arXiv subjects

J. Vasquez

Publications and source records attributed to J. Vasquez.

At least 19 recordsLinked to original sources

arXiv2024

The sPHENIX Micromegas Outer Tracker

The sPHENIX Time Projection Chamber Outer Tracker (TPOT) is a Micromegas based detector. It is a part of the sPHENIX experiment that aims to facilitate the calibration of the Time Projection Chamber, in particular the correction of the time-averaged and beam-induced distortions of the electron drift. This paper describes the detector mission, setup, construction, installation, commissioning and performance during the first year of sPHENIX data taking.

physics.ins-det↗

arXiv2021

A Microwave SQUID Multiplexer Optimized for Bolometric Applications

A microwave SQUID multiplexer ($μ$MUX) has been optimized for coupling to large arrays of superconducting transition-edge sensor (TES) bolometers. We present the scalable cryogenic multiplexer chip design in a 1820-channel multiplexer configuration for the 4-8 GHz rf band. The key metrics of yield, sensitivity, and crosstalk are determined through measurements of 455 readout channels, which span 4-5 GHz. The median white-noise level is 45 pA/$\sqrt{\textrm{Hz}}$, evaluated at 2 Hz, with a 1/f knee $\leq$ 20 mHz after common-mode subtraction. The white-noise level decreases the sensitivity of a TES bolometer optimized for detection of the cosmic microwave background at 150 GHz by only 3%. The measured crosstalk between any channel pair is $\leq$ 0.3%.

astro-ph.IM↗

arXiv2016

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

Based on the molecular emission in the $^{12}$CO(2-1) and $^{13}$CO(2-1) lines, and the continuum emission in the MIR and FIR towards the S21 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 S21. The total molecular mass in the shell amounts to 2900 solar masses and the original ambient density, 2.1 x 10$^3$ cm$^{-3}$, indicating that the bubble is evolving in a high density interstellar medium. The image at 24 $μ$m shows warm dust inside the bubble, while the emission in the range 250 to 870 $μ$m reveal cold dust in its outskirts, coincident with the molecular gas. The detection of radio continuun 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.

astro-ph.GA↗

arXiv2015

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 $μ$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.

astro-ph.GA↗

arXiv2015

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

We are presenting here a study of the cold dust in the infrared 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, that was probably triggered by the expansion of the ionization front. We use 870 micron data obtained with LABOCA to map the dust emission. The obtained LABOCA image was compared to archival IR,radio continuum, and optical images. The 870 micron emission follows the 8 micron (Spitzer), 250 micron, and 500 micron (Herschel) emission distributions showing the classical morphology of a spherical shell. We use the 870 micron and 250 micron 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 Mo and 2800 Mo, and volume densities between 1.1x10^3 cm^-3 and 2.04x10^5 cm^-3. The total mass of the clumps is 37600 Mo. The dust temperature of the clumps is in the range from 21 K to 32 K, while inside the HII region reaches ~ 40 K. The clump mass distribution is well-fitted by a power law dN/dlog(M/Mo) proportional to M^(-alpha), with alpha=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 microns emission shows that only 37% of them lie in or above the high-mass star formation threshold, most of them having candidate YSOs projected inside. 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 also be acting.

astro-ph.GA↗

arXiv2014

Molecular gas associated with IRAS 10361-5830

We analyze the distribution of the molecular gas and the dust in the molecular clump linked to IRAS 10361-5830, located in the environs of the bubble-shaped HII region Gum 31 in the Carina region, with the aim of determining the main parameters of the associated material and investigating the evolutionary state of the young stellar objects identified there. Using the APEX telescope, we mapped the molecular emission in the J=3-2 transition of three CO isotopologues, 12CO, 13CO and C18O, over a 1.5' x 1.5' region around the IRAS position. We also observed the high density tracers CS and HCO+ toward the source. The cold dust distribution was analyzed using submillimeter continuum data at 870 μ obtained with the APEX telescope. Complementary IR and radio data at different wavelengths were used to complete the study of the ISM. The molecular gas distribution reveals a cavity and a shell-like structure of ~ 0.32 pc in radius centered at the position of the IRAS source, with some young stellar objects (YSOs) projected onto the cavity. The total molecular mass in the shell and the mean H$_2$ volume density are ~ 40 solar masses and ~(1-2) x 10$^3$ cm$^{-3}$, respectively. The cold dust counterpart of the molecular shell has been detected in the far-IR at 870 μ and in Herschel data at 350 μ. Weak extended emission at 24 μ from warm dust is projected onto the cavity, as well as weak radio continuum emission. A comparison of the distribution of cold and warm dust, and molecular and ionized gas allows us to conclude that a compact HII region has developed in the molecular clump, indicating that this is an area of recent massive star formation. Probable exciting sources capable of creating the compact HII region are investigated. The 2MASS source 10380461-5846233 (MSX G286.3773-00.2563) seems to be responsible for the formation of the HII region.

