ABSTRACT We present Magellan/M2FS, Very Large Telescope/GIRAFFE, and Gemini South/GMOS spectroscopy of the newly discovered Milky Way satellite Reticulum II. Based on the spectra of 25 Ret II member ...stars selected from Dark Energy Survey imaging, we measure a mean heliocentric velocity of and a velocity dispersion of . The mass-to-light ratio of Ret II within its half-light radius is , demonstrating that it is a strongly dark matter-dominated system. Despite its spatial proximity to the Magellanic Clouds, the radial velocity of Ret II differs from that of the LMC and SMC by 199 and 83 , respectively, suggesting that it is not gravitationally bound to the Magellanic system. The likely member stars of Ret II span 1.3 dex in metallicity, with a dispersion of 0.28 0.09 dex, and we identify several extremely metal-poor stars with . In combination with its luminosity, size, and ellipticity, these results confirm that Ret II is an ultra-faint dwarf galaxy. With a mean metallicity of , Ret II matches Segue 1 as the most metal-poor galaxy known. Although Ret II is the third-closest dwarf galaxy to the Milky Way, the line-of-sight integral of the dark matter density squared is within 0 2, indicating that the predicted gamma-ray flux from dark matter annihilation in Ret II is lower than that of several other dwarf galaxies.
Characterization of the redshift distribution of ensembles of galaxies is pivotal for large scale structure cosmological studies. In this work, we focus on improving the Self-Organizing Map (SOM) ...methodology for photometric redshift estimation (SOMPZ), specifically in anticipation of the Dark Energy Survey Year 6 (DES Y6) data. This data set, featuring deeper and fainter galaxies than DES Year 3 (DES Y3), demands adapted techniques to ensure accurate recovery of the underlying redshift distribution. We investigate three strategies for enhancing the existing SOM-based approach used in DES Y3: 1) Replacing the Y3 SOM algorithm with one tailored for redshift estimation challenges; 2) Incorporating \(\textit{g}\)-band flux information to refine redshift estimates (i.e. using \(\textit{griz}\) fluxes as opposed to only \(\textit{riz}\)); 3) Augmenting redshift data for galaxies where available. These methods are applied to DES Y3 data, and results are compared to the Y3 fiducial ones. Our analysis indicates significant improvements with the first two strategies, notably reducing the overlap between redshift bins. By combining strategies 1 and 2, we have successfully managed to reduce redshift bin overlap in DES Y3 by up to 66\(\%\). Conversely, the third strategy, involving the addition of redshift data for selected galaxies as an additional feature in the method, yields inferior results and is abandoned. Our findings contribute to the advancement of weak lensing redshift characterization and lay the groundwork for better redshift characterization in DES Year 6 and future stage IV surveys, like the Rubin Observatory.
We present a Bayesian population modeling method to analyze the abundance of galaxy clusters identified by the South Pole Telescope (SPT) with a simultaneous mass calibration using weak gravitational ...lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST). We discuss and validate the modeling choices with a particular focus on a robust, weak-lensing-based mass calibration using DES data. For the DES Year 3 data, we report a systematic uncertainty in weak-lensing mass calibration that increases from 1% at \(z=0.25\) to 10% at \(z=0.95\), to which we add 2% in quadrature to account for uncertainties in the impact of baryonic effects. We implement an analysis pipeline that joins the cluster abundance likelihood with a multi-observable likelihood for the Sunyaev-Zel'dovich effect, optical richness, and weak-lensing measurements for each individual cluster. We validate that our analysis pipeline can recover unbiased cosmological constraints by analyzing mocks that closely resemble the cluster sample extracted from the SPT-SZ, SPTpol ECS, and SPTpol 500d surveys and the DES Year 3 and HST-39 weak-lensing datasets. This work represents a crucial prerequisite for the subsequent cosmological analysis of the real dataset.
