Galaxy questions
MCG/UGC example
TheSky6 uses the
Principal
Galaxy Catalog (PGC) dataset over the other catalogs that
are less complete/less accurate for the most part like the
NGC/IC, MCG, VCC, Hick, Arp, etc. The reason for this is the
900,000 galaxy entries in the current
Principal
Galaxy Catalog data is more complete and is the most accurate galaxy
catalog overall, in regard to positions, sizes, and magnitudes of galaxies, and
very easy to redistribute - with a royalty being paid!
In addition to using the PGC
galaxy data TheSky also supplies black and white thumbnail images from the
(arguably) first high resolution all sky mosaic - The Digitized Sky Survey.
These images are taken at a resolution of 1.7 arcseconds/pixel, good
detail, and accurate positions to be shown in TheSky display. Granted they are
only black and white thumbnails but for the most part pretty colors do little for
most galaxies, especially when position and size are important. But for those that feel
they must have color read on!
So instead of M104 the Sombrero
Galaxy being an oval it looks like the following.
Catalog data and image shown
Ovals or thumbnail you decide
Or this!
Color
Hubble Image of M104
Now this is not to say that other more
accurate specialized galaxy catalogs do not exist they do but for overall galaxy
plotting and searching for the masses
TheSky6 chooses to use the PGC as the primary galaxy catalog by
default since there isn't a better alternative at this writing. Of course
using
TheSky6's
Database Compiler
ANY dataset within reason can be used. That is, using SDB files is NOT
recommended for datasets that exceed 100,000 entries or more because of data
access times. Any dataset that contains object entries with RA and DEC and
additional text information can easily be compiled then searched, plotted,
slewed to, using
TheSky6.
Although the
Principal
Galaxy Catalog is being used it has also been cross referenced to the
other common galaxy datasets like those mentioned above. This allows you
to search for objects by other common names/numbers like NGC 4565, Arp 218,
M66, or MCG-2-35-10. But keep in mind the first entry for the data will
come from the PGC information AND the plotted galaxy ellipse and or position and
magnitude also come from the PGC data entry.
To demonstrate the following shows
a galaxy field centered on NGC7331 AKA PGC69327.
Note the descrepancies in
these two datasets!
Hmm. Interesting!
By plotting both the PGC data AND the NGC together you can see
they simply do not agree. Which is right? Technically neither is 100% accurate
but the PGC data tends to offer more accurate sizes and positions for galaxies
and is again why TheSky chooses it as the primary galaxy catalog.
Negative DSS photo in place!
Note: In addition to being
negative the histogram has also been altered on the image to show the extent or
size of the galaxies.
So you can see that both datasets the PGC and NGC are not as accurate as
possible but certainly very close and much better than previous entries! But
again, why the thumbnails are a feature of TheSky!
Example. Let's say you want to find the galaxy "MCG-2-35-10". In
TheSky6 use Edit |
Find and enter MCG-2-35-10. Click Frame Object and Object Information on
the Find dialog and you will be taken directly to the match and the information
is displayed. See below.
Edit | Find Dialog
Example
MCG-2-35-10
TheSky6 returns the
following data for this galaxy.
Object name: PGC 48179
Magnitude: 12.8
Equatorial: RA: 13h 38m 28s Dec: -09°49'47"(current)
Equatorial 2000: RA: 13h 38m 10s Dec: -09°48'04"
Horizon: Azim: 83°42'32" Alt: -26°27'57"
Size: 2.3 x 2.0
Visibility: Rise 12:50, Set 00:03
Transit time: 18:25
Object type: Spiral Galaxy
Source catalog: PGC (Principal Galaxies Catalog)
Type: SBm
Bar: B
Morphological code: 8.897
Radial velocity: 1117.330
Alias 1: DDO180
Alias 2: A1335-09
Alias 3: IRAS13355-0932
Alias 4: IRAS13355-0933
Alias 5: DENISP_G_J1338110-094747
Alias 6: DENISP_G_J1338110-094748
Position angle: 84°00'
Hour angle: -07h 41m 27s
Screen x,y: 349.00, 241.00
Sidereal time: 05:57
Click distance: 0.0000
Catalog number: 48179
Celestial type: 8
NGC/IC: 0
Julian date: 2453559.2840
Catalog: 0
To see a list of other galaxy
catalogs that have been cross referenced to the PGC or the MCG galaxies in our
example use the Find dialog then go down to Non-Stellar list and EXPAND the
entry "PGC cross Reference". See Below. Here are
the other galaxy catalogs the PGC has been cross referenced to by name.
