High Galactic Latitude Molecular Clouds Research Articles

High‐Latitude Molecular Clouds in an HiFilament toward the MBM 53, 54, and 55 Complex: Existence of an H2Cloud with Low CO Intensity

We carried out a CO survey of high Galactic latitude molecular clouds toward an H I filament that contains a molecular cloud complex, MBM 53, 54, and 55, with the NANTEN telescope. Our observation covered the whole area of the H I filament in 12CO (J = 1-0) with a 4' grid spacing. The filament is found to consist of a number of clumpy molecular clouds, and we identified 110 12CO clouds in the region, whose total mass is estimated to be ~1200 M☉. 13CO (J = 1-0) observations were carried out toward the region of high 12CO intensities in order to measure the optical depth of molecular gas. There is no detection in C18O (J = 1-0) line in the observed region, indicating that there are no clouds dense enough to form stars in the near future. These observations spatially resolved the entire gas distribution of MBM 53, 54, and 55 for the first time, and we have found a massive cloud, HLCG 92-35, around (l, b) ~ (92°, -35°) whose mass is ~330 M☉, corresponding to ~1/4 of the total mass. This CO cloud occupies the Galactic western half of a circular H I cloud toward (l, b) = (935, -355), and the H I to CO mass ratio is estimated to be the largest in the observed region. The far-infrared excess over H I emission, which is a good indicator of an existence of molecular hydrogen, toward HLCG 92-35 is the largest in the observed region. The ratio of the luminosity of the infrared excess to CO mass is also significantly larger than those of the other clouds, by a factor of ~5. These facts indicate that HLCG 92-35 is a CO-forming molecular cloud, which is younger than the MBM clouds in terms of molecular cloud formation. Some past explosive event has been suggested toward the H I filament. Toward HLCG 92-35, the molecular gas distributed along the western edge of the H I cloud, which implies that the molecular gas may be formed by a compression of expanding H I shell.

A Survey for High-Latitude Molecular Clouds toward Infrared-Excess Clouds with NANTEN

Abstract A survey for high Galactic latitude molecular clouds was carried out toward the far-infrared-excess clouds of Reach et al. (1998, AAA 070.131.207) using the NANTEN telescope. All 68 infrared-excess clouds that are observable from NANTEN were mapped in the $J = 1 \hbox{--} 0$ line of 12CO. CO emission was detected from 32 infrared excess clouds, corresponding to a CO detection rate of 47%. Most of these CO clouds were identified and mapped as high-latitude clouds for the first time. The CO detection rate for the cold ($T_\mathrm{dust} \lt 17 \,\mathrm{K}$) infrared excess clouds is 72%, which is more than a factor of two higher than that of warmer ones, 33%. This indicates that the cold clouds are well shielded from external UV radiation, resulting in a high CO abundance and a low temperature of the clouds. The infrared-excess clouds with no CO emission are most likely to be molecular hydrogen clouds because the temperature is similar to, or lower than, that of the surrounding H i gas. The molecular gas without CO emission seems to occupy more than 90% of the area of the infrared-excess clouds.

Discovery of WTTS candidates in high-galactic latitude translucent molecular clouds

The results of the survey of low-mass star formation in high-galactic latitude molecular clouds, especially those of the translucent category, based on the ROSAT All-Sky Survey are presented. Six new WTTS candidates have been discovered at high-galactic latitude, among which, two are found to be possibly associated with translucent molecular clouds MBM 19 and MBM 51 for projecting onto the vicinity or inner region of corresponding clouds. Further study on the 2 Li-rich X-ray active sources is needed to resolve the possibility of star formation in translucent molecular clouds.

Distances to the High Galactic Latitude Molecular Clouds G192−67 and MBM 23–24

We report on distance determinations for two high Galactic latitude cloud complexes, G192-67 and MBM 23-24. No distance determination exists in the literature for either cloud. Thirty-four early type stars were observed towards the two clouds, more than half of which have parallaxes measured by the Hipparcos satellite. For the remaining stars we have made spectroscopic distance estimates. The data consist of high resolution echelle spectra centered on the Na I D lines, and were obtained over six nights at the Coude Feed telescope at Kitt Peak National Observatory. Interstellar absorption lines were detected towards some of the stars, enabling estimates of the distances to the clouds of 109 +/- 14 pc for G192-67, and of 139 +/- 33 pc for MBM 23-24. We discuss the relationship of these clouds to other ISM features such as the Local Hot Bubble and the local cavity in neutral hydrogen.

