9,126 research outputs found
Star Formation Density and Halpha Luminosity Function of an Emission Line Selected Galaxy Sample at z ~ 0.24
We use narrowband imaging (FWHM = 70 A) to select a sample of emission line
galaxies between 0.20 <~ z <~ 1.22 in two fields covering 0.5 sq. deg. We use
spectroscopic follow-up to select a sub-sample of Halpha emitting galaxies at z
~ 0.24 and determine the Halpha luminosity function and star formation density
at z ~ 0.24 for both of our fields. Corrections are made for imaging and
spectroscopic incompleteness, extinction and interloper contamination on the
basis of the spectroscopic data. When compared to each other, we find the field
samples differ by \Delta \alpha = 0.2 in faint end slope and \Delta \log [ L*
(ergs/s) ] = 0.2 in luminosity. In the context of other recent surveys, our
sample has comparable faint end slope, but a fainter L* turn-over. We conclude
that systematic uncertainties and differences in selection criteria remain the
dominant sources of uncertainty between Halpha luminosity functions at this
redshift.
We also investigate average star formation rates as a function of local
environment and find typical values consistent with the field densities that we
probe, in agreement with previous results. However, we find tentative evidence
for an increase in star formation rate with respect to the local density of
star forming galaxies, consistent with the scenario that galaxy-galaxy
interactions are triggers for bursts of star formation.Comment: Accepted for publication in MNRAS. The paper contains 14 figures and
7 table
Environments and Morphologies of Red Sequence Galaxies with Residual Star Formation in Massive Clusters
We present a photometric investigation into recent star formation in galaxy
clusters at z ~ 0.1. We use spectral energy distribution templates to quantify
recent star formation in large X-ray selected clusters from the LARCS survey
using matched GALEX NUV photometry. These clusters all have signs of red
sequence galaxy recent star formation (as indicated by blue NUV-R colour),
regardless of cluster morphology and size. A trend in environment is found for
these galaxies, such that they prefer to occupy low density, high cluster
radius environments. The morphology of these UV bright galaxies suggests that
they are in fact red spirals, which we confirm with light curves and Galaxy Zoo
voting percentages as morphological proxies. These UV bright galaxies are
therefore seen to be either truncated spiral galaxies, caught by ram pressure
in falling into the cluster, or high mass spirals, with the photometry
dominated by the older stellar population.Comment: Accepted for publication in MNRAS, 11 pages, 11 figure
Evidence for HI replenishment in massive galaxies through gas accretion from the cosmic web
We examine the H i -to-stellar mass ratio (H i fraction) for galaxies near filament backbones within the nearby Universe (d < 181 Mpc). This work uses the 6 degree Field Galaxy Survey (6dFGS) and the Discrete Persistent Structures Extractor (DisPerSE) to define the filamentary structure of the local cosmic web. H i spectral stacking of H i Parkes All Sky Survey (HIPASS) observations yield the H i fraction for filament galaxies and a field control sample. The H i fraction is measured for different stellar masses and 5th nearest neighbour projected densities (ÎŁ5) to disentangle what influences cold gas in galaxies. For galaxies with stellar masses log(Mâ) †11 Mâ in projected densities 0 †Σ5 < 3 galaxies Mpcâ2, all H i fractions of galaxies near filaments are statistically indistinguishable from the control sample. Galaxies with stellar masses log(Mâ) â„ 11 Mâ have a systematically higher H i fraction near filaments than the control sample. The greatest difference is 0.75 dex, which is 5.5Ï difference at mean projected densities of 1.45 galaxies Mpcâ2. We suggest that this is evidence for massive galaxies accreting cold gas from the intra-filament medium which can replenish some H i gas. This supports cold mode accretion where filament galaxies with a large gravitational potential can draw gas from the large scale structure
The Clustering Of Galaxies Around Radio-Loud AGNs
We examine the hypothesis that mergers and close encounters between galaxies
can fuel AGNs by increasing the rate at which gas accretes towards the central
black hole. We compare the clustering of galaxies around radio-loud AGNs with
the clustering around a population of radio-quiet galaxies with similar masses,
colors and luminosities. Our catalog contains 2178 elliptical radio galaxies
with flux densities greater than 2.8 mJy at 1.4 GHz from the 6dFGS survey. We
find that radio AGNs with more than 200 times the median radio power have, on
average, more close (r<160 kpc) companions than their radio-quiet counterparts,
suggestive that mergers play a role in forming the most powerful radio
