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A multiwavelength study of the massive star-forming region IRAS 06055+2039 (RAFGL 5179)
Aims.We present a multiwavelength study of the massive star-formingregion associated with IRAS 06055+2039. Methods: .Narrow-bandnear-infrared (NIR) observations were carried out with UKIRT-UFTI inmolecular hydrogen and Brγ lines to trace the shocked and ionizedgases, respectively. We have used 2MASS {J H K}s data tostudy the nature of the embedded cluster associated with IRAS06055+2039. The radio emission from the ionized gas was mapped at 610and 1280 MHz using the Giant Metrewave Radio Telescope (GMRT), India.Emission from warm dust and the unidentified infrared bands (UIBs) wasestimated using the mid-infrared (8-21 μm) data from the MSX survey.Submillimetre emission from the cold dust at 450 and 850 μm wasstudied using JCMT-SCUBA. Results: .For the infrared clusterassociated with IRAS 06055+2039, we obtain a power-law slope of0.43±0.09 for the K_s-band luminosity function (KLF), which is ingood agreement with other young embedded clusters. We estimate an age of2-3 Myr for this cluster. Apart from the diffuse emission, thehigh-resolution 1280 MHz map also shows the presence of several discretesources that possibly represent high-density clumps. The morphology ofshocked molecular hydrogen forms an arc towards the N-E of the centralIRAS point source and envelopes the radio emission. Submillimetreemission shows the presence of a dense cloud core that is probably at anearlier evolutionary stage compared to the ionized region with shockedmolecular gas lying between the two. The total mass of the cloud isestimated to be 7000-9000 Mȯ from the submillimetreemission at 450 and 850 μm. Conclusions: .The multiwavelengthstudy of this star-forming complex reveals an interesting scenario whereregions are at different stages in the evolution of star formation.
| Abundance Gradients in the Galaxy
Six H II regions at galactocentric distances of R=10-15 kpc have beenobserved in the far-IR emission lines of [O III] (52 μm, 88 μm),[N III] (57 μm), and [S III] (19 μm) using the Kuiper AirborneObservatory. These observations have been combined with Very Large Arrayradio continuum observations of these sources to determine theabundances of O++, N++, and S++relative to hydrogen. In addition, eight of the most recent sets ofmeasurements of ionic line strengths in H II regions have beenreanalyzed in order to attempt to reconcile differences in opticalversus far-IR abundance determinations. We have in total 168 sets ofobservations of 117 H II regions in our analysis. The new analysisincluded updating the atomic constants (transition probabilities andcollision cross sections), recalculation of some of the physicalconditions in the H II regions (ne and Te), andthe use of new photoionization models to determine stellar effectivetemperatures of the exciting stars. We also use the most recent dataavailable for the distances for these objects, although for most westill rely on kinematic distance determinations. Our analysis findslittle indication of differences between optical and infraredobservations of the nitrogen abundances, but some differences are seenin the oxygen and sulfur abundances. A very significant offset continuesto be seen between optical and infrared measurements of the N/Oabundance ratio.
| New infrared star clusters in the Northern and Equatorial Milky Way with 2MASS
We carried out a survey of infrared star clusters and stellar groups onthe 2MASS J, H and Ks all-sky release Atlas in the Northernand Equatorial Milky Way (350deg < l < 360deg, 0deg < l < 230 deg). Thesearch in this zone complements that in the Southern Milky Way (Dutra etal. \cite{Dutra03}a). The method concentrates efforts on the directionsof known optical and radio nebulae. The present study provides 167 newinfrared clusters, stellar groups and candidates. Combining the twostudies for the whole Milky Way, 346 infrared clusters, stellar groupsand candidates were discovered, whereas 315 objects were previouslyknown. They constitute an important new sample for future detailedstudies.
| Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/399/141
| The impact of mass loss on star cluster formation - I. Analytical results
We study analytically the disruptive effect of instantaneous gas removalfrom a cluster containing O stars. We set up an iterative calculationbased on the stellar velocity distribution function to compute thefraction of stars that remain bound once the cluster has ejected the gasand is out of equilibrium. We show that the stellar bound fraction is afunction of the initial cluster distribution function as well as thestar-formation efficiency, ɛ, taken constant throughout thecluster. The case of the Plummer sphere is dealt with in greater detail,where we find that up to ~=50 per cent of the stars may remain boundwhen ɛ assumes values <1/2, contrary to expectations derivedfrom the virial theorem. The fraction of bound stars is expressedalgebraically for polytropic distribution functions.
