分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We apply the empirical galaxy--halo connection model UniverseMachine to dark matter-only zoom-in simulations of isolated Milky Way (MW)--mass halos along with their parent cosmological simulations. This application extends \textsc{UniverseMachine} predictions into the ultra-faint dwarf galaxy regime ( 10^{2}\,\mathrm{M_{\odot}} \leqslant M_{\ast} \leqslant 10^{5}\,\mathrm{M_{\odot}}) and yields a well-resolved stellar mass--halo mass (SMHM) relation over the peak halo mass range 10^8\,\mathrm{M_{\odot}} to 10^{15}\,\mathrm{M_{\odot}}. The extensive dynamic range provided by the zoom-in simulations allows us to assess specific aspects of dwarf galaxy evolution predicted by \textsc{UniverseMachine}. In particular, although UniverseMachine is not constrained for dwarf galaxies with M_* \lesssim 10^{8}\,\mathrm{M_{\odot}}, our predicted SMHM relation is consistent with that inferred for MW satellite galaxies at z=0 using abundance matching. However, UniverseMachine predicts that nearly all galaxies are actively star forming below M_{\ast}\sim 10^{7}\,\mathrm{M_{\odot}} and that these systems typically form more than half of their stars at z\lesssim 4, which is discrepant with the star formation histories of Local Group dwarf galaxies that favor early quenching. This indicates that the current UniverseMachine model does not fully capture galaxy quenching physics at the low-mass end. We highlight specific improvements necessary to incorporate environmental and reionization-driven quenching for dwarf galaxies, and provide a new tool to connect dark matter accretion to star formation over the full dynamic range that hosts galaxies.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We report the discovery of an ultrafaint dwarf (UFD) galaxy, Pegasus W, located on the far side of the Milky Way-M31 system and outside the virial radius of M31. The distance to the galaxy is 915 (+60/-91) kpc, measured using the luminosity of horizontal branch (HB) stars identified in Hubble Space Telescope optical imaging. The galaxy has a half-light radius (r_h) of 100 (+11/-13) pc, M_V = -7.20 (+0.17/-0.16) mag, and a present-day stellar mass of 6.5 (+1.1/-1.4) x 10^4 Msun. We identify sources in the color-magnitude diagram (CMD) that may be younger than ~500 Myr suggesting late-time star formation in the UFD galaxy, although further study is needed to confirm these are bona fide young stars in the galaxy. Based on fitting the CMD with stellar evolution libraries, Pegasus W shows an extended star formation history (SFH). Using the tau_90 metric (defined as the timescale by which the galaxy formed 90% of its stellar mass), the galaxy was quenched only 7.4 (+2.2/-2.6) Gyr ago, which is similar to the quenching timescale of a number of UFD satellites of M31 but significantly more recent than the UFD satellites of the Milky Way. Such late-time quenching is inconsistent with the more rapid timescale expected by reionization and suggests that, while not currently a satellite of M31, Pegasus W was nonetheless slowly quenched by environmental processes.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Kuan Wang
Yao-Yuan Mao
Andrew R. Zentner
Hong Guo
Johannes U. Lange
Frank C. van den Bosch
Lorena Mezini
摘要： We present observational constraints on the galaxy-halo connection, focusing particularly on galaxy assembly bias, from a novel combination of counts-in-cylinders statistics, P(N_{\rm{CIC}}), with the standard measurements of the projected two-point correlation function, w_{\rm{p}}(r_{\rm{p}}), and number density, n_{\rm{gal}}, of galaxies. We measure n_{\rm{gal}}, w_{\rm{p}}(r_{\rm{p}}) and P(N_{\rm{CIC}}) for volume-limited, luminosity-threshold samples of galaxies selected from SDSS DR7, and use them to constrain halo occupation distribution (HOD) models, including a model in which galaxy occupation depends upon a secondary halo property, namely halo concentration. We detect significant positive central assembly bias for the M_r<-20.0 and M_r<-19.5 samples. Central galaxies preferentially reside within haloes of high concentration at fixed mass. Positive central assembly bias is also favoured in the M_r<-20.5 and M_r<-19.0 samples. We find no evidence of central assembly bias in the M_r<-21.0 sample. We observe only a marginal preference for negative satellite assembly bias in the M_r<-20.0 and M_r<-19.0 samples, and non-zero satellite assembly bias is not indicated in other samples. Our findings underscore the necessity of accounting for galaxy assembly bias when interpreting galaxy survey data, and demonstrate the potential of count statistics in extracting information from the spatial distribution of galaxies, which could be applied to both galaxy-halo connection studies and cosmological analyses.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Zhongxu Zhai
