Galaxies - Basic Catalogs and Data Collections
From my (biased?) observer's point of view, data on galaxies is
where we must start in understanding them. With electronic collections,
getting the numbers is easier than ever before. However, it still
helps to know where the numbers come from, and what the initial
selection of various catalogs was. In particular, just how a catalog
sample was compiled may have a great influence on what one can learn
Surface-brightness and flux selection criteria are especially important
in this regard. Furthermore, there is a big difference between an
and a catalog including uniform physical data for each entry.
To catalog something, we must (1) see that an object is there and (2)
see that it is not something else. For galaxies, we must detect them at
some wavelength and distinguish them from stars, planetary nebulae,
galactic cirrus, and navigation satellites. Most surveys to this point
have been done in the optical, by and large from examination of
photographic plates. This implies certain detection limits:
(1) Anything less than about 1 arcsecond in size looks like a star on
normal ground-based images, and can be distinguished only by nonstellar
colors or spectrum (QSOs, compact galaxies; this worked fine for the
SDSS, for example). HST imagery shows
that there are lots of faint galaxies
at high redshift which could masquerade as faint stars from the ground
(in practice this enters only for magnitudes fainter than V=20).
(2) Any object with surface brightness too low (much less than about 1%
of the night-sky brightness) would only be found when near enough for
individual stars to be seen (this is how the Sculptor dwarf galaxy was
Surface brightness (received flux per unit solid angle) is often
measured in the definitely non-SI units of magnitude per square
for optical and near-IR passbands; one also encounters MJy/steradian,
S(10) (the light of a V=10 star per square degree), and very
the SI unit of a nit (candela per square meter). Major components in
the optical are airglow (much in isolated atomic and molecular emission
and scattered starlight from Solar System dust (zodiaal light) and
interstellar dust. From a dark site, the dust/airglow contributions
are about equal in the V band. In the near-IR, airglow molecular
OH bands, the "OH forest") become extremely bright; gains of many
sensitivity are possible by going to space. Details on typial
sky brightnesses may be found in
Leinert et al. 1998 (A&ASuppl 127, 1),
Representative dark-sky values in magnitudes per square arcsecond are
in the B band and 21.5-22.0 in V. About a factor of 2 variation occurs
the solar cycle, with airglow faintest at sunspot minimum. Arp took
advantage of this for many of his peculiar-galaxy photographs.
These limits translate to biases on the kinds of galaxies found by a
particular technique; see the discussion in Mihalas and Binney (p. 371)
on the detection problem and The Light of the Night Sky by
Roach and Gordon (Reidel, 1973)
for discussion of sources of confusing light (airglow, scattered
sunlight and starlight, and unresolved galaxy light). Disney (1976,
Nature 263, 573) described a visibility function for galaxies
incorporating these quantities.
Arp noted this problem in the Atlas of
Peculiar Galaxies, and the issue
is discussed at some length by Mihalas and Binney (their fig. 5-47, p.
The plot below was made from the 1036 galaxies in the RC2 with known
integrated B magnitude, redshift, and characteristic diameter D25,
using the same reference lines for surface-brightness limits as were
adopted by Mihalas and Binney.
The upper dashed line indicates where confusion with foreground
Galactic stars sets in (depending on the image quality; HST compact
galaxies occur with effective diameter
of order 2 kpc and B up to -21 or so). The lower limit is
where most of a galaxy falls below the surface-brightness threshold
set by the night-sky brightness (usually a few percent of the sky
Objects have now been found outside these limits. Compact objects
cannot escape detection in complete spectroscopic studies of faint
samples, while low-surface-brightness (LSB) objects require very deep
imaging studies. Numerous LSB dwarfs are known, and the census is not
regarded as complete even within the Local Group. Photographic
amplification techniques have led to the discovery of LSB giant
galaxies (Bothun et al. 1987 AJ 94,23; Impey and Bothun 1989 ApJ 341,
89; Bothun et al. 1990 ApJ 360, 427).
These systems are very luminous but so large as to have escaped
previous detection. It is quite fair to question how far our
understanding of galaxy formation and evolution is influenced by
selection effects in what we consider typical galaxy properties to be.
