39 research outputs found
HST Observations and Models of The Gravitational Lens System MG 0414+0534
Quadruple gravitational lens systems offer the possibility of measuring time
delays for image pairs, microlensing effects, and extinction in distant
galaxies. Observations of these systems may be used to obtain estimates of H_o
and to study the various mass components of lens galaxies at high redshifts.
With HST, we have observed the reddest known gravitational lens system, MG
0414+0534. We used WFPC2/PC1 to obtain deep, high-resolution images with two
filters, F675W and F814W. We present a detailed analysis of all of the
components, as well as macrolens models. Our main results are: (1) confirmation
that MG 0414+0534 is inescapably a gravitational lens system; (2) discovery of
a blue arc connecting the 3 brightest images of the QSO central core; (3)
accurate positions and apparent brightnesses for all 4 known images of the QSO
central core and for the lens galaxy G; (4) a good representation of the
brightness distribution of G by elliptical isophotes with a De Vaucouleurs
profile, characteristic of an elliptical galaxy; (5) models that consist of
simple elliptical potentials and account qualitatively, not quantitatively, for
the HST image positions, arc morphology and radio flux ratios for the images of
the QSO central core; (6) a possible new test to distinguish between reddening
in the host galaxy of the QSO and in the lens galaxy, based on future accurate
measurements of spatial variations in the color of the arc; and (7) the
suggestion that microlensing is a plausible cause for the differences between
the radio and optical flux ratios for the brightest images, A1 and A2. Further
observations and measurements such as of the redshift of the lens galaxy, can
be used fruitfully to study microlensing for this system.Comment: 27 pages, 8 .ps figs, AAS Latex, AJ, in press, Feb 199
Lensed Quasar Hosts
Gravitational lensing assists in the detection of quasar hosts by amplifying
and distorting the host light away from the unresolved quasar core images. We
present the results of HST observations of 30 quasar hosts at redshifts 1 < z <
4.5. The hosts are small in size (r_e <~ 6 kpc), and span a range of
morphologies consistent with early-types (though smaller in mass) to
disky/late-type. The ratio of the black hole mass (MBH, from the virial
technique) to the bulge mass (M_bulge, from the stellar luminosity) at 1<z<1.7
is broadly consistent with the local value; while MBH/M_bulge at z>1.7 is a
factor of 3--6 higher than the local value. But, depending on the stellar
content the ratio may decline at z>4 (if E/S0-like), flatten off to 6--10 times
the local value (if Sbc-like), or continue to rise (if Im-like). We infer that
galaxy bulge masses must have grown by a factor of 3--6 over the redshift range
3>z>1, and then changed little since z~1. This suggests that the peak epoch of
galaxy formation for massive galaxies is above z~1. We also estimate the duty
cycle of luminous AGNs at z>1 to be ~1%, or 10^7 yrs, with sizable scatter.Comment: 8 pages, 6 figures, review article with C. Impey at the conference on
"QSO Host Galaxies: Evolution and Environment", Aug. 29-Sep. 2, 2005, Lorentz
Center, Leiden, The Netherland
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
First Results from a Photometric Survey of Strong Gravitational Lens Environments
Many strong gravitational lenses lie in complex environments, such as poor
groups of galaxies, that significantly bias conclusions from lens analyses. We
are undertaking a photometric survey of all known galaxy-mass strong lenses to
characterize their environments and include them in careful lens modeling, and
to build a large, uniform sample of galaxy groups at intermediate redshifts for
evolutionary studies. In this paper we present wide-field photometry of the
environments of twelve lens systems with 0.24 < z_lens < 0.5. Using a
red-sequence identifying technique, we find that eight of the twelve lenses lie
in groups, and that ten group-like structures are projected along the line of
sight towards seven of these lenses. Follow-up spectroscopy of a subset of
these fields confirms these results. For lenses in groups, the group centroid
