Galactic Legacy Infrared Mid-Plane Survey Extraordinaire Research Articles

IDENTIFICATION OF YOUNG STAR OBJECTS NEAR DUST BUBBLE N10

Over the past decade, the most important observations of the interstellar medium have been made in the infrared and radio regions of electromagnetic radiation. Of particular interest were GLIMPSE (Galactic Legacy Infrared Midplane Survey Extraordinaire), MIPSGAL and WISE (Wide-field Infrared Survey Explorer) surveys of several areas of star formation. Distinctive features of the infrared view of the Galactic disk at wavelengths from 3.4 μm to 22 μm include regions of ionized hydrogen HII, infrared bubbles, young stellar objects, massive star formation, infrared dark clouds, diffuse dust, include hydrocarbons and radiation from millions of stars. Based on current literature, infrared signatures in hot regions around young massive stars have been identified as dust bubbles, so in this paper, the regions around bubble N10, one of the northern infrared bubbles included in Churchwell's catalog, were investigated. Using archival data from the WISE and 2MASS catalogs, we searched for candidates for young stellar objects around the N10 dust bubble and found 117 emission objects. Koenig et al. (2014) plotted diagrams of their color indices and energy distribution in the spectrum for each studied object under different classification conditions. According to the results of studies around the infrared dust bubble N10, objects at an early stage of evolution were discovered: 13 objects are young class I stars and 13 objects are young class II stars, 3 objects are classified as transitional disks.

Gas Dynamics in the Star-forming Region G18.148–0.283: Is It a Manifestation of Two Colliding Molecular Clouds?

Abstract We report the results obtained from a multiwavelength study of the H ii region G18.148−0.283 using the upgraded Giant Metrewave Radio Telescope at 1350 MHz, along with other archival data. In addition to the radio continuum emission, we have detected the H169α and H170α radio recombination lines toward G18.148−0.283 using a correlator bandwidth of 100 MHz. The moment-1 map of the ionized gas reveals a velocity gradient of approximately 10 km s−1 across the radio continuum peaks. The 12CO (J = 3−2) molecular line data from the CO High-Resolution Survey (COHRS) also show the presence of two velocity components that are very close to the velocities detected in the ionized gas. The spectrum and position–velocity diagram from CO emission reveal molecular gas at an intermediate-velocity range bridging the velocity components. We see mid-infrared absorption and far-infrared emission establishing the presence of a filamentary infrared dark cloud, the extent of which includes the targeted H ii region. The magnetic field inferred from dust polarization is perpendicular to the filament within the H ii region. We have also identified two O9 stars and 30 young stellar objects toward the target using data from the Two Micron All Sky Survey (2MASS), UKIRT Infrared Deep Sky Survey (UKIDSS), and Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE). Cumulatively, this suggests that the region is the site of a cloud–cloud collision that has triggered massive star formation and subsequent formation of an H ii region.

Kinematics and star formation toward W33: a central hub as a hub–filament system

Aims. We investigate the gas kinematics and physical properties toward the W33 complex and its surrounding filaments. We study clump formation and star formation in a hub–filament system. Methods. We performed a large-scale mapping observation toward the W33 complex and its surroundings, covering an area of 1.3° × 1.0°, in 12CO (1–0), 13CO (1–0), and C18O (1–0) lines from the Purple Mountain Observatory (PMO). Infrared archival data were obtained from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), the Multi-band Imaging Photometer Survey of the Galaxy (MIPSGAL), and the Herschel Infrared Galactic Plane Survey (Hi-GAL). We distinguished the dense clumps from the ATLASGAL survey. We used the GLIMPSE I catalogue to extract young stellar objects. Results. We found a new hub–filament system ranging from 30 to 38.5 km s−1 located at the W33 complex. Three supercritical filaments are directly converging into the central hub W33. Velocity gradients are detected along the filaments and the accretion rates are in order of 10−3 M⊙ yr−1. The central hub W33 has a total mass of ~1.8 × 105 M⊙, accounting for ~60% of the mass of the hub–filament system. This indicates that the central hub is the mass reservoir of the hub-filament system. Furthermore, 49 ATLASGAL clumps are associated with the hub–filament system. We find 57% of the clumps to be situated in the central hub W33 and clustered at the intersections between the filaments and the W33 complex. Moreover, the distribution of Class I young stellar objects forms a structure resembling the hub–filament system and peaks at where the clumps group; it seems to suggest that the mechanisms of clump formation and star formation in this region are correlated. Conclusions. Gas flows along the filaments are likely to feed the materials into the intersections and lead to the clustering and formation of the clumps in the hub–filament system W33. The star formation in the intersections between the filaments and the W33 complex might be triggered by the motion of gas converging into the intersections.

