Bright Component Research Articles

Renewed Activity in the Radio Galaxy PKS B1545−321: Twin Edge‐brightened Beams within Diffuse Radio Lobes

Australia Telescope Compact Array images of the giant radio galaxy PKS B1545-321 show a pair of oppositely directed beams emerging from a radio core and ending in bright components that are symmetrically located on either side. These inner beams are embedded within edge-brightened outer lobes of lower surface brightness, and the bright ends of the inner beams are well recessed from the ends of the outer lobes. The inner beams and diffuse surrounding lobes share a common central core and radio axis. We propose that the observed inner beams are double lobes that have been created within relic outer lobes as a consequence of a restarting of the central activity; therefore, PKS B1545-321 is a rare opportunity for examining the development of restarted beams within a relic synchrotron plasma cocoon. The inner double representing the new episode has among the highest axial ratios found in typical edge-brightened radio galaxies. The low radio luminosity of the inner double, the narrow and constant transverse extent of its cocoon, and the relatively low brightness of the hot spots at its ends are consistent with the almost ballistic propagation expected for a beam that has a low density contrast and is advancing within a relatively light ambient medium.

The Quintuple Quasar: Radio and Optical Observations

We present results from high-resolution radio and optical observations of PMN J0134-0931, a gravitational lens with a unique radio morphology and an extremely red optical counterpart. Our data support the theory of Keeton & Winn (2003): five of the six observed radio components are multiple images of a single quasar, produced by a pair of lens galaxies. Multi-frequency VLBA maps show that the sixth and faintest component has a different radio spectrum than the others, confirming that it represents a second component of the background source rather than a sixth image. The lens models predict that there should be additional faint images of this second source component, and we find evidence for one of the predicted images. The previously-observed large angular sizes of two of the five bright components are not intrinsic (which would have excluded the possibility that they are lensed images), but are instead due to scatter broadening. Both the extended radio emission observed at low frequencies, and the intrinsic image shapes observed at high frequencies, can be explained by the lens models. The pair of lens galaxies is marginally detected in HST images. The differential extinction of the quasar images suggests that the extreme red color of the quasar is at least partly due to dust in the lens galaxies.

EVN observation of three Broad Absorption Line quasars

We present the results of European VLBI Network observations of 3 Broad Absorption Line quasars at 1.6 GHz. They are all compact with linear sizes less than 1 kpc. The flat spectral source, J1556+3517, is unresolved at about 20 mas resolution, indicating that the orientation of the radio jet in this source is probably near the line of sight. J1312+2319 shows asymmetric two-sided structure on a scale of several hundred pc. This structure resembles that of Compact Symmetric Objects (CSO), however it has a bright central component at the present resolution. The jet orientation of J1312+2319 may be far from the line of sight. J0957+2356 is also unresolved, but with a steep spectrum, therefore the jet orientation in this source is unclear. These results are not consistent with the unification of BAL and non-BAL quasars by orientation.

Giant low surface brightness haloes in distant radio galaxies: USS0828+193

We present results on the spectroscopic study of the ionized gas in the high-redshift radio galaxy USS0828+193 at z = 2.57. Thanks to the high signal-to-noise (S/N) ratio of the emission lines in the Keck spectrum, we have been able to perform a detailed kinematic study by means of the spectral decomposition of the emission line profiles. This study reveals the existence of two types of material in this object: (i) a low surface brightness component with apparent quiescent kinematics consistent with gravitational motions and (ii) a perturbed component with rather extreme kinematics. The quiescent halo extends across the entire object for ∼80 kpc. It is enriched with heavy elements and apparently ionized by the continuum from the active nucleus. The properties of the quiescent halo and its origin are discussed in this paper. We propose that it could be part of a structure that surrounds the entire object, although its nature is not clear (a rotating disc? low surface brightness satellites? a cooling flow nebula? material ejected in galactic winds? other?).