Atomic and Molecular Interstellar Absorption Lines toward the High Galactic Latitude Stars HD 141569 and HD 157841 at Ultra–High Resolution

We present ultra-high-resolution (0.32 km s-1) spectra obtained with the 3.9 m Anglo-Australian Telescope (AAT) and Ultra-High-Resolution Facility (UHRF) of interstellar Na I D1, Na I D2, Ca II K, K I, and CH absorption toward two high Galactic latitude stars HD 141569 and HD 157841. We have compared our data with 21 cm observations obtained from the Leiden/Dwingeloo H I survey. We derive the velocity structure and column densities of the clouds represented by the various components and identify the clouds with ISM structures seen in the region at other wavelengths. We further derive abundances, linear depletions, and H2 fractional abundances for these clouds wherever possible. Both stars are located in regions of IRAS 100 μm emission associated with high Galactic latitude molecular clouds (HLCs): HD 141569 lies, in projection, close to MBM 37 and the Lynds dark cloud L134N, whereas HD 157841 is in the vicinity of the MBM 151. Toward HD 141569 we detect two components in our UHRF spectra: a weak, broad b = 4.5 km s-1 component at -15 km s-1, seen only in Ca II K absorption, and another component at 0 km s-1, seen in Na I D1, Na I D2, Ca II K, K I, and CH absorption. The cloud represented by the -15 km s-1 component is warm and may be located in a region close to the star. The cloud represented by the 0 km s-1 component has a Ca linear depletion δ(Ca) = 1.4 × 10-4 and shows evidence for the presence of dust, consistent with strong 100 μm emission seen in this region. The H2 fractional abundance f(H2) derived for this cloud is 0.4, which is typically what is observed toward HLCs. We conclude that this 0 km s-1 cloud is associated with MBM 37 and L134N based on the presence of dust and molecular gas (CH) and good velocity agreement with CO emission from these two clouds. This places HD 141569 beyond MBM 37 and L134N, which are estimated to be at ≈ 110 pc. In the case of the HD 157841 sight line, a total of six components are seen on our UHRF spectra in Na I D1, Na I D2, Ca II K, K I, and CH absorption. Two of these six components are seen only in a single species. The cloud represented by the components at 1.85 km s-1 has a Ca linear depletion δ(Ca) = 2.8 × 10-4, indicating the presence of dust. The f(H2) derived for this cloud is 0.45, and there is good velocity agreement with CO emission from MBM 151. To the best of our knowledge, this 1.85 km s-1 component toward HD 157841 is the first one found to have relative line widths that are consistent with pure thermal broadening only. We associate the 1.85 km s-1 cloud seen in our UHRF spectra with MBM 151 and conclude that HD 157841 must lie beyond ~200 pc, the estimated distance to MBM 151.

Atomic Carbon in Southern Hemisphere High‐Latitude Clouds

We report the detection of atomic carbon in a sample of eight southern hemisphere high Galactic latitude molecular clouds, using the Antarctic Submillimeter Telescope and Remote Observatory. The 492 GHz (3P1 →3P0) transition of [C I] was detected in all of the clouds observed. The C/CO column density ratio ranges from 0.4 to 2.5 and is similar to the values previously measured in high-latitude clouds MBM 12 and HD 210121. For all 10 high-latitude clouds observed in [C I], C/CO averages ~1.2 and decreases with increasing total gas column density NH, as predicted by translucent cloud models. Quantitative comparison with chemical models of homogeneous clouds is unsatisfactory, however, and we conclude that the clumpy structure of clouds must be taken into account in order to interpret the data properly.

