G. Coleman

Bio: G. Coleman is an academic researcher. The author has contributed to research in topics: Emission spectrum & Spectral line. The author has an hindex of 4, co-authored 6 publications receiving 61 citations.

The spectrum of the QSO PHL 957.

Abstract: Observations of PHL 957 have been made with the Steward Observatory echelette spectrograph and with the Lick Observatory image-tube scanner The stronger emission lines are found to have markedly different profiles, making emission redshift determinations rather inaccurate No He II lambda1640 emission was detected Wavelengths and approximate strengths of 203 absorption features are given, and two redshift systems (z/sub A/=23088, z/sub K/=17969) are shown to have a low probability of chance occurrence Most of the lines observed shortward of emission Lcap alpha appear to be due to Lcap alpha in clouds of sufficiently low optical depth that Lbeta is not detected Systems A and K are similar in character to the absorption systems seen in 1331+170 The relative redshifts with respect to the emission systems are the same in the two QSOs and as such may provide evidence for Lyman line to Lyman continuum locking (AIP)

The spectrum of the QSO PHL 957

Abstract: Observations of PHL 957 have been made with the Steward Observatory echelette spectrograph and with the Lick Observatory image-tube scanner. The stronger emission lines are found to have markedly different profiles, making emission redshift determinations rather inaccurate. No He II lambda1640 emission was detected. Wavelengths and approximate strengths of 203 absorption features are given, and two redshift systems (z/sub A/=2.3088, z/sub K/=1.7969) are shown to have a low probability of chance occurrence. Most of the lines observed shortward of emission L..cap alpha.. appear to be due to L..cap alpha.. in clouds of sufficiently low optical depth that L..beta.. is not detected. Systems A and K are similar in character to the absorption systems seen in 1331+170. The relative redshifts with respect to the emission systems are the same in the two QSOs and as such may provide evidence for Lyman line to Lyman continuum locking. (AIP)

The emission lines of quasars and similar objects

Abstract: Much of our information about quasars is derived from their emission-line spectra. The analysis of such spectra has become an intricate subject which differs considerably from traditional, low-density nebular astrophysics. This review is intended to explain our present understanding of the situation, including some aspects of galactic nuclei whose luminosities are more modest than quasars. Quasars' line-emitting regions are probably photoionized (even if supplementary heating processes also occur). So far, models have been constructed which include ionization and thermal equilibria, the transfer of resonance-line and related photons, and the likely effects of absorption and scattering by dust grains. From comparisons between emission-line intensities produced in these models and observed quasars' spectra, it appears that certain densities and pressures and size scales occur in or around quasars. The relative abundances of elements are not very far from solar values, although it is suspected that heavy elements---carbon, nitrogen, and oxygen in particular---are moderately "overabundant" in quasars. The emission-line intensities also provide indirect information about quasars' ultraviolet and soft-x-ray continua; there are hints that photons with energies between 20 and 300 eV---which are not directly observable---may even represent the peak of the luminous output of a typical quasar. Finally, some gas-dynamical questions, while extremely important, are very difficult to answer, because of a lack of observables.

Cold gas properties of the Herschel Reference Survey - I. 12CO(1–0) and HI data

Abstract: We present new (CO)-C-12(1-0) observations of 59 late-type galaxies belonging to the Herschel Reference Survey (HRS), a complete K-band-selected, volume-limited (15 less than or similar to D less than or similar to 25 Mpc) sample of nearby galaxies spanning a wide ranee in morphological type and luminosity. We studied different recipes to correct single-beam observations of nearby galaxies of different sizes and inclinations for aperture effects. This was done by comparing single-beam and multiple-beam observations along the major axis, which were corrected for aperture effects using different empirical or analytical prescriptions, to integrated maps of several nearby galaxies, including edge-on systems observed by different surveys. The resulting recipe is an analytical function determined by assuming that late-type galaxies are 3D exponentially declining discs with a characteristic scale length r(CO) = 0.2 r(24.5) where r(24.5) is the optical, g- (or B-) band isophotal radius at the 24.5 mag arcsec(-2) (25 mag arcsec-2), as well as a scale height z(CO) = 1/100 r(24.5). Our new CO data are then combined with those available in the literature to produce the most updated catalogue of CO observations for the HRS, now including 225 out of the 322 galaxies of the complete sample. The 3D exponential disc integration is applied to all the galaxies of the sample to measure their total CO fluxes, which are later transformed into molecular gas masses using a constant and a luminosity-dependent X-CO conversion factor. We also collect HI data for 315 HRS galaxies from the literature and present it in a homogenised form.

Cold gas properties of the Herschel Reference Survey. I. 12CO(1-0) and HI data

Abstract: We present new 12CO(1-0) observations of 59 late-type galaxies belonging to the Herschel Reference Survey (HRS), a complete K-band-selected, volume-limited (15

QSO Lyman limit absorption

Abstract: The redshift distribution of QSO absorption systems which are optically thick in the Lyman continuum matches that of a non-evolving population of absorbers in a standard Friedmann cosmological model over the redshift range 0.4–3.5. The density of absorbers per unit velocity in the QSO rest frame is roughly constant for −0.01 ≲ v/c ≲ 0.2 and shows a rapid increase with QSO emission redshift, in accord with an ‘intervening’ origin for the absorbers but contrary to expectation were the material intrinsic to the QSOs.

Line-driven radiative outflows in luminous quasars

Abstract: An analysis of ≃19 500 narrow (.200 km s −1 ) C IV λ λ 1548.2,1550.8 absorbers in ≃34 000 Sloan Digital Sky Survey quasar spectra is presented. The statistics of the number of absorbers as a function of outflow-velocity shows that in appro ximately two-thirds of outflows, with multiple C IV absorbers present, absorbers are line-locked at the 500 km s −1 velocity separation of the C IV absorber doublet; appearing as ‘triplets’ in the quasar spe ctra. Line-locking is an observational signature of radiative line driving in o utflowing material, where the successive shielding of ‘clouds’ of material in the outflow lock s the clouds together in outflow velocity. Line-locked absorbers are seen in both broad absorption line quasars (BALs) and nonBAL quasars with comparable frequencies and with velocities out to at least 20 000 km s −1 . There are no detectable differences in the absorber properties and the dust content of single C IV doublets and line-locked C IV doublets. The gas associated with both single and line-locked C IV absorption systems includes material with a wide range of ionization potential (14-138 eV). Both single and line-locked C IV absorber systems show strong systematic trends in their ionization as a function of outflow velocity, with ionization decreasing rapidly with increasing outflow velocity. Initial simulations, emp loying CLOUDY, demonstrate that a rich spectrum of line-locked signals at various velocities may be expected due to significant opacities from resonance lines of Li-, He- and H-like ions of O, C and N, along with contributions from He II and H I resonance lines. The simulations confirm that line driving c an be the dominant acceleration mechanism for clouds with N(H I)≃10 19 cm −2 .