Normal Quasars Research Articles

The infrared color evolution of active nuclei

view Abstract Citations (14) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Infrared Color Evolution of Active Nuclei Baan, Willem A. Abstract The far-infrared color evolution is studied for galaxies with a nuclear starburst or an AGN. The nuclear source heats the surrounding dust to an effective blackbody temperature (T_d_ = 50-100 K). The color and luminosity evolution for such galaxies is simulated by letting the central heating source and the resulting warm dust emission (the primary source) decay exponentially in combination with a slower decaying secondary IR emission source. Secondary spectral components can be nonthermal or (hot or cold) thermal in nature and may be associated with the nuclear activity or with the rest of the galaxy. The evolving far-infrared (FIR) galaxy traverses the FIR color diagrams in a rather systematic fashion, and an FIR galaxy can be modeled very effectively with an appropriate mixture of primary and secondary luminosity contributions. The secondary components must have an initial strength of 0.1-0.005 relative to the primary source. Superluminous FIR sources with dominant nuclear sources lie at the start of the simulated evolutionary tracks in the color-color diagrams. While these sources evolve across the color diagram they will reveal more of their nuclear characteristics and eventually they may appear to the observer as normal Seyferts or quasars. The group of powerful FIR sources also incorporates the OH megamaser galaxies. A luminosity function is constructed for the family of nuclear FIR sources. A single distribution of nuclear FIR sources can account for the observed luminosity function at high L_IR_. Another distribution of nonnuclear sources is required to explain the low-luminosity end. Publication: The Astrophysical Journal Pub Date: July 1988 DOI: 10.1086/166508 Bibcode: 1988ApJ...330..743B Keywords: Active Galactic Nuclei; Color-Color Diagram; Infrared Sources (Astronomy); Seyfert Galaxies; Far Infrared Radiation; Infrared Spectra; Interstellar Matter; Luminosity; Starburst Galaxies; Astrophysics; GALAXIES: NUCLEI; INFRARED: SOURCES; INTERSTELLAR: GRAINS full text sources ADS | data products SIMBAD (10) NED (6)

Far-infrared variability in active galactic nuclei

Pointed IRAS observations of 20 active galaxies were examined in the first detailed search for far-infrared variability in a large sample of active galaxies. Less extensive survey data were also checked for evidence of strong 6-month variability in 45 active galaxies. The far-infrared fluxes of three highly polarized objects ('blazars') appeared to vary by up to a factor of 2 on time scales of a few months. No convincing cases of variability greater than about 15 percent (rms) were found in any of the normal quasars or Seyfert galaxies studied. It appears that blazars tend to be variable at all wavelengths, but most active galaxies may be systematically less variable in the far-infrared than at higher frequencies.

Low Frequency Cutoffs in the Spectra of Radioquiet Quasars

Radio-quiet and normal radio-loud quasars have very similar spectral properties in the ultraviolet, optical and near infrared regions, but their radio powers differ by several orders of magnitude. Somewhere between the near infrared and the radio their spectra must diverge dramatically.The IRAS survey detected 17 radio quiet quasars and luminous Seyfert 1's with −29. 5 ≤ Mv ≤ −21.6 (for Ho = 75). By coadding the survey data and using pointed observations, we have detections of most of these objects in all four IRAS passbands. The spectra are all rising with wavelength all the way to 100μ. We are measuring fluxes in the centimeter, millimeter, and, together with R Cutri, the near infrared and optical regions for each of these objects. Our goal is to constrain the location, shape, and spectral context of the low frequency cutoffs. Here we present the IRAS, millimeter and centimeter data. Measurements at the other wavelengths are still in progress.Although the spectra are rising steeply between 60μ and 100μ, we find that all of our objects are undetectable at 1.3 mm with the NRAO 12-m telescope. Our limits are typically an order of magnitude below the 100μ fluxes. (Ennis et al (1982) and Robson et al (1985) have already shown that the 1 mm fluxes of some radio quiet quasars must be below the extrapolation of the near infrared continuum.) Our objects are all extremely weak or undetected with the VLA at 2 cm and 1.3 cm, at levels typically three orders of magnitude below the 100μ fluxes. The sharpness of the required cutoffs allows us to rule out the hypothesis that the infrared is synchrotron radiation with the cutoff due to an absence of low energy electrons. The high frequency of the cutoffs makes free-free absorption implausible, but not impossible. It is possible that synchrotron self-absorption is suppressing the radio. There is circumstantial evidence that the far infrared is thermal dust emission. This would require a lower cutoff in the distribution of dust temperatures, which we think we can explain.

