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NASA NTRS1990

Probing the Interstellar Medium of External Galaxies Using Quasar Absorption Lines: the 3C 232/NGC 3067 System

Quasar absorption lines offer unique opportunities to probe the interstellar medium of external galaxies. Researchers present new optical and UV absorption line spectroscopy of the quasar 3C232 (z=0.55) revealing new detail in the foreground absorption system due to the bright, spiral galaxy NGC 3067 (cz=1420 km/s). Specifically, the spectra show evidence for two and possibly three separate absorption components in CaII and Na I spanning approx. 150 km/s. The original HI detection of Haschick and Burke (1975) corresponds to the strongest of these metal systems which exhibits doublet ratios consistent with saturation in both CaII and Na I. Due to the recent detection in HI emission of a tidal tail or finger of HI extending from the western edge of NGC 3067 through the position of 3C 232 (Carilli, van Gorkom and Stocke, 1989), the morphology of the HI absorber is now known and is not either a warped disk nor a spherical halo as had been proposed. New deep continuum and H alpha imaging provides a sensitive upper limit on the the ionizing continuum impinging upon this cloud (and thus a limit on the intensity of the extragalactic ionizing radiation field). Together with the observed UV spectrum of 3C 232, the optical emission line ratios and the deep H alpha imaging set a minimum distance between the quasar and the HI cloud disregarding redshift information. This limit strains the non-cosmological redshift interpretation for 3C 232 -- and this quasar is one of the original 5 3C quasars found to be too close to NGC galaxies as if by chance (Burbidge, Burbidge, Solomon and Strittmatter, 1972).

Stocke, John T.↗
NASA NTRS1983

Interstellar absorption lines in the spectrum of 3C 273

Absorption lines near the rest wavelengths of the Si IV doublet (wavelengths 1393.76, 1402.77) with equivalent widths 533 and 235 mA are reported in the spectrum of QSO 3C 273. The profiles show the nature of hot gas along a high-latitude (b = 64 deg) line of sight through our entire halo. The lines have full width at half-maxima of 100 km/s, compared to an instrumental resolution of 35 km/s, are centered at zero velocity, and show no evidence for components with equivalent widths greater than 50 mA at an absolute value of v greater than 75 km/s. The absence of high peculiar velocities is consistent with published spectra of halo gas over shorter pathlengths. The implications of this result are discussed, with particular reference to the possible connection between galactic halos and QSO absorption lines, for which C IV and Si IV usually have a broader velocity range.

York, D. G.↗
NASA NTRS1990

Radio line and continuum observations of quasar-galaxy pairs and the origin of low reshift quasar absorption line systems

There are a number of known quasars for which our line of sight to the high redshift quasar passes within a few Holmberg radii of a low redshift galaxy. In a few of these cases, spectra of the quasar reveal absorption by gas associated with the low redshift galaxy. A number of these pairs imply absorption by gas which lies well outside the optical disk of the associated galaxy, leading to models of galaxies with 'halos' or 'disks' of gas extending to large radii. The authors present observations of 4 such pairs. In three of the four cases, they find that the associated galaxy is highly disturbed, typically due to a gravitational interaction with a companion galaxy, while in the fourth case the absorption can be explained by clouds in the optical disk of the associated galaxy. They are led to an alternative hypothesis concerning the origin of the low redshift absorption line systems: the absorption is by gas clouds which have been gravitationally stripped from the associated galaxy. These galaxies are rapidly evolving, and should not be used as examples of absorption by clouds in halos of field spirals. The authors conclude by considering the role extended gas in interacting systems plays in the origin of higher redshift quasar absorption line systems.

Carilli, C. L.↗
NASA NTRS1978

A study of the absorption-line spectra of six high-redshift quasi-stellar objects

High-resolution spectrograms of six QSOs with apparent visual magnitudes of 17.0 to 18.5 and redshifts greater than 2 are studied for absorption lines. Accurate wavelengths are measured for all the absorption lines that could be detected, attempts are made to identify redshift systems, and the redshifts in each object are examined. Analysis of the absorption-line spectra shows that: (1) a large number of redshifts covering a wide range of values are present in five of the QSOs; (2) about two-thirds of the absorption lines remain unidentified, cannot be of Galactic origin, and are not associated with existing redshift systems; (3) many comparatively small absorption redshifts exist which, if they are due to intervening galaxies, must be produced by very large halos; and (4) in one QSO there is a possible redshift system containing five lines with an absorption redshift that is significantly greater than the emission redshift.

