90 research outputs found
Asia Rising: Ships of State?
The commercial-strategic linkages and state support for PRC port and shipping ventures resemble a twenty-first-century version of the Dutch East India Company. These notionally commercial enterprises operate globally with the full financial and military backing of their home state, and the vessels that connect the ports are âships of state,â functioning as instruments of Chinese national strategy while they sail as commercial carriers
Distribution, species composition and management implications of seed banks in southern New England coastal plain ponds
Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Biological Conservation 142 (2009): 1350-1361, doi:10.1016/j.biocon.2009.01.020.Buried seeds that germinate during periods of low water or water level drawdown can play
important roles in shaping plant community composition, community dynamics and species
richness in ecosystems with fluctuating water levels. Northeastern US coastal plain ponds have
fluctuating water levels and contain a characteristic shoreline flora that contains many rare
plants. The objectives of this study were to: (1) test whether geographically distant ponds in
Cape Cod and Marthaâs Vineyard had distinct seed banks, (2) determine if hydrologic status as
permanent and ephemeral ponds led to differences in seed banks, and (3) examine seed diversity
and seed abundance across gradients of shoreline elevations and sediment characteristics. Viable
seeds of 45 plant species were identified from 9 ponds. Native species dominated pond-shore
seed banks and made up 89 to 100% of all species. There was high overlap in seed bank
composition across hydrological classes and geographic regions. One hydrological class captured
73-76% of total species and one geographical region captured 69-78% of the total species
recovered from the entire suite of seed bank samples. Seeds were relatively evenly distributed
along the shorelines of ephemeral ponds but seed diversity and abundance were lower at low
elevations in permanent ponds. Results suggest that strategies to protect pond shorelines to
capture maximum diversity of coastal plain pond plants contained in pond sediment seed banks
should be implemented across pond hydrologic classes and across a wide geographic area.
Shoreline seed distributions indicate that ground-water withdrawals or climate changes that
lower pond water levels in permanent ponds will reduce the diversity and abundance of plants
recovered from seed banks by shifting water levels to a shoreline zone of high sediment organic
matter where seed densities are lower. This effect will be much less in ephemeral ponds where
seed diversity and abundance on pond bottoms was high.This study was funded by the Massachusetts
Environmental Trust and the Barnstable Water Company
STIS spectroscopy of the emission line gas in the nuclei of nearby FR-I galaxies
We present the results of the analysis of a set of medium resolution spectra,
obtained by the Space Telescope Imaging Spectrograph on board the Hubble Space
Telescope, of the emission line gas present in the nuclei of a complete sample
of 21 nearby, early-type galaxies with radio jets (the UGC FR-I Sample). For
each galaxy nucleus we present spectroscopic data in the region of H-alpha and
the dervived kinematics.
We find that in 67% of the nuclei the gas appears to be rotating and, with
one exception, the cases where rotation is not seen are either face on or have
complex central morphologies. We find that in 62% of the nuclei the fit to the
central spectrum is improved by the inclusion of a broad component. The broad
components have a mean velocity dispersion of 1349 +/- 345 km\s and are
redshifted from the narrow line components (assuming an origin in H-alpha) by
486 +/- 443 km\s.Comment: 119 pages, 26 figures, ApJS Accepted, version with full figures
available at http://www.astro.columbia.edu/~jake/pub/fr1datapaper.pd
An optical-IR jet in 3C133
We report the discovery of a new optical-IR synchrotron jet in the radio
galaxy 3C133 from our HST/NICMOS snapshot survey. The jet and eastern hotspot
are well resolved, and visible at both optical and IR wavelengths. The IR jet
follows the morphology of the inner part of the radio jet, with three distinct
knots identified with features in the radio. The radio-IR SED's of the knots
are examined, along with those of two more distant hotspots at the eastern
extreme of the radio feature. The detected emission appears to be synchrotron,
with peaks in the NIR for all except one case, which exhibits a power-law
