F. Macchetto

Imaging observations of gas and dust in NGC 4696 and implications for cooling flow models

Continuum and emission-line direct CCD observations of the gas and dust in NGC 4696 are analyzed. The wavelength-dependence of extinction is normal. Line luminosities are derived and evidence that the gas and dust are well-mixed is presented. A total power output of the dust lane of roughly 2 x 10 to the 43rd ergs/s is deduced. Constraints on the physical conditions and geometry in the emission-line gas are inferred. An external origin for the dust-lane material is favored from the observations; infall from a gas-rich companion with a normal interstellar medium may have recently taken place. The energy input to the dust and gas of the dust lane by saturated heat conduction from the hot X-ray gas is sufficient to power the optical and infrared emission. If conduction operates, the cool gas and dust act as a heat sink for the hot X-ray atmosphere and this may mimic some of the peripheral properties of a cooling flow. 57 refs.

HST/FOC imaging of the narrow-line region of NGC 1068

We present imaging observations of NGC 1068 taken with the COSTAR-corrected (Corrective-Optics Space Telescope Axial Replacement) Faint Object Camera (FOC) on board the Hubble Space Telescope (HST) in the UV and optical continuum and (O III) emission lines. From these observations the structure of the nuclear region of NGC 1068 is shown to be very complex. Bright filamentary and patchy structures are intermingled with dark lanes. Other interesting features are identified, including the location of the UV peak with respect to the peak of line emission, the existence of an unusual twin-crescent object near the nucleus, and point sources in the field. In the UV to optical flux ratio image, an extended conical region stands out for its blue color which may be tracing reflected nuclear light.

HST and Merlin Observations of 3C 264—A Laboratory for Jet Physics and Unified Schemes

We present new HST optical continuum and emission line WFPC2 images and MERLIN radio observations of 3C 264 at ~01 resolution. The jet is well resolved in both the optical and radio images. In addition, we report the discovery of an apparent optical ring at a projected radius of ~300-400 pc. The ring is most likely the manifestation of absorption by a nearly face-on circumnuclear dust disk. We discuss the evolution of the jet properties with distance. The jet collimation, brightness, and orientation change dramatically as it crosses the outer boundary of the ring suggesting an interaction between the jet and dense circumnuclear gas. We present a model for the jet propagation in which an initially relativistic jet decelerates as it crosses through a region of dense cold gas in the inner region of the galaxy. We derive the equations for brightness variations along an adiabatically expanding relativistic jet, and we model the jet brightness in 3C 264 as the combined effects of Doppler boosting, and adiabatic losses as traced through the jet velocity and width. We find that the data are consistent with a model in which the jet is initially highly relativistic (v ~ 0.98c, γ = 5) and we view it at roughly 50° inclination. We suggest that 3C 264 may serve as a laboratory for the study of relativistic entraining jets and may help us to understand the deceleration of jets, which is required in unifying schemes for FRI radio galaxies and BL Lac objects.

3C 236: Radio Source, Interrupted?

We present new Hubble Space Telescope Space Telescope Imaging Spectrograph MAMA near-UV images and archival Wide Field Planetary Camera 2 (WFPC2) V- and R-band images that reveal the presence of four star-forming regions in an arc along the edge of the dust lane in the giant (4 Mpc) radio galaxy 3C 236. Two of the star-forming regions are relatively young, with ages of order ~107 yr, while the other two are older, with ages of order ~108–109 yr, which is comparable to the estimated age of the giant radio source. Based on dynamical and spectral aging arguments, we suggest that the fuel supply to the active galactic nucleus (AGN) was interrupted for ~107 yr and has now been restored, resulting in the formation of the inner 2 kpc–scale radio source. This timescale is similar to that of the age of the youngest of the star-forming regions. We suggest that the transport of gas in the disk is nonsteady and that this produces the multiple episodes of star formation in the disk, as well as the multiple epochs of radio source activity. If the inner radio source and the youngest star-forming region are related by the same event of gas transport, the gas must be transported from the hundreds of parsec scale to the subparsec scale on a timescale of ~107 yr, which is similar to the dynamical timescale of the gas on the hundreds of parsec scale.

