The statistics of triggered star formation: an overdensity of massive YSOs around Spitzer bubbles
M. A. Thompson, J. S. Urquhart, T. J. T. Moore, L. K. Morgan
备注：
12 pages, 8 figures. Accepted by MNRAS. This version incorporates minor suggestions by the referee. A version with higher resolution Figure 1 is available upon request
We present a detailed statistical study of massive star formation in the environment of 322 Spitzer mid-infrared bubbles by using the RMS survey for massive Young Stellar Objects (YSOs). Using a combination of simple surface density plots and a more sophisticated angular cross-correlation function analysis we show that there is a statistically significant overdensity of RMS YSOs towards the bubbles. There is a clear peak in the surface density and angular cross-correlation function of YSOs projected against the rim of the bubbles. By investigating the autocorrelation function of the RMS YSOs we show that this is not due to intrinsic clustering of the RMS YSO sample. RMS YSOs and Spitzer bubbles are essentially uncorrelated with each other beyond a normalised angular distance of two bubble radii. The bubbles associated with RMS YSOs tend to be both smaller and thinner than those that are not associated with YSOs. We interpret this tendency to be due to an age effect, with YSOs being preferentially found around smaller and younger bubbles. We find no evidence to suggest that the YSOs associated with the bubbles are any more luminous than the rest of the RMS YSO population, which suggests that the triggering process does not produce a top heavy luminosity function or initial mass function. We suggest that it is likely that the YSOs were triggered by the expansion of the bubbles and estimate that the fraction of massive stars in the Milky Way formed by this process could be between 14 and 30%.
The HII complex N44 in the Large Magellanic Cloud (LMC) provides an excellent site to perform a detailed study of star formation in a mild starburst, as it hosts three regions of star formation at different evolutionary stages and it is not as complicated and confusing as the 30 Doradus giant HII region. We have obtained Spitzer Space Telescope observations and complementary ground-based 4m uBVIJK observations of N44 to identify candidate massive young stellar objects (YSOs). We further classify the YSOs into Types I, II, and III, according to their spectral energy distributions (SEDs). In our…
The most luminous Spitzer point sources in the 30 Doradus triggered second generation are investigated coherently in the 3-8 micron region. Remarkable diversity and complexity in their natures are revealed. Some are also among the brightest JHK sources, while others are not. Several of them are multiple when examined at higher angular resolutions with HST NICMOS and WFPC2/WFC3 as available, or with VISTA/VMC otherwise. One is a dusty compact H II region near the far northwestern edge of the complex, containing a half dozen bright I-band sources. Three others appear closely associated with lumi…
The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper we present analysis of candidate massive young stellar objects (YSOs), i.e., {\it in situ, current} massive star formation (MSF) in the Bridge using {\it Spitzer} mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are $\sim10 M_\odot$, $\ll45 M_\odot$ found in the Large Magellanic Cloud (LMC). The intensity of MSF in the Bridge also appe…
We present the {\it Spitzer}-IRAC images of the S235 star forming complex that includes the East~1 & 2, Central and S235 A & B regions. In addition, we present the near-infrared images of the S235 A & B regions. The IRAC photometry reveals on-going star formation, with 86 Class 0/I and 144 Class II YSOs in the entire S235 complex. Nearly 73% of these YSOs are present in clusters with a maximum surface density of 120 YSOs/pc$^{2}$ (in the vicinity of S235A & B regions). A few YSOs, possibly in an arc-like formation, are identified towards the south of S235A region, which may be speculated as an…
The G333 giant molecular cloud contains a few star clusters and H II regions, plus a number of condensations currently forming stars. We have mapped 13 of these sources with the appearance of young stellar objects (YSOs) with the Spitzer Infrared Spectrograph in the SL, SH, and LH modules (5-36 micron). We use these spectra plus available photometry and images to characterize the YSOs. The spectral energy distributions (SEDs) of all sources peak between 35 and 110 micron, thereby showing their young age. The objects are divided into two groups: YSOs associated with extended emission in IRAC ba…