Properties of the close binary and circumbinary torus of the Red Rectangle

New diffraction-limited speckle images of the Red Rectangle in the wavelength range 2.1-3.3 µm with angular resolutions of 44-68 mas (Tuthill et al. 2002) and previous speckle images at 0.7-2.2 µm (Osterbart et al. 1997; Men'shchikov et al. 1998) revealed well-resolved bright bipolar outflow lobes and long X-shaped spikes originating deep inside the outflow cavities. This set of high-resolution images stimulated us to reanalyze all infrared observations of the Red Rectangle using our two-dimensional radiative transfer code. The high-resolution images imply a geometrically and optically thick torus-like density distribution with bipolar conical cavities and are inconsistent with the flat disk geometry frequently used to visualize bipolar nebulae. The new detailed modeling, together with estimates of the interstellar extinction in the direction of the Red Rectangle enabled us to more accurately determine one of the key parameters, the distance D ≈ 710pc with model uncertainties of 70pc, which is twice as far as the commonly used estimate of 330pc. The central binary is surrounded by a compact, massive (M ≈ 1.2M⊙), very dense dusty torus with hydrogen densities reaching nH ≈ 2.5 ×10 12 cm −3 (dust-to-gas mass ratiod/� ≈ 0.01). The model implies that most of the dust mass in the dense torus is in very large particles and, on scales of more than an arcsecond, the polar outflow regions are denser than the surrounding medium. The bright component of the spectroscopic binary HD44179 is a post-AGB star with mass M⋆ ≈ 0.57M⊙, luminosity L⋆ ≈ 6000L⊙, and effective temperature T⋆ ≈ 7750K. Based on the orbital elements of the binary, we identify its invisible component with a helium white dwarf with MWD ≈ 0.35M⊙, LWD ∼ 100L⊙, and TWD ∼ 6 ×10 4 K. The hot white dwarf ionizes the low-density bipolar outflow cavities inside the dense torus, producing a small HII region observed at radio wavelengths. We propose an evolutionary scenario for the formation of the Red Rectangle nebula, in which the binary initially had 2.3 and 1.9M⊙ components at a separation of ∼ 130R⊙. The nebula was formed in the ejection of a common envelope after Roche lobe overflow by the present post-AGB star.

Spectrophotometric Observations of Blue Compact Dwarf Galaxies: Markarian 370

We present results from a detailed spectrophotometric analysis of the blue compact dwarf galaxy (BCD) Mrk 370, based on deep UBVRI broadband and Hα narrowband observations, and on long-slit and two-dimensional spectroscopy of its brightest knots. The spectroscopic data are used to derive the internal extinction and to compute metallicities, electronic density, and temperature in the knots. By subtracting the contribution of the underlying older stellar population, modeled by an exponential function, removing the contribution from emission lines, and correcting for extinction, we can measure the true colors of the young star-forming knots. We show that the colors obtained this way differ significantly from those derived without the above corrections and lead to different estimates of the ages and star-forming history of the knots. Using predictions of evolutionary synthesis models, we estimate the ages of both the starburst regions and the underlying stellar component. We found that we can reproduce the colors of all the knots with an instantaneous burst of star formation and the Salpeter initial mass function (IMF) with an upper mass limit of 100 M☉. The resulting ages range between 3 and 6 Myr. The colors of the low surface brightness component are consistent with ages larger than 5 Gyr. The kinematic results suggest ordered motion around the major axis of the galaxy.

H[CLC]e[/CLC] [CSC]i[/CSC] 1.083 μ[CLC]m[/CLC] Emission and Absorption in DG Tauri: Line Excitations in the Jet, Hot Wind, and Accretion Flow

We present long-slit spectroscopy and spectroastrometry of He I 1.083 μm emission in the T Tauri star DG Tauri. We identify three components in the He I feature: (1) a blueshifted emission component at v -200 km s-1, (2) a bright emission component at zero velocity with a FWZI of ~500 km s-1, and (3) a blueshifted absorption feature at velocities between -250 and -500 km s-1. The position and velocity of the blueshifted He I emission coincide with a high-velocity component of the [Fe II] 1.257 μm emission, which arises from a jet within an arcsecond of the star. The presence of such a high-excitation line (with an excitation energy of ~20 eV) within the jet supports the scenario of shock heating. The bright He I component does not show any spatial extension, and it is likely to arise from magnetospheric accretion columns. The blueshifted absorption shows greater velocities than that in Hα, suggesting that these absorption features arise from the accelerating wind close to the star.

Restarting activity in radio galaxies

We present observations of two radio galaxies, J1835+620 and 3C338, both with signs of having passed through different stages of core activity. The former presents two symmetric and bright components within a typical FR II structure, possibly resulting from two distinct phases of activity; the latter is a FR I radio galaxy with two separated regions with different age properties, possibly due to a switch-off and -on cycle in its core. In both sources, the optical counterpart lies in a group of galaxies with indications of mutual interaction, a scenario often invoked to explain triggering of core activity.

