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We present new HST/STIS observations of Centaurus A. [SIII] 9533A was used to study the kinematics in the nuclear region with a 0.1" spatial resolution. The STIS data and the VLT/ISAAC spectra by Marconi et al. (2001) provide independent and consistent measures of the BH mass, which are in agreement with our previous estimate based on the ISAAC data alone: MBH=(1.1+/-0.1) 10^8 Msun for a disk inclination of i=25deg or or MBH=(6.5+/-0.7) 10^7 Msun for i=35deg, the largest i value allowed by the data. We find that the choice of the intrinsic surface brightness distribution, a crucial element in the modeling, has no effects on MBH but has a large impact on the gas velocity dispersion. A mismatch between the observed and model velocity dispersion is not necessarily an indication of non-circular motions or kinematically hot gas, but is as easily due to an inaccurate computation arising from too course a model grid, or the adoption of an intrinsic brightness distribution which is too smooth. The observed velocity dispersion, line profiles and the higher order moments in the Hermite expansion, h_3 and h_4, are consistent with emission from a rotating disk. Results from gas kinematical estimate are in good agreement with a recent stellar dynamical estimate of MBH. The BH mass in Centaurus A agrees with the correlation with infrared luminosity and mass of the host spheroid but is not in disagreement with the stellar velocity dispersion if one takes into account the intrinsic scatter of the MBH-sigma correlation. Finally, using HST data we can constrain the size of any cluster of dark objects alternative to a BH to r<0.035" (~0.6pc). Thus Centaurus A ranks among the best cases for supermassive Black Holes in galactic nuclei. (ABRIDGED)

Mrk 1039 and IRAS F08208+2816 are two new Wolf-Rayet galaxies whose optical spectroscopic observations suggest that star formation in these galaxies occurs in brief bursts for starburst ages of only ~4 × 106 yr. Other observational diagnostics are needed to measure the contributions of older and less massive stars to the total luminosity of Wolf-Rayet galaxies. Both far-infrared (FIR) and radio continuum emission provide such diagnostics for stars with masses as low as 5 M☉ and lifetimes of several times 107 yr. We observed these two Wolf-Rayet galaxies at 20, 6, and 2 cm wavelengths using the B, C, and D configurations of the VLA, respectively. Mrk 1039 contains a fairly small (dr < 500 pc), primarily thermal radio source whose FIR/radio flux ratio is consistent with the isolated H II region expected if the starburst in Mrk 1039 is really very young (τ ~ 4 × 106 yr). In contrast, F08208+2816 has a nonthermal radio spectrum and obeys the FIR/radio correlation. These two radio properties indicate that the young Wolf-Rayet starburst in F08208+2816 is embedded in a large and luminous galaxy that has hosted comparably luminous starburst activity extending 3 × 107 yr in the past.

Radio observations were used to detect the "active" galaxy population within rich clusters of galaxies in a nonbiased manner that is not plagued by dust extinction or the K-correction. We present wide-field radio, optical (imaging and spectroscopy), and ROSAT All-Sky Survey (RASS) X-ray data for a sample of 30 very rich Abell (R ≥ 2) clusters with z ≤ 0.25. The VLA radio data samples the ultrafaint radio (L1.4 ≥ 2 × 1022 W Hz-1) galaxy population within these extremely rich clusters for galaxies with MR ≤ -21. This is the largest sample of low-luminosity 20 cm radio galaxies within rich Abell clusters collected to date.

