710 research outputs found
FIR statistics of paired galaxies
Much progress has been made in understanding the effects of interaction on galaxies (see reviews in this volume by Heckman and Kennicutt). Evidence for enhanced emission from galaxies in pairs first emerged in the radio (Sulentic 1976) and optical (Larson and Tinsley 1978) domains. Results in the far infrared (FIR) lagged behind until the advent of the Infrared Astronomy Satellite (IRAS). The last five years have seen numerous FIR studies of optical and IR selected samples of interacting galaxies (e.g., Cutri and McAlary 1985; Joseph and Wright 1985; Kennicutt et al. 1987; Haynes and Herter 1988). Despite all of this work, there are still contradictory ideas about the level and, even, the reality of an FIR enhancement in interacting galaxies. Much of the confusion originates in differences between the galaxy samples that were studied (i.e., optical morphology and redshift coverage). Here, the authors report on a study of the FIR detection properties for a large sample of interacting galaxies and a matching control sample. They focus on the distance independent detection fraction (DF) statistics of the sample. The results prove useful in interpreting the previously published work. A clarification of the phenomenology provides valuable clues about the physics of the FIR enhancement in galaxies
Quasars in the 4D Eigenvector 1 Context: A stroll down memory lane
Recently some pessimism has been expressed about our lack of progress in
understanding quasars over the 50+ year since their discovery. It is worthwhile
to look back at some of the progress that has been made - but still lies under
the radar - perhaps because few people are working on optical/UV spectroscopy
in this field. Great advances in understanding quasar phenomenology have
emerged using eigenvector techniques. The 4D eigenvector 1 context provides a
surrogate H-R Diagram for quasars with a source main sequence driven by
Eddington ratio convolved with line-of-sight orientation. Appreciating the
striking differences between quasars at opposite ends of the main sequence
(so-called population A and B sources) opens the door towards a unified model
of quasar physics, geometry and kinematics. We present a review of some of the
progress that has been made over the past 15 years, and point out unsolved
issues.Comment: 27 pages, 6 figure
Highly Accreting Quasars: Sample Definition and Possible Cosmological Implications
We propose a method to identify quasars radiating closest to the Eddington
limit, defining primary and secondary selection criteria in the optical, UV and
X-ray spectral range based on the 4D eigenvector 1 formalism. We then show that
it is possible to derive a redshift-independent estimate of luminosity for
extreme Eddington ratio sources. Using preliminary samples of these sources in
three redshift intervals (as well as two mock samples), we test a range of
cosmological models. Results are consistent with concordance cosmology but the
data are insufficient for deriving strong constraints. Mock samples indicate
that application of the method proposed in this paper using dedicated
observations would allow to set stringent limits on Omega_M and significant
constraints on Omega_Lambda.Comment: Accepted for publication in MNRA
The Intermediate Line Region in AGN: a region "praeter necessitatem"?
As a consequence of improved S/N, spectral resolution and wavelength coverage
various authors have introduced, without strong justification, new emitting
regions to account for various emission line profile differences in AGN. The
so-called CIVlambda1549 intermediate line region (ILR) appears to be especially
ill-defined. We present observational evidence that suggests the ILR is
statistically indistinguishable from the classical narrow line region (NLR). We
present the results of theoretical models showing that a smooth density
gradient in the NLR can produce CIV and Balmer emission lines with different
widths. The putative ILR component has often been included with the broad line
profile in studies of CIV BLR properties. Failure to account for the composite
nature of CIV emission, and for the presence of sometimes appreciable NLR CIV
emission, has important consequences for our understanding of the BLR.Comment: 3 Figs. 1 Table, accepted for publication in Astrophysical Journal
Letter
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