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Comparison of the Integrated emission of the C18O (in red), SO (in green) molecules toward and the H40a radio recombination line (RRL) towards the Mon R2 high-mass star-forming region. The C18O and SO lines are tracing the molecular gas at different densities, while the H40a RRL is tracing the UC HII region. Figure from Treviño-Morales et. al., (in prep.).
Dynamical signs of a rotating accreting spiral structure
Dynamical signs of a rotating accreting spiral structure
High-mass stars and star clusters commonly form within hub-filament systems. Monoceros R2 (hereafter Mon R2), at a distance of 778 pc (Zucker et al., 2019, ApJ, 879, 125), harbors one of the closest of these systems, making it an excellent target for case studies. We have used the IRAM-30m telescope to conduct an observational study towards MonR2 star-forming region with the main goal of building a picture of its global dynamical properties (Treviño-Morales et. al., 2019). The properties of Mon R2 are in agreement with a scenario of a massive star-forming region that has been formed by a global non-isotropic collapse. Where the gas is flowing along a number of filaments that converge in the central hub from different directions.
The advent of ALMA allows now the study of these filament-hub systems with unprecedented resolution and sensitivity. New ALMA observations reveals that the large scale filaments survive within the hub, where they twist to form an spiral-like structure (Figure). We find signs of rotation and gas infall motions following spiral features, suggesting that they are feeding a central cluster with massive star formation ongoing (with a Macc of few 10-3M☉/yr; Treviño-Morales in prep.).
Comparison of Orion A (top) and G357 (bottom) molecular clouds. The figures show column density maps derived from Herschel (Orion A; Stutz & Kainulainen 2015) and dust extinction (G357; Treviño-Morales et. al., in. prep.). The green and white boxes indicates the filament area studied in Kainulainen et. al., (2017) and Treviño-Morales et. al., (in. prep.), respectively.
Evolutionary sequence of high line-mass filaments
Evolutionary sequence of high line-mass filaments
High line-mass filaments are birthplaces of massive stars and star clusters and thus important for Galactic scale star formation. However, their fragmentation, collapse, and dynamics remain to be well understood. One key open question is how the evolution of fragmentation proceeds. Our team has performed a sensitive fragmentation and dynamical study of two high line-mass filaments presenting different evolutionary states. The dense integral-shape filament (ISF) in Orion A, and the more quiescent infrared-dark cloud G357. For the ISF, we identify fragmentation and clustering in different scales along the filament, with cores strongly grouped along the filament with separations of about 0.25 pc. We find a lower number of fragments in G357, with an average separation of about 1 pc, and with similar intensities/masses as those found in the ISF. Moreover, we find complex kinematics throughout G357. Where it is possible to identify gas in-falls and outflows associated with different fragments in the filament. The presence of outflows and in-falls along the filament suggest different stages of star formation. The comparison of the fragmentation and dynamics of G357 and the ISF provide the first observational constraints for the evolutionary sequence of fragmentation in massive filaments.
Left: CO+ integrated emission. The pink dashed line indicates the direction of the intensity cuts. The colored circles indicate the positions where spectra were extracted. Right: panel A) to E) show the intensity cuts (red continuum lines) of CO+, H13CO+, [CII], H2, and PAHs. In these panels, the gray continuum lines indicates the errors in the cuts. Panel F) shows the comparison of the intensity cuts scaled to unity. In panels A) to F), the pink dot-dashed lines indicate the 3σ level for each species and the gray area indicates the position of the UC HII region. Panel G) shows the CO+, [CII], H13CO+, and HCO+ spectra at IF, MP2, and PDR3. The color of the boxes are related to these positions (circles in left panel). Figure from Treviño-Morales et. al., (2016).
A quest for the CO+ reactive ion in embedded HII regions
A quest for the CO+ reactive ion in embedded HII regions
The CO+ reactive ion is thought to be a tracer of the boundary between a HII region and the hot molecular gas, and its distribution is potentially an excellent diagnostic tool to learn about the physical structure of HII regions and photon-dominated regions (PDR). With the goal of better understanding the effects of the UV radiation on these regions, we have conducted a systematic search for CO+ in a sample of 19 HII regions with different physical properties. For this we have use the Atacama Pathfinder EXperiment (APEX, Chile) and the IRAM-30m telescope (Spain). Recently, we reported the first map of this reactive ion (Treviño-Morales et. al., 2016). We studied the spatial distribution of the CO+ rotational emission toward the Mon R2 star-forming region. The spatial distribution of CO+ consists of a ring-like structure, tracing the layer between the HII region and the molecular gas. Our analysis suggests that CO+ might be originated in photo-evaporating clumps distributed along the PDR layer.
Histogram comparing the deuterium fractions in different regions: the dark cloud TMC 1, the young protostellar object Barnard 1, the hot corino IRAS+16293-2422, the hot core Orion KL, and the PDRs in the Orion Bar and Mon R2 (see Treviño-Morales et al. 2014, and references therein).
Deuteration in high mass star-forming regions
Deuteration in high mass star-forming regions
Deuterated chemistry is an important tool in the understanding of the star formation processes. Observationally, deuteration has been widely studied in cold pre-stellar regions (Fontani et al. 2008, 2011) and hot corinos (Ceccarelli et al. 2007). Much less studied is the deuteration in warm (Tk = 30 - 70 K) cores, in which the dust temperature is too high for the deuteration to proceed efficiently via H2D+ and it is not high enough for the icy mantles to evaporate. Photon-dominated regions (PDRs) are the best sites to study deuteration under warm conditions (Tk ∼ 50 K). We used the IRAM-30m telescope to carry out an unbiased spectral survey toward in Mon R2. This spectral survey is the observational basis of our study of the deuteration in this massive star-forming region (Treviño-Morales et al. 2014). We found a rich chemistry of deuterated species at both positions, with detections of C2D, DCN, DNC, DCO+, D2CO, HDCO, NH2D, and N2D+ and their corresponding hydrogenated species and rarer isotopologs. We have derived a deuterium fractions (Dfrac = [XD]/[XH]) of ~0.01 for all the observed species, except for HCO+ and N2H+ which have values 10 times lower. We found that the deuteration in warm environments like Mon R2 proceeds in the gas-phase via CH2D+ and C2HD+. We found deuterium fraction values consistent with the predictions of the gas-phase model at an early time of 0.1 Myr. This is in agreement with the ages estimated for UC HII regions, suggesting that deuterium chemistry can be a good chemical clock for both low-mass and high-mass star-forming regions.
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