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[eng] Star formation is a fundamental and still largely unsolved problem of astrophysics and cosmology. Its complexity stems from the complex interaction of turbulence, magnetic fields and gravity, and from the onset of different feedback mechanisms from massive stars, such as stellar winds, ionizing radiation and supernovae (SNe). This complexity makes it hard to develop purely analytical theories, so future progress in this field relies heavily on numerical simulations. The main goals of this thesis are to improve our understanding of the formation, evolution and dynamical state of star-forming clouds. This is pursued primarily through the analysis of numerical simulations. In Chapter 1, Chapter 2 and Chapter 3, I give the general scientific background and introduce the methods used throughout the thesis. Chapter 4 consists of the paper where we investigate the effect of SN explosions on the dynamics of molecular clouds (MCs). This work is based on the analysis of a simulation of magneto-hydrodynamic (MHD), SN- driven turbulence in a large interstellar medium (ISM) volume (250 pc). The position and timing of SNe is computed self-consistently for the first time by resolving the formation of individual massive stars. The main conclusions are that SNe are able to generate the turbulence observed within MCs, and they may also be the main mechanism for their formation and dispersal. Chapter 5 is the paper where we study the global properties of MC clumps, that are usually considered as possible progenitors of massive stars. This is achieved by comparing synthetic dust continuum observations of our SN- driven simulation with Herschel's observations. We generate a very large catalog of synthetic compact sources that have properties consistent with the observations. The comparison shows that the observed clumps are often projection effects, so their mass is usually overestimated by a large factor. In addition, a large fraction of clumps that are believed to contain a protostar, based on their spectral-energy distribution, are probably starless. Chapter 6 consists of the publications where we compute and analyze synthetic N2H+ line profiles of a sub-sample of our catalog of synthetic compact sources. Thanks to the line data, we study the dynamical state of the compact sources. We show that the observations largely overestimate the virial parameter of the most massive clumps. This generates an observational correlation between the mass and virial parameters of massive clumps that, according to our results, is primarily and observational artifact. In Chapter 7, I summarize the main conclusions of the papers presented in the thesis and briefly discuss future research directions., [spa] La formación de estrellas es un problema fundamental y aún en gran parte sin resolver de la astrofísica y la cosmología. Su complejidad se deriva en parte de la existencia de diferentes mecanismos de retroalimentación de las estrellas masivas, como las supernovas (SNe). Los principales objetivos de esta tesis son mejorar nuestra comprensión de la formación, evolución y estado dinámico de las nubes de formación estelar. Esto se persigue principalmente a través del análisis de simulaciones numéricas. En el Capítulo 1, Capítulo 2 y Capítulo 3, doy los antecedentes científicos generales e introduzco los métodos utilizados a lo largo de la tesis. El Capítulo 4 consiste en el artículo en el que investigamos el efecto de las explosiones de SN en la dinámica de las nubes moleculares (MC). Este trabajo se basa en el análisis de una simulación de turbulencia magneto- hidrodinámica (MHD) impulsada por SN en un gran volumen de medio interestelar (ISM) de 250 pc. Las principales conclusiones son que las SNe son capaces de generar la turbulencia observada dentro de las MC, y también pueden ser el principal mecanismo para su formación y dispersión. El Capítulo 5 es el artículo en el que estudiamos las propiedades globales de cúmulos masivos, que normalmente se consideran posibles progenitores de estrellas masivas. Esto se logra comparando las observaciones del continuo de polvo sintético de nuestra simulación impulsada por SN con las observaciones de Herschel. Generamos un catálogo muy grande de fuentes compactas sintéticas que tienen propiedades consistentes con las observaciones. La comparación muestra que los cumulos observados son a menudo efectos de proyección, por lo que su masa suele sobreestimarse por un factor importante. El Capítulo 6 consta del artículo en el que calculamos y analizamos los perfiles de línea de N2H+ sintético de una muestra de nuestro catálogo de fuentes compactas sintéticas, para estudiar su estado dinámico. Mostramos que las observaciones sobrestiman en gran medida el parámetro virial de las fuentes más masivas. En el Capítulo 7, resumo las principales conclusiones de los artículos presentados en la tesis y discuto brevemente las direcciones de investigación futuras.

[Context] Jets and outflows are associated with young stellar objects across the stellar mass spectrum, from brown dwarf protostars to massive Ae/Be stars. Frequently the jet morphology is spatially discontinuous because of the temporal variability of the ejection from the driving source. Images covering a wide field of view around the jet-driving source are useful to map the large-scale jet emission and to explore the mass ejection history. [Aims] The aim of our work was to search for large-scale optical Herbig-Haro (HH) objects lying in a wide field around a sample of IRAS sources, which are candidates to trace young stellar objects. [Methods] Deep narrowband images through the Hα and [S II] emission lines, and through an off-line continuum filter, covering a wide (~15′) field around the IRAS targets were acquired. The images in the three filters were analyzed to identify shock-excited line emission (i.e., HH) in contrast to scattered line emission. [Results] New images of a sample of 15 IRAS sources, obtained in a homogeneous way are presented. HH emission was detected in six fields, and the astrometry of the knot features is given. The nature of the extended emission as scattered emission around nine of the IRAS targets is confirmed. For seven IRAS sources with unclear optical counterparts, a more plausible counterpart is proposed. A refined value of the source distance is reported for seven targets. An update of the main data available for each of the sampled fields, including images from public data archives, is also presented.

