Yun-Ting Cheng

Galactic Dust Modeling with Gas Tracers

Cheng, Y.-T., Hensley, B., Chang, T.-C., & Doré, O.
2024, ApJ, 971, 159 (ADS, arXiv: 2411.12801)

Neutral hydrogen (HI) emission is a powerful tracer for dust extinction at high Galactic latitude, which is a critical systematics for precision cosmology. In this work, we improve high-latitude HI-based dust templates by incorporating data from ionized and molecular gas phases. We make further improvements by employing a clustering analysis on the H I spectral data to identify discrete clouds with distinct dust properties. Our template has large-scale residuals at the level of <20% when fitting to the dust emission from Planck. We quantify the contributions to these residuals from variations in the dust-to-gas ratio, dust temperature and opacity, and magnetic field orientation using ancillary datasets.

Bayesian Multi-line Intensity Mapping

Cheng, Y.-T., Wang, K., Wandelt, B., Chang, T.-C., & Doré, O.
2024, ApJ, 971, 159 (ADS, arXiv: 2403.19740)

Line intensity mapping (LIM) is a promising tool for probing the 3D large-scale structure through the aggregate emission of spectral lines. However, the presence of interloper lines poses a crucial challenge in extracting the signal from the target line in LIM. In this work, we introduce a novel method for LIM analysis that simultaneously extracts line signals from multiple spectral lines, utilizing the covariance of native LIM data elements defined in the spectral-angular space. We leverage correlated information from different lines to perform joint inference on all lines simultaneously, employing a Bayesian analysis framework. We demonstrate that our technique can extract multiple lines from SPHEREx with high sensitivity using mock power spectra. Our technique offers a flexible framework for LIM analysis, enabling simultaneous inference of signals from multiple line emissions while accommodating diverse modeling constraints and parameterizations.

Cosmic Dipole with Radio Sources - a Test of the ΛCDM model

Cheng, Y.-T., Chang, T.-C., & Lidz, A.
2024, ApJ, 965, 32 (ADS, arXiv: 2309.02490)

The dipole moment in the angular distribution of the cosmic microwave background (CMB) is thought to originate from the Doppler effect and our motion relative to the CMB frame. Observations of large-scale structure should exhibit a related "kinematic dipole" and help test the kinematic origin of the CMB dipole. Intriguingly, many previous LSS dipole studies suggest discrepancies with the expectations from the CMB. In this work, we reassess this tension by incorporating a model of clustering and shot noise in the NVSS dipole, which have been ignored in some previous works. Our results show that the NVSS dipole is consistent with a kinematic origin for the CMB dipole within the ΛCDM model, demonstrating the importance of accounting for clustering and shot-noise fluctuations in evaluating the dipole consistency.

Data-driven Cosmology from Three-dimensional Light Cones

Cheng, Y.-T., Wandelt, B., Chang, T.-C., & Doré, O.
2023, ApJ, 944, 151 (ADS, arXiv: 2210.10052)

To exploit the vast amount of information in large-scale surveys spanning multiple frequency bands, we develop a novel data-driven technique for studying cosmology from a 3D light cone observed in multi-band large-scale images. Unlike traditional galaxy surveys that detect only bright sources, or line intensity mapping which probes emissions from specific spectral lines, our approach utilize information from "all photons." We simultaneously determine the spectral and spatial distribution of all emitting sources, as well as the underlying large-scale structure traced by them. Our method holds broad applicability for upcoming cosmological surveys and offers complementary information to detection-based galaxy redshift surveys such as SPHEREx, Roman, Euclid, etc.

EBL Tomography with SPHEREx-galaxy Cross Correlations

Cheng, Y.-T., & Chang, T.-C.,
2022, ApJ, 925, 136 (ADS, arXiv: 2109.10914)

The extragalactic background light (EBL) represents the total emission from all extragalactic sources across the line of sight. The upcoming NASA satellite mission, SPHEREx, is set to perform an all-sky spectral mapping survey in the near-infrared wavelength range (0.75 - 5 µm), providing a unique dataset for probing the EBL. In this study, we forecast the sensitivity of employing galaxy cross-correlations with SPHEREx data to delineate the spectral and redshift dependences of the EBL.