| Embedded Clusters in Molecular Clouds
Stellar clusters are born embedded within giant molecular clouds (GMCs)and during their formation and early evolution are often only visible atinfrared wavelengths, being heavily obscured by dust. Over the past 15years advances in infrared detection capabilities have enabled the firstsystematic studies of embedded clusters in galactic molecular clouds. Inthis article we review the current state of empirical knowledgeconcerning these extremely young protocluster systems. From a survey ofthe literature we compile the first extensive catalog of galacticembedded clusters. We use the catalog to construct the mass function andestimate the birthrate for embedded clusters within 2 kpc of the sun. Wefind that the embedded cluster birthrate exceeds that of visible openclusters by an order of magnitude or more indicating a high infantmortality rate for protocluster systems. Less than 4-7% of embeddedclusters survive emergence from molecular clouds to become boundclusters of Pleiades age. The vast majority (90%) of stars that form inembedded clusters form in rich clusters of 100 or more members withmasses in excess of 50 Mȯ. Moreover, observations ofnearby cloud complexes indicate that embedded clusters account for asignificant (70-90%) fraction of all stars formed in GMCs. We review therole of embedded clusters in investigating the nature of the initialmass function (IMF) that, in one nearby example, has been measured overthe entire range of stellar and substellar mass, from OB stars tosubstellar objects near the deuterium burning limit. We also review therole embedded clusters play in the investigation of circumstellar diskevolution and the important constraints they provide for understandingthe origin of planetary systems. Finally, we discuss current ideasconcerning the origin and dynamical evolution of embedded clusters andthe implications for the formation of bound open clusters.
| Deep Near-Infrared Survey toward the M17 Region
We conducted a deep JHKs-band imaging survey of the M17region, using a near-infrared camera, the Simultaneous 3-color InfraRedImager for Unbiased Survey (SIRIUS), mounted on the InfraRed SurveyFacility (IRSF) 1.4 m telescope at the South African AstronomicalObservatory. This survey covers an area of ~200 arcmin2 with10 σ limiting magnitudes of J~18.7, H~18.2, andKs~17.5. The near-infrared (NIR) images reveal anunprecedented view of the region. The NIR nebulae are highly structured,with two nebular bars corresponding to, but a little larger than, the HII region defined by Felli, Massi, & Churchwell, constructing aconical shape. Fine structures are found all over the nebular area. Thecentral region contains a congregation of intermediate- to high-massstars. From the slope of the Ks-band luminosity function andthe frequency of young stellar objects (YSOs) we infer that the centralcluster has an age less than 3 Myr. The central OB cluster providestremendous energy that heats and ionizes its surrounding materials,triggering the star formation of second-generation in the nebular bars.The second generation stars are so numerous that could they affect thestar formation efficiency in the whole region. To the southwest of thecentral cluster and the nebular bars, where a giant molecular cloud coreis located, a large number of red stars are detected. We argue thatthese red stars are most probably associated YSOs with intrinsic colorexcesses, not normal field stars reddened by the molecular cloud infront of them. Being located beyond the photodissociation region, thestar-forming process in the molecular region could be independent of theimpact of the central cluster.
| Protogalactic Starbursts at High Redshift
We have computed the evolving ultraviolet-millimeter spectral energydistribution (SED) produced by protogalactic starbursts at highredshift, incorporating the chemical evolution of the interstellarmedium in a consistent manner. Dust extinction is calculated in a novelway that is not based on empirical calibrations of extinction curves,but rather on the lifetime of molecular clouds which delays theemergence of each successive generation of stars at ultravioletwavelengths by typically 15 Myr. The predicted rest-framefar-infrared-to-millimeter-wave emission includes the calculation ofmolecular emission-line luminosities (12CO and O2among other molecules) consistent with the evolving chemical abundances.Here we present details of this new model along with the results ofcomparing its predictions with several high-redshift observables,namely, the ultraviolet SEDs of Lyman limit galaxies, the high-redshiftradio galaxies 4C 41.17 and 8C 1435, the SCUBA submillimeter survey ofthe Hubble Deep Field (HDF), and the SEDs of intermediate-redshiftelliptical galaxies. With our new reddening method, we are able to fitthe spectrum of the Lyman limit galaxy 1512-cB58, and we find anextinction of about 1.9 mag at 1600 Å. This extinction applies tostarbursts with spectral slope α in the range0<~α<~1.5. The model also predicts that most Lyman limitgalaxies should have a value of α inside that range, as isobserved. The 850 μm flux density of a typical Lyman limit galaxy isexpected to be only ~=0.5 mJy, and therefore the optical counterparts ofthe most luminous submillimeter sources in the HDF (or any othercurrently feasible submillimeter survey) are unlikely to be Lyman breakgalaxies. The passive evolution of our starburst model is also comparedwith Keck observations of the reddest known elliptical galaxy at z~1.5and with the SED of a typical nearby elliptical galaxy. The SED of thehigh-redshift elliptical is nicely matched by the starburst model withan age of 4 Gyr and the SED of the nearby elliptical galaxy with an ageof 13 Gyr.