spectrum throughout.Comment: ApJ accepted. 14 pages, 6 figure
Dominant Nuclear Outflow Driving Mechanisms in Powerful Radio Galaxies
In order to identify the dominant nuclear outflow mechanisms in Active
Galactic Nuclei, we have undertaken deep, high resolution observations of two
compact radio sources (PKS 1549-79 and PKS 1345+12) with the Advanced Camera
for Surveys (ACS) aboard the Hubble Space Telescope. Not only are these targets
known to have powerful emission line outflows, but they also contain all the
potential drivers for the outflows: relativistic jets, quasar nuclei and
starbursts. ACS allows the compact nature (<0.15") of these radio sources to be
optically resolved for the first time. Through comparison with existing radio
maps we have seen consistency in the nuclear position angles of both the
optical emission line and radio data. There is no evidence for bi-conical
emission line features on the large-scale and there is a divergance in the
relative position angles of the optical and radio structure. This enables us to
exclude starburst driven outflows. However, we are unable to clearly
distinguish between radiative AGN wind driven outflows and outflows powered by
relativistic radio jets. The small scale bi-conical features, indicative of
such mechanisms could be below the resolution limit of ACS, especially if
aligned close to the line of sight. In addition, there may be offsets between
the radio and optical nuclei induced by heavy dust obscuration, nebular
continuum or scattered light from the AGN.Comment: 9 pages, 8 figures, emulateapj, ApJ Accepte
Infrared Emission from the Nearby Cool Core Cluster Abell 2597
We observed the brightest central galaxy (BCG) in the nearby (z=0.0821) cool
core galaxy cluster Abell 2597 with the IRAC and MIPS instruments on board the
Spitzer Space Telescope. The BCG was clearly detected in all Spitzer
bandpasses, including the 70 and 160 micron wavebands. We report aperture
photometry of the BCG. The spectral energy distribution exhibits a clear excess
in the FIR over a Rayleigh-Jeans stellar tail, indicating a star formation rate
of ~4-5 solar masses per year, consistent with the estimates from the UV and
its H-alpha luminosity. This large FIR luminosity is consistent with that of a
starburst or a Luminous Infrared Galaxy (LIRG), but together with a very
massive and old population of stars that dominate the energy output of the
galaxy. If the dust is at one temperature, the ratio of 70 to 160 micron fluxes
indicate that the dust emitting mid-IR in this source is somewhat hotter than
the dust emitting mid-IR in two BCGs at higher-redshift (z~0.2-0.3) and higher
FIR luminosities observed earlier by Spitzer, in clusters Abell 1835 and Zwicky
3146.Comment: Accepted at Ap
VLBA Observations of Sub-Parsec Structure in Mrk 231: Interaction between a Relativistic Jet and a BAL Wind
We report on the first high frequency VLBI observations of the nearby broad
absorption line quasar (BALQSO), Mrk 231. Three epochs of observations were
achieved at 15 GHz and 22 GHz, two of these included 43 GHz observations as
well. The nuclear radio source is resolved as a compact double. The core
component experienced a strong flare in which the flux density at 22 GHz
increased by (45 mJy) in three months. Theoretical models of the flare
imply that the emission is likely enhanced by very strong Doppler boosting of a
highly relativistic ejecta with a kinetic energy flux, . Combining our data with two previous epochs of 15 GHz data,
shows marginal evidence for the slow advance of the secondary component
(located pc from the core) over a 9.4 year span. We estimate
that the long term time averaged kinetic energy flux of the secondary at
. Low frequency VLBA observations
indicate that the secondary is seen through a shroud of free-free absorbing gas
with an emission measure of . The
steep spectrum secondary component appears to be a compact radio lobe that is
associated with a working surface between the ram-pressure confined jet, and a
dense medium that is likely to be the source of the free-free absorption. The
properties of the dense gas are consistent with the temperatures, displacement
from the nucleus and the column density of total hydrogen commonly associated
with the BAL wind.Comment: To appear in Ap
Gemini IFU, VLA, and HST observations of the OH megamaser galaxy IRAS F23199 + 0123 : the hidden monster and its outflow