Other galaxy catalogs
Cross referenced to the PGC
For example. If you wish to
see the list of "Arp Peculiar Galaxies" expand the ARP entry in the list.
The 300+ Arp Galaxies are then individually listed.
List of Arp Galaxies
Scroll down the list to see all
Same for any of the other catalog
listed like the MCG entries.
Browsing the MCG data
Use Find rather than Browsing the entire list
NOTE: Scrolling down a list
of thousands of entries can be cumbersome at best. First try searching for
the data with a regular Edit | Find and type in the entry. If that does
not yield the result you want due to Syntax or something else then you can
resort to browsing the entire list.
Scroll down looong Enough!
And you will find your entry
Now to see exactly why the PGC
data is being used over say the Morphological Catalog of Galaxies
(MCG)
data we will plot the original MCG dataset with the 29,003
entries from that catalog in
TheSky6 for
comparison. By searching the MCG SDB data for the same entry we get the
following MCG entry.
Object name: MCG Galaxies:
MCG-02-35-010
Magnitude: 13.0
Equatorial: RA: 13h 38m 32s Dec: -09°48'57"(current)
Equatorial 2000: RA: 13h 38m 14s Dec: -09°47'14"
Horizon: Azim: 121°29'27" Alt: +23°28'31"
Visibility: Rise 12:50, Set 00:03
Transit time: 18:25
Source catalog: Sky Database: MCG Galaxies
Type: MCG Number: MCG-02-35-010
Bar: NGC/IC number:
Type: Magnitude: 13.
Multiple: Major Axis (inner): 9.
DB field 5: Minor Axis (inner): 2.
Morphological code: Major Axis (full): 20.
Radial velocity: Minor Axis (full): 20.
Hour angle: -03h 29m 52s
Air mass: 2.51
Screen x,y: 268.00, 227.00
Sidereal time: 10:08
Click distance: 0.0000
Celestial type: 55
Index: 24903
Julian date: 2453559.4582
Catalog: 9
The reference marker on the
following display is being plotted using the MCG data. The complete MCG
SDB used can be downloaded from the following page,
Keep in mind there is no need to
have the SDB for the MCG galaxies anymore because TheSky6 has taken care of
this.
MCG versus PGC
But wait what is that bright star doing there?
And lastly using the photographs
from the Palomar data known as the Digitized Sky Survey we have the following
photograph of the field. The photograph is not subject to galaxy
positional errors since galaxies for the most part don't move appreciably over
thousands of years unlike
stars with high proper motion like Barnard's Star that actually move
appreciably in a small amount of time like 5 years! The photograph shows
the accurate position and size of the galaxy in favor of the PGC catalog.
Photograph from the Palomar
data
Look no bright star!
Why isn't there a photograph for
every galaxy like there is for M51, NGC4565 and others? Because when
creating the black and white thumbnails from the Palomar Sky Survey 102 CD data
thumbnails for ONLY galaxies that are larger than about 2.5 arc minutes in size were
created to save space.
As to what the bright star is
located at the center of the galaxy no it is not a super nova but rather it is
another catalog error found in the "Guide Star Catalog". The Guide Star
catalog was created scanning the Palomar photographic plates and there were
about 3 million entry errors of this kind. The newer stellar catalogs used
by TheSky6, USNO B1 subset, UCAC, Hipparcos/Tycho, are not prone to these kinds
of erroneous entries. Disable the GSC catalog using View | Stellar Options
| Catalogs/Astrometry and the star will disappear. See below.
