Showing papers by "Carol J. Lonsdale published in 1999"
TL;DR: In this paper, the authors performed global VLBI observations of the OH megamaser galaxies III Zw 35 and IRAS 17208-0014 and detected strong and compact 1667 MHz OH emission from each galaxy, but, apart from one weak detection of a single 1665 MHz OH feature in IIIZw 35, no 1665, 1720 MHz, or continuum emission are detected.
Abstract: We have performed global VLBI observations of the OH megamaser galaxies III Zw 35 and IRAS 17208-0014. We detect strong and compact 1667 MHz OH emission from each galaxy, but, apart from one weak detection of a single 1665 MHz OH feature in III Zw 35, no 1665, 1720 MHz, or continuum emission are detected, which indicates that they occur on size scales greater than 01. We surmise that the OH emission consists of two components. One is diffuse, has unsaturated masers pumped by far-infrared radiation, and is readily explained by the classical OH megamaser model. The second is compact, consists of saturated masers, is responsible for up to 65% of the 1667 MHz flux density, is not associated with any compact continuum emission, and may be pumped by a combination of collisional and radiative processes. One component in III Zw 35 exhibits a well-defined velocity gradient of 32±4 km s-1 pc-1 along a 5.5 pc line of masers. This indicates strong rotation of a molecular cloud with an enclosed mass density of ~6×104 M☉ pc-3.
63 citations
TL;DR: In this article, the authors highlight new results on two classical LIGs which span the range of LIGradio activity: Arp 220, which reveals luminous radio supernovae (RSN) produced in an intense starburst, and Mrk231, which has a powerful compact, AGN radio core.
Abstract: As described by Colin Lonsdale in this Workshop, VLBI observations reveal thepresence of both AGN and Starburst activity in Luminous Infrared Galaxies.We highlight new results on two classical LIGs which span the range of LIGradio activity: Arp 220, which reveals luminous radio supernovae (RSN)produced in an intense starburst, and Mrk231, which has a powerful compact,AGN radio core. Second epoch observations of the compact radio sources inArp 220 confirm their nature as luminous Radio Supernovae, but indicate alower luminous RSN frequency (νLRSN ≲ 0.3 yr-1) andconsequent slower decay rate than previously suggested. We interpret thisas due to the dense starburst medium into which the supernovaedetonate. The compact radio morphology of Mrk231 places it among theCompact Symmetric Objects (CSOs) which are suggested to be young radio sources in which asymmetric lobes or hotspots reveal theworking surface of a relativistic jet upon the ambient medium. Assumingthat the lobes in Mrk 231 are confined by ram pressure, we estimate an agefor the jet/compact source, τ ≲ 106yr. We interpret Mrk 231as a newly formed QSO emerging from a starburst.
8 citations
Posted Content•
TL;DR: In this paper, the authors used the far-infrared data to study the behavior of the IR continuum in comparison with expectations from competing thermal and non-thermal models, and determined which mechanism dominates, is the measurement of the peak wavelength of the emission and the shape of the far IR--mm turnover.
Abstract: ISO provides a key new far-infrared window through which to observe the multi-wavelength spectral energy distributions (SEDs) of quasars and active galactic nuclei (AGN). It allows us, for the first time, to observe a substantial fraction of the quasar population in the far-IR, and to obtain simultaneous, multi-wavelength observations from 5--200 microns. With these data we can study the behavior of the IR continuum in comparison with expectations from competing thermal and non-thermal models. A key to determining which mechanism dominates, is the measurement of the peak wavelength of the emission and the shape of the far-IR--mm turnover. Turnovers which are steeper than frequency^2.5 indicate thermal dust emission in the far-IR.
Preliminary results from our ISO data show broad, fairly smooth, IR continuum emission with far-IR turnovers generally too steep to be explained by non-thermal synchrotron emission. Assuming thermal emission throughout leads to a wide inferred temperature range of 50-1000 K. The hotter material, often called the AGN component, probably originates in dust close to and heated by the central source, e.g. the ubiquitous molecular torus. The cooler emission is too strong to be due purely to cool, host galaxy dust, and so indicates either the presence of a starburst in addition to the AGN or AGN-heated dust covering a wider range of temperatures than present in the standard, optically thick torus models.
1 citations
01 Jan 1999
TL;DR: In this article, the authors highlight new results on two classical LIGs which span the range of LIGradio activity: Arp 220, which reveals luminous radio supernovae (RSN) produced in an intense starburst, and Mrk231, which has a powerful compact, AGN radio core.
Abstract: As described by Colin Lonsdale in this Workshop, VLBI observations reveal thepresence of both AGN and Starburst activity in Luminous Infrared Galaxies.We highlight new results on two classical LIGs which span the range of LIGradio activity: Arp 220, which reveals luminous radio supernovae (RSN)produced in an intense starburst, and Mrk231, which has a powerful compact,AGN radio core. Second epoch observations of the compact radio sources inArp 220 confirm their nature as luminous Radio Supernovae, but indicate alower luminous RSN frequency (νLRSN ≲ 0.3 yr-1) andconsequent slower decay rate than previously suggested. We interpret thisas due to the dense starburst medium into which the supernovaedetonate. The compact radio morphology of Mrk231 places it among theCompact Symmetric Objects (CSOs) which are suggested to be young radio sources in which asymmetric lobes or hotspots reveal theworking surface of a relativistic jet upon the ambient medium. Assumingthat the lobes in Mrk 231 are confined by ram pressure, we estimate an agefor the jet/compact source, τ ≲ 106yr. We interpret Mrk 231as a newly formed QSO emerging from a starburst.
Posted Content•
TL;DR: The US ISO Key Project on quasar spectral energy distributions seeks to better understand the very broad-band emission features of quasars from radio to X-rays as mentioned in this paper, using the ISOPHOT instrument at 8 bands from 5 to 200 microns.
Abstract: Author(s): Hooper, Eric J; Wilkes, Belinda J; McLeod, Kim K; Elvis, Martin S; Impey, Chris D; Lonsdale, Carol J; Malkan, Matt A; McDowell, Jonathan C | Abstract: The US ISO Key Project on quasar spectral energy distributions seeks to better understand the very broad-band emission features of quasars from radio to X-rays A key element of this project is observations of 72 quasars with the ISOPHOT instrument at 8 bands, from 5 to 200 microns The sample was chosen to span a wide range of redshifts and quasar types This paper presents an overview of the analysis and reduction techniques, as well as general trends within the data set (comparisons with IRAS fluxes, uncertainties as a function of background sky brightness, and an analysis of vignetting corrections in chopped observing mode) A more detailed look at a few objects in the sample is presented in Wilkes et al 1999, astro-ph/9902084