M. E. Ortega

Interactions of the Infrared bubble N4 with ITS surroundings

The physical mechanisms that induce the transformation of a certain mass of gas in new stars are far from being well understood. Infrared bubbles associated with H II regions have been considered to be good samples for investigating triggered star formation. In this paper we report on the investigation of the dust properties of the infrared bubble N4 around the H II. region G11.898+0.747, analyzing its interaction with its surroundings and star formation histories therein, with the aim of determining the possibility of star formation triggered by the expansion of the bubble. Using Herschel PACS and SPIRE images with a wide wavelength coverage, we reveal the dust properties over the entire bubble. Meanwhile, we are able to identify six dust clumps surrounding the bubble, with a mean size of 0.50 pc, temperature of about 22 K, mean column density of 1.7 x 10(22) cm(-2), mean volume density of about 4.4 x 10(4) cm(-3), and a mean mass of 320M(circle dot). In addition, from PAH emission seen at 8 mu m, free-free emission detected at 20 cm, and a probability density function in special regions, we could identify clear signatures of the influence of the H II region on the surroundings. There are hints of star formation, though further investigation is required to demonstrate that N4 is the triggering source.

A molecular outflow revealing star formation activity in the vicinity of the HII region G034.8-0.7 and the SNR W44

Aims. This work aims at investigating the molecular gas component in the vicinity of two young stellar object (YSO) candidates identified at the border of the HII region G034.8-0.7 that is evolving within a molecular cloud shocked by the SNR W44. The purpose is to explore signatures of star forming activity in this complex region. Methods. We performed a near and mid infrared study towards the border of the HII region G034.8-0.7 and observed a 90 �� ×90 �� region near 18 h 56 m 48 s , +01 ◦ 18 � 45 �� (J2000) using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12 CO J = 3−2, 13 CO J = 3−2, HCO + J = 4− 3a nd CSJ = 7−6 lines with an angular resolution of 22 �� . Results. Based on the infrared study we propose that the source 2MASS 18564827+0118471 (IR1 in this work) is a YSO candidate. We discovered a bipolar 12 CO outflow in the direction of the line of sight and a HCO + clump towards IR1, confirming that it is a YSO. From the detection of the CS J = 7−6 line we infer the presence of high density (>10 7 cm −3 )a nd warm (>60 K) gas towards IR1, probably belonging to the protostellar envelope where the YSO is forming. We investigated the possible connection of IR1 with the SNR and the HII region. By comparing the dynamical time of the outflows and the age of the SNR W44, we conclude that the possibility that the SNR triggered the formation of IR1 is unlikely. On the other hand, we suggest that the expansion of the HII region G034.8-0.7 is responsible for the formation of IR1 through the “collect and collapse” process.

A view of Large Magellanic Cloud H ii regions N159, N132, and N166 through the 345-GHz window

Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

Outflow activity in the UCHII region G045.47+0.05

Aims. This work aims at investigating the molecular gas in the surroundings of the ultra-compact HII region G045.47+0.05 looking for evidence of molecular outflows. Methods. We carried out observations towards a region of 2 � × 2 � centered at RA = 19 h 14 m 25.6 s ,D ec =+ 11 ◦ 09 � 27.6 �� (J2000) using the Atacama Submillimeter Telescope Experiment (ASTE; Chile) in the 12 CO J = 3–2, 13 CO J = 3–2, HCO + J = 4–3, and CS J = 7–6 lines with an angular resolution of 22 �� . We complement these observations with public infrared data. Results. We characterize the physical parameters of the molecular clump where G045.47+0.0 is embedded. The detection of the CS J = 7–6 line emission in the region reveals that the ultra-compact HII region G045.47+0.0 has not completely disrupted the dense gas where it was born. The HCO + abundance observed towards G045.47+0.0 suggests there is molecular outflow activity in the region. From the analysis of the 12 CO J = 3–2 transition we report bipolar molecular outflows with a total mass of about 300 M� . We derive a dynamical time (flow’s age) of about 10 5 yr for the outflow gas, in agreement with the presence of an ultra-compact HII region. We identify the source 2MASS 19142564+1109283 as the massive protostar candidate to drive the molecular outflows. Based on the analysis of its spectral energy distribution, we infer that it is an early B-type star of about 15 M� . The results of this work support the scenario where the formation of massive stars, at least up to early B-type stars, is similar to that of low-mass stars.

The interstellar medium and the massive stellar content towards the SNR G18.1−0.1 and neighbouring H ii regions

Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio(i); Argentina;

Unveiling the circumstellar environment toward a massive young stellar object

Aims. As a continuation of a previous work, in which we found strong evidence of massive molecular outflows toward a massive starforming site, we present a new study of this region based on very high angular resolution observations with the aim of discovering the outflow-driven mechanism. Methods. Using near-IR data acquired with Gemini-NIRI at the broad H -a ndKs-bands, we studied a region of 22 �� × 22 �� around the UCHii region G045.47+0.05, a massive-star forming site at a distance of about 8 kpc. To image the source with the highest spatial resolution possible we employed the adaptative optics system ALTAIR, achieving an angular resolution of about 0. �� 15. Results. We discovered a cone shaped nebula that has an opening angle of about 90 ◦ and extends eastward of the IR source 2MASS J19142564+1109283, which is very likely a massive young stellar object (MYSO). This morphology suggests a cavity that was cleared in the circumstellar material, and its emission may arise from scattered continuum light, warm dust, and probably also from emission lines from shock-excited gas. The nebula, which presents arc-like features, is connected with the IR source through a jet-like structure, which is aligned with the blueshifted CO outflow found in a previous study. The near-IR structure lies ∼3 �� north of the radio continuum emission, revealing that it is not spatially coincident with the UCHii region. The observed morphology and structure of the near-IR nebula strongly suggest the presence of a precessing jet. We resolved the circumstellar environment (in scale of a thousand AU) of a distant MYSO, indeed one of the farthest currently known.

