J/A+A/709/A21ivo://CDS.VizieR/J/A+A/709/A21CDSSampaio V.M.Jaffe Y.Lima-Dias C.Veliz Astudillo S.Martinez-Marin M.,Mendez-Hernandez H.Herrera-Camus R.Monachesi A.2026-05-19T14:14:26Z2026-04-28T12:06:01ZCDS support team

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

cds-question@unistra.frgalaxiesvisible-astronomycatalogsgalaxy-classification-systemsphotometryGalaxy morphology encodes key information about formation and evolution. Large imaging surveys require automated, reproducible methods beyond visual inspection. Nonparametric indices provide a useful framework, but their performance must be quantitatively assessed. We present a homogeneous catalog of nonparametric morphological indices for DECaLS galaxies with effective radii larger than 2 arcsec. Our goal is to evaluate the reliability of indices in separating spirals and ellipticals, test their consistency with existing classification schemes, and establish their applicability for the upcoming surveys focused on the southern hemisphere. We developed galmex, a modular Python package for preprocessing images and measuring a variety of nonparametric indices. Using bona fide spirals and ellipticals as control samples, we assessed the discriminatory power of each index, and compared them with CNN-based T-Types and Galaxy Zoo DECaLS labels. We used the indices as input for a light gradient boosting machine (LightGBM) to obtain probabilistic classifications. Concentration is the most reliable parameter from the concentration and asymmetry and smoothness system (CAS), while asymmetry-based indices (A and S) are limited to detecting disturbed morphologies. MEGG indices (M20, Entropy, Gini, G2) provide stronger separation and trace a gradient with T-Type. By using a simple binary (0 or 1) label for ellipticals and spirals, classifiers trained on nonparametric indices achieve high accuracy and well-calibrated probabilities, dominated by entropy, concentration, and Gini. We release the first public catalog of CA[AS]S+MEGG indices for DECaLS, together with galmex. We combine the nonparametric indices with machine learning framework to derive spiral and elliptical separation for galaxies below z~0.15 through a probabilistic approach.2026A&A...709A..21Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/709/A21CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/709/A21https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/709/A21http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/709/A21https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/709/A21https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/709/A21http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/709/A21GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/709/A21/elliptic (Galaxy Zoo 1 Spiral galaxies that are also present in the Galaxy Zoo DECaLS)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/709/A21/elliptic?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/709/A21/elliptic?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/709/A21/elliptic?GETtext/xml+votable180.050000true0.183966629830.672999434020.005555555555555556Cone search capability for table J/A+A/709/A21/spirals (GZ 1 Elliptical galaxies that are also present in the Galaxy Zoo DECaLS)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/709/A21/spirals?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/709/A21/spirals?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/709/A21/spirals?GETtext/xml+votable180.050000true177.574615564343.956028314740.005555555555555556Cone search capability for table J/A+A/709/A21/full (1.7 million galaxies from the Legacy Survey)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/709/A21/full?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/709/A21/full?