3,056 research outputs found
Narrow-line Seyfert 1 Galaxies and the M_BH - sigma Relation
We have studied the location of narrow-line Seyfert 1 (NLS1) galaxies and
broad-line Seyfert 1 (BLS1) galaxies on the M_BH - sigma relation of non-active
galaxies. We find that NLS1 galaxies as a class - as well as the BLS1 galaxies
of our comparison sample - do follow the M_BH-sigma relation of non-active
galaxies if we use the width of the [SII]6716,6731 emission lines as surrogate
for stellar velocity dispersion, sigma_*. We also find that the width of
[OIII]5007 is a good surrogate for sigma_*, but only after (a) removal of
asymmetric blue wings, and, more important, after (b) excluding core [OIII]
lines with strong blueshifts (i.e., excluding galaxies which have their [OIII]
velocity fields dominated by radial motions, presumably outflows). The same
galaxies which are extreme outliers in [OIII] still follow the M_BH - sigma
relation in [SII]. We confirm previous findings that NLS1 galaxies are
systematically off-set from the M_BH - sigma relation if the full [OIII]
profile is used to measure sigma. We systematically investigate the influence
of several parameters on the NSL1 galaxies' location on the M_BH - sigma plane:
[OIII]_core blueshift, L/L_Edd, intensity ratio FeII/H_beta, NLR density, and
absolute magnitude. Implications for NLS1 models and for their evolution along
the M_BH - sigma relation are discussed.Comment: ApJ Letters, in press (3 figures, one in colour
Constraints on a Primordial Magnetic Field
We derive an upper limit of
Gauss on the present strength of any primordial homogeneous magnetic field. The
microwave background anisotropy created by cosmological magnetic fields is
calculated in the most general flat and open anisotropic cosmologies containing
expansion-rate and 3-curvature anisotropies. Our limit is derived from a
statistical analysis of the 4-year Cosmic Background Explorer data for
anisotropy patterns characteristic of homogeneous anisotropy averaged over all
possible sky orientations with respect to the COBE receiver. The limits we
obtain are considerably stronger than those imposed by primordial
nucleosynthesis and ensure that other magnetic field effects on the microwave
background structure are unobservably small.Comment: 4 pages, uses RevTex, submitted to PR
Flaring of tidally compressed dark-matter clumps
We explore the physics and observational consequences of tidal compression
events (TCEs) of dark-matter clumps (DMCs) by supermassive black holes (SMBHs).
Our analytic calculations show that a DMC approaching a SMBH much closer than
the tidal radius undergoes significant compression along the axis perpendicular
to the orbital plane, shortly after pericenter passage. For DMCs composed of
self-annihilating dark-matter particles, we find that the boosted DMC density
and velocity dispersion lead to a flaring of the annihilation rate, most
pronounced for a velocity- dependent annihilation cross section. If the end
products of the annihilation are photons, this results in a gamma-ray flare,
detectable (and possibly already detected) by the Fermi telescope for a range
of model parameters. If the end products of dark-matter annihilation are
relativistic electrons and positrons and the local magnetic field is large
enough, TCEs of DMCs can lead to flares of synchrotron radiation. Finally, TCEs
of DMCs lead to a burst of gravitational waves, in addition to the ones
radiated by the orbital motion alone, and with a different frequency spectrum.
These transient phenomena provide interesting new avenues to explore the
properties of dark matter.Comment: 11 pages, 6 figures; Minor changes; Version as published in PR
Measuring the Radiative Histories of QSOs with the Transverse Proximity Effect
Since the photons that stream from QSOs alter the ionization state of the gas
they traverse, any changes to a QSO's luminosity will produce
outward-propagating ionization gradients in the surrounding intergalactic gas.
This paper shows that at redshift z~3 the gradients will alter the gas's
Lyman-alpha absorption opacity enough to produce a detectable signature in the
spectra of faint background galaxies. By obtaining noisy (S:N~4) low-resolution
(~7A) spectra of a several dozen background galaxies in an R~20' field
surrounding an isotropically radiating 18th magnitude QSO at z=3, it should be
possible to detect any order-of-magnitude changes to the QSO's luminosity over
the previous 50--100 Myr and to measure the time t_Q since the onset of the
QSO's current luminous outburst with an accuracy of ~5 Myr for t_Q<~50 Myr.
