815 research outputs found
Contact structures at a granodiorite intrusion, Piccaninny Point, north-east Tasmania
At Piccaninny Point, structures developed at the contact between the Piccaninny Creek Pluton and the Mathinna Beds have, a bearing on the mode of emplacement of this body and other granodiorite plutons in north-eastern Tasmania. The contact has both concordant and irregularly discordant segments, and a dilational mode of intrusion is indicated. During the late crystallisation stage flattening of partially crystallised
magma against the contact produced a secondary cataclastic foliation and flattened xenoliths, and caused injection of cross-cutting leucocratic dykes. Magmatic pressure on the wall continued after the marginal granodiorite had crystallised,
producing conjugate faults and quartz gash-veining. The Piccaninny Point contact has features analogous to regional features of the granodiorite plutons of the Blue Tier Batholith to the north. The granodioritic plutons appear to have been emplaced by fracture controlled dilation, with upwelling of magma in the centre and lateral spreading against the walls
Examples of intrusive acid dykes in E. Tasmania
Observations of the relationship between linear
or planar features on either side of dykes usually
form the basis of a field determination of their
mode of emplacement, although it is known that
sections oblique to planar features may lead to conflicting
results. In Eastern Tasmania only rarely
are examples encountered where dyke wall-rock
units are of use. However, dyke wall irregularities
are common and a comparison of opposite walls
have shown the dykes to be intrusive. Disproportionate
offsets of corresponding wall irregularities
due to connecting cross-dykes are general,
which results in intrusive bodies resembling those
of a replacement origin
The Formation of High Redshift Submillimeter Galaxies
We describe a model for the formation of \zsim 2 Submillimeter Galaxies
(SMGs) which simultaneously accounts for both average and bright SMGs while
providing a reasonable match to their mean observed spectral energy
distributions (SEDs). By coupling hydrodynamic simulations of galaxy mergers
with the high resolution 3D polychromatic radiative transfer code Sunrise, we
find that a mass sequence of merger models which use observational constraints
as physical input naturally yield objects which exhibit black hole, bulge, and
H2 gas masses similar to those observed in SMGs. The dominant drivers behind
the 850 micron flux are the masses of the merging galaxies and the stellar
birthcloud covering fraction. The most luminous (S850 ~ 15 mJy) sources are
recovered by ~10^13 Msun 1:1 major mergers with a birthcloud covering fraction
close to unity, whereas more average SMGs ~5-7 mJy) may be formed in lower mass
halos ~5x10^12 Msun. These models demonstrate the need for high spatial
resolution hydrodynamic and radiative transfer simulations in matching both the
most luminous sources as well as the full SEDs of SMGs. While these models
suggest a natural formation mechanism for SMGs, they do not attempt to match
cosmological statistics of galaxy populations; future efforts along this line
will help ascertain the robustness of these models.Comment: MNRAS Accepted; Revised version includes expanded discussion of
simulated radio properties of SMG
Understanding fixed effects in human well-being
In studies of subjective well-being, economists and other researchers typically use a fixed or random effect estimation to control for unobservable heterogeneity across individuals. Such individual heterogeneity, although substantially reducing the estimated effect of many characteristics, is little understood. This paper shows that personality measures can account for 20% of this heterogeneity and a further 13% can be accounted for by other observable between-person information. This paper then demonstrates that the use of personality measures, in a new technique developed by [Plumper, T., Troeger, V.E. (2007). Efficient estimation of time-invariant and rarely changing variables in finite sample panel analyses with unit fixed effects, Political Analysis, 15(2), 124-139.], can help researchers obtain improved estimates for important characteristics such as marital status, disability and income. The paper argues that this has important practical implications
Separating line emission from star formation, shocks, and AGN ionization in NGC 1068
In the optical spectra of galaxies, the separation of line emission from gas ionized by star formation and an active galactic nucleus (AGN), or by star formation and shocks, are very well-understood problems. However, separating line emission between AGN and shocks has proven difficult. With the aid of a new three-dimensional diagnostic diagram, we show the simultaneous separation of line emission from star formation, shocks, and AGN in NGC 1068, and quantify the ratio of star formation, shocks, and AGN in each spaxel. The AGN, shock, and star formation luminosity distributions across the galaxy accurately align with X-ray, radio, and CO(3–2) observations, respectively. Comparisons with previous separation methods show that the shocked emission heavily mixes with the AGN emission. We also show that if the H α flux is to be used as a star formation rate indicator, separating line emission from as many sources as possible should be attempted to ensure accurate results.Parts of this research were conducted by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), through project number CE170100013.