We present galaxy-galaxy lensing measurements using a sample of low surface brightness galaxies (LSBGs) drawn from the Dark Energy Survey Year 3 (Y3) data as lenses. LSBGs are diffuse galaxies with a ...surface brightness dimmer than the ambient night sky. These dark-matter-dominated objects are intriguing due to potentially unusual formation channels that lead to their diffuse stellar component. Given the faintness of LSBGs, using standard observational techniques to characterize their total masses proves challenging. Weak gravitational lensing, which is less sensitive to the stellar component of galaxies, could be a promising avenue to estimate the masses of LSBGs. Our LSBG sample consists of 23,790 galaxies separated into red and blue color types at \(g-i\ge 0.60\) and \(g-i< 0.60\), respectively. Combined with the DES Y3 shear catalog, we measure the tangential shear around these LSBGs and find signal-to-noise ratios of 6.67 for the red sample, 2.17 for the blue sample, and 5.30 for the full sample. We use the clustering redshifts method to obtain redshift distributions for the red and blue LSBG samples. Assuming all red LSBGs are satellites, we fit a simple model to the measurements and estimate the host halo mass of these LSBGs to be \(\log(M_{\rm host}/M_{\odot}) = 12.98 ^{+0.10}_{-0.11}\). We place a 95% upper bound on the subhalo mass at \(\log(M_{\rm sub}/M_{\odot})<11.51\). By contrast, we assume the blue LSBGs are centrals, and place a 95% upper bound on the halo mass at \(\log(M_\mathrm{host}/M_\odot) < 11.84\). We find that the stellar-to-halo mass ratio of the LSBG samples is consistent with that of the general galaxy population. This work illustrates the viability of using weak gravitational lensing to constrain the halo masses of LSBGs.
We present results for the first three years of OzDES, a six-year program to obtain redshifts for objects in the Dark Energy Survey (DES) supernova fields using the 2dF fibre positioner and AAOmega ...spectrograph on the Anglo-Australian Telescope. OzDES is a multi-object spectroscopic survey targeting multiple types of targets at multiple epochs over a multi-year baseline, and is one of the first multi-object spectroscopic surveys to dynamically include transients into the target list soon after their discovery. At the end of three years, OzDES has spectroscopically confirmed almost 100 supernovae, and has measured redshifts for 17,000 objects, including the redshifts of 2,566 supernova hosts. We examine how our ability to measure redshifts for targets of various types depends on signal-to-noise, magnitude, and exposure time, finding that our redshift success rate increases significantly at a signal-to-noise of 2 to 3 per 1-A° ngstrom bin. We also find that the change in signal-to-noise with exposure time closely matches the Poisson limit for stacked exposures as long as 10 hours.We use these results to predict the redshift yield of the full OzDES survey, as well as the potential yields of future surveys on other facilities such as 4MOST, PFS, and MSE. This work marks the first OzDES data release, comprising 15,327 redshifts. OzDES is on target to obtain over 30,000 redshifts over the six-year duration of the survey, including a yield of approximately 5,700 supernova host-galaxy redshifts.
We search for signatures of cosmological shocks in gas pressure profiles of galaxy clusters using the cluster catalogs from three surveys: the Dark Energy Survey (DES) Year 3, the South Pole ...Telescope (SPT) SZ survey, and the Atacama Cosmology Telescope (ACT) data releases 4, 5, and 6, and using thermal Sunyaev-Zeldovich (SZ) maps from SPT and ACT. The combined cluster sample contains around \(10^5\) clusters with mass and redshift ranges \(10^{13.7} < M_{\rm 200m}/M_\odot < 10^{15.5}\) and \(0.1 < z < 2\), and the total sky coverage of the maps is \(\approx 15,000 \,\,{\rm deg}^2\). We find a clear pressure deficit at \(R/R_{\rm 200m}\approx 1.1\) in SZ profiles around both ACT and SPT clusters, estimated at \(6\sigma\) significance, which is qualitatively consistent with a shock-induced thermal non-equilibrium between electrons and ions. The feature is not as clearly determined in profiles around DES clusters. We verify that measurements using SPT or ACT maps are consistent across all scales, including in the deficit feature. The SZ profiles of optically selected and SZ-selected clusters are also consistent for higher mass clusters. Those of less massive, optically selected clusters are suppressed on small scales by factors of 2-5 compared to predictions, and we discuss possible interpretations of this behavior. An oriented stacking of clusters -- where the orientation is inferred from the SZ image, the brightest cluster galaxy, or the surrounding large-scale structure measured using galaxy catalogs -- shows the normalization of the one-halo and two-halo terms vary with orientation. Finally, the location of the pressure deficit feature is statistically consistent with existing estimates of the splashback radius.