Probing the Intra-Halo Light in the Near-infrared Extragalactic Background Light

Cheng, Y.-T., & Bock, J.
2022, ApJ, 940, 115 (ADS, arXiv: 2207.13712)

Cheng, Y.-T. + CIBER collaboration
2021, ApJ, 919, 69 (ADS, arXiv: 2103.03882)

Previous analyses of extragalactic background light (EBL) fluctuations have shown that the intra-halo light (IHL) significantly contributes to the near-infrared background. The IHL originates from stars that have been tidally stripped from their parent galaxies and now reside within the surrounding dark matter halo, exhibiting an extended spatial distribution. In Cheng et al. 2021, we use a stacking analysis technique with CIBER imaging data to constrain the IHL around normal galaxies within the redshift range of 0.2 < z < 0.5. In Cheng & Bock 2022, we use simulations to determine how the EBL power spectrum depends on nonlinear clustering caused by satellite galaxies and various IHL models.

Optimal Mapping Strategy for Large-Scale Structure Survey

Cheng, Y.-T., de Putter, R., Chang, T.-C., & Doré, O.
2019, ApJ, 877, 86 (ADS, arXiv: 1809.06384)

Conventional large-scale structure surveys reply on galaxy detection (GD) methods, while intensity mapping (IM) employs the integrated intensity to trace the underlying density field. In Cheng et al. 2019, we developed a unified framework to describe the information content in both IM and GD using Fisher formalism. This approach enables us to show that depending on the level of source confusion and instrument noise, GD, IM, or a hybrid approach may be optimal. In addition, this framework can serve as an effective tool for optimizing survey design and mapping strategies for upcoming large-scale structure surveys.

Spectral Line De-blending in Line Intensity Mapping

Cheng, Y.-T., Chang, T.-C., Bock, J., Bradford, C. M., & Cooray, A.
2016, ApJ, 832, 165 (ADS, arXiv: 1604.07833)

Cheng, Y.-T., Chang, T.-C., & Bock, J.
2020, ApJ, 901, 142 (ADS, arXiv: 2005.05341)

Line intensity mapping (LIM) traces the three-dimensional distribution of the universe by mapping the emission from specific spectral lines. It leverages the frequency-redshift relation to infer the line-of-sight distance of emission sources. However, interloper line foreground is one of a critical challenge for LIM. These are spectral lines from sources at different redshifts that overlap in the observed frequencies. For example, the [C II] intensity map aimed at the Epoch of Reionization (EoR) can be contaminated by several low-redshift CO rotational transition lines at the same observed frequencies. Traditional methods for separating these lines include masking and cross-correlation, both of which depend on high-quality external datasets, like deep galaxy catalogs, to effectively remove interloper lines. We developed two novel techniques for line de-blending in Fourier space and map space, respectively, which do not require external data. These methods offer innovative solutions to the interloper foreground challenge in LIM analysis.

Fourier (Power Spectrum) Space Line De-blending
In LIM, the two-dimensional power spectrum of interloper lines manifests an anisotropic shape when projected onto a common coordinate frame. In Cheng et al. 2016, we introduced a technique that exploits this anisotropy in the power spectrum to differentiate the large-scale fluctuations attributed to various lines in LIM. With simulated data, we successfully applied this method to simultaneously extract emissions from both the target and interloper lines in a LIM survey aimed at the [C II] line during the EoR.

Phase-Space (Map-Space) Line De-blending
In Cheng et al. 2020, we presented a novel approach for line de-blending in LIM surveys in map space to reconstruct the three-dimensional spatial distribution of line-emitting sources. This technique utilizes the fact that spectral lines emitted by sources at different redshifts map onto distinct observed frequencies, creating identifiable patterns in the observed spectrum. By modeling these patterns and fitting them with templates using a sparse approximation algorithm, we achieved successful de-confusion of lines in both the TIME-like and SPHEREx-like survey setups.

Research Summary