分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Extragalactic Fast Radio Bursts (FRBs) have large dispersion measures (DMs) and are unique probes of intergalactic electron density fluctuations. By using the recently released First CHIME/FRB Catalog, we reexamined the structure function (SF) of DM fluctuations. It shows a large DM fluctuation similar to that previously reported in Xu & Zhang (2020), but no clear correlation hinting towards large scale turbulence is reproduced with this larger sample. To suppress the distortion effect from FRB distances and their host DMs, we focus on a subset of CHIME catalog with DM $<500$ pc cm$^{-3}$. A trend of non-constant SF and non-zero correlation function (CF) at angular separations $\theta$ less than $10^\circ$ is seen, but with large statistical uncertainties. The difference found between SF and that derived from CF at $\theta \lesssim 10^\circ$ can be ascribed to the large statistical uncertainties or the density inhomogeneities on scales on the order of $100$ Mpc. The possible correlation of electron density fluctuations and inhomogeneities of density distribution should be tested when several thousands of FRBs are available.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yun Wang
Zhongxu Zhai
Anahita Alavi
Elena Massara
Alice Pisani
Andrew Benson
Christopher M. Hirata
Lado Samushia
David H. Weinberg
James Colbert
Olivier Doré
Tim Eifler
Chen Heinrich
Shirley Ho
Elisabeth Krause
Nikhil Padmanabhan
David Spergel
Harry I. Teplitz
摘要： The Nancy Grace Roman Space Telescope will conduct a High Latitude Spectroscopic Survey (HLSS) over a large volume at high redshift, using the near-IR grism (1.0-1.93 $\mu$m, $R=435-865$) and the 0.28 deg$^2$ wide field camera. We present a reference HLSS which maps 2000 deg$^2$ and achieves an emission line flux limit of 10$^{-16}$ erg/s/cm$^2$ at 6.5$\sigma$, requiring $\sim$0.6 yrs of observing time. We summarize the flowdown of the Roman science objectives to the science and technical requirements of the HLSS. We construct a mock redshift survey over the full HLSS volume by applying a semi-analytic galaxy formation model to a cosmological N-body simulation, and use this mock survey to create pixel-level simulations of 4 deg$^2$ of HLSS grism spectroscopy. We find that the reference HLSS would measure $\sim$ 10 million H$\alpha$ galaxy redshifts that densely map large scale structure at $z=1-2$ and 2 million [OIII] galaxy redshifts that sparsely map structures at $z=2-3$. We forecast the performance of this survey for measurements of the cosmic expansion history with baryon acoustic oscillations and the growth of large scale structure with redshift space distortions. We also study possible deviations from the reference design, and find that a deep HLSS at $f_{\rm line}>7\times10^{-17}$erg/s/cm$^2$ over 4000 deg$^2$ (requiring $\sim$1.5 yrs of observing time) provides the most compelling stand-alone constraints on dark energy from Roman alone. This provides a useful reference for future optimizations. The reference survey, simulated data sets, and forecasts presented here will inform community decisions on the final scope and design of the Roman HLSS.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Andrew P. Cooper
Sergey E. Koposov
Carlos Allende Prieto
Christopher J. Manser
Namitha Kizhuprakkat
Adam D. Myers
Arjun Dey
Boris T. Gaensicke
Ting S. Li
Constance Rockosi
Monica Valluri
Joan Najita
Alis Deason
Anand Raichoor
Mei-Yu Wang
Yuan-Sen Ting
Bokyoung Kim
Andreia Carrillo
Wenting Wang
Leandro Beraldo e Silva
摘要： We describe the Milky Way Survey (MWS) that will be undertaken with the Dark Energy Spectroscopic Instrument (DESI) on the Mayall 4m telescope at the Kitt Peak National Observatory. Over the next 5 yr DESI MWS will observe approximately seven million stars at Galactic latitudes |b|>20 degrees, with an inclusive target selection scheme focused on the thick disk and stellar halo. MWS will also include several high-completeness samples of rare stellar types, including white dwarfs, low-mass stars within 100pc of the Sun, and horizontal branch stars. We summarize the potential of DESI to advance understanding of Galactic structure and stellar evolution. We introduce the final definitions of the main MWS target classes and estimate the number of stars in each class that will be observed. We describe our pipelines for deriving radial velocities, atmospheric parameters, and chemical abundances. We use ~500,000 spectra of unique stellar targets from the DESI Survey Validation program (SV) to demonstrate that our pipelines can measure radial velocities to ~1 km/s and [Fe/H] accurate to ~0.2 dex for typical stars in our main sample. We find the stellar parameter distributions from ~100 sq. deg of SV observations with >90% completeness on our main sample are in good agreement with expectations from mock catalogs and previous surveys.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Naim Göksel Karaçaylı
