Search

Calculations modeling the effects of stellar evolution on elliptical galaxies (e.g., Bruzual and Kron 1980, Bruzual 1981) suggest that the shape of the spectral flux distribution should remain almost constant in the red and near-infrared out to at least z ~ 2. Thus, it should be possible to derive the redshift of a distant elliptical galaxy by fitting a model galaxy spectrum to broadband near-infrared (RIJHK) photometry.

This paper is concerned with the distant radio galaxies in a sample of bright sources selected at 178 MHz by Laing, Riley & Longair (1982). This sample is 96% complete for sources with θ 20, using the VIA at a wavelength of 6 cm (Laing, Owen & Puschell, in preparation), in order to search for radio cores. We have so far located cores in 16/23 sources and set 5σ upper limits of 0.6 mJy for the remainder. None of the cores had been detected previously. In all cases, the cores coincide with optical objects, although one source (3C 340) had been misidentified. Several ambiguities have now been resolved.

The purpose of this communication is to update our knowledge of the radio structural properties of quasars and blank field radio sources (blank field ≡ any radio source without an identification on the Palomar Sky Survey prints). The quasar sample consists of all sources (25) with angular sizes greater than 10 arcsec in the list of Jodrell Bank quasars observed by Owen, Porcas and Neff (1978). The blank fields consist of 16 3CR sources also with structures >10 arcsec based on Cambridge 5 km telescope observations. The sources were selected in low-frequency surveys; their emission at v < 1 GHz is dominated by extended components with steep spectra. Thus, both samples should be oriented randomly in space except for a slight bias to be in the plane of the sky.

Observations simultaneously made at visual (B, V, and R) wavelengths, at 1, 1.4, and 3.4 mm and at 1.3, 2, 6, and 20 cm of 9 QSOs and BL Lac objects are reported. The range of the millimeter visual spectral index ɑ_(mv) was only 0.65-0.82, typical of optically thin synchrotron emission. This may indicate that the electrons radiating synchrotron emission in this portion of the spectrum are not subjected to large radiative losses, and therefore relativistic bulk motion with Doppler factors ~10 are required. The visual spectral index is much more broadly distributed and typically larger than ɑ_(mv). The spectral energy distributions have not changed much in the last 2-5 years except for 2251 + 15 and perhaps 0235 + 164. Only 1749 +09 shows a sharp spectral break shortward of 1 mm. Sixteen other sources were observed at 1 mm, of which seven were detected.

Calculations modeling the effects of stellar evolution on elliptical galaxies (e.g., Bruzual and Kron 1980, Bruzual 1981) suggest that the shape of the spectral flux distribution should remain almost constant in the red and near-infrared out to at least z ∼ 2. Thus, it should be possible to derive the redshift of a distant elliptical galaxy by fitting a model galaxy spectrum to broadband near-infrared (RIJHK) photometry.

In a search for radio emission from bright, optically selected quasars, we detected ∼50% of the quasars at 5 GHz. This radio detection rate is so much higher than that for faint quasars (

This paper is concerned with the distant radio galaxies in a sample of bright sources selected at 178 MHz by Laing, Riley & Longair (1982). This sample is 96% complete for sources with θ < 10′ and the bias of the 3CR catalogue against sources of large angular size has also been reduced. Deep optical searches have located many candidate identifications, but the probability of a chance coincidence with an unrelated object is appreciable, especially in the faintest cases, unless the area to be searched is small. We have therefore mapped the sources with candidate identifications having V > 20, using the VLA at a wavelength of 6 cm (Laing, Owen & Puschell, in preparation), in order to search for radio cores. We have so far located cores in 16/23 sources and set 5σ upper limits of 0.6 mJy for the remainder. None of the cores had been detected previously. In all cases, the cores coincide with optical objects, although one source (3C 340) had been misidentified. Several ambiguities have now been resolved.

The purpose of this communication is to update our knowledge of the radio structural properties of quasars and blank field radio sources (blank field ≡ any radio source without an identification on the Palomar Sky Survey prints). The quasar sample consists of all sources (25) with angular sizes greater than 10 arcsec in the list of Jodrell Bank quasars observed by Owen, Porcas and Neff (1978). The blank fields consist of 16 3CR sources also with structures >10 arcsec based on Cambridge 5 km telescope observations. The sources were selected in low-frequency surveys; their emission at ν < 1 GHz is dominated by extended components with steep spectra. Thus, both samples should be oriented randomly in space except for a slight bias to be in the plane of the sky.