The Structure of the Galactic Magnetic Field toward the High‐Latitude Clouds

We present the results of an optical polarization survey toward the galactic anticenter, in the area 5(h) greater than or equal to alpha greater than or equal to 2(h) and 6 degrees less than or equal to delta less than or equal to 12 degrees. This region is characterized by the presence of a stream of high-velocity H I as well as high galactic latitude molecular clouds. We used our polarization data together with 100 mu m IRAS maps of the region to study the relation between the dust distribution and the geometry of the magnetic field. We find that there is a correlation between the percent polarization and the 100 mu m flux such that P(%) less than or equal to (0.16 +/- 0.05)F-100. When the IRAS flux is converted into H I column densities this becomes P(%) less than or equal to (0.13 +/- 0.03)N-20 - 0.22, which is consistent with previous interstellar medium studies on the relation between reddening and polarization. This correlation indicates that our survey is as deep as IRAS and that the magnetic field geometry does not change strongly with the optical depth in the lines of sight that we have studied. The implied lower limit to the distance of our survey is 500-700 pc at galactic latitudes b = -20 degrees and 100 pc at b = -50 degrees. Our main finding is that the magnetic field is perpendicular to the H I high-velocity stream as well as the molecular cloud MBM 16 in the high-latitude region. The field is also perpendicular to the velocity gradient in the stream. Closer to the plane, the magnetic field is parallel to the dust filaments that extend like a plume toward the halo. Our observations indicate that the galactic magnetic field toward the high-latitude clouds is toroidal. We propose a model in which flux tubes that rise out of the galactic plane become force-free and predominantly toroidal at high latitudes. The high-latitude clouds may be gas streams that are falling back toward the galactic plane within such buoyant braided ropes of magnetic flux.

Spectroscopy of possible Hα emission stars in regions of high galactic latitude molecular clouds

We present mid-resolution spectroscopic observations of 63 faint (V =12-16) stars identified by Kun (1992) as Hα emission candidates in an objective prism survey of several high galactic latitude molecular clouds. Only 4 stars in our sample (6%) are bona fide T Tauri stars on the basis of their strong Li I absorption and Hα emission features. They have late M spectral types (M4–M5.5) and two of them form a visual binary with separation . The new T Tauris are associated with the L 134 molecular complex, the northernmost extension of the Scorpio – Ophiuchus star forming region, which has been traditionally considered as a non-star forming region. In the other high latitude clouds surveyed by Kun (1992), we have not found any T Tauri star in our follow-up spectroscopy. Most of the observed stars (~80%) are late type dwarfs without detectable Hα emission in our spectra. Eight stars are M-dwarfs with Hα in emission, but no detectable Li I λ 6708 absorption. They could be post T Tauri stars or older dMe stars; more data is necessary in order to establish their evolutionary status. Our results show that Kun (1992) was able to detect weak Hα emission lines (down to equivalent width of ~ 1.5 A) in faint stars near the plate magnitude limit (V ~16), but in many cases plate defects, absorption bands and/or overlying stars were taken as possible Hα emission. In this paper we correct Kun's previous indication that there may be numerous young stars associated to high latitude molecular clouds, and we severely constrain the presence of a population of T Tauri stars in these clouds. We note that none of our four T Tauri stars is located in an isolated translucent molecular cloud.

The association of high-latitude molecular clouds with H I gas

view Abstract Citations (43) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Association of High-Latitude Molecular Clouds with H i Gas Gir, Be-Young ; Blitz, Leo ; Magnani, L. Abstract The relationhip between the High Galactic latitude molecular clouds (HCLs) and associated atomic hydrogen gas is investigate. In a global study, we examine a total of 75 HLCs observed in the CO (J=1-0) transition and found that all HCLs are associated with H I gas in both position and velocity with most of the HCLs located along filamentary or looplike H I structures. A small-scale comparison, using Green Bank 43 m H I data toward 10 regions associated with 18 HLCs, shows that the positions of the CO and H I peaks are typically offset from one another by approximately 1.5 deg, comparable to the linear size of the HCLs. No obvious pattern for these CO-H I offsets was found either in relation to the Galactic plane or to an arbitrary explosion center. Typical velocity dispersions of the CO and its associated H I are found to be 0.6 and 3.0 km/s, with a mean H I/CO linewidths ratio of 5.7, which is close to the square root of the ratio of mass of Co/H I possibly indicating energy equipartition between the two phases. The data suggest that the molecular clouds condensed from the atomic gas in situ, rather than having been entrained in the H I. Moreover, the data are consistent with formation from the H I by means of a phase transition in pressure equilibrium. A few cloud complexes are anomalous, perhaps indicating variants in how the clouds formed. We find a minimum total hydrogen column density of 5 x 1020/sq cm and a minimum relative abundance of H2 nucleons of 50% in the 18 clouds we observed. Two of the 10 observed H I clouds, those associated with the molecular clouds MBM 27-29 and MBM 53-55, show clear arclike structures and the latter appear to be expanding with a velocity of about 18 km/s. The kinetic energy of this expanding shell is estimated to be about 4 x 1049 ergs, consistent with having been produced as a result of a supernova explosion or a stellar wind. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174713 Bibcode: 1994ApJ...434..162G Keywords: H I Regions; Interstellar Gas; Milky Way Galaxy; Molecular Clouds; Spatial Distribution; Velocity Distribution; Abundance; Carbon Monoxide; Stellar Winds; Supernovae; Astrophysics; ISM: CLOUDS; ISM: MOLECULES; RADIO LINES: ISM full text sources ADS | data products SIMBAD (18)