| SH 138: a compact H II region excited by a very young cluster region excited by a very young cluster
We present a photometric and spectroscopic study of the compact H iiregion Sh 138 and its associated stellar cluster. The positions andBVRIJHK magnitudes are obtained for more than 400 stars over a field ofabout 4arcmin square centred on the H ii region. Sh 138 is excited by acluster of young massive stars. At the cluster's very centre are atleast four O-B2 stars separated by less than 4arcsec . The brightest ofthese, both in the visible and the near infrared, exhibits a spectrumsimilar to those of the more massive Herbig Ae/Be stars. This star, ourNo. 183, is overluminous by a factor of 2.5 in the visible and four inthe near IR with respect to the O9.5 V star required to account for theionization level of the H ii region. However star 183's position in theJ - H versus H - K diagram does not indicate a near-IR excess. Wesuggest that this star is a young massive object belonging to a binaryor multiple system. The stellar cluster associated with Sh 138 is veryreminiscent of the Orion Trapezium cluster: it is centrally peakedaround several massive stars, and is dense - more than 550 stars pc(-2)at its centre. The visual extinction in the cluster varies between 5 magand more than 35 mag; large variations are observed over very smallscales (for example, more than 20 mag over less than 4arcsec among thecentral massive stars). Based on observations done at the Observatoirede Haute Provence and the Observatoire du Pic du Midi, France, and atthe Canada-France-Hawaii Telescope. The CFHT is operated by the CentreNational de la Recherche Scientifique of France, the National ResearchCouncil of Canada and the University of Hawaii. Table 1 is available inelectronic form at the CDS (via anonymous ftp to cdsarc.u-strasbg.fr orvia http://cdsweb.u-strasbg.fr/Abstract.html) as well as athttp://www-obs.cnrs-mrs.fr/matiere/sh138-t1.html.
| A Near-Infrared Imaging Survey of NGC 2282
We present the first near-infrared (JHK) imaging and photometry of ayoung cluster associated with NGC 2282, a reflection nebula inMonoceros. Our observations reveal that the cluster is centrallyconcentrated with a surface density that falls as r(-1) . The clusterhas a radius of roughly 1.6 pc and contains at least 100 members,approximately 9% of which exhibit infrared excess emissioncharacteristic of young stellar objects. Infrared extinction mapssuggest that the cluster is located at the edge of a molecular cloud andis not heavily reddened. We construct the K-band luminosity function(KLF) of the cluster and find that it increases with magnitude up to thecompleteness limit of our observations (mK = 15.0). The shapeof the KLF is similar to those of other young clusters, such as IC 348and the Trapezium, which suggest that the cluster contains a significantpopulation of pre-main sequence stars. However, at the distance of NGC2282 (1.7 kpc) our observations are not deep enough to sample the lowmass end of the cluster IMF\@. Consequently, our KLF does not providemeaningful constraints on either the age of the cluster or the durationof star formation within it. On the other hand, the low extinctiontoward the cluster, its location at the edge of a molecular cloud, andthe relatively small fraction of infrared excess sources suggest that itis a relatively evolved cluster of pre-main sequence stars with an ageof 5-10 x 10(6) years.
| The chemical composition of HII regions in the outer Galaxy
New spectroscopic observations, including the optical and near-infraredranges, have been obtained for a sample of HII regions located towardsthe Galactic anticentre. The sample includes HII regions with knowngalactocentric distances, their ionizing stars having been clearlyidentified from previous work. The spectra correspond tolow-to-intermediate excitation nebulae, ionized by one/few late O/earlyB star(s). The global parameters of the regions, as well as theirphysical parameters such as electron density and temperature, arepresented. Abundances have been computed using direct (spectroscopic)determinations of the electron temperature for some of the objects oralternatively assuming an adopted electron temperature derived fromphotoionization model fitting. Overall, the data appear to show asubstantially flat gradient for the nitrogen abundance, going up to 18kpc of galactocentric distance, as well as a mild gradient, if any, foroxygen. The data points for sulphur, although less numerous, giveabundances which are consistent with the behaviour observed for theother elements. The N/O ratio also presents a very flat gradient acrossthe outer Galaxy, with a value similar to the one derived fromobservations of optical emission lines of HII regions in the solarneighbourhood.
| IRAS sources beyond the solar circle. VI. Analysis of the FIR, H_2_O, and CO emission.
