I review the radio to X-ray properties of gigahertz peaked-spectrum (GPS) and compact steep- spectrum (CSS) sources, the current hypotheses for their origin, and their use to constrain the evolution of powerful radio galaxies. The GPS and CSS sources are compact, powerful radio sources with well-defined peaks in their radio spectra (near 1 GHz in the GPS and near 100 MHz in the CSS). The GPS sources are entirely contained within the extent of the narrow-line region (&1 kpc), while the CSS sources are contained entirely within the host galaxy (&15 kpc). The peaks in the spectra are probably due to synchrotron self-absorption, though free-free absorption through an inhomogeneous screen may also play a role. The turnover frequency varies with linear size l as , suggesting a simple physical relationship between these parameters. The radio 20.65 n / l m morphologies are strikingly like those of the large-scale classical doubles, though some sources can have very distorted morphologies suggestive of interactions. Radio polarization tends to be low, and in some cases the Faraday rotation measures can be extremely large. The IR properties are consistent with stellar populations and active galactic nucleus (AGN) bolometric luminosity similar to that of the 3CR classical doubles. The optical host galaxy properties (absolute magnitude, Hubble diagram, evidence for interaction) are consistent with those of the 3CR classical doubles. CSS sources at all redshifts exhibit high surface brightness optical light (most likely emission-line gas) that is aligned with the radio axis. The optical emission-line properties suggest (1) interaction of the radio source with the emission-line gas and (2) the presence of dust toward the emission-line regions. X- ray observations of high-redshift GPS quasars and a couple of GPS galaxies suggest the presence of significant columns of gas toward the nuclei. Searches for cold gas in the host galaxies have revealed large amounts of molecular gas and smaller amounts of atomic gas in several sources, though probably not enough to confine the radio sources. The main competing models for the GPS and CSS sources are that (1) they are frustrated by interaction with dense gas in their environments and (2) they are young and evolving radio sources that will become large-scale sources. Combining the bright GPS and CSS samples with the 3CR results in a sample spanning a range in source size of 10 5 that can be used to study source evolution. The number density versus linear size relation is consistent with a picture in which the sources expand with constant velocity and the radio power drops with linear size l according to . This strong evolution suggests that at least some of the 20.5 P / l GPS and CSS sources evolve to become lower luminosity FR 1 radio sources. The GPS and CSS sources are important probes of their host galaxies and will provide critical clues to the origin and evolution of powerful radio sources.

https://iopscience.iop.org/article/10.1086/316162/pdf

The Compact Steep-Spectrum and Gigahertz Peaked-Spectrum Radio Sources

Circumstellar disks are thought to experience a rapid transition phase in their evolution that can have a considerable impact on the formation and early development of planetary systems. We present new and archival high angular resolution (03 40-75 AU) Submillimeter Array (SMA) observations of the 880 μm (340 GHz) dust continuum emission from 12 such transition disks in nearby star-forming regions. In each case, we directly resolve a dust-depleted disk cavity around the central star. Using two-dimensional Monte Carlo radiative transfer calculations, we interpret these dust disk structures in a homogeneous, parametric model framework by reproducing their SMA continuum visibilities and spectral energy distributions. The cavities in these disks are large (R cav = 15-73 AU) and substantially depleted of small (~μm-sized) dust grains, although their mass contents are still uncertain. The structures of the remnant material at larger radii are comparable to normal disks. We demonstrate that these large cavities are relatively common among the millimeter-bright disk population, comprising at least 1 in 5 (20%) of the disks in the bright half (and ≥26% of the upper quartile) of the millimeter luminosity (disk mass) distribution. Utilizing these results, we assess some of the physical mechanisms proposed to account for transition disk structures. As has been shown before, photoevaporation models do not produce the large cavity sizes, accretion rates, and disk masses representative of this sample. A sufficient decrease of the dust optical depths in these cavities by particle growth would be difficult to achieve: substantial growth (to meter sizes or beyond) must occur in large (tens of AU) regions of low turbulence without also producing an abundance of small particles. Given those challenges, we suggest instead that the observations are most commensurate with dynamical clearing due to tidal interactions with low-mass companions—very young (~1 Myr) brown dwarfs or giant planets on long-period orbits.

