Near-Infrared H 2 and Continuum Survey of Extended Green Objects. II. Complete Census for the Northern Galactic Plane (original) (raw)
Related papers
2009
We present the results of a high angular resolution Very Large Array (VLA) Class I 44 GHz and Class II 6.7 GHz CH 3 OH maser survey of a sample of ∼20 massive young stellar object (MYSO) outflow candidates selected on the basis of extended 4.5 µm emission in Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) images. These 4.5 µm-selected candidates are referred to as extended green objects (EGOs), for the common coding of this band as green in three-color IRAC images. The detection rate of 6.7 GHz Class II CH 3 OH masers, which are associated exclusively with massive YSOs, towards EGOs is 64%-nearly double the detection rate of surveys using other MYSO selection criteria. The detection rate of Class I 44 GHz CH 3 OH masers, which trace molecular outflows, is ∼89% towards EGOs associated with 6.7 GHz CH 3 OH masers. The two types of CH 3 OH masers exhibit different spatial distributions: 6.7 GHz masers are centrally concentrated and usually coincide with 24 µm emission, while 44 GHz masers are widely distributed and generally trace diffuse 4.5 µm features. We also present results of a complementary James Clerk Maxwell Telescope (JCMT) single-pointing molecular line survey of EGOs in the outflow tracers HCO + (3-2) and SiO(5-4). The HCO + line profiles and high SiO detection rate (90%) are indicative of the presence of active outflows. No 44 GHz continuum emission is detected at the 5 mJy beam −1 (5σ) level towards 95% of EGOs surveyed, excluding bright ultracompact H II regions as powering sources for the 4.5 µm outflows. The results of our surveys constitute strong evidence that EGOs are young, massive YSOs, with active outflows, presumably powered by ongoing accretion.
ON THE RELATIONSHIP OF UC H ii REGIONS AND CLASS II METHANOL MASERS. I. SOURCE CATALOGS
The Astrophysical Journal
We conducted VLA C-configuration observations to measure positions and luminosities of Galactic Class II 6.7 GHz methanol masers and their associated ultra-compact H II regions. The spectral resolution was 3.90625 kHz and the continuum sensitivity reached 45 µJy beam −1. We mapped 372 methanol masers with peak flux densities of more than 2 Jy selected from the literature, 367 of them were detected. Absolute positions have nominal uncertainties of 0.3. In this first paper on the data analysis, we present three catalogs, the first gives information on the strongest feature of 367 methanol maser sources, and the second on all detected maser spots. The third catalog present derived data of the 279 radio continuum sources found in the vicinity of maser sources. Among them, 140 show evidence of physical association with maser sources. Our catalogs list properties including distance, flux density, radial velocity and the distribution of masers on the Galactic plane is then provided as well. We found no significant relationship between luminosities of masers and their associated radio continuum counterparts.
Search for class I methanol maser emission in various types of objects in the interstellar medium
Astronomy Reports, 2011
Observations of various types of objects in the northern sky were obtained at 44 GHz in the 7 0 −6 1 A + methanol line on the 20-m Onsala radio telescope (Sweden), in order to search for Class I methanol maser emission in the interstellar medium: regions of formation of high-mass stars, dust rings around HII regions, and protostellar candidates associated with powerful molecular outflows and Galactic HII regions. Seven new Class I methanol masers have been discovered toward regions of formation of highmass stars, and the existence of two previously observed masers confirmed. The following conclusions are drawn: (1) neither the association of a bipolar outflow manifest in the wings of CO lines with a highmass protostellar object (HMPO) nor the presence of thermal emission in lines of complex molecules are sufficient conditions for the detection of Class I methanol emission; no association with HMPOs radiating at 44 GHz was found for EGOs (a new class of object tracing bipolar outflows); (2) the existence of H 2 O masers and Class II methanol masers in the region of a HMPO enhances the probability of detecting Class I methanol emission toward the HMPO; Class II methanol masers with stronger line fluxes are associated with Class I methanol masers.