We present Gemini Multi-Object Spectrograph (GMOS) Integral field Unit (IFU), Very Large Array (VLA), and Hubble Space Telescope (HST) observations of the OH megamaser (OHM) galaxy IRAS F23199+0123. Our observations show that this system is an interacting pair, with two OHM sources associated with the eastern (IRAS 23199E) member. The two members of the pair present somewhat extended radio emission at 3 and 20 cm, with flux peaks at each nucleus. The GMOS-IFU observations cover the inner âŒ6 kpc of IRAS 23199E at a spatial resolution of 2.3 kpc. The GMOS-IFU flux distributions in Hα and [N II] λ6583 are similar to that of an HST [N II]+Hα narrow-band image, being more extended along the north-eastâsouthwest direction, as also observed in the continuum HST F814W image. The GMOS-IFU Hα flux map of IRAS 23199E shows three extranuclear knots attributed to star-forming complexes. We have discovered a Seyfert 1 nucleus in this galaxy, as its nuclear spectrum shows an unresolved broad (full width at half-maximum â2170 km sâ1) double-peaked Hα component, from which we derive a black hole mass of MBH = 3.8+0.3â0.2Ă 106M . The gas kinematics shows low velocity dispersions (Ï) and low [NII]/Hα ratios for the star-forming complexes and higher Ï and [N II]/Hα surrounding the radio emission region, supporting interaction between the radio plasma and ambient gas. The two OH masers detected in IRAS F23199E are observed in the vicinity of these enhanced Ï regions, supporting their association with the active nucleus and its interaction with the surrounding gas. The gas velocity field can be partially reproduced by rotation in a disc, with residuals along the northâsouth direction being tentatively attributed to emission from the front walls of a bipolar outflow
An infrared survey of brightest cluster galaxies: Paper I
We report on an imaging survey with the Spitzer Space Telescope of 62
brightest cluster galaxies with optical line emission. These galaxies are
located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky
Survey. We find that about half of these sources have a sign of excess infrared
emission; 22 objects out of 62 are detected at 70 microns, 18 have 8 to 5.8
micron flux ratios above 1.0 and 28 have 24 to 8 micron flux ratios above 1.0.
Altogether 35 of 62 objects in our survey exhibit at least one of these signs
of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 micron
flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at
8 microns. Three of these have high measured [OIII](5007A)/Hbeta flux ratios
suggesting that these four, Abell 1068, Abell 2146, and Zwicky 2089, and
R0821+07, host dusty active galactic nuclei (AGNs). 9 objects (including the
four hosting dusty AGNs) have infrared luminosities greater than 10^11 L_sol
and so can be classified as luminous infrared galaxies (LIRGs). Excluding the
four systems hosting dusty AGNs, the excess mid-infrared emission in the
remaining brightest cluster galaxies is likely related to star formation.Comment: accepted for publication in ApJ
HST/STIS Spectroscopy of the Lyman-Alpha Emission Line in the Central Dominant Galaxies in A426, A1795, and A2597: Constraints on Clouds in the Intracluster Medium
We report on HST/STIS spectra of the Lyman-alpha emission in the central
dominant galaxies in three rich clusters of galaxies. We find evidence for a
population of clouds in the intracluster medium.We detect 10 Ly-alpha
absorption systems towards the nucleus of NGC1275 with columns of N(HI)
1E12-1E14 cm-2. The detected absorption features are most consistent with
associated nuclear absorption systems. There is very little nuclear absorption
at the systemic velocity in NGC1275. This implies that the large columns
detected in the 21 cm line towards the parsec scale radio source avoid the line
of sight to the nucleus. This gas may be located in a circumnuclear disk or
torus. We detect at least one and possibly two absorption features towards the
extended Ly-alpha in A426. We do not detect absorption towards the extended
Ly-alpha emission in A1795, and A2597 with upper limits N(HI) 1E13 cm-2 for
optically thin absorbers. Our data constrain the covering factor of any high
column density gas in the ICM to be less than 25%. Our results suggest that the
lack of observed intermediate temperature gas is not explained by obscuration.
In addition, the low columns of gas on the 100 kpc scales in the ICM suggests
that (1) the rate at which cold gas accumulates in the ICM on these scales is
very low, and (2) the dense nebulae in the central 10 kpc must have cooled or
been deposited in situ.Comment: 6 figure
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