[eng] In this thesis, we are aimed to better understand the massive star formation process paying special attention to the role of the magnetic field. To do this, we will carry out a multi-scale analysis with a double approach, theoretical and observational. a) The role of the magnetic field in the fragmentation process: the case of G14.225-0.506 In this first work, we study the fragmentation of an infrared dark cloud that has a filamentary structure and two hubs. We will pay special attention to the magnetic field present in the environment of the hubs and we will try to relate it to the different levels of fragmentation that these hubs present. In order to carry out this study, we present the result of the CSO observations at 350 um, towards both hubs, North and South, in the infrared dark cloud G14.225-0.506 (from here G14.2). We also show the analysis of polarization and intensity gradient making use of the method developed by Koch et al. 2012, Koch et al. 2012b. In the N-hub we find a magnetic field with a uniform distribution along the east-west direction. However, in the southern hub the B-field shows a bimodal distribution. The intensity-gradient in the N-hub shows a single local minimum. In the S-hub, the intensity gradient reveals two minima reflecting the bimodal distribution of the magnetic field where each component points to each of the minima of the intensity gradient. Analysis of the maps |delta| and Sigma_B in the N-hub indicates that, in the vicinity of the hub, gravity dominates the magnetic field. We have also estimated the intensity of the magnetic field finding higher values in the N-hub than in the S-hub. This supports the idea that the different levels of fragmentation exhibited by hubs depend on differences in magnetic field. b) Modeling the accretion disk around the high-mass protostar GGD 27-MM1 In this second project, we descend to accretion disk scales to understand how massive stars form and evolve. In this work we have used ALMA observations at a wavelength of 1.14~mm with very high angular resolution that resolve the disk around the massive star GGD27-MM1. Motivated by the similarity of this system to those found in low mass, we have modeled the emission of the disk using the models developed by D'Alessio et al. 2006 for low mass stars. The main objective is to investigate whether the assumptions that are valid for disks around low-mass stars could be extrapolated to the case of massive stars. As a result we have found a very massive disk of about ~5 Msun which represents around 25 % of the stellar mass. This mass is consistent with the calculated dynamic mass. The disk has a radius of ~170 au with a 49º of inclination. We have compared the temperature and density structure obtained with our model with potential functions and show that the GGD~27--MM1 system is a potential template for future similar studies in other high-mass protostars. Specifically, we have found a flared disk with a maximum scale height of ~13 au and a temperature profile that goes from ~150 K on the outside of the disk to ~ 1400 K on the inner edge of the disk. Analysis of the Toomre parameter Q evaluated at the midplane temperature of the disk indicates that the disk is stable up to a radius 100 au. This work shows that D'Alessio's models can be used as a first approximation and also obtain various observational predictions., [spa] En esta tesis, pretendemos contribuir a explicar el proceso de formación de estrellas masivas prestando especial atención al papel del campo magnético. Para ello, realizaremos un análisis multiescala con una doble aproximación, teórica y observacional. Por un lado investigaremos el proceso de acrecimiento a través de un disco de acrecimiento entorno a una estrella de alta masa. a) El papel del campo magnético en el proceso de fragmentación: el caso de G14.225-0.506 En este primer trabajo, estudiamos la fragmentación de una nube oscura infrarroja que presenta una estructura filamentaria y dos hubs. Prestaremos especial atención al campo magnético presente en el entorno de los hubs y trataremos de relacionarlo con los distintos niveles de fragmentación que presentan estos hubs. Para poder llevar a cabo este estudio presentamos el resultado de las observaciones del CSO a 350 masas solares, hacia ambos hubs, Norte y Sur, en la nube oscura infrarroja G14.225-0.506 (desde aquí G14.2). También mostramos el análisis de la polarización y gradiente de intensidad haciendo uso del método desarrollado por (Koch et al. 2012, Koch et al. 2012b). b) El modelado del disco de acrecimiento entorno a la protoestrella masiva GGD 27-MM1 En este segundo proyecto, descendemos hasta escalas de discos de acrecimiento para entender como las estrellas masivas se forman y evolucionan. En este trabajo hemos usado observaciones de ALMA a una longitud de onda de 1.14 mm con muy alta resolución angular (aproximadamente 40 mili-segundos de arco) que resuelven el disco entorno a la estrella masiva GGD27-MM1. El disco se dispone perpendicularmente al espectacular chorro de 10 pc de longitud que emana de la fuente, conocido como HH80-81. Motivados por el parecido de este sistema a los que encontramos en baja masa, hemos modelado la emisión del disco haciendo uso de los modelos desarrollados por D'Alessio et al. 2006 para estrellas de baja masa.

We show herein that a proto-cluster of Ly α emitting galaxies, spectroscopically confirmed at redshift 6.5, produces a remarkable number of ionizing continuum photons. We start from the Ly α fluxes measured in the spectra of the sources detected spectroscopically. From these fluxes, we derive the ionizing emissivity of continuum photons of the protocluster, which we compare with the ionizing emissivity required to reionize the protocluster volume. We find that the sources in the protocluster are capable of ionizing a large bubble, indeed larger than the volume occupied by the protocluster. For various calculations, we have used the model AMIGA, in particular to derive the emissivity of the Lyman continuum photons required to maintain the observed volume ionized. Besides, we have assumed the ionizing photons escape fraction given by AMIGA at this redshift., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2016, Tutora: María Rosario Isabel López Hermoso, The aim of this work is to search optical spectra of Herbig-Haro objects in Taurus star-forming region and analyse it to make a diagnosis on their physical conditions. We study the degree of excitation, tracers of electron density, electron temperature and degree of ionization that are properties which are studied by the analysis on the forbidden emission lines. From a total of 57 catalogued objects, the lines of a sample of 30 knots are presented. It is obtained a range on electron temperature from 0:9 x 104K and > 1:5 x 104K, an average electron density of 2:5 x 10 3cm -3 and a minimum electron excitation of 15%

AIMS: We develop a new theoretical framework to generate Besançon Galaxy Model Fast Approximate Simulations (BGM FASt) to address fundamental questions of the Galactic structure and evolution performing multi-parameter inference. The flexibility of BGM FASt allows the inference of fundamental parameters related to the stellar initial mass function (IMF), the star formation history (SFH), the density distribution, the kinematics and the chemo-dynamics, among others. BGM FASt allows the study of different Milky Way (MW) components. In this thesis we are focused in a first application of our strategy to simultaneously infer the IMF and the SFH of the MW disc. METHOD: BGM FASt is based on a reweighing scheme, that uses a specific pre-sampled simulation. We use BGM FASt together with an approximate Bayesian computation algorithm to obtain the posterior probability distribution function of the inferred parameters, by automatically comparing synthetic versus observed data. Our full strategy is codified to run on Apache Spark and Hadoop, suited to deal with large surveys. BGM FASt is implemented in the big data infrastructure known as Gaia Data Analytics Framework (GDAF) at the University of Barcelona. To evaluate the performance of BGM FASt we execute a set of validation tests comparing density, colour, mass and age distributions of BGM FASt versus BGM standard simulations. We present two scientific cases that compare synthetic versus Tycho-2 colour-magnitude diagrams. We obtain for the first time using BGM an IMF and SFH of the thin disc by exploring a 6-Dimensional parameter space. We use Gaia data-release 2 magnitudes, colours, and parallaxes for stars with G

The epoch corresponding to a redshift of z $\sim 6.5$ is close to full re-ionisation of the Universe, and early enough to provide an intriguing environment to observe the early stage of large-scale structure formation. It is also en epoch that can be used to verify the abundance of a large population of low luminosity star-forming galaxies, that are deemed responsible for cosmic re-ionisation. Here, we present the results of follow-up multi-object spectroscopy using OSIRIS at Gran Telescopio Canarias (GTC) of 16 Ly$\alpha$ emitter (LAE) candidates discovered in the Subaru/XMM Newton Deep Survey. We have securely confirmed 10 LAEs with sufficient signal-to-noise ratio of the Ly$\alpha$ emission line. The inferred star formation rates of the confirmed LAEs are on the low side, within the range 0.9-4.7 M$_{\odot}$ yr$^{-1}$. However, they show relatively high Ly$\alpha$ rest frame equivalent widths. Finally we have shown that the mechanical energy released by the star formation episodes in these galaxies is enough to create holes in the neutral hydrogen medium such that Lyman continuum photons can escape to the intergalactic medium, thus contributing to the re-ionisation of the Universe., Comment: 14 pages, 22 figures. Accepted for publication in MNRAS

