Engineering Papers⌕ Search

Engineering topics

Baldwin, J. A.

Publications and source records attributed to Baldwin, J. A..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Physical Conditions in Low Ionization Regions of the Orion Nebula

We reexamine the spectroscopic underpinnings of recent claims that low ionization (O(I)) and (Fe(II)) lines from the Orion H(II) region are produced in a region where the iron-carrying grains have been destroyed and the electron density is surprisingly high. Our new HST and CTIO observations show that previous reported detections of(O(I)) lambda 5577 were strongly affected by telluric emission. Our line limits consistent with a moderate density (approx. 10(exp 4)/cu. cm photoionized gas. We show that a previously proposed model of the Orion H(II) region reproduces the observed (O(I)) and (Fe(II)) spectrum. These lines are fully consistent with formation in a moderate density dusty region.

Baldwin, J. A.↗
NASA NTRS1994

The optical-ultraviolet-gamma-ray spectrum of 3C 279

We have obtained spectrosocpy of the violently variable quasar 3C 279, simultaneous with gamma-ray observations, in 1992 April. Our combined optical (McDonald Observatory and Cerro Tololo InterAmerican Observatory (CTIO) and ultraviolet (HST) observations, made when the source was faint, show a very steep power-law continuum (F(sub nu) is proportional to nu(exp -1.95), and strong broad emission lines. This is the first time that the broad ultraviolet lines of this object have been measured, and we note several unusual properties of the spectrum. In particular, the profiles of C IV lambda 1549 and Mg II lambda 2798 are asymmetric, with very strong red wings, in contrast to the symmetic profiles of Ly alpha C III lambda 1909, and possible H-beta. The observed asymmetry cannot be explained by a simple outflow associted with the eruption of the source. In addition, the C IV lambda 1549/Ly-alpha and C III lambda 1909/Ly-alpha line intensity ratios are the largest we have observed in out Hubble Space Telescope (HST) sample of more than 30 radio-loud quasars, even though the C III llambda 1909/C IV lambda 1549 ratio is quite typical. 3C 279 was observed in the gamma-ray region by EGRET (Energetic Gamma-Ray Experiment Telescope) at the same time as our optical-ultraviolet observations. The extrapolated ultraviolet continuum falls nine orders of magnitude below the gamma-ray point and we show that this, combined with the optical UV continuum slope, is enough to rule out several synchtoyotron-self-Compton models suggested to explain the multiwavelength spectra of blazars.

Netzer, Hagai↗
NASA NTRS1993

The narrow-line region of high-luminosity active galactic nuclei

The HST's Faint Object Spectrograph and Kitt Peak ground instruments have been used to gather high S/N spectroscopic observations of seven radio-loud quasars; the resolutions obtained allow a separation of emission line broad and narrow components to be made. Attention is given to the relative weakness of the narrow UV lines, in contradiction to the predictions of dust-free photoionization models; there is not a single definite detection of a narrow UV line in any of the seven quasars. Two explanations of the observed reddening are discussed.

Wills, Beverley J.↗
NASA NTRS1991

Kinematics and ionization of extended gas in active galaxies. VI - The Seyfert 2 galaxy NGC 1386

Results are presented of direct imaging with a CCD detector and long-slit medium- and low-dispersion spectroscopy of the spatially extended narrow-line-emitting gas in the nearby Seyfert 2 galaxy NGC 1386. The distribution, kinematics, and ionization structure of the excited gas were examined in the regions surrounding the nucleus out to a distance of about 1.0. Results present evidence for a spiral structure in this galaxy and for the presence of H II regions in the disk (supporting the classification of NGC 1386 as a Sa galaxy).

Weaver, K. A.↗
NASA NTRS1989

0714 - 2914 (M4-1) - Another Seyfert galaxy with aligned radio continuum and optical emission-line morphologies

Direct imaging and long-slit spectroscopic mapping of the emission-line gas in the Seyfert 2 galaxy 0714 - 2914 (M4-1, MCG - 5-18-2) are reported. The nuclear regions contain an extended (1 kpc size), high-excitation nebulosity that is well aligned with the jet-like nonthermal radio source. The profiles of Forbidden O III 5007A are asymmetric, with extended red wings to the north and west of the nucleus and extended blue wings to the south and east. This switch in the sense of asymmetry is accounted for in terms of a combination of normal rotational motions in the galaxy disk and high-velocity outflow or infall associated with the Seyfert activity.

