THE SPITZER SURVEY OF INTERSTELLAR CLOUDS IN THE GOULD BELT. III. A MULTI-WAVELENGTH VIEW OF CORONA AUSTRALIS

We have used archival HST H$\alpha$ images to study the immediate environments of massive and intermediate-mass young stellar object (YSO) candidates in the Large Magellanic Cloud (LMC). The sample of YSO candidates, taken from Gruendl & Chu (2009), was selected based on Spitzer IRAC and MIPS observations of the entire LMC and complementary ground-based optical and near-infrared observations. We found HST H$\alpha$ images for 99 YSO candidates in the LMC, of which 82 appear to be genuine YSOs. More than 95% of the YSOs are found to be associated with molecular clouds. YSOs are seen in three different kinds of environments in the H$\alpha$ images: in dark clouds, inside or on the tip of bright-rimmed dust pillars, and in small H II regions. Comparisons of spectral energy distributions for YSOs in these three different kinds of environments suggest that YSOs in dark clouds are the youngest, YSOs with small H II regions are the most evolved, and YSOs in bright-rimmed dust pillars span a range of intermediate evolutionary stages. This rough evolutionary sequence is substantiated by the presence of silicate absorption features in the Spitzer IRS spectra of some YSOs in dark clouds and in bright-rimmed dust pillars, but not those of YSOs in small H II regions. We present a discussion on triggered star formation for YSOs in bright-rimmed dust pillars or in dark clouds adjacent to H II regions. As many as 50% of the YSOs are resolved into multiple sources in high-resolution HST images. This illustrates the importance of using high-resolution images to probe the true nature and physical properties of YSOs in the LMC.

Stars form in molecular clouds under the influence of their local environments, yet the role of massive stellar feedback in either triggering or suppressing star formation remains a fundamental question in astrophysics. The Pillars of Creation in the Eagle Nebula—sculpted by ionizing radiation and stellar winds from massive stars in NGC 6611—offer a natural laboratory for investigating this question. Here we present high-resolution observations of the Pillars of Creation using the JWST Near Infrared Camera and Mid-Infrared Instrument, revealing 253 young stellar object (YSO) candidates. These YSO candidates show spatial correlations with the edges of feedback-driven structures, with overdensities along the boundaries. A weak trend of decreasing stellar age with increasing distance from the ionizing source was tentatively observed. There also appears to be an enhancement in the star formation rate within the past 1 Myr in this region. Such age and spatial associations suggest that while the bulk of the YSOs may have formed contemporaneously with the central cluster, a subset could be associated with triggered star formation. The JWST image of intricate structures—including a spiral-like disk and bi-reflection nebulae at the tips of Pillar I and Pillar II—further highlights the complexity of star formation processes. JWST reveals 253 YSO candidates in the Pillars of Creation, concentrated along the pillar edges with tentative age gradients and an enhanced star formation rate within 1 Myr. These findings suggest that some may have formed via triggered star formation.

We have calculated bolometric temperature (Tbol) and bolometric luminosity (Lbol) for 383 young stellar objects (YSOs) in five molecular clouds within 200 pc in Corona Australis (CrA), Ophiuchus (Oph), Taurus (Tau), Chamaeleon (Cha), and Lupus (Lup). We used Tbol, Lbol, and bolometric luminosity-temperature (BLT) diagrams to characterize and compare the overall-star-formation activity of the clouds on a self-consistent basis. The main results are the following: (1) the YSO populations in the clouds can be differentiated by the fraction of their low-Tbol sources, which increases systematically from Lup and Cha to Tau and to Oph and CrA. This trend is interpreted as increasing current star-forming activity in the same order; (2) the clouds with higher cold source fractions also seem to have higher bright source fractions; (3) In the BLT diagram, the CrA and Oph sources are more uniformly distributed while the Cha and Lup sources are aggregated near the zero-age mainsequence (ZAMS). Tau sources appear to be an intermediate case. Taurus also seems to contain more cold (Tbol < 1000 K) and low-luminosity (Lbol < 1 L?) sources than the other complexes; (4) the YSOs show a characteristic distribution in the median BLT diagram. This distribution is qualitatively consistent with the early YSO evolution from a protostar to a pre-main-sequence star and provides a unique observational test to star-formation models; (5) for Lup pre-main-sequence stars, the ratio of their Tbol to Teff increases during their approach to the ZAMS. This increase can be explained by the disk and envelope dissipation during the pre-main-sequence evolution; (6) the most active star-forming clouds (Oph and CrA) also have denser molecular cores as measured by C18O J = 1-0 line emission, suggesting that the star formation occurs in the densest parts of the molecular clouds; and (7) we find an anti-correlation between Tbol and C18O emission for the class 0 and I Tau sources (Tbol < 650 K). This shows that Tbol measures the intrinsic redness of YSOs, rather than their disk-envelope orientation. The disk orientation may have a more important effect on Tbol of the pre-main-sequence stars.