position is consistent with the direction of the external tidal shear required
by lens models. Lens galaxies are not all super-L_* ellipticals; the median
lens luminosity is < L_*, and the distribution of lens luminosities extends 3
magnitudes below L_* (in agreement with theoretical models). Only two of the
lenses in groups are the brightest group galaxy, in qualitative agreement with
theoretical predictions. As in the local Universe, the highest
velocity-dispersion groups contain a brightest member spatially coincident with
the group centroid, whereas lower-dispersion groups tend to have an offset
brightest group galaxy. This suggests that higher-dispersion groups are more
dynamically relaxed than lower-dispersion groups and that at least some evolved
groups exist by z ~ 0.5.Comment: Accepted for publication to the Astrophysical Journal. Figure 1
reduced in resolution. Requires emulateapj.sty. Table 6 to be published
electronically. Revised version includes moderate changes to text, minor
changes to conclusions, addition of one subsectio
Probing the Coevolution of Supermassive Black Holes and Galaxies Using Gravitationally Lensed Quasar Hosts
In the present-day universe, supermassive black hole masses (MBH) appear to
be strongly correlated with their galaxy's bulge luminosity, among other
properties. In this study, we explore the analogous relationship between MBH,
derived using the virial method, and the stellar R-band bulge luminosity (Lr)
or stellar bulge mass (M*) at epochs of 1 < z < 4.5 using a sample of 31
gravitationally lensed AGNs and 20 non-lensed AGNs. At redshifts z > 1.7
(10--12 Gyrs ago), we find that the observed MBH--Lr relation is nearly the
same (to within ~0.3 mag) as it is today. When the observed Lr are corrected
for luminosity evolution, this means that the black holes grew in mass faster
than their hosts, with the MBH/M* mass ratio being a factor of > 4(+2)(-1)
times larger at z > 1.7 than it is today. By the redshift range 1<z<1.7 (8-10
Gyrs ago), the MBH/M* ratio is at most two times higher than today, but it may
be consistent with no evolution. Combining the results, we conclude that the
ratio MBH/M* rises with look-back time, although it may saturate at ~6 times
the local value. Scenarios in which moderately luminous quasar hosts at z>1.7
were fully formed bulges that passively faded to the present epoch are ruled
out.Comment: ApJ accepted, includes Referee comments and statistics to better
quantify the statistical significance of results. 23 pages, 11 figures, 4
table
Radio Astronomy
Contains table of contents and reports on seven research projects.National Science Foundation (Grant AST 86-17172)National Aeronautics and Space AdministrationJet Propulsion LaboratoryNASA/Goddard Space Flight Center (Grant NAG5-10)SM Systems and Research, Inc.U.S. Navy Office of Naval Research (Contract N00014-86-C-2114)Center for Advanced Television StudiesNASA/Goddard Space Flight Center (Grant NAG5-537
Radio Astronomy
Contains table of contents for Section 4 and reports on twelve research projects.National Science Foundation Grant AST 88-19848Jet Propulsion Laboratory Contract 957687National Aeronautics and Space Administration Grant NAGW 1386National Science Foundation Grant AST 88-19848Annie Jump Cannon AwardSM Systems and Research, Inc.U.S. Navy Office of Naval Research Contract N00014-88-K-2016NASA/Goddard Space Flight Center Grant NAG 5-537NASA/Goddard Space Flight Center Grant NAG 5-10Woods Hole Oceanographic Institution Contract SC-28860Leaders for Manufacturing Progra
Radio Astronomy
Contains table of contents for Section 4 and reports on nine research projects.National Science Foundation Grant AST 88-19848National Science Foundation Grant AST 90-22501Alfred P. Sloan FellowshipNational Science Foundation Presidential Young Investigator AwardNational Aeronautics and Space Administration Grant NAGW-2310David and Lucile Packard FellowshipSM Systems and Research CorporationNational Aeronautics and Space Administration/Goddard Space Flight Center Contract NAS 5-30791National Aeronautics and Space Administration/Goddard Space Flight Center Grant NAG5-10Leaders for Manufacturing Progra