astro-ph.GA↗

arXiv2014

Molecules, dust, and protostars in NGC 3503

We are presenting here a follow-up study of the molecular gas and dust in the environs of the star forming region NGC 3503. This study aims at dealing with the interaction of NGC 3503 with its parental molecular cloud, and also with the star formation in the region. To analyze the molecular gas we use CO(2-1), 13CO(2-1), C18O(2-1), and HCN(3-2) line data obtained with the APEX telescope. To study the distribution of the dust, we make use of images at 870 microns from the ATLASGAL survey and IRAC-GLIMPSE archival images. We use public 2MASS and WISE data to search for candidate YSOs in the region. The new APEX observations allowed the substructure of the molecular gas in the velocity range from -28 to -23 km/s to be imaged in detail. The morphology of the molecular gas close to the nebula, the location of the PDR, and the shape of radio continuum emission suggest that the ionized gas is expanding against its parental cloud, and confirm the "champagne flow" scenario. We have identified several molecular clumps and determined some of their physical and dynamical properties. We have compared the physical properties of the clumps to investigate how the molecular gas has been affected by the HII region. Clumps adjacent to the ionization fronts of NGC 3503 and/or the bright rimmed cloud SFO62 have been heated and compressed by the ionized gas, but their line width is not different to those that are too distant to the ionization fronts. We identified several candidate YSOs in the region. Their spatial distribution suggests that stellar formation might have been boosted by the expansion of the nebula. We discard the "collect and collapse" scenario and propose alternative mechanisms such as radiatively driven implosion on pre-existing molecular clumps or small-scale Jeans gravitational instabilities.

astro-ph.GA↗

arXiv2012

Molecular gas towards G18.8+1.8

This work aims at investigating the characteristics of the molecular gas associated with the nebula G18.8+1.8, linked to the Wolf-Rayet star HD168206 (WR 113), and its relation to other components of its local interstellar medium. We carried out molecular observations of the 12CO(J=1-0) and (J=2-1) lines with angular resolution of 44 arcsec and 22 arcsec using the SEST telescope. Complementary NANTEN data of the 12CO(1-0) line were also used. The dust emission was analyzed using Spitzer-IRAC images at 8.0 microns, and WISE data at 3.4, 4.6, and 12.0 microns. The SEST data allowed us to identify a molecular component (Cloud 3) having velocities in the interval from ~ +30 to +36 km/s which is most probably linked to the nebula. Morphological and kinematical properties suggest that Cloud 3 constitute a wind-blown molecular half-shell, which expands around WR113. The ratio R_(2-1/1-0) and excitation temperatures indicate that the molecular gas is being irradiated by strong UV radiation. The location of the inner optical ring in the outer edge of Cloud 3 suggests that the stars SerOB2-1, -2, -3, -63, and -64 are responsables for the ionization of Cloud 3 and the inner ring nebula. A comparison between the spatial distribution of the molecular gas and the PAH emission at 8 $μ$m indicates the existence of a PDR between the ionized and the molecular gas. A search for candidate young stellar objects (YSOs) in the region around G18.8+1.8 based on available 2MASS, MSX, IRAS, and Spitzer-IRAC catalogs resulted in the detection of about sixty sources, some of them projected onto Cloud 3. Two small spots of clustered candidates YSOs are projected near the outer border of Cloud 3, although a triggered stellar formation scenario is doubtful.