An X-Ray View of Two Infrared Dark Clouds G034.43+00.24 and G035.39−00.33

Abstract We present a high spatial resolution Chandra X-ray study of two infrared dark clouds (IRDCs), G034.43+00.24 and G035.39−00.33, which are expected to be in the early phases of star cluster formation. We detect 112 and 209 valid X-ray point sources toward G034.43+00.24 and G035.39−00.33, respectively. We cross-match the X-ray point sources with the Two Micron All Sky Survey (2MASS), Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE), and Wide-field Infrared Survey Explorer (WISE) catalogs and find 53% and 59% of the X-ray sources in G034.43+00.24 and in G035.39−00.33 have corresponding infrared counterparts, respectively. These sources are probable members of young massive clusters in formation, and using stellar isochrones we estimate that a population of 1–2 Myr old, intermediate- to high-mass young stellar objects (YSOs) exist in both IRDCs. Two and 10 Class II counterparts to X-ray sources were identified in G034.43+00.24 and in G035.39−00.33, respectively, which are located in or near dark filaments. The X-ray luminosity function (XLF) of G035.39−00.33 implies that the total mass consists of up to ∼1700M ⊙ of stars, using the XLF of the well-studied Orion Nebula Cluster as a calibrator. This corresponds to a star formation efficiency of at most 5%, indicating the system is still very much gas dominated and in an early stage of the star formation process. The population of G034.43+00.24 is less well determined due to the lower sensitivity of its observations.

Cause and effects of the massive star formation in Messier 8 East

Context. Messier 8 (M8), one of the brightest H II regions in our Galaxy, is powered by massive O-type stars and is associated with recent and ongoing massive star formation. Two prominent massive star-forming regions associated with M8 are M8-Main, the particularly bright part of the large-scale H II region (mainly) ionized by the stellar system Herschel 36 (Her 36) and M8 East (M8 E), which is mainly powered by a deeply embedded young stellar object (YSO), the bright infrared (IR) source M8E-IR. Aims. We study the interaction of the massive star-forming region M8 E with its surroundings using observations of assorted diffuse and dense gas tracers that allow quantifying the kinetic temperatures and volume densities in this region. With a multiwavelength view of M8 E, we investigate the cause of star formation. Moreover, we compare the star-forming environments of M8-Main and M8 E, based on their physical conditions and the abundances of the various observed species toward them. Methods. We used the Institut de Radioastronomía Millimétrica 30 m telescope to perform an imaging spectroscopy survey of the ~1 pc scale molecular environment of M8E-IR and also performed deep integrations toward the source itself. We imaged and analyzed data for the J = 1 → 0 rotational transitions of 12CO, 13CO, N2H+, HCN, H13CN, HCO+, H13CO+, HNC, and HN13C observed for the first time toward M8 E. To visualize the distribution of the dense and diffuse gas in M8 E, we compared our velocity-integrated intensity maps of 12CO, 13CO, and N2H+ with ancillary data taken at IR and submillimeter wavelengths. We used techniques that assume local thermodynamic equilibrium (LTE) and non-LTE to determine column densities of the observed species and constrain the physical conditions of the gas that causes their emission. Examining the class 0/ I and class II YSO populations in M8 E, allows us to explore the observed ionization front (IF) as seen in the high resolution Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) 8 μm emission image. The difference between the ages of the YSOs and their distribution in M8 E were used to estimate the speed of the IF. Results. We find that 12CO probes the warm diffuse gas also traced by the GLIMPSE 8 μm emission, while N2H+ traces the cool and dense gas following the emission distribution of the APEX Telescope Large Area Survey of the Galaxy 870 μm dust continuum. We find that the star-formation in M8 E appears to be triggered by the earlier formed stellar cluster NGC 6530, which powers an H II region giving rise to an IF that is moving at a speed ≥0.26 km s−1 across M8 E. Based on our qualitative and quantitative analysis, the J = 1 → 0 transition lines of N2H+ and HN13C appear to be more direct tracers of dense molecular gas than the J = 1 → 0 transition lines of HCN and HCO+. We derive temperatures of 80 and 30 K for the warm and cool gas components, respectively, and constrain the H2 volume densities to be in the range of 104–106 cm−3. Comparison of the observed abundances of various species reflects the fact that M8 E is at an earlier stage of massive star formation than M8-Main.

