4,063 research outputs found
A Common Origin for Quasar Extended Emission-Line Regions and Their Broad-Line Regions
We present a correlation between the presence of luminous extended
emission-line regions (EELRs) and the metallicity of the broad-line regions
(BLRs) of low-redshift quasars. The result is based on ground-based [O III]
5007 narrow-band imaging and Hubble Space Telescope UV spectra of 12 quasars at
0.20 < z < 0.45. Quasars showing luminous EELRs have low-metallicity BLRs (Z <
0.6 Z_Solar), while the remaining quasars show typical metal-rich gas (Z >
Z_Solar). Previous studies have shown that EELRs themselves also have low
metallicities (Z < 0.5 Z_Solar). The correlation between the occurrence of
EELRs and the metallicity of the BLRs, strengthened by the sub-Solar
metallicity in both regions, indicates a common external origin for the gas,
almost certainly from the merger of a gas-rich galaxy. Our results provide the
first direct observational evidence that the gas from a merger can indeed be
driven down to the immediate vicinity (< 1 pc) of the central black hole.Comment: Accepted for publication in ApJ Letters. 4 pages, 1 figure, 1 tabl
Searching for intrinsic charm in the proton at the LHC
Despite rather long-term theoretical and experimental studies, the hypothesis
of the non-zero intrinsic (or valence-like) heavy quark component of the proton
distribution functions has not yet been confirmed or rejected. The LHC with
-collisions at 7--14 TeV will obviously supply extra unique
information concerning the above-mentioned component of the proton. To use the
LHC potential, first of all, one should select the parton-level (sub)processes
(and final-state signatures) that are most sensitive to the intrinsic heavy
quark contributions. To this end inclusive production of -jets
accompanied by photons is considered. On the basis of the performed theoretical
study it is demonstrated that the investigation of the intrinsic heavy quark
contributions looks very promising at the LHC in processes such as
.Comment: 13 pages, 6 figure
PG 1700+518 Revisited: Adaptive Optics Imaging and a Revised Starburst Age for the Companion
We present the results of adaptive-optics imaging of the z=0.2923 QSO PG
1700+518 in the J and H bands. The extension to the north of the QSO is clearly
seen to be a discrete companion with a well-defined tidal tail, rather than a
feature associated with the host galaxy of PG 1700+518 itself. On the other
hand, an extension to the southwest of the QSO (seen best in deeper, but
lower-resolution, optical images) does likely comprise tidal material from the
host galaxy. The SED derived from images in J, H, and two non-standard optical
bands indicates the presence of dust intermixed with the stellar component. We
use our previously reported Keck spectrum of the companion, the SED found from
the imaging data, and updated spectral-synthesis models to constrain the
stellar populations in the companion and to redetermine the age of the
starburst. While our best-fit age of 0.085 Gyr is nearly the same as our
earlier determination, the fit of the new models is considerably better. This
age is found to be remarkably robust with respect to different assumptions
about the nature of the older stellar component and the effects of dust.Comment: 11 pages; includes two eps figures. Latex (AASTEX). Two additional
figures in gif format. Postscript version including all figs. (424 kb) can be
obtained from http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
ApJ. Letter
Bayesian estimation for selective trace gas detection
We present a Bayesian estimation analysis for a particular trace gas
detection technique with species separation provided by differential diffusion.
The proposed method collects a sample containing multiple gas species into a
common volume, and then allows it to diffuse across a linear array of optical
absorption detectors, using, for example, high-finesse Fabry-Perot cavities.