Faint Object Camera imaging and spectroscopy of NGC 4151

We describe ultraviolet and optical imaging and spectroscopy within the central few arcseconds of the Seyfert galaxy NGC 4151, obtained with the Faint Object Camera on the Hubble Space Telescope. A narrowband image including (O III) lambda(5007) shows a bright nucleus centered on a complex biconical structure having apparent opening angle approximately 65 deg and axis at a position angle along 65 deg-245 deg; images in bands including Lyman-alpha and C IV lambda(1550) and in the optical continuum near 5500 A, show only the bright nucleus. In an off-nuclear optical long-slit spectrum we find a high and a low radial velocity component within the narrow emission lines. We identify the low-velocity component with the bright, extended, knotty structure within the cones, and the high-velocity component with more confined diffuse emission. Also present are strong continuum emission and broad Balmer emission line components, which we attribute to the extended point spread function arising from the intense nuclear emission. Adopting the geometry pointed out by Pedlar et al. (1993) to explain the observed misalignment of the radio jets and the main optical structure we model an ionizing radiation bicone, originating within a galactic disk, with apex at the active nucleus and axis centered on the extended radio jets. We confirm that through density bounding the gross spatial structure of the emission line region can be reproduced with a wide opening angle that includes the line of sight, consistent with the presence of a simple opaque torus allowing direct view of the nucleus. In particular, our modelling reproduces the observed decrease in position angle with distance from the nucleus, progressing initially from the direction of the extended radio jet, through our optical structure, and on to the extended narrow-line region. We explore the kinematics of the narrow-line low- and high-velocity components on the basis of our spectroscopy and adopted model structure.

Preliminary analysis of an ultraviolet Hubble Space Telescope faint object camera image of the center of M31

A 5161 s exposure was taken with the FOC on the central 44 arcsec of M31, through a filter centered at 1750 A. Much of the light is redleak from visible wavelengths, but nearly half of it is genuine UV. The image shows the same central peak found earlier by Stratoscope, with a somewhat steeper dropoff outside that peak. More than 100 individual objects are seen, some pointlike and some slightly extended. We identify them as post-asymptotic giant branch stars, some of them surrounded by a contribution from their accompanying planetary nebulae. These objects contribute almost a fifth of the total UV light, but fall far short of accounting for all of it. We suggest that the remainder may result from the corresponding evolutionary tracks in a population more metal-rich than solar.

HST observations of 3C 66B - A double-stranded optical jet

The Faint Object Camera on the Hubble Space Telescope was used to observe the radio galaxy PKS 0521 - 36 which hosts a prominent radio jet. Images of the jet show spatial structure comparable to VLA data and significantly better than optical ground-based observations. The jet structure is resolved at FOC resolution. In addition to the radio knot, well resolved by the FOC, an extension of the jet toward the nucleus is apparent. The rest of the jet does not show much clumpiness, implying that the synchrotron electrons must be accelerated all along the jet to account for the extent in the optical region.

First results from the Faint Object Camera : high-resolution observations of the central object R136 in the 30 Doradus nebula

R136 is the luminous central object of the giant H II region 30 Doradus in the Large Magellanic Cloud. We report on the first high-resolution observations of R136 with the Faint Object Camera on board the Hubble Space Telescope. The physical nature of the brightest component R136a has been a matter of some controversy over the last few years. The UV images obtained show that R131a is a very compact star cluster consisting of more than eight stars within 0″.7 diameter. From these high-resolution images a mass upper limit can be derived for the most luminous stars observed in R136

Observations of SN 1987A with the COSTAR-corrected Faint Object Camera

New near-ultraviolet and visible (O III) observations of SN 1987A obtained 2511 and 2533 days after outburst with the Corrective Optics Space Telescope Axial Replacement (COSTAR) corrected Faint Object Camera (FOC) on board the Hubble Space Telescope (HST) are presented. Even though the supernova is now very faint (m approximately equal to 19), the new data are of dramatically higher quality than those obtained previously with the aberrated telescope. The images -- which are now no longer hampered by the spherical aberration halos of the two nearby companion stars -- reveal a well-resolved symmetrical expanding envelope that can be traced out to a radius of approximately equal to 275 mas or approximately equal to 9400 km/s in the near-UV. The apparent diameter of the ejecta has grown to 255 +/- 2 mas Full Width at Half Maximum (FWHM) in the near-UV and 167 +/- 5 mas (FWHM) in the visible, in close agreement with the expansion rates inferred from earlier FOC observations obtained on days 1275 and 1754. The improved shell-like crescent has started to form within the inner approximately equals 60 mas core of the nebula.

Polarization of the jet of PKS 0521 - 36

Optical polarization has been detected from the jet in the radio galaxy PKS 0521 - 36. Except for M87 and 3C 66B, PKS 0521 - 36 is the only other radio galaxy whose jet has been measured to be optically polarized. The polarization position angle contrasts with that of M87 but is similar to that of the quasar 3C 273 in that the magnetic field is aligned parallel to the jet. PKS 0521 - 36 contains a luminous BL Lac type nucleus whose polarization is approximately parallel to the jet. The difference in the observed polarization directions between the PKS 0521 - 36 and M87 jets may be connected with the presence of this bright optical nucleus. Either the core of PKS 0521 - 36 is currently more active than M87 or the jet axis is oriented closer to the line of sight. 27 refs.