Roberts, D. H.↗
NASA NTRS1999

Multiple Velocity Components in the C IV Absorption Line of NGC 5548

We have observed the much-studied Seyfert 1 galaxy NGC 5548 with the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). Our 14 ks observation covers the C IV emission line at a resolution of greater than 20,000. Our purpose was to study the absorption line found at lower resolution by IUE and the HST Faint Object Spectrograph. We found that the C IV absorption line resolves into six separate doublets with equivalent widths of 0.07-0.38 Angstrom. The absorption lines have blueshifts relative to the systemic velocity of the galaxy of 380-1250 km s(exp -1), except for one, which has a redshift of 250 km s(exp -1), suggesting both inflow and outflow. The inflowing component may be related to the accretion flow into the nuclear black hole. All the doublet lines are resolved by the GHRS. Three doublets are narrow, with FWHM greater than or approximately 100 km s(exp -1), and three are broad, FWHM approximately 160-290 km s(exp -1). We find evidence of partial covering by the narrow absorption lines. Either (but not both) of the two strongest broad doublets could be from the same material that produces the X-ray ionized absorber seen in soft X-rays. The remaining five systems must be at least 10 times less ionized (and so of lower total column density) to remain consistent with the X-ray spectra.

Mathur, Smita↗
NASA NTRS1983

High-velocity iron absorption lines in supernova remnant 1006

The very strong, broad absorption lines of a sdOB star continuum shown in the International Ultraviolet Explorer spectrum of the Schweizer-Middleditch star projected near the center of supernova remnant SNR 1006 are investigated. It is found that strong Fe(+) resonance absorption lines are present whose centers show zero radial velocity while their profiles are broadened by approximately 5000-6000 km/s. Also identified are redshifted Si(+), Si(2+), and Si(3+) lines at velocities of approximately 5000 km/s. Results show that the absorptions must occur in the ejecta of the supernova. The strength and symmetric width of the Fe(+) line indicates that the bulk of the ejecta is iron, in agreement with the current theory for the origin of Type I supernova. It is suggested that the previous failure to detect strong Fe emission lines in the X-ray spectra of this and other young Type I SNRs may be a result of the ejecta not having had time to interact significantly with the ambient medium. In addition, the presence of redshifted adsorption lines due to supernova ejecta in its spectrum shows that this star is located behind the SNR and is not physically associated with it.

Wu, C.-C.↗
NASA NTRS2017

Synthetic Absorption Lines for a Clumpy Medium: A Spectral Signature for Cloud Acceleration in AGN?

There is increasing evidence that the highly ionized multiphase components of AGN disc winds may be due to thermal instability. The ions responsible for forming the observed X-ray absorption lines may only exist in relatively cool clumps that can be identified with the so-called warm absorbers. Here we calculate synthetic absorption lines for such warm absorbers from first principles by combining 2D hydrodynamic solutions of a two-phase medium with a dense grid of photoionization models to determine the detailed ionization structure of the gas. Our calculations reveal that cloud disruption, which leads to a highly complicated velocity field (i.e. a clumpy flow), will only mildly affect line shapes and strengths when the warm gas becomes highly mixed but not depleted. Prior to complete disruption, clouds that are optically thin to the driving UV resonance lines will cause absorption at an increasingly blueshifted line-of-sight velocity as they are accelerated. This behavior will imprint an identifiable signature on the line profile if warm absorbers are enshrouded in an even broader absorption line produced by a high column of intercloud gas. Interestingly, we show that it is possible to develop a spectral diagnostic for cloud acceleration by differencing the absorption components of a doublet line, a result that can be qualitatively understood using a simple partial covering model. Our calculations also permit us to comment on the spectral differences between cloud disruption and ionization changes driven by flux variability. Notably, cloud disruption offers another possibility for explaining absorption line variability.

line: formation – galaxies: nuclei – quasars: ↗
NASA NTRS1979

Absorption lines in the spectra of distant objects

Studies that can be carried out with the Space Telescope of absorption line systems which may be expected to occur in the spectra of distant objects are discussed. The phenomenology of quasar absorption line systems is described and the principal suggested explanations are summarized. It is proposed that the numerous Ly-alpha systems are caused by 'extremely large hydrogenic halos around galaxies or clusters of galaxies. Two tests are also described for the origins of known absorption systems, the results of which will favor either the cosmological or intrinsic hypothesis. Absorption lines that are likely to be strongest are listed and a sample observing program is presented.

Bahcall, J. N.↗
NASA NTRS1978

A comparison of neutral hydrogen 21 cm observations with UV and optical absorption-line measurements

Several absorption components detected in visible or UV lines have been identified with emission features in new high-resolution, high signal-to-noise 21 cm observations. Stars for which direct overlap is obtained are HD 28497, lambda Ori, mu Col, HD 50896, rho Leo, HD 93521, and HD 219881. With the use of the inferred H I column densities from 21 cm profiles, rather than the integrated column densities obtained from L-alpha, more reliable densities can be derived from the existence of molecular hydrogen. Hence the cloud thicknesses are better determined; and 21 cm emission maps near these stars can be used to obtain dimensions on the plane of the sky. It is now feasible to derive detailed geometries for isolated clumps of gas which produce visual absorption features.

