Impact of noise on a dynamical system: prediction and uncertainties from a swarm-optimized neural network

In this study, an artificial neural network (ANN) based on particle swarm optimization (PSO) was developed for the time series prediction. The hybrid ANN+PSO algorithm was applied on Mackey--Glass chaotic time series in the short-term $x(t+6)$. The performance prediction was evaluated and compared with another studies available in the literature. Also, we presented properties of the dynamical system via the study of chaotic behaviour obtained from the predicted time series. Next, the hybrid ANN+PSO algorithm was complemented with a Gaussian stochastic procedure (called {\it stochastic} hybrid ANN+PSO) in order to obtain a new estimator of the predictions, which also allowed us to compute uncertainties of predictions for noisy Mackey--Glass chaotic time series. Thus, we studied the impact of noise for several cases with a white noise level ($\sigma_{N}$) from 0.01 to 0.1.Comment: 11 pages, 8 figure

Molecular gas and star formation towards the IR dust bubble S24 and its environs

We present a multi-wavelength analysis of the infrared dust bubble S24, and its environs, with the aim of investigating the characteristics of the molecular gas and the interstellar dust linked to them, and analyzing the evolutionary status of the young stellar objects (YSOs) identified there. Using APEX data, we mapped the molecular emission in the CO(2-1), $^{13}$CO(2-1), C$^{18}$O(2-1), and $^{13}$CO(3-2) lines in a region of about 5'x 5' in size around the bubble. The cold dust distribution was analyzed using ATLASGAL and Herschel images. Complementary IR and radio data were also used.The molecular gas linked to the S24 bubble, G341.220-0.213, and G341.217-0.237 has velocities between -48.0 km sec$^{-1}$ and -40.0 km sec$^{-1}$. The gas distribution reveals a shell-like molecular structure of $\sim$0.8 pc in radius bordering the bubble. A cold dust counterpart of the shell is detected in the LABOCA and Herschel images.The presence of extended emission at 24 $\mu$m and radio continuum emission inside the bubble indicates that the bubble is a compact HII region. Part of the molecular gas bordering S24 coincides with the extended infrared dust cloud SDC341.194-0.221. A cold molecular clump is present at the interface between S24 and G341.217-0.237. As regards G341.220-0.213, the presence of an arc-like molecular structure at the northern and eastern sections of this IR source indicates that G341.220-0.213 is interacting with the molecular gas. Several YSO candidates are found to be linked to the IR extended sources, thus confirming their nature as active star-forming regions. The total gas mass in the region and the H$_2$ ambient density amount to 10300 M$_{\odot}$ and 5900 cm$^{-3}$, indicating that G341.220-0.213, G341.217-0.237, and the S24 HII region are evolving in a high density medium. A triggering star formation scenario is also investigated.Comment: 17 pages, 16 figures. Submitted to A&A. Revised according to the referee repor

870 μm continuum observations of the bubble-shaped nebula Gum 31

Aims. We present here a study of the cold dust in the close environs of the ring nebula Gum 31. We aim at deriving the physical properties of the molecular gas and dust associated with the nebula, and investigating its correlation with the star formation in the region, which was probably triggered by the expansion of the ionization front against its environment. Methods. We make use of 870 μm emission data obtained with the Large APEX Bolometer Camera (LABOCA) to map the dust emission. The 870 μm emission provides an excellent probe of mass and density of dense molecular clouds. The obtained LABOCA image was compared to archival infrared, radio continuum, and optical images. Results. The 870 μm emission follows the 8 μm (Spitzer), 250 μm, and 500 μm (Herschel) emission distributions showing the classical morphology of a two-dimensional projection of a spherical shell. We use the 870 μm and 250 μm images to identify 60 dust clumps in the collected layers of molecular gas using the Gaussclumps algorithm. The clumps have effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 M⊙ and 2800 M⊙, and volume densities between 1.1 × 103 cm-3 and ~2.04 × 105 cm-3. The total mass of the clumps is ~37 600 M⊙. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the Hii region it reaches ~40 K. The clump mass distribution for the sample is fitted by a power law dN/dlog (M/M⊙) ∝ M-α, with α = 0.93 ± 0.28. The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps detected in the 870 μm emission shows that only 37% of them lie in or above the high-mass star formation threshold. Most of this 37% have candidate YSOs projected inside their limits. A comparison of the dynamical age of the Hii region with the fragmentation time, allowed us to conclude that the collect-and-collapse mechanism may be important for the star formation at the edge of Gum 31, although other processes may be acting simultaneously. The position of the identified young stellar objects in the region is also a strong indicator that the collect-and-collapse process is acting.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

