J/AJ/170/8ivo://CDS.VizieR/J/AJ/170/8doi:10.26093/cds/vizier/be-5a-8CDSClark C.J.R.Roman-Duval J.C.Madden S.C.Mertens M.Murray C.E.,Stutzki J.Tarantino E.Tchernyshyov K.2026-07-02T11:52:39Z2026-03-24T16:36:26ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frchemical-abundancesinfrared-sourcesinterstellar-mediumstellar-atmospheric-opacityCarbon plays key roles in the interstellar medium (ISM)-as a constituent of dust, as the carrier of the dominant far-infrared (FIR) cooling line, and as a component of various important molecules. But despite this, there are very few measurements of the abundance and depletion of carbon in the diffuse ISM. As with other elements, these measurements are traditionally performed in the ultraviolet. But for carbon, such measurements are extremely difficult, and fewer than 20 have been reported in the literature to date. Here, we present a novel method of measuring the abundance and depletion of carbon in the diffuse ISM: by observing absorption of the 158um [C II] line in the FIR. We present a catalog of 432 candidate sightlines that use bright nearby galaxies as background sources, and predict the [C II] absorption expected toward each. We conducted a pilot study using SOFIA, targeting sightlines toward the galaxies IC 342 and Circinus. We report a potential detection of Galactic [C II] absorption along the IC 342 sightline, although it requires disentangling [C II] emission from IC 342 itself. The Circinus sightline had an insufficiently stable instrumental baseline to allow a detection. This SOFIA study informs the prospects for [C II] absorption measurements with future facilities. To that end, we explore the potential for four proposed future FIR telescopes-PRIMA, FIRSST, SALTUS, and Origins-to detect [C II] absorption. We find that all four facilities would be able to detect [C II] absorption along a significant number of sightlines.2025AJ....170....8Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/170/8CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/simbad : Simbad objects catalogue (M.Wenger 2000)J/ApJ/700/1299 : Gas-phase element depletions in the ISM (Jenkins, 2009)J/MNRAS/394/1857 : H_2_/HI ratio in galaxies (Obreschkow+, 2009)J/ApJ/734/65 : CI radial velocities with HST/STIS (Jenkins+, 2011)J/ApJ/744/20 : S^4^MC project: 6 star forming regions PAHs (Sandstrom+, 2012)J/ApJ/774/68 : [CII]157.7um feature in LIRGs (Diaz-Santos+, 2013)J/A+A/571/A53 : 4 IRDC data cubes (Beuther+, 2014)J/MNRAS/449/2274 : Characterization of Herschel SPIRE FTS (Hopwood+, 2015)J/ApJ/801/127 : 3.6um, 4.5um, B and V light curves of NGC 6418 (Vazquez+, 2015)J/A+A/594/A116 : HI4PI spectra and column density maps (HI4PI team+, 2016)J/A+A/586/A37 : M33 center and BCLMP302 [CII] spectroscopy (Mookerjea+, 2016)J/ApJ/845/96 : [CII] emission in the ISM of 20 nearby galaxies (Croxall+, 2017)J/ApJS/233/22 : xCOLD GASS catalog (Saintonge+, 2017)J/MNRAS/474/2094 : Inferring probabilistic stellar rot. periods (Angus+, 2018)J/A+A/620/A112 : Template SED of DustPedia galaxies (Bianchi+, 2018)J/A+A/609/A37 : 875 nearby galaxies multiwavelength photometry (Clark+, 2018)J/A+A/636/A16 : M43, Horsehead, MonR2, M17SW [CII]158um spect. (Guevara+, 2020)J/ApJ/895/38 : MIR extinction toward Cyg OB2-12 ISM (Hensley+, 2020)J/ApJ/915/92 : SOFIA CII and NII obs. of M101 and NGC6946 (Tarantino+, 2021)J/A+A/659/A36 : Self-absorption in RCW 120 (Kabanovic+, 2022)J/A+A/680/A4 : IRAM NOEMA CO(1-0) cubes for IC342 (Querejeta+, 2023)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/170/8https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/170/8http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/170/8https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/170/8https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/170/8http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/170/8GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/170/8/catalog (Catalog of candidate sightlines and predicted observation parameters for observing Milky Way [CII] absorption (Tables 3 and 