https://iopscience.iop.org/article/10.1088/0004-637X/732/1/42/pdf

Resolved Images of Large Cavities in Protoplanetary Transition Disks

We present the results of a high angular resolution (0.''3 {approx} 40 AU) Submillimeter Array survey of the 345 GHz (870 {mu}m) thermal continuum emission from nine of the brightest, and therefore most massive, circumstellar disks in the {approx}1 Myr-old Ophiuchus star-forming region. Using two-dimensional radiative transfer calculations, we simultaneously fit the observed continuum visibilities and broadband spectral energy distribution for each disk with a parametric structure model. Compared to previous millimeter studies, this survey includes significant upgrades in modeling, data quality, and angular resolution that provide improved constraints on key structure parameters, particularly those that characterize the spatial distribution of mass in the disks. In the context of a surface density profile motivated by similarity solutions for viscous accretion disks, {sigma} {proportional_to} (R/R{sub c} ){sup -{gamma}}exp [ - (R/R{sub c} ){sup 2-{gamma}}], the best-fit models for the sample disks have characteristic radii R{sub c} {approx} 20-200 AU, high disk masses M{sub d} {approx} 0.005-0.14 M {sub sun} (a sample selection bias), and a narrow range of radial {sigma} gradients ({gamma} {approx} 0.4-1.0) around a median {gamma} = 0.9. These density structures are used in conjunction with accretion rate estimates from the literature to help characterize the viscous evolution ofmore » the disk material. Using the standard prescription for disk viscosities, those combined constraints indicate that {alpha} {approx} 0.0005-0.08. Three of the sample disks show large (R {approx} 20-40 AU) central cavities in their continuum emission morphologies, marking extensive zones where dust has been physically removed and/or has significantly diminished opacities. Based on the current requirements of planet formation models, these emission cavities and the structure constraints for the sample as a whole suggest that these young disks may eventually produce planetary systems, and have perhaps already started.« less

https://iopscience.iop.org/article/10.1088/0004-637X/700/2/1502/pdf

Protoplanetary disk structures in ophiuchus

The VIIth catalogue of galactic Wolf–Rayet stars

X-ray bursts

We present a comprehensive study of dust grains in the p Ophiuchi dark cloud. By combining new polarimetric, optical photometric, and spectral classification data for 134 stars, cloud material is probed to an absorption depth of A V ≤ 5-7 mag. For stars with R determined from the color-difference method, a mean value of R = 3.99 ± 0.18 at a mean extinction of A V = 3.25 mag is found. R scales with the wavelength of maximum polarization at the rate R = 5.7λ max , consistent with results from other studies. Grain size, as deduced from λ max , increases with optical depth in a manner that is consistent with a simple model of turbulence-driven coagulative grain growth

An investigation of grain properties in the Rho Ophiuchi dark cloud

The radio and optical properties of a complete 5 GHz sample of strong radio sources are studied. High polarization is strongly correlated with the fraction of the total 5 GHz flux density found in a milliarcsec core. The detection rate of radio galaxies containing optical cores with high polarization is consistent with the hypothesis that all radio sources contain optically polarized cores, with strength proportional to the core radio flux density. High optical polarization, optical power-law fraction, line-to-continuum ratio, emission lines of small equivalent widths, and large amplitude flux variability are all strongly correlated with the fraction of the 5 GHz radio flux density that is unresolved on VLBI scales. The distributions of these properties are well matched by a model where radio and optical radiation have the same beaming geometry and with Doppler boosting of a factor of 10-100 in the optical. A striking alignment of the position angle of the VLBI structure axis and the position angle of optical polarization in highly polarized sources is confirmed.

Optical polarization of a complete sample of radio sources

Polarization Variability among Wolf-Rayet Stars. I. Linear Polarization of a Complete Sample of Southern Galactic WC Stars

We present the first comprehensive polarimetric study of grains and magnetic field in a massive dark could, R Coronae Australis. By combining photometric and spectroscopic data with multicolar polarimetry for a large number of background stars which do not have circumstaller shells, we probe the cloud for the regime A/sub V/< or approx. =5mag(n< or approx. =10/sup 3/ cm/sup -3/). The data show that the cloud grains are typically much larger and have a larger size dispersion than those in the general interstellar medium (IM), with grain size increasing with optical depth. The ratio of total-to-selective extinction has a mean value of 4.5 (with a total range of 3.4). Grain alignment is poorer than in the IM (mean P/sub V/(%)/A/sub V/(mag)roughly-equal0.66) and decreases with optical depth. Various mechanisms are discussed which explain the observed grain alignment and size properties.

Observations of grain and magnetic field properties of the R Coronae Australis dark cloud.

New observations of the peculiar Wolf-Rayet star EZ Canis Majoris collected since 1987 are presented, and photometric, polarimetric, spectroscopic, and spectropolarimetric data are discussed Linear polarization data are well fitted with an eccentric binary model where an additional free parameter is included to allow for epoch-dependent changes of the geometrical electron distribution in the W-R envelope This yields a set of basic parameters, including an eccentricity e = 039 +/- 002 and an orbital inclination i = 114 deg +/- 3 deg The spectroscopic data show global profile variations for all three observed strong emission lines He II 5412 A, C IV 5807 A, and He I 5876 A Radial velocities of the lines vary with the 3766-day period Radially expanding inhomogeneities are superposed on the line profiles and variable polarization in the lines is observed

S. Tapia

Papers

An investigation of grain properties in the Rho Ophiuchi dark cloud

Optical polarization of a complete sample of radio sources

Polarization Variability among Wolf-Rayet Stars. I. Linear Polarization of a Complete Sample of Southern Galactic WC Stars

Observations of grain and magnetic field properties of the R Coronae Australis dark cloud.

Photometry, polarimetry, spectroscopy, and spectropolarimetry of the enigmatic Wolf-Rayet star EZ Canis Majoris