25 research outputs found
Hydrogeology of an alpine rockfall aquifer system and its role in flood attenuation and maintaining baseflow
The frequency and intensity of extreme hydrological events in Alpine regions
is projected to increase with climate change. The goal of this study is to
better understand the functioning of aquifers composed of complex alluvial
and rockfall deposits in Alpine valleys and to quantify the role of these
natural storage spaces in flood attenuation and baseflow maintenance.
Geomorphological and hydrogeological mapping, tracer tests, and continuous
flow measurements were conducted in the Reintal (German Alps), where
runoff from a karst spring infiltrates a series of postglacial
alluvial/rockfall aquifers. During high-flow conditions, groundwater
velocities of 30 m h<sup>−1</sup> were determined along 500 m; hydrograph analyses
revealed short lag times (5 h) between discharge peaks upstream and
downstream from the aquifer series; the maximum discharge ratio downstream
(22) and the peak recession coefficient (0.196 d<sup>−1</sup>) are low compared
with other Alpine catchments. During low-flow conditions, the underground
flow path length increased to 2 km and groundwater velocities decreased to
13 m h<sup>−1</sup>. Downstream hydrographs revealed a delayed discharge response after
101 h and peaks damped by a factor of 1.5. These results indicate that
alluvial/rockfall aquifers might play an important role in the flow regime
and attenuation of floods in Alpine regions
The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source?
Context. Radio-loud AGNs with powerful relativistic jets are thought to be
associated with rapidly spinning black holes (BHs). BH spin-up may result from
a number of processes, including accretion of matter onto the BH itself, and
catastrophic events such as BH-BH mergers. Aims. We study the intriguing
properties of the powerful (L_bol ~ 10^47 erg s^-1) radio-loud quasar 3C 186.
This object shows peculiar features both in the images and in the spectra.
Methods. We utilize near-IR Hubble Space Telescope (HST) images to study the
properties of the host galaxy, and HST UV and Sloan Digital Sky Survey optical
spectra to study the kinematics of the source. Chandra X-ray data are also used
to better constrain the physical interpretation. Results. HST imaging shows
that the active nucleus is offset by 1.3 +- 0.1 arcsec (i.e. ~11 kpc) with
respect to the center of the host galaxy. Spectroscopic data show that the
broad emission lines are offset by -2140 +-390 km/s with respect to the narrow
lines. Velocity shifts are often seen in QSO spectra, in particular in
high-ionization broad emission lines. The host galaxy of the quasar displays a
distorted morphology with possible tidal features that are typical of the late
stages of a galaxy merger. Conclusions. A number of scenarios can be envisaged
to account for the observed features. While the presence of a peculiar outflow
cannot be completely ruled out, all of the observed features are consistent
with those expected if the QSO is associated with a gravitational wave (GW)
recoiling BH. Future detailed studies of this object will allow us to confirm
this type of scenario and will enable a better understanding of both the
physics of BH-BH mergers and the phenomena associated with the emission of GW
from astrophysical sources.Comment: 16 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. New appendix adde
High‐Temperature Phase Change Material (PCM) Selection for Concentrating Solar Power Tower Applications
POWERFUL ACTIVITY IN THE BRIGHT AGES. I. A VISIBLE/IR SURVEY OF HIGH REDSHIFT 3C RADIO GALAXIES AND QUASARS
We present new rest frame UV and visible observations of 22 high-redshift (1
< z < 2.5) 3C radio galaxies and QSOs obtained with the Hubble Space
Telescope's (HST) Wide Field Camera 3 (WFC3) instrument. Using a custom data
reduction strategy in order to assure the removal of cosmic rays, persistence
signal, and other data artifacts, we have produced high-quality science-ready
images of the targets and their local environments. We observe targets with
regions of UV emission suggestive of active star formation. In addition,
several targets exhibit highly distorted host galaxy morphologies in the rest
frame visible images. Photometric analyses reveals that brighter QSOs tend to
be generally redder than their dimmer counterparts. Using emission line fluxes
from the literature, we estimate that emission line contamination is relatively
small in the rest frame UV images for the QSOs. Using archival VLA data, we
have also created radio map overlays for each of our targets, allowing for
analysis of the optical and radio axes alignment.Comment: 25 pages, 54 figures; Accepted for publication in ApJ
Simvastatin reduces leucocyte– and platelet–endothelial cell interaction in murine antigen-induced arthritis in vivo
THE ENVIRONMENT OF z
We study the cluster environment for a sample of 21 radio loud AGN from the
3CR catalog at z>1, 12 radio galaxies and 9 quasars with HST images in the
optical and IR. We use two different approaches to determine cluster
candidates. We identify the early type galaxies (ETGs) in every field by
modeling each of the sources within a 40" radius of the targets with a Sersic
profile. Using a simple passive evolution model, we derive the expected
location of the ETGs on the red sequence (RS) in the color-magnitude diagram
for each of the fields of our sources. For seven targets, the model coincides
with the position of the ETGs. A second approach involves a search for over
densities. We compare the object densities of the sample as a whole and
individually against control fields taken from the GOODS-S region of 3D-HST
survey. With this method we determine the fields of 10 targets to be cluster
candidates. Four cluster candidates are found by both methods. The two methods
disagree in some cases, depending on the specific properties of each field. For
the most distant radio galaxy in the 3CR catalog (3C257 at z = 2.47), we
identify a population of bluer ETGs that lie on the expected location of the RS
model for that redshift. This appears to be the general behavior of ETGs in our
fields and it is possibly a signature of the evolution of such galaxies. Our
results are consistent with half of the z > 1 radio galaxies being located in
dense, rapidly evolving environments.Comment: 12 pages, 8 figures, accepted for publication in the Astrophysical
Journa