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A Sensitive Survey for Water Maser Emission Toward Bok Globules Using the Robledo 70 m Antenna
We report on the most sensitive water maser survey toward Bok globulesto date, performed using NASA's 70 m antenna at Robledo de Chavela(Spain). We observed 207 positions within the Clemens and Barvainiscatalog with a higher probability of harboring a young star, using asselection criteria the presence of radio continuum emission (fromsubmillimeter to centimeter wavelengths), geometric centers of molecularoutflows, peaks in maps of high-density gas tracers (NH3 orCS), and IRAS point sources. We have obtained seven maser detections,six of which (in CB 34, CB 54, CB 65, CB 101, CB 199, and CB 232) arereported for the first time here. Most of the water masers we detectedare likely to be associated with young stellar objects (YSOs), exceptfor CB 101 (probably an evolved object) and CB 65 (uncertain nature).The water maser in CB 199 shows a relatively high shift (~=30 kms-1) of its velocity centroid with respect to the cloudvelocity, which is unusual for low-mass YSOs. We speculate thathigh-velocity masers in this kind of object could be related to episodesof energetic mass loss in close binaries. Alternatively, the maser in CB199 could be pumped by a protoplanetary or a young planetary nebula. CB232 is the smallest Bok globule (~=0.6 pc) known to be associated withwater maser emission, although it would be superseded by the cases of CB65 (~=0.3 pc) and CB 199 (~=0.5 pc) if their association with YSOs isconfirmed. All our selection criteria have statistically compatibledetection rates, except for IRAS sources, which tend to be somewhatworse predictors for the presence of maser emission.
| The small scale distribution of interstellar dust from studies of obscured galaxies
We have selected four galaxies lying behind Galactic molecular clouds inorder to probe the small scale structure of the latter. Using broad-band(B, V, R, and I) CCD images, we searched for surface brightnessfluctuations which might be attributable to spatial structure in theforeground extinction. Towards the three galaxies occulted by localclouds, we fail to detect such variations: from the lack of``granularity'' and/or high degree of symmetry displayed by brightnessprofiles, upper limits on delta A_V/A_V as low as 5% are inferred forscales of about 0.002 pc (400 AU). In front of Maffei 1, the extinctionis also smooth even if significant fluctuations are seen in addition toa prominent fragment, presumably located at 3.3 kpc in the Perseus arm.12CO and 13CO (J = 1-0 and 2-1) observations ofthese four quiescent clouds have been made using the 30 m IRAM telescopein order to perform a correlated study of these tracers and dust. Inagreement with previous studies, 12CO and 13COemission appear to display a much higher degree of variability at smallspatial scales than dust extinction. Our study reveals no evidence forubiquitous fragments with size l > 400 AU in the distribution of dustgrains and confirms that the good correlation seen between extinctionand CO and 13CO emission on large scales no longer holds atsmall scales. The local dust-to-gas ratio is then likely to vary locallywhich may in turn affect the physical and chemical evolution of the gas.We argue that the small scale structure in the density field (i.e.n({H}_2)) is neither traced accurately by minor molecules like CO,13CO or C18O (due e.g. to self-shielding andexcitation effects) nor by visible extinction (due to the inertia ofsolid particles). Therefore, direct observations of H_2 itself areneeded to decide whether or not a significant fraction of the mass isreally located within dense cells occupying a small part of the cloudvolume. Based on observations made at Observatoire de Haute Provence(France, operated by the CNRS), Observatoire du Pic du Midi, CFHT and atthe 30\,m IRAM telescope (Pico Veleta, Spain)
| Millimetre dust emission from northern BOK globules.
We present the results of a 1.3mm continuum study of 59 Bok globuleslocated north of -30° declination. The catalogue of Clemens &Barvainis (1988ApJS...68..257C) served as a search list for the targetobjects investigated here. Based on the analysis of the IRAS pointsource colour-colour diagram, four distinct groups of globules aredistinguished. It is shown that indeed each of these groups hasdistinctive properties and represents a different stage of starformation. For our observations, we selected a number of candidatepre-protostellar cores, all candidates for globules with protostellarcores, as well as a number of strong 12μm IRAS point sources whichare candidates for T Tauri stars associated with globules. Individualdistances of the globules are derived with a method which associates theglobules with larger molecular cloud complexes. It is shown that mostglobules are associated with such cloud complexes from which theyprobably formed. The derived distances range from 140pc to 2kpc with themajority of the globules being related to Gould's Belt at distances of200 to 300pc. The average distance of our sample of globules is derivedto be 500pc. Out of the 59 globule cores observed at 1.3mm, 21 objectswere detected with average 3σ detection limits of 17mJy/12" and39mJy/23". This corresponds to an overall detection rate of 35%. Whilemost of the detected objects are protostellar cores, fourpre-protostellar cores and one T Tauri star were detected furthermore.The typical mass of a star formed in a Bok globule is derived to be=~0.5Msun_. Using the detection rates and the relativefrequencies of the globule groups, lifetimes of the differentevolutionary stages are derived. Assuming that all globules form starsat some time of their evolution, the typical lifetime of a Bok globuleis derived to be some 10^6^years. It is speculated that the existence ofisolated T Tauri stars can be explained by star formation in Bokglobules. In addition, the results of the continuum measurements arecompared with observations of different molecular lines.
