We present the results of a correlation of the ROSAT All-Sky Survey with the April 1997 release of the VLA 20cm FIRST catalogue. We focus our analysis on the 843 X-ray sources which have unique radio counterparts. The majority of these objects (84%) have optical counterparts on the POSS 1 plates. Approximately 30% have been previously classified and we obtain new spectroscopic classifications for 85 sources by comparison with the ongoing FIRST Bright Quasar Survey and 106 additional sources from our own new spectroscopic data. Approximately 51% of the sources are presently classified, and the majority of the unclassified objects are optically faint. The newly classified sources are generally radio weak, exhibiting properties intermediate with previous samples of radio- and X- ray selected AGN. This also holds for the subsample of 71 BL Lacs which includes many intermediate objects. The 146 quasars show no evidence for a bimodal distribution in their radio-loudness parameter, indicating that the supposed division between radio-quiet and radio-loud AGN may not be real. The X-ray and radio luminosities are correlated over two decades in radio luminosity, spanning the radio-loud and radio-quiet regimes, with radio-quiet quasars showing a linear correlation between the two luminosities. Many of the sources show pecu- liar or unusual properties which call for more detailed follow-up observations. We also give the X-ray and radio data for the 518 X-ray sources for which more than one radio object is found. Because of the difficulties inherent in identifying optical coun- terparts to these complex sources, we do not consider these data in the current analysis 1 .
view Abstract Citations (56) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio Constraints on Relativistic Beaming Models of BL Lacertae Objects Kollgaard, R. I. ; Palma, C. ; Laurent-Muehleisen, S. A. ; Feigelson, E. D. Abstract We present new deep radio images of seven X-ray-selected BL Lacertae objects (XBLs) completing our survey of XBLs detected by HEAO 1. The diffuse, extended radio structures of XBLs have extended radio luminosities in the range of 10^23^-10^25^ W Hz^-1^. These radio measurements are compared with similar data for radio-selected BL Lacertae objects (RBLs) and galaxies. All three classes have parallel correlations between the radio luminosity of the core and extended radio luminosities with P_ext_ is proportional to P_core_^1.2^. The cores of the XBLs and RBLs are on average 160 and 4000 times (respectively) stronger than the galaxy cores when normalized to a constant extended radio luminosity. This result is consistent with the expectations of unified schemes connecting BL Lacertae objects and radio galaxies via different jet orientations. The high level of core enhancement in BL Lacertae objects is incompatible with simple models assuming a continuous jet requiring jets with a few discrete components. Assuming a constant jet Lorentz factor {GAMMA}, the core enhancements require that {GAMMA} > 4.5 and probably exceed {GAMMA} = 6, with average angles to the line of sight of approximately 60^deg^, 20^deg^, and 10^deg^ for the galaxies, XBLs, and RBLs (respectively). These results are consistent with independent estimates from studies of BL Lacertae objects' superluminal speeds and luminosity functions. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177406 Bibcode: 1996ApJ...465..115K Keywords: GALAXIES: BL LACERTAE OBJECTS: GENERAL; GALAXIES: JETS; RADIO CONTINUUM: GALAXIES; X-RAYS: GALAXIES full text sources ADS | data products NED (80) SIMBAD (6)
We report the discovery of a small-separation quasar pair (z=0.586, O=18.4, 19.2, and a separation of 23) associated with the radio source FIRST J164311.3+315618 (S1400=120 mJy). The spectrum of the brighter quasar (A) has a much stronger narrow emission line spectrum than the other (B), and it also has stronger Balmer lines relative to the continuum. The continuum ratio of the spectra is flat in the blue (λobs<6000 Å) at about 2.1 but falls to 1.5 at longer wavelengths. A K' image shows two unresolved sources with a flux ratio of 1.3. The different colors appear to result from the contribution of the host galaxy of B, which is evident from Ca II and high-order Balmer absorption lines that are indicative of a substantial young stellar population. New 3.6 cm VLA observations show that the compact radio source is coincident with quasar A (B is only marginally detected). We rule out the lensing hypothesis because the optical flux ratio is A/B≈1.5-2, while the radio flux ratio is A/B≳40, and conclude that this system is a binary. Moreover, the radio-loud quasar is a compact, steep spectrum source. FIRST J164311.3+315618A, B is the lowest redshift and smallest separation binary quasar yet identified.
