J/AJ/137/4795 Dynamical state of brightest cluster galaxies (Coziol+, 2009)
The dynamical state of brightest cluster galaxies and the formation of clusters.
Coziol R., Andernach H., Caretta C.A., Alamo Martinez K.A., Tago E.
<Astron. J. 137, 4795 (2009)>
=2009AJ....137.4795C 2009AJ....137.4795C (erratum in 2011AJ....142..142C 2011AJ....142..142C)
ADC_Keywords: Clusters, galaxy ; Velocity dispersion
Keywords: galaxies: clusters: general; galaxies: formation;
large-scale structure of universe
Abstract:
A large sample of Abell clusters of galaxies, selected for the
likely presence of a dominant galaxy, is used to study the dynamical
properties of the brightest cluster members (BCMs). From visual
inspection of Digitized Sky Survey images combined with redshift
information we identify 1426 candidate BCMs located in 1221 different
redshift components associated with 1169 different Abell clusters.
This is the largest sample published so far of such galaxies. From our
own morphological classification we find that ∼92% of the BCMs in our
sample are early-type galaxies and 48% are of cD type. We confirm what
was previously observed based on much smaller samples, namely, that a
large fraction of BCMs have significant peculiar velocities.
From a subsample of 452 clusters having at least 10 measured radial
velocities, we estimate a median BCM peculiar velocity of 32% of their
host clusters' radial velocity dispersion. This suggests that most
BCMs are not at rest in the potential well of their clusters. This
phenomenon is common to galaxy clusters in our sample, and not a
special trait of clusters hosting cD galaxies. We show that the
peculiar velocity of the BCM is independent of cluster richness and
only slightly dependent on the Bautz-Morgan type. We also find a weak
trend for the peculiar velocity to rise with the cluster velocity
dispersion. The strongest dependence is with the morphological type of
the BCM: cD galaxies tend to have lower relative peculiar velocities
than elliptical galaxies. This result points to a connection between
the formation of the BCMs and that of their clusters. Our data are
qualitatively consistent with the merging-groups scenario, where BCMs
in clusters formed first in smaller subsystems comparable to compact
groups of galaxies. In this scenario, clusters would have formed
recently from the mergers of many such groups and would still be
in a dynamically unrelaxed state.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 143 1426 Identification and Properties of the BCMs
(brightest cluster members) and their host cluster
table2.dat 77 238 Identification of discarded BCMs (brightest cluster
members) and the clusters on which they are projected
table3.dat 51 38 List of Discarded Clusters
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- BCM-ID Galaxy identification by rank (1)
9- 10 I2 h RAh Hour of Right Ascension (J2000)
11- 12 I2 min RAm Minute of Right Ascension (J2000)
13- 17 F5.2 s RAs Second of Right Ascension (J2000)
18 A1 --- DE- Sign of the Declination (J2000)
19- 20 I2 deg DEd Degree of Declination (J2000)
21- 22 I2 arcmin DEm Arcminute of Declination (J2000)
23- 26 F4.1 arcsec DEs Arcsecond of Declination (J2000)
28 I1 --- R Abell richness class
30- 33 A4 --- BM Bautz-Morgan type of Abell cluster (2)
35- 39 A5 --- RS Rood-Sastry type or ACO1989 note (2)
41- 46 I6 km/s Vcl Heliocentric cluster mean velocity
47 A1 --- f_Vcl [en*:] Note on Vcl origin or problems (G1)
49 A1 --- l_Nz Limit flag on Nz
50- 52 I3 --- Nz ? Number of galaxies used to determine redshift
54- 57 I4 km/s sigV ? Cluster velocity dispersion (4)
60- 64 I5 km/s VBCM ? Heliocentric velocity of brightest cluster member
65 A1 --- f_VBCM [*?:] Note on VBCM origin or problems (G2)
67- 71 I5 km/s Vpec ? Peculiar velocity of galaxy (5)
73- 77 F5.2 --- Ratio ? Ratio Vpec/sigV (6)
79- 85 A7 --- Morph Optical morphological type of the galaxy
87-105 A19 --- 2MASX The 2MASX identification of the galaxy
107-143 A37 --- OName Other identification of the galaxy
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Note (1): The first 5 bytes are the Abell cluster name, followed by the
redshift component of the cluster (A,B,C,...), followed by the rank of
the galaxy within this component (a,b,c,...). Either of the last two
characters may be blank.
Note (2): BM types were converted from roman numbers I, I-II, ... III, to
1, 2, ... 5, and are given in parenthesis if this cluster has a
discarded BCM candidate in Table 2. BM type is taken from Abell et al.
(1989, Cat. VII/110). For southern clusters without RS type, we
indicate whether the notes in Tables 7A, B, or C of ACO 1989 suggest
the presence of a galaxy of cD type (listed as "NcD") or one with a
"corona" (listed as "Ncor").
Note (4): the cluster velocity dispersion is taken from the literature
whenever Vcl is also taken from literature
Note (5): calculated according to Vpec=(VBCM-Vcl)/[1+(Vcl/c])
Note (6): Note that the online journal table incorrectly says
"Ratio is calculated as Vpec/(1+z)/sigV"
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Abell Abell identification number
7- 8 I2 h RAh Hour of Right Ascension (J2000)
9- 10 I2 min RAm Minute of Right Ascension (J2000)
11- 15 F5.2 s RAs Second of Right Ascension (J2000)
16 A1 --- DE- Sign of the Declination (J2000)
17- 18 I2 deg DEd Degree of Declination (J2000)
19- 20 I2 arcmin DEm Arcminute of Declination (J2000)
21- 24 F4.1 arcsec DEs Arcsecond of Declination (J2000)
26- 31 I6 km/s Vcl Heliocentric cluster mean velocity (1)
32- 33 A2 --- f_Vcl Note on Vcl origin or problems (G1)
35- 39 I5 km/s VBCM ? Heliocentric velocity of discarded object
40- 41 A2 --- f_VBCM Note on VBCM origin or problems (G2)
43- 77 A35 --- OName Other identification(s) of the discarded object
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Note (1): Only one radial velocity for a representative cluster component
is given for clusters with known superposition; we made sure that
VBCM is incompatible with all redshift components known to us.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Abell Abell identification number
7- 51 A45 --- Reason Reason for discarding the cluster
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Global Notes:
Note (G1): flag as follows:
n = taken from literature;
e = photometric estimate;
: = uncertain, or poor spectrum;
* = factor 2 to 4 different from photometric estimate.
Note (G2): flag as follows:
: = poor spectrum;
* = taken from Andernach & Tago's database;
b = in the background of the cluster.
e = photometric estimate
History:
Reformatted more economically from electronic version of the journal;
Tables 1 and 2 from erratum AJ, 142, 142 (2011).
(End) H. Andernach (Univ. Guanajuato) 23-Oct-2011