702 research outputs found
Galaxy And Mass Assembly (GAMA) blended spectra catalogue: strong galaxy-galaxy lens and occulting galaxy pair candidates
We present the catalogue of blended galaxy spectra from the Galaxy And Mass Assembly (GAMA) survey. These are cases where light from two galaxies are significantly detected in a single GAMA fibre. Galaxy pairs identified from their blended spectrum fall into two principal classes: they are either strong lenses, a passive galaxy lensing an emission-line galaxy; or occulting galaxies, serendipitous overlaps of two galaxies, of any type. Blended spectra can thus be used to reliably identify strong lenses for follow-up observations (high-resolution imaging) and occulting pairs, especially those that are a late-type partly obscuring an early-type galaxy which are of interest for the study of dust content of spiral and irregular galaxies. The GAMA survey setup and its AUTOZ automated redshift determination were used to identify candidate blended galaxy spectra from the cross-correlation peaks. We identify 280 blended spectra with a minimum velocity separation of 600 km s−1, of which 104 are lens pair candidates, 71 emission-line-passive pairs, 78 are pairs of emission-line galaxies and 27 are pairs of galaxies with passive spectra. We have visually inspected the candidates in the Sloan Digital Sky Survey (SDSS) and Kilo Degree Survey (KiDS) images. Many blended objects are ellipticals with blue fuzz (Ef in our classification). These latter ‘Ef’ classifications are candidates for possible strong lenses, massive ellipticals with an emission-line galaxy in one or more lensed images. The GAMA lens and occulting galaxy candidate samples are similar in size to those identified in the entire SDSS. This blended spectrum sample stands as a testament of the power of this highly complete, second-largest spectroscopic survey in existence and offers the possibility to expand e.g. strong gravitational lens surveys
All NIRspec needs is HST/WFC3 pre-imaging? The use of Milky Way Stars in WFC3 Imaging to Register NIRspec MSA Observations
The James Webb Space Telescope (JWST) will be an exquisite new near-infrared
observatory with imaging and multi-object spectroscopy through ESA's NIRspec
instrument with its unique Micro-Shutter Array (MSA), allowing for slits to be
positioned on astronomical targets by opening specific 0.002"-wide micro
shutter doors.
To ensure proper target acquisition, the on-sky position of the MSA needs to
be verified before spectroscopic observations start. An onboard centroiding
program registers the position of pre-identified guide stars in a Target
Acquisition (TA) image, a short pre-spectroscopy exposure without dispersion
(image mode) through the MSA with all shutters open.
The outstanding issue is the availability of Galactic stars in the right
luminosity range for TA relative to typical high redshift targets. We explore
this here using the stars and candidate galaxies identified in the
source extractor catalogs of Brightest of Reionizing Galaxies survey
(BoRG[z8]), a pure-parallel program with Hubble Space Telescope Wide-Field
Camera 3.
We find that (a) a single WFC3 field contains enough Galactic stars to
satisfy the NIRspec astrometry requirement (20 milli-arcseconds), provided its
and the NIRspec TA's are AB in WFC3 F125W, (b) a single WFC3
image can therefore serve as the pre-image if need be, (c) a WFC3 mosaic and
accompanying TA image satisfy the astrometry requirement at AB mag in
WFC3 F125W, (d) no specific Galactic latitude requires deeper TA imaging due to
a lack of Galactic stars, and (e) a depth of AB mag in WFC3 F125W is
needed if a guide star in the same MSA quadrant as a target is required.
We take the example of a BoRG identified candidate galaxy and
require a Galactic star within 20" of it. In this case, a depth of 25.5 AB in
F125W is required (with 97% confidence).Comment: 17 pages, 15 figures, to appear in the Journal of Astronomical
Instrumentatio
Kinetics of the reduction of metalloproteins by chromous ion
The reduction of Cu(330) in Rhus vernicifera laccase by chromous ion is 30% faster than reduction of Cu(614) at room temperature [pH 4.8, µ = 0.1 (NaCl)], and two parallel first-order paths, attributed to heterogeneity of the protein, are observed at both wavelengths. The reactions of stellacyanin, spinach and French-bean plastocyanins, and cytochrome c with chromous ion under similar conditions are faster than that with laccase by factors of 102 to 104, and are first order in protein concentration. Comparison of rates and activation parameters for the reduction of "blue" copper in laccase, stellacyanin, and the two plastocyanins indicates that reduction of the Cu(614) site in laccase may occur by intramolecular electron transfer from one of the Cu(330) sites. Our value of ΔH (17.4 kcal/mol) for the chromous ion reduction of cytochrome c is consistent with a mechanism in which major conformational changes in the protein must accompany electron transfer
The Opacity of Spiral Galaxy Disks IV: Radial Extinction Profiles from Counts of Distant Galaxies seen through Foreground Disks
Dust extinction can be determined from the number of distant field galaxies
seen through a spiral disk. To calibrate this number for the crowding and
confusion introduced by the foreground image, Gonzalez et al.(1998) and
Holwerda et al. (2005) developed the ``Synthetic Field Method'' (SFM), which
analyses synthetic fields constructed by adding various deep exposures of
unobstructed background fields to the candidate foreground galaxy field.