We develop a new method to identify YSOs from star-forming regions using the photometry data from Spitzer's c2d Legacy Project. The aim is to obtain YSO lists as complete as possible for studying the statistical properties, such as Star Formation Rate (SFR) and lifetimes of YSOs in different evolutionary stages. The largest obstacle for identifying YSOs comes from background galaxies with similar SEDs to YSOs. Traditionally, selected color-color and color-magnitude criteria are used to separate YSOs and galaxies. However, since there is no obvious boundary between YSOs and galaxies in Color-Co…
The Spitzer Space Telescope mapped the Perseus molecular cloud complex with IRAC and MIPS as part of the c2d Spitzer Legacy project. This paper combines the observations from both instruments giving an overview of low-mass star formation across Perseus from 3.6 to 70 micron. We provide an updated list of young stellar objects with new classifications and source fluxes from previous works, identifying 369 YSOs in Perseus with the Spitzer dataset. By synthesizing the IRAC and MIPS maps of Perseus and building on the work of previous papers in this series (Jorgensen et al. 2006, Rebull et al. 200…
We present observations in eight wavebands from 1.25-24 microns of four dense cores: L204C-2, L1152, L1155C-2, and L1228. Our goals are to study the YSO population of these cores and to measure the mid-infrared extinction law. With our combined near-infrared and Spitzer photometry, we classify each source in the cores as, among other things, background stars, galaxies, or embedded young stellar objects (YSOs). L1152 contains three YSOs and L1228 has seven, but neither L204C-2 nor L1155C-2 appear to contain any YSOs. We estimate an upper limit of 7x10^-5 to 5x10^-4 solar luminosities for any un…
We present results from our spectroscopic study, using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, designed to identify massive young stellar objects (YSOs) in the Galactic Center (GC). Our sample of 107 YSO candidates was selected based on IRAC colors from the high spatial resolution, high sensitivity Spitzer/IRAC images in the Central Molecular Zone (CMZ), which spans the central ~300 pc region of the Milky Way Galaxy. We obtained IRS spectra over 5um to 35um using both high- and low-resolution IRS modules. We spectroscopically identify massive YSOs by the presence o…
Spitzer IRAC images (3.6, 4.5, 5.8 and 8.0$μ$m) and photometry of the star forming region M8 are presented. IRAC photometry reveals ongoing star formation in the M8 complex, with 64 Class 0/I and 168 Class II sources identified in several locations in the vicinity of sub-mm gas cores/clumps. Nearly 60% of these YSOs occur in about 7 small clusters. The spatial surface density of the clustered YSOs is determined to be about 10-20 YSOs/pc$^{2}$. Fresh star formation by the process of "collect and collapse" might have been triggered by the expanding HII regions and winds from massive stars. IRAC …
We report the first results of imaging the Carina Nebula with Spitzer/IRAC, providing a catalog of point sources and YSOs based on SED fits. We discuss several aspects of the extended emission, including dust pillars that result when a clumpy molecular cloud is shredded by massive star feedback. There are few "extended green objects" (EGOs) normally taken as signposts of outflow activity, and none of the HH jets detected optically are seen as EGOs. A population of "extended red objects" tends to be found around OB stars, some with clear bow-shocks. These are dusty shocks where stellar winds co…
We present a survey of the Orion A and B molecular clouds undertaken with the IRAC and MIPS instruments onboard Spitzer. In total, five distinct fields were mapped covering 9 sq. degrees in five mid-IR bands spanning 3-24 microns. The survey includes the Orion Nebula Cluster, the Lynds 1641, 1630 and 1622 dark clouds, and the NGC 2023, 2024, 2068 and 2071 nebulae. These data are merged with the 2MASS point source catalog to generate a catalog of eight band photometry. We identify 3479 dusty young stellar objects (YSOs) in the Orion molecular clouds by searching for point sources with mid-IR co…
We present the results from Chandra X-ray observations, and near- and mid-infrared analysis, using VISTA/VVV and Spitzer/GLIMPSE catalogs, of the high-mass star-forming region IRAS 16562-3959, which contains a candidate for a high mass protostar. We detected 249 X-ray sources within the ACIS-I field-of-view. The majority of the X-ray sources have low count rates (< 0.638 cts/ks), and hard X-ray spectra. The search for YSOs in the region using VISTA/VVV and Spitzer/GLIMPSE catalogs resulted in a total of 799 YSOs, with 66 Class I and 733 Class II YSOs. The search for near- and mid-infrared coun…
The HII complex N159 in the Large Magellanic Cloud (LMC) is used to study massive star formation in different environments, as it contains three giant molecular clouds (GMCs) that have similar sizes and masses but exhibit different intensities of star formation. We identify candidate massive young stellar objects (YSOs) using infrared photometry, and model their SEDs to constrain mass and evolutionary state. Good fits are obtained for less evolved Type I, I/II, and II sources. Our analysis suggests that there are massive embedded YSOs in N159B, a maser source, and several ultracompact HII regi…