Probing GLIMPSE Extended Green Objects (EGOs) with hydroxyl masers

ABSTRACT We present a study of 18 cm OH maser emission toward 20 high-mass young stellar object outflow candidates (Extended Green Objects, EGOs) identified from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). All four OH ground state lines at 1612, 1665, 1667, and 1720 MHz, together with 20-cm continuum emission, were observed with the Karl G. Jansky Very Large Array C-configuration. Follow-up polarimetric single-dish observations with the Nançay radio telescope were performed for the same OH transitions, except 1612 MHz. OH maser emission is found to be an uncommon feature of the sample, with a 50 per cent detection rate for the entire sample and a ∼44 per cent detection rate for the ‘likely’ EGOs. No 20-cm continuum emission is detected toward any of the sources. In most cases, the detected OH maser emission arises in vicinity to compact central sources; OH masers coexist with the 6.7 GHz methanol masers, but are found in more diffuse and extended halo-shaped regions of several thousand astronomical units in size. Comparing EGO samples with OH maser detection and non-detection, EGOs showing OH maser emission tend to have lower dust clump masses, but higher 24 and 4.5 μm flux densities. Thus, OH maser emission might be an indicator of more evolved EGOs, since strong compact mid-infrared emission in the absence of compact radio continuum emission is thought to be associated with the later stage of massive star formation.

Observational study of hydrocarbons in the bright photodissociation region of Messier 8

Aims. Hydrocarbons are ubiquitous in the interstellar medium, but their formation is still not well understood, depending on the physical environment in which they are found. Messier 8 (M8) is host to one of the brightest H II regions and photodissociation regions (PDRs) in our galaxy. With the observed C2H and c-C3H2 data toward M8, we aim at obtaining their densities and abundances and to shed some light on their formation mechanism. Methods. Using the Atacama Pathfinder Experiment (APEX) 12 m, and the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescopes, we performed a line survey toward Herschel 36 (Her 36), which is the main ionizing stellar system in M8, and an imaging survey within 1.3 × 1.3 pc around Her 36 of various transitions of C2H and c-C3H2. We used both local thermodynamic equilibrium (LTE) and non-LTE methods to determine the physical conditions of the emitting gas along with the column densities and abundances of the observed species, which we compared with (updated) gas-phase photochemical PDR models. In order to examine the role of polycyclic aromatic hydrocarbons (PAHs) in the formation of small hydrocarbons and to investigate their association with the H II region, the PDR and the molecular cloud, we compared archival Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) 8 μm and the Spectral and Photometric Imaging Receiver (SPIRE) 250 μm continuum images with the C2H emission maps. Results. We observed a total of three rotational transitions of C2H with their hyperfine structure components and four rotational transitions of c-C3H2 with ortho and para symmetries toward the H II region and the PDR of M8. Fragmentation of PAHs seems less likely to contribute to the formation of small hydrocarbons as the 8 μm emission does not follow the distribution of C2H emission, which is more associated with the molecular cloud toward the north west of Her 36. From the quantitative analysis, we obtained abundances of ~10−8 and 10−9 for C2H and c-C3H2 respectively, and volume densities of the hydrocarbon emitting gas in the range n(H2) ~5 × 104–5 × 106 cm−3. Conclusions. The observed column densities of C2H and c-C3H2 are reproduced reasonably well by our PDR models. This supports the idea that in high-UV flux PDRs, gas-phase chemistry is sufficient to explain hydrocarbon abundances.