Jeremy L. Tinker
Arka Banerjee
Joseph DeRose
Hong Guo
Yao-Yuan Mao
Sean McLaughlin
Kate Storey-Fisher
Risa H. Wechsler
摘要： We analyze clustering measurements of BOSS galaxies using a simulation-based emulator of two-point statistics. We focus on the monopole and quadrupole of the redshift-space correlation function, and the projected correlation function, at scales of 0.1\sim60~h^{-1}Mpc. Although our simulations are based on wCDM with general relativity (GR), we include a scaling parameter of the halo velocity field, \gamma_f, defined as the amplitude of the halo velocity field relative to the GR prediction. We divide the BOSS data into three redshift bins. After marginalizing over other cosmological parameters, galaxy bias parameters, and the velocity scaling parameter, we find f\sigma_{8}(z=0.25) = 0.404\pm0.03, f\sigma_{8}(z=0.4) = 0.444\pm0.025 and f\sigma_{8}(z=0.55) = 0.385\pm0.019. Compared with Planck observations using a flat \LambdaCDM model, our results are lower by 2.29\sigma, 1.3\sigma and 4.58\sigma respectively. These results are consistent with other recent simulation-based results at non-linear scales, including weak lensing measurements of BOSS LOWZ galaxies, two-point clustering of eBOSS LRGs, and an independent clustering analysis of BOSS LOWZ. All these results are generally consistent with a combination of \gamma_f^{1/2}\sigma_8\approx 0.75. We note, however, that the BOSS data is well fit assuming GR, i.e. \gamma_f=1. We cannot rule out an unknown systematic error in the galaxy bias model at non-linear scales, but near-future data and modeling will enhance our understanding of the galaxy--halo connection, and provide a strong test of new physics beyond the standard model.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Rongpu Zhou
Jeffrey A. Newman
Yao-Yuan Mao
Aaron Meisner
John Moustakas
Adam D. Myers
Abhishek Prakash
Andrew R. Zentner
David Brooks
Yutong Duan
Martin Landriau
Michael E. Levi
Francisco Prada
Gregory Tarle
摘要： We present measurements of the redshift-dependent clustering of a DESI-like luminous red galaxy (LRG) sample selected from the Legacy Survey imaging dataset, and use the halo occupation distribution (HOD) framework to fit the clustering signal. The photometric LRG sample in this study contains 2.7 million objects over the redshift range of 0.4 < z < 0.9 over 5655 deg^2. We have developed new photometric redshift (photo-z) estimates using the Legacy Survey DECam and WISE photometry, with \sigma_{\mathrm{NMAD}} = 0.02 precision for LRGs. We compute the projected correlation function using new methods that maximize signal-to-noise ratio while incorporating redshift uncertainties. We present a novel algorithm for dividing irregular survey geometries into equal-area patches for jackknife resampling. For a five-parameter HOD model fit using the MultiDark halo catalog, we find that there is little evolution in HOD parameters except at the highest redshifts. The inferred large-scale structure bias is largely consistent with constant clustering amplitude over time. In an appendix, we explore limitations of Markov chain Monte Carlo fitting using stochastic likelihood estimates resulting from applying HOD methods to N-body catalogs, and present a new technique for finding best-fit parameters in this situation. Accompanying this paper we have released the Photometric Redshifts for the Legacy Surveys (PRLS) catalog of photo-z's obtained by applying the methods used in this work to the full Legacy Survey Data Release 8 dataset. This catalog provides accurate photometric redshifts for objects with z < 21 over more than 16,000 deg^2 of sky.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02
Xiao, Y [Xiao, Ying][ 1 ]
Wang, XY [Wang, Xiaoyan][ 1,2 ]
Xia, YG [Xia, Yonggao][ 1 ]
Yao, Y [Yao, Yuan][ 3 ]
Metwalli, E [Metwalli, Ezzeldin][ 3 ]
Zhang, Q [Zhang, Qian][ 1 ]
Liu, R [Liu, Rui][ 4,5 ]
Qiu, B [Qiu, Bao][ 1 ]
Rasool, M [Rasool, Majid][ 3 ]
Liu, ZP [Liu, Zhaoping][ 1 ]
摘要： A green facile scalable method inspired by polymeric dental restorative composite is developed to synthesize TiO2/carbon nanocomposites for manipulation of the intercala- tion potential of TiO2 as lithium-ion battery anode. Poorly crystallized TiO2 nanoparticles with average sizes of 4−6 nm are homogeneously embedded in carbon matrix with the TiO2 mass content varied between 28 and 65%. Characteristic discharge/ charge plateaus of TiO2 are significantly diminished and voltage continues to change along with proceeding discharge/charge process. The tap density, gravimetric and volumetric capacities, and cyclic and rate performance of the TiO2/C composites are effectively improved.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yao-Yuan Mao
Annika H. G. Peter
Susmita Adhikari
Keith Bechtol
Simeon Bird
Simon Birrer
Jonathan Blazek
Jeffrey L. Carlin
Nushkia Chamba