Paul Martini
David H. Weinberg
Vid Iršič
J. Aguilar
S. Ahlen
D. Brooks
A. de la Macorra
A. Font-Ribera
S. Gontcho A Gontcho
J. Guy
T. Kisner
R. Miquel
C. Poppett
C. Ravoux
M. Schubnell
G. Tarlé
B. A. Weaver
Z. Zhou
摘要： The abundance, temperature, and clustering of metals in the intergalactic medium are important parameters for understanding their cosmic evolution and quantifying their impact on cosmological analysis with the Ly $\alpha$ forest. The properties of these systems are typically measured from individual quasar spectra redward of the quasar's Ly $\alpha$ emission line, yet that approach may provide biased results due to selection effects. We present an alternative approach to measure these properties in an unbiased manner with the two-point statistics commonly employed to quantify large-scale structure. Our model treats the observed flux of a large sample of quasar spectra as a continuous field and describes the one-dimensional, two-point statistics of this field with three parameters per ion: the abundance (column density distribution), temperature (Doppler parameter) and clustering (cloud-cloud correlation function). We demonstrate this approach on multiple ions (e.g., C IV, Si IV, Mg II) with early data from the Dark Energy Spectroscopic Instrument (DESI) and high-resolution spectra from the literature. Our initial results show some evidence that the C IV abundance is higher than previous measurements and evidence for abundance evolution over time. The first full year of DESI observations will have over an order of magnitude more quasar spectra than this study. In a future paper we will use those data to measure the growth of clustering and its impact on the Ly $\alpha$ forest, as well as test other DESI analysis infrastructure such as the pipeline noise estimates and the resolution matrix.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hao-Yi Wu
Matteo Costanzi
Chun-Hao To
Andrés N. Salcedo
David H. Weinberg
James Annis
Sebastian Bocquet
Maria Elidaiana da Silva Pereira
Joseph DeRose
Johnny Esteves
Arya Farahi
Sebastian Grandis
Eduardo Rozo
Eli S. Rykoff
Tamás N. Varga
Risa H. Wechsler
Chenxiao Zeng
Yuanyuan Zhang
Zhuowen Zhang
摘要： Cosmological constraints from current and upcoming galaxy cluster surveys are limited by the accuracy of cluster mass calibration. In particular, optically identified galaxy clusters are prone to selection effects that can bias the weak lensing mass calibration. We investigate the selection bias of the stacked cluster lensing signal associated with optically selected clusters, using clusters identified by the redMaPPer algorithm in the Buzzard simulations as a case study. We find that at a given cluster halo mass, the residuals of redMaPPer richness and weak lensing signal are positively correlated. As a result, for a given richness selection, the stacked lensing signal is biased high compared with what we would expect from the underlying halo mass probability distribution. The cluster lensing selection bias can thus lead to overestimated mean cluster mass and biased cosmology results. We show that the lensing selection bias exhibits a strong scale-dependence and is approximately 20 to 60 percent for $\Delta\Sigma$ at large scales. This selection bias largely originates from spurious member galaxies within +/- 20 to 60 Mpc/h along the line of sight, highlighting the importance of quantifying projection effects associated with the broad redshift distribution of member galaxies in photometric cluster surveys. While our results qualitatively agree with those in the literature, accurate quantitative modelling of the selection bias is needed to achieve the goals of cluster lensing cosmology and will require synthetic catalogues covering a wide range of galaxy-halo connection models.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Shuiyao Huang
Neal Katz
Evan Scannapieco
J'Neil Cottle
Romeel Davé
David H. Weinberg
Molly S. Peeples
Marcus Brüggen
摘要： The propagation and evolution of cold galactic winds in galactic haloes is crucial to galaxy formation models. However, modelling of this process in hydrodynamic simulations of galaxy formation is over-simplified owing to a lack of numerical resolution and often neglects critical physical processes such as hydrodynamic instabilities and thermal conduction. We propose an analytic model, Physically Evolved Winds (PhEW), that calculates the evolution of individual clouds moving supersonically through a uniform ambient medium. Our model reproduces predictions from very high resolution cloud-crushing simulations that include isotropic thermal conduction over a wide range of physical conditions. We discuss the implementation of this model into cosmological hydrodynamic simulations of galaxy formation as a sub-grid prescription to model galactic winds more robustly both physically and numerically.