Uj Schwarz

Distances to galactic high-velocity clouds: Complex C

We report the first determination of a distance bracket for the high- velocity cloud (HVC) complex C. Combined with previous measurements showing that this cloud has a metallicity of 0.15 times solar, these results provide ample evidence that complex C traces the continuing accretion of intergalactic gas falling onto the Milky Way. Accounting for both neutral and ionized hydrogen as well as He, the distance bracket implies a mass of (3-14) x 10(6) M-circle dot, and the complex represents a mass inflow of 0.1-0.25 M-circle dot yr(-1). We base our distance bracket on the detection of Ca II absorption in the spectrum of the blue horizontal branch (BHB) star SDSS J120404.78 + 623345.6, in combination with a significant nondetection toward the BHB star BS 16034-0114. These results set a strong distance bracket of 3.7-11.2 kpc on the distance to complex C. A more weakly supported lower limit of 6.7 kpc may be derived from the spectrum of the BHB star BS 16079-0017.

A confirmed location in the Galactic halo for the high-velocity cloud 'chain A'

The high-velocity clouds of atomic hydrogen, discovered about 35 years ago,, have velocities inconsistent with simple Galactic rotation models that generally fit the stars and gas in the Milky Way disk. Their origins and role in Galactic evolution remain poorly understood, largely for lack of information on their distances. The high-velocity clouds might result from gas blown from the Milky Way disk into the halo by supernovae,, in which case they would enrich the Galaxy with heavy elements as they fall back onto the disk. Alternatively, they may consist of metal-poor gas—remnants of the era of galaxy formation,, accreted by the Galaxy and reducing its metal abundance. Or they might be truly extragalactic objects in the Local Group of galaxies. Here we report a firm distance bracket for a large high-velocity cloud, chain A, which places it in the Milky Way halo (2.5 to 7 kiloparsecs above the Galactic plane), rather than at an extragalactic distance, and constrains its gas mass to between 105 and 2×106 solar masses.

RECOMBINATION-LINE OBSERVATIONS OF THE GALACTIC-CENTER

Aperture-synthesis observations of the H76α and H11Oα recombination lines are presented for the inner (3pc) region of the Galactic Nucleus. The large line width measured with single dishes (Pauls et al., 1974) is caused by well-ordered large-scale motions of the ionized gas. The velocities of the NeII clumps (Lacy et al., 1980) fit well into our smooth velocity field and smooth intensity distribution. We suggest therefore that the cloud picture of the Ne11 gas is (at least partly) invalid.

The Nature, Location and Environment of SgrA East

We have observed SgrA at 332 MHz (92 cm) with a resolution of 12 arcsec (0.6 pc) using the four configurations of the VLA. These results illustrate the dramatic and almost unique variation of radio spectral index within the central 3–4 arcmin of the galactic center. SgrA East is a non-thermal shell source that could be a supernova remnant or a very low-luminosity example of a radio component associated with the active nucleus of a spiral galaxy. The most dramatic aspect of the new 332 MHz observations is the appearance of the the SgrA West spiral features in absorption against SgrA East. Based on these results, SgrA East is situated behind SgrA West, the center of the galaxy. The halo is in front of or surrounds the former sources. The HII regions to the east of SgrA East (1 = -0°.02, b = -0°.07) are probably associated with the 50 km/s molecular cloud. The 7 arcmin halo (20 pc) has a non-thermal spectrum with turn-over below 1 GHz.

HI Associated with Cas A

A small HI absorption feature has been detected in front of Cas A at a velocity of -66 km/s. This HI feature can probably be associated with a recombined high density QSF.

Electronic analysis of 21 cm line profiles into Gaussian components

Decomposition of spectral line profiles into a few Gaussian components is carried out on the ZEBRA electronic computer. The method is described with particular emphasis on the criteria for choosing the best out of several possible solutions. The program is suitable for application in several other fields of research.