Context. The Central Molecular Zone (CMZ), a ∼200 pc sized region around the Galactic Centre, is peculiar in that it shows a star formation rate (SFR) that is suppressed with respect to the available dense gas. To study the SFR in the CMZ, young stellar objects (YSOs) can be investigated. Here we present radio observations of 334 2.2 μm infrared sources that have been identified as YSO candidates. Aims. Our goal is to investigate the presence of centimetre wavelength radio continuum counterparts to this sample of YSO candidates which we use to constrain the current SFR in the CMZ. Methods. As part of the GLObal view on STAR formation (GLOSTAR) survey, D-configuration Very Large Array data were obtained for the Galactic Centre, covering −2° &lt; l &lt; 2° and −1° &lt; b &lt; 1° with a frequency coverage of 4–8 GHz. We matched YSOs with radio continuum sources based on selection criteria and classified these radio sources as potential H II regions and determined their physical properties. Results. Of the 334 YSO candidates, we found 35 with radio continuum counterparts. We find that 94 YSOs are associated with dense dust condensations identified in the 870 μm ATLASGAL survey, of which 14 have a GLOSTAR counterpart. Of the 35 YSOs with radio counterparts, 11 are confirmed as H II regions based on their spectral indices and the literature. We estimated their Lyman continuum photon flux in order to estimate the mass of the ionising star. Combining these with known sources, the present-day SFR in the CMZ is calculated to be ∼0.068 M⊙ yr−1, which is ∼6.8% of the Galactic SFR. Candidate YSOs that lack radio counterparts may not have yet evolved to the stage of exhibiting an H II region or, conversely, are older and have dispersed their natal clouds. Since many lack dust emission, the latter is more likely. Our SFR estimate in the CMZ is in agreement with previous estimates in the literature.

The Orion cloud complex presents a variety of star formation mechanisms and properties and it is still one of the most intriguing targets for star formation studies. We present VISTA/VIRCAM near-infrared observations of the L1630N star forming region, including the stellar clusters NGC 2068 and NGC 2071, in the Orion molecular cloud B and discuss them in combination with Spitzer data. We select 186 young stellar object (YSO) candidates in the region on the basis of multi-colour criteria, confirm the YSO nature of the majority of them using published spectroscopy from the literature, and use this sample to investigate the overall star formation properties in L1630N. The K-band luminosity function of L1630N is remarkably similar to that of the Trapezium cluster, i.e., it presents a broad peak in the range 0.3-0.7 M$_\odot$ and a fraction of sub-stellar objects of $\sim$20%. The fraction of YSOs still surrounded by disk/envelopes is very high ($\sim$85%) compared to other star forming regions of similar age (1-2 Myr), but includes some uncertain corrections for diskless YSOs. Yet, a possibly high disk fraction together with the fact that 1/3 of the cloud mass has a gas surface density above the threshold for star formation ($\sim$129 M$_\odot$ pc$^{-2}$), points towards a still on-going star formation activity in L1630N. The star formation efficiency (SFE), star formation rate (SFR) and density of star formation of L1630N are within the ranges estimated for galactic star forming regions by the Spitzer "core to disk" and "Gould's Belt" surveys. However, the SFE and SFR are lower than the average value measured in the Orion A cloud and, in particular, lower than that in the southern regions of L1630. This might suggest different star formation mechanisms within the L1630 cloud complex.

We present 102 embedded young stellar object (YSO) candidates associated with the H72.97-69.39 super star cluster (SSC) in the Large Magellanic Cloud (LMC). With the use of the James Webb Space Telescope Mid-Infrared Instrument (MIRI) imaging mode, we utilize an F770W – F1000W versus F1000W color–magnitude diagram to select 70 YSO candidates. An additional 27 YSO candidates are selected based on model fitting using the four MIRI imaging filters employed for this study (F770W, F1000W, F1500W, and F2100W). The central region of H72.97-69.39 is saturated in MIRI imaging, however it is covered by observations made with the Medium Resolution Spectrometer (MRS), leading to the identification of five additional massive YSOs. The total star formation rate inferred based on the 102 YSO candidates is 0.02 M ⊙ yr−1, similar to other high-mass star-forming regions in the LMC which have undergone several generations of starburst events. Due to its young age, however, H72.97-69.39's stellar production rate is expected to increase. The central five YSOs identified with MRS have masses ranging from 21.1 to 40.3 M ⊙ and total luminosity over 106 L ⊙, making H72.97-69.39 a very compact and luminous star-forming region similar to other known SSCs. We theorize that the central five massive YSOs were formed via filamentary collision, while other YSO candidates of varying masses were triggered by wind, radiation, and expanding H ii shells based on their spatial distribution.

