Abstract
Does the environment of a galaxy directly influence the quenching history of a galaxy? Here, we investigate the detailed morphological structures and star formation histories of a sample of ...SDSS group galaxies with both classifications from Galaxy Zoo 2 and near ultra-violet (NUV) detections in GALEX. We use the optical and NUV colours to infer the quenching time and rate describing a simple exponentially declining star formation history for each galaxy, along with a control sample of field galaxies. We find that the time since quenching and the rate of quenching do not correlate with the relative velocity of a satellite but are correlated with the group potential. This quenching occurs within an average quenching time-scale of ∼ 2.5 Gyr from star forming to complete quiescence, during an average infall time (from ∼10R
200 to 0.01R
200) of ∼ 2.6 Gyr. Our results suggest that the environment does play a direct role in galaxy quenching through quenching mechanisms that are correlated with the group potential, such as harassment, interactions or starvation. Environmental quenching mechanisms that are correlated with satellite velocity, such as ram-pressure stripping, are not the main cause of quenching in the group environment. We find that no single mechanism dominates over another, except in the most extreme environments or masses. Instead, an interplay of mergers, mass and morphological quenching and environment-driven quenching mechanisms dependent on the group potential drive galaxy evolution in groups.
We present photometric redshift estimates for galaxies used in the weak lensing analysis of the Dark Energy Survey Science Verification (DES SV) data. Four model- or machine learning-based ...photometric redshift methods-annz2, bpz calibrated against BCC-Ufig simulations, skynet, and tpz-are analyzed. For training, calibration, and testing of these methods, we construct a catalogue of spectroscopically confirmed galaxies matched against DES SV data. The performance of the methods is evaluated against the matched spectroscopic catalogue, focusing on metrics relevant for weak lensing analyses, with additional validation against COSMOS photo-z's. From the galaxies in the DES SV shear catalogue, which have mean redshift 0.72 + or - 0.01 over the range 0.3 < z< 1.3, we construct three tomographic bins with means of z= {0.45,0.67,1.00}. These bins each have systematic uncertainties delta sub(z)<, ~ 0.05 in the mean of the fiducial skynet photo-z n(z). We propagate the errors in the redshift distributions through to their impact on cosmological parameters estimated with cosmic shear, and find that they cause shifts in the value of sigma sub(8) of approximately 3%. This shift is within the one sigma statistical errors on sigma sub(8) for the DES SV shear catalogue. We further study the potential impact of systematic differences on the critical surface density, capital sigma sub(crit), finding levels of bias safely less than the statistical power of DES SV data. We recommend a final Gaussian prior for the photo-z bias in the mean of n(z) of width 0.05 for each of the three tomographic bins, and show that this is a sufficient bias model for the corresponding cosmology analysis.
The Galaxy And Mass Assembly (GAMA) survey is one of the largest contemporary spectroscopic surveys of low redshift galaxies. Covering an area of ∼286 deg2 (split among five survey regions) down to a ...limiting magnitude of r < 19.8 mag, we have collected spectra and reliable redshifts for 238 000 objects using the AAOmega spectrograph on the Anglo-Australian Telescope. In addition, we have assembled imaging data from a number of independent surveys in order to generate photometry spanning the wavelength range 1 nm–1 m. Here, we report on the recently completed spectroscopic survey and present a series of diagnostics to assess its final state and the quality of the redshift data. We also describe a number of survey aspects and procedures, or updates thereof, including changes to the input catalogue, redshifting and re-redshifting, and the derivation of ultraviolet, optical and near-infrared photometry. Finally, we present the second public release of GAMA data. In this release, we provide input catalogue and targeting information, spectra, redshifts, ultraviolet, optical and near-infrared photometry, single-component Sérsic fits, stellar masses, Hα-derived star formation rates, environment information, and group properties for all galaxies with r < 19.0 mag in two of our survey regions, and for all galaxies with r < 19.4 mag in a third region (72 225 objects in total). The data base serving these data is available at http://www.gama-survey.org/.