We present ALMA Atacama Compact Array (ACA) 870 micron continuum maps of 28 infrared-bright SDSS quasars with Herschel/SPIRE detections at redshifts 2-4, the largest such sample ever observed with ALMA. The ACA detections are centred on the SDSS coordinates to within 1 arcsec for about 80 per cent of the sample. Larger offsets indicate that the far-infrared (FIR) emission detected by Herschel might come from a companion source. The majority of the objects (about 70 per cent) have unique ACA counterparts within the SPIRE beam down to 3-4 arcsec resolution. Only 30 per cent of the sample shows clear evidence for multiple sources with secondary counterparts contributing to the total 870 micron flux within the SPIRE beam to at least 25 per cent. We discuss the limitations of the data based on simulated pairs of point-like sources at the resolution of the ACA and present an extensive comparison of our findings with recent works on the multiplicities of sub-millimetre galaxies. We conclude that, despite the coarse resolution of the ACA, our data support the idea that, for a large fraction of FIR-bright quasars, the sub-mm emission comes from single sources. Our results suggest that, on average, optically bright quasars with strong FIR emission are not triggered by early-stage mergers but are, instead, together with their associated star formation rates, the outcome of either late-stage mergers or secular processes., 16 pages, 10 figures

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2018, Tutor: Josep Maria Solanes Majúa, This research work is the first statistical study of the properties of the galaxies included in the final data release (A-100) of the Arecibo Legacy Fast ALFA survey (ALFALFA). The recently completed ALFALFA survey constitutes a representative sample of the nearby Universe in the 21 cm line of the neutral Hidrogen (HI), with more than 30 000 extragalactic sources out to z 0:06. Its substantial overlap with wide-area surveys conducted at other wavelengths has been used to create a consistent multi-wavelength catalog of parameters for galaxies within about 250 Mpc (800 million light-years) from us. We have characterized the gas-rich galaxies by comparing their content of atomic hydrogen with several properties from the optical window ranging from intrinsic luminosities and colors to estimators of the morphology and structure. Our results corroborate earlier findings that there does not appear to be a significant population of optically dark but HI-rich galaxies and that most HI-rich galaxies are very blue, while we find that their colors and HI masses are more strongly correlated than previously suspected. In addition, we have (not just confirmed but) found a clearer decrement of the bar fraction with increasing HI content, an anti-correlation that is not explained by known trends for more massive (stellar) and redder disc galaxies to host more bars and have lower gas contents

Extensive surveys of star-forming regions with Spitzer have revealed populations of disk-bearing young stellar objects. These have provided crucial constraints, such as the timescale of dispersal of protoplanetary disks, obtained by carefully combining infrared data with spectroscopic or X-ray data. While observations in various regions agree with the general trend of decreasing disk fraction with age, the Lupus V and VI regions appeared to have been at odds, having an extremely low disk fraction. Here we show, using the recent Gaia data release 2 (DR2), that these extremely low disk fractions are actually due to a very high contamination by background giants. Out of the 83 candidate young stellar objects (YSOs) in these clouds observed by Gaia, only five have distances of 150 pc, similar to YSOs in the other Lupus clouds, and have similar proper motions to other members in this star-forming complex. Of these five targets, four have optically thick (Class II) disks. On the one hand, this result resolves the conundrum of the puzzling low disk fraction in these clouds, while, on the other hand, it further clarifies the need to confirm the Spitzer selected diskless population with other tracers, especially in regions at low galactic latitude like Lupus V and VI. The use of Gaia astrometry is now an independent and reliable way to further assess the membership of candidate YSOs in these, and potentially other, star-forming regions., Accepted for publication on Astronomy&Astrophysics Letters

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2018, Tutor: Eduard Salvador Solé, Observation shows that, over cosmic history, star formation increased until z = 2. After that it su ered a strong quenching. Various internal and external causes have been postulated to explain this phenomenon. In this paper, we investigate a third more fundamental possibility, which we call \natural quenching". This quenching would simply arise as the consequence of the growth of halos. According to numerical simulations, the more massive halos, the less concentrated they are so that the gas trapped within them cools at a lower rate. Consequently, over cosmic evolution, the accretion of gas onto galaxies slows down, which translates into a lower star formation rate. The aim of this study is to find the characteristic time at which this natural quenching becomes effective and check whether it coincides with a redshift of about 2.

Màster Oficial d'Astrofísica, Física de Partícules i Cosmologia, Facultat de Física, Universitat de Barcelona, Curs: 2016-2017, Tutors: Gemma Busquet, Robert Estalella, A distinguished kind of molecular clouds, the infrared dark clouds (hereafter IRDCs), are believed to be relevant for describing the initial conditions for high-mass star formation. They are characterized by their lack of detectable emission in the mid-infrared: they appear as a dark silhouette against the corresponding mid-infrared background. IRDCs were first recognized in images from the Infrared Space Observatory (ISO, Egan et al. 1998) and the Midcourse Space Experiment (MSX, Perault et al. 1996)

[eng] Turbulence, magnetic fields and gravity driven flows are important for the formation of new stars. Although magnetic fields have been proven to be important in the formation of stars, only a few works have been done combining magnetic field and kinematic information. Such studies are important to analyze both gravity and gas dynamics and be able to compare them with the magnetic field. In this thesis we will combine dust polarization studies with kinematic analysis towards different star-forming regions. We aim to study the physical properties at core scales (, [spa] La turbulencia, el campo magnético y la gravedad juegan un papel importante en la formación estelar. Aunque se ha mostrado que el campo magnético es importante, sólo se han llevado a cabo un número limitado de trabajos combinando el estudio del campo magnético y la cinemática del gas. Este tipo de trabajos son esenciales para estudiar la gravedad y la dinámica del gas y poder compararlas con el campo magnético a las mismas escalas espaciales. En este trabajo combinamos estudios de polarización a partir de la emisión del polvo, con el análisis de la cinemática del gas en diferentes regiones de formación estelar. El objetivo es estudiar las propiedades físicas a escalas de núcleos densos (