Wilson, A. S.↗
NASA NTRS1989

Emission-line properties of optically and radio-selected complete quasar samples

Spectrophotometry of two complete samples of quasars, one obtained from the flat radio spectra of the objects and the other from their optical colors, is presented. It is confirmed that the equivalent widths of the major UV emission lines decrease with increasing continuum luminosity (the Baldwin effect) and that the (Ly-alpha + N V)/C IV and 1909 A/C IV intensity ratios are also luminosity-dependent by virtue of the C IV luminosity dependence. It is shown that the Mg II/C IV intensity ratio and possibly the strengths of the blue Fe II emission features and the FWHM of the 1909 A blend are luminosity-dependent. These results generally support the Mushotzky and Ferland (1984) interpretation of the Baldwin effect in terms of a weak inverse correlation between the continuum luminosity and ionization parameter.

Baldwin, J. A.↗
NASA NTRS1988

Kinematics and ionization of extended gas in active galaxies. IV - The Seyfert 2 galaxy NGC 4388

The results of direct CCD imaging and long-slit medium-dispersion spectroscopy of the extended narrow-line-emitting gas in the nearby Seyfert 2 galaxy NGC 4388 are presented. The spectra are used to investigate the distribution, kinematics, and ionization structure of the excited gas in the regions surrounding the nucleus out to a distance of about 4.8 kpc. The data support earlier suggestions that the galaxy, which appears to lie near the core of the Virgo cluster, has been tidally distorted, possibly by the nearby cluster core galaxies M84 or IC 3303. Much of the highly ionized gas in the galaxy appears to be distributed in two wide cones originating from the nucleus and extending above and below the disk. Explanations are offered for the distribution of this gas and for the remainder of the gas above and below the disk.

Corbin, Michael R.↗
NASA NTRS1985

Kinematics and ionization of extended ionized gas in active galaxies. I - The X-ray luminous galaxies NGC 2110, NGC 5506, and MCG -5-23-16

Direct CCD imaging and long-slit Vidicon spectroscopy have been used to map the emission-line ratios, profiles, and velocity fields over the extended narrow-line regions in three nearby Seyfert galaxies, NGC 2110, NGC 5506, and MCG -5-23-16. The gas in the letter is spatially unresolved. Similarities between the other two nebulae include the excitation mechanism (photoionization by a central nonthermal source) and the overall profiles of the very broad emission lines close to the nucleus. The nebulae are, however, quite different in their global kinematic behavior. In NGC 2110, the gas appears to lie in a disk or flattened spheroid and to be in ordered rotation, with a classical rotation curve, about an axis parallel to the minor axis of the stellar isophotes. The velocity field of NGC 5506 is quite irregular, but a component of rotation in the plane of the galaxy seems to exist.

Wilson, A. S.↗
NASA NTRS1985

NGC 2110 - A Seyfert and X-ray elliptical galaxy with displaced kinematic and light centers

Kinematic and imaging observations of NGC 2110 are reported and it is found that the interstellar gas is orbiting with projected rotation axis parallel to the minor axis of the stellar light. The rotation curve is steep close to the center and flat farther out. However, the nucleus is displaced by about 220 pc from the apparent mass center of the galaxy. This last result is discussed in terms of models invoking differential obscuration of stars and gas, non-Keplerian motion of the gas, or a large mass of unseen material which dominates the rotation curve.

Wilson, A. S.↗
NASA NTRS1984

Spectrophotometry of two complete samples of flat radio spectrum quasars

Spectrophotometry of two complete samples of flat-spectrum radio quasars show that for these objects there is a strong correlation between the equivalent width of the C IV 1550 A emission line and the luminosity of the underlying continuum. Assuming Friedmann cosmologies, the scatter in this correlation is a minimum for Q(O) approximately unity. Alternatively, luminosity evolution can be invoked to give compact distributions for Q(O) approximately zero models. A sample of Seyfert galaxies observed with IUE shows that despite some dispersion the average equivalent width of C IV 1550 A in Seyfert galaxies is independent of the underlying continuum luminosity. New redshifts are given for four quasars.

