Bright Central Region Research Articles

A cluster of Nascent galaxies at Z = 2?

On a 6 hr Wide Field Camera exposure with the Hubble Space Telescope of the rich cluster CL 0939 + 4713, we have identified an apparent cluster of about 30 faint, extended objects with magnitudes in the range of 22 to 25. The objects are typically 1 arcsec in size with bright central regions only a few tenths of an arcsecond in size, and are distributed over a region approximately 40 arcsec long and 20 arcsec wide. A simple statistical analysis indicates that the clustering is probably real. The size and appearance of the individual objects, their blue colors, and their clustering, leads us to speculate that they are associated, and that they are considerably more distant than the cluster CL 0939 + 4713 at z = 0.40, probably at a redshift greater than 1. Among the strongest concentration of these objects is an unresolved, extremely blue object with the spectrum of a QSO at z = 2.055. We suggest that many of the small, faint objects could be physically associated with this QSO.

HUBBLE SPACE TELESCOPE IMAGES AND FOLLOW-UP SPECTROSCOPY OF THE ORION NEBULA

ABSTRACT Recently published HST images of the Orion nebula reveal elephant-trunk structures, an apparent jet of material, and fine-scale structure in the Herbig-Haro object HH2, which is located at the base of an elephant trunk. High-resolution spectroscopy shows that the apparent jet is actually an ionization front seen edge-on. HH2 shows a complex structure in the several stages of ionization observed. There seem to be two velocity systems characterized by a bright central region and an accompanying shell-like emission. These two systems are most likely to be the result of a bow shock and corresponding Mach disk formed from the interaction of a collimated jet and the ambient gas of the nebula.

Images in the rocket ultraviolet - Star formation and extinction in the M51 system

UV images of M51 with up to 15" resolution were obtained by a rocket- borne telescope. The bandwidth was 970 A with maximum response at 2650 A. The two most prominent features of M51 in the UV are the bright central region and a region of intense star formation about 2.5' NE of the nucleus toward the companion NGC 5195. This complex is the source of 20% of the total UV flux in M51. The companion is much less prominent in the UV than in optical bands. Spiral arms show much higher contrast in UV and U bands than in the R band. The nuclear region in the UV band shows clumped emission from probable star-forming regions, possibly associated with the inner Lindblad resonance. These regions are probably the UV counterparts of FIR sources discovered in an EW scan across the nucleus. UV/U colors of most bright H II regions with known extinction are consistent with O star spectra reddened by amounts estimated from radio and Balmer line measurements. However, some of the brightest H II regions have redder UV/U colors, probably indicating the presence of cooler stars which contribute in the U band. CO and IR observations indicate that the companion NGC 5195 may be a reddened starburst in spite of its faintness in the UV.

A compact radio source in the nucleus of M87

The nucleus and jet of the giant elliptical galaxy M87 have been studied at radio wavelengths with resolutions ranging upwards from a few milliarc seconds1–3. The higher-resolution maps show that the nucleus consists of a bright central region with a feature with smoothly decaying brightness pointing in the direction of the larger-scale radio/optical/X-ray jet. Moreover, these maps indicate that collimation of the jet occurs within 10 marc s of the nucleus (that is, within 1 pc of the nucleus, as M87 lies at a distance of 12–20 Mpc4). We report here high-resolution, very-long-baseline interferometric (VLBI) observations at 1.35 cm wavelength, which reveal the existence of a compact core (≲0.2 marc s) and an associated extended feature (∼0.3 marc s), again pointing in the same direction as the large-scale jet. Our observations show that the radio jet is formed on a size scale of ≲10−2pc, thus strengthening the evidence for the presence of a massive black hole in the nucleus of M87.

A photometric study of the M51 system

Photoelectric and photographic data are presented for the two components of the M51 system, NGC 5194 and NGC 5195. The photoelectric observations (UBV and I) are presented as a series of drift scans with various diaphragm sizes covering the bright central and faint outer regions. These data indicate the complexity and the very large extent of the system. Colors and magnitudes of the spiral arms are presented. The I data in particular show the broad spiral features first shown photographically by Zwicky. Deep, integrated photographic plates (IIIa-J) also show the large, structured outer regions and the complex nature of the region between the two galaxies. Calibrated contour maps and integrated luminosities of the system are presented.The maximum detected extent of the system is 40 arcmin or 120kpc. If a M/L ratio of 10 is assumed, the mass in the outer envelope is equal to the mass obtained for the more familiar bright optical components.These data and their presentation in the form of photoelectric drift scans, composite photographs, contour maps, and three-dimensional plots show the marvelous complexity of the system. It would seem that the individual galaxies, NGC 5194 and NGC 5195, cannot be considered separately but must be studied inmore » the context of their being members of the M51 system.« less

The Peculiar Galaxy NGC 4194

view Abstract Citations (13) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Peculiar Galaxy NGC 4194 Demoulin, Marie-Helene Abstract The galaxy NGC 4194 has an emission-line spectrum showing the presence of highly excited gas. The line [0 I} X6300 appears not only in the nucleus, but also in the very bright central region 1400 Pc in diameter. The velocity gradients in the excited gas have been interpreted as rotation providing a value for the mass of a few times 1O~ Mo. The uncertainties of this value may be large; they are due to the possible presence of non-circular motions and the impossibility of determining the orientation of the galaxy. In many respects NGC 4194 has a strong similarity to NGC 7714, studied previously Publication: The Astrophysical Journal Pub Date: April 1969 DOI: 10.1086/149967 Bibcode: 1969ApJ...156..325D full text sources ADS | data products SIMBAD (1) NED (1)

Dynamics of the Orion Nebula

The collision of supersonic gas streams within anHII region is studied. A system of stationary shock waves is set up. Theoretical line profiles through these shocked regions are compared with those obtained in the bright central regions of the Orion Nebula. There is good agreement between the predicted and observed magnitude of line splitting in the forbidden lines of O+ and O++.