Zwicky used his "morphological
approach" to ask what kinds of galaxies might exist, on the
premise that all physical objects not prohibited from existing
must be out there, and positing not only dwarf and compact galaxies,
but pygmy and gnome objects as well. Others have referred to this
procedure as dividing parameter space into Zwicky boxes and ruling out
the ones that
violate physical law.
The giant LSB galaxies are well represented by Malin 1, an object
hiding behind the Virgo Cluster. These images are from a single
B-band image provided by Greg Bothun, first with a typical intensity
mapping and then with a high-contrast stretch about the sky level.
The faint galaxy disk almost fills the frame, but at more usual
thresholds it appears to be a much smaller and fainter system.
At the other end of the scale, QSOs furnish a test of our ability to
find unresolved extragalactic objects (without necessarily suggesting
they are the only kinds of compact extragalactic objects). The first
discoveries were as identifications of radio sources (3C 48, 3C 273),
with Zwicky compact galaxies not far behind. The most productive
optical search techniques for
these are multicolor surveys (looking in some n-dimensional
space for things that fall off the sequence defined by galactic stars)
or slitless spectroscopy, in which emission lines or peculiar continuum
shapes may be identified wholesale. X-ray source identifications may be
the most fruitful of all, especially since large-area deep surveys are
in hand. (For examples
of multiwavelength ID, see the extensive
compendium of quasar
candidates put together by a New Zealand amateur!)
Space observations (or those with adaptive optics) help most for
angularly small objects (HST resolves numerous compact galaxies that
look stellar from the ground). The background at V is not much darker
from Earth orbit than from a dark ground site, since half the sky light
comes from sunlight or other starlight scattered by zodiacal or
interstellar grains. The situation improves dramatically either into
the UV or the far red.
Searches for some subclasses of galaxies can be more efficient,
approaching the flux-limited ideal. This includes, for example,
infrared- or radio-bright galaxies. In these instances, confusion with
galactic objects (i.e. stars) is minimized, so that high spatial
resolution is not required to recognize galaxies and they may be
identified with rather coarse beams, provided the galaxies have high
enough integrated fluxes at the relevant frequency. Large beam sizes
reduce the risk of losing objects due to
limited surface-brightness sensitivity.
A basic question arises at this point - just what is a
galaxy? For theorists of galaxy formation, it is a collapsing
high-density region of gas. For observers, we might require that the
gas at some time formed some stars -
but then what about the few intergalactic H I clouds? When do they
cease being protogalaxies and become gas-rich dwarfs? Does a lump of
material torn out of a spiral during a tidal encounter deserve the
name? Is it then newly formed? Kinematics suggest that a galaxy is
collected in a dark-matter
potential well, while even the biggest star clusters are not - that is,
globular clusters have no dark-matter problem, while essentially all
galaxies do (even if they're no brighter than an individual globular
Thought experiment: In our night sky (with skyglow and looking no
fainter than, say, 19th visual magnitude) stars are much more prominent
than galaxies. Why is this, and what would we have to change to reverse
Optical surveys that are complete within any sort of useful limits
were long based on Schmidt sky-survey plates - from the Palomar, ESO,
or UK Schmidts. Such surveys include the UGC, MCG, and ESO/Uppsala
catalogs (see reference list) - but most of the 107 or so
galaxies on these plates are too faint to be of more than statistical
interest. These surveys are based on visual inspection, so that optical
catalogs now lag behind radio and IR surveys. There has long been a
crying need for a digital optical sky survey,
filled to an important extent by the Sloan
Digital Sky Survey (SDSS).
Optical surveys are sensitive to the intermediate-temperature stellar
component exemplified by older main-sequence stars (like the Sun,
which is not exactly a coincidence) and K-type red giants. The old
populations, and dusty ones, are well sampled by near-IR surveys,
of which 2MASS has now surveyed the whole sky with modest
I describe first the specific catalogs
containing most well-studied galaxies and active nuclei, then
point to useful (mostly electronic, by now) compendia that every
working on galaxies should have in their bookmark list.