Context. The central molecular zone (CMZ) is a ~200 pc region around the Galactic centre. The study of star formation in the central part of the Milky Way is of great interest as it provides a template for the closest galactic nuclei. Aims. We present a spectroscopic follow-up of photometrically selected young stellar object (YSO) candidates in the CMZ of the Galactic centre. Our goal is to quantify the contamination of this YSO sample by reddened giant stars with circumstellar envelopes and to determine the star formation rate (SFR) in the CMZ. Methods. We obtained KMOS low-resolution near-infrared spectra (R ~ 4000) between 2.0 and 2.5 μm of sources, many of which have been previously identified by mid-infrared photometric criteria as massive YSOs in the Galactic centre. Our final sample consists of 91 stars with good signal-to-noise ratio. We separated YSOs from cool late-type stars based on spectral features of CO and Brγ at 2.3 μm and 2.16 μm, respectively. We made use of spectral energy distribution (SED) model fits to the observed photometric data points from 1.25 to 24 μm to estimate approximate masses for the YSOs. Results. Using the spectroscopically identified YSOs in our sample, we confirm that existing colour–colour diagrams and colour-magnitude diagrams are unable to efficiently separate YSOs and cool late-type stars. In addition, we define a new colour–colour criterion that separates YSOs from cool late-type stars in the H−KS vs. H −[8.0] diagram. We use this new criterion to identify YSO candidates in the |l| &lt; 1.̊5, |b| &lt; 0.̊5, region and use model SED fits to estimate their approximate masses. By assuming an appropriate initial mass function (IMF) and extrapolating the stellar IMF down to lower masses, we determine a SFR of ~0.046 ± 0.026 M⊙ yr-1 assuming an average age of 0.75 ± 0.25 Myr for the YSOs. This value is lower than estimates found using the YSO counting method in the literature. Conclusions. Our SFR estimate in the CMZ agrees with the previous estimates from various methods and reaffirms that star formation in the CMZ is proceeding at a lower rate than predicted by various star forming models.

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 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 majority of our YSO candidates are massive protostars with an accreting envelope in the initial stages of formation. We fit the mass distribution of the Stage I YSOs with a Kroupa initial mass function and determine a global star formation rate of 0.039 $\mathrm{M}_{\odot } \, \mathrm{yr}^{-1}$. This is higher than star formation rate estimates based on integrated UV fluxes. The new YSO candidates are preferentially located in clusters which correspond to seven active high-mass star-formation regions which are strongly correlated with the 8 and 24 μm emission from PAHs and warm dust. This analysis reveals an embedded high-mass star formation region, Spitzer I, which hosts the highest number of massive YSO candidates in NGC 6822. The properties of Spitzer I suggest it is younger and more active than the other prominent H ii and star-formation regions in the galaxy.

We have performed a deep [SII]6717/6731 wide field Herbig-Haro (HH) object survey toward the Vela C molecular cloud with a sky coverage of about 2 deg2. In total, 18 new HH objects, HH 1090-1107, are discovered and the two previously known HH objects, HH 73-74, are also detected in our [SII] images. We also present an investigation of mid-infrared outflows in the Vela C molecular cloud using the Wide-field Infrared Survey Explorer images taken from AllWISE data release. Using the method suggested by Zhang & Wang, eleven extended green objects (EGOs) are identified to be the mid-infrared outflows, including 6 new mid-infrared outflows that have not been detected previously at other wavelengths and 5 mid-infrared counterparts of the HH objects detected in this work. Using the AllWISE Source Catalog and the source classification scheme suggested by Koenig et al., we have identified 56 young stellar object (YSO) candidates in the Vela C molecular cloud. The possible driving sources of the HH objects and EGOs are discussed based on the morphology of HH objects and EGOs and the locations of HH objects, EGOs and YSO candidates. Finally we associate 12 HH objects and five EGOs with 10 YSOs and YSO candidates. The median length of the outflows in Vela C is 0.35pc and the outflows seem to be oriented randomly.

