38 research outputs found
Filaments and Ionized Gas in the Vicinity of 3C 244.1
We present results of Hubble Space Telescope observations of the radio galaxy
3C 244.1. The broadband F702W (R) and F555W (V) images (WFPC2/PC) show an
elliptical galaxy and gaseous filaments and blobs surrounding it. In the
narrow-band ramp filter, dominated by [OIII]lambda5007, these filaments are
bright and have the same morphology as the broad band images. To the south, the
filaments have a cone-shaped structure and the radio jet is located at the
center of this cone. To the north of the galaxy, the structure is found near
the nucleus of the galaxy within its elliptical profile. From the photometry,
the two brighter structures seem to be extended narrow line emission regions
(ENLRs). The comparison with diagnostic line ratios shows that the observed
emission is consistent with interactions between the expanding radio-jet and
the local denser medium.Comment: 10 pages and 3 figures, accepted for publication in Ap
The Nature of Blue Cores in Spheroids: a Possible Connection with AGN and Star Formation
We investigate the physical nature of blue cores in early-type galaxies
through the first multi-wavelength analysis of a serendipitously discovered
field blue-nucleated spheroid in the background of the deep ACS/WFC griz
multicolor observations of the cluster Abell 1689. The resolved g-r, r-i and
i-z color maps reveal a prominent blue core identifying this galaxy as a
``typical'' case study, exhibiting variations of 0.5-1.0 mag in color between
the center and the outer regions, opposite to the expectations of reddened
metallicity induced gradients in passively evolved ellipticals. From a
Magellan-Clay spectrum we secure the galaxy redshift at . We find a
strong X-ray source coincident with the spheroid galaxy. Spectral features and
a high X-ray luminosity indicate the presence of an AGN in the galaxy. However,
a comparison of the X-ray luminosity to a sample derived from the Chandra Deep
Field South displays Lx to be comparable to Type I/QSO galaxies while the
optical flux is consistent with a normal star-forming galaxy. We conclude that
the galaxy's non-thermal component dominates at high-energy wavelengths while
we associate the spheroid blue light with the stellar spectrum of normal
star-forming galaxies. We argue about a probable association between the
presence of blue cores in spheroids and AGN activity.Comment: Accepted for publication in the Astrophysical Journal. 6 pages, 3
figures. Full resolution images available at
http://acs.pha.jhu.edu/~felipe/e-print
The Extended Line Region of 3C 299
We present results of HST observations of the radio galaxy 3C 299. The
broad-band F702W (R) and F555W (V) images (WFPC2/PC) show an elliptical galaxy,
with a comet-like structure extending to the NE in the radio jet direction. The
[OIII]5007 emission line map, shows a bi-conical structure centered on
the nucleus, that overlaps the structure found in the broad-band filters. The
radio core coincides with the center of the bi-conical structure and the radio
axes are aligned with the direction of the cones. These data show clear
evidence of a strong interaction between the radio jet and the NE morphology of
the galaxy. We show evidence that this NE region is an ENLR; the line-ratio
diagnostics show that models involving gas shocked by the radio-jet plus
ionization from a precursor HII region, produced itself by the ionizing photons
of the postshocked gas on the preshocked gas provide a good match to the
observations. We investigate the spatial behavior of the ionizing parameter
, by determining the [OIII]/[OII] line ratio which is sensitive to the
change of the ionization parameter, and trace its behavior over the ENLR along
the radio jet direction. We find that [OIII]/[OII] does not follow a simple
dilution model, but rather that it is approximately constant over a large range
of distance from the nucleus thus requiring a local source of ionization which
seems to be compatible with the shock models driven by the radio jet.Comment: 17 pages, 9 Postscript figures, ApJ accepted, uses aaspp.st
The nuclei of radio galaxies in the UV: the signature of different emission processes
We have studied the nuclei of 28 radio galaxies from the 3CR sample in the UV
band. Unresolved nuclei (central compact cores, CCC) are observed in 10 of the
13 FR I, and in 5 of the 15 FR II. All sources that do not have a CCC in the
optical, do not have a CCC in the UV. Two FR I (3C 270 and 3C 296) have a CCC
in the optical but do not show the UV counterpart. Both of them show large
dusty disks observed almost edge-on, possibly implying that they play a role in
obscuring the nuclear emission. We have measured optical-UV spectral indices
alpha_o,UV between ~0.6 and ~7.0. BLRG have the flattest spectra and their
values of alpha_o,UV are also confined to a very narrow range. This is
consistent with radiation produced in a geometrically thin, optically thick
accretion disk. On the other hand, FR I nuclei, which are most plausibly
originated by synchrotron emission from the inner relativistic jet, show a wide
range of alpha_o,UV. There is a clear trend with orientation in that sources
observed almost edge-on or with clear signs of dust absorption have the
steepest spectra. These observations imply that in FR I obscuration can be
present, but the obscuring material is not in a ``standard'' geometrically
thick torus. The most striking difference between these absorbing structures
and the classic AGN ``tori'' resides in the lower optical depth of the FR I
obscuring material.Comment: 15 pages, 4 figures, accepted for publication on Ap
Discovery of Two Distant Type Ia Supernovae in the Hubble Deep Field North with the Advanced Camera for Surveys
We present observations of the first two supernovae discovered with the
recently installed Advanced Camera for Surveys (ACS) on the Hubble Space
Telescope. The supernovae were found in Wide Field Camera images of the Hubble
Deep Field North taken with the F775W, F850LP, and G800L optical elements as
part of the ACS guaranteed time observation program. Spectra extracted from the
ACS G800L grism exposures confirm that the objects are Type Ia supernovae (SNe
Ia) at redshifts z=0.47 and z=0.95. Follow-up HST observations have been
conducted with ACS in F775W and F850LP and with NICMOS in the near-infrared
F110W bandpass, yielding a total of 9 flux measurements in the 3 bandpasses
over a period of 50 days in the observed frame. We discuss many of the
important issues in doing accurate photometry with the ACS. We analyze the
multi-band light curves using two different fitting methods to calibrate the
supernovae luminosities and place them on the SNe Ia Hubble diagram. The
resulting distances are consistent with the redshift-distance relation of the
accelerating universe model, although evolving intergalactic grey dust remains
as a less likely possibility. The relative ease with which these SNe Ia were
found, confirmed, and monitored demonstrates the potential ACS holds for
revolutionizing the field of high-redshift SNe Ia, and therefore of testing the
accelerating universe cosmology and constraining the "epoch of deceleration".Comment: 11 pages, 8 embedded figures. Accepted for publication in Ap
Can Habitat Management Mitigate Disease Impacts on Threatened Amphibians?