galaxies. For ellipticals of fixed stellar mass, the radio power is not a
function of large-scale environment nor halo mass, consistent with the radio
powers of ellipticals varying by orders of magnitude over billions of years.Comment: 12 pages, 6 figure
Halo detection via large-scale Bayesian inference
We present a proof-of-concept of a novel and fully Bayesian methodology
designed to detect halos of different masses in cosmological observations
subject to noise and systematic uncertainties. Our methodology combines the
previously published Bayesian large-scale structure inference algorithm, HADES,
and a Bayesian chain rule (the Blackwell-Rao Estimator), which we use to
connect the inferred density field to the properties of dark matter halos. To
demonstrate the capability of our approach we construct a realistic galaxy mock
catalogue emulating the wide-area 6-degree Field Galaxy Survey, which has a
median redshift of approximately 0.05. Application of HADES to the catalogue
provides us with accurately inferred three-dimensional density fields and
corresponding quantification of uncertainties inherent to any cosmological
observation. We then use a cosmological simulation to relate the amplitude of
the density field to the probability of detecting a halo with mass above a
specified threshold. With this information we can sum over the HADES density
field realisations to construct maps of detection probabilities and demonstrate
the validity of this approach within our mock scenario. We find that the
probability of successful of detection of halos in the mock catalogue increases
as a function of the signal-to-noise of the local galaxy observations. Our
proposed methodology can easily be extended to account for more complex
scientific questions and is a promising novel tool to analyse the cosmic
large-scale structure in observations.Comment: 17 pages, 13 figures. Accepted for publication in MNRAS following
moderate correction
The 6dF Galaxy Survey: Dependence of halo occupation on stellar mass
In this paper we study the stellar-mass dependence of galaxy clustering in
the 6dF Galaxy Survey. The near-infrared selection of 6dFGS allows more
reliable stellar mass estimates compared to optical bands used in other galaxy
surveys. Using the Halo Occupation Distribution (HOD) model, we investigate the
trend of dark matter halo mass and satellite fraction with stellar mass by
measuring the projected correlation function, . We find that the
typical halo mass () as well as the satellite power law index ()
increase with stellar mass. This indicates, (1) that galaxies with higher
stellar mass sit in more massive dark matter halos and (2) that these more
massive dark matter halos accumulate satellites faster with growing mass
compared to halos occupied by low stellar mass galaxies. Furthermore we find a
relation between and the minimum dark matter halo mass () of
, in agreement with similar findings for SDSS
galaxies. The satellite fraction of 6dFGS galaxies declines with increasing
stellar mass from 21% at
to 12% at indicating that
high stellar mass galaxies are more likely to be central galaxies. We compare
our results to two different semi-analytic models derived from the Millennium
Simulation, finding some disagreement. Our results can be used for placing new
constraints on semi-analytic models in the future, particularly the behaviour
of luminous red satellites. Finally we compare our results to studies of halo
occupation using galaxy-galaxy weak lensing. We find good overall agreement,
representing a valuable crosscheck for these two different tools of studying
the matter distribution in the Universe.Comment: 17 pages, 11 figures. arXiv admin note: text overlap with
arXiv:1104.2447 by other author
Second Data Release of the 6dF Galaxy Survey
The 6dF Galaxy Survey is measuring around 150000 redshifts and 15000 peculiar
velocities from galaxies over the southern sky at |b|>10 degrees. When
complete, it will be the largest survey of its kind by more than an order of
magnitude. Here we describe the characteristics of the Second Incremental Data
Release (DR2) and provide an update of the survey. This follows earlier data
made public in December 2002 and March 2004. A total of 83014 sources now have
their spectra, redshifts, near-infrared and optical photometry available online
and searchable through an SQL database at http://www-wfau.roe.ac.uk/6dFGS/.Comment: 11 pages, 7 figures. Submitted to PASA. High resolution versions of
the figures can be obtained from
http://www.aao.gov.au/local/www/6df/Publication
The Southern 2MASS AGN Survey: spectroscopic follow-up with 6dF
The Two Micron All-Sky Survey (2MASS) has provided a uniform photometric
catalog to search for previously unknown red AGN and QSOs. We have extended the
search to the southern equatorial sky by obtaining spectra for 1182 AGN
candidates using the 6dF multifibre spectrograph on the UK Schmidt Telescope.