1200-3200 A IUE spectra of the nucleus of NGC 4552 (M89) were obtained in order to investigate the nature of the strong 10 micron source in this Galaxy. There is a strong, extended UV source in NGC 4552 which has a spatial distribution nearly identical with that at optical wavelengths and is undoubedly stellar in origin. Its properties are consistent with the correlation between UV source strength and metallicity pointed out by Faber (1983). There is no evidence for a nonthermal point source in the UV. It appears unlikely that the 10 micron emission is from heated dust grains. Instead, it is believed the 10 micron radiation is nonthermal in origin, implying a remarkably small size of only 0.1 AU for this source.

Single-epoch multifrequency data are presented for the radio-quiet low-redshift QSO Ton 1542, spanning radio through ultraviolet wavelengths. A 3 Sigma upper limit of 9.2 mJy is obtained for the 20.3 GHz flux density; the first ultraviolet spectrum of this object is presented and discussed. A particularly strong excess of flux density is found at about 3000 A, which is likely to be dominated by Balmer continuum emission. An L-alpha/beta-hydrogen flux ratio of about 17 is also found, which is higher than that usually observed in QSOs.

Optical-infrared (0.36-3.5 microns) photometric data of the radio galaxy 3C 382, obtained in 1976, show a distinct excess at the longest wavelengths, an ultraviolet excess, and a significant increase in brightness since previous photometry by Sandage (1972). A flux excess at infrared wavelengths has also been observed from 3C 227. These properties demonstrate the presence of emission not attributable to stars, probably originating in the nucleus, extending into the infrared portion of the spectrum.

Results are reported for braod-band photometry of the BL Lac object AO 0235+164 carried out over the spectral range from 0.36 to 3.5 microns in December 1975 and in October and November 1976. It is found that the continuum of this object steepened at visible wavelengths between December 1975 and October 1976, but maintained a relatively constant slope in the near-IR despite a factor-of-ten decrease in flux from the maximum level. Visible-wavelength data are cited which appear to suggest that the steepening of the visible spectrum occurred in less than 300 days, while the near-IR level may have been nearly constant. It is shown that the observed change in the spectral shape of the visible-wavelength continuum cannot be explained in terms of a 'composite' model consisting of an unchanging galaxy and a varying nonthermal source with constant spectral index. Two other general classes of models are considered: intrinsic variability and extrinsic modulation.

On a obtenu des mesures de la polarisation lineaire multifrequences, simultanees, entre 1,4 GHz et 90 GHz pour environ 20 radiosources compactes, actives, a six epoques entre decembre 1977 et juillet 1980

Photometric observations are presented for outbursts of the quasi-stellar object QSO 1156+295 in 1981 and 1982. High time resolution photometry is included showing variations on time scales of weeks to about half an hour. Data from early plate material show that the object may have been quite bright at the beginning of this century but was quite faint and probably inactive between about 1950 and the beginning of recent activity in 1977-1979. Some results of optical linear polarization are discussed. In examining spectrophotometric results, broadband spectra show very little change in spectral shape during changes in continuum brightness. High resolution spectra (0.1-A FWHM) show no evidence for the Mg II 2798-A absorption sometimes seen in optically violent variables and other QSOs. The radio flux density variations at several frequencies are documented and discussed and compared with the optical light curve. Models for 1156+295 are discussed including variability time scales, and the observed energy output is compared with a magnetic accretion disk model proposed by Shields and Wheeler (1976). Results are summarized and the different sizes of active and inactive regions of the object are compared.

The characteristics of the changes in the shapes of the spectral-flux distributions of variable extragalactic sources have been observed over the wavelength range 0.36..mu..m to 3.5..mu..m. Pronounced activity has been observed in the sources AO 0235+164, 3C 120, PKS 0735+178, OJ 287 (0851+202), and B2 1308+326. The slope of the spectral-flux distribution has been observed to change significantly in some cases during transitions in observed flux. These changes are interpreted in terms of injection and energy loss of high-energy electrons radiating synchrotron radiation.

Calculations modeling the effects of stellar evolution on the observed colors of elliptical galaxies suggest that the shape of their spectra should remain almost constant in the red and near-infrared for red shifts greater than two. In order to test this idea, JHK photometry of optically faint radio source identifications believed to be faint elliptical galaxies were carried out. Photometric redshift estimates have been made using three different models: a nonevolving elliptical galaxy spectrum, an evolving spectrum based on one of Bruzual's calculations, and an empirical model derived from photometry of distant elliptical galaxies. Redshifts greater than 0.5 are systematically under-estimated by the first two models and for galaxies whose colors are not consistent with the models, deviations occur not only in the optical bands but also in the infrared. The difficulties are not resolved by the addition of a quasar-like nucleus to the galaxies.

