SIMBAD references

2002MNRAS.337..385S - Mon. Not. R. Astron. Soc., 337, 385-400 (2002/December-1)

Multiwavelength observations of the M15 intermediate-velocity cloud.


Abstract (from CDS):

We present Westerbork Synthesis Radio Telescope Hi images, Lovell telescope multibeam Hi wide-field mapping, William Herschel Telescope long-slit echelle Caii observations, Wisconsin Hα Mapper (WHAM) facility images, and IRAS ISSA 60- and 100-1µm co-added images towards the intermediate-velocity cloud (IVC) at +70 km.s–1, located in the general direction of the M15 globular cluster. When combined with previously published Arecibo data, the Hi gas in the IVC is found to be clumpy, with a peak Hi column density of ∼1.5x1020 cm –2, inferred volume density (assuming spherical symmetry) of ∼24 cm–3/ D (kpc) and a maximum brightness temperature at a resolution of 81x14 arcsec2 of ∼14 K. The major axis of this part of the IVC lies approximately parallel to the Galactic plane, as does the low-velocity Hi gas and IRAS emission. The Hi gas in the cloud is warm, with a minimum value of the full width at half-maximum velocity width of 5 km.s–1 corresponding to a kinetic temperature, in the absence of turbulence, of ∼540 K. From the Hi data, there are indications of two-component velocity structure. Similarly, the Caii spectra, of resolution 7 km.s–1, also show tentative evidence of velocity structure, perhaps indicative of cloudlets. Assuming that there are no unresolved narrow-velocity components, the mean values of log10 [N(Caii K) cm –2 ]∼ 12.0 and Caii/Hi∼2.5x10–8 are typical of observations of high Galactic latitude clouds. This compares with a value of Caii/Hi> 10 –6 for IVC absorption towards HD 203664, a halo star of distance 3 kpc, some {formmu10} from the main M15 IVC condensation. The main IVC condensation is detected by WHAM in Hα with central local-standard-of-rest velocities of ∼60-70 km.s–1, and intensities uncorrected for Galactic extinction of up to 1.3 R, indicating that the gas is partially ionized. The FWHM values of the Hα IVC component, at a resolution of 1°, exceed 30 km.s–1 . This is some 10 km.s–1 larger than the corresponding Hi value at a similar resolution, and indicates that the two components may not be mixed. However, the spatial and velocity coincidence of the Hα and Hi peaks in emission towards the main IVC component is qualitatively good. If the Hα emission is caused solely by photoionization, the Lyman continuum flux towards the main IVC condensation is ∼2.7x106 photon cm –2 s –1. There is not a corresponding IVC Hα detection towards the halo star HD 203664 at velocities exceeding ∼60 km.s–1. Finally, both the 60- and 100-µm IRAS images show spatial coincidence, over a 0.675x0.625 deg2 field, with both low- and intermediate-velocity Hi gas (previously observed with the Arecibo telescope), indicating that the IVC may contain dust. Both the Hα and tentative IRAS detections discriminate this IVC from high-velocity clouds, although the Hi properties do not. When combined with the Hi and optical results, these data point to a Galactic origin for at least parts of this IVC.

Abstract Copyright: RAS

Journal keyword(s): ISM: clouds - ISM: general - ISM: individual: Complex gp - ISM: structure - globular clusters: individual: M15 - radio lines: ISM

Nomenclature: Fig.10: [SHK2002] A (Nos D, E).

CDS comments: Fig.10: (A) = M 15, (AR) = IVC in M 15.

Simbad objects: 14

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