SOFIA FORCAST Photometry of 12 Extended Green Objects in the Milky Way

Abstract Massive young stellar objects (MYSOs) are known to undergo an evolutionary phase in which high mass accretion rates drive strong outflows. A class of objects believed to trace this phase accurately is the Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE) Extended Green Object (EGO) sample, so named for the presence of extended 4.5 μm emission on size scales of ∼0.1 pc in Spitzer images. We have been conducting a multiwavelength examination of a sample of 12 EGOs with distances of 1–5 kpc. In this paper, we present mid-infrared images and photometry of these EGOs obtained with the Stratospheric Observatory for Infrared Astronomy and subsequently construct spectral energy distributions (SEDs) for these sources from the near-infrared to submillimeter regimes using additional archival data. We compare the results from graybody models and several publicly available software packages that produce model SEDs in the context of a single massive protostar. The models yield typical R ⋆ ∼ 10 R ⊙, T ⋆ ∼ 103–104 K, and L ⋆ ∼ 1–40 × 103 L ⊙; the median L/M for our sample is 24.7 L ⊙/M ⊙. Model results rarely converge for R ⋆ and T ⋆, but they do for L ⋆, which we take to be an indication of the multiplicity and inherently clustered nature of these sources even though, typically, only a single source dominates in the mid-infrared. The median L/M value for the sample suggests that these objects may be in a transitional stage between the commonly described “IR-quiet” and “IR-bright” stages of MYSO evolution. The median T dust for the sample is less conclusive but suggests that these objects are either in this transitional stage or occupy the cooler (and presumably younger) part of the IR-bright stage.

A multiwavelength study of filamentary cloud G341.244-00.265

We present a multiwavelength study toward the filamentary molecular cloud G341.244-00.265, to investigate the physical and chemical properties, as well as star formation activities taking place therein. Our radio continuum and molecular line data were obtained from the Sydney University Molonglo Sky Survey (SUMSS), Atacama Pathfinder Experiment Telescope Large Area Survey of the Galaxy (ATLASGAL), Structure, excitation, and dynamics of the inner Galactic interstellar medium (SEDIGISM) and Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90). The infrared archival data come from Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE), Wide-field Infrared Survey Explorer (WISE), and Herschel InfraRed Galactic Plane Survey (Hi-GAL). G341.244-00.265 displays an elongated filamentary structure both in far-infrared and molecular line emissions; the “head” and “tail” of this molecular cloud are associated with known infrared bubbles S21, S22, and S24. We made H2 column density and dust temperature maps of this region by the spectral energy distribution (SED) method. G341.244-00.265 has a linear mass density of about 1654 M⊙ pc−1 and has a projected length of 11.1 pc. The cloud is prone to collapse based on the virial analysis. Even though the interactions between this filamentary cloud and its surrounding bubbles are evident, we found these bubbles are too young to trigger the next generation of star formation in G341.244-00.265. From the ATLASGAL catalog, we found eight dense massive clumps associated with this filamentary cloud. All of these clumps have sufficient mass to form massive stars. Using data from the GLIMPSE and WISE survey, we search the young stellar objects (YSOs) in G341.244-00.265. We found an age gradient of star formation in this filamentary cloud: most of the YSOs distributed in the center are Class I sources, while most Class II candidates are located in the head and tail of G341.244-00.265, indicating star formation at the two ends of this filament is prior to the center. The abundance ratio of N(N2H+)/N(C18O) is higher in the center than that in the two ends, also indicating that the gas in the center is less evolved. Taking into account the distributions of YSOs and the N(N2H+)/N(C18O) ratio map, our study is in agreement with the prediction of the so-called “end-dominated collapse” star formation scenario.