Gaskell, C. M.↗
NASA NTRS1983

Spectrophotometry of 2 complete samples of flat radio spectrum quasars

Spectrophotometry of two complete samples of flat-spectrum radio quasars show that for these objects there is a strong correlation between the equivalent width of the CIV wavelength 1550 emission line and the luminosity of the underlying continuum. Assuming Friedmann cosmologies, the scatter in this correlation is a minimum for q (sub o) is approximately 1. Alternatively, luminosity evolution can be invoked to give compact distributions for q (sub o) is approximately 0 models. A sample of Seyfert galaxies observed with IUE shows that despite some dispersion the average equivalent width of CIV wavelength 1550 in Seyfert galaxies is independent of the underlying continuum luminosity. New redshifts for 4 quasars are given.

Wampler, E. J.↗
NASA NTRS1981

Spectroscopy of neutral-colored QSO candidates

Spectroscopic observations of 21 QSO candidates are discussed; the candidates were taken mainly from sets of objects described as neutral colored that have been listed as possible identifications of radio sources. Candidate identifications are accepted for study without color discrimination (that is, neutral-colored and even reddish objects are examined) in the hope of removing possible bias against finding QSOs with z greater than approximately 3.5. The largest redshift among the objects described here, however, is z = 2.43. The observations therefore support the tentative conclusion that the decline in numbers of objects with z greater than approximately 3 among these samples is real.

Baldwin, J. A.↗
NASA NTRS1980

The nebulosity associated with 3C 120

Spectrophotometric observations have been made of the nebulosity surrounding the Seyfert (or N) galaxy 3C 120, as well as of the nucleus. Observations of the nebulosity reveal an extensive network of H II regions characterized by a high ionization level, which, it is argued, is due to photoionizations by the nucleus. The O/H and N/O abundance ratios in this gas, at least as far out as 8 kpc from the nucleus, must be within a factor of 20 of the solar values. The velocity field of this gas is very chaotic, but the systematic gas velocities, relative to the nucleus, are mostly positive to one side of an axis passing through the nucleus at P.A. 72 deg and mostly negative on the other side. The position angle of this axis is consistent with the direction (P.A. 65 deg) along which the compact radio source in the nucleus is expanding, but it is about 45 deg away from the major or minor axes of the fainter elliptical structure visible on previously published broad-band direct plates.

Baldwin, J. A.↗
NASA NTRS1977

Spectrophotometric observations of Molonglo radio source identifications

The paper presents spectrophotometric observations of 76 optical objects identified with radio sources from the MC2 and MC3 catalogs. Line intensities, equivalent widths, line widths, and optical spectral indices are presented for 44 objects confirmed as quasi-stellar objects. The statistical and physical properties of the Molonglo sample are briefly discussed.

Smith, H. E.↗
NASA NTRS1975

The nebulosity around 3C 48

Results are reported for spectrophotometric measurements of the nebulosity around the quasar 3C 48 which were made with an image-tube scanner on a 3-m telescope. The forbidden emission lines of O III (5007 and 4959 A), Ne III (3869 A), and O II (3727 A) are detected in the nebulosity north of the quasar nucleus and are found to be narrower than those present in the nucleus, but with larger equivalent widths and a slightly larger redshift. No emission lines are detected south of the nucleus, and the continuum on the north is shown to be dominated by scattered continuum radiation from the central quasar. It is suggested that the hot gas responsible for the emission lines may be either part of a shell or disk rotating about the quasar or gas ejected from it.

Wampler, E. J.↗
NASA NTRS1975

The nature of BL Lacertae

Spectrophotometric measurements of the nebula around BL Lacertae have been made with the Lick image-tube scanner on the 3-m telescope. No absorption features were seen, and, although the nebular spectrum is curved and steeper than that of BL Lac itself, it is not a good match to the energy distribution of a normal elliptical galaxy. Thus we do not confirm the observations by Oke and Gunn in which absorption features were seen corresponding to those in the redshifted spectrum of an elliptical galaxy. We have found no evidence that the nebula around BL Lac is a normal galaxy of stars.

Baldwin, J. A.↗