A submillimeter study of the IR dust bubble S 21 and its environs

Based on the molecular emission in the 12CO(2-1) and 13CO(2-1) lines, and on the continuum emission in the MIR and FIR towards the S 21 IR dust bubble, we analyze the physical characteristics of the gas and dust linked to the nebula and the presence of young stellar objects (YSOs) in its environs. The line emission reveals a clumpy molecular shell, 1.4 pc in radius, encircling S 21. The total molecular mass in the shell amounts to 2900 M⊙ and the original ambient density, 2.1 ×10 3 cm − 3 , indicating that the bubble is evolving in a high density interstellar medium. The image at 24 µm shows warm dust inside the bubble, while the emission in the range 250 to 870 µm reveals cold dust in its outskirts, coincident with the molecular gas. The detection of radio continuum emission indicates that the bubble is a compact Hii region. A search for YSOs using photometric criteria allowed to identify many candidates projected onto the molecular clumps. We analize if the collect and collapse process has triggered a new generation of stars.Basados en la emisión molecular en las líneas 12CO(2-1) y 13CO(2-1), y en la emisión en el continuo en el mediano y lejano infrarrojo hacia la burbuja S 21, analizamos las características físicas del gas y polvo asociado con S 21 y la presencia de objetos estelares jóvenes (YSOs) en su entorno. La emisión molecular revela una cáscara grumosa de 1.4 pc de radio rodeando a S 21. Su masa molecular es de 2900 M⊙ y la densidad ambiental original en la región, 2.1 ×10 3 cm − 3 , lo que indica que la burbuja evoluciona en un medio de alta densidad. La imagen a 24 µ m muestra polvo tibio dentro de la burbuja, mientras que la emisión en el rango 250 a 870 µm revela que hay polvo frío en la vecindad, coincidente con el gas molecular. La detección de emisión en el continuo de radio indica que S 21 es una región Hii compacta. Una búsqueda de YSOs utilizando criterios fotométricos permitió identificar muchos candidatos coincidentes con los grumos moleculares. Se analiza si el proceso de collect and collapse ha dado origen a una nueva generación de estrellas.Fil: Cappa, Cristina Elisabeth. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Duronea, Nicolas Urbano. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Vasquez, Javier. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Rubio, M.. Universidad de Chile. Facultad de Ciencias Fisicas y Matematicas; ChileFil: Firpo, V.. Universidad de la Serena; ChileFil: López Caraballo, C. H.. Universidad Católica de Chile; ChileFil: Borissova, J.. Universidad de Valparaiso; Chil

28 -- 40 GHz variability and polarimetry of bright compact sources in the QUIJOTE cosmological fields

We observed 51 sources in the Q-U-I JOint TEnerife (QUIJOTE) cosmological fields which were brighter than 1 Jy at 30 GHz in the Planck Point Source Catalogue (version 1), with the Very Large Array at 28 -- 40 GHz, in order to characterise their high-radio-frequency variability and polarization properties. We find a roughly log-normal distribution of polarization fractions with a median of 2%, in agreement with previous studies, and a median rotation measure (RM) of $\approx$ 1110 rad m$^{-2}$ with one outlier up to $\approx$ 64000 rad m$^{-2}$ which is among the highest RMs measured in quasar cores. We find hints of a correlation between the total intensity flux density and median polarization fraction. We find 59% of sources are variable in total intensity, and 100% in polarization at $3\sigma$ level, with no apparent correlation between total intensity variability and polarization variability. This indicates that it will be difficult to model these sources without simultaneous polarimetric monitoring observations and they will need to be masked for cosmological analysis.Comment: 17 pages, 14 figures, accepted to MNRA