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/709/A21/full?GETtext/xml+votable180.050000true17.49760005798-88.726388021330.0055555555555555561/17 26 34-35 2/16-18 32-34 73-78 82 88 98-99 101-103 108-110 123 126 128 131 133-135 175-177 179-180 3/8 10-11 32 76 80 140 144 160 192-193 196-197 208 256-257 260-261 269-271 289-291 316 320 322 341 343 358 360-361 364 384 386-388 390-391 403 444 490-491 518-519 521-523 529-531 576 578 584 586 605 607-608 610 616 618 629 631 637 639 683-686 690-691 694-697 699 712-713 715 724-725 728-729 737 739 765 767 4/0 2 8 10-11 36 38-39 56 132-134 136-138 308-310 312-314 324-326 328-330 384-385 387-390 393 564-566 568-570 580-582 584-586 644-646 648-650 781 792-793 796-797 836-838 840-841 1032-1033 1036-1037 1052-1053 1055 1070-1071 1073 1075 1155 1268-1270 1272-1274 1286 1292 1294-1295 1361 1369 1397 1399 1405 1426 1448-1450 1460 1464-1465 1540 1542-1543 1556 1558 1601 1605 1607 1609-1611 1780-1782 1784-1786 1876-1877 1879 1947 1950 1952 1954-1955 1957-1959 1999 2034-2035 2038 2040-2042 2113-2115 2391 2397-2399 2419 2425 2427 2513 2515 2521 2523 2545 2547 2553 2555 2560-2562 2564-2565 2715 2717-2719 2726-2727 2731 2748-2750 2754-2755 2758-2759 2768-2770 2773 2792-2793 2795 2856-2857 2859 2904-2906 2908-2909 2911 2920-2922 2930-2931 2936 2945 2947 2953 2960 2962-2966 2968 2970 3010 3038-3039 3059 3065 3067 5/4 6 12 14 36 38-39 56 58-59 148 150-151 232 234-235 540-542 556 560-562 576 578 640-642 648 1244-1246 1260 1264-1265 1308 1324-1325 1328 1330 1344 1346 1408-1410 1544-1545 1547 1564 1580 1584 1600-1601 2268-2269 2284 2286 2288 2332 2348 2350 2352 2354 2368 2432 2588 2604 2608 2624 2688 3104-3105 3108-3109 3120-3121 3123 3176-3177 3180-3181 3192-3193 3196-3198 3356-3358 3376-3378 3380 3392-3394 3396 4136-4138 4156-4157 4192 4195-4197 4200 4217-4219 4238 4248 4253-4254 4270 4277-4279 4297-4299 4615 4617-4619 5084-5086 5100-5102 5104-5106 5108 5138 5174 5320 5322 5344 5346 5354-5355 5452-5453 5455 5485 5584-5585 5587 5593 5628-5629 5631 5696 5698 5700 5710-5711 5720 5722 5744 5746 5752 5754-5755 5804-5806 5808 5810 5812-5813 5815-5816 5821 5848-5850 5864-5865 5868-5870 5872 5874 5973 6164-6166 6228 6230 6236 6238-6239 6401-6402 6410 6412 6414-6417 6419 6425-6427 6434-6435 7132 7148 7152 7493 7495 7513 7541 7680 7682 7688 7690 7720 7722-7723 7726 7736 7743 7783 7785-7787 7806-7807 7812 7814 7976 7978-7979 7981-7983 7992 7994-7995 8130-8132 8134 8146-8147 8156 8172 8176 8256-8258 8264 8266-8267 8282-8283 8285-8287 8320-8322 8324-8325 8327-8328 8330-8331 8333-8335 8448-8449 8451 9232 9240 9266 9272 9274 9360 9362 9368 9370 9392 9394 9400 9559 9563 9583 9585 9587 9669 9671 9699 9707 9744 9746 9754 9758-9759 9780 9915-9916 9918 10049 10051 10057 10059 10081 10083 10089 10179 10264 10304-10306 10308-10309 10846-10847 10855 10858-10859 10865-10867 10901-10903 10917-10919 10921-10923 11004-11006 11026-11027 11029-11031 11086-11089 11091 11097-11099 11176-11177 11179 11432-11433 11435 11628-11629 11640-11642 11692 11696-11697 11703 11712 11714 11733-11734 11748-11749 11760 11769 11775 11779 11785 11821 11844-11845 11847 11868-11869 11876-11878 11884 11888 11893 11920-11921 11923-11925 11927 11933 11968 11970 11976 11990 12032 12064 12066 12094 12114 12117 12122 12137 12149-12151 12173-12175 12196 12210 12231-12234 6/20-21 52 54 60 62 148 150-151 202-203 230 250-251 598-599 776 808 810-811 814 932 934-935 946 952 2172-2174 2228-2230 2232-2234 2252 2256-2258 2272 2308-2310 2316 2336-2338 2572 2574 2576 2578 2596 4988 4990 5044-5046 5048-5050 5064-5066 5068 5072-5073 5236-5238 5240-5242 5304-5306 5316-5318 5324 5344 5380-5382 5388 5408 5644 5648 5664 6185 6187 6260-6262 6264-6265 6273 6276-6277 6279 6284-6285 6287 6311 6324-6326 6328-6329 6340-6342 6344-6346 6408-6410 6412 6416 9080-9082 9140-9142 9150-9151 9156-9158 9160-9162 9184 9332-9334 9336-9338 9341-9343 9396-9398 9404 9412-9414 9428-9429 9476-9478 9480-9482 9732-9734 9736-9738 9760 10356-10358 10360-10362 10420-10422 10424-10426 10436-10438 10440-10442 10500-10502 10504-10506 10513-10516 10756-10758 10760-10762 12424-12425 12428-12429 12440 12444-12445 12488-12489 12491 12517 