Johann Cohen-Tanugi
Francis-Yan Cyr-Racine
Tansu Daylan
Birendra Dhanasingham
Alex Drlica-Wagner
Cora Dvorkin
Christopher Fassnacht
Eric Gawiser
Maurizio Giannotti
Vera Gluscevic
Alma Gonzalez-Morales
摘要： Establishing that Vera C. Rubin Observatory is a flagship dark matter experiment is an essential pathway toward understanding the physical nature of dark matter. In the past two decades, wide-field astronomical surveys and terrestrial laboratories have jointly created a phase transition in the ecosystem of dark matter models and probes. Going forward, any robust understanding of dark matter requires astronomical observations, which still provide the only empirical evidence for dark matter to date. We have a unique opportunity right now to create a dark matter experiment with Rubin Observatory Legacy Survey of Space and Time (LSST). This experiment will be a coordinated effort to perform dark matter research, and provide a large collaborative team of scientists with the necessary organizational and funding supports. This approach leverages existing investments in Rubin. Studies of dark matter with Rubin LSST will also guide the design of, and confirm the results from, other dark matter experiments. Supporting a collaborative team to carry out a dark matter experiment with Rubin LSST is the key to achieving the dark matter science goals that have already been identified as high priority by the high-energy physics and astronomy communities.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Alex Drlica-Wagner
Chanda Prescod-Weinstein
Hai-Bo Yu
Andrea Albert
Mustafa Amin
Arka Banerjee
Masha Baryakhtar
Keith Bechtol
Simeon Bird
Simon Birrer
Torsten Bringmann
Regina Caputo
Sukanya Chakrabarti
Thomas Y. Chen
Djuna Croon
Francis-Yan Cyr-Racine
William A. Dawson
Cora Dvorkin
Vera Gluscevic
Daniel Gilman
摘要： Cosmological and astrophysical observations currently provide the only robust, positive evidence for dark matter. Cosmic probes of dark matter, which seek to determine the fundamental properties of dark matter through observations of the cosmos, have emerged as a promising means to reveal the nature of dark matter. This report summarizes the current status and future potential of cosmic probes to inform our understanding of the fundamental nature of dark matter in the coming decade.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Elise Darragh-Ford
John F. Wu
Yao-Yuan Mao
Risa H. Wechsler
Marla Geha
Jaime E. Forero-Romero
ChangHoon Hahn
Nitya Kallivayalil
John Moustakas
Ethan O. Nadler
Marta Nowotka
J. E. G. Peek
Erik J. Tollerud
Benjamin Weiner
J. Aguilar
S. Ahlen
D. Brooks
A. P. Cooper
A. de la Macorra
A. Dey
摘要： We introduce the DESI LOW-Z Secondary Target Survey, which combines the wide
area capabilities of the Dark Energy Spectroscopic Instrument (DESI) with an
efficient, low-redshift target selection method. Our selection consists of a
set of color and surface brightness cuts, combined with modern machine learning
methods, to optimally target low-redshift dwarf galaxies (z 95% complete in target
selection at z < 0.03 between 19
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-05-02
Wang, MM [Wang, Meimei][ 1,2 ]
Xia, YG [Xia, Yonggao][ 1 ]
Wang, XY [Wang, Xiaoyan][ 1,3 ]
Xiao, Y [Xiao, Ying][ 1 ]
Liu, R [Liu, Rui][ 4,5 ]
Wu, Q [Wu, Qiang][ 6 ]
Qiu, B [Qiu, Bao][ 1 ]
Metwalli, E [Metwalli, Ezzeldin][ 7 ]
Xia, SL [Xia, Senlin][ 7 ]
Yao, Y [Yao, Yuan][ 7 ]
Chen, GX [Chen, Guoxin][ 1 ]
Liu, Y [Liu, Yan][ 1 ]
Liu, ZP [Liu, Zhaoping][ 1 ]
Meng, JQ [Meng, Jian-Qjang][ 3 ]
Yang, ZH [Yang, Zhaohui][ 6 ]
Sun, LD [Sun, Ling-Dong][ 4,5 ]
Yan, CH [Yan, Chun-Hua][ 4,5 ]
Muller-Buschbaum, P [Mueller-Buschbaum, Peter][ 7 ]
Pan, J [Pan, Jing][ 2 ]
Cheng, YJ [Cheng, Ya-Jun][ 1 ]
摘要： A new facile scalable method has been developed to synthesize silicon oxycarbide (SiOC)/carbon nanohybrids using difunctional dental methacrylate monomers as solvent and carbon source and the silane coupling agent as the precursor for SiOC. The content (from 100% to 40% by mass) and structure (ratio of disor- dered carbon over ordered carbon) of the free carbon matrix have been systematically tuned by varying the mass ratio of methacryloxy- propyltrimethoxysilane (MPTMS) over the total mass of the resin monomers from 0.0 to 6.0. Compared to the bare carbon anode, the introduction of MPTMS significantly improves the electrochemical performance as a lithium-ion battery anode. The initial and cycled discharge/charge capacities of the SiOC/C nanohybrid anodes reach maximum with the MPTMS ratio of 0.50, which displays very good rate performance as well. Detailed structures and electrochemical performance as lithium-ion battery anodes have been systematically investigated. The structure−property correlation and corresponding mechanism have been discussed.
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