See also the PASP paper Near-Infrared Galaxy Morphology Atlas for analysis and postscript figures

See also the classic 1959 paper by De Vaucouleurs on Galaxy Classification and Morphology that set the standard for decades to come. The PASP paper Near-Infrared Galaxy Morphology Atlas presents a full statistical analysis of the atlas.

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Ellipticals
Spirals : Lenticulars normal normal/barred barred
Dwarfs Compact
Peculiar AGN
Composite
Notes

Spirals Generic Spirals (spiral classification tentative) page 1: 9.7 < Ks < 10.7 page 2: 10.8 < Ks < 11.1 page 3: 11.1 < Ks < 11.4 page 4: 11.4 < Ks < 11.6 page 5: 11.6 < Ks < 11.8 page 6: 11.8 < Ks < 12.0 page 7: 12.0 < Ks < 12.1 page 8: 12.1 < Ks < 12.3 page 9: 12.3 < Ks < 12.4 page 10: 12.4 < Ks < 12.6

NGC 3363: 2MASX 1045094+220441

Elliptical - Spiral Transition

S0/SA0 (lenticulars) page 1: 7.8 < Ks < 10.2 page 2: 10.2 < Ks < 10.7 page 3: 10.7 < Ks < 11.2 page 4: 11.2 < Ks < 11.6 page 5: 11.6 < Ks < 12.1 page 6: 12.1 < Ks < 12.5 page 7: 12.5 < Ks < 13.2 page 8: 13.2 < Ks < 14.2

NGC 5010: 2MASX 1312263-154752

Normal Spirals

Sa/SAa page 1: 5.6 < Ks < 10.5 page 2: 10.5 < Ks < 11.2 page 3: 11.2 < Ks < 11.6 page 4: 10.0 < Ks < 12.2 page 5: 12.2 < Ks < 12.9 page 6: 12.9 < Ks < 14.5

NGC 4868: 2MASX 1259089+371837

SAb/Sb page 1: 6.8 < Ks < 10.4 page 2: 10.4 < Ks < 11.1 page 3: 11.1 < Ks < 11.5 page 4: 11.5 < Ks < 11.8 page 5: 11.8 < Ks < 12.1 page 6: 12.1 < Ks < 12.4 page 7: 12.4 < Ks < 12.7 page 8: 12.7 < Ks < 13.8

UGC 06680: 2MASX 1143021+193859

SAc/Sc/Sd (late-type spiral) page 1: 7.1 < Ks < 11.2 page 2: 11.2 < Ks < 11.7 page 3: 11.7 < Ks < 12.1 page 4: 12.1 < Ks < 12.4 page 5: 12.4 < Ks < 12.8 page 6: 12.8 < Ks < 13.1 page 7: 13.1 < Ks < 13.4 page 8: 13.4 < Ks < 13.9

NGC 3140: 2MASX 1009278-163741

Sd only (extreme late-type spiral) page 1: 10.4 < Ks < 13.1 page 2: 13.4 < Ks < 14.3 page 3: 14.3 < Ks < 15.3

UGC 08702: 2MASX 1345272+475522

Normal - Barred Transition Spirals

SABa (normal/barred, early-type) page 1: 6.7 < Ks < 11.4 page 2: 11.4 < Ks < 13.3

NGC 3788: 2MASX 1139445+315552

SABb (normal/barred, intermediate-type) page 1: 6.5 < Ks < 11.5 page 2: 11.5 < Ks < 13.2

NGC 4017: 2MASX 1158456+272709

SABc/SABcd (normal/barred, late-type) page 1: 8.1 < Ks < 12.3 page 2: 12.5 < Ks < 14.3

NGC 5595: 2MASX 1424133-164322



Barred Spirals

SB0/SBa (barred early-type spiral) page 1: 7.1 < Ks < 10.0 page 2: 10.0 < Ks < 10.6 page 3: 10.6 < Ks < 11.4 page 4: 11.4 < Ks < 12.0 page 5: 12.0 < Ks < 12.5 page 6: 12.5 < Ks < 14.6

NGC 5915: 2MASX 1521330-130530

SBb (barred intermediate-type spiral) page 1: 7.8 < Ks < 10.8 page 2: 10.8 < Ks < 11.8 page 3: 11.8 < Ks < 13.3 page 4: 13.3 < Ks < 14.0

NGC 3110: 2MASX 1004019-062829

SBc/SBd (barred late-type spiral) page 1: 8.0 < Ks < 11.3 page 2: 11.3 < Ks < 12.6 page 3: 12.6 < Ks < 15.0 page 4: 15.0 < Ks

NGC 5260: 2MASX 1340199-235129

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Ellipticals/Spheroidals Generic Elliptical page 1: 6.9 < Ks < 10.4 page 2: 10.4 < Ks < 11.2 page 3: 11.2 < Ks < 11.5 page 4: 11.5 < Ks < 12.1 page 5: 12.1 < Ks < 12.5 page 6: 12.5 < Ks < 13.2 page 7: 13.2 < Ks < 14.0 page 8: 14.0 < Ks < 15