Proto--Brown Dwarfs. I. Methods and Results for High-Latitude Clouds

view Abstract Citations (31) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Proto--Brown Dwarfs. I. Methods and Results for High-Latitude Clouds Pound, Marc W. ; Blitz, Leo Abstract We describe a method for finding substellar-mass self-gravitating clumps ("proto-brown dwarfs") in nearby molecular clouds, using millimeter-wave telescopes. This method represents a novel approach to looking for brown dwarfs and, for the nearest molecular clouds, has a greater mass sensitivity than traditional methods. We describe how the method can distinguish between various functional forms of the low-mass (<0.2 Msun) stellar initial mass function, which is currently poorly constrained. We present results of a search for proto-brown dwarfs in high galactic latitude molecular clouds. The clouds have relatively low densities [n(H2) ≲ 104 cm-3], are at an average distance of 100 pc, and are apparently not forming stars. We find little unambiguous evidence for self-gravitating objects of any mass in them, although there are clearly clumps with masses as low as 3 MJupiter. We find two clumps in MBM 12(=L1457), the nearest molecular cloud to the sun, which have luminous masses within a factor of 3 of that needed to be gravitationally bound. One of these has a dense core which appears to be in hydrostatic equilibrium. If so, then it is the first known self-gravitating core in a high-latitude cloud. The mean pressure in the clumps is P/k = 2.9 × 105 K cm-3, at least one order of magnitude higher than the general ISM pressure. We therefore conclude that either the clumps are transient structures in regions of typical ISM pressure, or the clouds themselves are short-lived objects in overpressured regions. In the latter case, the clouds will disperse in less than about 106 yr. The search for pro to-brown dwarfs is being expanded to include known star-forming regions in the Ophiuchus and Taurus complexes. The results in Ophiuchus and Taurus will tightly constrain the functional form of the stellar initial mass function at very low masses regardless of whether or not any proto-brown dwarfs are found. The present results already exclude a single power-law initial mass function with index ≳2. Publication: The Astrophysical Journal Pub Date: November 1993 DOI: 10.1086/173394 Bibcode: 1993ApJ...418..328P Keywords: ISM: CLOUDS; ISM: INDIVIDUAL ALPHANUMERIC: L1257; ISM: STRUCTURE; RADIO CONTINUUM: STARS; STARS: LOW-MASS; BROWN DWARFS full text sources ADS | data products SIMBAD (14) Related Materials (2) Erratum: 1995ApJ...444..487P Part 2: 1995ApJ...444..270P

Photometric and spectroscopic analysis of high galactic latitude molecular clouds. II - High-resolution spectroscopic observations of NA I, CA II, CA I, CH, and CH(+1)

High-resolution spectroscopic observations in the wavelengths of the atomic species Na I, Ca II, and Ca I and the molecular species CH and CH + have been conducted toward stars behind a variety of high Galactic latitude molecular clouds (HLCs), and 17 new detections of molecular absorption are reported. For 13 regions, multiple detections of Na I absorption lines are used to map the spatial extent and possible dynamics of the HLCs, and to constrain the distance and velocities of the clouds more accurately. New and improved distance estimates are reported for several clouds, including the Ursa Major complex MBM 29-MBM 31 and MBM 151, which are found to be at 100 pc < d < 120 pc, and d < 50 pc, respectively

Photometric and spectroscopic analysis of high Galactic latitude molecular clouds. I - Distances and extinctions of stars toward 25 selected regions

New photoelectric photometry in the UBV, uvby, and Hβ systems is presented for 320 stars at high Galactic latitudes, selected for their proximity to the densest portions of a variety of high Galactic latitude atomic and molecular clouds. Low-resolution digital spectra are used to classify 115 of the stars, using both stellar line strengths and statistical tests against a library of standard stars of all spectral types. Several new techniques are developed for automatic digital spectral classification, and for dereddening Stromgren uvbyβ and Johnson UBV, Hβ photometry