The advantage of the SFM is that it gives the average opacity for area of
galaxy disk without assumptions about either the distribution of absorbers or
of the disk starlight. However it is limited by low statistics of the surviving
field galaxies, hence the need to combine a larger sample of fields. This paper
presents the first results for a sample of 32 deep HST/WFPC2 archival fields of
29 spirals.
The radial profiles of average dust extinction in spiral galaxies based on
calibrated counts of distant field galaxies is presented here, both for
individual galaxies as well as for composites from our sample. The effects of
inclination, spiral arms and Hubble type on the radial extinction profile are
discussed. (Abbreviated)Comment: 43 pages, 16 figures, 3 tables, accepted for publication in the
Astronomical Journal, (typos, table update, updates abstract
The Opacity of Spiral Galaxy Disks VI: Extinction, stellar light and color
In this paper we explore the relation between dust extinction and stellar
light distribution in disks of spiral galaxies. Extinction influences our
dynamical and photometric perception of disks, since it can distort our
measurement of the contribution of the stellar component. To characterize the
total extinction by a foreground disk, Gonzalez et al. (1998) proposed the
``Synthetic Field Method'' (SFM), which uses the calibrated number of distant
galaxies seen through the foreground disk as a direct indication of extinction.
The method is described in Gonzalez et al. (1998) and Holwerda et al. (2005a).
To obtain good statistics, the method was applied to a set of HST/WFPC2 fields
Holwerda et al. (2005b) and radial extinction profiles were derived, based on
these counts. In the present paper, we explore the relation of opacity with
surface brightness or color from 2MASS images, as well as the relation between
the scalelengths for extinction and light in the I band. We find that there is
indeed a relation between the opacity (A_I) and the surface brightness,
particularly at the higher surface brightnesses. No strong relation between
near infrared (H-J, H-K) color and opacity is found. The scalelengths of the
extinction are uncertain for individual galaxies but seem to indicate that the
dust distribution is much more extended than the stellar light. The results
from the distant galaxy counts are also compared to the reddening derived from
the Cepheids light-curves Freedman et al. (2001). The extinction values are
consistent, provided the selection effect against Cepheids with higher values
of A_I is taken into account. The implications from these relations for disk
photometry, M/L conversion and galaxy dynamical modeling are briefly discussed.Comment: 9 pages, 2 tables, 10 figures, accepted by A&
HST followup observations of two bright z ~ 8 candidate galaxies from the BoRG pure-parallel survey
We present followup imaging of two bright (L > L*) galaxy candidates at z > 8
from the Brightest of Reionizing Galaxies (BoRG) survey with the F098M filter
on HST/WFC3. The F098M filter provides an additional constraint on the flux
blueward of the spectral break, and the observations are designed to
discriminate between low- and high-z photometric redshift solutions for these
galaxies. Our results confirm one galaxy, BoRG 0116+1425 747, as a highly
probable z ~ 8 source, but reveal that BoRG 0116+1425 630 - previously the
brightest known z > 8 candidate (mAB = 24.5) - is likely to be a z ~ 2
interloper. As this source was substantially brighter than any other z > 8
candidate, removing it from the sample has a significant impact on the derived
UV luminosity function in this epoch. We show that while previous BoRG results
favored a shallow power-law decline in the bright end of the luminosity
function prior to reionization, there is now no evidence for departure from a
Schechter function form and therefore no evidence for a difference in galaxy
formation processes before and after reionization.Comment: Accepted by ApJL, 7 pages, 4 figure
Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8
The presence of a well-defined and narrow dust lane in an edge-on spiral
galaxy is the observational signature of a thin and dense molecular disk, in
which gravitational collapse has overcome turbulence. Using a sample of
galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction
of massive disks that display a dust lane. Our goal is to explore the evolution
in the stability of the molecular ISM disks in spiral galaxies over a cosmic
timescale. We check the reliability of our morphological classifications
against changes in restframe wavelength, resolution, and cosmic dimming with
(artificially redshifted) images of local galaxies from SDSS. We find that the
fraction of L* disks with dust lanes in COSMOS is consistent with the local
fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly
lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively
supports the notion that a high specific star formation rate can efficiently
destroy or inhibit a dense molecular disk. A small subsample of higher redshift
COSMOS galaxies display low internal reddening (E[B-V]), as well as a low
incidence of dust lanes. These may be disks in which the growth of the dusty
ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most
massive galaxies display a lower dust lane fraction than lower mass galaxies. A
small contribution of recent mergers or starbursts to this most massive
population may be responsible. The fact that the fraction of galaxies with dust
lanes in COSMOS is consistent with little or no evolution implies that models
to explain the Spectral Energy Distribution or the host galaxy dust extinction
of supernovae based on local galaxies are still applicable to higher redshift
spirals. It also suggests that dust lanes are long lived phenomena or can be
reformed over very short time-scales.Comment: 14 pages, 9 figures, 2 tables, accepted for publication by Ap
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