NGC 5223: 2MASX 1334251+344125

E0 page 1: 7.4 < Ks < 14.2

NGC 4283 : 2MASX 1220207+291839

E1 page 1: 6.5 < Ks < 14.2

NGC 4687 : 2MASX 1247237+352107

E2 page 1: 7.7 < Ks < 14.3

NGC 5354 : 2MASX 1353267+401809

E3 page 1: 7.8 < Ks < 14.0 page 2: 14.0 < Ks < 14.4

NGC 3158 : 2MASX 101350+384553

E4 page 1: 6.9 < Ks < 14.5

NGC 3605: 2MASX 1116466+180101

E5 page 1: 7.9 < Ks < 14.3

NPM1G+32.0347: 2MASX 1325026+323310

E6 page 1: 6.7 < Ks < 14.6

NGC 5028: 2MASX 131458-130232

E7 page 1: 11.7 < Ks < 14.4

NGP9F270-14581: 2MASX 1325151+324016

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Dwarf Ellipticals/Spheroidals/Spirals page 1: 10.9 < Ks < 13.4 page 2: 13.4 < Ks < 15

NGC 3101: 2MASX 1217196+115636

Compact and BCD page 1: 10.9 < Ks < 12.6 page 2: 12.6 < Ks < 13.1 page 3: 13.1 < Ks < 13.7 page 4: 13.7 < Ks < 14.1 page 5: 14.1 < Ks < 15

IC 3017: 2MASX 1209249+133429

IRR/IM/Sm/Pec page 1: 8.6 < Ks < 12.3 page 2: 12.3 < Ks < 13.7 page 3: 13.7 < Ks < 15.1 page 4: Ks > 15

NGC 4004: 2MASX 158051+275243

AGN/Seyferts/LINERS page 1: 10.1 < Ks < 12.6 page 2: 12.6 < Ks < 13.5 page 3: 13.5 < Ks < 14.4

MRK 0463E: 2MASX 1356028+182218

2MASS extended sources (e.g., galaxies) are identified and characterized with a "pipeline" software package called GALWORKS. An overview and description of the algorithms can be found at 2MASS Extended Source Catalog. For a more general overview of the 2MASS pipeline reduction and resultant data products, see the Explanatory Supplement to the 2MASS Spring 1999 Incremental Data Release.

Fits Data Cube

Each extended source in the 2MASS database includes a small image data cube, representing the J, H and Ks "postage stamp" images (planes 1,2 and 3, respectively), derived from the full resolution Atlas images. The size of the cube is dynamically selected, scaled according to the measureed "size" of the extended source (see below), with minima/maxima of 21 and 101 pixels (each pixel is 1 arcsec in width). The variable image size was needed for purely practical reasons (limited disk storage). For the largest galaxies (typically Ks < 9th mag) the image size is not large enough and the outer parts of the galaxy are clipped off. Note that the 2MASS survery is *not* complete for galaxies larger than ~1' in width (the reason is that the overlap between "scans" is ~50"; hence galaxies falling near a scan edge will be clipped and may not be extracted, depending on the severity of the flux loss).

The jpeg images show a 3-color "rgb"=="JHK_s" representation for each galaxy, overlayed with J-band contours. The contours start with the intensity level equal to 3*sigma (thrice the background sky noise) or (if larger) the level equal to 5% of the J-band peak. Each successive contour is multiplied by a factor of two (i.e., 20%, 30%,...).

The images were "color stretched" generated using the following recipe. We would like to differentiate the true color of the galaxy. Hence, we stretch the color scale relative to the color of a "normal" galaxy, which turns out to be J-K = 1.0 and H-K = 0.28 (plus or minus 10-20%). We first get the K_s peak of the galaxy (and convert it to a mJy flux unit). We then deduce the J and H peaks using the color of a "normal" galaxy (again, we have converted the mags to a calibrated flux unit). The J,H K_s flux peak represents the upper color-stretch limit. The lower limit is chosen as follows: take -7.5% of the peak; here put a floor on the respective peaks of 5 dn ("data number", representing the raw uncalibrared pixel value) -- this is needed for the low surface brightness galaxies.

We assigned the "blue" intensity scale to the J-band image; "green" to the H-band image, and "red" to the K_s image. The resultant color-stretch will allow sufficient contrast between the galaxy core and the low surface brightness emission in the disks. Normal galaxies (J-K ~1) will appear to the eye as white or yellowish in appearance. Red galaxies (J-K > 1.2) will appear to the eye as "reddish". Blue galaxies (J-K < 1; late-type spirals may have this color) will appear blue or greenish. For faint sources (or alternatively, LSB galaxies), the background noise becomes appreciable (compared to the galaxy flux) and the contrast between the cores and background is greatly increased (the background is brighter with the ubiquitous H-band airglow more apparent).

A figure caption is included with the jpegs: NED name, morphological type, size of image (arcsec), 2MASS name, K_s mag and J-K_s color. The 2MASS name maps into the equatorial position of the source (hhmmsss+-ddmmss).

Galaxy Size and Photometry

The galaxy K_s flux and J-K_s color shown in the jpeg images correspond to the "K-band fiducial" 20 mag/arcsec² elliptical isophotal photometry. Here the elliptical orientation (position angle and ellipticity) of the galaxy is determined from the K_s image (at roughly the isophote corresponding to 3 times the background RMS "noise"). The radius, or semi-major axis, is derived from the K_s 20 mag/arcsec² elliptical isophote (which is approximately equal to 1 times the background RMS "noise"). It is this "radius" that represents the size of the galaxy. The JHK_s photometry is then performed in an aperture given by the K_s position angle and ellipticity (derived from the 3-sigma isophote) and the semi-major axis (derived from ~1-sigma isophote); hence the term "K_s fiducial", allowing comparison between bands and color computations.

Caveats and Known Problems