The estimation procedure assumes that all gas parameters (e.g. diffusion
constants, optical cross sections) are known except for the number population
of each species, which are determined from the time-of-flight absorption
profiles in each detector
Oxygen Gas Abundances at 0.4<z<1.5: Implications for the Chemical Evolution History of Galaxies
We report VLT-ISAAC and Keck-NIRSPEC near-infrared spectroscopy for a sample
of 30 0.47<z<0.92 CFRS galaxies and five [OII]-selected, M_B,AB<-21.5, z~1.4
galaxies. We have measured Halpha and [NII] line fluxes for the CFRS galaxies
which have [OII], Hbeta and [OIII] line fluxes available from optical
spectroscopy. For the z~1.4 objects we measured Hbeta and [OIII] emission line
fluxes from J-band spectra, and Halpha line fluxes plus upper limits for [NII]
fluxes from H-band spectra. We derive the extinction and oxygen abundances for
the sample using a method based on a set of ionisation parameter and oxygen
abundance diagnostics, simultaneously fitting the [OII], Hbeta, [OIII], Halpha
and [NII] line fluxes. Our most salient conclusions are: a) the source of gas
ionisation in the 30 CFRS and in all z~1.4 galaxies is not due to AGN activity;
b) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have
substantially lower metallicities than local galaxies with similar luminosities
and star formation rates; c) comparison with a chemical evolution model
indicates that these low metallicity galaxies are unlikely to be the
progenitors of metal-poor dwarf galaxies at z~0, but more likely the
progenitors of massive spirals; d) the z~1.4 galaxies are characterized by the
high [OIII]/[OII] line ratios, low extinction and low metallicity that are
typical of lower luminosity CADIS galaxies at 0.4<z<0.7, and of more luminous
Lyman Break Galaxies at z~3.1, but not seen in CFRS galaxies at 0.4<z<1.0; e)
the properties of the z~1.4 galaxies suggest that the period of rapid chemical
evolution takes place progressively in lower mass systems as the universe ages,
and thus provides further support for a downsizing picture of galaxy formation,
at least from z~1.4 to today.Comment: Proceedings contribution for "The Fabulous Destiny of Galaxies;
Bridging Past and Present", Marseille, 200
High-Resolution K' Imaging of the z = 1.786 Radio Galaxy 3C 294
We have obtained imaging in the K' band (~I-band rest frame) of the z=1.786
radio galaxy 3C 294 with the 36-element curvature-sensing adaptive optics
system Hokupa`a and the Canada-France-Hawaii Telescope. At a resolution of <
\~0."15, the galaxy is seen as a group of small but resolved knots distributed
over a roughly triangular region ~1."4 across. The interpretation of the
structure depends on the location of the nucleus, as indicated by the compact
radio core. Its position is uncertain by > ~0."5 (2-sigma) because of
uncertainties in the optical astrometry, but our best estimate places it at or
near the southern apex of the distribution. If this location is correct, the
most likely interpretation is that of a hidden quasar nucleus illuminating
dusty infalling dwarf-galaxy-like clumps having characteristic sizes of ~1.5
kpc.Comment: 8 pages. One figure in gif format. Postscript version including fig.
(240 kb) available at http://www.ifa.hawaii.edu/~canaguby/preprints.html To
appear in ApJ. Letter
Near-Infrared Spectroscopy of 0.4<z<1.0 CFRS Galaxies: Oxygen Abundances, SFRs and Dust
Using new J-band VLT-ISAAC and Keck-NIRSPEC spectroscopy, we have measured
Halpha and [NII] line fluxes for 0.47<z<0.92 CFRS galaxies which have [OII],
Hbeta and [OIII]a line fluxes available from optical spectroscopy, to
investigate how the properties of the star forming gas in galaxies evolve with
redshift. We derive the extinction and oxygen abundances for the sample using a
method based on a set of ionisation parameter and oxygen abundance diagnostics,
simultaneously fitting the [OII], Hbeta,[OIII], Halpha, and [NII] line fluxes.
The individual reddening measurements allow us to accurately correct the
Halpha-based star formation rate (SFR) estimates for extinction. Our most
salient conclusions are: a) in all 30 CFRS galaxies the source of gas
ionisation is not due to AGN activity; b) we find a range of 0<AV<3, suggesting
that it is important to determine the extinction for every single galaxy in
order to reliably measure SFRs and oxygen abundances in high redshift galaxies;
c) high values of [NII]/Halpha >0.1 for most (but not all) of the CFRS galaxies
indicate that they lie on the high-metallicity branch of the R23 calibration;
d) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have lower
metallicities than local galaxies with similar luminosities and star formation
rates; e) comparison with a chemical evolution model indicates that these low
metallicity galaxies are unlikely to be the progenitors of metal-poor dwarf
galaxies at z~0.Comment: Accepted for publication in the Astrophysical Journa
A photoisomerizable muscarinic antagonist. Studies of binding and of conductance relaxations in frog heart