One effect of random a/sub 1/, the skew quadrupole field error, is to perturb the beta -functions. This effect may be large in proton accelerators using superconducting magnets, because of the relatively large random a/sub 1/ expected in these magnets. This effect has been studied in the RHIC accelerator (the Relativistic Heavy Ion Collider proposed at Brookhaven National Laboratory). An analytic result has been found for the changes in the beta functions caused by the random a/sub 1/. This result indicates that the important harmonics of a/sub 1/ that need to be controlled are the harmonics near nu /sub x/+ nu /sub y/. This has been verified in computer studies.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Intravenous coronary angiograms of human subjects are now available from the National Synchrotron Light Source (NSLS). The high (4.4-T) magnetic field used under normal operation of the superconducting wiggler magnet on the X-17 beam line at NSLS yields a high critical energy (18.7 keV) and a large harmonic contamination of the desired X-ray flux at the K-edge of iodine (33.169 keV). The 66- and 99-keV contamination is a factor of 2.29 and 5.32 worse than for the human angiograms taken at the Stanford Synchrotron Radiation Laboratory, where a critical energy of 13.0 keV was obtained at beam line IV-2. This increased harmonic contamination produces severe artifacts in the images, especially where the patient's ribs cross the left ventrical and aorta, which are filled with contrast agent. An algorithm was developed to remove these artifacts by solving the two simultaneous transcendental equations for the fractional X-ray transmissions through iodine and through water. The parameters are derived from measurements on a Lucite step-wedge phantom. Human angiograms taken at 4.4 T are shown before and after the correction algorithm is applied. These corrected angiograms are compared to uncorrected angiograms taken at 3.0 T.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A description of some of the methods used in neuroreceptor imaging to distinguish changes in receptor availability has been presented in this chapter. It is necessary to look beyond regional uptake of the tracer since uptake generally is affected by factors other than the number of receptors for which the tracer has affinity. An exception is the infusion method producing an equilibrium state. The techniques vary in complexity some requiring arterial blood measurements of unmetabolized tracer and multiple time uptake data. Others require only a few plasma and uptake measurements and those based on a reference region require no plasma measurements. We have outlined some of the limitations of the different methods. Laruelle (1999) has pointed out that test/retest studies to which various methods can be applied are crucial in determining the optimal method for a particular study. The choice of method will also depend upon the application. In a clinical setting, methods not involving arterial blood sampling are generally preferred. In the future techniques for externally measuring arterial plasma radioactivity with only a few blood samples for metabolite correction will extend the modeling options of clinical PET. Also since parametric images can provide information beyond that of ROI analysis, improved techniques for generating such images will be important, particularly for ligands requiring more than a one-compartment model. Techniques such as the wavelet transform proposed by Turkheimer et al. (2000) may prove to be important in reducing noise and improving quantitation.

We present the main results from our 940 ks observation of the Chandra Deep Field-South using the source catalog described in an accompanying paper by Giacconi et al. We extend the measurement of source number counts to 5.5 × 10-17 ergs cm-2 s-1 in the soft 0.5-2 keV band and 4.5 × 10-16 ergs cm-2 s-1 in the hard 2-10 keV band. The hard-band log N-log S shows a significant flattening (slope 0.6) below ≈10-14 ergs cm-2 s-1, leaving at most 10%-15% of the X-ray background to be resolved, the main uncertainty lying in the measurement of the total flux of the X-ray background (XRB). On the other hand, the analysis in the very hard 5-10 keV band reveals a relatively steep log N-log S (slope 1.3) down to 10-15 ergs cm-2 s-1. Together with the evidence of a progressive flattening of the average X-ray spectrum near the flux limit, this indicates that there is still a nonnegligible population of faint hard sources to be discovered at energies not well probed by Chandra, which possibly contributes to the 30 keV bump in the spectrum of the XRB. We use optical redshifts and identifications, obtained with the Very Large Telescope, for one-quarter of the sample to characterize the combined optical and X-ray properties of the Chandra Deep Field-South sample. Different source types are well separated in a parameter space that includes X-ray luminosity, hardness ratio, and R-K color. Type II objects, while redder on average than the field population, have colors that are consistent with being hosted by a range of galaxy types. Type II active galactic nuclei are mostly found at z 1, in contrast with predictions based on active galactic nucleus population synthesis models, thus suggesting a revision of their evolutionary parameters.