Gas kinematics and star formation in the filamentary molecular cloud G47.06+0.26

Aims. We performed a multi-wavelength study toward the filamentary cloud G47.06+0.26 to investigate the gas kinematics and star formation. Methods. We present the 12CO (J = 1−0), 13CO (J = 1−0) and C18O (J = 1−0) observations of G47.06+0.26 obtained with the Purple Mountain Observation (PMO) 13.7 m radio telescope to investigate the detailed kinematics of the filament. Radio continuum and infrared archival data were obtained from the NRAO VLA Sky Survey (NVSS), the APEX Telescope Large Area Survey of the Galaxy (ATLASGAL), the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) survey, and the Multi-band Imaging Photometer Survey of the Galaxy (MIPSGAL). To trace massive clumps and extract young stellar objects in G47.06+0.26, we used the BGPS catalog v2.0 and the GLIMPSE I catalog, respectively. Results. The 12CO (J = 1−0) and 13CO (J = 1−0) emission of G47.06+0.26 appear to show a filamentary structure. The filament extends about 45′ (58.1 pc) along the east-west direction. The mean width is about 6.8 pc, as traced by the 13CO (J = 1−0) emission. G47.06+0.26 has a linear mass density of ~361.5 M⊙pc-1. The external pressure (due to neighboring bubbles and H II regions) may help preventing the filament from dispersing under the effects of turbulence. From the velocity-field map, we discern a velocity gradient perpendicular to G47.06+0.26. From the Bolocam Galactic Plane Survey (BGPS) catalog, we found nine BGPS sources in G47.06+0.26, that appear to these sources have sufficient mass to form massive stars. We obtained that the clump formation efficiency (CFE) is ~18% in the filament. Four infrared bubbles were found to be located in, and adjacent to, G47.06+0.26. Particularly, infrared bubble N98 shows a cometary structure. CO molecular gas adjacent to N98 also shows a very intense emission. H II regions associated with infrared bubbles can inject the energy to surrounding gas. We calculated the kinetic energy, ionization energy, and thermal energy of two H II regions in G47.06+0.26. From the GLIMPSE I catalog, we selected some Class I sources with an age of ~105 yr, which are clustered along the filament. The feedback from the H II regions may cause the formation of a new generation of stars in filament G47.06+0.26.

MALT-45: a 7 mm survey of the southern Galaxy – I. Techniques and spectral line data

We present the first results from the MALT-45 (Millimetre Astronomer's Legacy Team - 45 GHz) Galactic Plane survey. We have observed 5 square-degrees ($l = 330 - 335$, $b = \pm0.5$) for spectral lines in the 7 mm band (42-44 and 48-49 GHz), including $\text{CS}$ $(1-0)$, class I $\text{CH}_3\text{OH}$ masers in the $7(0,7)-6(1,6)$ $\text{A}^{+}$ transition and $\text{SiO}$ $(1-0)$ $v=0,1,2,3$. MALT-45 is the first unbiased, large-scale, sensitive spectral line survey in this frequency range. In this paper, we present data from the survey as well as a few intriguing results; rigorous analyses of these science cases are reserved for future publications. Across the survey region, we detected 77 class I $\text{CH}_3\text{OH}$ masers, of which 58 are new detections, along with many sites of thermal and maser $\text{SiO}$ emission and thermal $\text{CS}$. We found that 35 class I $\text{CH}_3\text{OH}$ masers were associated with the published locations of class II $\text{CH}_3\text{OH}$, $\text{H}_2\text{O}$ and $\text{OH}$ masers but 42 have no known masers within 60 arcsec. We compared the MALT-45 $\text{CS}$ with $\text{NH}_3$ (1,1) to reveal regions of $\text{CS}$ depletion and high opacity, as well as evolved star-forming regions with a high ratio of $\text{CS}$ to $\text{NH}_3$. All $\text{SiO}$ masers are new detections, and appear to be associated with evolved stars from the $\it{Spitzer}$ Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Generally, within $\text{SiO}$ regions of multiple vibrational modes, the intensity decreases as $v=1,2,3$, but there are a few exceptions where $v=2$ is stronger than $v=1$.

Study of morphology and stellar content of the Galactic H ii region IRAS 16148−5011