New multi-frequency radio observations of a large sample of radio-selected BAL quasars, along with a very well matched sample of normal quasars, are presented. The observations were made one immediately after the other at 4.9 and 8.4 GHz with the goal of measuring the radio spectral index of each source. We have identified, for the first time, a significant difference in the spectral index distributions of BAL versus non-BAL quasars, with BAL sources showing an overabundance of steep-spectrum sources. This is the first direct observation suggesting that BAL quasars are more likely to be seen farther from the radio jet axis, although a range of orientations is needed to explain the width of the distribution. Utilizing a few different relationships between spectral index and viewing angle, we have also performed Monte-Carlo simulations to quantify the viewing angle to these sources. We find that the difference in the distributions of spectral index can be explained by allowing the BAL sources to have viewing angles extending about 10 degrees farther from the jet axis than non-BAL quasars.
This paper presents an analysis of a Keck HIRES spectrum of the QSO FIRST J104459.6+365605, covering the rest wavelength range from 2260 to 2900 Å. The line of sight toward the QSO contains two clusters of outflowing clouds that give rise to broad blue-shifted absorption lines. The outflow velocities of the clouds range from -200 to -1200 km s-1 and from -3400 to -5200 km s-1, respectively. The width of the individual absorption lines ranges from 50 to more than 1000 km s-1. The most prominent absorption lines are those of Mg II, Mg I, and Fe II, and Mn II is also present. The low-ionization absorption lines occur at the same velocities as the most saturated Mg II lines, showing that the Fe II, Mg I, and Mg II line-forming regions must be closely associated. Many absorption lines from excited states of Fe II are present, allowing a determination of the population of several low-lying energy levels. The populations of the excited levels are found to be considerably smaller than expected for LTE and imply an electron density in the Fe II line-forming regions of ne ~ 4 × 103 cm-3. Modeling the ionization state of the absorbing gas with this value of the electron density as a constraint, we find that the distance between the Fe II and Mg I line-forming region and the continuum source is ~7 × 102 pc. From the correspondence in velocity between the Fe II, Mg I, and Mg II lines we infer that the Mg II lines must be formed at the same distance. The Mg II absorption fulfills the criteria for broad absorption lines defined by Weymann and coworkers. Therefore, the distance we find between the Mg II line-forming region and the continuum source is surprising, since BALs are generally thought to be formed in outflows at a much smaller distance from the nucleus.
We present the broad band, radio - to - X-ray, prop- erties of a large sample of mostly previously optically unidenti- ed radio-loud X-ray sources from the correlation of a ROSAT All-Sky Survey source list with the 5 GHz Green Bank Survey of the northern sky (RGB sample) which is one of the largest well-dened flux-limited surveys of AGN ever obtained. Fur- ther, the RGB pushes 1-2 orders of magnitude deeper in both X-ray and radio flux compared to previous unbiased wide-area AGN surveys. Follow up VLA observations of the candidate objects yielded positions with arcsec accuracy which were used to nd optical counterparts to the sources from digitized POSS plates. The sources are divided into three classes according to the po- sitional offset between the X-ray and radio candidates and the spatial resolution of the radio observations, reflecting the vari- ous degrees of condence about the correctness of the proposed association. Although the nature of the sources as well as their redshifts remain to be determined in spectroscopic follow up observa- tions, the derived flux ratios lead to the conclusion that the ma- jority of them are quasars. Hardly any correlations could be found between different source parameters, possibly due to the fact that most of the objects are found in a relatively small flux range near the sensitivity limit of the radio catalogue. The majority of the new RGB sources have broad-band properties between those of traditional radio-selected and X- ray selected AGN. There is no bimodal distribution in the radio- loudnessdistribution,andthetraditionaldivisionbetweenradio- quiet and radio-loud AGN may not be warranted
A sample of 4208 objects with magnitude 15 < g* < 22 and colors of main-sequence A stars have been selected from 370 deg2 of Sloan Digital Sky Survey (SDSS) commissioning observations. The data is from two long, narrow stripes, each with an opening angle of greater than 60°, at Galactic latitudes 36° < |b| < 63° on the celestial equator. Relative photometric calibrations good to 2% and consistent absolute photometry allows this uniform sample to be treated statistically over the large area. An examination of the sample's distribution shows that these stars trace considerable substructure in the halo. Large overdensities of A-colored stars in the north at (l, b, R) = (350°, 50°, 46 kpc) and in the south at (157, -58, 33 kpc) and extending over tens of degrees are present in the halo of the Milky Way. Ivezic et al. have detected the northern structure from a sample of RR Lyrae stars in the SDSS.