We present results from 300 ks of X-ray observations of the Chandra Deep Field-South. The field of the four combined exposures is now 0.1035 deg(2), and we reach a flux limit of 10(-16) ergs s(-1) cm(-2) in the 0.5-2 keV soft band and 10(-15) ergs s(-1) cm(-2) in the 2-10 keV hard band, i.e., a factor of 2 fainter than the previous 120 ks exposure. The total catalog is composed of 197 sources including 22 sources detected only in the hard band, 51 only in the soft band, and 124 detected in both bands. We now have the optical spectra for 86 optical counterparts. The log N-log S relationship of the whole sample confirms the flattening with respect to the ASCA hard counts and the ROSAT soft counts. The average logarithmic slopes of the number counts are alpha = 0.66 +/- 0.06 and alpha = 0.92 +/- 0.12 in the soft and hard bands, respectively. Double power-law fits to the differential counts show evidence of further flattening at the very faint end to slopes of 0.5 +/- 0.1 and 0.6 +/- 0.2 in the soft and hard bands, respectively. We compute the total contribution to the X-ray background (XRB) in the 2-10 keV band, which now amounts to (1.45 +/- 0.15) x 10(-11) ergs cm(-2) s(-1) deg(-2) (after the inclusion of the ASCA sources to account for the bright end) to a lower flux limit of 10(-15) ergs s(-1) cm(-2). This corresponds to 60%-90% of the unresolved hard XRB, given the uncertainties on its actual value. We confirm previous findings on the average spectrum of the sources, which is well described by a power law with Gamma = 1.44 +/- 0.03, and the progressive hardening of the sources at lower fluxes. In particular, we find that the average spectral slope of the sources is flatter than the average for fluxes lower than 9 x 10(-15) ergs s(-1) cm(-2) in the hard band. The hardening of the spectra is consistent with an increasing fraction of absorbed objects (N-H &gt; 10(22) cm(-2)) at low fluxes. From 86 redshifts available at present, we find that hard sources have on average lower redshifts (z less than or equal to 1) than soft sources. Their typical luminosities and optical spectra show that most of these sources are obscured active galactic nuclei (AGNs), as expected by AGN population synthesis models of the XRB. We are still in the process of finding hard sources that constitute the remaining fraction of the total XRB. Most of the sources detected only in the soft band appear to be optically normal galaxies with luminosities L-x similar or equal to 10(40) -10(42) ergs s(-1). This population appears to be a mix of normal galaxies, possibly with enhanced star formation, and galaxies with low-level nuclear activity.

This paper presents 08 to 3'' resolution images of 1.3 and 3.3 mm continuum emission in the massive molecular outflow in W75 N. The mass of warm gas and dust near the center of the outflow is ~450 M☉ and represents approximately 45% of the core mass in the molecular cloud. Comparison of the distribution of warm dust emission with the locations of ultracompact H II regions indicates that the source VLA 3 probably contributes the most to the outflow dynamics. The location of VLA 2 near the 1 mm continuum peak and the presence of H2O masers suggests that this source may also contribute to the flow dynamics. The thermal jet source, VLA 1, has an estimated momentum rate that is 3 to 4 orders of magnitude less than that required to drive the large-scale CO outflow. If the ionized jet is the only outflow component, VLA 1 does not appear to be able to contribute significantly to the outflow energetics. Outflow parameter estimates that have been corrected for inclination and optical depth imply an outflow mass of more than a thousand solar masses and a mass outflow rate of ~0.2 M☉ yr-1. It is extremely unlikely that a single young stellar object can produce a flow of this magnitude; thus, several energetic outflows may be active.

We report new radio imaging of the large scale radio structure of M87 with the VLA at 90 cm. These new images show the complex structure of the radio emission more clearly than previous attempts, some of which date back to the 1940's. The images suggest that the outward flow from the M87 nucleus extends well beyond the 2 kpc jet. Two ``bubbles'' of synchrotron emission appear to be inflated by this flow. A simple model of the emission, combined with our knowledge of the inner jet, suggests that the energy input into this region from the M87 nucleus exceeds the energy being radiated away as X-rays. This argues that the region within 40 kpc of the center of M87 is currently dominated by energy input from the M87 nucleus. The gas in the region is expanding, not flowing inward as is envisioned in the cooling flow model.