THE UNUSUAL HERBIG Ae/Be STAR XY Per A

The results of an investigation of XY Per based on photoelectric observations in the Stromgren system are presented. It is shown that the brighter component in the binary system XY Per AB, classified earlier as A2 II, is a variable of the Herbig Ae/Be type. At the same time, our estimates gave M V (XY Per A) = +1.25. An analysis of the variation of the indices β and c showed that XY Per A is a typical shell star: along with intense hydrogen absorption lines it displays an appreciable emission deficit in the Balmer continuum. The most noteworthy are the results of observations indicating that as the brightness decreases, the opacity of the shell increases both in lines and in the Balmer continuum. This observational fact can scarcely be explained in terms of the model of brightness variation due to dust clouds revolving around the star.

Reconstruction of radio images of the sun obtained by the siberian solar radio telescope

Reconstruction of radio images of the Sun obtained by the Siberian Solar Radio Telescope (SSRT) encounters two main problems. First, since the solar radio images at a wavelength of 5.2 cm have a high contrast, the amplitude–phase distribution in the antenna–feeder section should be known with a very high accuracy. Second, since such images comprise not only bright compact components but also low-contrast diffuse areas, there is a problem of deconvolution of these diffuse sources, which is inherent to the CLEAN algorithm. To solve the first problem, we determine the amplitude–phase distortions by an iterative analysis of the image itself, in which the opposite sidelobes of the point-source response are compared. To suppress the influence of other sources on the response, we analyze several compact sources. The phase distortions are determined from the asymmetry of the sidelobes, and the amplitude distortions, from sidelobe values. The image is corrected in the spatial-spectrum domain after each iteration. On the one hand, the problems encountered when reconstructing extended sources are related to the fact that the CLEAN algorithm requires significant computer resources. On the other hand, reconstructing images of extended areas requires that the number of cycles of this algorithm should be increased. Another problem consists in the fact that the use of the same “clean” antenna pattern for reconstructing compact and extended sources results in appearance of high-frequency distortions of the latter sources. If the CLEAN algorithm is applied, then the computer resources are mainly spent to shift the pattern and to find the maximum of the initial image. We decrease the time necessary for shifting the pattern by excluding the points near the zero value from the antenna-pattern data set and by sorting the remaining data points. The time of finding the maximum was decreased by using a local search window. In addition, we use a number of cutoff levels and search the next maximum in the whole image only after reconstructing the windowed image down to the current cut level. To reconstruct bright compact sources, we use the ”clean” antenna pattern close to the ideal pattern. To reconstruct low-contrast diffuse areas, we use the model patterns obtained by convolving the antenna pattern with the images of extended sources.

VLA Images of Two Extended Radio Galaxies

There is some evidence from earlier studies that the two sources 0235 — 197 and 1203 + 043 exhibit low frequency (< 1 GHz) variability. This work shows that both sources have linear polarizations, if any, below the detection limits at 320 MHz, so we cannot explain the variability as being due to instrumental polarization effects as has been suggested for 3C159. Refractive scintillation may be the cause of the variability in 0235—197. The radio source 1203+043 lacks any bright compact component thereby ruling out a refractive scintillation mechanism for its variability. Consequently, it is possible that claims of variability in this source are spurious. However, the 320 MHz VLA observations show that 1203+043 has an ‘X'-shaped radio structure.

PMN J1632−0033: A New Gravitationally Lensed Quasar

We report the discovery of a gravitationally lensed quasar resulting from our survey for lenses in the southern sky. Radio images of J1632-0033 with the Very Large Array and the Australia Telescope Compact Array exhibit two compact, flat-spectrum components with separation 147 and flux density ratio 13.2. Images with the Hubble Space Telescope reveal the optical counterparts to the radio components and also the lens galaxy. An optical spectrum of the bright component obtained with the first Magellan telescope reveals quasar emission lines at redshift 3.42. Deeper radio images with the Multi-Element Radio Linked Interferometry Network and the Very Long Baseline Array reveal a faint third radio component located near the center of the lens galaxy, which is either a third image of the background quasar or faint emission from the lens galaxy.