For a sample of 1357 IRAS sources with FIR colours of young stellarobjects we have compared the occurrence and properties of H_2_O maser-and ^12^CO(1-0) emission with the observed and derived IRAS parameters.We find that the distribution of differences between the CO and H_2_Ovelocities is a Gaussian with a FWHM of about 11km/s. The mean velocitydifference is nearly zero. The velocity of the peak H_2_O emission isnot at a preferred location within the velocity interval where emissionis detected. The H_2_O maser detection rate increases with both the FIRluminosity and the ^12^CO(1-0) line width: belowlog(L_FIR_/Lsun_)=3.5, less than 10% of the sources showmaser emission, whereas H_2_O is detected towards almost all of thesources above log(L_FIR_/Lsun_)=4.5. For the sources withH_2_O maser emission, the average CO line width (FWHM about 5.0km/s) isapproximately twice as large as for those without detected H_2_Oemission, an effect which is independent of the sources' FIR luminosity.However a significant fraction of sources with no detected H_2_Oemission still have line widths larger than 1.9km/s, the median valuefor the quiescent gas not associated with the IRAS sources. The maximumH_2_O maser luminosity at each FIR luminosity is proportional to L_FIR_:L_H_2_O_/Lsun_=10^-7.4^(L_FIR_/Lsun_). In IRAScolour-colour plots, sources can be distinguished in maser-like andnon-maser-like sources according to their CO line widths and FIRluminosity. At a given L_FIR_ the maximum T^*^_A_ found for ^12^CO(1-0)decreases with distance from the Sun, likely due to beam fillingeffects. Few sources with maser emission have T^*^_A_ below 7.5K, whenobserved with the IRAM 30-m telescope. There is no difference in themaximum T^*^_A_ of sources with maser-like and non-maser-like IRAScolours. We have derived the intrinsic luminosity- and mass distributionof sources with (non)-maser-like IRAS colours, correcting forincompleteness effects at lower luminosities. The slope of the IMF forsources with maser-like colours and mass larger than 10Msun_is found to be -2.8+/-0.3.
| An IRAS Survey of H II Regions
Abstract image available at:http://adsabs.harvard.edu/abs/1995AJ....109.2611C
| Galactocentric Distance Dependence of Molecular Cloud Core Density
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| The distance of the sun from the Galactic Center and the rotation curve from kinematic HI and HII data.
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| A VLA survey of optically visible galactic H II regions
Radio continuum observations of 109 optically visible Galactic H IIregions were obtained with the Very Large Array. Contour plots of theimages of those that were well resolved and tables of radio continuumflux density for all detected objects are presented. The measured totalflux densities matched well with the results of single-dish surveys, andthus it is expected that the problem of missing 'zero-spacing flux' hasnot contributed greatly to the morphologies seen in the resultingimages. The relative numbers of objects of each morphological type werevery similar to the numbers seen in the survey of ultracompact H IIregions by Wood and Churchwell (1989) even though the objects in thisnew survey are on average 50 times larger (in radius) and thereforepresumably more evolved.
| Abundances in H II regions at the edge of the Galaxy
Optical spectra, supplemented by some observations of radiorecombination lines, have been used to estimate the abundances ofhelium, oxygen, nitrogen, sulfur, and argon in 18 H II regions in theouter Galaxy. Assuming that R0 (the distance from the center of theGalaxy to the sun) is 8.5 kpc, these H II regions are located between11.5 and 17.9 kpc from the Galactic center and include many of the mostdistant (from the center) H II regions known in our Galaxy. The singlemost striking result of these observations is the apparent high nitrogenabundances in the H II regions at the outer edge of the visible disk ofthe Galaxy.
| Fabry-Perot H-alpha observations of Galactic H II regions
The radial velocity and linewidth of H-alpha emission from 284 objectslisted in Galactic H II region catalogs were observed using aFabry-Perot spectrometer. A few of these objects are supernova remnantsor planetary nebula. The rest of this sample encompasses most of the HII regions that are visible optically from the Northern Hemisphere.These observations are compared to previous H-alpha observations as wellas to radio recombination line and CO observations. The averageradial-velocity difference V(CO) - V(H-alpha) is 0.50 + or - 0.48 km/sand the (1-sigma) dispersion is 6.44 km/s. The implications of thesevalues are discussed in terms of a very simple kinematic and extinctionH II region model. Total H-alpha luminosities for the sample areestimated, and the Galactic H II region luminosity function is comparedto that recently found for other galaxies.