12528-12529 12531-12534 12781 12783 12796 12798 13136-13137 13140 13436-13438 13472-13473 13476-13477 13488 13493 13516 13524 13536 13580 13582 13588 13592 13600-13602 16556-16557 16560-16562 16564-16565 16608 16613 16633 16637 16772-16774 16776-16778 16792 16794 16804-16805 16808-16809 16812 16827 16831 16864-16865 16867 16946-16947 16949-16951 16956 16958 16971 16990-16991 17001 17010-17011 17020 17023 17064 17066 17073-17076 17078-17079 17084-17086 17098-17099 17101-17103 17107 17157 17159 17167 17184 17186-17187 18432 18434 18440 18447 18453-18455 18457-18459 18465 18467 20348-20350 20412-20414 20428-20430 20440 20448 20544-20546 20549-20550 20558 20560 20600 20602 20688 20690-20691 20702 20906 21248 21250 21256 21258 21408 21410 21434-21435 21765 21767 21773 21775 21817-21819 21895 21901 21903 21925 21936-21937 21939 21949 22369 22371 22380-22381 22383 22469 22471 22477 22788-22789 22791 22798 22832 22834 22837 22839 22982 22988 22990-22991 23012-23014 23032 23034 23228 23230-23231 23238 23268 23272-23273 23293 23376 23378-23379 23384 23404 23406 23464-23465 23468 23484-23486 23492 23494 23520 23522 23528 23901 23903 24668 24670-24671 24916 24924 24926 24948 24950 25601-25603 25612-25614 25632-25634 25636 25652 25654-25655 25672-25674 25698-25699 25728-25730 25733-25735 28532-28534 28536-28538 28596-28598 28600-28602 28612-28614 28616-28618 29968-29969 29979 30001 30004-30005 30049 30060-30061 30063 30161 30732 30734-30735 30756 30758-30759 30764 30766 30856 30858-30860 30862 30884 30886-30887 30898-30899 30901 30903 30909 30952-30953 30966-30967 30970-30971 31118-31119 31130-31131 31137-31139 31178 31218-31219 31222-31223 31310-31311 31882 31910-31911 31921-31923 31962-31963 31972 31974-31975 32160 32162-32163 32168-32170 32172 32174-32175 32186 32512 32514-32515 32517-32519 32532 32540 32542-32543 32577-32579 32582 32602-32603 32606-32607 32628 32630 32632-32634 32692-32694 32696-32698 32708-32710 32712-32714 33036-33037 33039-33042 33060 33063 33073-33074 33081-33083 33085-33087 33108 33111 33117-33119 33138-33139 33292 33305 33307 33329-33331 33800 33802-33803 36932 36934 36936 36938-36939 36968 36970-36971 37056 37058 37608-37610 38229 38231 38233-38235 38247 38251 38327 38337 38339 38345 38347 38611 38614-38615 38617 38619-38622 38675 38681 38683 38703 38789 38791 38821 38823 39008-39010 39023 39027 39030 39104 39106 39109 39111-39112 39114 39124 39126 39128-39129 39136 39138 39144 39146 39488 39490 39496 39626 39642 39648 39653-39656 39658-39659 39668 39670 39676 40195 40201 40203 40225 40233 40235 40329 40331 40364-40365 40367 40709-40711 40741 40743 40749 40837 40871 40877 40879 41008-41010 41012-41013 41016 41060-41061 41073 41076 41088 41090 41092 41096 41228-41230 41240-41241 41280-41282 41284-41285 42927 42939 42942-42943 42990-42991 43261 43263 43373-43375 43381-43383 43407 43415 43417-43419 43429-43431 43457-43459 43581-43583 43597 43599 43601-43603 43663 43683 44028-44030 44046-44047 44057-44059 44061-44063 44098-44099 44102-44103 44114-44115 44336-44338 44343 44360-44361 44363 44385-44387 44400 44404-44405 44407-44408 44410 44413 44712 45737 45739 46520 46522 46524-46525 46527 46572-46573 46575 46772 46776-46777 46792 46794 46800-46801 46804-46805 46807 46809-46811 46832-46833 46836-46838 46852 46862 46879 46922-46923 46925 46927 46929-46931 46940-46941 46944-46946 46952 46954-46955 47000-47001 47005 47008-47009 47011-47014 47044 47046 47048-47049 47051-47052 47073 47075 47081 47084-47085 47094-47095 47108-47109 47111 47115 47137 47148-47149 47151 47237 47239 47245 47281 47293 47295 47385-47387 47480 47485-47487 47516-47518 47544 47556 47560 47569 47571 47581 47637 47639 47704-47705 47707 47716-47717 47741 47876-47878 47912-47913 47949 47951 47954-47955 47964 47968-47969 48132 48134 48136-48137 48260 48262 48369-48372 48374 48380 48382 48413 48415 48437 48477 48480 48482-48483 48486 48492 48494 48511 48527 48565 48567 48573 48591 48595 48670-48671 48687 48736 48738 48765 