A New Wide Pair of Cool White Dwarfs in the Solar Neighborhood

We report the discovery of a wide pair (93'' angular separation) of extremely cool (Teff < 4000 K) white dwarfs with a very large common proper motion (~19 yr-1). The objects were discovered in a high proper motion survey in the poorly investigated southern sky region with δ < -60° using SuperCOSMOS Sky Survey (SSS) data. Both objects, SSSPM J2231-7514 and SSSPM J2231-7515, show featureless optical spectra. Fits of blackbody models to the spectra yield effective temperatures of 3810 and 3600 K, respectively, for the bright (V = 16.60) and faint (V = 16.87) components. Both degenerates are much brighter than other recent discoveries of cool white dwarfs with comparable effective temperatures and/or BJ-R colors. Therefore, they should be relatively nearby objects. The comparison with other cool white dwarfs and a photometric distance determination yield distance estimates between 9 and 14 pc. The latter seems to be more realistic since the good agreement of the proper motion of both components within the errors of about 8 mas yr-1 and the angular separation between the two stars support a distance of about 15 pc, with relatively small masses of the components. With a smaller distance we should be able to measure a differential proper motion due to orbital motion if the orbital plane is not strongly inclined and if the present orbital velocity vector is not close to the line of sight. The space velocity based on that distance and assumptions on radial velocity make the new pair of extremely cool white dwarfs probably some of the oldest members of the Galactic disk population, although the possibility that these objects are part of a Galactic halo dark matter component also cannot yet be ruled out.

The X-ray emission from Nova V382 Velorum - I. The hard component observed withBeppoSAX

We present BeppoSAX observations of Nova Velorum 1999 (V382 Vel), carried out in a broad X-ray band covering 0.1–300 keV only 15 d after the discovery and again after 6 months. The nova was detected at day 15 with the BeppoSAX instruments which measured a flux Fx≃1.8×10−11 erg cm−2 s−1 in the 0.1–10 keV range and a 2σ upper limit Fx<6.7×10−12 erg cm−2 s−1 in the 15–60 keV range. We attribute the emission to shocked nebular ejecta at a plasma temperature kT≃6 keV. At six months no bright component emerged in the 15–60 keV range, but a bright central supersoft X-ray source appeared. The hot nebular component previously detected had cooled to a plasma temperature kT<1 keV. There was strong intrinsic absorption of the ejecta in the first observation and not in the second, because the column density of neutral hydrogen decreased from N(H)≃1.7×1023 to N(H)≃1021 cm−2 (close to the interstellar value). The unabsorbed X-ray flux also decreased from Fx = 4.3×10−11 to Fx≃10−12 erg cm−2 s−1.

Two-sided radio emission in ON 231 (W Comae)

Recent radio images of the BL Lac object ON 231 (W Com, 1219+285) show remarkable new features in the source structure compared to those previously published. The images were obtained from observations made with the European VLBI Network plus MERLIN at 1.6 GHz and 5 GHz after the exceptional optical outburst occurred in Spring 1998. The up-to-date B band historic light curve of ON 231 is also presented together with the R band luminosity evolution in the period 1994-1999. We identify the source core in the radio images with the brightest component having the flattest spectrum. A consequence of this assumption is the existence of a two-sided emission in ON 231 not detected in previous VLBI images. A further new feature is a large bend in the jet at about 10 mas from the core. The emission extends for about 20 mas after the bend, which might be due to strong interaction with the environment surrounding the nucleus. We suggest some possible interpretations to relate the changes in the source structure with the optical and radio flux density variation in the frame of the unification model.

The Fundamental Plane as a consequence of Clausius’ virial minimum

In order to explain the main features of the Fundamental Plane for pressure-supported, elliptical galaxies, we analysed the virialized state, at Clausius’ virial minimum, of a bright component which is completely embedded inside a dark halo. It was assumed that the two subsystems are concentric and coaxial, similar, heterogeneous spheroids, with two different, power-law density distributions. The peculiarities of Clausius’ virial minimum are: (i) it provides an induced scale length for the luminous structure, which, at given mass distributions, corresponds to the maximum virial dimension with minimal random kinetic energy; (ii) it shares in almost equal amounts, tidal-potential energy due to a dark halo, and self-potential energy. These properties and the structure of dark matter halo, which allows the existence of the virial minimum, turn out to be the key for understanding the observed properties of FP. A universal, dark matter distribution of exponent d≃0.5 inside the luminous subsystem, seems to be required when comparing with the observed tilt of FP.