An investigation of the IRAS 16148−5011 region – a cluster at a distance of 3.6 kpc – is presented here, carried out using multiwavelength data in near-infrared (NIR) from the 1.4 m Infrared Survey Facility telescope, mid-infrared (MIR) from the archival Spitzer GLIMPSE (Galactic Legacy Infrared Midplane Survey Extraordinaire) survey, far-infrared (FIR) from the Herschel archive, and low-frequency radio continuum observations at 1280 and 843 MHz from the Giant Metrewave Radio Telescope and Molonglo Survey archive, respectively. A combination of NIR and MIR data is used to identify 7 Class I and 133 Class II sources in the region. Spectral energy distribution (SED) analysis of selected sources reveals a 9.6 M⊙ high-mass source embedded in nebulosity. However, Lyman continuum luminosity calculation using radio emission – which shows a compact H ii region – indicates the spectral type of the ionizing source to be earlier than B0-O9.5. Free–free emission SED modelling yields the electron density as 138 cm−3, and thus the mass of the ionized hydrogen as ∼16.4 M⊙. Thermal dust emission modelling, using the FIR data from Herschel and performing modified blackbody fits, helped us construct the temperature and column density maps of the region, which show peak values of 30 K and 3.3 × 1022 cm−2, respectively. The column density maps reveal an AV > 20 mag extinction associated with the nebular emission, and weak filamentary structures connecting dense clumps. The clump associated with this IRAS object is found to have dimensions of ∼ 1.1 pc × 0.8 pc, and a mass of 1023 M⊙.

Sample of optically unidentified X-ray binaries in the Galactic bulge: constraints on the physical nature from infrared photometric surveys

We report on archival near-infrared and mid-infrared observations of seven persistent X-ray sources situated in the Galactic bulge, using data from the UK Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS), the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and the Wide-field Infrared Survey Explorer (WISE) all-sky survey. We were able to successfully identify or provide upper flux limits for the systems SAX J1747.0−2853, IGR J17464−2811, AX J1754.2−2754, IGR J17597−2201, IGR J18134−1636, IGR J18256−1035 and Ser X−1 and constrain the nature of these systems. In the case of IGR J17597−2201, we present arguments that the source accretes matter from the stellar wind rather than via Roche-lobe overflow of the secondary. We suggest that, at its X-ray luminosity of 1034 − 35 erg s−1, we are probing the poorly known class of wind-fed low-mass X-ray binaries (LMXBs).

Star formation associated with a large-scale infrared bubble

Using the data from the Galactic Ring Survey (GRS) and Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), we performed a study for a large-scale infrared bubble with a size of about 16 pc at a distance of 2.0 kpc. We present the 12CO J=1-0, 13CO J=1-0 and C18O J=1-0 observations of HII region G53.54-0.01 (Sh2-82) obtained at the the Purple Mountain Observation (PMO) 13.7 m radio telescope to investigate the detailed distribution of associated molecular material. The large-scale infrared bubble shows a half-shell morphology at 8 um. H II regions G53.54-0.01, G53.64+0.24, and G54.09-0.06 are situated on the bubble. Comparing the radio recombination line velocities and associated 13CO J=1-0 components of the three H II regions, we found that the 8 um emission associated with H II region G53.54-0.01 should belong to the foreground emission, and only overlap with the large-scale infrared bubble in the line of sight. Three extended green objects (EGOs, the candidate massive young stellar objects), as well as three H II regions and two small-scale bubbles are found located in the G54.09-0.06 complex, indicating an active massive star-forming region. C18O J=1-0 emission presents four cloud clumps on the northeastern border of H II region G53.54-0.01. Via comparing the spectral profiles of 12CO J=1-0, 13CO J=1-0, and C18O J=1-0 peak at each clump, we found the collected gas in the three clumps, except for the clump coincided with a massive YSO (IRAS 19282+1814). Using the evolutive model of H II region, we derived that the age of H II region G53.54-0.01 is 1.5*10^6 yr. The significant enhancement of several Class I and Class II YSOs around G53.54-0.01 indicates the presence of some recently formed stars, which may be triggered by this H II region through the collect and collapse (CC) process.

The catalogues and mid-infrared environment of interstellar OH masers

Data for a number of OH maser lines have been collected from surveys. The positions are compared with recent mid-infrared (MIR) surveys such as the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and Wide-field Infrared Survey Explorer (WISE) surveys, restricting the comparison to point sources. The colours and intensities of the IR sources are compared. There are many 18-cm OH masers, but far fewer in lines arising from higher energy levels. We also make a comparison with 5-cm Class II methanol masers. We have divided the results into three subsamples: those associated with OH masers only, those associated with OH masers and Class II methanol masers and those associated with Class II methanol masers only. There are no obvious differences in the colour-colour or colour-magnitude results for the GLIMPSE point sources. However, according to the results from the WISE 22-mu m survey, the sources associated with OH masers are brighter than those associated with methanol masers. We interpret the presence of OH and methanol masers as marking the locations of regions where stars are forming. The OH masers are located on the borders of sharp features found in the IR. These are referred to as bubbles. If the OH masers mark the positions of protostars, the result provides indirect evidence for triggered star formation caused by the expansion of the bubbles.