48767 48773-48775 48780-48781 48788 48790 48792-48793 48797 48799 48821 48853 48864 48907 48910 48918-48919 48923 48941 48943 49029-49031 49036-49037 49039 49061 49063 49069 49071https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/709/A21?format=asciiOpticaldefaultJ/A+A/709/A21/ellipticGalaxy Zoo 1 Spiral galaxies that are also present in the Galaxy Zoo DECaLSrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIAUNameIAU designation of the galaxy (iauname)meta.id;meta.maincharRAJ2000Right ascension (J2000) of the galaxy (ra)degpos.eq.ra;meta.mainDEJ2000Declination (J2000) of the galaxy (dec)degpos.eq.dec;meta.mainaSemi-major axis of the object (a)pixphys.angSize.smajAxisdoublebSemi-minor axis of the object (b)pixphys.angSize.sminAxisdoublethetaPosition angle of the object (theta)radpos.posAngdoubleCConcentration index (C)meta.code;spect.indexdoubler20Radius containing 20% of the flux, from elliptical apertures (r20)arcsecphys.angSize;srcdoubler80Radius containing 80% of the flux, from elliptical apertures (r80)arcsecphys.angSize;srcdoubleNpixNumber of pixels in the segmentation mask (Npix_segmmask)meta.numberintA? Asymmetry index (A)meta.code;spect.indexdoublenullableS? Smoothness index (S)src.morph.paramdoublenullableM20? M20 index (M20)src.morph.paramdoublenullableE? Shannon entropy index (E)src.morph.paramdoublenullableGini? Gini index (Gini)src.morph.paramdoublenullableG2? Gradient pattern asymmetry index ( G2)src.morph.paramdoublenullableMainGalFlag[0] Flag set to 1 if no object is detected at the image center (maingalaxy_flag)meta.codeintrFlagPixRadius of the circular aperture used in flagging (1.5 Rp) (rflag_pixels)pixstat.fit.paramdoubleEdgeFlag[0/1] Flag set to 1 if zero- or NaN-valued pixels are present within the flagging area (edge_flag)meta.codeintNrcheckNumber of secondary objects within the flagging area (N_rcheck)meta.numberintNsecFlag[0/1] Flag set to 1 if more than 4 objects are found within the flagging area (Nsec_flag)meta.codeintNdeltaMAGNumber of objects with magnitude difference smaller than 1 (N_deltaMAG)meta.numberintminMagDiff? Magnitude difference to the brightest secondary object (minMAG_diff)magphot.mag;arith.diffdoublenullabledistminMagdiff? Distance to the brightest secondary object (dist_minMAG_diff)pixpos.angDistancedoublenullableBrightObjFlag[0/1] Flag set to 1 if a bright object is present within the flagging radius (BrightObj_flag)meta.codeintnDistClosest? Distance to the closest secondary object, normalized by Rp (normDist_closest)pos.distancedoublenullableStatus[0/2] Processing status flag (status) (1)meta.code.error;time.processingintErrCode[0] Error code indicating why processing failed (err_code)meta.codeintWarnMaskWarning bitmask encoding non-fatal processing issues (warn_mask) (2)meta.codeintJ/A+A/709/A21/spiralsGZ 1 Elliptical galaxies that are also present in the Galaxy Zoo DECaLSbSemi-minor axis of the object (b)pixphys.angSize.sminAxisdoubleS? Smoothness index (S)src.morph.paramdoublenullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIAUNameIAU designation of the galaxy (iauname)meta.id;meta.maincharRAJ2000Right ascension (J2000) of the galaxy (ra)degpos.eq.ra;meta.mainindexedDEJ2000Declination (J2000) of the galaxy (dec)degpos.eq.dec;meta.mainindexedaSemi-major axis of the object (a)pixphys.angSize.smajAxisdoublethetaPosition angle of the object (theta)radpos.posAngdoubleCConcentration index (C)meta.code;spect.indexdoubler20Radius containing 20% of the flux, from elliptical apertures (r20)arcsecphys.angSize;srcdoubler80Radius containing 80% of the flux, from elliptical apertures (r80)arcsecphys.angSize;srcdoubleNpixNumber of pixels in the segmentation mask (Npix_segmmask)meta.numberintA? Asymmetry index (A)meta.code;spect.indexdoublenullableM20? M20 index (M20)src.morph.paramdoublenullableE? Shannon entropy index (E)src.morph.paramdoublenullableGini? Gini index (Gini)src.morph.paramdoublenullableG2? Gradient pattern asymmetry