891 research outputs found
A large narrow band H survey at : the bright end of the luminosity function, cosmic variance and clustering across cosmic time
We carried out the largest ( Mpc, 26 deg) H
narrow band survey to date at in the SA22, W2 and XMMLSS
extragalactic fields. Our survey covers a large enough volume to overcome
cosmic variance and to sample bright and rare H emitters up to an
observed luminosity of erg s, equivalent to yr. Using our sample of sources brighter than
erg s ( yr), we derive H
luminosity functions, which are well described by a Schechter function with
Mpc and
erg s (with a fixed faint end slope ). We find that
surveys probing smaller volumes ( Mpc) are heavily
affected by cosmic variance, which can lead to errors of over per cent in
the characteristic density and luminosity of the H luminosity function.
We derive a star formation rate density of yr, in agreement with the redshift-dependent
H parametrisation from Sobral et al. (2013). The two-point correlation
function is described by a single power law , corresponding to a clustering length of Mpc/h. We find that the most luminous H emitters at
are more strongly clustered than the relatively fainter ones. The
H emitters at in our sample reside in
dark matter haloes. This implies that the most
star forming galaxies always reside in relatively massive haloes or group-like
environments and that the typical host halo mass of star-forming galaxies is
independent of redshift if scaled by , as
proposed by Sobral et al. (2010).Comment: Accepted for publication in MNRAS; 18 pages, 19 figures, 6 table
A Comparative Study of Density Field Estimation for Galaxies: New Insights into the Evolution of Galaxies with Environment in COSMOS out to z~3
It is well-known that galaxy environment has a fundamental effect in shaping
its properties. We study the environmental effects on galaxy evolution, with an
emphasis on the environment defined as the local number density of galaxies.
The density field is estimated with different estimators (weighted adaptive
kernel smoothing, 10 and 5 nearest neighbors, Voronoi and
Delaunay tessellation) for a K24 sample of 190,000 galaxies in the
COSMOS field at 0.1z3.1. The performance of each estimator is evaluated
with extensive simulations. We show that overall, there is a good agreement
between the estimated density fields using different methods over 2 dex
in overdensity values. However, our simulations show that adaptive kernel and
Voronoi tessellation outperform other methods. Using the Voronoi tessellation
method, we assign surface densities to a mass complete sample of quiescent and
star-forming galaxies out to z3. We show that at a fixed stellar mass,
the median color of quiescent galaxies does not depend on their host
environment out to z3. We find that the number and stellar mass density
of massive (10M) star-forming galaxies have not
significantly changed since z3, regardless of their environment. However,
for massive quiescent systems at lower redshifts (z1.3), we find a
significant evolution in the number and stellar mass densities in denser
environments compared to lower density regions. Our results suggest that the
relation between stellar mass and local density is more fundamental than the
color-density relation and that environment plays a significant role in
quenching star formation activity in galaxies at z1.Comment: 20 pages, 11 figures, main figures 4,5,8 and 1
Identification of the brightest Ly\alpha\ emitters at z=6.6: implications for the evolution of the luminosity function in the re-ionisation era
Using wide field narrow-band surveys, we provide a new measurement of the
Lyman- Emitter (LAE) luminosity function (LF), which
constraints the bright end for the first time. We use a combination of archival
narrow-band NB921 data in UDS and new NB921 measurements in SA22 and
COSMOS/UltraVISTA, all observed with the Subaru telescope, with a total area of
deg. We exclude lower redshift interlopers by using broad-band
optical and near-infrared photometry and also exclude three supernovae with
data split over multiple epochs. Combining the UDS and COSMOS samples we find
no evolution of the bright end of the Ly LF between and ,
which is supported by spectroscopic follow-up, and conclude that sources with
\emph{Himiko}-like luminosity are not as rare as previously thought, with
number densities of Mpc. Combined with our
wide-field SA22 measurements, our results indicate a non-Schechter-like bright
end of the LF at and a different evolution of \emph{observed} faint and
bright LAEs. This differential evolution is also seen in the spectroscopic
follow-up of UV selected galaxies and is now also confirmed for Ly
emitters, and we argue that it may be an effect of re-ionisation. Using a
toy-model, we show that such differential evolution of the LF is expected,
since brighter sources are able to ionise their surroundings earlier, such that
Ly photons are able to escape. Our targets are excellent candidates for
detailed follow-up studies and provide the possibility to give a unique view on
the earliest stages in the formation of galaxies and re-ionisation process.Comment: 20 pages, main results shown in Fig. 6 and Fig. 7, accepted by MNRA
Neutral hydrogen gas, past and future star-formation in galaxies in and around the 'Sausage' merging galaxy cluster
CIZA J2242.8+5301 (, nicknamed 'Sausage') is an extremely massive
( ), merging cluster with shock waves
towards its outskirts, which was found to host numerous emission-line galaxies.
