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TIME Commissioning Observations: I. Mapping Dust and Molecular Gas in the Sgr A Molecular Cloud Complex at the Galactic Center

Selina F. Yang, Sophie M. McAtee, Benjamin J. Vaughan, Abigail T. Crites, Victoria L. Butler, Dongwoo T. Chung, Ryan P. Keenan, Dang Pham, Shwetha Prakash, James J. Bock, Charles M. Bradford, Tzu-Ching Chang, Yun-Ting Cheng, Audrey Dunn, Nicholas Emerson, Clifford Frez, Jonathon Hunacek, Chao-Te Li, Ian N. Lowe, King Lau, Daniel P. Marrone, Evan C. Mayer, Guochao Sun, Isaac Trumper, Anthony D. Turner, Ta-Shun Wei, Michael Zemcov

TL;DR

This paper reports the first TIME commissioning observations of the Sgr A complex to validate hyperspectral imaging for line-intensity mapping. It describes Jupiter-based calibration, a multi-stage TOD filtering workflow, and map-domain PCA to identify residual systematics, demonstrating robust recovery of $^{12}$CO(2-1)$ and $^{13}$CO(2-1) emission and continuum components in a crowded Galactic center field. The study achieves ~5% agreement with BGPS for broadband flux and derives consistent $\mathrm{H}_2$ masses (order $10^5$–$10^6\,M_\odot$) via CO line ratios, supporting TIME’s readiness for future extragalactic CO and [C II] LIM surveys. The results highlight dominant instrument-origin correlated noise in the 0.5–5 Hz band and advocate for enhanced detector yield and refined bandpass calibration to further improve flux fidelity and spectral accuracy.

Abstract

We present the processing of an observation of Sagittarius A (Sgr A) with the Tomographic Ionized-carbon Mapping Experiment (TIME), part of the 2021-2022 commissioning run to verify TIME's hyperspectral imaging capabilities for future line-intensity mapping. Using an observation of Jupiter to calibrate detector gains and pointing offsets, we process the Sgr A observation in a purpose-built pipeline that removes correlated noise through common-mode subtraction with correlation-weighted scaling, and uses map-domain principal component analysis to identify further systematic errors. The resulting frequency-resolved maps recover strong 12CO(2-1) and 13CO(2-1) emission, and a continuum component whose spectral index discriminates free-free emission in the circumnuclear disk (CND) versus thermal dust emission in the 20 km s$^{-1}$ and 50 km s$^{-1}$ molecular clouds. Broadband continuum flux comparisons with the Bolocam Galactic Plane Survey (BGPS) show agreement to within $\sim$5% in high-SNR molecular clouds in the Sgr A region. From the CO line detections, we estimate a molecular hydrogen mass of between $5.4 \times 10^5 M_\odot$ and $5.7 \times 10^5 M_\odot$, consistent with prior studies. These results demonstrate TIME's ability to recover both continuum and spectral-line signals in complex Galactic fields, validating its readiness for upcoming extragalactic CO and [C II] surveys.

TIME Commissioning Observations: I. Mapping Dust and Molecular Gas in the Sgr A Molecular Cloud Complex at the Galactic Center

TL;DR

This paper reports the first TIME commissioning observations of the Sgr A complex to validate hyperspectral imaging for line-intensity mapping. It describes Jupiter-based calibration, a multi-stage TOD filtering workflow, and map-domain PCA to identify residual systematics, demonstrating robust recovery of CO(2-1)^{13}\mathrm{H}_210^510^6\,M_\odot$) via CO line ratios, supporting TIME’s readiness for future extragalactic CO and [C II] LIM surveys. The results highlight dominant instrument-origin correlated noise in the 0.5–5 Hz band and advocate for enhanced detector yield and refined bandpass calibration to further improve flux fidelity and spectral accuracy.