Millimeter and far-IR study of the IRDC SDC341.232-0.268

We analyze the molecular gas and dust associated with the infrared dark cloud SDC341.232-0.268 in order to investigate the characteristics and parameters of the gas, determine the evolutionary status of four embedded EGO candidates, and es- tablish possible infall or outflow gas motions. We base our study on 12CO(2-1), 13CO(2-1), and C18O(2-1) data obtained with the APEX telescope, molecular data of high density tracers from the MALT90 survey and IR images from Spitzer, Herschel and ATLASGAL. The study reveals two clumps at −44 km s−1 towards the IRDC, with densities of > 104cm−3, typical of IRDCs, while high density tracers show H2 densities > 105. FIR images reveals the presence of cold dust linked to the molecular clumps and EGOs. A comparison of the spectra of the optically thin and optically thick molecular lines towards the EGOs suggests the existence of infall and outflow motions.Analizamos el gas molecular y el polvo asociado a la nube oscura infrarroja SDC341.232-0.268 con el fin de investigar las características y parámetros físicos del gas, determinar el estado evolutivo de los cuatro EGOs embebidos y establecer posibles movimientos de acreción o flujo molecular. Nos basamos en datos de 12CO(2-1), 13CO(2-1) y C18O(2-1) obtenidos con el telescopio APEX, trazadores de alta densidad extraídos de MALT90, e imágenes infrarrojas de Spitzer, Herschel y ATLASGAL. El estudio revela dos grumos moleculares a −44 km s−1 coincidentes con la IRDC con una densidad > 104cm−3, típica de IRDCs. Los trazadores de alta densidad arrojan densidades de H2 > 105. Las imágenes en el lejano IR muestran polvo frío asociado a los grumos moleculares y a los EGOs. La comparación de espectros moleculares ópticamente gruesos y finos sugiere la existencia de acreción y flujos moleculares.Facultad de Ciencias Astronómicas y Geofísica

870 μm continuum observations of the bubble-shaped nebula Gum 31

Aims. We present here a study of the cold dust in the close environs of the ring nebula Gum 31. We aim at deriving the physical properties of the molecular gas and dust associated with the nebula, and investigating its correlation with the star formation in the region, which was probably triggered by the expansion of the ionization front against its environment. Methods. We make use of 870 μm emission data obtained with the Large APEX Bolometer Camera (LABOCA) to map the dust emission. The 870 μm emission provides an excellent probe of mass and density of dense molecular clouds. The obtained LABOCA image was compared to archival infrared, radio continuum, and optical images. Results. The 870 μm emission follows the 8 μm (Spitzer), 250 μm, and 500 μm (Herschel) emission distributions showing the classical morphology of a two-dimensional projection of a spherical shell. We use the 870 μm and 250 μm images to identify 60 dust clumps in the collected layers of molecular gas using the Gaussclumps algorithm. The clumps have effective deconvolved radii between 0.16 pc and 1.35 pc, masses between 70 M⊙ and 2800 M⊙, and volume densities between 1.1 × 103 cm-3 and ~2.04 × 105 cm-3. The total mass of the clumps is ~37 600 M⊙. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the Hii region it reaches ~40 K. The clump mass distribution for the sample is fitted by a power law dN/dlog (M/M⊙) ∝ M-α, with α = 0.93 ± 0.28. The slope differs from those obtained for the stellar IMF in the solar neighborhood, suggesting that the clumps are not direct progenitors of single stars/protostars. The mass-radius relationship for the 41 clumps detected in the 870 μm emission shows that only 37% of them lie in or above the high-mass star formation threshold. Most of this 37% have candidate YSOs projected inside their limits. A comparison of the dynamical age of the Hii region with the fragmentation time, allowed us to conclude that the collect-and-collapse mechanism may be important for the star formation at the edge of Gum 31, although other processes may be acting simultaneously. The position of the identified young stellar objects in the region is also a strong indicator that the collect-and-collapse process is acting.Facultad de Ciencias Astronómicas y GeofísicasInstituto Argentino de Radioastronomí