We performed extremely deep Westerbork Synthesis Radio Telescope HI
observations of the 'Sausage' cluster to investigate the effect of the merger
and the shocks on the gas reservoirs fuelling present and future star formation
(SF) in cluster members. By using spectral stacking, we find that the
emission-line galaxies in the 'Sausage' cluster have, on average, as much HI
gas as field galaxies (when accounting for the fact cluster galaxies are more
massive than the field galaxies), contrary to previous studies. Since the
cluster galaxies are more massive than the field spirals, they may have been
able to retain their gas during the cluster merger. The large HI reservoirs are
expected to be consumed within Gyr by the vigorous SF and AGN
activity and/or driven out by the out-flows we observe. We find that the
star-formation rate in a large fraction of H emission-line cluster
galaxies correlates well with the radio broad band emission, tracing supernova
remnant emission. This suggests that the cluster galaxies, all located in
post-shock regions, may have been undergoing sustained SFR for at least 100
Myr. This fully supports the interpretation proposed by Stroe et al. (2015) and
Sobral et al. (2015) that gas-rich cluster galaxies have been triggered to form
stars by the passage of the shock.Comment: Accepted to MNRAS, 14 pages, 9 figures, 7 table
VIS³COS. III. Environmental effects on the star formation histories of galaxies at z ∼ 0.8 seen in [O II], Hδ, and D_n4000
We present spectroscopic observations of 466 galaxies in and around a superstructure at z ∼ 0.84 targeted by the VIMOS Spectroscopic Survey of a Supercluster in the COSMOS field (VIS³COS). We use [OII]λ3727, Hδ, and D_n4000 to trace recent, medium-, and long-term star formation histories and investigate the effect of stellar mass and local environment on them. By studying trends in individual and composite galaxy spectra, we find that stellar mass and environment play a role in the observed galactic properties. Galaxies with low stellar mass (10 11) shows an increase in Hδ absorption strengths in intermediate-density environments (e.g. filaments). Galaxies with intermediate stellar mass (10.5 < log₁₀ (M⋆/M⊙) < 11) have similar Hδ absorption profiles in all environments, but show an indication of enhanced [OII] emission in intermediate-density environments. This indicates that field galaxies with low stellar mass and filament galaxies with high stellar mass are more likely to have experienced a recent burst of star formation, while galaxies of the intermediate stellar-mass show an increase of star formation at filament-like densities. We also find that the median [OII] equivalent width (|EW_([OII])|) decreases from 27 ± 2 Å to 2.0^(+0.5)_(−0.4) Å and D_n4000 increases from 1.09 ± 0.01 to 1.56 ± 0.03 with increasing stellar mass (from ∼10^(9.25) to ∼10^(11.35) M⊙). For the dependence on the environment, we find that at fixed stellar mass, |EW_([OII])| is tentatively lower in environments with higher density. We find for D_n4000 that the increase with stellar mass is sharper in denser environments, which indicates that these environments may accelerate galaxy evolution. Moreover, we find higher D_n4000 values in denser environments at fixed stellar mass, suggesting that galaxies are on average older and/or more metal rich in these dense environments. This set of tracers depicts a scenario where the most massive galaxies have, on average, the lowest specific star formation rates and the oldest stellar populations (age ≳ 1 Gyr, showing a mass-downsizing effect). We also hypothesize that the observed increase in star formation (higher EW_([OII]|), higher specific star formation rate) at intermediate densities may lead to quenching because we find that the quenched fraction increases sharply from the filament to cluster-like regions at similar stellar masses
The rise and fall of star-formation in merging galaxy clusters
CIZA J2242.8+5301 (`Sausage') and 1RXS J0603.3+4213 (`Toothbrush') are two
low-redshift (), massive (), post-core
passage merging clusters, which host shock waves traced by diffuse radio
emission. To study their star-formation properties, we uniformly survey the
`Sausage' and `Toothbrush' clusters in broad and narrow band filters and select
a sample of and line emitters, down to a rest-frame equivalent
width ({\AA}). We robustly separate between H and higher redshift
emitters using a combination of optical multi-band (B, g, V, r, i, z) and
spectroscopic data. We build H luminosity functions for the entire
cluster region, near the shock fronts, and away from the shock fronts and find
