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FUSE Observations of Interstellar and Intergalactic Absorption toward the X-Ray-bright BL Lacertae Object Markarian 421
High-quality Far Ultraviolet Spectroscopic Explorer (FUSE) observationsat 20 km s-1 resolution of interstellar and intergalacticabsorption from 910 to 1187 Å are presented for the X-ray-brightBL Lac object Mrk 421. These observations are supplemented with FUSEdata for the distant halo stars BD +38°2182 and HD 93521 near theMrk 421 line of sight, in order to obtain information about the distanceto absorbing structures in the Milky Way toward Mrk 421. The FUSE ISMobservations provide measures of absorption by O VI and many otherspecies commonly found in warm neutral and warm ionized gas, including HI, C II, C III, O I, N I, N II, Fe II, and Fe III. In this study weconsider the O VI absorption between -140 and 165 km s-1 andits relationship to the lower ionization absorption and strongabsorption produced by O VII and O VIII at X-ray wavelengths. The O VIabsorption extending from -140 to 60 km s-1 is associatedwith strong low-ionization gas absorption and originates in the Galacticthick disk/halo. This O VI appears to be produced by a combination ofprocesses, including conductive interfaces between warm and hot gas andpossibly cooling Galactic fountain gas and hot halo gas bubbles. The OVI absorption extending from 60 to 165 km s-1 has unusualionization properties in that there is very little associatedlow-ionization absorption, with the exception of C III. This absorptionis not observed toward the two halo stars, implying that it occurs ingas more distant than 3.5 kpc from the Galactic disk. Over the 60-165 kms-1 velocity range, O VI and C III absorption have the samekinematic behavior. The ratio N(OVI)/N(CIII)=10+/-3 over the 60-120 kms-1 velocity range. Given the association of O VI with C III,it is unlikely that the high-velocity O VI coexists with the hotter gasresponsible for the O VII and O VIII absorption. The O VI positivevelocity absorption wing might be tracing cooler gas entrained in a hotGalactic fountain outflow. The O VII and O VIII absorption observed byChandra and XMM-Newton may trace the hot gas in a highly extended (~100kpc) Galactic corona or hot gas in the Local Group. The low resolutionof the current X-ray observations (~750-900 km s-1) and thekinematical complexity of the O VI absorption along typical lines ofsight through the Milky Way halo make it difficult to clearly associatethe O VI absorption with that produced by O VII and O VIII. A search formetal lines associated with the Lyα absorber at z=0.01, which issituated in a galactic void, was unsuccessful.
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| Accurate Positions for MCG Galaxies
We have measured accurate celestial coordinates for 4741 extragalacticobjects, primarily drawn from a list of MCG galaxies with no recentlypublished accurate positions. The standard deviations in the newpositions depend slightly on the measurement method but are on the orderof 1.0" to 1.2". Standard deviations in the original MCG positions areconfirmed to be at the 1.5′-2.0′ level. These new positionswere integrated into NED in 1997 December.
| Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
| Photometry of Shakhbazian I
The galaxies of the compact cluster Shakhbazian I have been studied byphotographic photometry. Contrary to earlier claims, they are ordinaryelliptical galaxies of average luminosity, and are not appreciablycompact. The dynamics of this possibly prototypical group is brieflydiscussed.
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