Results of an objective prism Schmidt survey are combined with IRAS survey data in order to assess the star-forming activity in the Cepheus Flare, a nearby giant molecular cloud complex at ~+15° above the Galactic equator. The distribution of absorbing matter along the line of sight was also studied. The Wolf diagrams, displaying the cumulative distribution of field star distance moduli, show that the interstellar matter in this region is concentrated at three characteristic distances: 200, 300, and 450 pc. The three components, though partly overlapping, can be separated along the Galactic latitude. Within the area of the Cepheus Flare, distances are determined for 14 Lynds dark clouds and for some other clouds. In order to compile a sample of young stellar object (YSO) candidates, three types of star formation signposts were searched for the following: 1. Prestellar cores in the IRAS 100 μm optical depth image of the region, 2. Far-infrared sources representing embedded YSOs and optically visible pre-main-sequence star candidates using IRAS Point Source Catalog, Faint Source Catalog, and calibrated IRAS detector scans, 3. Hα emission stars appearing on low-dispersion objective prism Schmidt plates as candidate pre-main-sequence stars. The IRAS 100 μm optical depth image of the region revealed 107 dense cores. Most of them are probably starless cores and, as such, potential sites of future star formation. One hundred twenty-two IRAS point sources were selected as probable YSOs at various evolutionary stages. An objective prism search for Hα emission stars covering an area of about 150 deg2 resulted in the detection of 142 Hα emission stars. Infrared fluxes taken from the IRAS catalogs or determined from the detector scans are listed for 95 of them. This sample is expected to consist of mostly T Tauri stars associated with the cloud complex. Finding charts and catalogs of the young stellar object candidates are also given. These results may serve as a basis for further dedicated studies of the region and will be useful for comparison when star-forming activity in other cloud complexes is investigated.

We present analysis of the energetic star-forming region Henize 206 (N206) located near the southern edge of the Large Magellanic Cloud (LMC) based on photometric data from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE-LMC; IRAC 3.6, 4.5, 5.8, 8.0 μm and MIPS 24 μm), Infrared Survey Facility near-infrared survey (J, H, Ks), and the Magellanic Clouds Photometric Survey (MCPS UBVI) covering a wavelength range of 0.36–24 μm. Young stellar object (YSO) candidates are identified based upon their location in infrared color–magnitude space and classified by the shapes of their spectral energy distributions in comparison with a pre-computed grid of YSO models. We identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks. Careful examination of the individual sources and their surrounding environment allows us to identify a factor of ∼14.5 more YSO candidates than have already been identified. The total mass of these well-fit YSO candidates is ∼520 M☉. We calculate a current star formation rate of 0.27 × 10−1 M☉ yr−1 kpc−2. The distribution of YSO candidates appears to follow shells of neutral material in the interstellar medium.

Context.TheGaiathird Data Release (DR3) presents the first catalogue of full-sky variable young stellar object (YSO) candidates observed by theGaiaspace telescope during the initial 34 months of science operations.Aims.Numerous types of variable stars were classified using photometric data collected byGaia. One of the new classes presented in theGaiaDR3 is the class of YSOs showing brightness variability. We analysed 79 375 sources classified as YSO candidates in order to validate their young nature and investigate the completeness and purity of the sample.Methods.We cross-matched theGaiaDR3 YSO sample with numerous catalogues from the literature, including YSO catalogues based on optical and infrared data, as well as catalogues of extragalactic sources and Galactic variable stars. YSO catalogues were used to quantify the completeness of theGaiaDR3 YSO sample, while others were inspected to calculate the contamination.Results.Among the 79 375 potential YSO candidates published in theGaiaDR3 variable star catalogue, the majority of these objects are distributed along the line of sight of well-known star forming regions and the Galactic midplane. We find that the upper limit of contamination is 26.7%, depending on the external catalogue used for the estimation, but find an average of ∼10% in general, while the completeness is at the percent level, taking into account that theGaiaDR3 YSO sample is based on sources that showed significant variability during the data-collection period. The number of sources in our sample that had not previously been catalogued as YSO candidates is ∼40 000 objects.