Basic Object Catalogs
NGC = New General Catalog. Includes star clusters,
galaxies, gaseous nebulae, and hallucinations, mostly from the visual
surveys by the Herschels. Produced by J. Dreyer in the 1880s. The
modern version is the Revised New General Catalog of Nonstellar
Astronomical Objects, Sulentic and Tifft, Univ. Arizona 1973. The
entries are ordered by right
ascension at epoch 1855, which makes things somewhat confusing in
coordinates (especially when there are large declination jumps between
version at the CDS)
IC = Index Catalog, supplement to the above, with another 7000+
NGC 2000 compilation includes both NGC and IC lists.
3C = Third Cambridge Catalog of radio sources selected at 178
MHz. Optical identifications of extragalactic sources are given by
Spinrad, Djorgovski, and Aguilar 1985 PASP 97, 932. (
CDS electronic version)
Reference Catalog of Bright Galaxies, G. and A. de Vaucouleurs, U.
Texas, Austin 1964. Includes literature citations and descriptions of
individual structures. Although superseded by the RC2 and RC3,
are still available.
Second Reference Catalog of Bright Galaxies (RC2), de Vaucouleurs,
de Vaucouleurs, and Corwin, U. Texas, Austin 1976. Much updated
redshifts, magnitudes, and classifications. Long the basic reference.
Third Reference Catalog of Bright Galaxies (RC3), de Vaucouleurs
et al., Springer 1991.
Beyond belief, best approached on disk. Three volumes on paper.
Comparing the three RC versions gives some sense of how much data
collection has accelerated in the last three decades.
of the revised edition. The mix of different kinds
of designations, plus the disorder among NGC and IC systems produced
by precession since their original epochs, makes finding a given
object by name interesting. On Unix systems, grep is your
Revised Shapley-Ames Catalog of Bright Galaxies (RSA), A. Sandage
and G. Tammann, Carnegie Inst. of Washington 1981. Complete data for
1300 galaxies brighter than B=13.2, with a selection of photographs
illustrating Sandage's version of the Hubble system.
Uppsala General Catalog of Galaxies (UGC), P. Nilsson, 1973,
Uppsala Obs. Publ. 12942 galaxies larger than 1 arcminute in diameter
from a full examination of the Palomar Sky Survey. Covers the sky north
ESO/Uppsala Survey of the ESO(B) Atlas, Lauberts 1982 , ESO
Garching. Galaxies, nebulae, and star clusters south of -17°, from
examination of the ESO Quick Blue Survey. Classifications compatible
with the UGC.
Lauberts and Valentijn (ESO, 1989) did densitometry of the plates for
galaxies, producing an extensive photometric catalog including shape
and orientation parameters.
Morphological Catalog of Galaxies (Morfologicheskii Katalog
Galaktik, lacking a good Cyrillic font)}, Vorontsov-Velyaminov and
coworkers, 4 vol., Shternberg State Astronomical Institute, Moscow.
Objects north of -33° from PSS. Uses VV's own system of
classification, sometimes wonderfully descriptive but not easy to mesh
with standard Hubble types. Strictly keyed to PSS fields - no running
numbers, so a typical name is MCG 8-11-11 (leading minus signs are
for example, MCG 8-11-11 and MCG -8-11-11 are both Seyfert galaxies, a
wonderful chance for total confusion). The VV designations have never
been very popular with Western astronomers, in part because the
designations could hardly have been designed
to be less friendly for ASCII coding and
searching, and because the lack of a single running designation
made them unnecessarily difficult for early digital work.
A fifth volume of the MCG covers southern galaxies to declination
-58° from the PSS red-light extension, changing the magnitude
version does not include the original set of nontypographical
symbols used for some of the classifications, and splits
Volume 5 as separate files.
Catalog of Galaxies and Clusters of Galaxies, Zwicky and
coworkers. Yet another examination of the PSS, with emphasis on groups
and clusters. These are the blue books, in six volumes. The
includes data on individual galaxies.