Excess hard X-ray emission from the obscured low luminosity AGN in the nearby galaxy M 51 (NGC 5194)

We observed the nearby galaxy M 51 (NGC 5194) with BeppoSAX. The X-ray properties of the nucleus below 10 keV are almost the same as the ASCA results regarding the hard component and the neutral Fe K line, but the intensity is about half of the ASCA 1993 data. Beyond this, in the BeppoSAX PDS data, we detected a bright hard X-ray emission component which dominates above 10 keV. The 10{100 keV flux and luminosity of this component are respectively 2 10 11 erg s 1 cm 2 and 2 10 41 erg s 1 . These are about 10 times higher than the extrapolation from the soft X-ray band, and similar to the flux observed with Ginga, which found a bright power law component in 2{20 keV band. Considering other wavelength properties and the X-ray luminosity, together with strong neutral Fe K line, the hard X-ray emission most likely arises from a low luminosity active nucleus, which is obscured with a column density of 10 24 cm 2 . This suggests that hidden low luminosity AGNs may well be present in other nearby galaxies. We interpret the discrepancy between Ginga and other X-ray satellites to be due to a large variability of absorption column density toward the line of sight over several years, suggesting that the Compton thick absorption material may be present on a spatial scale of a parsec. Apart from the nucleus, several ultra-luminous o-nuclear X-ray sources detected in M 51 exhibit long-term time variability, suggesting the state transition similar to that observed in Galactic black hole candidates.

Gliese 569B: A Young Multiple Brown Dwarf System?

The nearby late M star Gliese 569B was recently found by adaptive optics imaging to be a double with separation ~1 AU. To explore the orbital motion and masses, we have undertaken a high-resolution (~005) astrometric study. Images were obtained over 1.5 yr with bispectrum speckle interferometry at the 6.5 m Multiple Mirror Telescope (MMT) and 6 m Special Astrophysical Observatory telescope. Our data show motion corresponding to more than half the orbital period and constrain the total mass to be greater than 0.115 M☉, with a most probable value of 0.145 M☉. Higher masses cannot be excluded without more extended observations, but from statistical analysis we find an 80% probability that the total mass is less than 0.21 M☉. An infrared spectrum of the blended B double obtained with the MMT has been modeled as a blend of two different spectral types, chosen to be consistent with the measured J- and K-band brightness difference of a factor of ~2. The blended fit is not nearly as good as that to a pure M8.5+ template. Therefore, we hypothesize that the brighter component likely has two unresolved components with near equal masses, each the same as the fainter component. If Gl 569B is a triple, our dynamical limits suggest each component has a mass of 50 MJup. We infer an age for the system of 300 Myr from its kinematic motion, which places it as a member of the Ursa Major moving group. All the above parameters are consistent with the latest DUSTY evolution models for brown dwarfs.

Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies. I. Surface Brightness Distribution, Morphology, and Structural Parameters

Broadband observations in B, V, R, and I have been performed for a sample of 28 galaxies cataloged as blue compact dwarf galaxies (BCDs). Our deep imaging, reaching surface brightness levels of a few percent of the sky brightness, has allowed the detection of underlying emission or low surface brightness features for a substantial fraction of the sample. In this paper we present the first results of the program: deep contour maps in the B band, surface brightness profiles, and color profiles for all the galaxies. The information derived for this sample of galaxies has allowed us to analyze the morphology and the structural components of BCDs. Over 70% of the galaxies show complex profiles that preclude fitting by a single standard law, with extra structure at high to intermediate intensity levels. In 21 galaxies of the sample, an underlying low surface brightness component has been detected.

An Imaging and Spectroscopic Study of the Very Metal-deficient Blue Compact Dwarf Galaxy Tol 1214−277

We present a spectrophotometric study based on VLT/FORS I observations of one of the most metal-deficient blue compact dwarf (BCD) galaxies known, Tol 1214-277 (Z ∼ Z⊙/25). The data show that roughly half of the total luminosity of the BCD originates from a bright and compact starburst region located at the northeastern tip of a faint dwarf galaxy with cometary appearance. The starburst has ignited less than 4 Myr ago and its emission is powered by several thousand O7V stars and ∼170 late-type nitrogen Wolf-Rayet stars located within a compact region with ≲500 pc in diameter. For the first time in a BCD, a relatively strong [Fe V] λ4227 emission line is seen which together with intense He II λ4686 emission indicates the presence of a very hard radiation field in Tol 1214-277. We argue that this extraordinarily hard radiation originates from both Wolf-Rayet stars and radiative shocks in the starburst region. The structural properties of the low surface brightness (LSB) component underlying the starburst have been investigated by means of surface photometry down to 28 B mag arcsec-2. We find that, for a surface brightness level fainter than ∼24.5 B mag arcsec-2, an exponential fitting law provides an adequate approximation to its radial intensity distribution. The broadband colors in the outskirts of the LSB component of Tol 1214-277 are nearly constant and are consistent with an age below one Gyr. This conclusion is supported by the comparison of the observed spectral energy distribution (SED) of the LSB host with theoretical SEDs.