Although galaxies, groups, and clusters contain {approx}10% of the baryons, many more reside in the photoionized and shocked-heated intergalactic medium (IGM) and in the circumgalactic medium (CGM). We update the baryon census in the (H I) Ly{alpha} forest and warm-hot IGM (WHIM) at 10{sup 5-6} K traced by O VI {lambda}1032, 1038 absorption. From Enzo cosmological simulations of heating, cooling, and metal transport, we improve the H I and O VI baryon surveys using spatially averaged corrections for metallicity (Z/Z {sub Sun }) and ionization fractions (f {sub HI}, f {sub OVI}). Statistically, the O VI correction product correlates with column density, (Z/Z {sub Sun })f {sub OVI} Almost-Equal-To (0.015)(N {sub OVI}/10{sup 14} cm{sup -2}){sup 0.70}, with an N {sub OVI}-weighted mean of 0.01, which doubles previous estimates of WHIM baryon content. We also update the Ly{alpha} forest contribution to baryon density out to z = 0.4, correcting for the (1 + z){sup 3} increase in absorber density, the (1 + z){sup 4.4} rise in photoionizing background, and cosmological proper length dl/dz. We find substantial baryon fractions in the photoionized Ly{alpha} forest (28% {+-} 11%) and WHIM traced by O VI and broad-Ly{alpha} absorbers (25% {+-} 8%). The collapsed phasemore » (galaxies, groups, clusters, CGM) contains 18% {+-} 4%, leaving an apparent baryon shortfall of 29% {+-} 13%. Our simulations suggest that {approx}15% reside in hotter WHIM (T {>=} 10{sup 6} K). Additional baryons could be detected in weaker Ly{alpha} and O VI absorbers. Further progress requires higher-precision baryon surveys of weak absorbers, down to minimum column densities N {sub HI} {>=} 10{sup 12.0} cm{sup -2}, N {sub OVI} {>=} 10{sup 12.5} cm{sup -2}, N {sub OVII} {>=} 10{sup 14.5} cm{sup -2}, using high signal-to-noise data from high-resolution UV and X-ray spectrographs.« less

https://iopscience.iop.org/article/10.1088/0004-637X/759/1/23/pdf

The Baryon Census in a Multiphase Intergalactic Medium: 30% of the Baryons May Still Be Missing

We present the light curves obtained during an 8 yr program of optical spectroscopic monitoring of nine Seyfert 1 galaxies: 3C 120, Akn 120, Mrk 79, Mrk 110, Mrk 335, Mrk 509, Mrk 590, Mrk 704, and Mrk 817. All objects show significant variability in both the continuum and emission-line fluxes. We use cross-correlation analysis to derive the sizes of the broad Hβ-emitting regions based on emission-line time delays, or lags. We successfully measure time delays for eight of the nine sources and find values ranging from about 2 weeks to a little over 2 months. Combining the measured lags and widths of the variable parts of the emission lines allows us to make virial mass estimates for the active nucleus in each galaxy. The virial masses are in the range 107-108 M☉.

https://iopscience.iop.org/article/10.1086/305813/pdf

Optical Continuum and Emission-Line Variability of Seyfert 1 Galaxies

Supermassive black holes reside at the centers of most, if not all, massive galaxies: the difference between active and quiescent galaxies is due to differences in mass accretion rate and radiative efficiency rather than whether or not they have nuclear black holes. In this contribution, methods for measuring the masses of supermassive black holes are discussed, with emphasis on reverberation mapping which is most generally applicable to accreting supermassive black holes and, in particular, to distant quasars where time resolution can be used as a surrogate for angular resolution. Indirect methods based on scaling relationships from reverberation mapping studies are also discussed, along with their current limitations.

http://www.astronomy.ohio-state.edu/~peterson//Docs/petersonISSI.pdf

Measuring the Masses of Supermassive Black Holes

An 8 month monitoring campaign on the Seyfert 1 galaxy Fairall 9 has been conducted with the International Ultraviolet Explorer in an attempt to obtain reliable estimates of continuum-continuum and continuum-emission-line delays for a high-luminosity active galactic nucleus (AGN). While the results of this campaign are more ambiguous than those of previous monitoring campaigns on lower luminosity sources, we find general agreement with the earlier results: (1) there is no measurable lag between ultraviolet continuum bands, and (2) the measured emission-line time lags are very short. It is especially notable that the Ly? + N V emission-line lag is about 1 order of magnitude smaller than determined from a previous campaign by Clavel, Wamsteker, & Glass (1989) when Fairall 9 was in a more luminous state. In other well-monitored sources, specifically NGC 5548 and NGC 3783, the highest ionization lines are found to respond to continuum variations more rapidly than the lower ionization lines, which suggests a radially ionization-stratified broad-line region. In this case, the results are less certain, since none of the emission-line lags are very well determined. The best-determined emission line lag is Ly? + N V, for which we find that the centroid of the continuum-emission-line cross-correlation function is ?cent ? 14-20 days. We measure a lag ?cent 4 days for He II ?1640; this result is consistent with the ionization-stratification pattern seen in lower luminosity sources, but the relatively large uncertainties in the emission-line lags measured here cannot rule out similar lags for Ly? + N V and He II ?1640 at a high level of significance. We are unable to determine a reliable lag for C IV ?1550, but we note that the profiles of the variable parts of Ly? and C IV ?1550 are not the same, which does not support the hypothesis that the strongest variations in these two lines arise in the same region.

/pdf/steps-toward-determination-of-the-size-and-structure-of-the-1l447x3h9r.pdf

Steps toward Determination of the Size and Structure of the Broad-Line Region in Active Galactic Nuclei. IX. Ultraviolet Observations of Fairall 9

We present the light curves obtained during an eight-year program of optical spectroscopic monitoring of nine Seyfert 1 galaxies: 3C 120, Akn 120, Mrk 79, Mrk 110, Mrk 335, Mrk 509, Mrk 590, Mrk 704, and Mrk 817. All objects show significant variability in both the continuum and emission-line fluxes. We use cross-correlation analysis to derive the sizes of the broad Hbeta-emitting regions based on emission-line time delays, or lags. We successfully measure time delays for eight of the nine sources, and find values ranging from about two weeks to a little over two months. Combining the measured lags and widths of the variable parts of the emission lines allows us to make virial mass estimates for the active nucleus in each galaxy. The virial masses are in the range 10^{7-8} solar masses.

/pdf/optical-continuum-and-emission-line-variability-of-seyfert-1-52pybdfedc.pdf

Editorial. Part 1: I. Achievements of the Present Generation of Space Observatories. II. Achievements of the Present Generation of Ground--Based Telescopes. III. Stars. IV. Interstellar Medium and Galaxies. V. Cosmology. VI. Observations at Many Wavelengths: Panel Discussion on Coordination of Observations at Many Wavelengths. VII. The New Generation of Large Ground--Based Telescopes. VIII. The New Generation Space Telescopes. IX. New Technologies for Astronomy. X. Summary, Priorities and Objectives for the 21st Century. Part 2: XI. Stars. XII. Interstellar Medium and Galaxies. XIII. New Technologies for Astronomy. Index.

W. Wamsteker

Papers

Frontiers of space and ground-based astronomy : the astrophysics of the 21st century