The emission-line regions in broad absorption line quasars

view Abstract Citations (89) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Emission-Line Regions in Broad Absorption Line Quasars Hartig, G. F. ; Baldwin, J. A. Abstract The properties of the emission-line regions in 16 broad absorption line (BAL) quasars are compared to those of non-BAL quasars. It is found that about half the BAL quasars, those having detached BALs, are significantly different from the comparison samples of normal quasars. They have large Al III/semiforbidden C III intensity ratios, strong Fe II emission, and unusually weak C IV emission lines whose profiles do not agree well with those of the lower ionization emission lines. New spectra of the Mg II 2798 A region in 13 of these BAL quasars show a few cases of possible weak Mg II BAL absorption, but no unambiguously strong cases. Thus, it is concluded that strong BAL absorption in Mg II is rare. The quasar H0335 -336 has very narrow emission lines (1000 km/s), and thus may offer a rare opportunity to measure many weak or normally blended emission lines which can give information about physical conditions in the emission-line gas. Publication: The Astrophysical Journal Pub Date: March 1986 DOI: 10.1086/163974 Bibcode: 1986ApJ...302...64H Keywords: Astronomical Spectroscopy; Emission Spectra; Quasars; Spectral Energy Distribution; Spectral Line Width; Abundance; Aluminum; Carbon; Iron; Spectrum Analysis; Astrophysics; QUASARS full text sources ADS | data products SIMBAD (18) NED (17)

Variability of Lyman-alpha and the ultraviolet continuum of 3C 446

IUE observations have been conducted over the 1230-3175 A range for the violently variable quasar 3C 446, beginning in June 1980, at intervals of 1.2, 2.2, 0.5, and 0.4 yr. Strong absorption of the continuum was found below 1830 A, probably corresponding to a Lyman edge at z of 1.00 + or - 0.01. The absence of Mg II 2798 A absorption implies that the column density is in the lower end of the range, unless the gas is metal-poor. The Lyman-alpha emission line was detected in five spectra; relative to the number of ionizing protons, the line strengths are the same as in normal quasars, and line equivalent widths are small due to the continuum's rise redward of 912 A, which is much steeper than in normal quasars. The Lyman-alpha line and the nearby continuum vary so as to maintain constant equivalent width.

The ultraviolet excess of quasars. III - The highly polarized quasars PKS 0736 + 017 and PKS 1510 - 089

Ultraviolet/optical/infrared spectrophotometry of the highly-polarized quasars (HPQ's) PKS 0736 + 047 and PKS 1510 089 is analyzed. A blazer continuum component like that in BL Lac objects (e.g. with violent variability, high polarization, and a steep power-law shape) contributes about half the visual light of 1510 - 089, and at least three-quarters of that in 0736 + 017. The remaining light has the same spectrum as normal (low-polarization) quasars, including an ultraviolet excess or blue bump, which is easily detected in the IUE spectra of 1510 - 089, and weakly detected in 0736 + 017. The line fluxes do vary, but not as much as the continuum. The ratios of the broad emission lines, and the Balmer continuum are normal in both quasars.

CONTINUUM AND LINE FLUXES OF OJ 287 AT MINIMUM LIGHT.

ABSTRACT The authors report optical-infrared continuum observations of OJ 287 during its lowest recorded flux level. The spectrum was steeper than previously seen, but does not unambiguously show the presence of any underlying galaxy. It is suggested that this is primarily due to the object's still being too bright to make such a detection in this manner. The authors also report spectroscopic observations of OJ 287 showing the presence of Hα, Hβ, and [O III] emission lines. These lines confirm a redshift z = 0.306. The data are also used to compare the emitted luminosities in these lines to those of other active extragalactic objects. These lines are intrinsically underluminous compared to quasars of similar ionizing luminosities. The data are consistent with OJ 287 being deficient in gas compared to normal quasars or with the observed continuum flux having a Doppler factor of δ ≡ 4.