Disable GSC star plotting
To see proper motion on stars enable it here
For more complete details
on how
TheSky6 accesses data
as well as more information explaining special cases please refer to the
following in depth page
Nearly identical to the above
MCG galaxy example above let's
take galaxy UGC 8387. First use the cross
reference from the UGC data to the more accurate and more complete
PGC data. Edit | Find in TheSky6 and
Expand the Non-Stellar PGC Cross
reference to show the UGC individual entries. By scrolling
down the entries under the Non-Stellar PGC Cross reference | UGC you
will find the entry for "UGC 8387".
Or simply use Edit | Find UGC8387.
TheSky6 returns the
following for UGC 8387,
Object name: IC 883
Other ID: PGC 46560
Magnitude: 15.0
Equatorial: RA: 13h 20m 21s Dec: +34°09'43"(current)
Equatorial 2000: RA: 13h 20m 35s Dec: +34°08'23"
Horizon: Azim: 57°21'26" Alt: +14°29'55"
Size: 1.0 x 0.7
Visibility: Rise 22:18, Set 15:03
Transit time: 06:42
Object type: Irregular Galaxy
Source catalog: PGC (Principal Galaxies Catalog)
Type: Irr
Morphological code: 10.000
Radial velocity: 7030.540
Alias 1: UGC8387
Alias 2: CGCG189-54
Alias 3: ARP193
Alias 4: VV821
Alias 5: 1ZW56
Alias 6: IRAS13183+3423
Position angle: 144°00'
Hour angle: -06h 39m 36s
Air mass: 3.97
Screen x,y: 623.00, 463.00
Sidereal time: 06:41
Click distance: 0.0000
Catalog number: 46560
Celestial type: 9
NGC/IC: -883
Julian date: 2449718.7917
Catalog: 0
How can this be you may ask, surely
you jest. No I am not surely and yes I am completely serious
;).
Do you mean to tell me this galaxy
is an IC galaxy, a UGC galaxy, and a PGC galaxy?! A resounding
"YES", and then some. Note the other entries above, Arp, CGC,
VV82, and so on.
Again, the coordinates for galaxies
that are found in the PGC data use the PGC size, position, and
position angle, and magnitude. Meaning the PGC data has
precedence.
Now using the 102 Palomar Sky
Survey image as created by
TheSky6/CCDSoft
we get the following image for a very small 5 arc minute field.
Because TheSky6 allows plotting both the
NGC/IC and
PGC data at the same time you can see both
entries plotted for comparison.
Conclusion: This is why
TheSky6 uses the PGC data for galaxies and also why the thumbnail
images are supplied!
Which is
correct??
I will argue technically neither is
100% correct!
A Histogram stretch
shows the true extent of the galaxy which is not encompassed even in
the PGC galaxy entry.
Keep in mind this is one single
object out of potentially 1 billion+!
Please
refer to the contents of the README file distributed with this
dataset!
The PGC data is NOT cross referenced to the Abell Galaxy Clusters
catalog. Nor is the Abell/Zwicky Clusters SDB part of the
"CORE" databases as distributed with TheSky. The data is made
available using an
SDB file.
This is partly due to the fact these are not single object entries
but rather very subjective positions for the centers of clusters of
galaxies. Therefore one cannot assign a set of galaxies to a
single existing object. The coordinates are theoretically the
center of the cluster of galaxies.
Keep in mind that a position for a "cluster" of galaxies is far more
subjective then a position for a single galaxy. And magnitude
simply doesn't apply nor does position angle or size.
Assuming you have the
SDB file
for the
Abell Galaxy Clusters/Zwicky <- Click to download
(included with TheSky6) you can search them using Edit | Find
Abell Galaxy Clusters followed by the number you want.
Or you can expand the SDB entry and see all of them listed
individually as shown below. Then you can scroll through the
list. If you want them centered and identified as you go
enable "Frame Object" and/or "Object information" as shown below.
