Diffuse Continuum Emission Research Articles

Diffuse continuum emission from the inner Galaxy: First results from INTEGRAL/SPI

We present a preliminary analysis of the diffuse hard X- and soft γ -ray continuum emission from the inner Galactic ridge using INTEGRAL/SPI data from the first Galactic Plane Deep Exposure and Galactic Plane Scans. The spectrum is consistent with results from previous experiments. These early results demonstrate the potential of the INTEGRAL mission for improving our understanding of this emission.

A quasar in a compact group of galaxies at z = 0.7

In a programme of deep imaging of quasar fields, we have found an unusual compact group of galaxies associated with the radio-loud quasar MRC B0941-200 at z = 0.715. The group of galaxies comprises at least five obvious members projected within 10 arcsec (∼75 kpc) of the quasar, all with very similar optical and infrared colours. Spectroscopy has confirmed that the brightest galaxies are at z = 0.715, and infers a minimum age of 3 Gyr for their dominant stellar populations. In addition, the galaxy group is embedded in diffuse continuum emission, visible from B through to K band and with observed B - I colours 2 mag or more bluer than the galaxies. Extended narrow-line emission is also detected across the whole region of the diffuse continuum emission. At greater distances (∼500 kpc) from the quasar, we have also detected an excess of faint, red galaxies with colours identical to those of the group galaxies. This suggests that the group, including MRC B0941-200, lies at the edge of a larger structure of galaxies, akin to a loose group or cluster. We show how the characteristics of the field of MRC B0941-200 can be understood using our knowledge of extended emission-line regions in high-redshift radio sources, and by extrapolating our understanding of nearby compact groups to high redshift, allowing for increased star formation rates and galactic gas content in high-redshift galaxies.

The Variable Diffuse Continuum Emission of Broad‐Line Clouds

We investigate the wavelength-dependent intensity and reverberation properties of the UV-optical diffuse continuum emission expected from broad emission line gas. The locally optimally emitting clouds picture is adopted, with the cloud distribution functions in gas density and distance from the ionizing source determined by a fit to the mean UV emission line spectrum from the 1993 HST campaign of NGC5548 in our previous paper. The model Balmer continuum's strength and variability characteristics are in agreement with those derived from the observations of NGC5548. A key prediction is a wavelength dependent lag across the UV-optical spectrum which can broadly mimic the signature from X-ray reprocessing in an accretion disk, calling into question the discovery claims of the latter in NGC7469. The influence of the diffuse continuum on the optical continuum may result in a small yet significant underestimation of the characteristic sizes of the regions emitting the optical emission lines. Its contribution can also alter the inferred spectral energy distribution of the UV-optical continuum, even well outside the spectral region near the well-known Balmer jump. The reverberation of the diffuse continuum emitted by the BLR may account for perhaps one-third of the observed effect that the 1350-5100 Angstrom continuum becomes bluer as it becomes brighter (even after accounting for non-variable optical starlight). And as in other models of the broad emission line gas, a significant yet unobserved Lyman jump is predicted. (abridged)

High‐Resolution Observations of HiZeeman Absorption toward DR 21

DR 21 has been imaged in H I at high resolution (~5'') in both left and right circular polarization with the VLA. The continuum emission is nearly totally absorbed with opacities > 5 over about 20 km s-1; the FWHM line width is unusually large (~35 km s-1). At least three components are present: two narrow ones at VLSR = -5 km s-1 and +10 km s-1 and a negative-velocity wing whose opacity can be measured out to VLSR = -30 km s-1 in some places. No positive-velocity wing is detected. The midpoint of the negative-velocity wing varies between -25 and -10 km s-1, and the full extent is typically 20 km s-1. The wing is detected over most of the H II region core except in the very southwest corner, near H II region C and in the northern region around H II region D. The opacity in the wing is ~0.5 toward the eastern diffuse continuum emission and rises to ~2 toward the H II core. This negative-velocity H I absorption is probably associated with the high-velocity outflow seen in CO. The velocity field of this outflow gas shows a high negative-velocity tube through the center of the H II region with lower negative velocities near the edge of the tube. The H I gas appears to be accelerating away from the southwest of the core, from a position close to H II region C. This location for the origin of the outflow is consistent with that inferred from the CO observations. Zeeman measurements were made toward the DR 21 compact H II region core. No magnetic field (|B| < 50 μG) is detected in the narrow-line component at VLSR = +10 km s-1; a strong magnetic field of a few hundred microgauss is observed at a position near the H II core in the H I gas at negative velocities.

Excitation of the Extended Gas in NGC 1068

We present photoionization models of high exitation gas in the Extended Narrow Line Region (ENLR) of NGC 1068. The ENLR line fluxes have been calculated allowing for attenuation of the nuclear ionizing continuum as a function of distance from the central source. The diffuse continuum emission from the low density gas is also included as an important secondary source of ionizing radiation. The observed emission from high excitation gas, in the ENLR of NGC 1068, is reproduced by assuming the central luminosity to be 3.5 × 1044 erg s-1 between 1014.6 and 1018.4 Hz. The column density attenuating the central continuum is Nh=1022 cm-2. The predicted reflected continuum from the gas located at a distance of 1.5 kpc is about 10 % of the observed extended soft X-ray continuum in NGC 1068.