We present Submillimeter Array (SMA) 1.35 mm subarcsecond angular resolution observations toward the LkH{\alpha} 234 intermediate-mass star-forming region. The dust emission arises from a filamentary structure of $\sim$5 arcsec ($\sim$4500 au) enclosing VLA 1-3 and MM 1, perpendicular to the different outflows detected in the region. The most evolved objects are located at the southeastern edge of the dust filamentary structure and the youngest ones at the northeastern edge. The circumstellar structures around VLA 1, VLA 3, and MM 1 have radii between $\sim$200 and $\sim$375 au and masses in the $\sim$0.08-0.3 M$_{\odot}$ range. The 1.35 mm emission of VLA 2 arises from an unresolved (r$< 135$ au) circumstellar disk with a mass of $\sim$0.02 M$_{\odot}$. This source is powering a compact ($\sim$4000 au), low radial velocity ($\sim$7 km s$^{-1}$) SiO bipolar outflow, close to the plane of the sky. We conclude that this outflow is the "large-scale" counterpart of the short-lived, episodic, bipolar outflow observed through H$_2$O masers at much smaller scales ($\sim $180 au), and that has been created by the accumulation of the ejection of several episodic collimated events of material. The circumstellar gas around VLA 2 and VLA 3 is hot ($\sim$130 K) and exhibits velocity gradients that could trace rotation. There is a bridge of warm and dense molecular gas connecting VLA 2 and VLA 3. We discuss the possibility that this bridge could trace a stream of gas between VLA 3 and VLA 2, increasing the accretion rate onto VLA 2 to explain why this source has an important outflow activity., Comment: 11 pages, 9 figures, accepted for publication in MNRAS

We present a comparison of molecular clouds (MCs) from a simulation of supernova-driven interstellar medium (ISM) turbulence with real MCs from the Outer Galaxy Survey. The radiative transfer calculations to compute synthetic CO spectra are carried out assuming the CO relative abundance depends only on gas density, according to four different models. Synthetic MCs are selected above a threshold brightness temperature value, $T_{\rm B,min}=1.4$ K, of the $J=1-0$ $^{12}$CO line, generating 16 synthetic catalogs (four different spatial resolutions and four CO abundance models), each containing up to several thousands MCs. The comparison with the observations focuses on the mass and size distributions and on the velocity-size and mass-size Larson relations. The mass and size distributions are found to be consistent with the observations, with no significant variations with spatial resolution or chemical model, except in the case of the unrealistic model with constant CO abundance. The velocity-size relation is slightly too steep for some of the models, while the mass-size relation is a bit too shallow for all models only at a spatial resolution $dx\approx 1$ pc. The normalizations of the Larson relations show a clear dependence on spatial resolution, for both the synthetic and the real MCs. The comparison of the velocity-size normalization suggests that the SN rate in the Perseus arm is approximately 70\% or less of the rate adopted in the simulation. Overall, the realistic properties of the synthetic clouds confirm that supernova-driven turbulence can explain the origin and dynamics of MCs., accepted for publication in ApJ

Turbulence is ubiquitous in molecular clouds (MCs), but its origin is still unclear because MCs are usually assumed to live longer than the turbulence dissipation time. Interstellar medium (ISM) turbulence is likely driven by SN explosions, but it has never been demonstrated that SN explosions can establish and maintain a turbulent cascade inside MCs consistent with the observations. In this work, we carry out a simulation of SN-driven turbulence in a volume of (250 pc)$^3$, specifically designed to test if SN driving alone can be responsible for the observed turbulence inside MCs. We find that SN driving establishes a velocity scaling consistent with the usual scaling laws of supersonic turbulence, suggesting that previous idealized simulations of MC turbulence, driven with a random, large-scale volume force, were correctly adopted as appropriate models for MC turbulence, despite the artificial driving. We also find that the same scaling laws extend to the interior of MCs, and that the velocity-size relation of the MCs selected from our simulation is consistent with that of MCs from the Outer-Galaxy Survey, the largest MC sample available. The mass-size relation and the mass and size probability distributions also compare successfully with those of the Outer Galaxy Survey. Finally, we show that MC turbulence is super-Alfv\'{e}nic with respect to both the mean and rms magnetic-field strength. We conclude that MC structure and dynamics are the natural result of SN-driven turbulence., Comment: ApJ, in press

The compressibility of molecular cloud (MC) turbulence plays a crucial role in star formation models, because it controls the amplitude and distribution of density fluctuations. The relation between the compressive ratio (the ratio of powers in compressive and solenoidal motions) and the statistics of turbulence has been previously studied systematically only in idealized simulations with random external forces. In this work, we analyze a simulation of large-scale turbulence (250 pc) driven by supernova (SN) explosions that has been shown to yield realistic MC properties. We demonstrate that SN driving results in MC turbulence with a broad lognormal distribution of the compressive ratio, with a mean value $\approx 0.3$, lower than the equilibrium value of $\approx 0.5$ found in the inertial range of isothermal simulations with random solenoidal driving. We also find that the compressibility of the turbulence is not noticeably affected by gravity, nor are the mean cloud radial (expansion or contraction) and solid-body rotation velocities. Furthermore, the clouds follow a general relation between the rms density and the rms Mach number similar to that of supersonic isothermal turbulence, though with a large scatter, and their average gas density PDF is described well by a lognormal distribution, with the addition of a high-density power-law tail when self-gravity is included., Accepted by ApJ

Aims. Massive stars form in clusters, and their influence on nearby starless cores is still poorly understood. The protocluster associated with IRAS 22134+5834 represents an excellent laboratory for studying the influence of massive YSOs on nearby starless cores and the possible implications in the clustered star formation process. Methods. IRAS 22134+5834 was observed in the cm range with (E)VLA, 3 mm with CARMA, 2 mm with PdBI, and 1.3 mm with SMA, to study both the continuum emission and the molecular lines that trace different physical conditions of the gas. Results. The multiwavelength centimeter continuum observations revealed two radio sources within the cluster, VLA1 and VLA2. VLA1 is considered to be an optically thin UCHii region with a size of 0.01 pc that sits at the edge of the near infrared (NIR) cluster. The flux of ionizing photons of the VLA1 corresponds to a B1 ZAMS star. VLA2 is associated with an infrared point source and has a negative spectral index. We resolved six millimeter continuum cores at 2 mm, MM2 is associated with the UCHii region VLA1, and other dense cores are distributed around the UCHii region. Two high-mass starless clumps (HMSC), HMSC-E (east) and HMSC-W (west), are detected around the NIR cluster with NH(1-0) and NH emission, and they show different physical and chemical properties. Two ND cores are detected on an NH filament close to the UCHii region with a projected separation of ~8000 AU at the assumed distance of 2.6 kpc. The kinematic properties of the molecular line emission confirm that the UCHii region is expanding and that the molecular cloud around the NIR cluster is also expanding. Conclusions. Our multiwavelength study has revealed different generations of star formation in IRAS 22134+5834. The formed intermediate-to-massive stars show a strong impact on nearby starless clumps. We propose that the starless clumps and HMPOs formed at the edge of the cluster while the stellar wind from the UCHii region and the NIR cluster drives the large scale bubble. © 2016 ESO., The work is supported by the STARFORM Sinergia Project CRSII2_141880 funded by the Swiss National Science Foundation. Y.W. also acknowledges support by the NSFC 11303097 and 11203081, China. A.S.-M. acknowledges support by the collaborative research center project SFB 956, funded by the Deutsche Forschungsgemeinschaft (DFG). G.B. is supported by the Spanish MICINN grant AYA2011-30228-C03-01 (cofunded with FEDER funds). A.P. acknowledges financial support from a UNAM-DGAPA-PAPIIT IA102815 grant, Mexico.