These experiments employ the photoisomerizable compound, 3,3'-bis- [alpha-(trimethylammonium)methyl]azobenzene (Bis-Q), to study the response to muscarinic agents in frog myocardium. In homogenates from the heart, trans-Bis-Q blocks the binding of [3H]-N-methylscopolamine to muscarinic receptors. In voltage-clamped atrial trabeculae, trans- Bis-Q blocks the agonist-induced potassium conductance. The equilibrium dose-response curve for carbachol is shifted to the right, suggesting competitive blockade. Both the biochemical and electrophysiological data yield a dissociation constant of 4-5 microM for trans-Bis-Q; the cis configuration is severalfold less potent as a muscarinic blocker. Voltage-clamped preparations were exposed simultaneously to carbachol and Bis-Q and were subjected to appropriately filtered flashes (less than 1 ms duration) from a xenon flashlamp. Trans leads to cis and cis leads to trans photoisomerizations cause small (less than 20%) increases and decreases, respectively, in the agonist-induced current. The relaxation follows an S-shaped time course, including an initial delay or period of zero slope. The entire waveform is described by [1 - exp(-kt)]n. At 23 degrees C, k is approximately 3 s-1 and n is 2. Neither k nor n is affected when: (a) [Bis-Q] is varied between 5 and 100 microM; (b) [carbachol] is varied between 1 and 50 microM; (c) carbachol is replaced by other agonists (muscarine, acetylcholine, or acetyl-beta-methylcholine); or (d) the voltage is varied between the normal resting potential and a depolarization of 80 mV. However, in the range of 13-30 degrees C, k increases with temperature; the Q10 is between 2 and 2.5. In the same range, n does not change significantly. Like other investigators, we conclude that the activation kinetics of the muscarinic K+ conductance are not determined by ligand-receptor binding, but rather by a subsequent sequence of two (or more) steps with a high activation energy
The Host Galaxy and The Extended Emission-Line Region of The Radio Galaxy 3C 79
We present extensive ground-based spectroscopy and HST imaging of 3C79, an FR
II radio galaxy associated with a luminous extended emission-line region
(EELR). Surface brightness modeling of an emission-line-free HST R-band image
reveals that the host galaxy is a massive elliptical with a compact companion
0.8" away and 4 magnitudes fainter. The host galaxy spectrum is best described
by an intermediate-age (1.3 Gyr) stellar population (4% by mass), superimposed
on a 10 Gyr old population and a power law (\alpha_{\lambda} = -1.8); the
stellar populations are consistent with super-solar metallicities, with the
best fit given by the 2.5 Z_sun models. We derive a dynamical mass of 4E11
M_sun within the effective radius from the velocity dispersion. The EELR
spectra clearly indicate that the EELR is photoionized by the hidden central
engine. Photoionization modeling shows evidence that the gas metallicity in
both the EELR and the nuclear narrow-line region is mildly sub-solar (0.3 - 0.7
Z_sun) -- significantly lower than the super-solar metallicities deduced from
typical active galactic nuclei in the SDSS. The more luminous filaments in the
EELR exhibit a velocity field consistent with a common disk rotation. Fainter
clouds, however, show high approaching velocities that are uncoupled with this
apparent disk rotation. The striking similarities between this EELR and the
EELRs around steep-spectrum radio-loud quasars provide further evidence for the
orientation-dependent unification schemes. The metal-poor gas is almost
certainly not native to the massive host galaxy. We suggest that the close
companion galaxy could be the tidally stripped bulge of a late-type galaxy that
is merging with the host galaxy. The interstellar medium of such a galaxy is
probably the source for the low-metallicity gas in 3C79.Comment: Accepted for publication in ApJ. 13 pages, 12 figures, 3 tables.
Paper with figures at full resolution uploaded in this versio
The Extended Emission-Line Region of 4C 37.43
We have explored the nature of the extended emission-line region around the
z=0.37 quasar 4C 37.43, using extensive ground-based and HST imaging and
spectroscopy. The velocity field of the ionized gas shows gradual gradients
within components but large jumps between components, with no obvious global
organization. The HST [O III] image shows radial linear features on the east
side of the QSO that appear to mark the edges of an ionization cone.
Concentrating on the bright emission peaks ~4\arcsec$ east of the quasar, we
find through modeling that we require at least two density regimes contributing
significantly to the observed emission-line spectrum: one with a density of ~2
cm^-3, having essentially unity filling factor, and one with a density of ~500
cm^-3, having a very small (~10^-5) filling factor. Because the temperatures of
these two components are similar, they cannot be in pressure equilibrium, and
there is no obvious source of confinement for the dense regions. We estimate
that the dense regions will dissipate on timescales <~10^4 years and therefore
need to be continuously regenerated, most likely by shocks. Because we know
that some QSOs, at least, begin their lives in conjunction with merger-driven
massive starbursts in their host galaxies, an attractive interpretation is that
the extended emission region comprises gas that has been expelled as a result
of tidal forces during the merger and is now being shocked by the galactic
superwind from the starburst. This picture is supported by the observed
distribution of the ionized gas, the presence of velocities ranging up to ~700
km s^{-1}, and the existence of at least two QSOs having similarly luminous and
complex extended emission regions that are known to have ultra-luminous IR
galaxy hosts with current or recent starbursts.Comment: 22 pages, incl. 7 figures; to be published in The Astrophysical
Journal, 572 (June 20, 2002 issue
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