Abstract
We measure a value for the cosmic expansion of H(z) = 89 ± 23(stat) ± 44(syst) km s−1 Mpc−1 at a redshift of z ≃ 0.47 based on the differential age technique. This technique, also known as ...cosmic chronometers, uses the age difference between two redshifts for a passively evolving population of galaxies to calculate the expansion rate of the Universe. Our measurement is based on the analysis of high-quality spectra of luminous red galaxies obtained with the Southern African Large Telescope in two narrow redshift ranges of z ≃ 0.40 and 0.55 as part of an initial pilot study. Ages were estimated by fitting single stellar population models to the observed spectra. This measurement presents one of the best estimates of H(z) via this method at z ∼ 0.5 to date.
Context. In the last decade, astronomers have found a new type of supernova called superluminous supernovae (SLSNe) due to their high peak luminosity and long light-curves. These hydrogen-free ...explosions (SLSNe-I) can be seen to z ~ 4 and therefore, offer the possibility of probing the distant Universe. Aims. We aim to investigate the possibility of detecting SLSNe-I using ESA’s Euclid satellite, scheduled for launch in 2020. In particular, we study the Euclid Deep Survey (EDS) which will provide a unique combination of area, depth and cadence over the mission. Methods. We estimated the redshift distribution of Euclid SLSNe-I using the latest information on their rates and spectral energy distribution, as well as known Euclid instrument and survey parameters, including the cadence and depth of the EDS. To estimate the uncertainties, we calculated their distribution with two different set-ups, namely optimistic and pessimistic, adopting different star formation densities and rates. We also applied a standardization method to the peak magnitudes to create a simulated Hubble diagram to explore possible cosmological constraints. Results. We show that Euclid should detect approximately 140 high-quality SLSNe-I to z ~ 3.5 over the first five years of the mission (with an additional 70 if we lower our photometric classification criteria). This sample could revolutionize the study of SLSNe-I at z > 1 and open up their use as probes of star-formation rates, galaxy populations, the interstellar and intergalactic medium. In addition, a sample of such SLSNe-I could improve constraints on a time-dependent dark energy equation-of-state, namely w(a), when combined with local SLSNe-I and the expected SN Ia sample from the Dark Energy Survey. Conclusions. We show that Euclid will observe hundreds of SLSNe-I for free. These luminous transients will be in the Euclid data-stream and we should prepare now to identify them as they offer a new probe of the high-redshift Universe for both astrophysics and cosmology.
We measure the cross-correlation between weak lensing of galaxy images and of the cosmic microwave background (CMB). The effects of gravitational lensing on different sources will be correlated if ...the lensing is caused by the same mass fluctuations. We use galaxy shape measurements from 139 deg2 of the Dark Energy Survey (DES) Science Verification data and overlapping CMB lensing from the South Pole Telescope (SPT) and Planck. The DES source galaxies have a median redshift of z
med ∼ 0.7, while the CMB lensing kernel is broad and peaks at z ∼ 2. The resulting cross-correlation is maximally sensitive to mass fluctuations at z ∼ 0.44. Assuming the Planck 2015 best-fitting cosmology, the amplitude of the DES×SPT cross-power is found to be A
SPT = 0.88 ± 0.30 and that from DES×Planck to be APlanck
= 0.86 ± 0.39, where A = 1 corresponds to the theoretical prediction. These are consistent with the expected signal and correspond to significances of 2.9σ and 2.2σ, respectively. We demonstrate that our results are robust to a number of important systematic effects including the shear measurement method, estimator choice, photo-z uncertainty and CMB lensing systematics. We calculate a value of A = 1.08 ± 0.36 for DES×SPT when we correct the observations with a simple intrinsic alignment model. With three measurements of this cross-correlation now existing in the literature, there is not yet reliable evidence for any deviation from the expected LCDM level of cross-correlation. We provide forecasts for the expected signal-to-noise ratio of the combination of the five-year DES survey and SPT-3G.