We present observations of the 1.3 mm continuum emission toward hub-N and hub-S of the infrared dark cloud G14.225-0.506 carried out with the Submillimeter Array, together with observations of the dust emission at 870 and 350 microns obtained with APEX and CSO telescopes. The large scale dust emission of both hubs consists of a single peaked clump elongated in the direction of the associated filament. At small scales, the SMA images reveal that both hubs fragment into several dust condensations. The fragmentation level was assessed under the same conditions and we found that hub-N presents 4 fragments while hub-S is more fragmented, with 13 fragments identified. We studied the density structure by means of a simultaneous fit of the radial intensity profile at 870 and 350 microns and the spectral energy distribution adopting a Plummer-like function to describe the density structure. The parameters inferred from the model are remarkably similar in both hubs, suggesting that density structure could not be responsible in determining the fragmentation level. We estimated several physical parameters such as the level of turbulence and the magnetic field strength, and we found no significant differences between these hubs. The Jeans analysis indicates that the observed fragmentation is more consistent with thermal Jeans fragmentation compared with a scenario that turbulent support is included. The lower fragmentation level observed in hub-N could be explained in terms of stronger UV radiation effects from a nearby HII region, evolutionary effects, and/or stronger magnetic fields at small scales, a scenario that should be further investigated., Comment: 14 pages, 5 figures. Accepted for publication in ApJ

We combine observational data on a dozen independent cosmic properties at high-$z$ with the information on reionization drawn from the spectra of distant luminous sources and the cosmic microwave background (CMB) to constrain the interconnected evolution of galaxies and the intergalactic medium since the dark ages. The only acceptable solutions are concentrated in two narrow sets. In one of them reionization proceeds in two phases: a first one driven by Population III stars, completed at $z\sim 10$, and after a short recombination period a second one driven by normal galaxies, completed at $z\sim 6$. In the other set both kinds of sources work in parallel until full reionization at $z\sim 6$. The best solution with double reionization gives excellent fits to all the observed cosmic histories, but the CMB optical depth is 3-$\sigma$ larger than the recent estimate from the Planck data. Alternatively, the best solution with single reionization gives less good fits to the observed star formation rate density and cold gas mass density histories, but the CMB optical depth is consistent with that estimate. We make several predictions, testable with future observations, that should discriminate between the two reionization scenarios. As a byproduct our models provide a natural explanation to some characteristic features of the cosmic properties at high-$z$, as well as to the origin of globular clusters., Comment: 25 pages, 13 figures. Accepted for publication in ApJ. Minor typos corrected

In order to shed light on the main physical processes controlling fragmentation of massive dense cores, we present a uniform study of the density structure of 19 massive dense cores, selected to be at similar evolutionary stages, for which their relative fragmentation level was assessed in a previous work. We inferred the density structure of the 19 cores through a simultaneous fit of the radial intensity profiles at 450 and 850 micron (or 1.2 mm in two cases) and the Spectral Energy Distribution, assuming spherical symmetry and that the density and temperature of the cores decrease with radius following power-laws. We find a weak (inverse) trend of fragmentation level and density power-law index, with steeper density profiles tending to show lower fragmentation, and vice versa. In addition, we find a trend of fragmentation increasing with density within a given radius, which arises from a combination of flat density profile and high central density and is consistent with Jeans fragmentation. We considered the effects of rotational-to-gravitational energy ratio, non-thermal velocity dispersion, and turbulence mode on the density structure of the cores, and found that compressive turbulence seems to yield higher central densities. Finally, a possible explanation for the origin of cores with concentrated density profiles, which are the cores showing no fragmentation, could be related with a strong magnetic field, consistent with the outcome of radiation magnetohydrodynamic simulations., Comment: accepted for publication in ApJ; a version with all (high resolution) figures is available at: http://www.ice.csic.es/files/palau/Palau14.pdf

