660 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
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Structure and Evolution of the Opacity of Spiral Disks
The opacity of a spiral disk due to dust absorption influences every measurement we make of it in the UV and optical. Two separate techniques directly measure the total absorption by dust in the disk: calibrated distant galaxy counts and overlapping galaxy pairs. The main results from both so far are a semi-transparent disk with more opaque arms and a relation between surface brightness and disk opacity. In the Spitzer era, spectral energy distribution models of spiral disks add a new perspective on the role of dust in spiral disks. Combined with the overall opacity from galaxy counts, we can derive a typical optical depth of the dusty interstellar medium clouds: 0.4 which implies a size of ∼ 60 pc. Current work on galaxy counts is in the ACS fields of M 51, M 101 and M 81. Occulting galaxies offer the possibility of probing the history of disk opacity from higher redshift occulting pairs. Evolution in disk opacity could influence distance measurements (SN1a, Tully-Fisher relation). Here, we present first results from spectroscopically selected occulting pairs in the Sloan Digital Sky Survey. The redshift range for this sample is limited but does offer a first insight into disk opacity evolution as well as a reference for higher redshift measurements
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
The Luminosity Function at z~8 from 97 Y-band dropouts: Inferences About Reionization
[Abbreviated] We present the largest search to date for Lyman break
galaxies (LBGs) based on 350 arcmin of HST observations in the V-, Y-, J-
and H-bands from the Brightest of Reionizing Galaxies (BoRG) survey. The BoRG
dataset includes 50 arcmin of new data and deeper observations of two
previous BoRG pointings, from which we present 9 new LBG candidates,
bringing the total number of BoRG LBGs to 38 with (AB system). We introduce a new Bayesian formalism for
estimating the galaxy luminosity function (LF), which does not require binning
(and thus smearing) of the data and includes a likelihood based on the formally
correct binomial distribution as opposed to the often used approximate Poisson
distribution. We demonstrate the utility of the new method on a sample of
LBGs that combines the bright BoRG galaxies with the fainter sources published
in Bouwens et al. (2012) from the HUDF and ERS programs. We show that the
LF is well described by a Schechter function with a characteristic
magnitude , a faint-end slope of , and a number density of . Integrated down to this
LF yields a luminosity density, . Our LF analysis
is consistent with previously published determinations within 1. We
discuss the implication of our study for the physics of reionization. By
assuming theoretically motivated priors on the clumping factor and the photon
escape fraction we show that the UV LF from galaxy samples down to
can ionize only 10-50% of the neutral hydrogen at . Full reionization
would require extending the LF down to .Comment: Accepted for publication in ApJ, 22 pages, 15 figure
Herschel/SPIRE observations of the dusty disk of NGC 4244
We present Herschel/SPIRE images at 250, 350, and 500 mu m of NGC 4244, a typical low-mass, disk-only and edge-on spiral galaxy. The dust disk is clumpy and shows signs of truncation at the break radius of the stellar disk. This disk coincides with the densest part of the Hi disk. We compare the spectral energy distribution (SED), including the new SPIRE fluxes, to 3D radiative transfer models; a smooth model disk and a clumpy model with embedded heating. Each model requires a very high value for the dust scale-length (h(d) = 2-5 h(*)), higher dust masses than previous models of NGC 4244 (M-d = 0.47-1.39 x 10(7) M-circle dot) and a face-on optical depth of tau(f.o.)(V) = 0.4-1.12, in agreement with previous disk opacity studies. The vertical scales of stars and dust are similar. The clumpy model much better mimics the general morphology in the sub-mm images and the general SED. The inferred gas-to-dust mass ratio is compatible with those of similar low-mass disks. The relatively large radial scale-length of the dust disk points to radial mixing of the dusty ISM within the stellar disk. The large vertical dust scale and the clumpy dust distribution of our SED model are both consistent with a scenario in which the vertical structure of the ISM is dictated by the balance of turbulence and self-gravity
UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
The remarkable HST datasets from the CANDELS, HUDF09, HUDF12, ERS, and
BoRG/HIPPIES programs have allowed us to map out the evolution of the UV LF
from z~10 to z~4. We have identified 5859, 3001, 857, 481, 217, and 6 galaxy
candidates at z~4, z~5, z~6, z~7, z~8, and z~10, respectively from the ~1000
arcmin**2 area probed. The selection of z~4-8 galaxies over the five CANDELS
fields allows us to assess the cosmic variance; the largest variations are
apparent at z>=7. Our new LF determinations at z~4 and z~5 span a 6-mag
baseline (-22.5 to -16 AB mag). These determinations agree well with previous
estimates, but the larger samples and volumes probed here result in a more
reliable sampling of >L* galaxies and allow us to reassess the form of the UV
LFs. Our new LF results strengthen our earlier findings to 3.4 sigma
significance for a steeper faint-end slope to the UV LF at z>4, with alpha
evolving from alpha=-1.64+/-0.04 at z~4 to alpha=-2.06+/-0.13 at z~7 (and alpha
= -2.02+/-0.23 at z~8), consistent with that expected from the evolution of the
halo mass function. With our improved constraints at the bright end, we find
less evolution in the characteristic luminosity M* over the redshift range z~4
to z~7; the observed evolution in the LF is now largely represented by changes
in phi*. No evidence for a non-Schechter-like form to the z~4-8 LFs is found. A
simple conditional LF model based on halo growth and evolution in the M/L ratio
of halos ((1+z)**-1.5) provides a good representation of the observed
evolution.Comment: 53 pages, 28 figures, 11 tables, accepted for publication in the
Astrophysical Journa
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