4,088 research outputs found
Spectroscopy of Close Companions to QSOs and the Ages of Interaction-Induced Starbursts
We present low-resolution absorption-line spectra of three candidate close (
< 3 arcsec) companions to the low redshift QSOs 3CR 323.1, PG 1700+518, and PKS
2135-147. The spectra were obtained with LRIS on the Keck telescopes and with
the Faint Object Spectrograph on the University of Hawaii 2.2 m telescope. For
3CR 323.1 and PG 1700+518, we measure relative velocities that are consistent
with an association between the QSOs and their companion galaxies. The spectral
features of the companion galaxy to 3CR 323.1 indicate a stellar population of
intermediate age (approx. 2.3 Gyr). In contrast, the spectrum of the companion
object to PG 1700+518 shows strong Balmer absorption lines from a relatively
young stellar population, along with the Mg Ib absorption feature and the 4000
A break from an older population. By modeling the two stellar components of
this spectrum, it is possible to estimate the time that has elapsed since the
end of the most recent major starburst event: we obtain approx. 0.1 Gyr. This
event may have coincided with an interaction that triggered the QSO activity.
Finally, our spectroscopy shows conclusively that the supposed companion to PKS
2135-147 is actually a projected Galactic G star.Comment: 10 pages, 5 Postscript figures. Latex (AASTEX). To appear in ApJ.
Letters, Volume 480 (1997
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
The use of ERTS-1 multispectral imagery for crop identification in a semi-arid climate
Crop identification using multispectral satellite imagery and multivariate pattern recognition was used to identify wheat accurately in Greeley County, Kansas. A classification accuracy of 97 percent was found for wheat and the wheat estimate in hectares was within 5 percent of the USDA's Statistical Reporting Service estimate for 1973. The multispectral response of cotton and sorghum in Texas was not unique enough to distinguish between them nor to separate them from other cultivated crops
A Companion Galaxy to the Post-Starburst Quasar UN J1025-0040
UN J1025-0040 is a quasar at z = 0.6344 that shows an extremely bright post
starburst population of age ~ 400 Myr (Brotherton et al. 1999). Images of UN
J1025-0040 show a nearly stellar object 4.2 arcseconds SSW of the quasar. We
present imaging and spectroscopy that confirm that this object is a companion
galaxy at redshift z = 0.6341. We estimate an age of ~ 800 Myr for the dominant
stellar population in the companion. The companion appears to be interacting
with the quasar host galaxy, and this interaction may have triggered both the
starburst and the quasar activity in UN J1025-0040.Comment: 8 pages plus 4 figures (2 postscript, 2 jpg). Postscript version
available at http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
the January 2000 issue of A
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
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
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
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
The Circumgalactic Medium of Submillimeter Galaxies. II. Unobscured QSOs within Dusty Starbursts and QSO Sightlines with Impact Parameters below 100 Kiloparsec
We present Atacama Large Millimeter/submillimeter Array (ALMA) 870um
observations of 29 bright Herschel sources near high-redshift QSOs. The
observations confirm that 20 of the Herschel sources are submillimeter-bright
galaxies (SMGs) and identify 16 new SMG-QSO pairs that are useful to studies of
the circumgalactic medium (CGM) of SMGs. Eight out of the 20 SMGs are blends of
multiple 870um sources. The angular separations for six of the Herschel-QSO
pairs are less than 10", comparable to the sizes of the Herschel beam and the
ALMA primary beam. We find that four of these six "pairs" are actually QSOs
hosted by SMGs. No additional submillimeter companions are detected around
these QSOs and the rest-frame ultraviolet spectra of the QSOs show no evidence
of significant reddening. Black hole accretion and star formation contribute
almost equally in bolometric luminosity in these galaxies. The SMGs hosting
QSOs show similar source sizes, dust surface densities, and SFR surface
densities as other SMGs in the sample. We find that the black holes are growing
3 faster than the galaxies when compared to the present-day
black-hole-galaxy mass ratio, suggesting a QSO duty cycle of 30% in
SMGs at z ~ 3. The remaining two Herschel-detected QSOs are undetected at 870um
but each has an SMG "companion" only 9" and 12" away (71 and 95 kpc at z = 3).
They could be either merging or projected pairs. If the former, they would
represent a rare class of "wet-dry" mergers. If the latter, the QSOs would, for
the first time, probe the CGM of SMGs at impact parameters below 100 kpc.Comment: ApJ accepte
- …