| Search and redshift survey for IRAS galaxies behind the Northern Milky Way
We made a search for IRAS galaxies behind the Northern Milky Way byinfrared selection using IRAS Point Source Catalog and visual inspectionon POSS (Palomar Observatory Sky Survey) paper prints, and carried out aredshift survey of the identified objects. This paper presents a catalogof 649 IRAS galaxies with f_60_>=0.6 Jy between l=150deg and 240degat |b|<=15deg , which contains 254 newly identified galaxies and 188newly measured radial velocities. Due to galactic extinction, our sampleis a lower limit sample of the flux limited sample of IRAS galaxies, butit can give some information on the distribution of galaxies in theregion perpendicular to the Supergalactic Plane. We confirm two regionswith enhanced density at l=~160deg , cz=~5000 km/s and l=~190deg ,cz=~5000 km/s and at least two possible voids.
| A search for IRAS galaxies behind the southern Milky Way
We systematically searched for IRAS galaxies with 60 micrometer fluxdensity larger than 0.6 Jy by using the UK Schmidt Infrared and IIIa-JAtlases in the Milky Way region (absolute value of b less than 15 deg)between l = 210 deg and 360 deg. We first selected about 4000 IRAS pointsources by using our far-infrared criteria, which are optimized for thesearch of IRAS galaxies behind the Milky Way region, and then inspectedvisually the optical counterparts of them on the Schmidt Atlas filmcopies. We found 966 IRAS sources associated with galaxy-like objects.The list of the objects is presented here with the IRAS source name,Galactic coordinates, IRAS flux densities, field number and emulsion ofthe Atlas, type and size of galaxy (-like) image, redshift,multiplicity, and cross-identification. Of these, 423 galaxies arealready cataloged in the Catalog of Galaxies and Quasars Observed in theIRAS Survey, and most of the remaining 543 galaxy candidates are newlyidentified in this search. Although the radial velocities are known foronly 387 galaxies, of which 60 were newly measured by us so far, weinferred the contamination by Galactic objects to be small from the goodcorrelation between the sky distributions of the newly identified galaxycandidates and the previously cataloged galaxies. In the regions wherethe Galactic molecular clouds dominate, almost all the sources were notidentified as galaxies. The detected galaxies are clustered in the threeregions around l = 240 deg, 280 deg, and 315 deg, where the projectednumber densities are higher than the whole-sky average of IRAS galaxiesof the same flux limit.
| A search for galaxies behind the Milky Way between L = 210 deg and 230 deg
A report is presented on a systematic galaxy search at an anticenterregion behind the Milky Way between l = 209 deg and 234 deg at b = 0 degcovering about 500 sq deg. The search is carried out by means of a studyof 18 film copies of the UK Schmidt Southern Infrared Atlas of theaforementioned region which were made at an effective wavelength of 790nm with a 190 nm bandwidth. A total of 2411 galaxies were detected; ofthese, 30 have been given in catalogs of galaxies, and 81 are IRASgalaxies. A catalog of the detected galaxies is made with respect toposition, size, galaxy type, and cross identification. It is found thatthe number of galaxies detected per sq deg, Ngal, decreases withincreasing column density of hydrogen atoms in the Galaxy, N(H I), as afunction of the galactic latitude ranging from 1 to 9 x 10 to the 21/cmsq. For a size-limited survey of galaxies with diameters larger than0.45 arcmin the relation log(Ngal/1.4) = -N(H I)/1.1 x 10 to the 22 =-0.57AiN(H I), where Ai is the Galactic extinction coefficient. Threecandidates for clusters of galaxies are found around b = 5 deg with asize of 3 deg.
| IRAS sources beyond the solar circle. I - CO observations
C-12O (J = 1-0) has been observed with the 15-m SEST and the 30-m IRAMtelescope in the direction of 1302 IRAS sources with colors of starforming regions located within 10 deg of the galactic plane in theinterval between 85 and 280 deg. Emission components with line profilesthat are non-Gaussian (showing, e.g., possible self-absorption or wings)are identified; this information may serve as a basis for selectingsources for future research. For all components, kinematic heliocentricand galactocentric distances, and distances from the galactic plane arederived. For those components which may be associated with the IRASsources, bolometric luminosities are derived. These data will beanalyzed and compared with HI data in subsequent papers.
| A catalog of small, optically selected molecular clouds - Optical, infrared, and millimeter properties
A catalog of small, optically selected molecular clouds is presented.The relevant selection criteria were small angular size, large centralopacity, and freedom from connecting opaque material. The meanellipticity of the clouds in the catalog is 2.0, with a maximumellipticity of 7. The position angle of the clouds is uncorrelated withthe direction of the Galactic plane. About 60 percent of the catalogedclouds have associated IRAS Point Source Catalog (PSC) sources in theircores or envelopes. The likelihood of a detection of a PSC source issome 6.1 times higher for the core regions of the clouds than for theenvelopes, indicating a strong association of FIR sources and Bokglobules. Of a sample of 97 of the clouds observed in the J = 2-1 lineof (C-12)O, 70 percent have cold gas kinetic temperatures andapproximately sonic line widths. The remaining 30 percent are aboutequally divided between those clouds likely to be radiatively heated bynearby stars and those undergoing active protostellar collapse oroutflows with no bulk gas heating.
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