H ii REGION G46.5-0.2: THE INTERPLAY BETWEEN IONIZING RADIATION, MOLECULAR GAS, AND STAR FORMATION

Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

A multiwavelength study of the star forming region IRAS 18544+0112

Aims. This work aims at investigating the molecular and infrared components in the massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is to determine the nature and the origin of this infrared source. Methods. To analyze the molecular gas towards IRAS 18544+0112, we have carried out observations in a 90 �� × 90 �� region around l = 34. ◦ 69, b = −0. ◦ 65, using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12 CO J = 3–2, 13 CO J = 3–2, HCO + J = 4–3 and CS J = 7–6 lines with an angular resolution of 22 �� . The infrared emission in the area has been analyzed using 2MASS and Spitzer public data. Results. From the molecular analysis, we find self-absorbed 12 CO J = 3–2 profiles, which are typical in star forming regions, but we do not find any evidence of outflow activity. Moreover, we do not detect either HCO + J = 4–3 or CS J = 7–6 in the region, which are species normally enhanced in molecular outflows and high density envelopes. The 12 CO J = 3–2 emission profile suggests the presence of expanding gas in the region. The Spitzer images reveal that the infrared source has a conspicuous extended emission bright at 8 μm with an evident shell-like morphology of ∼1. 5i n size (∼1.4 pc at the proposed distance of 3 kpc) that encircles the 24 μm emission. The non-detection of ionized gas related to IRAS 18544+0112 together with the fact that it is still embedded in a molecular clump suggest that IRAS 18544+0112 has not reached the UCHII region stage yet. Based on near infrared photometry we search for YSO candidates in the region and propose that 2MASS 18565878+0116233 is the infrared point source associated with IRAS 18544+0112. Finally, we suggest that the expansion of a larger nearby HII region, G034.8−0.7, might be related to the formation of IRAS 18544+0112.

Exploring the 13CO/C18O abundance ratio towards Galactic young stellar objects and HII regions

Determining molecular abundance ratios is important not only for the study of the Galactic chemistry but also because they are useful to estimate physical parameters in a large variety of interstellar medium environments. The CO is one of the most important molecules to trace the molecular gas in the interstellar medium, and the 13CO/C18O abundance ratio is usually used to estimate molecular masses and densities of regions with moderate to high densities. Nowadays this kind of isotopes ratios are in general indirectly derived from elemental abundances ratios. We present the first 13CO/C18O abundance ratio study performed from CO isotopes observations towards a large sample of Galactic sources of different nature at different locations. To study the 13CO/C18O abundance ratio it was used 12CO J=3-2 data obtained form the CO High-Resolution Survey, 13CO and C18O J=3-2 data from the 13CO/C18O (J=3-2) Heterodyne Inner Milky Way Plane Survey, and some complementary data extracted from the James Clerk Maxwell Telescope database. It was analyzed a sample of 198 sources composed by young stellar objects (YSOs), HII and diffuse HII regions as catalogued in the Red MSX Source Survey in 27.5 < l < 46.5 and |b| < 0.5. Most of the analyzed sources are located in the galactocentric distance range 4.0-6.5 kpc. We found that YSOs have, in average, smaller 13CO/C18O abundance ratios than HII and diffuse HII regions. Taking into account that the gas associated with YSOs should be less affected by the radiation than in the case of the others sources, selective far-UV photodissociation of C18O is confirmed. The 13CO/C18O abundance ratios obtained in this work are systematically lower than the predicted from the known elemental abundance relations. These results would be useful in future studies of molecular gas related to YSOs and HII regions based on the observation of these isotopes.

The southern molecular environment of SNR G18.8+0.3

Aims. In a previous paper we have investigated the molecular environment towards the eastern border of the SNR G18.8+0.3. Continuing with the study of the surroundings of this SNR, in this work we focus on its southern border, which in the radio continuum emission shows a very peculiar morphology with a corrugated corner and a very flattened southern flank. Methods. We observed two regions towards the south of SNR G18.8+0.3 using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12 CO J=3‐2. One of these regions was also surveyed in 13 CO and C 18 O J=3‐2. The angular and spectral resolution of these observations were 22 ′′ , and 0.11 km s −1 . We compared the CO emission to 20 cm radio continuum maps obtain as part of the Multi-Array Galactic Plane Imaging Survey (MAGPIS) and 870µm dust emission extracted from the APEX Telescope Large Area Survey of the Galaxy. Results. We discovered a molecular feature with a good morphological correspondence with the SNR’s southernmost corner. In particular, there are indentations in the radio continuum map that are complemented by protrusions in the molecular CO image, strongly suggesting that the SNR shock is interacting with a molecular cloud. Towards this region we found that the 12 CO peak is not correlated with the observed 13 CO peaks, which are likely related to a nearby Hii region. Regarding the most flattened border of SNR G18.8+0.3, where an interaction of the SNR with dense material was previously suggested, our 12 CO J=3‐2 map show no obvious