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present novel constraints on the underlying galaxy formation physics (e.g., mass loading factor, star formation history, metal retention) at $z \gtrsim 7$ for the low-mass ($M_*\sim10^5$ M$_\odot$) Local Group ultra-faint dwarf galaxy (UFD) Eridanus II (Eri II) Using a hierarchical Bayesian framework, we apply a one-zone chemical evolution model to Eri II's CaHK-based photometric metallicity distribution function (MDF; [Fe/H]) and find that the evolution of Eri II is well-characterized by a short, exponentially declining star-formation history ($\tau_\text{SFH} = 0.39\pm_{0.13}^{0.18}$ Gyr), a low star-formation efficiency ($\tau_\text{SFE} = 27.56\pm_{12.92}^{25.14}$ Gyr), and a large mass-loading factor ($\eta = 194.53\pm_{42.67}^{33.37}$). Our results are consistent with Eri II forming the majority of its stars before the end of reionization. The large mass-loading factor is consistent with strong outflows in Eri II and is in good agreement with theoretical predictions for momentum-driven galactic winds. It also results in the ejection of $>$90% of the metals produced in Eri II. We make predictions for the distribution of [Mg/Fe]-[Fe/H] in Eri II as well as the prevalence of ultra metal-poor stars, both of which can be tested by future chemical abundance measurements. Spectroscopic follow-up of the highest metallicity stars in Eri II ($\text{[Fe/H]}> -2$) will greatly improve model constraints. Our new framework can readily be applied to all UFDs throughout the Local Group, providing new insights in to the underlying physics governing the evolution of the faintest galaxies in the reionization-era.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Although galactic winds play a critical role in regulating galaxy formation, hydrodynamic cosmological simulations do not resolve the scales that govern the interaction between winds and the ambient circumgalactic medium (CGM). We implement the Physically Evolved Wind (PhEW) model of Huang et al. (2020) in the GIZMO hydrodynamics code and perform test cosmological simulations with different choices of model parameters and numerical resolution. PhEW adopts an explicit subgrid model that treats each wind particle as a collection of clouds that exchange mass, metals, and momentum with their surroundings and evaporate by conduction and hydrodynamic instabilities as calibrated on much higher resolution cloud scale simulations. In contrast to a conventional wind algorithm, we find that PhEW results are robust to numerical resolution and implementation details because the small scale interactions are defined by the model itself. Compared to conventional wind simulations with the same resolution, our PhEW simulations produce similar galaxy stellar mass functions at $z\geq 1$ but are in better agreement with low-redshift observations at $M_* < 10^{11}M_\odot$ because PhEW particles shed mass to the CGM before escaping low mass halos. PhEW radically alters the CGM metal distribution because PhEW particles disperse metals to the ambient medium as their clouds dissipate, producing a CGM metallicity distribution that is skewed but unimodal and is similar between cold and hot gas. While the temperature distributions and radial profiles of gaseous halos are similar in simulations with PhEW and conventional winds, these changes in metal distribution will affect their predicted UV/X-ray properties in absorption and emission.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We forecast constraints on the amplitude of matter clustering sigma_8(z) achievable with the combination of cluster weak lensing and number counts, in current and next-generation weak lensing surveys. We advocate an approach, analogous to galaxy-galaxy lensing, in which the observables in each redshift bin are the mean number counts and the mean weak lensing profile of clusters above a mass proxy threshold. The primary astrophysical nuisance parameter is the logarithmic scatter between the mass proxy and true mass near the threshold. For surveys similar to the Dark Energy Survey (DES), the Roman Space Telescope High Latitude Survey (HLS), and the Rubin Observatory Legacy Survey of Space and Time (LSST), we forecast aggregate precision on sigma_8 of 0.26%, 0.24%, and 0.10%, respectively, if the mass-observable scatter has an external prior better than 0.01. These constraints would be degraded by about 20% for a 0.05 prior on scatter in the case of DES or HLS and for a 0.016 prior for LSST. A one-month observing program with Roman Space Telescope targeting approximately 2500 massive clusters could achieve a 0.5% constraint on sigma_8(z=0.7) on its own, or a ~0.33% constraint in combination with the HLS. Realizing the constraining power of clusters requires accurate knowledge of the mass-observable relation and stringent control of systematics. We provide analytic approximations to our numerical results that allow easy scaling to other survey assumptions or other methods of cluster mass estimation.
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