We analyze near-infrared UKIDSS observations of a sample of 8325 objects taken from a catalog of intrinsically red sources in the Galactic plane selected in the Spitzer-GLIMPSE survey. Given the differences in angular resolution (factor >2 better in UKIDSS), our aim is to investigate whether there are multiple UKIDSS sources that might all contribute to the GLIMPSE flux, or there is only one dominant UKIDSS counterpart. We then study possible corrections to estimates of the SFR based on counts of GLIMPSE young stellar objects (YSOs). This represents an exploratory work towards the construction…
We present {\it Spitzer} IRAC mid-infrared photometry on the massive star forming region AFGL 437 (IRAS 03035+5819). From the IRAC colour-colour diagram, we identify several new embedded YSOs within 64 arcsec of the central compact cluster. Using the IRAC ratio images, we investigate the molecular outflows associated with the highly embedded young stellar object WK34 in the central cluster. We attribute the lobes seen (extended to $\sim$ 0.16 pc in the north) in the ratio map to shocked molecular hydrogen emission. IRAC images reveal a large diffuse nebulosity associated with the central clust…
In this paper we undertake a study of the 21 square degree SMOG field, a Spitzer cryogenic mission Legacy program to map a region of the outer Milky Way towards the Perseus and Outer spiral arms with the IRAC and MIPS instruments. We identify 4648 YSOs across the field. Using the DBSCAN method we identify 68 clusters or aggregations of YSOs in the region, having 8 or more members. We identify 1197 class Is, 2632 class IIs, 819 class IIIs, of which 45 are candidate transition disk objects, utilizing the MIPS 24 photometry. The ratio of YSOs identified as members of clusters was 2872/4648, or 62…
We present initial results from a population synthesis model aimed at determining the star formation rate of the Milky-Way. We find that a total star formation rate of 0.68 to 1.45 Msun/yr is able to reproduce the observed number of young stellar objects in the Spitzer/IRAC GLIMPSE survey of the Galactic plane, assuming simple prescriptions for the 3D Galactic distributions of YSOs and interstellar dust, and using model SEDs to predict the brightness and color of the synthetic YSOs at different wavelengths. This is the first Galaxy-wide measurement derived from pre-main-sequence objects themse…
Tracing star formation across the Rosette nebula using deep Spitzer imaging
University of St Andrews（圣安德鲁斯大学）；Universidade de Lisboa（里斯本大学）；Univ. Bordeaux（波尔多大学）；European Southern Observatory（欧洲南方天文台）；Istituto Nazionale di Astrofisica (INAF) – Osservatorio Astronomico di Palermo（意大利国家天体物理研究所（INAF）- 巴勒莫天文台）
We present ~120,000 Spitzer/IRAC candidate young stellar objects (YSOs) based on surveys of the Galactic midplane between l~255 deg and 110 deg, including the GLIMPSE I, II, and 3D, Vela-Carina, Cygnus X, and SMOG surveys (613 square degrees), augmented by near-infrared catalogs. We employed a classification scheme that uses the flexibility of a tailored statistical learning method and curated YSO datasets to take full advantage of IRAC's spatial resolution and sensitivity in the mid-infrared ~3-9 micron range. Multi-wavelength color/magnitude distributions provide intuition about how the clas…
NH3 and CH3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and HCOOCH3. Despite a number of recent studies, little is known about their abundances in the solid state. (...) In this work, we investigate the ~ 8-10 micron region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass young stellar objects (YSOs). These data are part of a survey of interstellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for t…
We present 737 candidate Young Stellar Objects (YSOs) near the W51 Giant Molecular Cloud (GMC) over an area of 1.25 deg x 1.00 deg selected from Spitzer Space Telescope data. We use spectral energy distribution (SED) fits to identify YSOs and distinguish them from main-sequence or red giant stars, asymptotic giant branch stars, and background galaxies. Based on extinction of each YSO, we separate a total of 437 YSOs associated with the W51 region from the possible foreground sources. We identify 69 highly embedded Stage 0/I candidate YSOs in our field with masses > 5 Msun (corresponding to mid…
We investigate the distribution of different classes of spectroscopically identified sources and theoretical models in the color-color diagrams (CCDs) combining the near-infrared (NIR) and mid-infrared (MIR) data to develop a method to classify Outer Galaxy sources detected with the Spitzer Space Telescope (hereafter Spitzer) SMOG survey in the IRAC 3.6 and 8.0 micrometer and MIPS 24 micrometer bands. We supplement the Spitzer data with the data from other satellite and ground-based surveys. The main goal of our study is to discover and characterize the population of intermediate- and low-mass…
