Faint Field Galaxy Surveys

Matthew A. Bershady


Spectral Classification of Galaxies

bk type
Galaxies can be classified by their spectral energy distributions (SEDs) instead of by their apparent morphology. For many applications, particularly for studying distant galaxies (e.g. evolution and cosmology), a spectral classification is desirable. Spectral classification is possible even using broad-band photometry because of the distinct curvature in the continuum of galaxy SEDs.

A simple, but physical classification scheme can be derived in terms of the principle stellar types that contributes to a galaxy's SED. It turns out that only two stellar types are needed for a given galaxy, and the specific combination varies from galaxy to galaxy in a well-defined way. Representing the classical MK stellar types with lower case letters a, b, f, g, k, m, the spectral classification of galaxies consists only of pairs bk, bm, am, fm, gm.

Examples of these different spectral types are illustrated here (above for bk-type, and to the left for bm- through gm-type) as selected from a survey of galaxies at intermediate redshift. Galaxies are sorted in redshift in each panel, and range from 0.01-0.35. For each galaxy, there are two panels: (Left) B band image; (Right) K band image. Notice the large range in apparent morphological types in a given spectral class, as well as the significant overlap in types between classes.

Several papers discuss the data, analysis, and further analysis of color-luminosity relations, as cited below and under Recent publications. The data used for this classification analysis is publically available under Personal data and software archive.

The Optical and Near-Infared Colors of Galaxies. I. The Photometric Data, Bershady, M. A., Hereld, M., Kron, R. G., Koo, D. C., Munn, J. A., Majewski, S. R. 1994, AJ, 108, 870

The Optical and Near-Infared Colors of Galaxies. II. Spectral Classification, Bershady, M. A. 1995, AJ, 109, 87

Spectral Classification, Morphology, and Detection of Distant Galaxies, Bershady, M. A. 1993, PASP, 105, 1028

Spectral Classification of Galaxies: An Orthogonal Approach Connolly, A. J., Szalay, A. S., Bershady, M. A., Kinney, A. L., Calzetti, D. 1995, AJ, 110, 1071

Galaxy Form and Spectral-Type: A Physical Framework for Measuring Evolution, Bershady, M. A. 1999, Ap&SS, 269, 183 (reprint: [UW Preprint] [astro-ph/9910037])

bm type

am type
fm type

gm type

Deep Optical and Near-Infrared Imaging Program Highlights

Near-Infrared Galaxy Counts to J and K ~ 24 as a Function of Image Size, Bershady, M. A., Lowenthal, J., Koo, D. C. 1998, ApJ, 550, 50 (reprint: [high resolution] [astro-ph/9804093])

Deep, Near-Infrared Imaging with the Keck Telescope, Bershady, M.A. 1995, in "Galaxies in the Young Universe", eds. H. Hippelein, K. Meisenheimer, H.-J. Roser (Springer, Lecture Notes in Physics), p. 125 [reprint]

H-alpha Imaging with HST + NICMOS of an Elusive Damped Ly-alpha Cloud at z = 0.6, Bouche, N., Lowenthal, J.D., Charlton, J.C., Bershady, M.A., Churchill, C.W., Steidel, C.C. 2001, ApJ, 550, 585 (reprint: [astro-ph/0011374])

The Unusual Infrared Object HDF-N J123656.3+621322, Mark Dickinson, Christopher Hanley, Richard Elston, Peter R. Eisenhardt, S. A. Stanford, Kurt L. Adelberger, Alice Shapley, Charles C. Steidel, Casey Papovich, Alexander S. Szalay, Matthew A. Bershady, Christopher J. Conselice, Henry C. Ferguson, Andrew S. Fruchter, 2000, ApJ, 531, 2645 (reprint: [astro-ph/9908083])

The Distribution of High Redshift Galaxy Colors: Line of Sight Variations in Neutral Hydrogen Absorption, Bershady, M. A., Charlton, J. C., Geoffroy, J. M. 1999, ApJ, 518, 103 (reprint: [UW Preprint)] [(astro-ph/9901197])

   The Luminosity Function for L > L* Galaxies at z > 3, Bershady, M. A., Majewski, S. R., Koo, D. C., Kron, R. G., Munn, J. A. 1997, ApJ Letters , 490, L41 [astro-ph/9709216 preprint] [reprint]

Deep U B V R I Photometric Calibration of High Latitude Fields: SA 57 (1307+30) and Hercules (1720+50), Majewski, S. R., Kron, R. G., Koo, D. C., Bershady, M. A. 1994, PASP, 108, 1258

last updated: Nov 20, 2001 (mab@astro.wisc.edu)