The high energy astrophysics, specifically the gamma-ray astrophysics, studies the processes that cannot be caused by hot matter but by other mechanisms colled non thermaland processes, which involve matter with energies above ~ 1 MeV. There are currently a number of instruments able to detect this radiation, such as AGILE and Fermi satellites or Cherenkov telescopes like MAGIC at the Earth's surface. In this thesis we studied two main types of systems that, as it has been observed or theoretically predicted, can produce gamma radiation : young stellar objects and high-mass X-ray binaries. Young stellar objects are found in regions of star formation, which are the cradles where new stars are being formed. The star-forming regions are populated with protostars and young stars, among other objects. Protostars still accrete matter from the parent cloud through an accretion disk, while expelling material through a jet formed by magnetic interaction. In these jets the particles are ejected at high speeds out of the system and in some cases reach relativistic velocities, as evidenced by the detection of non-thermal radio emission in some of these objects. In this thesis we are interested to find more evidence of young stellar objects that present non-thermal emission, either in the range of X-rays or gamma rays. To find new candidates have used the first catalog of the Fermi satellite and the catalogs of young systems in our Galaxy. Besides the search through catalogs, we did a study using archival X-ray XMM-Newton data on the young stellar object IRAS 16547-4247, which is known to display non-thermal radio emission. This object is a protostar still accretes material through an accretion disk and also ejects jets of material through particle. We discovered its X-ray counterpart and studied the interaction of its jets through a theoretical model. Finally, we studied a region of star formation that has been found in spatial coincidence with a second Fermi source catalog, known as Monoceros R2 . We analyzed the Fermi data from this source and our results allow us to say that the detected gamma-ray emission is consistent with that expected by the collective effects of a population of protostars. Among the other large block of this thesis there are high-mass X-ray binares. The most relevant of which we have studied is MWC 656. This system consists of a Be star and a black hole, a combination that has never been detected before. We have observed this source with XMM-Newton in X-rays and with the MAGIC Telescopes in very high energy gamma rays. Our X-ray observation has led to the discovery of the X-ray counterpart of this binary system and has allowed us to classify it as a high-mass X-ray binary, the first composed of a Be star and a black hole. Other systems we studied with MAGIC are HESS J0632 +057 and SS 433. HESS J0632 +057 is a binary system consisting of a Be star and a compact object of unknown nature and was identified by us as a gamma-ray emitter. We have also observed SS 433, the first microquasar ever discovered. We observed this source during 2010 May and June, but it has not been detected. We have calculated upper limits to the emission of very high energy gamma-rays to put constraints on the physical parameters of the system., L'astrofísica d'altes energies i en concret l'astrofísica de raigs gamma, estudia els processos d'emissió que no poden ser causats per matèria calenta, sinó per altres mecanismes que anomenem no tèrmics i que comporten que la matèria que emet aquesta radiació tingui energies per sobre d'1~MeV. Actualment disposem d'un bon nombre d'instruments capaços de detectar aquesta emissió, com ara els satèl•lits Fermi i AGILE o els telescopis Cherenkov com MAGIC, a la superfície terrestre. En aquesta tesi hem estudiat principalment dos tipus de sistemes que, tal com s'ha observat o predit teòricament, poden produir radiació gamma: els objectes estel•lars joves i els sistemes binaris de raigs X d’alta massa. Els objectes estel•lars joves els trobem a les regions de formació estel•lar, que són els bressols on noves estrelles s'estan formant. Els pobladors de les regions de formació estel•lar són les protoestrelles i les estrelles joves, entre altres objectes celests. Les protoestrelles encara acretem matèria del núvol progenitor a través d'un disc d'acreció, i al mateix temps expulsen material per mitjà d'uns dolls formats per interacció magnètica. En aquests dolls les partícules són expulsades a grans velocitats cap a fora del sistema i en alguns casos assoleixen velocitats relativistes tal com evidencia la detecció d'emissió ràdio no tèrmica en alguns d'aquests objectes. En aquesta tesi ens hem interessat per trobar evidència de més objectes estel•lars joves que presentin emissió no tèrmica, ja sigui en el rang dels raigs X o dels raigs gamma. Per a trobar nous candidats hem aprofitat el primer catàleg del satèl•lit Fermi i l'hem creuat amb catàlegs d'objectes joves de la Galàxia. A més a més de la cerca per mitjà de catàlegs, hem fet un estudi en raigs X a partir de dades d'arxiu disponibles sobre un objecte estel•lar jove del que ja es coneix emissió no tèrmica en ràdio: IRAS 16547-4247. Aquest objecte és una protoestrella que encara acreta material per mitjà d'un disc d'acreció i que alhora expulsa material a través de dolls de partícules. Hem descobert la contrapartida en raigs X d'aquest sistema i l'hem estudiat per mitjà d'un model teòric. Finalment, hem estudiat una regió de formació estel•lar que s'ha trobat en coincidència espacial amb una font del segon catàleg de Fermi, coneguda com Monoceros R2. Hem analitzat les dades de Fermi d'aquesta font i els nostres resultats ens permeten dir que l'emissió gamma detectada és compatible amb el que s'esperaria que produissin un conjunt de protoestrelles. Dins de l'altre gran bloc d'aquesta tesi trobem les estrelles binàries de raigs X d'alta massa. El cas més rellevant dels que hem estudiat és el de MWC 656. Aquest sistema està format per una estrella Be i un forat negre, una combinació que mai s'havia detectat. Nosaltres hem observat aquesta font amb el telescopi de raigs X XMM-Newton i amb els Telescopis MAGIC, en raigs gamma de molt alta energia. La nostra observació de raigs X ha suposat la descoberta de la contrapartida de raigs X d'aquest sistema binari i ens ha permès classificar-la com a binària de raigs X d'alta massa, la primera composada per una estrella Be i un forat negre. Altres sistemes que hem estudiat amb MAGIC són HESS J0632+057 i SS 433. HESS J0632+057 és un sistema binari format per una estrella Be i un objecte compacte de natura desconeguda i va ser detectat per nosaltres com a emissor de raigs gamma. També hem observat SS 433, el primer microquàsar que es va descobrir. Hem observat aquesta font durant els mesos de maig i juny de 2010 però no s'ha detectat. Així, hem calculat límits superiors a l'emissió gamma de molt alta energia que serveixen per a posar restriccions en paràmetres físics.

There are a number of very high energy sources in the Galaxy that remain unidentified. Multi-wavelength and variability studies, and catalogue searches, are powerful tools to identify the physical counterpart, given the uncertainty in the source location and extension. This work carries out a thorough multi-wavelength study of the unidentified, very high energy source HESS J1858+020 and its environs. Giant Metrewave Radio Telescope observations at 610 MHz and 1.4 GHz have been done to obtain a deep, low-frequency radio image of the region surrounding HESS J1858+020. Archival radio, infrared, and X-ray data have been analysed as well. This observational information, combined with molecular data, catalogue sources, and a nearby Fermi gamma-ray detection of unidentified origin, are combined to explore possible counterparts to the very high energy source. We provide with a deep radio image of a supernova remnant that might be related to the GeV and TeV emission in the region. We confirm the presence of an H II region next to the supernova remnant and coincident with molecular emission. A potential region of star formation is also identified. We identify several radio and X-ray sources in the surroundings. Some of these sources are known planetary nebulae, whereas others may be non-thermal extended emitters and embedded young stellar objects. Three old, background Galactic pulsars also neighbour HESS J1858+020 along the line of sight. The region surrounding HESS J1858+020 is rich in molecular structures and non-thermal objects that may potentially be linked to this unidentified very high energy source. In particular, a supernova remnant interacting with nearby molecular clouds may be a good candidate, but a star forming region, or a non-thermal radio source of yet unclear nature, may also be behind the gamma-ray source. Further observational studies are needed., Comment: 8 pages, 5 figures. Accepted for publication in A&A

The CORNISH project is the highest resolution radio continuum survey of the Galactic plane to date. It is the 5 GHz radio continuum part of a series of multi-wavelength surveys that focus on the northern GLIMPSE region (10 deg < l < 65 deg), observed by the Spitzer satellite in the mid-infrared. Observations with the Very Large Array in B and BnA configurations have yielded a 1.5" resolution Stokes I map with a root-mean-squared noise level better than 0.4 mJy/beam. Here we describe the data-processing methods and data characteristics, and present a new, uniform catalogue of compact radio-emission. This includes an implementation of automatic deconvolution that provides much more reliable imaging than standard CLEANing. A rigorous investigation of the noise characteristics and reliability of source detection has been carried out. We show that the survey is optimised to detect emission on size scales up to 14" and for unresolved sources the catalogue is more than 90 percent complete at a flux density of 3.9 mJy. We have detected 3,062 sources above a 7-sigma detection limit and present their ensemble properties. The catalogue is highly reliable away from regions containing poorly-sampled extended emission, which comprise less than two percent of the survey area. Imaging problems have been mitigated by down-weighting the shortest spacings and potential artefacts flagged via a rigorous manual inspection with reference to the Spitzer infrared data. We present images of the most common source types found: regions, planetary nebulae and radio-galaxies. The CORNISH data and catalogue are available online at http://cornish.leeds.ac.uk, 25 pages, 22 figures. To appear in ApJ. Sup