The first detection of the C60 (Buckminsterfullerene) molecule in massive embedded young stellar objects (YSOs) is reported. Observations with Spitzer IRS reveal the presence of C60 in YSOs ISOGAL-P J174639.6-284126 and SSTGC 372630 in the Central Molecular Zone in the Galactic centre, and in a YSO candidate, 2MASS J06314796+0419381, in the Rosette nebula. The first detection of C60 in a Herbig Ae/Be star, HD 97300, is also reported. These observations extend the range of astrophysical environments in which C60 is found to YSOs and a pre-main sequence star. C60 excitation and formation mechani…
We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc$^{-2}$ to over 10,000 pc$^{-2}$, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader …
Observed Young Stellar Objects (YSOs) are used to study star formation and characterize star forming regions. For this purpose, YSO candidate catalogs are compiled from various surveys, especially in the infrared (IR), and simple selection schemes in colour-magnitude diagrams (CMDs) are often used to identify and classify YSOs. We propose a methodology for YSO classification through Machine Learning (ML) using Spitzer IR data. We detail our approach in order to ensure reproducibility and provide an in-depth example on how to efficiently apply ML to an astrophysical classification. We used feed…
We present a supervised machine learning methodology to classify stellar populations in the Local Group dwarf-irregular galaxy NGC6822. Near-IR colours (J-H, H-K, and J-K), K-band magnitudes and far-IR surface brightness (at 70 and 160 micron) measured from Spitzer and Herschel images are the features used to train a Probabilistic Random Forest (PRF) classifier. Point-sources are classified into eight target classes: young stellar objects (YSOs), oxygen- and carbon-rich asymptotic giant branch stars, red giant branch and red super-giant stars, active galactic nuclei, massive main-sequence star…
Through analysis of archival images and photometry from the Spitzer GLIMPSE and MIPSGAL surveys combined with 2MASS and MSX data, we have identified 488 candidate young stellar objects (YSOs) in the giant molecular cloud M17 SWex, which extends ~50 pc southwest from the prominent Galactic H II region M17. Our sample includes >200 YSOs with masses >3 Msun that will become B-type stars on the main sequence. Extrapolating over the stellar initial mass function (IMF), we find that M17 SWex contains >1.3x10^4 young stars, representing a proto-OB association. The YSO mass function is significantly s…
We present an observational study of small-scale feedback processes operating in the star-forming region located in the wall of the expanding supershell around the Cyg OB1 association. The interstellar gas and dust content and pre-stellar populations in the vicinity of the open star cluster vdB 130 are analysed based on new optical and IR observations performed with the 6-m (3D spectroscopic mapping in the [SII] doublet) and 2.5-m (optical and NIR images) Russian telescopes along with the archival data of Spitzer and Herschel space telescopes. Analysing ionized gas kinematics and emission spec…
We present a 9 deg^2 map of the North American and Pelican Nebulae regions obtained in all four IRAC channels with the Spitzer Space Telescope. The resulting photometry is merged with that at JHKs from 2MASS and a more spatially limited $BVI$ survey from previous ground-based work. We use a mixture of color- color diagrams to select a minimally contaminated set of more than 1600 objects that we claim are young stellar objects (YSOs) associated with the star forming region. Because our selection technique uses IR excess as a requirement, our sample is strongly biased against inclusion of Class …
Accurate measurements of statistical properties, such as the star formation rate and the lifetime of young stellar objects (YSOs) in different stages, is essential for constraining star formation theories. However, it is a difficult task to separate galaxies and YSOs based on spectral energy distributions (SEDs) alone, because they contain both thermal emission from stars and dust around them and no reliable theories can be applied to distinguish them. Here we compare different machine learning algorithms and develop the Spectrum Classifier of Astronomical Objects (SCAO), based on Fully Connec…
Based on a multiwavelength study, the interstellar medium and young stellar objects (YSOs) around the HII region Sh2-82 have been analyzed. Two molecular clumps were found from the archival data of the Galactic Ring Survey, and using the Two Micron All-Sky Survey catalog, we found two corresponding young clusters embedded in the molecular clumps. The very good relations between CO emission, infrared shells and YSOs suggest that it is probably a triggered star formation region from the expansion of Sh2-82. We further used the data from the Galactic Legacy Infrared Mid-Plane Survey Extraordinair…