Smaller fields-of-view are acceptable for shorter QSO lifetimes. The major
uncertainty, aside from cosmic variance, will be the shape and orientation of
the QSO's ionization cone. This can be determined from the data if the number
of background sources is increased by a factor of a few. The method will then
provide a direct test of unification models for AGN.Comment: Accepted for publication in the ApJ. 16 page
Mechanical heating by active galaxies
Jets and winds are significant channels for energy loss from accreting black
holes. These outflows mechanically heat their surroundings, through shocks as
well as gentler forms of heating. We discuss recent efforts to understand the
nature and distribution of mechanical heating by central AGNs in clusters of
galaxies, using numerical simulations and analytic models. Specifically, we
will discuss whether the relatively gentle `effervescent heating' mechanism can
compensate for radiative losses in the central regions of clusters, and account
for the excess entropy observed at larger radii.Comment: 10 pages, no figures. Submitted to Philosophical Transactions of the
Royal Society (Series A: Mathematical, Physical and Engineering Sciences),
proceedings of the Poyal Society Discussion Meeting on the Impact of Active
Galaxies on the Universe at Large, London, February 16-17, 200
Cosmic Chemical Evolution with an Early Population of Intermediate Mass Stars
We explore the consequences of an early population of intermediate mass stars
in the 2 - 8 M\odot range on cosmic chemical evolution. We discuss the
implications of this population as it pertains to several cosmological and
astrophysical observables. For example, some very metal-poor galactic stars
show large enhancements of carbon, typical of the C-rich ejecta of low-mass
stars but not of supernovae; moreover, halo star carbon and oxygen abundances
show wide scatter, which imply a wide range of star-formation and
nucleosynthetic histories contributed to the first generations of stars. Also,
recent analyses of the 4He abundance in metal-poor extragalactic H II regions
suggest an elevated abundance Yp \simeq 0.256 by mass, higher than the
predicted result from big bang nucleosynthesis assuming the baryon density
determined by WMAP, Yp = 0.249. Although there are large uncertainties in the
observational determination of 4He, this offset may suggest a prompt initial
enrichment of 4He in early metal-poor structures. We also discuss the effect of
intermediate mass stars on global cosmic evolution, the reionization of the
Universe, the density of white dwarfs, as well as SNII and SNIa rates at high
redshift. We also comment on the early astration of D and 7Li. We conclude that
if intermediate mass stars are to be associated with Population III stars,
their relevance is limited (primarily from observed abundance patterns) to low
mass structures involving a limited fraction of the total baryon content of the
Universe.Comment: Submitted to MNRA
Evaluational adjectives
This paper demarcates a theoretically interesting class of "evaluational adjectives." This class includes predicates expressing various kinds of normative and epistemic evaluation, such as predicates of personal taste, aesthetic adjectives, moral adjectives, and epistemic adjectives, among others. Evaluational adjectives are distinguished, empirically, in exhibiting phenomena such as discourse-oriented use, felicitous embedding under the attitude verb `find', and sorites-susceptibility in the comparative form. A unified degree-based semantics is developed: What distinguishes evaluational adjectives, semantically, is that they denote context-dependent measure functions ("evaluational perspectives")âcontext-dependent mappings to degrees of taste, beauty, probability, etc., depending on the adjective. This perspective-sensitivity characterizing the class of evaluational adjectives cannot be assimilated to vagueness, sensitivity to an experiencer argument, or multidimensionality; and it cannot be demarcated in terms of pretheoretic notions of subjectivity, common in the literature. I propose that certain diagnostics for "subjective" expressions be analyzed instead in terms of a precisely specified kind of discourse-oriented use of context-sensitive language. I close by applying the account to `find x PRED' ascriptions
Molecular Lines as Diagnostics of High Redshift Objects
Models are presented for CO rotational line emission by high redshift
starburst galaxies. The influence of the cosmic microwave background on the
thermal balance and the level populations of atomic and molecular species is
explicitly included. Predictions are made for the observability of starburst
galaxies through line and continuum emission between z=5 and z=30. It is found
that the Millimeter Array could detect a starburst galaxy with ~10^5 Orion
regions, corresponding to a star formation rate of about 30 Mo yr^{-1}, equally
well at z=5 or z=30 due to the increasing cosmic microwave background
temperature with redshift. Line emission is a potentially more powerful probe
than dust continuum emission of very high redshift objects.Comment: 15 pages LaTex, uses aasms4.sty, Accepted by ApJ
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