Catalog of Selected Compact Galaxies and of Post-Eruptive
Zwicky 1971, Speich, Zürich. The red book; a real zoo of normal
galaxies, interacting systems, Seyferts, compact dwarfs,... The
introduction is amusing, and might be considered libellous today. Watch
for "scatter-brained", "appalling naivety of the theoreticians",
"high pope of American Astronomy", and "autistic interpretations".
This is finally
in electronic form.
Pictures of galaxies:
Hubble Atlas of Galaxies, Sandage 1961, Carnegie Inst. of
Washington. Basic reference for the Hubble classification scheme.
Atlas of Peculiar Galaxies, Arp 1966, Caltech, Pasadena (also in
reduced size in ApJSuppl 14,1). Picked for bizarre appearance -
interacting systems, plumes, dust lanes, twisted arms. Very deep
images of high quality are available from NED. The photographic
plates for the Atlas and the care of their preparation for publication
represented a high point in the photography of galaxies.
Atlas and Catalog of Interacting Galaxies (Atlas i katalog
vzaimodeistvuyuschikh galaktik), Vorontsov-Velyaminov, Shternberg
Institute (1959, part 1) and A& A Suppl 28,1 (1977, part 2). 355
and 500 systems, respectively, identified by sequential VV numbers.
More extensive than the Arp atlas, illustrated from the PSS, includes
many probably non-interacting systems such as clumpy irregular
galaxies. Very idiosyncratic arrangement and interpretation. Once
again, NED level 5 provides a
A Catalog of Selected Southern Peculiar Galaxies and Associations,
Arp and Madore, Cambridge 1987 (2 vol.). From a complete search of the
SERC(J) plates, with accurate positions. Vol. 2 contains nice photos
from the Schmidt plates of a large, representative sample of these.
This one also exists in
and scanned form at NED.
Atlas of Galaxies Useful for Measuring the Cosmological Distance
Scale, Sandage and Bedke, NASA SP-496 (1988). The book big enough to be
your coffee table. Mostly designed to show partial resolution into
stars for HST planning, but has large-scale images of lots of nearby
galaxies and allows an excellent impression of Sandage's classification
High-quality photographs of many Virgo galaxies appeared in Sandage
and Bedke 1985 AJ 90,1992; 90,2001; and 90,2006. Dwarf
members were illustrated in Sandage and Binggeli 1984 AJ 89, 919, and
spiral luminosity classes were covered by Sandage, Binggeli, and
Tammann 1985 AJ 90, 395.
Atlas de Galaxias Australes, Sersic 1967, Obs. Astronomico,
Cordoba, Argentina. Before the southern Schmidt surveys, these were the
usable photographs of many southern galaxies.
Galaxies, Ferris 1982, Sierra Club Books. Gorgeous photos, enough
to make people understand why galaxies are so fascinating.
Carnegie Atlas of Galaxies, A. Sandage and J. Bedke (1994, Carnegie
Inst. of Washington). Two immense volumes, virtually all galaxies in
the Revised Shapley-Ames catalog from large-scale photographs taken at
Palomar, Mt. Wilson, or Las Campanas. The biggest printed collection
(1168 galaxies) available to refine your classification talents.
de Vaucouleurs Atlas of Galaxies, collected by Buta, Corwin, and
Odewahn, Cambridge (any time now).
See the bright-galaxy compendia, plus these specific collections:
Huchra, Davis, Latham and Tonry 1983, ApJSuppl 52, 89. First part
of the CfA survey, 2401 Zwicky and UGC galaxies brighter than MZw=14.5.
Gisler and Friel, Index of Galaxy Spectra, 1979 Pachart,
Tucson. 2004 galaxies, surveys previously published data.
Palumbo, Tanzella-Nitti, and Vettolani, Catalog of Radial
Velocities of Galaxies, 1983, Gordon and Breach. 8250 galaxies from
Many sources from the NSSDC (and NED, if you can tell which
value is listed) are useful for current redshift-survey results, which
have passed the 1.5-million-galaxy mark, rising so fast that electronic
retrieval is the only way to keep up. The
Sloan Digital Sky Survey (SDSS) alone yielded 106 galaxy
in the northern galactic cap, and the AAT 2dF
survey delivered more than 220,000 in two southern fields.