G79.3+0.3 is an infrared dark cloud in the Cygnus-X complex that is home to massive deeply embedded young stellar objects (YSOs). We have produced a submillimeter array (SMA) 1.3 mm continuum image and $^{12}$CO line maps of the eastern section of G79.3+0.3 in which we detect five separate YSOs. We have estimated physical parameters for these five YSOs and others in the vicinity of G79.3+0.3 by fitting existing photometry from Spitzer, Herschel, and ground-based telescopes to spectral energy distribution models. Through these model fits we find that the most massive YSOs seen in the SMA 1.3mm …
The central kpc of the Milky Way might be expected to differ significantly from the rest of the Galaxy with regard to gas dynamics and the formation of YSOs. We probe this possibility with mid-infrared observations obtained with IRAC and MIPS on Spitzer and with MSX. We use color-color diagrams and SED fits to explore the nature of YSO candidates (including objects with 4.5 micron excesses possibly due to molecular emission). There is an asymmetry in the distribution of the candidate YSOs, which tend to be found at negative Galactic longitudes; this behavior contrasts with that of the molecula…
Complex organic molecules (COMs) are known to be abundant toward some low-mass young stellar objects (YSOs), but how these detections relate to typical COM abundance are not yet understood. We aim to constrain the frequency distribution of COMs during low-mass star formation, beginning with this pilot survey of COM lines toward six embedded YSOs using the IRAM 30m telescope. The sample was selected from the Spitzer c2d ice sample and covers a range of ice abundances. We detect multiple COMs, including CH3CN, toward two of the YSOs, and tentatively toward a third. Abundances with respect to CH3…
Infrared Dark Clouds are ideal laboratories to study the initial processes of high-mass star and star cluster formation. We investigated star formation activity of an unexplored filamentary dark cloud (~5.7pc x 1.9pc), which itself is part of a large filament (~20pc) located in the S254-S258 OB complex at a distance of 2.5kpc. Using MIPS Spitzer 24 micron data, we uncover 49 sources with SNR greater than 5. We identified 45 sources as candidate YSOs of Class I, Flat-spectrum & Class II nature. Additional 17 candidate YSOs (9 Class I & 8 Class II) are also identified using JHK and WISE photomet…
Studies of young stellar objects (YSOs) in the Galaxy have found that a significant fraction exhibit photometric variability. However, no systematic investigation has been conducted on the variability of extragalactic YSOs. Here we present the first variability study of massive YSOs in a $\sim 1.5\,\mathrm{deg^2}$ region of the Large Magellanic Cloud (LMC). The aim is to investigate whether the different environmental conditions in the metal-poor LMC ($\sim$ 0.4-0.5 Z_sun) have an impact on the variability characteristics. Multi-epoch near-infrared (NIR) photometry was obtained from the VISTA …
We present the results of our investigation of the star-forming complexes W51 and W43, two of the brightest in the first Galactic quadrant. In order to determine the young stellar object (YSO) populations in W51 and W43 we used color-magnitude relations based on Spitzer mid-infrared and 2MASS/UKIDSS near-infrared data. We identified 302 Class I YSOs and 1178 Class II/transition disk candidates in W51, and 917 Class I YSOs and 5187 Class II/transition disk candidates in W43. We also identified tens of groups of YSOs in both regions using the Minimal Spanning Tree (MST) method. We found similar …
W5-E has been observed with the Herschel-PACS and -SPIRE photometers, at 100, 160, 250, 350, and 500 microns. The dust temperature map shows a rather uniform temperature, in the range 17.5-20 K in the dense condensations or filaments, 21-22 K in the photodissociation regions, and 24-31 K in the direction of the ionized regions. The column densities are rather low, everywhere lower than 10^23 cm-2, and of the order of a few 10^21 cm-2 in the PDRs. About 8000 solar masses of neutral material surrounds the ionized region, which is low with respect to the volume of this HII region; we suggest that…
OB associations are home to newly formed massive stars, whose turbulent winds and ionizing flux create H II regions rich with star formation. Studying the distribution and abundance of young stellar objects (YSOs) in these ionized bubbles can provide essential insight into the physical processes that shape their formation, allowing us to test competing models of star formation. In this work, we examined one such OB association, Cepheus OB4 (Cep OB4) - a well-suited region for studying YSOs due to its Galactic location, proximity, and geometry. We created a photometric catalog from Spitzer/IRAC…