A submillimeter study of the ir dust bubble S 21 and its environs

Basados en la emisión molecular en las líneas 12CO(2-1) y 13CO(2-1), y en la emisión en el continuo en el mediano y lejano infrarrojo hacia la burbuja S 21, analizamos las características físicas del gas y polvo asociado con S 21 y la presencia de objetos estelares jóvenes (YSOs) en su entorno. La emisión molecular revela una cáscara grumosa de 1.4 pc de radio rodeando a S 21. Su masa molecular es de 2900 M⊙ y la densidad ambiental original en la región, 2.1×103 cm−3, lo que indica que la burbuja evoluciona en un medio de alta densidad. La imagen a 24 μm muestra polvo tibio dentro de la burbuja, mientras que la emisión en el rango 250 a 870 μm revela que hay polvo frío en la vecindad, coincidente con el gas molecular. La detección de emisión en el continuo de radio indica que S 21 es una región Hii compacta. Una búsqueda de YSOs utilizando criterios fotométricos permitió identificar muchos candidatos coincidentes con los grumos moleculares. Se analiza si el proceso de collect and collapse ha dado origen a una nueva generación de estrellas.Based on the molecular emission in the 12CO(2-1) and 13CO(2-1) lines, and on the continuum emission in the MIR and FIR towards the S 21 IR dust bubble, we analyze the physical characteristics of the gas and dust linked to the nebula and the presence of young stellar objects (YSOs) in its environs. The line emission reveals a clumpy molecular shell, 1.4 pc in radius, encircling S 21. The total molecular mass in the shell amounts to 2900 M⊙ and the original ambient density, 2.1×103 cm−3, indicating that the bubble is evolving in a high density interstellar medium. The image at 24 μm shows warm dust inside the bubble, while the emission in the range 250 to 870 μm reveals cold dust in its outskirts, coincident with the molecular gas. The detection of radio continuum emission indicates that the bubble is a compact Hii region. A search for YSOs using photometric criteria allowed to identify many candidates projected onto the molecular clumps. We analize if the collect and collapse process has triggered a new generation of stars.Facultad de Ciencias Astronómicas y Geofísica

Constraints on the Polarization of the Anomalous Microwave Emission in the Perseus Molecular Complex from 7-year WMAP data

We have used the seven year Wilkinson Microwave Anisotropy Probe (WMAP) data in order to update the measurements of the intensity signal in the G159.6-18.5 region within the Perseus Molecular Complex, and to set constraints on the polarization level of the anomalous microwave emission in the frequency range where this emission is dominant. At 23, 33 and 41 GHz, we obtain upper limits on the fractional linear polarization of 1.0, 1.8 and 2.7% respectively (with a 95 per cent confidence level). These measurements rule out a significant number of models based on magnetic dipole emission of grains that consist of a simple domain (Draine & Lazarian 1999) as responsible of the anomalous emission. When combining our results with the measurement obtained with the COSMOSOMAS experiment at 11 GHz (Battistelli et al. 2006), we find consistency with the predictions of the electric dipole and resonance relaxation theory (Lazarian & Draine 2000) at this frequency range.Comment: 14 pages, 7 figures, ApJ submitte

First Season QUIET Observations: Measurements of CMB Polarization Power Spectra at 43 GHz in the Multipole Range 25 <= ell <= 475

The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and 95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to measure the anisotropy in the polarization of the CMB. QUIET primarily targets the B modes from primordial gravitational waves. The combination of these frequencies gives sensitivity to foreground contributions from diffuse Galactic synchrotron radiation. Between 2008 October and 2010 December, >10,000hours of data were collected, first with the 19-element 43GHz array (3458hours) and then with the 90-element 95GHz array. Each array observes the same four fields, selected for low foregrounds, together covering ~1000deg^2. This paper reports initial results from the 43GHz receiver which has an array sensitivity to CMB fluctuations of 69uK sqrt(s). The data were extensively studied with a large suite of null tests before the power spectra, determined with two independent pipelines, were examined. Analysis choices, including data selection, were modified until the null tests passed. Cross correlating maps with different telescope pointings is used to eliminate a bias. This paper reports the EE, BB and EB power spectra in the multipole range ell=25-475. With the exception of the lowest multipole bin for one of the fields, where a polarized foreground, consistent with Galactic synchrotron radiation, is detected with 3sigma significance, the E-mode spectrum is consistent with the LCDM model, confirming the only previous detection of the first acoustic peak. The B-mode spectrum is consistent with zero, leading to a measurement of the tensor-to-scalar ratio of r=0.35+1.06-0.87. The combination of a new time-stream double-demodulation technique, Mizuguchi-Dragone optics, natural sky rotation, and frequent boresight rotation leads to the lowest level of systematic contamination in the B-mode power so far reported, below the level of r=0.1Comment: 19 pages, 14 figures, higher quality figures are available at http://quiet.uchicago.edu/results/index.html; Fixed a typo and corrected statistical error values used as a reference in Figure 14, showing our systematic uncertainties (unchanged) vs. multipole; Revision to ApJ accepted version, this paper should be cited as "QUIET Collaboration et al. (2011)