astro-ph.GA↗

arXiv2011

NGC 3503 and its molecular environment

We present a study of the molecular gas and interstellar dust distribution in the environs of the HII region NGC 3503 associated with the open cluster Pis 17 with the aim of investigating the spatial distribution of the molecular gas linked to the nebula and achieving a better understanding of the interaction of the nebula and Pis 17 with their molecular environment. We based our study in ^{12}CO(1-0) observations of a region of ~0.6 deg. in size obtained with the 4-m NANTEN telescope, unpublished radio continuum data at 4800 and 8640 MHz obtained with the ATCA telescope, radio continuum data at 843 MHz obtained from SUMSS, and available IRAS, MSX, IRAC-GLIMPSE, and MIPSGAL images. We found a molecular cloud (Component 1) having a mean velocity of -24.7 km s^{-1}, compatible with the velocity of the ionized gas, which is associated with the nebula and its surroundings. Adopting a distance of 2.9 +/- 0.4 kpc the total molecular mass and density yield (7.6 +/- 2.1) x 10^3 Msun and 400 +/- 240 cm^{-3}, respectively. The radio continuum data confirm the existence of an electron density gradient in NGC 3503. The IR emission shows the presence of a PDR bordering the higher density regions of the nebula. The spatial distribution of the CO emission shows that the nebula coincides with a molecular clump, with the strongest CO emission peak located close to the higher electron density region. The more negative velocities of the molecular gas (about -27 km s^{-1}), is coincident with NGC 3503. Candidate YSOs were detected towards the HII region, suggesting that embedded star formation may be occurring in the neighbourhood of the nebula. The presence of a clear electron density gradient, along with the spatial distribution of the molecular gas and PAHs in the region indicates that NGC 3503 is a blister-type HII region that probably has undergone a champagne phase.

astro-ph.GA↗

arXiv2011

A multifrequency study of the active star forming complex NGC6357. I. Interstellar structures linked to the open cluster Pis24

We investigate the distribution of the gas (ionized, neutral atomic and molecular), and interstellar dust in the complex star forming region NGC6357 with the goal of studying the interplay between the massive stars in the open cluster Pis24 and the surrounding interstellar matter. Our study of the distribution of the ionized gas is based on narrow-band Hhalfa, [SII], and [OIII] images obtained with the Curtis-Schmidt Camera at CTIO, Chile, and on radio continuum observations at 1465 MHz taken with the VLA with a synthesized beam of 40 arcsec. The distribution of the molecular gas is analyzed using 12CO(1-0) data obtained with the Nanten radiotelescope, Chile (angular resolution = 2.7 arcmin). The interstellar dust distribution was studied using mid-infrared data from the GLIMPSE survey and far-infrared observations from IRAS. NGC6357 consists of a large ionized shell and a number of smaller optical nebulosities. The optical, radio continuum, and near- and mid-IR images delineate the distributions of the ionized gas and interstellar dust in the HII regions and in previously unknown wind blown bubbles linked to the massive stars in Pis24 revealing surrounding photodissociation regions. The CO line observations allowed us to identify the molecular counterparts of the ionized structures in the complex and to confirm the presence of photodissociation regions. The action of the WR star HD157504 on the surrounding gas was also investigated. The molecular mass in the complex is estimated to be (4+/-2)X10^5 Mo. Mean electron densities derived from the radio data suggest electron densities > 200 cm^-3, indicating that NGC6357 is a complex formed in a region of high ambient density. The known massive stars in Pis24 and a number of newly inferred massive stars are mainly responsible for the excitation and photodissociation of the parental molecular cloud.

astro-ph.GA↗

arXiv2010

Ionized gas, molecules, and dust in Sh2-132

We analyze the various interstellar components of the HII region Sh2-132. The main stellar source is the double binary system that includes the Wolf-Rayet star WR153ab. We use radio continuum images at 408 and 1420 MHz, and HI 21cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO(1-0) line at 115 GHz from the Five College Radio Astronomy Observatory, and available mid and far IR observations obtained with the MSX and IRAS satellites, respectively. Sh2-132 is composed of two shells showing radio continuum counterparts at both frequencies. The emission is thermal in nature. The estimated rms electron density and ionized mass of the nebula are n_e = 20 cm^{-3} and M_HII = 1500 Mo. The distribution of the CO emission shows molecular gas bordering the ionized nebula and interacting with it. The velocities of the molecular gas is in the range --38 to --53 km/s, similar to the velocity of the ionized gas. The emission at 8.3 mic. reveals a ring like feature of about 15' that encircles the bright optical regions. This emission is due to the PAHs and marks the location of photodissociation regions. The gas distribution in the environs of Sh2-132 can be explained in a scenario where the massive stars in the region photodissociated, ionized, and swept-up the dense molecular material from the parental cloud through their strong stellar winds and intense UV photon flux.

