) and the role of context (e.g. university departments other than mathematics) and students (who are not Latine). It highlights the value of introducing LS to examine the learning and meaning-making for participants. Practical implications: For professional developers, understanding the range of responses that faculty members had around a single activity offers opportunities for participants to pause and reflect on their identities or the meanings they are making, which could lead to greater empathy for colleagues and practices that support their collective reflections and actions. For mathematicians/scientists interested in rehumanizing STEM, case studies of faculty members with different backgrounds and different meanings of the experience might prompt them to consider how context and identities play out locally. Social implications: Many people have experienced mathematics in dehumanizing ways. This study highlights the efforts of one mathematics/statistics department engaged in LS to rehumanize mathematics, which could help citizens identify more robust definitions of equity for themselves. Additionally, such cases could help individuals identify strategies for navigating the political and personal aspects of equity work, even if not related to mathematics. Even for those who do not share identities with people featured, case studies can highlight why colleagues might experience intense emotions around equity-oriented work, catalyze greater empathy towards them and increase collective equity commitment. Originality/value: Empirical results on LS and mathematics have centered on K–12 teaching and learning; empirical studies on RM in college and/or university settings have focused on students’ experiences. We still know little about how university instructors might make sense of the RM framework or implement it in their teaching. This is the first study of RM practiced by a university mathematics department. Understanding how university mathematicians made sense of an LS model for learning about RM is important both for understanding how LS influenced the learning and application of RM and for highlighting the experiences of AfroLatina faculty. 

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 N₂H⁺(1−0), with a spatial resolution of ~0.02 pc. G353.41, at a distance of ~2kpc, is embedded in a larger-scale (~8 pc) filament and has a mass of ~2.5 × 10³M_⊙within 1.3 × 1.3 pc². We extracted the N₂H⁺(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 (~1 pc) and small scales (~0.2pc). We find good agreement between the N₂H⁺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) (~20 km s⁻¹pc⁻¹) that are well resolved (sizes ~0.1 pc), 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 VG⁻¹, and we interpret them as inflow timescales. The average inflow timescale is ~67 kyr, or about twice the free-fall time of cores in the same area (~33 kyr) but substantially shorter than protostar lifetime estimates (~0.5 Myr). We derived mass accretion rates in the range of (0.35–8.77) × 10⁻⁴M_⊙yr⁻¹. 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. 

Abstract Nitrate legacy is affecting groundwater sources across the tropics. This study describes isotopic and ionic spatial trends across a tropical, fractured, volcanic multi‐aquifer system in central Costa Rica in relation to land use change over four decades. Springs and wells (from 800 to 2,400 m asl) were sampled for NO₃⁻and Cl⁻concentrations, δ¹⁸O_water, δ¹⁵N_NO3, and δ¹⁸O_NO3. A Bayesian isotope mixing model was used to estimate potential source contributions to the nitrate legacy in groundwater. Land use change was evaluated using satellite imagery from 1979 to 2019. The lower nitrate concentrations (<1 mg/L NO₃⁻N) were reported in headwater springs near protected forested areas, while greater concentrations (up to ∼63 mg/L) were reported in wells (mid‐ and low‐elevation sites in the unconfined unit) and low‐elevation springs. High‐elevation springs were characterized by low Cl⁻and moderate NO₃⁻/Cl⁻ratios, indicating the potential influence of soil nitrogen (SN) inputs. Wells and low‐elevation springs exhibited greater NO₃⁻/Cl⁻ratios and Cl⁻concentrations above 100 μmol/L. Bayesian calculations suggest a mixture of sewage (domestic septic tanks), SN (forested recharge areas), and chemical fertilizers (coffee plantations), as a direct result of abrupt land use change in the last 40 years. Our results confirm the incipient trend in increasing groundwater nitrogen and highlight the urgent need for a multi‐municipal plan to transition from domestic septic tanks to regional sewage treatment and sustainable agricultural practices to prevent future groundwater quality degradation effectively. 

The stellar initial mass function (IMF) is critical to our understanding of star formation and the effects of young stars on their environment. On large scales, it enables us to use tracers such as UV or Hα emission to estimate the star formation rate of a system and interpret unresolved star clusters across the Universe. So far, there is little firm evidence of large-scale variations of the IMF, which is thus generally considered “universal”. Stars form from cores, and it is now possible to estimate core masses and compare the core mass function (CMF) with the IMF, which it presumably produces. The goal of the ALMA-IMF large programme is to measure the core mass function at high linear resolution (2700 au) in 15 typical Milky Way protoclusters spanning a mass range of 2.5 × 10³to 32.7 × 10³M_⊙. In this work, we used two different core extraction algorithms to extract ≈680 gravitationally bound cores from these 15 protoclusters. We adopted a per core temperature using the temperature estimate from the point-process mapping Bayesian method (PPMAP). A power-law fit to the CMF of the sub-sample of cores above the 1.64M_⊙completeness limit (330 cores) through the maximum likelihood estimate technique yields a slope of 1.97 ± 0.06, which is significantly flatter than the 2.35 Salpeter slope. Assuming a self-similar mapping between the CMF and the IMF, this result implies that these 15 high-mass protoclusters will generate atypical IMFs. This sample currently is the largest sample that was produced and analysed self-consistently, derived at matched physical resolution, with per core temperature estimates, and cores as massive as 150M_⊙. We provide both the raw source extraction catalogues and the catalogues listing the source size, temperature, mass, spectral indices, and so on in the 15 protoclusters. 

Context.The star formation process leads to an increased chemical complexity in the interstellar medium. 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. Aims.We aim to systematically search for and identify a sample of hot cores toward the 15 Galactic protoclusters of the ALMA-IMF Large Program and investigate their statistical properties. Methods.We built a comprehensive census of hot core candidates toward 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, a complex species commonly observed toward sites of star formation. We performed a cross-matching with the catalog of thermal dust continuum sources from the ALMA-IMF 1.3 mm continuum data to infer their physical properties. Results.We built a catalog of 76 hot core candidates with masses ranging from ~0.2M_⊙to ~80M_⊙, of which 56 are new detections. A large majority of these objects, identified from methyl formate emission, are compact and rather circular, with deconvolved full width at half maximum (FWHM) sizes of ~2300 au on average. The central sources of two target fields show more extended, but still rather circular, methyl formate emission with deconvolved FWHM sizes of ~6700 au and 13 400 au. About 30% of our sample of methyl formate sources have core masses above 8M_⊙and range in size from ~1000 au to 13 400 au, which is in line with measurements of archetypical hot cores. The origin of the CH₃OCHO emission toward the lower-mass cores may be explained as a mixture of contributions 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, suggesting that the brightest dust cores are all in the hot core phase. Conclusions.Our results suggest that most of these compact methyl formate sources are readily explained by simple symmetric models, while collective effects from radiative heating and shocks from compact protoclusters are needed to explain the observed extended CH₃OCHO emission. The large fraction of hot core candidates toward the most massive cores suggests that they rapidly enter the hot core phase and that feedback effects from the forming protostar(s) impact their environment on short timescales. 

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. 

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. 

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.