striking differences between the two clusters. In the dynamically younger,
Gyr old `Sausage' cluster we find numerous () H emitters above a
star-formation rate (SFR) of M_{\sun} yr surprisingly located
in close proximity to the shock fronts, embedded in very hot intra-cluster
medium plasma. The SFR density for the cluster population is at least at the
level of typical galaxies at . Down to the same star-formation rate,
the possibly dynamically more evolved `Toothbrush' cluster has only
H galaxies. The cluster H galaxies fall on the SFR-stellar mass
relation for the field. However, the `Sausage' cluster has an
H emitter density times that of blank fields. If the shock passes
through gas-rich cluster galaxies, the compressed gas could collapse into dense
clouds and excite star-formation for a few Myr. This process ultimately
leads to a rapid consumption of the molecular gas, accelerating the
transformation of gas-rich field spirals into cluster S0s or ellipticals.Comment: Accepted for publication in MNRAS after minor referee report. 21
pages, 15 figures, 5 table
The structural and size evolution of star-forming galaxies over the last 11 Gyrs
We present new results on the evolution of rest-frame blue/UV sizes and Sersic indices of H-selected star-forming galaxies over the last 11 Gyrs. We investigate how the perceived evolution can be affected by a range of biases and systematics such as cosmological dimming and resolution effects. We use GALFIT and an artificial redshifting technique, which includes the luminosity evolution of H-selected galaxies, to quantify the change on the measured structural parameters with redshift. We find typical sizes of 2 to 3 kpc and Sersic indices of n~1.2, close to pure exponential disks all the way from z=2.23 to z=0.4. At z=0 we find typical sizes of 4-5 kpc. Our results show that, when using GALFIT, cosmological dimming has a negligible impact on the derived effective radius for galaxies with
The HiZELS/UKIRT large area survey for bright Lyman-alpha emitters at z~9
We present the largest area survey to date (1.4 deg2) for Lyman-alpha
emitters (LAEs) at z~9, as part of the Hi-z Emission Line Survey (HiZELS). The
survey, which primarily targets H-alpha emitters at z < 3, uses the Wide Field
CAMera on the United Kingdom Infrared Telescope and a custom narrow-band filter
in the J band to reach a Lyman-alpha luminosity limit of ~10^43.8 erg/s over a
co-moving volume of 1.12x10^6 Mpc^3 at z = 8.96+-0.06. Two candidates were
found out of 1517 line emitters, but those were rejected as LAEs after
follow-up observations. This improves the limit on the space density of bright
Lyman-alpha emitters by 3 orders of magnitude and is consistent with
suppression of the bright end of the Lyman-alpha luminosity function beyond
z~6. Combined with upper limits from smaller but deeper surveys, this rules out
some of the most extreme models for high-redshift Lyman-alpha emitters. The
potential contamination of narrow-band Lyman-alpha surveys at z>7 by Galactic
brown dwarf stars is also examined, leading to the conclusion that such
contamination may well be significant for searches at 7.7 < z < 8.0, 9.1 < z <
9.5 and 11.7 < z < 12.2.Comment: To appear in proceedings of "UKIRT at 30: A British Success Story
HiZELS: the High Redshift Emission Line Survey with UKIRT
In these proceedings we report on HiZELS, the High-z Emission Line Survey,
our successful panoramic narrow-band Campaign Survey using WFCAM on UKIRT to
detect and study emission line galaxies at z~1-9. HiZELS employs the H2(S1)
narrow-band filter together with custom-made narrow-band filters in the J and
H-bands, with the primary aim of delivering large, identically-selected samples
of H-alpha emitting galaxies at redshifts of 0.84, 1.47 and 2.23. Comparisons
between the luminosity function, the host galaxy properties, the clustering,
and the variation with environment of these H-alpha-selected samples are
yielding unique constraints on the nature and evolution of star-forming
galaxies, across the peak epoch of star-formation activity in the Universe. We
provide a summary of the project status, and detail the main scientific results
obtained so far: the measurement of the evolution of the cosmic star-formation
rate density out to z > 2 using a single star-formation indicator,
determination of the morphologies, environments and dust-content of the
star-forming galaxies, and a detailed investigation of the evolution of their
clustering properties. We also summarise the on-going work and future goals of
the project.Comment: To appear in proceedings of "UKIRT at 30: A British Success Story"
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