Active Galactic Nuclei:
Handbook of Quasistellar and BL Lacertae Objects, E.R.
Craine 1977, Pachart, Tucson. Finding charts, fluxes, positions,
less necessary now than it was before the Web.
A Revised and Updated Catalog of Quasi-Stellar Objects,
Hewitt and Burbidge 1993, APJSuppl 87, 451. Basic data and citations
for 7225 QSOs and 90 BL Lac objects.
Optical Catalog of Radio Galaxies, Burbidge and Crowne 1979,
APJSuppl 40, 583. Similar data for radio galaxies.
Catalogue of Quasars and Active Nuclei, Veron-Cetty and Veron, 12th
Astron. Astrophys. (in press?), 2006. Also (and mosgt usefully)
Basic positional, flux, and type information for 85221 QSOs, 21737
nuclei, and 1122 BL Lac objects. Some of the low-level AGN
classifications at least
in the early editions were fantasy - if it was ever called so by
anyone, it will appear here. Did you know that the Andromeda Galaxy is
a Seyfert 2? QSOs are now being identified at a huge rate, especially
from followup of the FIRST radio survey and ROSAT all-sky survey in
soft X-rays, plus new optical multicolor work such as the Hamburg
Earlier catalogs do not appear to have been as complete as we thought.
Catalogue of Seyfert Galaxies and Related Objects, Kaneko 1986,
Hokkaido Univ., Sapporo. 560 objects; similarly loose definition of
A Catalogue of Seyfert Galaxies, Lipovetskii, Neizvestnii, and
Neizvestnaya, Publ. Special Astrophys. Obs. (USSR) vol. 55, 1987.
Includes 959 objects, with emission-line, IR, and radio fluxes, plus
morphological data on host galaxies.
An Optical Catalogue of Extragalactic Emission-Line Objects Similar
to Quasi-Stellar Objects, Hewitt and Burbidge ApJSuppl 75, 297 (1991).
Contorted way of saying Seyfert galaxies. 935 entries.
Handbook of Radio Sources, part 1, Pacholczyk 1978, Pachart,
Tucson. Selected extragalactic radio sources from 0-12 hours, with
maps, fluxes, and references. This was pre-VLA; still waiting for part
Palomar-Green Bright Quasar Survey: Schmidt and Green 1983, ApJ
269, 352 and Green, Schmidt, and Liebert 1986 ApJSuppl 61, 305. A
complete search for UV-excess objects brighter than B=16 in the
northern sky, with complete confirming spectroscopy. These objects have
very extensive further work (UV, X-ray, radio, variability, line
profiles) because it is the largest sample of bright AGN.
Markarian UV-excess galaxies are important, since they contain a
large fraction of Seyfert 1 objects and actively star-forming systems.
were 15 published lists from the original Byurakan objective-prism
surveys, all collected by Markarian, Lipovetskii, Stepanian, Erastova,
and Shapovalova, Publ. Special Astrophys. Obs. (USSR), vol. 62, 1989.
I have a local copy of their data table taken from
a diskette provided by Lipovetskii. Cross-correlation with
additional catalogs (notably the IRAS survey) was done by
Mazzarella and Balzano 1986, ApJSuppl 62, 751.
Additional surveys for UV-excess and emission-line galaxies have
been done by several groups:
Kazarian 1979-1982, in Astrofizika 15,5; 15, 193; 16,17 and 18,
High-surface-brightness galaxies based on catalog photometry and sizes.
Arakelian high-surface-brightness galaxies, Soobsch. Byurakan Obs.
47,3 (1975). High-surface-brightness galaxies based on catalog
photometry and sizes,
includes some prominent Seyferts.
Kiso UV-excess lists: Noguchi, Maehara, and Kondo, Ann. Tokyo
Astrophys. Obs. ser II 18, 53; Kondo, Noguchi, and Maehara, idem. 20,
130; Takase, Noguchi, and Maehara 1982, idem. 19, 440.
Michigan-Tololo emission-line survey:
ApJSuppl 34, 95 (1977); 35, 197(1977); 35, 203 (1977); 36, 587 (1978);
45, 113 (1981).
