We present results on a multiwavelength campaign to identify the nature of dust-reddened Type 1 quasars. These quasars were selected by matching FIRST, 2MASS and very red optical counterparts with r' − K > 5. We find a very high fraction of Low Ionization Broad Absorption Line Quasars (LoBALs) among AGN selected with this method, perhaps a sign of quasar feedback. From X-ray observations and Balmer decrement measurements, the obscuring dust is most likely located in a cold absorber such as the host galaxy, rather than from a torus near the AGN. Hubble ACS imaging of a sub-sample of these sources showed a very high fraction of interacting and merging systems. The quasars appear to be very young in which dust from the merging galaxies is still settling in. Spitzer IRS and MIPS data show star formation signatures and deep Silicate absorption features in these objects, but overall the quasar is the dominant source in the Mid-infrared.
We present moderate-resolution Keck spectroscopy of quasars at z = 5.82, 5.99, and 6.28, discovered by the Sloan Digital Sky Survey (SDSS). We find that the Lyα absorption in the spectra of these quasars evolves strongly with redshift. To z ∼ 5.7, the Lyα absorption evolves as expected from an extrapolation from lower redshifts. However, in the highest-redshift object, SDSSp J103027.10+052455.0 (z = 6.28), the average transmitted flux is 0.0038 ± 0.0026 times that of the continuum level over 8450 Å < λ < 8710 Å (5.95 < zabs < 6.16), consistent with zero flux. Thus the flux level drops by a factor of greater than 150 and is consistent with zero flux in the Lyα forest region immediately blueward of the Lyα emission line, compared with a drop by a factor of ∼10 at zabs ∼ 5.3. A similar break is seen at Lyβ; because of the decreased oscillator strength of this transition, this allows us to put a considerably stronger limit, τeff > 20, on the optical depth to Lyα absorption at z = 6. This is a clear detection of a complete Gunn-Peterson trough, caused by neutral hydrogen in the intergalactic medium. Even a small neutral hydrogen fraction in the intergalactic medium would result in an undetectable flux in the Lyα forest region. Therefore, the existence of the Gunn-Peterson trough by itself does not indicate that the quasar is observed prior to the reionization epoch. However, the fast evolution of the mean absorption in these high-redshift quasars suggests that the mean ionizing background along the line of sight to this quasar has declined significantly from z ∼ 5 to 6, and the universe is approaching the reionization epoch at z ∼ 6.
A program to identify optical counterparts of X-ray sources discovered with the Einstein Observatory has resulted in an independent identification of CH UMa as a cataclysmic variable. Spectrophotometric observations made with the Intensified Image Dissector Scanner on the 2.1-m telescope at KPNO revealed an emission line spectrum from a mb ~ 15 mag object similar to the spectra of cataclysmic variables. A subsequent search of the Harvard photographic plate collection revealed outbursts of 4 mag in amplitude.
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 .
New radio and X-ray observations of the galactic supernova remnant G29.7-0.3 show that it is composed of two spectrally distinct components: a steep-spectrum, incomplete shell 3 arcmin in extent enclosing a flat-spectrum, X-ray emitting region 30 arcsec across. Thus, G29.7-0.3 joins the ranks of supernova remnants which exhibit a combination of Crab-like and shell remnant attributes. The Crab-like core has the highest ratio of X-ray radio luminosity of all the Crab-like remnants observed to date, suggesting that it is an extremely young object.
view Abstract Citations (20) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of nine supernova remnants at 10.6 GHz. Becker, R. H. ; Kundu, M. R. Abstract Intensity contour and polarization observation maps of nine supernova remnants at a microwave frequency are presented and discussed. The data provided are the highest-frequency (10.6 GHz) measurements to date for several of these sources and should therefore be useful in determining their spectra. Polarization ranges from 2 or 3% to as high as 40-50%. Integrated fluxes for the sources vary from about 3 to more than 25. Publication: The Astronomical Journal Pub Date: September 1975 DOI: 10.1086/111797 Bibcode: 1975AJ.....80..679B Keywords: Astronomical Maps; Brightness; Polarization Characteristics; Supernova Remnants; Astronomical Coordinates; Radio Astronomy; Radio Sources (Astronomy); Radio Spectra; Spatial Distribution; Superhigh Frequencies; Astronomy full text sources ADS | data products SIMBAD (13)