Chytridiomycosis has decimated amphibian biodiversity. Management options for the disease are currently limited, but habitat manipulation holds promise due to the thermal and physicochemical sensitivities of chytrid fungi. Here, we quantify the extent to which habitat management could reduce metapopulation extinction risk for an Australian frog susceptible to chytridiomycosis. Our modeling revealed that: (1) habitat management is most effective in climates where hosts are already less susceptible to the disease; (2) creating habitat, particularly habitat with refugial properties adverse to the pathogen, may be substantially more effective than manipulating existing habitat; and (3) increasing metapopulation size and connectivity through strategic habitat creation can greatly reduce extinction risk. Controlling chytridiomycosis is a top priority for conserving amphibians. Our study provides impetus for experiments across a range of species and environments to test the capacity of habitat management to mitigate the impacts of this pervasive disease
The Near Infrared Imager and Slitless Spectrograph for JWST -- V. Kernel Phase Imaging and Data Analysis
Kernel phase imaging (KPI) enables the direct detection of substellar
companions and circumstellar dust close to and below the classical (Rayleigh)
diffraction limit. We present a kernel phase analysis of JWST NIRISS full pupil
images taken during the instrument commissioning and compare the performance to
closely related NIRISS aperture masking interferometry (AMI) observations. For
this purpose, we develop and make publicly available the custom "Kpi3Pipeline"
enabling the extraction of kernel phase observables from JWST images. The
extracted observables are saved into a new and versatile kernel phase FITS file
(KPFITS) data exchange format. Furthermore, we present our new and publicly
available "fouriever" toolkit which can be used to search for companions and
derive detection limits from KPI, AMI, and long-baseline interferometry
observations while accounting for correlated uncertainties in the model fitting
process. Among the four KPI targets that were observed during NIRISS instrument
commissioning, we discover a low-contrast (~1:5) close-in (~1 )
companion candidate around CPD-66~562 and a new high-contrast (~1:170)
detection separated by ~1.5 from 2MASS~J062802.01-663738.0. The
5- companion detection limits around the other two targets reach ~6.5
mag at ~200 mas and ~7 mag at ~400 mas. Comparing these limits to those
obtained from the NIRISS AMI commissioning observations, we find that KPI and
AMI perform similar in the same amount of observing time. Due to its 5.6 times
higher throughput if compared to AMI, KPI is beneficial for observing faint
targets and superior to AMI at separations >325 mas. At very small separations
(<100 mas) and between ~250-325 mas, AMI slightly outperforms KPI which suffers
from increased photon noise from the core and the first Airy ring of the
point-spread function.Comment: 34 pages, 17 figures, accepted for publication in PAS
Synaptic NMDA receptor activity boosts intrinsic antioxidant defenses
Intrinsic antioxidant defenses are important for neuronal longevity. We found that in rat neurons, synaptic activity, acting via NMDA receptor (NMDAR) signaling, boosted antioxidant defenses by making changes to the thioredoxin-peroxiredoxin (Prx) system. Synaptic activity enhanced thioredoxin activity, facilitated the reduction of overoxidized Prxs and promoted resistance to oxidative stress. Resistance was mediated by coordinated transcriptional changes; synaptic NMDAR activity inactivated a previously unknown Forkhead box O target gene, the thioredoxin inhibitor Txnip. Conversely, NMDAR blockade upregulated Txnip in vivo and in vitro, where it bound thioredoxin and promoted vulnerability to oxidative damage. Synaptic activity also upregulated the Prx reactivating genes Sesn2 (sestrin 2) and Srxn1 (sulfiredoxin), via C/EBPÎČ and AP-1, respectively. Mimicking these expression changes was sufficient to strengthen antioxidant defenses. Trans-synaptic stimulation of synaptic NMDARs was crucial for boosting antioxidant defenses; chronic bath activation of all (synaptic and extrasynaptic) NMDARs induced no antioxidative effects. Thus, synaptic NMDAR activity may influence the progression of pathological processes associated with oxidative damage