Abstract

We present the processing of an observation of Sagittarius A (Sgr A) with the Tomographic Ionized-carbon Mapping Experiment (TIME), part of the 2021-2022 commissioning run to verify TIME's hyperspectral imaging capabilities for future line-intensity mapping. Using an observation of Jupiter to calibrate detector gains and pointing offsets, we process the Sgr A observation in a purpose-built pipeline that removes correlated noise through common-mode subtraction with correlation-weighted scaling, and uses map-domain principal component analysis to identify further systematic errors. The resulting frequency-resolved maps recover strong 12CO(2-1) and 13CO(2-1) emission, and a continuum component whose spectral index discriminates free-free emission in the circumnuclear disk (CND) versus thermal dust emission in the 20 km s and 50 km s molecular clouds. Broadband continuum flux comparisons with the Bolocam Galactic Plane Survey (BGPS) show agreement to within 5% in high-SNR molecular clouds in the Sgr A region. From the CO line detections, we estimate a molecular hydrogen mass of between and , consistent with prior studies. These results demonstrate TIME's ability to recover both continuum and spectral-line signals in complex Galactic fields, validating its readiness for upcoming extragalactic CO and [C II] surveys.

Paper Structure

This paper contains 29 sections, 6 equations, 14 figures.

Table of Contents

  1. Introduction and Context
  2. Sgr A Complex in the Far-infrared Regime
  3. TIME Instrument Overview
  4. Observation and Raw Data
  5. Data Processing
  6. Calibration using SPACETIME
  7. Low-level Data Filtering During Calibration
  8. Feedhorn Offsets Correction
  9. Obtaining Per-Detector Gains
  10. TOD Filtering
  11. Basic High-pass Filtering and Normalization
  12. Common-mode Noise Removal
  13. First iteration (gray path in \ref{['fig:processing_flowchart']})
  14. Second iteration (blue path in \ref{['fig:processing_flowchart']})
  15. Third iteration (red path in \ref{['fig:processing_flowchart']})
  16. ...and 14 more sections

Figures (14)

  • Figure 1: False–color TIME image of the Sgr A region. The frequency range 183-326 GHz spanned by TIME was linearly mapped onto the colors corresponding to 700-400 nm, and the channels were then additively blended. This image is processed with Gaussian-smoothing and a second round of PCA for pure visual demonstrative purposes.
  • Figure 2: Scan pattern for the observation of Sgr A on February 8, 2022. The telescope steps in declination after completing each sweep in right ascension, producing 2D coverage of the field over the observation duration.
  • Figure 3: TOD Processing Pipeline: The workflow begins by using SPACETIME to determine per-detector gains ( \ref{['sec:gains']}) and feedhorn offsets (\ref{['sec:feedoffset']}). Raw TODs passing quality checks are filtered, normalized (\ref{['sec:highpass']}), and corrected using mux-c and frequency common-mode templates (\ref{['sec:common-mode-noise']}). Per-detector calibrated flux maps are generated (\ref{['sec: processing_map']}).To read this flowchart, follow the gray arrows for the general preparation of data and the first iteration of common-mode noise removal, continue along the blue arrows for the second iteration, and proceed to the red arrows for the third iteration. Each arrow is traced once. Detector mapping conventions such as (x,f) and mux-c are defined in \ref{['sec:TIME_Mechanical_overview']}
  • Figure 4: Per–detector gain factors derived from Jupiter observations on February 8, 2022. The gain is the multiplicative factor converting raw detector counts to Jy, as described in \ref{['sec:gains']}. Gaps correspond to detectors that did not pass quality checks.
  • Figure 5: Top: Correlation matrices of normalized detector TOD before common-mode template subtraction. The left panel shows the correlation coefficients for all 179 detectors, ordered by mux-c and then mux-r, with grid lines indicating mux-c-block templates. The right panel shows the same data ordered by frequency and spatial index, gridded by frequency-block templates. Bottom: Same as above, but for the correlation matrix after common-mode template subtraction. Blocks of high correlation indicate strong common-mode noise components, likely of instrumental origin (see \ref{['sec:discussion']}).
  • ...and 9 more figures