[eng] It is some observational evidence that dense cores are the birthplace of low-mass stars. These regions, apparently quiescent, are capable of surviving several free-fall times and, potentially, collapse and form stars. Despite its importance, little is known about the very first evolutionary stages of these objects. The observational challenge that studying these diffuse and extended objects represent is preventing us to reveal their properties. It is easier, from an observational point of view, to study brighter sources as the more evolved Class-0 objects. It is possible then, through theoretical models, to trace the history back of these objects and find the initial conditions that, ideally, are those of the dense cores on which they formed. On the other hand, from the theoretical point of view, many studies have considered for decades the effect of the magnetic field in models. However, the lacks of instrumentation and observational techniques have prevented us from testing the predictions. Fortunately, several telescopes have developed polarimetric system during the last years allowing us to study for the first time the magnetic fields in a reliable manner. The complex interplay in dense cores among gravity, thermal pressure, turbulence, rotation, and magnetic field, in not well characterized due to all the previously described issues and, as a consequence, not well understood theoretically. The aim is, then, to improve our understanding on how the low-mass starless dense cores form, survive, and evolve. We faced this aim in a twofold approach. Firstly, we characterized observationally the physical, chemical, and magnetic properties of magnetized dense cores in their most initial stages, in order to understand the real initial conditions of the star-formation process. Secondly, we have compared interferometric observations of a Class-0 source to theoretical models of magnetized cloud collapse to derive the bettersuited initial conditions to form it, and the most relevant physical processes involved. To study the very young dense cores, we selected the Pipe nebula. This cloud presents very low star-formation efficiency (~0.06 %) and it is permeated by a uniform magnetic field. The nebula harbours more than a hundred very young dense cores mostly quiescent. We have mapped dense cores with densities below 10(5) cm(-3), lower than the typical values reported in literature. These cores present structures compatible with Bonnor-Ebert spheres, which suggests that they can be in a state close to hydrostatic equilibrium with the environment. Moreover, we discovered a very rich and varied chemistry, unexpected taking into account previous works in similar sources. Even in such young and diffuse objects, it is possible to distinguish differentiated chemical properties that allow us to propose an observational characterization and to suggest a possible evolutionary sequence. Some of the cores present chemical properties compatible with ages of 1 million years, but the lack of signposts of collapse suggests that active supporting non-thermal sources are acting. The lack of spherical symmetry also implies that some anisotropic force is present. The reported sub-Alfvénic turbulence points to magnetic field as this agent, which would cause the flattened shapes. NGC 1333 IRAS 4A is the ideal source to test magnetized low-mass cloud collapse models as it is a young Class-0 source with a collapsing envelope of gas and dust and a detected magnetic field with a clear hour-glass shape. We have confirmed that its properties can be satisfactorily explained with the standard model of star formation. The ideal-MHD models lead to better results, and the use of a temperature profile improves the agreement with the observational data. The initial conditions of the models, with sizes of ~0.1 pc and centrally peaked densities, agree with the results found toward the Pipe nebula dense cores. The intensity of the magnetic fields used in the models can be scaled to the values obtained for the diffuse gas with a power-law such as B-alpha-ro (1/2) typical of magnetized clouds evolving through ambipolar diffusion. From a technical point of view, the method used can establish the starting point in the way the ALMA data will be analyzed. The high quality of the data will make possible this kind of analysis, and foresees a huge improvement in our understandings of the star-formation process., [cat] És una evidència observacional que els nuclis densos són llocs de naixement d’estrelles de baixa massa. Aquestes regions aparentment inactives són capaces de sobreviure diverses vegades l’escala temporal de caiguda lliure i, potencialment, col•lapsar per formar estrelles. Malgrat la seva importància se’n coneixen pocs detalls dels primers estadis evolutius d’aquests objectes. El desafiament observacional que representa estudiar objectes tan difusos i estesos ens dificulta revelar-ne les respostes. Resulta molt més senzill, des d’un punt de vista observacional, estudiar fonts més brillants com les més evolucionades Classe-0, de les quals se’n pot revertir la història en base a models teòrics i trobar-ne les condicions inicials que són, idealment, aquelles dels nuclis densos on s’han format. Per altra banda, des d’un punt de vista teòric, molts estudis han considerat l’efecte del camp magnètic en els seus models durant dècades. No obstant això, la mancança d’instrumentació i tècniques observacionals impedien contrastar-ne les prediccions. Per fortuna, diversos telescopis han desenvolupat sistemes polarimètrics durant els darrers anys permetent estudiar per primera vegada i de forma fiable el camp magnètic. Per tot això, la complexa interacció als nuclis densos entre gravitació, pressió tèrmica, turbulència, rotació i camp magnètic no està ben caracteritzada observacionalment i, com a conseqüència, tampoc ben entesa teòricament. L’objectiu és, aleshores, aprofundir en la comprensió de com es formen, sobreviuen i evolucionen els nuclis densos de baixa massa. Aquest objectiu l’hem enfrontat seguint dues vessants. En primer lloc, hem caracteritzat observacionalment les propietats físiques, químiques i magnètiques dels nuclis densos magnetitzats als seus estadis més primigenis, a fi d’entendre les vertaderes condicions inicials del procés de formació estel•lar. En segon lloc, hem comparat les observacions interferomètriques d’una font Classe-0 amb models teòrics de col•lapse de núvols magnetitzats, per derivar-ne les condicions inicials més adients per formar-la i els processos físics que n’han dominat l’evolució. Per a l’estudi dels nuclis densos primigenis hem seleccionat la nebulosa de la Pipa, que presenta una eficiència de formació estel•lar molt baixa (~0.06 %) i està penetrada per un camp magnètic uniforme. La nebulosa alberga més d’un centenar de nuclis densos molt joves majoritàriament inactius. Hem mapat nuclis densos amb densitat per sota de 10(5) cm(-3), molt per sota dels valors reportats a la literatura. Aquests nuclis presenten una estructura compatible amb esferes de Bonnor-Ebert, el que suggereix que es poden trobar en situació d’equilibri hidrostàtic amb el seu entorn. A més, hem descobert una química molt rica i variada, inesperada tenint en compte els treballs previs en fonts d’aquest tipus. Inclús en objectes tan joves i difusos, és possible distingir característiques químiques pròpies que permeten definir grups i establir una possible seqüència química evolutiva. Alguns dels objectes mostren propietats químiques típiques d’edats de 1 milió d’anys, però la mancança d’indicis de col•lapse gravitatori suggereix que hi ha actives fonts de suport no tèrmiques. La falta de simetria esfèrica també implica que alguna força anisotròpica està actuant. La turbulència sub-Alfvénica apunta a que el camp magnètic pot ser aquest agent, el que causaria les formes aplanades. NGC 1333 IRAS 4A és la font ideal per a testejar els model de col•lapse magnetitzat a baixa massa perquè es una Classe-0 jove amb un embolcall de gas i pols en fase de col•lapse on es detecta un camp magnètic amb clara morfologia de rellotge d’arena. Hem confirmat que les seves propietats poden ser explicades satisfactòriament amb el model estàndard de formació estel•lar. Els models de magnetohidrodinàmica idealitzada condueixen a millors resultats, i l’ús de un perfil de temperatura millora l’acord amb les dades. Les condicions inicials dels models, amb mides de ~0.1 pc i densitats creixents cap al centre, concorden amb els resultats als nuclis densos de la nebulosa de la Pipa. La intensitat del camp magnètic inicial usat pels models poden ser escalats als valors obtinguts per al gas difús de la Pipa amb una llei del tipus B-alfa-ro(1/2) típica de núvols magnetitzats. Des d’un punt de vista més tècnic, el mètode que hem emprat pot establir un punt de referència en la manera en que les futures dades d’ALMA seran analitzades. La alta qualitat de les dades farà possible aquest tipus d’anàlisis, i fa preveure una gran millora en l’enteniment del procés de formació estel•lar.