| The rotation curve of the Milky Way to 2 R(0)
A unified analysis of the Galactic rotation curve is presented using H ICO, and spectrophotometric data obtained in the northern hemisphere areused to determine the rotation curve from R = 3-17 kpc. A number ofdifferent functional forms are examined to fit the data, and the errorsand uncertainties that go into its determination are discussed. Theresults are compared with nine recent studies of the rotation curve, andspecific recommendations are made on the choice of curves to use inkinematic studies and mass modeling.
| Star formation in the outer Galaxy
Results are reported from a search for H2O and OH maser emission towardIRAS point sources near H II regions at galactocentric distances Rgreater than 14 kpc. Data obtained during 1985-1986 at 22 and 1.665 GHzwith the 100-m Effelsberg radio telescope, in the 6-cm continuum withthe D configuration of the VLA, and in the 115-271-GHz line of CO withthe 30-m IRAM telescope are presented in extensive tables and graphs andcharacterized in detail. A total of 25 H2O masers (15 in the outerGalaxy and 10 nearer the solar circle) and two OH masers (one in eachregion) were detected. The FIR luminosity distribution and the numberdensity (per H II region) of sources with IR luminosity greater than10,000 solar luminosities are found to be like those in the Per arm,while star formation per mass of H2 is like that near the sun. Thepresence of molecular outflows at R = 20 kpc is inferred from weak wingemission toward masers in S 270 and S 209.
| One-millimeter continuum observations of IRAS and FIRSSE sources
New 1 mm observations of galactic and extragalactic objects partlycontained in the FIRSSE and IRAS surveys are reported. Dusttemperatures, FIR wavelength dependence of dust opacity, and FIRluminosities of the observed sources are derived.
| Optical H II regions in the outer galaxy
The results of the CO survey of optical H II regions of Blitz, Fich, andStark (1982) are used to obtain the distribution of H II regions andtheir associated molecular clouds beyond the solar circle. H II regionsare observed in the Milky Way to distances as large as R = 20 kpc, butthere are very few beyond this distance. This limiting distance does notappear to be the result of extinction and appears to be the approximateedge of the stellar disk of the Galaxy. The scale height of H II regionsat 10 kpc is about 100 pc as measured by the z distance dispersion, butthere is considerable variation in this quantity. The smallest scaleheights appear to be related to the major spiral arms. Beyond 12 kpc theH II regions follow the warp of the H I plane. H II regions are smalleron average at large R and few very large H II regions are observedbeyond 12 kpc.
| The galactic abundance gradient
Chemical abundances in a large and representative sample of galactic HII regions covering a wide range in galactocentric radius RGwere measured using radio and optical spectroscopy. Accurate electrontemperatures in 67 H II regions spanning the range RG =3.5-13.7 kpc were determined using radio recombination lines and thesetemperatures were applied to optical spectra of 33 of the same H IIregions in order to determine the abundances of O, N, S, Ne, Ar, andHe(+). Among other results, it is found that some H II regions haveelectron temperatures below 5000 K and that the radio-determinedelectron temperatures agree well with those obtained from the opticalline ratios, in the light of standard models of H II regions. A gradientof H II region electron temperature with distance from the galacticcenter is found which equals +433 + or - 40 K/kpc, while the oxygenabundance gradient is -0.07 + or - 0.015 dex/kpc. The nitrogen abundancegradient is similar to that of oxygen, -0.09 + or 0.015 dex/kpc, whilethe sulfur abundance gradient (-0.01 + or - 0.02 dex/kpc) issignificantly flatter than that of oxygen. No significant gradient inHe(+)/H(+) is detected. In addition, evidence indicates that theabundance gradients may be steeper over the inner regions of thegalactic disk.
| Catalog of CO radial velocities toward galactic H II regions
This is a catalog of 242 molecular cloud complexes which are associatedwith optical H II regions. CO observations were made toward all but fiveof the H II regions in the Sharpless catalog and toward 62 additionalsuspected H II regions, 33 of which are previously uncataloged. Radialvelocities are tabulated for each molecular cloud complex found to beassociated with an H II region. The CO antenna temperature and linewidth are given for the most intense CO line seen toward each source.The catalog also summarizes previous CO observations as well as theoptical distances to the stars exciting the H II regions. Radio-quiet HII regions (those with 1.4 GHz flux densities less than 100 mJy) arefound to be well correlated with objects having no associated CO. A listof kinematically distinct complexes is tabulated to facilitateinvestigations of the motions of the complexes.
| Untersuchungen über Reflexionsnebel am Palomar Sky Survey I. Verzeichnis von Reflexionsnebeln
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| TThe source of luminosity in galactic nebulae.
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| The color of the nebulous stars.
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