35 research outputs found
Extremely Luminous Water Vapor Emission from a Type 2 Quasar at Redshift z = 0.66
A search for water masers in 47 Sloan Digital Sky Survey Type 2 quasars using
the Green Bank Telescope has yielded a detection at a redshift of z = 0.660.
This maser is more than an order of magnitude higher in redshift than any
previously known and, with a total isotropic luminosity of 23,000 L_sun, also
the most powerful. The presence and detectability of water masers in quasars at
z ~ 0.3-0.8 may provide a better understanding of quasar molecular tori and
disks, as well as fundamental quasar and galaxy properties such as black hole
masses. Water masers at cosmologically interesting distances may also
eventually provide, via direct distance determinations, a new cosmological
observable for testing the reality and properties of dark energy, currently
inferred primarily through Type 1a supernova measurements.Comment: 8 pages including 1 figure; accepted for publication in ApJ Letter
New CO and Millimeter Continuum Observations of the z=2.394 Radio Galaxy 53W002
The z=2.39 radio galaxy 53W002 lies in a cluster of Ly-alpha emission line
objects and may itself be undergoing a major burst of star formation. CO(3--2)
emission, at 102 GHz, was detected from 53W002 by Scoville et al. (1997a), who
also reported a possible 30 kpc extension and velocity gradient suggesting a
rotating gaseous disk. In this paper we present new interferometric CO(3--2)
observations which confirm the previous line detection with improved
signal-to-noise ratio, but show no evidence for source extension or velocity
gradient. The compact nature of the CO source and the molecular mass found in
this object are similar to luminous infrared galaxies and other AGNs previously
studied
A Submillimeter Survey of Gravitationally Lensed Quasars
Submillimeter (and in some cases millimeter) wavelength continuum
measurements are presented for a sample of 40 active galactic nuclei (probably
all quasars) lensed by foreground galaxies. The object of this study is to use
the lensing boost, anywhere from ~3- 20 times, to detect dust emission from
more typical AGNs than the extremely luminous ones currently accessible without
lensing. The sources are a mix of radio loud and radio quiet quasars, and,
after correction for synchrotron radation (in the few cases where necessary),
23 of the 40 (58%) are detected in dust emission at 850um; 11 are also detected
at 450um. Dust luminosities and masses are derived after correction for lensing
magnification, and luminosities are plotted against redshift from z = 1 to z =
4.4, the redshift range of the sample. The main conclusions are (1)
Monochromatic submillimeter luminosities of quasars are, on average, only a few
times greater than those of local IRAS galaxies; (2) Radio quiet and radio loud
quasars do not differ significantly in their dust lumimosity; (3) Mean dust
luminosities of quasars and radio galaxies over the same redshift range are
comparable; (4) Quasars and radio galaxies alike show evidence for more
luminous and massive dust sources toward higher redshift, consistent with an
early epoch of formation and possibly indicating that the percentage of
obscured AGNs increases with redshift.Comment: 10 pages, 4 figures, uses aastex.cls and emulateapj5.st
VLBA Imaging of Central Engines in Radio Quiet Quasars
We have used the Very Long Baseline Array (VLBA) to image five radio-quiet
quasars (RQQs) at milliarcsecond resolution, at frequencies between 1.4 and 5
GHz. These quasars have typical total flux densities of a few millijansky at
gigahertz frequencies, and are compact on arcsecond scales. The VLBA images
reveal that four of the quasars are dominated by unresolved radio cores, while
the fifth has an apparent two-sided jet. Typical core brightness temperatures
range from 10^8 K to at least 10^9 K. The compact radio morphologies and X-ray
luminosities of many objects in the RQQ sample seem to indicate classical
accretion onto black holes as massive as 10^9 solar masses, with emission
physics in many ways similar to their radio-loud counterparts. Therefore, the
relatively small amount of radiative energy emerging at radio wavelengths in
the RQQs may simply be due to the presence of less powerful radio jets.Comment: Accepted for ApJ, Vol. 621, March 1, 2005. 20 pages, 3 figure
Radio Variability of Radio Quiet and Radio Loud Quasars
The majority of quasars are weak in their radio emission, with flux densities
comparable to those in the optical, and energies far lower. A small fraction,
about 10%, are hundreds to thousands of times stronger in the radio.
Conventional wisdom holds that there are two classes of quasars, the radio
quiets and radio louds, with a deficit of sources having intermediate power.
Are there really two separate populations, and if so, is the physics of the
radio emission fundamentally different between them? This paper addresses the
second question, through a study of radio variability across the full range of
radio power, from quiet to loud. The basic findings are that the root mean
square amplitude of variability is independent of radio luminosity or
radio-to-optical flux density ratio, and that fractionally large variations can
occur on timescales of months or less in both radio quiet and radio loud
quasars. Combining this with similarities in other indicators, such as radio
spectral index and the presence of VLBI-scale components, leads to the
suggestion that the physics of radio emission in the inner regions of all
quasars is essentially the same, involving a compact, partially opaque core
together with a beamed jet.Comment: 32 pages, 9 figures. Astrophysical Journal, in pres