Support for AMM is provided by NASA through Hubble Fellowship grant #HST-HF2-51377 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555
The origin of the infrared emission in radio galaxies II: analysis of mid- to far-infrared Spitzer observations of the 2Jy sample
We present an analysis of deep mid- to far-infrared (MFIR) Spitzer
photometric observations of the southern 2Jy sample of powerful radio sources
(0.05 < z < 0.7), conducting a statistical investigation of the links between
radio jet, AGN, starburst activity and MFIR properties. This is part of an
ongoing extensive study of powerful radio galaxies that benefits from both
complete optical emission line information and a uniquely high detection rate
in the far-infrared (far-IR). We find tight correlations between the MFIR and
[OIII] emission luminosities, which are significantly better than those between
MFIR and extended radio luminosities, or between radio and [OIII] luminosities.
Since [OIII] is a known indicator of intrinsic AGN power, these correlations
confirm AGN illumination of the circum-nuclear dust as the primary heating
mechanism for the dust producing thermal MFIR emission at both 24 and 70
microns. We demonstrate that AGN heating is energetically feasible, and
identify the narrow line region clouds as the most likely location of the cool,
far-IR emitting dust. Starbursts make a major contribution to the heating of
the cool dust in only 15-28% of our targets.
We also investigate the orientation dependence of the continuum properties,
finding that the broad- and narrow-line objects in our sample with strong
emission lines have similar distributions of MFIR luminosities and colours.
Therefore our results are entirely consistent with the orientation-based
unified schemes for powerful radio galaxies. However, the weak line radio
galaxies (WLRG) form a separate class of objects with intrinsically low
luminosity AGN in which both the optical emission lines and the MFIR continuum
are weak.Comment: 29 pages, 5 figures, Accepted for publication in The Astrophysical
Journa
Metallicity and Far-Infrared Luminosity of High Redshift Quasars
We present the results of an exploratory study of broad line region (BLR)
metallicity in 34 2.2 < z < 4.6 quasars with far-infrared (FIR) luminosities
(L_FIR) from 10^13.4 to 10^12.1 L_\odot . Quasar samples sorted by L_FIR might
represent an evolutionary sequence if the star formation rates (SFRs) in quasar
hosts generally diminish across quasar lifetimes. We use rest-frame ultraviolet
spectra from the Sloan Digital Sky Survey to construct three composite spectra
sorted by L_FIR, corresponding to average SFRs of 4980, 2130 and 340 M_\odot
yr^-1 after correcting for a nominal quasar FIR contribution. The measured N V
{\lambda} 1240/C IV {\lambda} 1550 and Si IV {\lambda} 1397+O IV] {\lambda}
1402/C IV {\lambda} 1550 emission line ratios indicate super-solar BLR
metallicities in all three composites, with no evidence for a trend with the
star formation rate. The formal derived metallicities, Z ~ 5-9 Z_\odot , are
similar to those derived for the BLRs of other quasars at similar redshifts and
luminosities. These results suggest that the ongoing star formation in the host
is not responsible for the metal enrichment of the BLR gas. Instead, the BLR
gas must have been enriched before the visible quasar phase. These results for
high quasar metallicities, regardless of L_FIR, are consistent with evolution
scenarios wherein visibly bright quasars appear after the main episode(s) of
star formation and metal enrichment in the host galaxies. Finally, young
quasars, those more closely associated with a recent merger or a blowout of gas
and dust, may exhibit tracers of these events, such as redder continuum slopes
and higher incidence of narrow absorption lines. With the caveat of small
sample sizes, we find no relation between L_FIR and the reddening or the
incidence of absorption lines.Comment: 10 pages, 3 figures. Accepted to MNRAS, May 201
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