Giovanelli, R.↗
NASA NTRS1993

A sample of lobe-dominated quasars with Mg II absorption lines

We present a sample of quasars which are lobe-dominated in their radio emission and contain Mg II absorption line systems. This sample will be useful in a search for redshifted H I 21 cm absorbers which are along lines of sight different from the optical. These systems will allow the measurement of the linear size and related physical parameters of the absorption line clouds. We have defined a set of criteria for selecting these objects and obtained the necessary data to assemble a sample based on these criteria. Out of 4234 QSOs we find 31 lobe-dominated quasars which are appropriate for optical and radio absorption line study in the Northern Hemisphere. We have obtained or located optical spectra for 29 of these 31 quasars. In the optical spectra we find 17 Mg II absorption systems with redshifts between 0.3 and 1.4 and Mg II 2796 A rest equivalent widths between 0.3 and 2.0 A. Based on statistics of 21 cm absorption in Mg II selected QSOs we expect this sample of 17 systems to yield one or two new H I absorbers. In this paper we give an analysis of our criteria, discuss the sample, and present new VLA observations of 16 quasars.

Aldcroft, Thomas L.↗
NASA NTRS1979

Studies of interstellar absorption lines with IUE

The paper deals with a survey of interstellar absorption lines in the wavelength region from 1150 to 3200 A toward 25 stars. The spectra of 10 of these stars show very strong narrow absorption lines of Si IV and C IV. Lines of N V appear in eight directions. The N V lines can arise in the same gas that is responsible for the ubiquitous interstellar lines of O VI, observed previously with a Copernicus spectrometer, but the lines of Si IV and C IV must be formed in a cooler gas. The measured lines of Si IV and C IV can be produced by normal H II regions photoionized by the observed stars.

Black, J. H.↗
NASA NTRS1993

Ionization states of metallic absorption-line systems in continua of quasars

Ionization states of metallic absorption-line systems in continua of quasars (QSO's) are studied, assuming that the metallic lines arise in gaseous halos of high-redshift galaxies in photoionization equilibrium under the background UV radiation, and constraints on the intensity and spectral shape of the UV radiation are obtained. Then a structure of absorbers suitable for all of the metallic absorption line systems are discussed.

Denda, Kiyomi↗
NASA NTRS1989

Using X-ray absorption lines to determine the distances to clusters of galaxies

The stronger resonant X-ray lines from the intracluster gas should be observable as absorption lines in the spectrum of an X-ray emitting background quasar. The equivalent widths of the strongest absorption lines in a set of model clusters with typical parameters are calculated, and the strongest lines are found to have equivalent widths of several eV. By comparing the equivalent width of such a line and the flux from the same line seen in emission, the distance to the cluster can be directly determined, independent of the standard extragalactic distance scale. A method of analyzing the X-ray absorption and emission measurements is presented, and the effects of resonant scattering on the distances are discussed.

Sarazin, Craig L.↗
NASA NTRS1986

Abundances of interstellar atoms from ultaviolet absorption lines

The equivalent widths of interstellar absorption lines of Mg II, P II, Cl I and II, Mn II, Fe II, Cu II, and Ni II, obtained in a Copernicus survey of Bohlin et al (1983) have been analyzed to yield column densities along the lines of sight. The measured depletions are clearly correlated with n sub H, the mean hydrogen column density along the line of sight. Depletions also seem to be weakly correlated with various ratios of hydrogen to extinction by dust grains and also variations of extinction with wavelength, although part of these effects are a secondary result of the correlation with n sub H. The apparent coupling of depletion to the mean density are interpreted in terms of an idealized model due to Spitzer (1985), where each element has one value of depletion in the low-density, warm, neutral gas and an enhanced, different value in cold clouds. The difference of apparent depletions for Mg, P, Cl, Mn, and Fe between warm and cold clouds averages 0.44 + or - 0.12 (rms) dex, and, after an allowance for observational errors is made, the scatter of individual depletions from the overall trend predicted by method is only about 0.10 dex. The identification of the observed apparent depletions with actual ones, while very likely, is not entirely secure, because of the possible presence of highly saturated compoents with very narrow profiles and the possible contamination of the results by H II regions.

Jenkins, E. B.↗
NASA NTRS2019

Discovery of Highly Blueshifted Broad Balmer and Metastable Helium Absorption Lines in a Tidal Disruption Event

We report the discovery of nonstellar hydrogen Balmer and metastable helium absorption lines accompanying a transient, high-velocity (0.05c) broad absorption line (BAL) system in the optical spectra of the tidal disruption event (TDE) AT2018zr (z = 0.071). In the Hubble Space Telescope UV spectra, absorption of high- and low-ionization lines is also present at this velocity, making AT2018zr resemble a low-ionization BALQSO. We conclude that these transient absorption features are more likely to arise in fast outflows produced by the TDE than absorbed by the unbound debris. In accordance with the outflow picture, we are able to reproduce the flat-topped Hα emission in a spherically expanding medium without invoking the typical prescription of an elliptical disk. We also report the appearance of narrow (~1000 kms(exp −1)) N III λ4640, He II λ4686, Hα, and Hβ emission in the late-time optical spectra of AT2018zr, which may be a result of UV continuum hardening at late times, as observed by Swift. Including AT2018zr, we find a high association rate (three out of four) of BALs in the UV spectra of TDEs. This suggests that outflows may be ubiquitous among TDEs and less sensitive to viewing angle effects compared to QSO outflows.

Hung, T.↗