We present a multiwavelength investigation of the young stellar population and star formation activities around the \hii region Sharpless 311. Using our deep near-infrared observations and archival {\it Spitzer}-IRAC observations, we have detected a total of 125 young stellar objects (YSOs) in an area of $\sim$86 arcmin$^2$. The YSOs sample include 8 Class I and 117 Class II candidate YSOs. The mass completeness of the identified YSOs sample is estimated to be 1.0 \msun. The ages and masses of the majority of the candidate YSOs are estimated to be in the range of $\sim$0.1$-$5 Myr and $\sim$0.…
We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective to locate a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey (2MASS) and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identif…
Using Spitzer/IRAC observations of a region to be observed by the CoRoT satellite, we have unraveled a new complex star-forming region at low metallicity in the outer Galaxy. We perform a study of S284 in order to outline the chain of events in this star-forming region. We used four-band Spitzer/IRAC photometry as well as Halpha imaging obtained with INT/WFC. Combining these data with the optical photometry obtained in the frame of CoRoTs preparation and the 2MASS catalog we analysed the properties and distribution of young stellar objects (YSOs) associated with point-like sources. We also stu…
Wide-field searches for young stellar objects (YSOs) can place useful constraints on the prevalence of clustered versus distributed star formation. The Spitzer/IRAC Candidate YSO (SPICY) catalog is one of the largest compilations of such objects (~120,000 candidates in the Galactic midplane). Many SPICY candidates are spatially clustered, but, perhaps surprisingly, approximately half the candidates appear spatially distributed. To better characterize this unexpected population and confirm its nature, we obtained Palomar/DBSP spectroscopy for 26 of the optically-bright (G<15 mag) "isolated" YSO…
We report the detection of several molecular gas-phase and ice absorption features in three photometrically-selected young stellar object (YSO) candidates in the central 280 pc of the Milky Way. Our spectra, obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, reveal gas-phase absorption from CO2 (15.0um), C2H2 (13.7um) and HCN (14.0um). We attribute this absorption to warm, dense gas in massive YSOs. We also detect strong and broad 15um CO2 ice absorption features, with a remarkable double-peaked structure. The prominent long-wavelength peak is due to CH3OH-rich …
As nearby neighbors to the Milky Way, the Large and Small Magellanic Clouds (LMC and SMC) provide a unique opportunity to study star formation in the context of their galactic ecosystems. Thousands of young stellar objects (YSOs) have been characterized with large-scale Spitzer and Herschel surveys. In this paper, we present new near-IR spectroscopy of five high-mass YSOs in the LMC and one in the SMC. We detect multiple hydrogen recombination lines, as well as He I 2.058 $μ$m, H$_2$, [Fe II], and [S III] in these highly excited sources. We estimate the internal extinction of each source and f…
We present images and spectral energy distributions (SEDs) of massive young stellar objects (YSOs) in three star-forming H II regions of the Large Magellanic Cloud: N159A, N159 Papillon, and N160. We use photometry from SOFIA/FORCAST at 25.3--37.1 um to constrain model fits to the SEDs and determine luminosities, ages, and dust content of the embedded YSOs and their local environments. By placing these sources on mid-infrared color-magnitude and color-color diagrams, we analyze their dust properties and consider their evolutionary status. Since each object in the FORCAST images has an obvious …
IRAS 20050+2720 is young star forming region at a distance of 700 pc without apparent high mass stars. We present results of our multiwavelength study of IRAS 20050+2720 which includes observations by Chandra and Spitzer, and 2MASS and UBVRI photometry. In total, about 300 YSOs in different evolutionary stages are found. We characterize the distribution of young stellar objects (YSOs) in this region using a minimum spanning tree (MST) analysis. We newly identify a second cluster core, which consists mostly of class II objects, about 10 arcmin from the center of the cloud. YSOs of earlier evolu…
We present a comprehensive study of massive young stellar objects (YSOs) in the metal-poor galaxy NGC 6822 using IRAC and MIPS data obtained from the {\em Spitzer Space Telescope}. We find over 500 new YSO candidates in seven massive star-formation regions; these sources were selected using six colour-magnitude cuts. Via spectral energy distribution fitting to the data with YSO radiative transfer models we refine this list, identifying 105 high-confidence and 88 medium-confidence YSO candidates. For these sources we constrain their evolutionary state and estimate their physical properties. The…
