15,252 research outputs found
Spectroscopy of Luminous Compact Blue Galaxies in Distant Clusters I. Spectroscopic Data
We used the DEIMOS spectrograph on the Keck II Telescope to obtain spectra of
galaxies in the fields of five distant, rich galaxy clusters over the redshift
range 0.5 < z < 0.9 in a search for luminous, compact, blue galaxies (LCBGs).
Unlike traditional studies of galaxy clusters, we preferentially targeted blue
cluster members identified via multi-band photometric pre-selection based on
imaging data from the WIYN telescope. Of the 1288 sources that we targeted, we
determined secure spectroscopic redshifts for 848 sources, yielding a total
success rate of 66%. Our redshift measurements are in good agreement with those
previously reported in the literature, except for 11 targets which we believe
were previously in error. Within our sample, we confirm the presence of 53
LCBGs in the five galaxy clusters. The clusters all stand out as distinct peaks
in the redshift distribution of LCBGs with the average number density of LCBGs
ranging from 1.65+-0.25 Mpc^-3 at z=0.55 to 3.13+-0.65 Mpc^-3 at z=0.8. The
number density of LCBGs in clustes exceeds the field desnity by a factor of
749+-116 at z=0.55; at z=0.8, the corresponding ratio is E=416+-95. At z=0.55,
this enhancement is well above that seen for blue galaxies or the overall
cluster population, indicating that LCBGs are preferentially triggered in
high-density environments at intermediate redshifts.Comment: 45 pages, 19 figures, accepted to ApJ. For Full resolution figure and
data tables, see http://www.salt.ac.za/~crawford/projects/deimos
Development and test of video systems for airborne surveillance of oil spills
Five video systems - potentially useful for airborne surveillance of oil spills - were developed, flight tested, and evaluated. The systems are: (1) conventional black and white TV, (2) conventional TV with false color, (3) differential TV, (4) prototype Lunar Surface TV, and (5) field sequential TV. Wavelength and polarization filtering were utilized in all systems. Greatly enhanced detection of oil spills, relative to that possible with the unaided eye, was achieved. The most practical video system is a conventional TV camera with silicon-diode-array image tube, filtered with a Corning 7-54 filter and a polarizer oriented with its principal axis in the horizontal direction. Best contrast between oil and water was achieved when winds and sea states were low. The minimum detectable oil film thickness was about 0.1 micrometer
Cluster induced quenching of galaxies in the massive cluster XMMXCSJ2215.9-1738 at z~1.5 traced by enhanced metallicities inside half R200
(Abridged) We explore the massive cluster XMMXCSJ2215.9-1738 at z~1.5 with
KMOS spectroscopy of Halpha and [NII] covering a region that corresponds to
about one virial radius. Using published spectroscopic redshifts of 108
galaxies in and around the cluster we computed the location of galaxies in the
projected velocity vs. position phase-space to separate our cluster sample into
a virialized region of objects accreted longer ago (roughly inside half R200)
and a region of infalling galaxies. We measured oxygen abundances for ten
cluster galaxies with detected [NII] lines in the individual galaxy spectra and
compared the MZR of the galaxies inside half R200 with the infalling galaxies
and a field sample at similar redshifts. We find that the oxygen abundances of
individual z~1.5 star-forming cluster galaxies inside half R200 are comparable,
at the respective stellar mass, to the higher local SDSS metallicity values. We
find that the [NII]/Halpha line ratios inside half R200 are higher by 0.2 dex
and that the resultant metallicities of the galaxies in the inner part of the
cluster are higher by about 0.1 dex, at a given mass, than the metallicities of
infalling galaxies and of field galaxies at z~1.5. The enhanced metallicities
of cluster galaxies at z~1.5 inside half R200 indicate that the density of the
ICM in this massive cluster becomes high enough toward the cluster center such
that the ram pressure exceeds the restoring pressure of the hot gas reservoir
of cluster galaxies. This can remove the gas reservoir initiating quenching;
although the galaxies continue to form stars, albeit at slightly lower rates,
using the available cold gas in the disk which is not stripped.Comment: Accepted for publication in A&
The morpho-kinematics of the circumstellar envelope around the AGB star EP Aqr
ALMA observations of CO(1-0) and CO(2-1) emissions of the circumstellar
envelope of EP Aqr, an oxygen-rich AGB star, are reported. A thorough analysis
of their properties is presented using an original method based on the
separation of the data-cube into a low velocity component associated with an
equatorial outflow and a faster component associated with a bipolar outflow. A
number of important and new results are obtained concerning the distribution in
space of the effective emissivity, the temperature, the density and the flux of
matter. A mass loss rate of (1.60.4)10 solar masses per year is
measured. The main parameters defining the morphology and kinematics of the
envelope are evaluated and uncertainties inherent to de-projection are
critically discussed. Detailed properties of the equatorial region of the
envelope are presented including a measurement of the line width and a precise
description of the observed inhomogeneity of both morphology and kinematics. In
particular, in addition to the presence of a previously observed spiral
enhancement of the morphology at very small Doppler velocities, a similarly
significant but uncorrelated circular enhancement of the expansion velocity is
revealed, both close to the limit of sensitivity. The results of the analysis
place significant constraints on the parameters of models proposing
descriptions of the mass loss mechanism, but cannot choose among them with
confidence.Comment: 26 pages, 31 figures, accepted for publication in MNRA
Modeling the HeII Transverse Proximity Effect: Constraints on Quasar Lifetime and Obscuration
The HeII transverse proximity effect - enhanced HeII Ly{\alpha} transmission
in a background sightline caused by the ionizing radiation of a foreground
quasar - offers a unique opportunity to probe the emission properties of
quasars, in particular the emission geometry (obscuration, beaming) and the
quasar lifetime. Building on the foreground quasar survey published in