KPNO International Spectroscopic Survey (KISS): Salzer et al.
2000, AJ 120, 80 and later lists.
Madrid emission-line survey: Zamorano et al. 1994 ApJS 95, 387;
1996 ApJS 105, 343; Alonso et al. 1999 ApJS 122, 415
Radio and X-ray surveys: these are by now so extensive that they
sensibly approached digitally, from (for example) the FIRST,
NVSS, and HEASARC WWW
sites. The near-IR 2MASS
survey covered the
entire sky at a level
detecting tens of thousands of galaxies from 1.2-2.2 microns, though
surface-brightness level is not great for galaxy structures. Looking at
specific wavelength ranges:
Radio continuum surveys from about 6-90 cm are in excellent shape,
from the 3C and Parkes surveys plus a number of small fields surveyed
very deeply. Two different surveys at 20 cm (the NVSS and FIRST
projects) have been carried out with the VLA, covering most of the
accessible sky to flux limits typically a few mJy for
point sources. A radio galaxy such as M87 could be found anywhere
within z=10 by current techniques.
These wavelengths are domanated by nonthermal processes such as
The far-infrared survey by the Infrared Astronomical Satellite
produced measurements from 12-100 m for over 250,000
galaxies, seen via thermal dust emission. This is a treasure trove for
seekers both of the systematic and the exotic. At longer wavelengths,
current ESA Infrared Space Observatory (ISO) mission provided
dramatically improved sensitivity and somewhat better spatial
resolution for individual targets. The near-infrared bands are
to the cooler giant populations, and at longer wavelengths we see
interstellar dust heated by the assorted stellar components; at large
redshifts all these contributions naturally slide to longer
The IRAS survey is now being repeated with much better resolution
and sensitivity by the Akari
Note that the millimeter and submillimeter observations sample the
long-wavelength tail of the thermal dust emission normally seen in the
Radio line work is more difficult because of extra requirements of
angular resolution and the additional dimension of frequency space -
that is, such observations must generally be targeted at some known
galaxy, from optical or IR surveys. Hundreds (CO) or thousands (H I) of
galaxies have been observed well enough to measure a total line flux
and velocity profile.
A few large-solid-angle surveys in H I have been conducted, looking for
optically obscured galaxies behind the Milky Way. The problem here is
that existing receivers can take in only a fairly narrow redshift range
in a single observation. Submillimeter receivers are now being deployed
which can take in a wide redshift range at once using CO lines.
X-ray surveys took a huge leap with ROSAT. These energies sample
AGN, hot thermalized gas, and the X-ray binary population tying to the
recent star-forming history.
UV surveys remained primitive until the start of the
GALEX mission. A few galaxies were been photographed
from sounding rockets, the Large Magellanic Cloud was imaged from the
lunar surface by Apollo 16, and a few dozen galaxies were observed by
the Astro missions. It has been rumored that fields around Markarian
galaxies have been imaged by the Glazar payload on board Mir, but
inquiries in Moscow so far failed to produce anyone who admitted
knowing about this. O'Connell has summarized a number of advantages to
UV surveys, largely accruing from the very low scattered-light
background around 2500 Angstroms and the sensitivity of UV data to
(unreddened) hot stellar populations. HST parallel observations are
providing deep, high-resolution survey data over small areas of the sky.
Electronic archives and retrieval
The biggest news in data collections throughout astronomy has
been, of course,
network resources. For galaxies, the NASA Extragalactic Database
maintained at IPAC has ways of searching for basic data and literature
references by position or catalog designation (and even for objects
close to a
known one). Somewhat different searches (for example, by availability
2D or 3D kinematic information) are available using
http://www-obs.univ-lyon1.fr/hypercat/ (a descendant of LEDA,
the Lyon Extragalactic Database).
To deal with whole catalogs at once,
you can retrieve them from the CDS
in Strasbourg. Some of the most popular ones are also to be found on
the ADC CD-ROMs.
The HEASARC "browse" interface
includes powerful catalog search-and-plot routines.
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