These were scheduled as auxiliary targets for the 6dF Galaxy Redshift Survey.
The candidates were selected using a single color cut of J - Ks > 2 to Ks ~
15.5 and a galactic latitude of |b|>30 deg. 432 spectra were of sufficient
quality to enable a reliable classification. 116 sources (or ~27%) were
securely classified as type 1 AGN, 20 as probable type 1s, and 57 as probable
type 2 AGN. Most of them span the redshift range 0.05<z<0.5 and only 8 (or ~6%)
were previously identified as AGN or QSOs. Our selection leads to a
significantly higher AGN identification rate amongst local galaxies (>20%) than
in any previous galaxy survey. A small fraction of the type 1 AGN could have
their optical colors reddened by optically thin dust with A_V<2 mag relative to
optically selected QSOs. A handful show evidence for excess far-IR emission.
The equivalent width (EW) and color distributions of the type 1 and 2 AGN are
consistent with AGN unified models. In particular, the EW of the [OIII]
emission line weakly correlates with optical--near-IR color in each class of
AGN, suggesting anisotropic obscuration of the AGN continuum. Overall, the
optical properties of the 2MASS red AGN are not dramatically different from
those of optically-selected QSOs. Our near-IR selection appears to detect the
most near-IR luminous QSOs in the local universe to z~0.6 and provides
incentive to extend the search to deeper near-IR surveys.Comment: 57 pages, 12 figures, 4 tables, to appear in vol.27/4 of Publications
of the Astronomical Society of Australia (PASA
Near-ultraviolet signatures of environment-driven galaxy quenching in Sloan Digital Sky Survey groups
© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. We have investigated the effect of group environment on residual star formation in galaxies, using Galaxy Evolution Explorer near-ultraviolet (NUV) galaxy photometry with the Sloan Digital Sky Survey group catalogue of Yang et al. We compared the (NUV - r) colours of grouped and non-grouped galaxies, and find a significant increase in the fraction of red sequence galaxies with blue (NUV - r) colours outside of groups. When comparing galaxies in mass-matched samples of satellite (non-central), and non-grouped galaxies, we found a > 4Ï difference in the distribution of (NUV - r) colours, and an (NUV - r) blue fraction > 3Ï higher outside groups. A comparison of satellite and non-grouped samples has found the NUV fraction is a factor of ~2 lower for satellite galaxies between 10 10.5 and 10 10.7 M â , showing that higher mass galaxies are more likely to have residual star formation when not influenced by a group potential. There was a higher (NUV - r) blue fraction of galaxies with lower SĂ©rsic indices (n < 3) outside of groups, not seen in the satellite sample. We have used stellar population models of Bruzual & Charlot with multiple burst, or exponentially declining star formation histories to find that many of the (NUV - r) blue non-grouped galaxies can be explained by a slow (~2 Gyr) decay of star formation, compared to the satellite galaxies. We suggest that taken together, the difference in (NUV - r) colours between samples can be explained by a population of secularly evolving, non-grouped galaxies, where star formation declines slowly. This slow channel is less prevalent in group environments where more rapid quenching can occur
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