astro-ph.GA↗

arXiv2009

The radio and IR counterparts of the ring nebula around HD211564

We report the detection of the radio and infrared counterparts of the ring nebula around the WN3(h) star HD211564 (WR152), located to the southwest of the HII region Sh2132. Using radio continuum data from the Canadian Galactic Plane Survey, we identified the radio counterparts of the two concentric rings, of about 9' and 16' in radius, related to the star. After applying a filling factor f = 0.05-0.12, electron densities and ionized masses are in the range 10-16 cm^-3 and 450-700 Mo, respectively. The analysis of the HI gas emission distribution allowed the identification of 5900 Mo of neutral atomic gas with velocities between -52 and -43 km/s probably linked to the nebula. The region of the nebula is almost free of molecular gas. Only four small clumps were detected, with a total molecular mass of 790 Mo. About 310 Mo are related to a small infrared shell-like source linked to the inner ring, which is also detected in the MSX band A. An IRAS YSO candidate is detected in coincidence with the shell-like IR source. We suggest that the optical nebula and its neutral counterparts originated from the stellar winds from the WR star and its massive progenitor, and are evolving in the envelope of a slowly expanding shell centered at (l,b) = (102 30, -0 50), of about 31 pc in radius. The bubble's energy conversion efficiency is in agreement with recent numerical analysis and with observational results.

astro-ph.GA↗

arXiv2009

Four years of optical turbulence monitoring at the Cerro Tololo Inter-American Observatory (CTIO)

The optical turbulence conditions as measured between 2004 until end of 2008 above Cerro Tololo, their seasonal as well as nocturnal behavior are presented. A comparison with the MASS-DIMM system of the Thirty Meter Telescope site testing was conducted and identifies an artificially increased seeing component in the data collected by the CTIO DIMM system under northerly winds. Evidence is shown that this increased turbulence is caused by the telescope dome. A correction for this effect is attempted and applied to the CTIO DIMM data. The MASS data of this comparison campaign allow to set constraints on the general assumption of uniform turbulent layers above a site.

astro-ph.IM↗

arXiv2009

Thirty Meter Telescope Site Testing I: Overview

As part of the conceptual and preliminary design processes of the Thirty Meter Telescope (TMT), the TMT site testing team has spent the last five years measuring the atmospheric properties of five candidate mountains in North and South America with an unprecedented array of instrumentation. The site testing period was preceded by several years of analyses selecting the five candidates, Cerros Tolar, Armazones and Tolonchar in northern Chile; San Pedro Martir in Baja California, Mexico and the 13 North (13N) site on Mauna Kea, Hawaii. Site testing was concluded by the selection of two remaining sites for further consideration, Armazones and Mauna Kea 13N. It showed that all five candidates are excellent sites for an extremely large astronomical observatory and that none of the sites stands out as the obvious and only logical choice based on its combined properties. This is the first article in a series discussing the TMT site testing project.

astro-ph.IM↗

arXiv2008

Unveiling the birth and evolution of the HII region Sh2-173

Based on a multiwavelength study, the ISM around the HII region Sh2-173 has been analyzed. The ionized region is clearly detected in the optical and in the radio continuum images. The analysis of the HI data shows a region of low emissivity that has an excellent morphological correlation with the radio continuum emission. The HII region is partially bordered by a photodissociation region, which, in turn, is encircled by a molecular structure. Taking into account the presence of noncircular motions in the Perseus spiral arm, together with previous distance estimates for the region, we adopt a distance of 2.5 +- 0.5 kpc for Sh2-173. Seven hot stars were identified in the field of Sh2-173, being only one an O-type star. The amount of energetic photons emitted by this star is enough to keep the region ionized and heat the dust. Given that an expanding HII region may trigger star formation, a search for YSO candidates was made using different infrared point source catalogues. A population of 46 YSO candidates was identified projected onto the molecular clouds. On the other hand, Sh2-173 is located in a dense edge of a large HI shell. The possibility for Sh2-173 of being part of a hierarchical system of three generations is suggested. The ages of both, the HII region and the large shell, were estimated and compared. We concluded that Sh2-173 is a young HII region of about 0.6 - 1.0 Myr old. As for the large shell we obtained a dynamical age of 5 +- 1 Myr. These age estimates, together with the relative location of the different structures, support the hypothesis that Sh2-173 is part of a hierarchical system.

