IR dust bubbles: gas, dust and star formation IR dust bubbles: gas, dust and star formation in the S21 – S23 complex in the S21 – S23 complex C.E. Cappa 1,2 , J. Vasquez 1,2 , V. Firpo 1 , G.A. Romero 1 and M. Rubio 3 1 Facultad de Ciencias Astronómicas y Geofísicas, UNLP, Argentina; 2 Instituto Argentino de Radioastronomía, CONICET, Argentina; 3 Departamento de Astronomía, Universidad de Chile, Chile Introduction Churchwell et al. (2006) identified more than 300 bubbles in the GLIMPSE images at 8 μm. These IR dust bubbles have sizes in the range 1´-3´, show a filamentary appearance, and display smaller IR bubbles in their borders. About half of them coincide with classical and UC HII regions and massive stars (Churchwell et al. 2005, Deharveng et al. 2010). Among these bubbles, S 21, S 22, S 23, and S 24 [(l,b) = (341.25,-0.30)] conform a poorly studied complex at plenty of small scale bubbles, infrared dark clouds (IRDCs) and signposts of recent star formation, located at about 4 kpc. Here, we report on a molecular line and IR dust emission study towards S21, S22, and S23. Our work aims at investigating the characteristics of the molecular gas and dust linked to the bubbles, estimating their distances, and looking for the presence of young stellar objects. Database Molecular data. We mapped the molecular emission in the 12 CO(2-1), 13 CO(2-1), and C 18 O(2-1) lines using the Atacama Pathfinder EXperiment (APEX), located in the north of Chile. The data were taken in the OTF mode, with an angular resolution of about 28", a velocity resolution of 0.33 km/s, and an rms noise of 0.3 K. IR images. We analyzed IRAC-Spitzer images (at 3.6, 4.5, 5.8, and 8 µm), the MIPS-Spitzer image at 24 µm, Herschel images at 70, 250, 350, and 500 µm, and the emission at 870 µm obtained with LABOCA-APEX (Schuller et al. 2009). YSOs. Young stellar objects were searched for in the region using IR point source catalogues (IRAS, MSX, Spitzer). Summary Adopting a mean velocity of -46 km/s for the molecular gas associated with the three bubbles, kinematical distances of 3.7 or 12.3 kpc are predicted. Bearing in mind that the detection rate for bubbles at 8 µm peaks at 4.2 kpc, within an horizon of 8 kpc, we adopt the near kinematical distance of 3.7±0.8 kpc for the complex. This study allowed molecular shells linked to S21, S22, and S23 bubbles to be revealed. The total mass associated with each bubble is in the range (5x10 3 )-(10 4 ) Mo and ambient densities are a few times 10 3 cm -3 . Cold dust counterparts were revealed by Herschel and LABOCA images, showing the material available for new generations of stars. In addition to the presence of EGOs, a search for young stellar objets in the complex using available data at several wavelengths in the infrared revealed many active areas of star formation coincident with the densest regions. Sh2- 196 This open bubble is 1.0´ in radius. Mercer et al. (2005) identified an IR stellar cluster which may be responsible for the bubble. The emission at 8 µm delineates the borders of the bubble, where PAHs mark the position of a photodissociation region (PDR). The emission at 24 µm reveals warm dust inside the bubble, compatible with the presence of massive stars. The emission at 250 µm shows the existence of cold dust outside the PDR. The emission distribution of the 13 CO line in the range [-48.2,-42.5] km/s reveals a shell structure encircling the bubble. The strongest CO emission coincides with the emission of the cold dust. YSOs: * IRAS 16492-4421: UCHII (Chan+ 1996) V_CS = -45.5 km/s (Bronfman+ 1996) * MSX source: 1 MYSO * Spitzer sources: 9 YSOs Region 5 Region 3 Region 4 Regio n 2 S 24 S 22 S 23 S 21 Red: 250µm Green: 8 µm Blue: 4.5 µm R: 24 µm G: 8 µm B: 4.5 µm R: 250 µm G: 8 µm B: 4.5 µm Contours: 13CO(2-1) R: 250 µm G: 8 µm B: 4.5 µm S 23 S 21 This complete bubble is 0.74´ in radius. HD 329056 (B3) appears projected near its center. There is warm dust inside S21,as shown by the emission at 24 µm, and cold dust outside, as indicated by the emission at 250 µm. CO emission linked to the bubble was identified in the velocity range [-47.0,-42.5] km/s, and conforms an almost complete shell structure. The emission at v<-44.6 km/s surrounds the northwestern section of the bubble, while emission at v>- 44.5 km/s encircles the southern and eastern sections. R: 24 µm G: 8 µm B: 4.5 µm R: 250 µm G: 8 µm B: 4.5 µm R: 250 µm G: 8 µm B: 4.5 µm Contours: White: 13CO(2-1) at -43.4 km/s Light blue: 13CO(2-1) at -45.2 km/s S 22 This complete bubble (1.94' in radius) includes S 22 in its northern border. As shown by the 24 µm emission, warm dust is detected in the inner part. Molecular gas linked to the bubble is present in the interval [-49.7,-44.3] km/s. The white contours shows the emission at -46.8 km/s, where the eastern and southern sections of a molecular structure are better defined. S 22 coincides with the northern section of the shell. The spatial coincidence between the CO gas and the 8 µm IRAC emission is excellent in the eastern and southern section of S 23. R: 24 µm G: 8 µm B: 4.5 µm R: 250 µm G: 8 µm B: 4.5 µm R: 250 µm G: 8 µm B: 4.5 µm Cont: 13CO(2-1) IRDC IRDC An infrared dark cloud is revealed by the Spitzer-IRAC emission at 8 µm. Three EGOs (Cyganowski et al. 2006) projected onto it are evident at 4.5 µm. Dense molecular gas and cold dust coincide with the IRDC. Color scale: 870 µm Contours: C 18 O(2-1) Crosses: EGOs Red: 8 µm Green:4.5 µm White contours: 870 µm Crosses: EGOs CO spectra towards the EGOs: The spectra towards the EGOs resembles those obtained by Chen et al. (2010) towards EGOs, suggesting collapsing cores. Chen et al.2010 13CO(2-1) 12CO(2-1) ccappa@fcaglp.unlp.edu.ar