J. Vasquez

Unveiling the birth and evolution of the H II region Sh2-173

Based on a multiwavelength study, the interstellar medium around the H II region Sh2-173 has been analysed. The ionized region is clearly detected in the optical and the radio continuum images. The analysis of the H I data shows a region of low emissivity that has an excellent morphological correlation with the radio continuum emission. The H II region is partially bordered by a photodissociation region, which, in turn, is encircled by a molecular structure. The H I and CO structures related to Sh2-173 are observed in the velocity ranges from −25 to −31 km s −1 and from −27 to −39 km s −1 , respectively. Taking into account the presence of non-circular 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 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 H II region may trigger star formation, a search for young stellar object (YSO) candidates was made using different infrared point source catalogues. A population of 46 YSO candidates was identified, projected on to the molecular clouds. On the other hand, Sh2-173 is located in a dense edge of a large (∼5 ◦ )H I shell, GSH 117.8+1.5-35. The possibility of Sh2-173 being part of a hierarchical system of three generations is suggested. In this scenario, the large H I shell, which probably originated due to the action of Cas OB5, would have triggered the formation of Sh2-173, which, in turn, is triggering new stars in its surrounding molecular cloud. To test this hypothesis, the ages of both the H II region and the large shell were estimated and compared. We concluded that Sh2-173 is a young H II 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.

A multifrequency study of the active star-forming complex NGC 6357 – I. Interstellar structures linked to the open cluster Pis 24

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 Hα, [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 ′′ . The distribution of the molecular gas is analyzed using 12 CO(1-0) data obtained with the Nanten radiotelescope, Chile (angular resolution = 2. ′ 7). 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)×10 5 M⊙. 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.

Ionized gas, molecules and dust in Sh2-132

Fil: Vasquez, Javier. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico La Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

The radio and infrared counterparts of the ring nebula around HD 211564

We report the detection of the radio and infrared (IR) counterparts of the ring nebula around the WN3(h) star HD 211564 (WR 152), located to the south-west of the H II region Sh2 132. 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 arcmin 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 M ⊙ , respectively. The analysis of the H i gas emission distribution allowed the identification of 5900 M ⊙ of neutral atomic gas with velocities between -52 and -43 km s -1 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 M ⊙ . About 310 M ⊙ are related to a small IR shell-like source linked to the inner ring, which is also detected in the MSX band A. An IRAS young stellar object 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 Wolf-Rayet star and its massive progenitor, and are evolving in the envelope of a slowly expanding shell centred at (l, b) = (102°.30, -0°.50) of about 31 pc in radius. The bubbles energy conversion efficiency is in agreement with recent numerical analysis and with observational results.

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

Fil: Duronea, Nicolas Urbano. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico La Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

Molecules, dust, and protostars in NGC 3503

Aims. 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 the Hii region NGC 3503 with its parental molecular cloud, and also with the star formation in the region, that was possibly triggered by the expansion of the ionization front against the parental cloud . Methods. To analyze the molecular gas we use CO(J=2→1), 13 CO(J=2→1), C 18 O(J=2→1), and HCN(J=3→2) line data obtained with the on-the-fly technique from the APEX telescope. To stu dy the distribution of the dust, we make use of unpublished images at 870 µm from the ATLASGAL survey and IRAC-GLIMPSE archival images . We use public 2MASS and WISE data to search for infrared candidate YSOs in the region. Results. The new APEX observations allowed the substructure of the molecular gas in the velocity range from∼−28 to−23 km s −1 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” sce nario. We have identified several molecular clumps and determined som e of their physical and dynamical properties such as density, excitation temperature, mass, and line width. Clumps adjacent to the ionization front are expected to be affected by the Hii region, unlike those that are distant to it. We have compared the physical properties of the two kind of 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 SFO 62 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 spa tial distribution suggests that stellar formation might ha ve 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.

Molecular gas toward G18.8+1.8

Fil: Vasquez, Javier. Provincia de Buenos Aires. Gobernacion. Comision de Invest.cientificas. Instituto Argentino de Radioastronomia. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - la Plata. Instituto Argentino de Radioastronomia; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

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

Fil: Cappa, Cristina Elisabeth. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico la Plata. Instituto Argentino de Radioastronomia (i); Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronomicas y Geofisicas; Argentina

Molecular gas associated with IRAS 10361-5830

Aims. We analyze the distribution of the molecular gas and 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 of investigating the evolutionary state of the young stellar objects identified there. Methods. Using the APEX telescope, we mapped the molecular emission in the J = 3−2 transition of three CO isotopologues, 12 CO, 13 CO and C 18 O, over a 1. 5 × 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 μm obtained with the APEX telescope. Complementary IR and radio data at different wavelengths were used to complete the study of the interstellar medium. Results. 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 projected onto the cavity. The total molecular mass in the shell and the mean H2volume

NGC 3503 and its molecular environment

Context. Aims. 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 dist ribution 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. Methods. We based our study in 12 CO(1-0) observations of a region of∼ 0. ◦ 6 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. Results. 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)× 10 3 M⊙ 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. Conclusions.