astro-ph↗

arXiv2008

Multifrequency study of the ring nebula SG13

We investigate the morphology and kinematics of the interstellar medium in the environs of the open cluster Mrk50, which includes the Wolf-Rayet star WR157 and a number of early B-type stars. The analysis was performed using radio continuum images at 408 and 1420 MHz, and HI 21cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO (J=1-0) line at 115 GHz from the Five College Radio Astronomy Observatory and available mid and far IR observations obtained with the MSX and IRAS satellites, respectively. This study allowed identification of the radio continuum and molecular counterpart of the ring nebula SG13, while no neutral atomic structure was found to be associated. The nebula is also detected in images in the mid and far infrared, showing the existence of dust well mixed with the ionized gas. We estimate the main physical parameters of the material linked to the nebula. The interstellar gas distribution in the environs of Mrk50 is compatible with a stellar wind bubble created by the mass loss from WR157. The distribution of young stellar object (YSO) candidates in the region shows that stellar formation activity may be present in the molecular shell that encircles the ring nebula.

astro-ph↗

arXiv2007

The environs of the HII region Gum31

We analyze the distribution of the interstellar matter in the environs of the HII region Gum31, excited by the open cluster NGC3324, located in the complex Carina region, with the aim of investigating the action of the massive stars on the surrounding neutral material. We use neutral hydrogen 21-cm line data, radio continuum images at 0.843, 2.4 and 4.9 GHz, 12CO(1-0) observations, and IRAS and MSX infrared data. Adopting a distance of 3 kpc for the HII region and the ionizing cluster, we derived an electron density of 33+/-3 cm^-3 and an ionized mass of (3.3+/-1.1)x10^3 Mo based on the radio continuum data at 4.9 GHz. The HI 21-cm line images revealed an HI shell surrounding the HII region. The HI structure is 10.0+/-1.7 pc in radius, has a neutral mass of 1500+/-500 Mo, and is expanding at 11 km/s. The associated molecular gas amounts to 1.1+/-0.5)x10^5 Mo, being its volume density of about 350 cm^3. This molecular shell could represent the remains of the cloud where the young open cluster NGC3324 was born or could have originated by the shock front associated with the HII region. The difference between the ambient density and the electron density of the HII region suggests that the HII region is expanding. The distributions of the ionized and molecular material, along with that of the emission in the MSX band A, suggest that a photodissociation region has developed at the interface between the ionized and molecular gas. The characteristics of a relatively large number of the IRAS, MSX, and 2MASS point sources projected onto the molecular envelope are compatible with protostellar candidates, showing the presence of active star forming regions. Very probably, the expansion of the HII region has triggered stellar formation in the molecular shell.

astro-ph↗

arXiv2007

The environs of the HII region Gum31

We analyze the distribution of the interstellar matter in the environs of the \hii region Gum 31, excited by the open cluster NGC 3324, located in the complex Carina region, with the aim of investigating the action of the massive stars on the surrounding neutral material. We use 21cm-line data, radio continuum images at 0.843, 2.4 and 4.9 GHz, $^{12}${\bf CO(1-0)} observations, and IRAS and MSX infrared data. Adopting a distance of 3 kpc for the \hii\ region and the ionizing cluster, we have derived an electron density of 33$\pm$3 cm$^{-3}$ and an ionized mass of (3.3$\pm$1.1)$\times10^3$ M$_{\odot}$ based on the radio continuum data at 4.9 GHz. The \hi 21-cm line images revealed an \hi shell surrounding the H {\sc ii} region. The \hi structure is 10.0$\pm$1.7 pc in radius, has a neutral mass of 1500$\pm$500 M$_{\odot}$, and is expanding at 11 km s$^{-1}$. The associated molecular gas amounts to (1.5$\pm$0.5)$\times10^5$ M$_{\odot}$, being its volume density of about 500 cm^{-3}. This molecular material probably represents the remains of the cloud where the young open cluster NGC 3324 was born. The distributions of the ionized and molecular material, along with that of the emission in the MSX band A suggest that a photodissociation region has developed at the interface between the ionized and molecular gas. We conclude that either the massive stars in the open cluster have weak stellar winds or the stellar winds have blown during a very short period of time to create an interstellar bubble in an interstellar medium as dense as observed. IRAS, MSX, and 2MASS point sources projected onto the molecular envelope are compatible with protostellar candidates, showing the presence star forming regions. The expansion of the \hii region has triggered stellar formation in the molecular shell.

astro-ph↗