We take advantage of the very simple morphology of RCW 120 -- a perfect bubble -- to understand the mechanisms triggering star formation around an HII region and to establish what kind of stars are formed there. We present 870 microns observations of RCW 120, obtained with the APEX-LABOCA camera. These show the distribution of cold dust, and thus of neutral material. We use Spitzer-MIPS observations at 24 and 70 microns to detect the young stellar objects (YSOs) present in this region and to estimate their evolutionary stages. A layer of dense neutral material surrounds the HII region, having …
Stars form in clustered environments, but how they form when the available resources are shared is still not well understood. A related question is whether the IMF is in fact universal across galactic environments, a galactic initial mass function (IGIMF), or whether it is an average of local IMFs. One of the long-standing problems in resolving this question and in the study of young clusters is observational: the emission from multiple sources is frequently seen as blended because at different wavelengths or with different telescopes the beam sizes are different. The confusion hinders our abi…
This paper presents a study of the rate and efficiency of star formation in the NGC 6334 star forming region. We obtained observations at J, H, and Ks taken with the NOAO Extremely Wide-Field Infrared Imager (NEWFIRM) and combined them with observations taken with the Infrared Array Camera (IRAC) camera on the Spitzer Space Telescope at wavelengths λ = 3.6, 4.5, 5.8, and 8.0 μm. We also analyzed previous observations taken at 24 μm using the Spitzer MIPS camera as part of the MIPSGAL survey. We have produced a point source catalog with >700,000 entries. We have identified 2283 YSO candidates, …
Molecular outflows provide an alternative method of identifying protostellar cores, complementary to recent mid-infrared studies. Continuing our studies of Perseus, we investigate whether all Spitzer-identified protostars, and particularly those with low luminosities, drive outflows, and if any new protostellar cores (perhaps harbouring low-mass sources) can be identified via their outflows alone. We have used the heterodyne array receiver HARP on JCMT to make deep 12CO 3-2 maps of submm cores in Perseus, extending and deepening our earlier study with RxB and bringing the total number of SCUBA…
We present multi-wavelength analysis around mid-infrared bubble N14 to probe the signature of triggered star formation as well as the formation of new massive star(s) and/or cluster(s) on the borders of the bubble by the expansion of the H II region. Spitzer-IRAC ratio maps reveal that the bubble is traced by the polycyclic aromatic hydrocarbon emission following an almost circular morphology except in the south-west direction towards the low molecular density environment. The observational signatures of the collected molecular and cold dust material have been found around the bubble. We have …
We present $K$-band integral field spectroscopic observations towards 17 massive young stellar objects (YSOs) in the low metallicity Small Magellanic Cloud (SMC) and two YSO candidates in the compact H ii regions N81 and N88 A (also in the SMC). These sources, originally identified using $Spitzer$ photometry and/or spectroscopy, have been resolved into 29 $K$-band continuum sources. By comparing Br$γ$ emission luminosities with those presented for a Galactic sample of massive YSOs, we find tentative evidence for increased accretion rates in the SMC. Around half of our targets exhibit emission …
X-rays are a powerful probe of activity in early stages of star formation. They allow us to identify young stars even after they have lost the IR signatures of circumstellar disks and provide constraints on their distance. Here we report on XMM-Newton observations which detect 121 young stellar objects (YSOs) in two fields between L1641S and $κ$ Ori. These observations extend the Survey of Orion A with XMM and Spitzer (SOXS). The YSOs are contained in a ring of gas and dust apparent at millimeter wavelengths, and in far-IR and near-IR surveys. The X-ray luminosity function of the young stellar…
Far red spectra for 34 stars with V magnitudes between 15 and 18 in the direction of the North America and Pelican nebulae (NAP) star-forming region are obtained. Some of these stars were known earlier as emission-line objects, others were suspected as pre-main-sequence stars from photometry in the J, H, Ks and Vilnius systems. We confirm the presence of the H alpha line emission in the spectra of 19 stars, some of them exhibit also emission in the O I and Ca II lines. In some of the stars the H alpha absorption line is filled with emission. To estimate their evolutionary status, the spectral …