Schmidt+2017, we present a detailed model of the HeII transverse proximity
effect, specifically designed to include light travel time effects, finite
quasar ages, and quasar obscuration. We post-process outputs from a
cosmological hydrodynamical simulation with a fluctuating HeII UV background
model, plus the added effect of the radiation from a single bright foreground
quasar. We vary the age and obscured sky fractions
of the foreground quasar, and explore the resulting
effect on the HeII transverse proximity effect signal. Fluctuations in IGM
density and the UV background, as well as the unknown orientation of the
foreground quasar, result in a large variance of the HeII Ly{\alpha}
transmission along the background sightline. We develop a fully Bayesian
statistical formalism to compare far UV HeII Ly{\alpha} transmission spectra of
the background quasars to our models, and extract joint constraints on
and for the six Schmidt+2017 foreground
quasars with the highest implied HeII photoionization rates. Our analysis
suggests a bimodal distribution of quasar emission properties, whereby one
foreground quasar, associated with a strong HeII transmission spike, is
relatively old and unobscured ,
whereas three others are either younger than or highly
obscured .Comment: 19 pages, 6 figures, submitted to Ap
Astronomical image processing based on fractional calculus: the AstroFracTool
The implementation of fractional differential calculations can give new
possibilities for image processing tools, in particular for those that are
devoted to astronomical images analysis. As discussed in arxiv:0910.2381, the
fractional differentiation is able to enhance the quality of images, with
interesting effects in edge detection and image restoration. Here, we propose
the AstroFracTool, developed to provide a simple yet powerful enhancement
tool-set for astronomical images. This tool works evaluating the fractional
gradient of an image map. It can help produce an output image useful for
further research and scientific purposes, such as the detection of faint
objects and galaxy structures, or, in the case of planetary studies, the
enhancement of surface details.Comment: Keywords: Fractional calculation, image processing, astronom
Total and partial cloud amount detection during summer 2005 at Westerland (Sylt, Germany)
The detection of cloudiness is investigated by means of partial and total cloud amount estimations from pyrgeometer radiation measurements and visible all-sky imager observations. The measurements have been performed in Westerland, a seaside resort on the North Sea island of Sylt, Germany, during summer 2005.
An improvement to previous studies on this subject resulting in the first time partial cloud amounts (PCAs), defined as cloud amounts without high clouds calculated from longwave downward radiation (LDR) according to the APCADA algorithm (Dürr and Philipona, 2004), are validated against both human observations from the National Meteorological Servive DWD at the nearby airport of Sylt and digital all-sky imaging. The aim is to establish the APCADA scheme at a coastal midlatitude site for longterm observations of cloud cover and to quantify errors resulting from the different methods of detecting cloudiness.
Differences between the resulting total cloud amounts (TCAs), defined as cloud amount for all-cloud situations, derived from the camera images and from human observations are within ±1 octa in 72% and within ±2 octa in 85% of the cases. Compared to human observations, PCA measurements, according to APCADA, underestimate the observed cloud cover in 47% of all cases and the differences are within ±1 octa in 60% and ±2 octa in 74% of all cases. Since high cirrus clouds can not be derived from LDR, separate comparisons for all cases without high clouds have been performed showing an agreement within ±1(2) octa in 73(90)% for PCA and also for camera-derived TCA. For this coastal mid-latitude site under investigation, we find similar though slightly smaller agreements to human observations as reported by Dürr and Philipona (2004). Though limited to daytime, the cloud cover retrievals from the sky imager are not really affected by cirrus clouds and provide a more reliable cloud climatology for all-cloud conditions than APCADA
Super star cluster feedback driving ionization, shocks and outflows in the halo of the nearby starburst ESO 338-IG04
Stellar feedback strongly affects the interstellar medium (ISM) of galaxies.
Stellar feedback in the first galaxies likely plays a major role in enabling
the escape of LyC photons, which contribute to the re-ionization of the
Universe. Nearby starburst galaxies serve as local analogues allowing for a
spatially resolved assessment of the feedback processes in these galaxies. We
characterize the feedback effects from the star clusters in the local
high-redshift analogue ESO 338-IG04 on the ISM and compare the results with the
properties of the most massive clusters. We use high quality VLT/MUSE optical
integral field data to derive the physical properties of the ISM such as
ionization, density, shocks, and perform new fitting of the spectral energy
distributions of the brightest clusters in ESO 338-IG04 from HST imaging. ESO
338-IG04 has a large ionized halo which we detect to a distance of 9 kpc. We
identify 4 Wolf-Rayet (WR) clusters based on the blue and red WR bump. We
follow previously identified ionization cones and find that the ionization of
the halo increases with distance. Analysis of the galaxy kinematics shows two
complex outflows driven by the numerous young clusters in the galaxy. We find a
ring of shocked emission traced by an enhanced [OI]/H ratio surrounding
the starburst and at the end of the outflow. Finally we detect nitrogen
enriched gas associated with the outflow, likely caused by the WR stars in the
massive star clusters. Photo-ionization dominates the central starburst and
sets the ionization structure of the entire halo, resulting in a density
bounded halo, facilitating the escape of LyC photons. Outside the central
starburst, shocks triggered by an expanding super bubble become important. The
shocks at the end of the outflow suggest interaction between the hot outflowing
material and the more quiescent halo gas.Comment: Accepted for publication in Astronomy and Astrophysics, 22 pages, 15
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