THE X-RAY PROPERTIES OF FIVE GALACTIC SUPERNOVA REMNANTS DETECTED BY THESPITZERGLIMPSE SURVEY

(Abbreviated) We present a study of the X-ray properties of five Galactic supernova remnants (SNRs) -- Kes 17 (G304.6$+$0.1), G311.5$-$0.3, G346.6$-$0.2, CTB 37A (G348.5$+$0.1) and G348.5$-$0.0 -- that were detected in the infrared by Reach et al. (2006) in an analysis of data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) that was conducted by the Spitzer Space Telescope. We present and analyze archival ASCA observations of Kes 17, G311.5$-$0.3 and G346.6$-$0.2, archival XMM-Newton observations of Kes 17, CTB 37A and G348.5$-$0.0 and an archival Chandra observation of CTB 37A. All of the SNRs are clearly detected in the X-ray possibly except for G348.5$-$0.0. Our study reveals that the four detected SNRs all feature center-filled X-ray morphologies and that the observed emission from these sources is thermal in all cases. We argue that these SNRs should be classified as mixed-morphology SNRs (MM SNRs): our study strengthens the correlation between MM SNRs and SNRs interacting with molecular clouds and suggests that the origin of mixed-morphology SNRs may be due to the interactions between these SNRs and adjacent clouds. Our ASCA analysis of G311.5$-$0.3 reveals for the first time X-ray emission from this SNR: the X-ray emission is center-filled within the radio and infrared shells and thermal in nature ($kT$ $\sim$ 0.98 keV), thus motivating its classification as an MM SNR. We find considerable spectral variations in the properties associated with the plasmas of the other X-ray-detected SNRs, such as a possible overabundance of magnesium in the plasma of Kes 17. Finally, we also estimate such properties as electron density $n$$_e$, radiative age $t$$_{rad}$ and swept-up mass $M$$_X$ for each of the four X-ray-detected SNRs.

EFFECTS OF DIFFUSE BACKGROUND EMISSION AND SOURCE CROWDING ON PHOTOMETRIC COMPLETENESS IN SPITZER SPACE TELESCOPE IRAC SURVEYS: THE GLIMPSE CATALOGS AND ARCHIVES

We characterize the completeness of point source lists from Spitzer Space Telescope surveys in the four Infrared Array Camera (IRAC) bandpasses, emphasizing the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) programs (GLIMPSE I, II, 3D, 360; Deep GLIMPSE) and their resulting point source Catalogs and Archives. The analysis separately addresses effects of incompleteness resulting from high diffuse background emission and incompleteness resulting from point source confusion (i.e., crowding). An artificial star addition and extraction analysis demonstrates that completeness is strongly dependent on local background brightness and structure, with high-surface-brightness regions suffering up to five magnitudes of reduced sensitivity to point sources. This effect is most pronounced at the IRAC 5.8 and 8.0 μm bands where UV-excited polycyclic aromatic hydrocarbon emission produces bright, complex structures (photodissociation regions). With regard to diffuse background effects, we provide the completeness as a function of stellar magnitude and diffuse background level in graphical and tabular formats. These data are suitable for estimating completeness in the low-source-density limit in any of the four IRAC bands in GLIMPSE Catalogs and Archives and some other Spitzer IRAC programs that employ similar observational strategies and are processed by the GLIMPSE pipeline. By performing the same analysis on smoothed images we show that the point source incompleteness is primarily a consequence of structure in the diffuse background emission rather than photon noise. With regard to source confusion in the high-source-density regions of the Galactic Plane, we provide figures illustrating the 90% completeness levels as a function of point source density at each band. We caution that completeness of the GLIMPSE 360/Deep GLIMPSE Catalogs is suppressed relative to the corresponding Archives as a consequence of rejecting stars that lie in the point-spread function wings of saturated sources. This effect is minor in regions of low saturated star density, such as toward the Outer Galaxy; this effect is significant along sightlines having a high density of saturated sources, especially for Deep GLIMPSE and other programs observing closer to the Galactic center using 12 s or longer exposure times.