Abstract
Type Ia supernovae (SNe Ia) are more precise standardizable candles when measured in the near-infrared (NIR) than in the optical. With this motivation, from 2012 to 2017 we embarked on the ...RAISIN program with the Hubble Space Telescope (HST) to obtain rest-frame NIR light curves for a cosmologically distant sample of 37 SNe Ia (0.2 ≲
z
≲ 0.6) discovered by Pan-STARRS and the Dark Energy Survey. By comparing higher-
z
HST data with 42 SNe Ia at
z
< 0.1 observed in the NIR by the Carnegie Supernova Project, we construct a Hubble diagram from NIR observations (with only time of maximum light and some selection cuts from optical photometry) to pursue a unique avenue to constrain the dark energy equation-of-state parameter,
w
. We analyze the dependence of the full set of Hubble residuals on the SN Ia host galaxy mass and find Hubble residual steps of size ∼0.06-0.1 mag with 1.5
σ
−2.5
σ
significance depending on the method and step location used. Combining our NIR sample with cosmic microwave background constraints, we find 1 +
w
= −0.17 ± 0.12 (statistical + systematic errors). The largest systematic errors are the redshift-dependent SN selection biases and the properties of the NIR mass step. We also use these data to measure
H
0
= 75.9 ± 2.2 km s
−1
Mpc
−1
from stars with geometric distance calibration in the hosts of eight SNe Ia observed in the NIR versus
H
0
= 71.2 ± 3.8 km s
−1
Mpc
−1
using an inverse distance ladder approach tied to Planck. Using optical data, we find 1 +
w
= −0.10 ± 0.09, and with optical and NIR data combined, we find 1 +
w
= −0.06 ± 0.07; these shifts of up to ∼0.11 in
w
could point to inconsistency in the optical versus NIR SN models. There will be many opportunities to improve this NIR measurement and better understand systematic uncertainties through larger low-
z
samples, new light-curve models, calibration improvements, and eventually by building high-
z
samples from the Roman Space Telescope.
We describe the spectroscopic target selection for the Galaxy And Mass Assembly (GAMA) survey. The input catalogue is drawn from the Sloan Digital Sky Survey (SDSS) and UKIRT Infrared Deep Sky Survey ...(UKIDSS). The initial aim is to measure redshifts for galaxies in three 4°× 12° regions at 9, 12 and 14.5 h, on the celestial equator, with magnitude selections r < 19.4, z < 18.2 and KAB < 17.6 over all three regions, and r < 19.8 in the 12-h region. The target density is 1080 deg−2 in the 12-h region and 720 deg−2 in the other regions. The average GAMA target density and area are compared with completed and ongoing galaxy redshift surveys. The GAMA survey implements a highly complete star–galaxy separation that jointly uses an intensity-profile separator (Δsg=rpsf−rmodel as per the SDSS) and a colour separator. The colour separator is defined as Δsg,jk=J−K−f(g−i), where f(g−i) is a quadratic fit to the J−K colour of the stellar locus over the range 0.3 < g−i < 2.3. All galaxy populations investigated are well separated with Δsg,jk > 0.2. From 2 yr out of a 3-yr AAOmega program on the Anglo-Australian Telescope, we have obtained 79 599 unique galaxy redshifts. Previously known redshifts in the GAMA region bring the total up to 98 497. The median galaxy redshift is 0.2 with 99 per cent at z < 0.5. We present some of the global statistical properties of the survey, including K-band galaxy counts, colour–redshift relations and preliminary n(z).
We use 26×106 galaxies from the Dark Energy Survey (DES) Year 1 shape catalogs over 1321 deg2 of the sky to produce the most significant measurement of cosmic shear in a galaxy survey to date. We ...constrain cosmological parameters in both the flat ΛCDM and the wCDM models, while also varying the neutrino mass density. These results are shown to be robust using two independent shape catalogs, two independent photo-z calibration methods, and two independent analysis pipelines in a blind analysis. We find a 3.5% fractional uncertainty on σ8(Ωm/0.3)0.5=0.782−0.027+0.027 at 68% C.L., which is a factor of 2.5 improvement over the fractional constraining power of our DES Science Verification results. In wCDM, we find a 4.8% fractional uncertainty on σ8(Ωm/0.3)0.5=0.777−0.038+0.036 and a dark energy equation-of-state w=−0.95−0.39+0.33. We find results that are consistent with previous cosmic shear constraints in σ8-Ωm, and we see no evidence for disagreement of our weak lensing data with data from the cosmic microwave background. Finally, we find no evidence preferring a wCDM model allowing w≠−1. We expect further significant improvements with subsequent years of DES data, which will more than triple the sky coverage of our shape catalogs and double the effective integrated exposure time per galaxy.
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