SPIRE Spectral Feature Catalogue

3^rd public release, OCTOBER 2020

Contributors

The Spectral Feature Finder project is lead by Rosalind Hopwood (1,2) and with significant contribution by Ivan Valtchanov (2), L. D. Spencer (3), J. Scott (3), C. Benson (3), N. Marchili (4), N. Hładczuk (2), E. T. Polehampton (5), N. Lu (6), G. Makiwa (3), D. A. Naylor (3), G. Noble (7), M. J. Griffin (8) and with valuable inputs from members of the no longer active SPIRE Instrument and Control Centre.

(1) Imperial College, London; (2) Herschel Science Centre, ESAC, ESA; (3) University of Lethbridge, Canada; (4) APS-INAF, Roma, Italy; (5) RAL Space, UK; (6) China-Chile Joint Center for Astronomy, Santiago, Chile; (7) University of British Columbia, Canada; (8) Cardiff University, UK

Abstract

The SPIRE Spectral Feature Finder Catalogue is the result of an automated run of the Spectral Feature Finder (FF). The FF is designed to extract significant spectral features from SPIRE FTS data products. These spectral features are only identified for High Resolution (HR) sparse or mapping observations, while for Low Resolution (LR) sparse or mapping observations the FF only provides the best fit continuum parameters.

The FF engine iteratively searches for peaks over a set of signal-to-noise ratio (SNR) thresholds, either in the HR spectra of the central and off-axis detectors (sparse mode) or in each pixel (SPIRE Long Wavelength - SLW, and SPIRE Short Wavelength - SSW) of the two hyper-spectral cubes (mapping). At the end of each iteration, the FF simultaneously fits the continuum and features found, with the resulting residual spectrum used in the next iteration.

The final FF products report the frequency of the features found and the associated SNRs. Line flux determination is not included as part of the FF products, as extracting reliable line flux from SPIRE-FTS data is a complex process that requires careful evaluation and analysis of the spectra on a case-by-case basis.

The FF results are 100% complete for features with SNR greater than 10 and 50-70% complete at SNR of 5. The FF code and all FF products are publicly available. The final combined catalogue of all sparse and mapping observations lists 267,159 features at |SNR|>=5, from 874 (i.e., 669 sparse mode and 205 mapping mode) unique HR observations.

The off-axis line search reports an additional 33,840 spectral features. Continuum spectra parameters are provided for an additional 199 HR sparse mode observations, and 257 LR sparse mode (only for the central detectors) and 70 LR mapping mode (all spatial pixels) observations.

Important notes

• No line fluxes are provided in the FF products. The iteratively detected features, in emission or in absorption, are given with their estimated local signal-to-noise ratio (SNR). SNR is negative for absorption features.
• All frequency-depended results (spectral feature centroid, continua, postcards x-axis) are in the kinematic Local Standard of Rest (LSRk).
• The radial velocities, available in the FF products metadata, are derived from the data (Scott J. et al., in preparation) or taken from publications. They should be used with caution.

All the details regarding the Feature Finder and the derived products are presented in the Release Note and in a set of 4 papers:

• Hopwood et al. (2020), paper I, The Spectral Feature Finder and Catalogue;
• Scott et al. (2020), paper II, Estimating Radial Velocity of SPIRE Spectral Observation Sources;
• ​​​​Benson et al. (2020), paper III, Line Identification and Off-Axis Spectra;

• Scott et al. (2020), paper IV, Neutral Carbon Detection in the SPIRE FTS Spectra.

Access to the Spectral Feature Finder products

The FF products can be accessed in the Herschel Highly Processed Data Products Legacy Archive Area.

All products, postcards and documentation for version 3 are available in FFv3_products.tar.gz tarball (2 GB).

Spectral Feature Finder software

In folder software, we provide a copy of the original software used to produce the artefacts. The code is in jython and is made to use in the Herschel Interactive Processing Environment (HIPE).

We also provide a jupyter-lab python notebook (html version) with some basic and more advanced examples on accessing and using the Feature Finder products.

FF catalogue variants

The FF products provided depend on spectral resolution and observing mode.

High resolution (HR)

There are three sub-folders of FF products for HR sparse-mode and mapping observations, each containing folders that provide: the individual FF feature catalogues; the fitted continua as Herschel spectral products and as polynomial coefficients; and the associated postcards.

• HRpointProducts: contains FF products for point-source calibrated spectra
• HRextProducts: contains FF products for extended-source calibrated spectra for those sparse-mode observations of sources with some spatial extent. For these observations it is important to consider both sets of FF results. For fully-extended sources there may be fewer spurious detections and a better spectral shape of the continua seen in the extended-source calibrated FF products.
• HRmapping: contains FF products for mapping observations. Each spatial pixel in each of the two hyper-spectral cubes (for the two spectrometer arrays) is processed with the FeatureFinder and the results are stored in the output table.
• HRextProducts-offaxis: contains FF products for extended-source calibrated spectra for off-axis detectors in sparse mode observations.

hrSparseObservations.csv lists all HR observations for which there is a set of FF products and indicates the source extent of the source observed (pointLike, semiExtended or fullyExtended). If the source is known to be featureless, this is indicated in the knownFeatureless column, and there is no feature catalogue in the associated FF products. The dataUsed column indicates if special data was used, as explained in the Release Note.

The coma-separated-value files hrMappingObservations.csv, hrOffAxisObservations.csv, lrSparseObservations.csv and lrMappingObservations.csv provide a list of the OBSIDs used for the HR mapping, sparse HR observations for off-axis detectors and LR sparse and mapping observations respectively. For observations in H+LR mode the same OBSID will appear in both HR and LR lists.

In addition, the combined Spire Automated Feature Extraction CATalogue (SAFECAT), collates all features found for the point-source calibrated spectra of HR sparse and mapping mode observations.

Low resolution (LR)

For LR the best fit to the continua for the two spectral bands is provided, both as polynomial coefficients and as Herschel spectral products, along with the FF postcards. There are products for point-source calibrated spectra and extended-source calibrated spectra for all LR sparse-mode observations that were run with the FF.

The LR continua are also provided for spectral maps, both for the naive and convolution projection (CP) cube generation methods (see the SPIRE Data Reduction Guide for more details). For these observations the polynomial coefficients are provided for each cube pixel.

Individual FF catalogues and postcards

The FF catalogues can be accessed via a number of pages detailed in the tables below. The table provides links to the FF product tables in the left-hand column. The observations included on each page is given in the middle column, with the corresponding operational days in the right-hand column.

All products are described in greater detail in the Release Note. All individual feature catalogues, as well as SAFECAT, are provided as FITS files.

FF postcards

Each FF result is presented visually in a postcard. The appearence of the postcards depend on the observing mode and the ingredients are described in more details in the Release Note.

Additional information

In order to make full use of the Feature Finder products the following documents provide detailed background information regarding the SPIRE Fourier-Transform Spectrometer, its observing modes, calibration, pipelines and products:

• The FTS Flyer
• The SPIRE Quick-start Guide
• The SPIRE Handbook
• The SPIRE Data Reduction Guide

For further reading of documents related with all aspects of the SPIRE instrument, please consult The SPIRE Legacy Documentation Library.

Acknowledge the SPIRE Spectral Feature Finder Catalogue

Any use of the Spectral Feature Finder products or software should be acknowledged citing Hopwood et al., 2020, MNRAS, 496, 487 and the Feature Finder DOI: doi.org/10.5270/esa-lysf2yi​​​​​​​
 

Herschel Science Centre, September 2018