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CLASSY. II. A Technical Overview of the COS Legacy Archive Spectroscopic Survey

James, Bethan L. and Berg, Danielle A. and King, Teagan and Sahnow, David J. and Mingozzi, Matilde and Chisholm, John and Heckman, Timothy and Martin, Crystal L. and Stark, Dan P. and Aloisi, Alessandra and Amorín, Ricardo O. and Arellano-Córdova, Karla Z. and Bayliss, Matthew and Bordoloi, Rongmon and Brinchmann, Jarle and Charlot, Stéphane and Chen, Zuyi and Chevallard, Jacopo and Clark, Ilyse and Erb, Dawn K. and Feltre, Anna and Hayes, Matthew and Henry, Alaina and Hernandez, Svea and Jaskot, Anne and Kewley, Lisa J. and Kumari, Nimisha and Leitherer, Claus and Llerena, Mario and Maseda, Michael and Nanayakkara, Themiya and Ouchi, Masami and Plat, Adele and Pogge, Richard W. and Ravindranath, Swara and Rigby, Jane R. and Scarlata, Claudia and Senchyna, Peter and Skillman, Evan D. and Steidel, Charles C. and Strom, Allison L. and Sugahara, Yuma and Wilkins, Stephen M. and Wofford, Aida and Xu, Xinfeng (2022) CLASSY. II. A Technical Overview of the COS Legacy Archive Spectroscopic Survey. Astrophysical Journal Supplement Series, 262 (2). Art. No. 37. ISSN 0067-0049. doi:10.3847/1538-4365/ac8008.

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The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies that were chosen to cover similar properties to those seen at high z (z > 6). The prime high-level science product of CLASSY is accurately coadded UV spectra, ranging from ∼1000 to 2000 Å, derived from a combination of archival and new data obtained with HST's Cosmic Origins Spectrograph (COS). This paper details the multistage technical processes of creating this prime data product and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet and near-ultraviolet (NUV) spectra. We provide guidelines on how to successfully utilize COS observations of extended sources, despite COS being optimized for point sources, and best-practice recommendations for the coaddition of UV spectra in general. Moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the CLASSY data. In particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of NUV spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via C iii] nebular emission. Despite changes in spectral resolution of up to ∼25% between individual data sets (due to changes in the COS line-spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in part to our signal-to-noise regime of S/N < 20.

Item Type:Article
Related URLs:
URLURL TypeDescription
James, Bethan L.0000-0003-4372-2006
Berg, Danielle A.0000-0002-4153-053X
King, Teagan0000-0003-0834-4150
Sahnow, David J.0000-0001-9594-161X
Mingozzi, Matilde0000-0003-2589-762X
Chisholm, John0000-0002-0302-2577
Heckman, Timothy0000-0003-1127-7497
Martin, Crystal L.0000-0001-9189-7818
Aloisi, Alessandra0000-0003-4137-882X
Amorín, Ricardo O.0000-0001-5758-1000
Arellano-Córdova, Karla Z.0000-0002-2644-3518
Bayliss, Matthew0000-0003-1074-4807
Bordoloi, Rongmon0000-0002-3120-7173
Brinchmann, Jarle0000-0003-4359-8797
Charlot, Stéphane0000-0003-3458-2275
Chen, Zuyi0000-0002-2178-5471
Chevallard, Jacopo0000-0002-7636-0534
Clark, Ilyse0000-0003-3334-4267
Erb, Dawn K.0000-0001-9714-2758
Feltre, Anna0000-0001-6865-2871
Hayes, Matthew0000-0001-8587-218X
Henry, Alaina0000-0002-6586-4446
Hernandez, Svea0000-0003-4857-8699
Jaskot, Anne0000-0002-6790-5125
Kewley, Lisa J.0000-0001-8152-3943
Kumari, Nimisha0000-0002-5320-2568
Leitherer, Claus0000-0003-2685-4488
Llerena, Mario0000-0003-1354-4296
Maseda, Michael0000-0003-0695-4414
Nanayakkara, Themiya0000-0003-2804-0648
Ouchi, Masami0000-0002-1049-6658
Plat, Adele0000-0003-0390-0656
Pogge, Richard W.0000-0003-1435-3053
Ravindranath, Swara0000-0002-5269-6527
Rigby, Jane R.0000-0002-7627-6551
Scarlata, Claudia0000-0002-9136-8876
Senchyna, Peter0000-0002-9132-6561
Skillman, Evan D.0000-0003-0605-8732
Steidel, Charles C.0000-0002-4834-7260
Strom, Allison L.0000-0002-4834-7260
Sugahara, Yuma0000-0001-6958-7856
Wilkins, Stephen M.0000-0003-3903-6935
Wofford, Aida0000-0001-8289-3428
Xu, Xinfeng0000-0002-9217-7051
Additional Information:B.L.J. is thankful for support from the European Space Agency (ESA). D.A.B. is grateful for the support for this program, HST-GO-15840, that was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Associations of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. The CLASSY Collaboration extends special gratitude to the Lorentz Center for useful discussions during the "Characterizing Galaxies with Spectroscopy with a view for JWST" 2017 workshop that led to the formation of the CLASSY Collaboration and survey. The CLASSY Collaboration thanks the COS team for all their assistance and advice in the reduction of the COS data, with particular thanks to Elaine Frazer for NUV data extraction and Christian Johnson in assisting with error analysis.
Group:Astronomy Department
Funding AgencyGrant Number
European Space Agency (ESA)UNSPECIFIED
Issue or Number:2
Record Number:CaltechAUTHORS:20220928-285212100.17
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:117171
Deposited By: Melissa Ray
Deposited On:04 Oct 2022 17:32
Last Modified:04 Oct 2022 17:32

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