index ( G2)src.morph.paramdoublenullableMainGalFlag[0] Flag set to 1 if no object is detected at the image center (maingalaxy_flag)meta.codeintrFlagPixRadius of the circular aperture used in flagging (1.5 Rp) (rflag_pixels)pixstat.fit.paramdoubleEdgeFlag[0/1] Flag set to 1 if zero- or NaN-valued pixels are present within the flagging area (edge_flag)meta.codeintNrcheckNumber of secondary objects within the flagging area (N_rcheck)meta.numberintNsecFlag[0/1] Flag set to 1 if more than 4 objects are found within the flagging area (Nsec_flag)meta.codeintNdeltaMAGNumber of objects with magnitude difference smaller than 1 (N_deltaMAG)meta.numberintminMagDiff? Magnitude difference to the brightest secondary object (minMAG_diff)magphot.mag;arith.diffdoublenullabledistminMagdiff? Distance to the brightest secondary object (dist_minMAG_diff)pixpos.angDistancedoublenullableBrightObjFlag[0/1] Flag set to 1 if a bright object is present within the flagging radius (BrightObj_flag)meta.codeintnDistClosest? Distance to the closest secondary object, normalized by Rp (normDist_closest)pos.distancedoublenullableStatus[0/2] Processing status flag (status) (1)meta.code.error;time.processingintErrCode[0] Error code indicating why processing failed (err_code)meta.codeintWarnMaskWarning bitmask encoding non-fatal processing issues (warn_mask) (2)meta.codeintJ/A+A/709/A21/full1.7 million galaxies from the Legacy Surveyr20? Radius containing 20% of the flux, from elliptical apertures (r20)arcsecphys.angSize;srcdoublenullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000? Right ascension (J2000) of the galaxy (ra)degpos.eq.ra;meta.mainnullableindexedDEJ2000? Declination (J2000) of the galaxy (dec)degpos.eq.dec;meta.mainnullableindexeda? Semi-major axis of the object (a)pixphys.angSize.smajAxisdoublenullableb? Semi-minor axis of the object (b)pixphys.angSize.sminAxisdoublenullabletheta? Position angle of the object (theta)radpos.posAngdoublenullableC? Concentration index (C)meta.code;spect.indexdoublenullabler80? Radius containing 80% of the flux, from elliptical apertures (r80)arcsecphys.angSize;srcdoublenullableNpix? Number of pixels in the segmentation mask (Npix_segmmask)meta.numberintnullableA? Asymmetry index (A)meta.code;spect.indexdoublenullableS? Smoothness index (S)src.morph.paramdoublenullableM20? M20 index (M20)src.morph.paramdoublenullableE? Shannon entropy index (E)src.morph.paramdoublenullableGini? Gini index (Gini)src.morph.paramdoublenullableG2? Gradient pattern asymmetry index ( G2)src.morph.paramdoublenullableMainGalFlag[0]? Flag set to 1 if no object is detected at the image center (maingalaxy_flag)meta.codeintnullablerFlagPix? Radius of the circular aperture used in flagging (1.5 Rp) (rflag_pixels)pixstat.fit.paramdoublenullableEdgeFlag[0/1]? Flag set to 1 if zero- or NaN-valued pixels are present within the flagging area (edge_flag)meta.codeintnullableNrcheck? Number of secondary objects within the flagging area (N_rcheck)meta.numberintnullableNsecFlag[0/1]? Flag set to 1 if more than 4 objects are found within the flagging area (Nsec_flag)meta.codeintnullableNdeltaMAG? Number of objects with magnitude difference smaller than 1 (N_deltaMAG)meta.numberintnullableminMagDiff? Magnitude difference to the brightest secondary object (minMAG_diff)magphot.mag;arith.diffdoublenullabledistminMagdiff? Distance to the brightest secondary object (dist_minMAG_diff)pixpos.angDistancedoublenullableBrightObjFlag[0/1]? Flag set to 1 if a bright object is present within the flagging radius (BrightObj_flag)meta.codeintnullablenDistClosest? Distance to the closest secondary object, normalized by Rp (normDist_closest)pos.distancedoublenullableStatus[0/2]? Processing status flag (status) (1)meta.code.error;time.processingintnullableErrCode? Error code indicating why processing failed (err_code)meta.codeintnullableWarnMask? Warning bitmask encoding non-fatal processing issues (warn_mask) (2)meta.codeintnullable