TheSky
using the SDB file right or wrong returns the following,
Object name: ABELL galaxy
clusters: 1716
Magnitude: 0.0
Equatorial: RA: 13h 20m 41s Dec: +33°55'37"(current)
Equatorial 2000: RA: 13h 20m 54s Dec: +33°54'18"
Horizon: Azim: 57°30'16" Alt: +14°18'02"
Visibility: Rise 22:20, Set 15:02
Transit time: 06:43
Source catalog: Sky Database: ABELL galaxy clusters
DB field 1: Abell cluster #: 1716
DB field 2: Mag 10th brightest: 17.8
DB field 3: Dist,Richness group: 6 1
DB field 4: Area (sq degrees): 0.147
Hour angle: -06h 39m 55s
Air mass: 4.02
Screen x,y: 623.00, 463.00
Sidereal time: 06:41
Click distance: 1.0000
Celestial type: 55
Index: 1715
Julian date: 2449718.7917
Catalog: 9
And a 2 degree
field centered on the coordinates in the data using photograph from
the Palomar Sky Survey (DSS) data shows the following,
Only two galaxies
here in 2 degrees?
(Click for larger image)
Hmm.. Maybe the galaxy cluster
covers many degrees?
Now make using the
on-line Simbad database as
a source make a query entering Abell Cluster 1716 and then ask for
say 4 degrees of data around the coordinates they resolve.
Here is that query plotted in TheSky6.
Compare
TheSky SDB position and the
Simbad Query
for Abell Galaxy Cluster 1716
A 2 arcminute 22 arcsecond
difference in position
placing the galaxy cluster center very near
galaxy PGC 2031988 very subjective!
The above turquoise
markers are showing the entries created by performing a
Simbad query around the
object "Abell Galaxy Cluster 1716". You can see the Core
galaxies from TheSky plotted AND the new additions from the on-line
up-to-date Simbad query.
The following is from
the Simbad query performed
today Dec 23rd, 2005.
Object name: Simbad Abell 1716: [SMB88] 1912
Magnitude: 0.0
Equatorial: RA: 13h 20m 21s Dec: +33°27'17"(current)
Equatorial 2000: RA: 13h 20m 34s Dec: +33°25'58"
Horizon: Azim: 57°55'47" Alt: +14°03'36"
Visibility: Rise 22:22, Set 14:58
Transit time: 06:42
Source catalog: Sky Database: Simbad Abell 1716
DB field 1: Object Name: [SMB88] 1912
DB field 2: Object Number: [SMB88] 1912
DB field 3: MAGNITUDE:
DB field 4: otyp: G
DB field 5: B&V Magnitudes: 16.609
DB field 6: Spectral Type: Sa
DB field 7: nref: | 1
Hour angle: -06h 39m 35s
Air mass: 4.09
Screen x,y: 466.00, 538.00
Sidereal time: 06:41
Click distance: 0.0000
Celestial type: 54
Index: 228
Julian date: 2449718.7917
Catalog: 10
TheSky6 reports an
angular separation of 2 arcminutes and 22 arcseconds when using the Simbad query on
Abell 1716: [SMB88] 1912 versus that distributed with
TheSky SDB
(many years old).
Object name: NED
Data: ABELL 1716
Magnitude: 0.0
Equatorial: RA: 13h 20m 41s Dec: +33°55'37"(current)
Equatorial 2000: RA: 13h 20m 54s Dec: +33°54'18"
Horizon: Azim: 57°30'16" Alt: +14°18'02"
Visibility: Rise 22:20, Set 15:02
Transit time: 06:43
Source catalog: Sky Database: NED Data
DB field 1: Object Name: ABELL 1716
DB field 2: Object Number: 1
DB field 3: Velocity/Redshift km/sec z: 30000 0.182000
DB field 4: Qual:
DB field 5: Dist. arcminutes: 0.0
DB field 6: Refs Notes Phot: 13 0 0
DB field 7: Posn Vel/z Diam: 1 0 0
DB field 8: Assoc: 1
Hour angle: -06h 39m 55s
Air mass: 4.02
Screen x,y: 642.00, 370.00
Sidereal time: 06:41
Click distance: 0.0000
Celestial type: 72
Index: 0
Julian date: 2449718.7917
Catalog: 11
NOTE: This
places the center of the galaxy cluster very near the entry from the
SDB file
distributed with TheSky!
Since I knew you would
ask. A search of 120 arcminutes (2 degrees) in the NED page
returns over 3,000 objects! The first 3,000 are shown here.