4))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/170/8/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/170/8/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/170/8/catalog?GETtext/xml+votable180.050000true213.289-65.340.0055555555555555565/6928 6965 6984 6/697 764 909 2320 2409 3042 3506 4439 4447 4469 5124 5181 5183 5190 5198 5200 5241 5244 5332 5342 5429 5440 5469 5492 5617 5629 5715 5751 5762 5799 5966 5975-5976 6037 6042 6047 6087 6090 6104 7132 7241 7374 7385 7536 7606 7642 7655 7659 7662 7743 7898 8085 8106 8196 8330 8359 8492 9894 10151 10364 10380 10402 10475 10544 10637 10662 10672 10684 10739 10761 10769 10841 10847 10856 10888 10901 10911-10912 10924-10925 10930 10941 10954 10977 10979 10990 11006 11010 11026-11027 11074 11180 11263 11375 11434-11435 11457 12018 13511 13522 15204 16441 16479 16531 16655 17594 17606 17688 17693 17754 17927 18002 18212 18398 18809 20014 20875 21450 23171 23178 24957 25083 25344 25575 25599 25788 25790 25888 25890 25907 25935 25946 25971-25972 25997 26055 26068 26072 26090-26091 26119 26125 26128 26139 26161 26166 26175 26210 26214 26222-26223 26260 26264-26265 26271 26301-26303 26311 26317-26318 26320 26323 26329 26331 26336 26338 26340 26343-26344 26346-26347 26349 26351 26377 26388 26432 26472 26537 27030 27130 27186 27514 27555 27580 27603 27606 27653-27654 27668-27669 27677 27716 27718-27719 27721-27722 27725 27727-27728 27731 27735-27736 27738 27741 27750 27757-27758 27761 27763-27766 27773 27811 27814 27823 27830 27841 27855 27857 27907 27909 27913-27914 27917-27918 27922 27931 27934 27941 27943-27945 27947-27949 27955 28015 28032-28033 28035 28037-28039 28054 28091 28123 28126 28162 28167 28184 28191 28201 28208 28213 28220 28234 28258 28264 28294 28299 28304 28348 28404 28416 28496 28529 28538 28593 28631 28651 29795 33958 34273 34382 34404 34493-34494 34531 34534 34544 34641 35243 35536 35691 35746 35993 36194 36241 36756 36785 36974 38136 38139 38390 38639 38822 39201 39803 39836 39862 40124 40221 40373 40410 41586 42016 42027 43233 43262 43420 43626 43845 43881 44660 45914 46399 46615 46987https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/170/8?format=asciiInfrareddefaultJ/AJ/170/8/catalogCatalog of candidate sightlines and predicted observation parameters for observing Milky Way [CII] absorption (Tables 3 and 4)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameNamemeta.id;meta.maincharRAJ2000Right Ascension, sight line (J2000) (1)degpos.eq.ra;meta.mainDEJ2000Declination, sight line (J2000) (1)degpos.eq.dec;meta.mainNH[7e19/5.5e21] Total (HI+H2) hydrogen column density, cgscm**-2phys.columnDensitydoublefmol[0/0.2] Molecular gas fraction, Eq. 4phys.mass;arith.ratiofloatSimbadNameSimbad column added by the CDSmeta.idcharnullableSubErr[0/100] Median error on the sky subtraction (3)%stat.error;instr.skyLevelfloatNCII[1.5e16/1.1e18] Predicted column density of CII, cgs (2)cm**-2phys.columnDensitydoubletauCIIdv[0.1/7.3] Predicted, integrated line opacity (2)km/sphys.absorption.coefffloattauCIIpeak[0.003/0.35] Predicted line opacity at velocity where peak absorption occurs (2)phys.absorption.coefffloatFcont[0.03/313.7] 160 um flux density of the background source, measured within the defined apertureJyphot.flux.density;em.mm.1500-3000GHzfloatdFcont[-39.8/-0.001] Reduction in flux density expected at the wavelength absorption is greatest (2)Jyphot.flux;arith.ratiofloatCIIratio[0.1/2599] Predicted ratio between Milky Way [CII] emission and absorption for the sightline (2)phot.flux;arith.ratiofloattauCIIpeak-F[0.002/0.341] Predicted FIRSST line opacity at peak (1)phys.absorption.coeffdoubleIntTime-F[9.8e-5/157660] Predicted FIRSST integration time (2)stime.expodoubletauCIIpeak-P[-3.7e-14/0.1] Predicted PRIMA line opacity at peak (1)phys.absorption.coeffdoubleIntTime-P[1e-4/185801] Predicted PRIMA integration time (2)stime.expodoubletauCIIpeak-S[3e-3/0.345] Predicted SALTUS line opacity at peak (1)phys.absorption.coeffdoubleIntTime-S[7.2e-6/11605] Predicted SALTUS integration time (2)stime.expodoubletauCIIpeak-O[1e-3/0.299] Predicted Origins line opacity at peak (1)phys.absorption.coeffdoubleIntTime-O[4.6e-8/74.2] Predicted Origins integration time (2)stime.expodouble