NEWLY IDENTIFIED EXTENDED GREEN OBJECTS (EGOs) FROM THE SPITZER GLIMPSE II SURVEY. I. CATALOG

We have produced a catalog containing 98 newly identified massive young stellar object (MYSO) candidates associated with ongoing outflows (known as extended green objects, or EGOs). These have been identified from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) II data set and our new identifications increase the number of known EGOs to similar to 400 in our Galaxy, adding to the similar to 300 previously identified EGOs reported by Cyganowski et al. from the GLIMPSE I survey. The high detection rate (similar to 70%) of 95 GHz class I methanol masers achieved in a survey toward 57 of these new EGOs with the Mopra 22 m radio telescope demonstrates that the new EGOs are associated with outflows. Investigations of the mid-infrared properties and physical associations with other star formation tracers (e.g., infrared dark clouds, class I and II methanol masers, and millimeter Bolocam Galactic Plane Survey sources) reveal that the newly identified EGOs are very similar in nature to those in the sample of Cyganowski et al. All of the observational evidence supports the hypothesis that EGOs correspond to MYSOs at the earliest evolutionary stage, with ongoing outflow activity, and active rapid accretion.

Discovery of planetary nebulae using predictive mid-infrared diagnostics

We demonstrate a newly developed mid-infrared planetary nebula (PN) selection technique. It is designed to enable efficient searches for obscured, previously unknown, PN candidates present in the photometric source catalogues of Galactic plane MIR sky surveys. Such selection is now possible via new, sensitive, high-to-medium resolution, MIR satellite surveys such as those from the Spitzer Space Telescope and the all-sky Wide-Field Infrared Survey Explorer (WISE) satellite missions. MIR selection is based on how different colour-colour planes isolate zones (sometimes overlapping) that are predominately occupied by different astrophysical object types. These techniques depend on the reliability of the available MIR source photometry. In this pilot study we concentrate on MIR point source detections and show that it is dangerous to take the MIR GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) photometry from Spitzer for each candidate at face value without examining the actual MIR image data. About half of our selected sources are spurious detections due to the applied source detection algorithms being affected by complex MIR backgrounds and the de-blending of diffraction spikes around bright MIR point sources into point sources themselves. Nevertheless, once this additional visual diagnostic checking is performed, valuable MIR selected PN candidates are uncovered. Four turned out to have faint, compact, optical counterparts in our H-alpha survey data missed in previous optical searches. We confirm all of these as true PNe via our follow-up optical spectroscopy. This lends weight to the veracity of our MIR technique. It demonstrates sufficient robustness that high-confidence samples of new Galactic PN candidates can be extracted from these MIR surveys without confirmatory optical spectroscopy and imaging. This is problematic or impossible when the extinction is large.

The HII region G35.673-00.847: another case of triggered star formation?

As part of a systematic study that we are performing with the aim to increase the observational evidence of triggered star formation in the surroundings of HII regions, we analyze the ISM around the HII region G35.673-00.847, a poorly studied source. Using data from large-scale surveys: Two Micron All Sky Survey, Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), MIPSGAL, Galactic Ring Survey (GRS), VLA Galactic Plane Survey (VGPS), and NRAO VLA Sky Survey (NVSS) we performed a multiwavelength study of G35.673-00.847 and its surroundings. The mid IR emission, shows that G35.673-00.847 has an almost semi-ring like shape with a cut towards the galactic west. The radius of this semi-ring is about 1.5' (~1.6 pc, at the distance of ~3.7 kpc). The distance was estimated from an HI absorption study and from the analysis of the molecular gas. Indeed, we find a molecular shell composed by several clumps distributed around the HII region, suggesting that its expansion is collecting the surrounding material. We find several YSO candidates over the molecular shell. Finally, comparing the HII region dynamical age and the fragmentation time of the molecular shell, we discard the collect and collapse as the mechanism responsible for the YSOs formation, suggesting other processes such as radiative driven implosion and/or small-scale Jeans gravitational instabilities.