Spectrophotometry of the broad absorption-line QSO PHL 5200

Spectrophotometric observations of PHL 5200 conducted from 1974 to 1979 are presented. The semiforbidden C III 1909 and Mg II 2799 emission lines give an emission redshift of 1.981 + or - 0.002 using the peak of the profile. The semiforbidden C III 1909/C IV 1549 emission line ratio, after correction for absorption, is more than the average for normal quasars. In addition, the spectrum shows more structure between C IV 1549 emission and semiforbidden C III 1909 emission than in the case of normal quasars. The absorption profiles are investigated by using symmetrical logarithmic profiles to model the emission lines. The residual intensities at different wavelengths in the absorption troughs are employed to map optical depth as a function of velocity, assuming that the absorption region covers a small part of the sky as seen from the central source. Spectra from five observing seasons are compared, and no apparent changes in the C IV and Si IV absorption troughs are found.

The class of highly polarized quasars - Observations and description

view Abstract Citations (166) References (115) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The class of highly polarized quasars : observations and description. Moore, R. L. ; Stockman, H. S. Abstract The properties of the class of quasars whose optical continua are highly polarized are presented and discussed. A recent polarization survey of quasars has discovered ten new definite members of this class and eight possible members. There are now 17 highly polarized quasars known and an additional nine quasars which are possibly highly polarized. This represents a dramatic increase in the size of the class and allows a much better description of their properties. In general, highly polarized quasars are compact, flat-spectrum radio sources, have steep optical continua, and exhibit rapid large-amplitude variability. While their continua are very similar to BL Lac objects, their typical luminosities and emission line strengths appear to be similar to those of normal low-polarization quasars. As a link between normal quasars and BL Lac objects, the highly polarized quasars are a key test for theoretical models. Publication: The Astrophysical Journal Pub Date: January 1981 DOI: 10.1086/158567 Bibcode: 1981ApJ...243...60M Keywords: Astronomical Photometry; Bl Lacertae Objects; Optical Polarization; Quasars; Circular Polarization; Luminosity; Polarimetry; Red Shift; Variability; X Ray Sources; Astronomy full text sources ADS | data products SIMBAD (20) NED (18)

3C 206 - A resolved quasar in a cluster of galaxies

Spectroscopic and photometric observations obtained of the quasar 3C 206 and its resolved optical structure show that 3C 206 is a normal (optically variable) quasar, which is seated in a luminous elliptical galaxy. The resolved underlying galactic disk has the color and intrinsic luminosity considered normal for an elliptical galaxy with a red shift of 0.2; the spectrum displays low-excitation emission lines and Ca II (H and K) absorption lines with the quasar redshift. Moreover, 3C 206 is found to be centered in a rather compact cluster of fainter galaxies (Bautz-Morgan type I), at least one of which also has the quasar redshift.

Struktur und Entwicklung kompakter Radioquellen

AbstractA model is suggested which accounts for (i) the observed shape and angular variation of compact radio sources (especially the apparent superrelativistic velocities and the absence of contracting sources), (ii) the flux variation associated with the angular variation, and (iii) all the known cases of apparent occurence of surface brightness exceeding the theoretical upper limit provided by the inverse COMPTON effect, preserving the usual premises: cosmological origin of the redshift and incoherent synchrotron radiation of electrons. The model consists of a plasma ring expanding with moderate relativistic velocity.It provides two possibilities for estimating the distance of the sources by radio data: from the time dependence of the angular expansion and from the angular diameter and the shape of flux variation. In the context of cosmology this distances are „angular distances”︁ and therefore, if the redshift is also known, the HUBBLE constant or the acceleration parameter q0 may be obtained.The second method is applied to BL Lac yielding approximately 6 Mpc. So the underlying galaxy would be a dwarf system of M ≈︂–13. The active nucleus of M ≈︂ – 16 is rather below the normal quasars. This seems very satisfactory in view of the short time scale of variations in BL Lac compared to the quasars.