The outflow from the class 0 protostar HH 25MMS: methanol enhancement in a well-collimated flow
Monthly Notices of the Royal Astronomical Society, 1998
We present millimetre and submillimetre observations of HH 25MMS made with the James Clerk Maxwell Telescope (JCMT). From greybody fits to the continuum data we can confirm that HH 25MMS is a class 0 source, with a bolometric luminosity of ϳ6L ᭪ and T bol ¼ 34 Ϯ 2 K. The ratio of submillimetre-to-bolometric luminosity is ϳ0.05, more than 10 times higher than the defining value specified by André, Ward-Thompson & Barsony.
Near-Infrared H 2 and Continuum Survey of Extended Green Objects
The Astrophysical Journal Supplement Series, 2012
The Spitzer GLIMPSE survey has revealed a number of "Extended Green Objects" (EGOs) that display extended emission at 4.5 μm. These EGOs are potential candidates for high-mass protostellar outflows. We used high-resolution (<1 ) H 2 1-0 S(1) line, K-, and H-band images from the United Kingdom Infrared Telescope to study 34 EGOs to investigate their nature. We found that 12 EGOs exhibit H 2 outflows (two with chains of H 2 knotty structures, five with extended H 2 bipolar structures, three with extended H 2 lobes, and two with pairs of H 2 knots). Of the 12 EGOs with H 2 outflows, three exhibit similar morphologies between the 4.5 μm and H 2 emission. However, the remaining nine EGOs show that the H 2 features are more extended than the continuum features, and the H 2 emission is seldom associated with continuum emission. Furthermore, the morphologies of the near-infrared continuum and 4.5 μm emission are similar to each other for those EGOs with K-band emission, implying that at least part of the IRAC-band continuum emission of EGOs comes from scattered light from the embedded young stellar objects.
A general catalogue of molecular hydrogen emission-line objects (MHOs) in outflows from young stars
Astronomy and Astrophysics, 2010
We present a catalogue of Molecular Hydrogen emission-line Objects (MHOs) in outflows from young stars, most of which are deeply embedded. All objects are identified in the near-infrared lines of molecular hydrogen, all reside in the Milky Way, and all are associated with jets or molecular outflows. Objects in both low and high-mass star forming regions are included. This catalogue complements the existing database of Herbig-Haro objects; indeed, for completeness, HH objects that are detected in H 2 emission are included in the MHO catalogue.
Observational Studies on the Near-Infrared Unidentified Emission Bands in Galactic H II Regions
The Astrophysical Journal, 2014
Using a large collection of near-infrared spectra (2.5-5.4 µm) of Galactic H II regions and H II region-like objects, we perform a systematic investigation of the astronomical polycyclic aromatic hydrocarbon (PAH) features. 36 objects were observed by the use of the infrared camera onboard the AKARI satellite as a part of a directer's time program. In addition to the well-known 3.3-3.6 µm features, most spectra show a relatively-weak emission feature at 5.22 µm with sufficient signal-to-noise ratios, which we identify as the PAH 5.25 µm band previously reported. By careful analysis, we find good correlations between the 5.25 µm band and both the aromatic hydrocarbon feature at 3.3 µm and the aliphatic ones at around 3.4-3.6 µm. The present results give us convincing evidence that the astronomical 5.25 µm band is associated with C-H vibrations as suggested by previous studies and show its potential to probe the PAH size distribution. The analysis also shows that the aliphatic to aromatic ratio of I 3.4−3.6 µm /I 3.3 µm decreases against the ratio of the 3.7 µm continuum intensity to the 3.3 µm band, I cont,3.7 µm /I 3.3 µm , which is an indicator of the ionization fraction of PAHs. The mid-infrared color of I 9 µm /I 18 µm also declines steeply against the ratio of the hydrogen recombination line Brα at 4.05 µm to the 3.3 µm band, I Brα /I 3.3 µm. These facts indicate possible dust processing inside or at the boundary of ionized gas.
Far-Infrared Spectroscopy of the HH 1/2 Outflow
The Astronomical Journal, 2002
The HH 1/2 system has been observed with the two spectrometers on board the Infrared Space Observatory. Diffuse [Cii]158µm emission indicate the presence of a Photo-Dissociation Region (PDR) which is only in part due to the external Far-UV irradiation from the nearby Orion Nebula. Additional irradiation must be originated locally and we show that the FUV field produced in the recombination regions behind the shocks traced by the HH objects is sufficient to induce a PDR at the flow cavity walls.