Abstract
We use a stacking method to study the radial light profiles of luminous red galaxies (LRGs) at redshift ∼0.62 and ∼0.25, out to a radial range of 200 kpc. We do not find noticeable evolution ...of the profiles at the two redshifts. The LRG profiles appear to be well approximated by a single Sérsic profile, although some excess light can be seen outside 60 kpc. We quantify the excess light by measuring the integrated flux and find that the excess is about 10%—a non-dominant but still nonnegligible component.
We present cosmological constraints from the abundance of galaxy clusters selected via the thermal Sunyaev-Zel'dovich (SZ) effect in South Pole Telescope (SPT) data with a simultaneous mass ...calibration using weak gravitational lensing data from the Dark Energy Survey (DES) and the Hubble Space Telescope (HST). The cluster sample is constructed from the combined SPT-SZ, SPTpol ECS, and SPTpol 500d surveys, and comprises 1,005 confirmed clusters in the redshift range \(0.25-1.78\) over a total sky area of 5,200 deg\(^2\). We use DES Year 3 weak-lensing data for 688 clusters with redshifts \(z<0.95\) and HST weak-lensing data for 39 clusters with \(0.6<z<1.7\). The weak-lensing measurements enable robust mass measurements of sample clusters and allow us to empirically constrain the SZ observable--mass relation. For a flat \(\Lambda\)CDM cosmology, and marginalizing over the sum of massive neutrinos, we measure \(\Omega_\mathrm{m}=0.286\pm0.032\), \(\sigma_8=0.817\pm0.026\), and the parameter combination \(\sigma_8\,(\Omega_\mathrm{m}/0.3)^{0.25}=0.805\pm0.016\). Our measurement of \(S_8\equiv\sigma_8\,\sqrt{\Omega_\mathrm{m}/0.3}=0.795\pm0.029\) and the constraint from Planck CMB anisotropies (2018 TT,TE,EE+lowE) differ by \(1.1\sigma\). In combination with that Planck dataset, we place a 95% upper limit on the sum of neutrino masses \(\sum m_\nu<0.18\) eV. When additionally allowing the dark energy equation of state parameter \(w\) to vary, we obtain \(w=-1.45\pm0.31\) from our cluster-based analysis. In combination with Planck data, we measure \(w=-1.34^{+0.22}_{-0.15}\), or a \(2.2\sigma\) difference with a cosmological constant. We use the cluster abundance to measure \(\sigma_8\) in five redshift bins between 0.25 and 1.8, and we find the results to be consistent with structure growth as predicted by the \(\Lambda\)CDM model fit to Planck primary CMB data.
Extracting precise cosmology from weak lensing surveys requires modelling the non-linear matter power spectrum, which is suppressed at small scales due to baryonic feedback processes. However, ...hydrodynamical galaxy formation simulations make widely varying predictions for the amplitude and extent of this effect. We use measurements of Dark Energy Survey Year 3 weak lensing (WL) and Atacama Cosmology Telescope DR5 kinematic Sunyaev-Zel'dovich (kSZ) to jointly constrain cosmological and astrophysical baryonic feedback parameters using a flexible analytical model, `baryonification'. First, using WL only, we compare the \(S_8\) constraints using baryonification to a simulation-calibrated halo model, a simulation-based emulator model and the approach of discarding WL measurements on small angular scales. We find that model flexibility can shift the value of \(S_8\) and degrade the uncertainty. The kSZ provides additional constraints on the astrophysical parameters and shifts \(S_8\) to \(S_8=0.823^{+0.019}_{-0.020}\), a higher value than attained using the WL-only analysis. We measure the suppression of the non-linear matter power spectrum using WL + kSZ and constrain a mean feedback scenario that is more extreme than the predictions from most hydrodynamical simulations. We constrain the baryon fractions and the gas mass fractions and find them to be generally lower than inferred from X-ray observations and simulation predictions. We conclude that the WL + kSZ measurements provide a new and complementary benchmark for building a coherent picture of the impact of gas around galaxies across observations.
PDF