Single-epoch multifrequency data for the BL Lac objects OI 90.4 and 3C 66A, spanning radio through ultraviolet wavelengths, are presented, as well as other measurements relevant to intensity and spectral-shape variability. Both BL Lac objects exhibit spectral curvature in the infrared-to-ultraviolet region, a properity that is inferred to be usual for this object class. Variability in the ultraviolet spectral index of OI 90.4 is found, whereas the spectral index of 3C 66A is the same in two observations 17 months apart. A synchrotron self-Compton jet model is applied to each BL Lac object. The OI 90.4 data are found to be best satisfied by a jet with a relatively high degree of relativistic beaming, but emission at frequencies below about 50 GHz is not described by the model. Furthermore, 3C 66A may not always undergo strong relativistic beaming, and the model may incorporate the small fraction of the total radio emission below about 20 GHz that is from within about 1.5 milliarcsec of the core.

Nearly simultaneous radio and infrared-optical observations were obtained for several extragalactic radio sources which are strong at 90 GHz. The spectral-flux distributions are generally peaked or flat over the radio portion of the spectrum with a steeper, power-law behavior at infrared-optical frequencies. For all sources, the radio and infrared-optical portions of the spectral-flux distributions can be smoothly joined by physically sensible interpolations over the spectral gap, although spectral breaks are required. For many of the sources, this is consistent with a common (synchrotron) origin of the radio, millimeter, and infrared-optical radiation. However, proof, in terms of correlated temporal variations and polarization properties, is still generally lacking.

Results are reported for various sets of X-ray, UV, visual, IR, millimeter, and radio observations of OJ 287. The spectral information is used to constrain nonthermal energy production models for the source, and three possible models are considered. It is found that, in order to describe all the observed flux in the radio to X-ray bands with a synchrotron self-Compton model, a high degree of relativistic beaming is required such that the equivalent Doppler factor ranges from about 20 to 165. It is concluded that submillimeter flux and X-ray spectral measurements could distinguish between the two possible models that fit the present observations.

It is noted that in approximately a dozen sources, nearly simultaneous infrared and/or visual spectra are available, making it possible to examine the relationship between the infrared-visual and radio regimes. A simple transition to the steeper infrared spectra is seen as likely with a mean break wavelength of approximately 300 microns in the rest frame. These observations indicate a tapered source geometry, with the smallest structures roughly on the order of 10 to the 16th cm as estimated from the spectral break; this is consistent with scales estimated from optical variability time scales. Large amplitude variations on a six-month time interval are found to be fairly infrequent in most of the sources. A relatively model-independent way of categorizing flux variations as due to changes in source scale, or structure or the slope of the electron energy spectrum is suggested.

A very large-amplitude change in the visual wavelength flux from the radio galaxy 3C 382 occurred on a time scale of about a month during mid-1977. The infrared flux was constant during the onset of the outburst, but showed an increase at 2.28 ..mu..m about a year later. Such activity strongly suggests that the observed infrared radiation does not originate in the same component as the visual wavelength radiation. Extension of the spectral-flux distribution to 10 ..mu..m shows a flattening between 2.20 and 10 ..mu..m. A plausible origin for the infrared flux longward of 2.20 ..mu..m is thermal reradiation by hot dust.

Spectral measurements of the two BL Lac objects OQ 530 and ON 325 are presented. The measurements were taken at frequencies ranging from radio to ultraviolet. Both sources show spectral curvature between the infrared and ultraviolet frequencies. The intensity and spectral shape of OQ 530 vary, but the spectral shape of ON 325 appears to remain constant during intensity variability. A nonthermal theoretical model of jet emission is developed which incorporates both the spectral and time variability data. The model predicts that ON 325 radiates at X-ray frequencies with Compton radiation dominating over synchrotron emission. The angular size of the jet emission is predicted to be less than 0.1 milli-arcsec at high radio frequencies.

We present observations of 3C 371, made at frequencies from the radio to the ultraviolet, which were coordinated during two short time intervals separated by 3 months. We also present 1 keV X-ray flux densities measured at a different time. The multifrequency measurements indicate spectral steepening at visual wavelengths, and that an extrapolation of the ultraviolet continuum falls below the X-ray data. We explain the infrared through X-ray data as relativistically beamed synchrotron self-Compton emission and derive source parameters for two possible models. Our ultraviolet spectra both show strong Lyɑ emission at the same redshift as weak optical emission lines reported previously. We favor production of these lines by recombination of gas after its ionization by the ultraviolet to X-ray continuum radiation. We tentatively identify C IV and N v absorption lines in one of our ultraviolet spectra, which, if real, suggest the presence of a hot (~ 3 x 10^5 K) gaseous halo in 3C 371.