One must consider the on-line
databases can literally query terabytes of data, changes and updates
can easily be made to the datasets, and these are usually very well
funded some even using Tax Payers dollars.
Very few if any
datasets are 100% accurate and a good number of them are being
refined on a regular basis. The use of TheSky's database
compiler allows datasets to be accessed that simply did not exist
when the media was burned or have under gone updates since.
Also note that major
upgrades to TheSky do include the best datasets available at that
point in time in an effort to supply the most accurate data whenever
possible.
SSD-T-1-0338-0098-83
DOCUMENTATI0N FOR THE MACHINE-READABLE VERSION OF THE
CATALOGUE OF ABELL AND ZWICKY CLUSTERS OF GALAXIES
(BULGARIAN ACADEMY OF SCIENCES)
April, 1983
Contract NAS 5-27393
Robert S. Hill
Prepared for:
National Aeronautics and Space Administration
Goddard Space Flight Center
Greenbelt, Maryland 20771
Prepared by:
Systems and Applied Sciences Corporation
6811 Kenilworth Avenue, Suite 500
Riverdale, Maryland 20737
SECTION 1 - INTRODUCTION
A COPY OF THIS DOCUMENT SHOULD ACCOMPANY EVERY DISTRIBUTED COPY OF THE
MACHINE-READABLE CATALOGUE.
This document describes a machine-readable version of the "Catalogue of Abell
and Zwicky Clusters of Galaxies" prepared by the Bulgarian Academy of Sciences.
This catalogue consists of three files, as follows:
File 1 - Abell Clusters (Abell 1958)
File 2 - Zwicky Clusters (Zwicky et al. 1961-68)
File 3 - Zwicky Plate Number Cross-Identifications (Zwicky et al.
1961-68)
Files 1 and 2 contain some calculated quantities as well as the data from the
published versions of the catalogues. File 3 connects the sequential numbering
of the Zwicky clusters in file 2 with Zwicky's own field and cluster numbers.
The Abell clusters are rich, compact clusters of galaxies identified by G. O.
Abell. From these he selected a statistical sample for inferences about the
distribution of galaxies in space. These clusters were identified on the red
plates of the Palomar Observatory Sky Survey (POSS).
The Zwicky clusters were identified by F. Zwicky in 560 POSS fields. They are
rich clusters, each having at least 50 members within 3 magnitudes of the
brightest member.
REFERENCES:
Abell, G. O. 1958, Astrophys. J. Suppl. 3, 211.
Corwin, H. G. 1974, Astron. J. 79, 1356.
Hill, R., Documentation for the Machine-Readable Version of the Catalogue of
Galaxies and of Clusters of Galaxies: Data on Individual Galaxies, SASC,
Document #SSD-T-1-5069-022-82.
Kalinkov, M., Stavrev, K. and Kaneva, I. 1975, Astron. Zh. (Letters) 1, no. 2,7.
de Vaucouleurs, G., de Vaucouleurs, A., Corwin, H. G. 1976, Second Reference
of Bright Galaxies (Austin, University of Texas).
Zwicky, F., Herzog, E., Wild, P., Karpowicz, M. and Kowal, C. T. 1961-68,
Catalogue of Galaxies and of Clusters of Galaxies (Pasadena, California
Institute of Technology, 6 vols.).
SECTION 4 - REMARKS AND MODIFICATIONS
The Catalogue of Abell and Zwicky Clusters of Galaxies was received by
the Astronomical Data Center (ADC), NASA Goddard Space Flight Center,
from the Centre de Donnees Stellaires (CDS) in 1979. The catalogue had
been prepared originally by the Bulgarian Academy of Sciences. As
received, the catalogue contained a file of documentation in addition to
the three data files. Section 2 of this document merely expands on that
documentation file. The only modifications to the catalogue format made
at the ADC are as follows:
(1) The sign of declination was moved so that it always appears in the
same byte (all three files).
(2) The declination of Zwicky cluster no. 2343 was given as -2 deg 21
arcmin and the type as 6, due to transposition of digits; the correct
values are -2 deg 26 arcmin and 1, respectively. This correction was
made to file 2, and to file 3 as well, since the incorrect
declination had been carried over there.
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