Context. Accretion rates from protoplanetary discs onto forming stars are a key ingredient in star formation and protoplanetary disc evolution. Extensive efforts surveying different individual star-forming regions with spectroscopy and narrow-band photometry have been made to derive accretion rates on large populations of young stellar objects (YSOs). Aims. We use Gaia DR3 XP spectra to perform the first all-sky homogeneous analysis of YSO accretion properties within 500 pc. Methods. We characterise the H line emission of YSOs within 500 pc by using the H pseudo-equivalent widths and XP spectra provided by Gaia DR3. We derive accretion luminosities and mass accretion rates, together with stellar parameters, for 145 975 all-sky candidate YSO H emitters. We describe filtering strategies to select specific sub-samples of YSOs from this catalogue. Results. We identify a large population of low-accreting YSO candidates untraced by previous accretion rates surveys. We find previous surveys have mostly focused on YSO populations with significant infrared excess from disc emission. The population of low-accreting YSOs is mostly spatially dispersed, away from star-forming regions or the more clustered environments of star formation. Many YSOs appear entirely disconnected from young populations, and they are reminiscent of the long-lived ‘Peter Pan’ YSOs. We find L acc ∝ L ⋆ 1.41 ± 0.02 and Ṁ acc ∝ M ⋆ 2.4 ± 0.1 for the purest all-sky sample of YSO candidates. By fitting an exponential function to the fraction of accreting stars in clusters of different ages in the Sco-Cen complex, we obtain an accretion timescale of τ acc = 2.7 ± 0.4 Myr. The percentage of accretors found by fitting a power law function is 70% at 2 Myr and 2.8% at 10 Myr. Conclusions. With this new catalogue of H emitters, we significantly increase the number of YSO candidates with accretion rate estimations in the local neighbourhood. This allows us to study accretion timescales and the spatial and physical properties of YSO accretion from a large, all-sky, and homogeneous sample for the first time.

We present a catalog of 1439 young stellar objects (YSOs) spanning the 1.42 deg^2 field surveyed by the Chandra Carina Complex Project (CCCP), which includes the major ionizing clusters and the most active sites of ongoing star formation within the Great Nebula in Carina. Candidate YSOs were identified via infrared (IR) excess emission from dusty circumstellar disks and envelopes, using data from the Spitzer Space Telescope Vela--Carina survey and the Two-Micron All Sky Survey. We model the 1--24 /mu m IR spectral energy distributions of the YSOs to constrain physical properties. Our Pan-Carina YSO Catalog (PCYC) is dominated by intermediate-mass (2 Msun < m < 10 Msun) objects with disks, including Herbig Ae/Be stars and their less evolved progenitors. The PCYC provides a valuable complementary dataset to the CCCP X-ray source catalogs, identifying 1029 YSOs in Carina with no X-ray detection. We also catalog 410 YSOs with X-ray counterparts, including 62 candidate protostars. Candidate protostars with X-ray detections tend to be more evolved than those without. In most cases, X-ray emission apparently originating from intermediate-mass, disk-dominated YSOs is consistent with the presence of low-mass companions, but we also find that X-ray emission correlates with cooler stellar photospheres and higher disk masses. We suggest that intermediate-mass YSOs produce X-rays during their early pre-main sequence evolution, perhaps driven by magnetic dynamo activity during the convective atmosphere phase, but this emission dies off as the stars approach the main sequence. Extrapolating over the stellar initial mass function scaled to the PCYC population, we predict a total population of >2x10^4 YSOs and a present-day star formation rate (SFR) of >0.008 Msun/yr. The global SFR in the Carina Nebula, averaged over the past ~5 Myr, has been approximately constant.

As a part of the Milky Way Imaging Scroll Painting (MWISP) survey, we performed a simultaneous 12CO(1-0), 13CO(1-0), C18O(1-0) mapping toward molecular clouds in a region encompassing 3.75 square degrees. We reveal three molecular clouds, the 15 km/s cloud, the 27 km/s cloud, and the 50 km/s cloud, in the surveyed region. The 50 km/s cloud is resolved with an angular resolution of around 1' for the first time. Investigating their morphology and velocity structures, we find that the 27 km/s cloud is likely affected by feedback from the stellar association Mon OB3 and the 50 km/s cloud is characterised by three large expanding molecular shells. The region is mapped in C18O (1-0) for the first time. We discover seven C18O clumps, which are likely to form massive stars, and 15 dust clumps based on the BGPS archival data. Using infrared color-color diagrams, we find 56 Class I and 107 Class II young stellar object (YSO) candidates. According to the distribution of YSO candidates, an overdensity is found around the HII region S287 and the intersection of two shells, indicative of triggering. The star formation efficiency and rate of the 27~km/s cloud are discussed. Comparing the observed values of the filament S287-main with the models of fragmentation, we suggest that turbulence controls the large scale of fragmentation in the filament while gravitational fragmentation plays an important role in the formation of YSOs on the small scale. We find that star-forming gas tends to have higher excitation temperature, higher 13CO opacity, and higher column density than non-star-forming gas, which is consistent with the point that star formation happens in denser gas and star-forming gas is heated by YSOs. Using the 1.1 mm dust emission to trace dense gas, we obtain a dense gas fraction of 2.7%-10.4% for the 27 km/s cloud.