We describe the motivation, design, and implementation of the CORNISH survey, an arcsecondresolution radio continuum survey of the inner galactic plane at 5 GHz using the Very Large Array (VLA). It is a blind survey coordinated with the northern SpitzerGLIMPSE I region covering 10°

[spa] En este trabajo se han observado 4 regiones de formación estelar en modo de cúmulo a longitudes de onda milimétricas y submilimétricas con alta resolución angular (2''-4'') y alta sensibilidad. Para llevar a cabo el proceso de selección de las regiones, se han observado 8 regiones con el radiointerferómetro Very Large Array y el radiotelescopio IRAM 30m. Para cada una de las 4 regiones seleccionadas, se ha estudiado la naturaleza de los objetos estelares jóvenes y la interacción entre ellos, con el objetivo de comprender mejor la formación estelar en cúmulos. En la región HH211 no se ha encontrado evidencia de interacción entre las diferentes fuentes. Se ha estudiado con el interferómetro Submillimeter Array la formación de uno de los miembros más jóvenes, HH211mm, en el continuo submilimétrico y en CO(3-2) y SiO(8-7). La emisión de CO y SiO muestra un chorro de gas molecular de alta velocidad muy colimado, mientras que la emisión de continuo submilimétrico revela una fuente compacta en el centro de simetría del chorro y ligeramente alargada en la dirección perpendicular al chorro, que traza el disco protoestelar. Además, se ha encontrado que un viento de ángulo ancho parece ser el mecanismo que impulsa el chorro altamente colimado de esta fuente. Por tanto, HH211mm constituye un claro ejemplo de una estrella formándose de modo aislado, aun dentro de un cumulo. Para el caso de IRAS 00117+6412, observada con el interferómetro Plateau de Bure a 1 y 3 mm, en N2H+(1-0), CS(5-4) y CH3OH(5-4), se han detectado dos fuentes compactas en el milimétrico, sumergidas en una nube de gas denso trazada por N2H+, y que parecen estar asociadas a objetos estelares jóvenes en diferentes estados evolutivos. Justo en el borde este de la nube de gas denso se ha detectado una región de gas ionizado ultracompacta, por lo que IRAS 00117+6412 es un excelente candidato para estudiar la interacción entre un frente de ionización y una nube molecular con formación estelar activa. La región IRAS 20343+4129 se ha observado con el Submillimeter Array a 1 mm y en CO(2-1), y se ha descubierto un flujo molecular bipolar alargado en la dirección este-oeste que está impulsado por una fuente infrarroja clasificada como Clase I de masa intermedia. Se propone que otra de las fuentes infrarrojas está creando una cavidad y acumulando material ambiente en sus paredes, trazado por las fuentes milimétricas que se han detectado, que parecen estar asociadas a condensación es en un estado previo a la formación estelar. Finalmente, en la región IRAS 20293+3952, observada con el interferómetro Berkeley-Illinois-Maryland Array, se ha encontrado dos nubes de gas denso trazado por N2H+(1-0) y NH3(1,1) y NH3(2,2), y una gran variedad de objetos estelares jóvenes, la mayoría asociados a la zona norte de la nube principal. Los diferentes objetos estelares abarcan como mínimo un orden de magnitud en masa y se encuentran en estados evolutivos diferentes, indicando formación estelar continuada. Se ha derivado mapas de temperatura rotación al y densidad columnar de NH3 en las dos nubes, y se ha encontrado que la diferenciación química en la nube principal es importante, así como la interacción entre las diferentes fuentes. Con estos nuevos datos y otros recogidos de la literatura, se ha compilado una tabla de 5 regiones que albergan protoestrellas de masa intermedia/alta observadas con sensibilidades mejores que 1 masa solar, y se ha encontrado que el número de fuentes milimétricas alrededor de la protoestrella de alta masa es menor que el número de fuentes infrarrojas. Dado que nuestras observaciones sugieren que la formación estelar en cúmulos es continuada, el menor número de fuentes milimétricas parece indicar que la escala de tiempo en que un objeto estelar joven es brillante en el milimétrico es menor que la escala de tiempo en que un objeto estelar joven es brillante en el infrarrojo. Además, se ha encontrado una escala espacial típica de 0.1-0.3 pc asociada a un estado evolutivo particular. Para acabar, la distribución espacial de los objetos estelares jóvenes en las regiones estudiadas no se puede explicar únicamente por la interacción entre los diferentes objetos, sino que además es necesario suponer diferentes condiciones iniciales en la nube molecular original. Aun así, las interacciones pueden inducir la formación estelar en algunos casos concretos.

Context. After the release of the gamma-ray source catalog produced by the Fermi satellite during its first two years of operation, a significant fraction of sources still remain unassociated at lower energies. In addition to well-known high-energy emitters (pulsars, blazars, supernova remnants, etc.), theoretical expectations predict new classes of gamma-ray sources. In particular, gamma-ray emission could be associated with some of the early phases of stellar evolution, but this interesting possibility is still poorly understood. Aims. The aim of this paper is to assess the possibility of the Fermi gamma-ray source 2FGL J0607.5-0618c being associated with the massive star forming region Monoceros R2. Methods. A multi-wavelength analysis of the Monoceros R2 region is carried out using archival data at radio, infrared, X-ray, and gamma-ray wavelengths. The resulting observational properties are used to estimate the physical parameters needed to test the different physical scenarios. Results. We confirm the 2FGL J0607.5-0618c detection with improved confidence over the Fermi two-year catalog. We find that a combined effect of the multiple young stellar objects in Monoceros R2 is a viable picture for the nature of the source., Facultad de Ciencias Astronómicas y Geofísicas, Instituto Argentino de Radioastronomía

We report a study of the low-mass Class 0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H13CO+ (J = 3–2), CS (J = 5–4), and CCH (N = 3–2) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circumbinary VLA 1623A disk, as well as the VLA 1623B disk. We found that the minor axis of the circumbinary disk of VLA 1623A is misaligned by about 12° with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circumbinary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be 5–16 au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circumbinary disk. The origin of its opposite gradient is also discussed.