75 research outputs found
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
Quenching or Bursting: Star Formation Acceleration--A New Methodology for Tracing Galaxy Evolution
We introduce a new methodology for the direct extraction of galaxy physical
parameters from multi-wavelength photometry and spectroscopy. We use
semi-analytic models that describe galaxy evolution in the context of large
scale cosmological simulation to provide a catalog of galaxies, star formation
histories, and physical parameters. We then apply stellar population synthesis
models and a simple extinction model to calculate the observable broad-band
fluxes and spectral indices for these galaxies. We use a linear regression
analysis to relate physical parameters to observed colors and spectral indices.
The result is a set of coefficients that can be used to translate observed
colors and indices into stellar mass, star formation rate, and many other
parameters, including the instantaneous time derivative of the star formation
rate which we denote the {\it Star Formation Acceleration (SFA)}, We apply the
method to a test sample of galaxies with GALEX photometry and SDSS
spectroscopy, deriving relationships between stellar mass, specific star
formation rate, and star formation acceleration. We find evidence for a
mass-dependent SFA in the green valley, with low mass galaxies showing greater
quenching and higher mass galaxies greater bursting. We also find evidence for
an increase in average quenching in galaxies hosting AGN. A simple scenario in
which lower mass galaxies accrete and become satellite galaxies, having their
star forming gas tidally and/or ram-pressure stripped, while higher mass
galaxies receive this gas and react with new star formation can qualitatively
explain our results.Comment: 33 pages, 31 figures, ApJ accepte
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
Identification of postcranial elements of Gerbillinae (Mammalia: Rodentia) in pellet contents, with special reference to the species Meriones zarudnyi
Birds of prey feed mainly on small vertebrates and regurgitate indigestible remains, such as hair and bones of their prey, as pellet. Hence, the analysis of pellets provides valuable information on the distribution of the prey species. In this paper, we used elements of the postcranial skeleton for the identification of gerbilline rodents in pellets of birds of prey in Iran for the first time. These pellets were collected during several field campaigns in 11 regions of North, Razavi, and South Khorasan provinces (Iran), and supplemented with museum data from 13 regions in Razavi Khorasan, Golestan, and Chaharmahal and Bakhtiari provinces (Iran). A total of 320 rodent individuals from 102 different pellets were identified, of which 44 (13%) rodent specimens belong to Gerbillinae. The gerbilline species Meriones crassus, M. zarudnyi and Tatera indica were recognized based on diagnostic traits of their postcranium. Identification based on postcranial traits was confirmed by skull and tooth identifications. Using pellet remains, the record of Zarudny's jird (M. zarudnyi) expanded the distribution range of the species. We also provided some notes on the shape and size of the pellets of birds of prey. Further studies are necessary to evaluate the role of postcranial elements in identification of rodents
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
Spectroscopic study of star-forming galaxies in filaments and the field at 0.5:evidence for environmental dependence of electron density
We study the physical properties of a spectroscopic sample of 28 star-forming galaxies in a large filamentary structure in the COSMOS field at 0.53, with spectroscopic data taken with the Keck/DEIMOS spectrograph, and compare them with a control sample of 30 field galaxies. We spectroscopically confirm the presence of a large galaxy filament ( 8 Mpc), along which five confirmed X-ray groups exist. We show that within the uncertainties, the ionization parameter, equivalent width (EW), EW versus specific star-formation rate (sSFR) relation, EW versus stellar mass relation, line-of-sight velocity dispersion, dynamical mass, and stellar-to-dynamical mass ratio are similar for filament and field star-forming galaxies. However, we show that on average, filament star-forming galaxies are more metal-enriched ( 0.10.15 dex), possibly due to the inflow of the already enriched intrafilamentary gas into filament galaxies. Moreover, we show that electron densities are significantly lower (a factor of 17) in filament star-forming systems compared to those in the field, possibly because of a longer star-formation timescale for filament star-forming galaxies. Our results highlight the potential pre-processing role of galaxy filaments and intermediate-density environments on the evolution of galaxies, which has been highly underestimated
Similar Scaling Relations for the Gas Content of Galaxies Across Environments to z ~ 3.5
We study the effects of the local environment on the molecular gas content of a large sample of log(M*/M⊙) ≳ 10 star-forming and starburst galaxies with specific star formation rates (sSFRs) on and above the main sequence (MS) to z ~ 3.5. ALMA observations of the dust continuum in the COSMOS field are used to estimate molecular gas masses at z ≈ 0.5–3.5. We also use a local universe sample from the ALFALFA H I survey after converting it into molecular masses. The molecular mass (M_(ISM)) scaling relation shows a dependence on z, M *, and sSFR relative to the MS, but no dependence on environmental overdensity Δ(M_(ISM) ∝ Δ^(0.03)). Similarly, gas mass fraction (f_(gas)) and depletion timescale (τ) show no environmental dependence to z ~ 3.5. At〈z〉~ 1.8, the average〈M_(ISM) 〉,〈f_(gas) 〉, and〈τ〉in densest regions is (1.6 ± 0.2) × 10^(11) M⊙, 55 ± 2%, and 0.8 ± 0.1 Gyr, respectively, similar to those in the lowest density bin. Independent of the environment, f_(gas) decreases and τincreases with increasing cosmic time. Cosmic molecular mass density (ρ) in the lowest density bins peaks at z ~ 1–2, and this peak happens at z < 1 in densest bins. This differential evolution of ρ across environments is likely due to the growth of the large-scale structure with cosmic time. Our results suggest that the molecular gas content and the subsequent star formation activity of log(M*/M⊙) ≳ 10 star-forming and starburst galaxies is primarily driven by internal processes, and not by their local environment since z ~ 3.5
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