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Notes for object Coma Cluster

7 note(s) found in NED.


1. 2007ApJ...655...30V
Re:COMA CLUSTER
COMA (ABELL 1656) The value of c_0_ in equation (8) is set to that of the nearby
Coma Cluster. This choice is arbitrary, as adding a constant to all values of
{delta}log(M/L_B_) does not change our results in any way. We use the sample of
Jorgensen et al. (1996). Structural parameters measured in the B band are given
in Jorgensen et al. (1995a), and velocity dispersions corrected to a 1.7" radius
aperture are listed in Jorgensen et al. (1995b). The listed surface brightnesses
are corrected from the average brightness within the effective radius {mu}_e_ to
that at the effective radius: {mu}_e_ = {mu}_e_ + 1.393. Effective radii are
converted from arcseconds to kiloparsecs by adopting a Hubble flow velocity
v_flow_ = 7376 +/- 223 km s^-1^ (see vdMvD06b).
Restricting the sample to early-type galaxies with M > 10^11^ M_{sun}_,
we find c_0_ = -9.626. The value of {DELTA}log(M/L_B_) is zero by definition,
with a random uncertainty of +/-0.014. The systematic uncertainty in log(M/L_B_)
is a combination of several factors. Zero-point uncertainties in the B-band
photometry give +/-0.010 (Jorgensen et al. 1992), and the uncertainty in v_flow_
implies +/-0.013. A comparison of studies by different authors gives +/-0.02
(see Hudson et al. 2001; vdMvD06b); this uncertainty includes (and may be
dominated by) systematic differences in the methodology for deriving structural
parameters and velocity dispersions. As discussed in vdMvD06b, several other
systematic uncertainties cancel in the comparison to the distant clusters. For
example, the uncertainty in the Hubble constant cancels because we are only
concerned with the evolution of the M/L_B_ ratio and not with the absolute
value. Also, as discu ssed in van Dokkum & Franx (1996), our methodology for
measuring velocity dispersions of galaxies in distant clusters mimics that of
Jorgensen et al. (1992) in the nearby universe. The combined systematic error is
0.026, and assuming that the random and systematic errors can be added in
quadrature, we obtain {DELTA} log(M/L_B_) = 0.000 +/- 0.029.

2. 2004ApJ...608..166N
Re:COMA CLUSTER
Coma. The well-known Seyfert 1 galaxy X-Comae is just at the edge of the
MECS FOV. Fusco-Femiano et al. (1999) used MECS data to show that the
allowed upper flux level for X-Comae is ~15% of the hard X-ray excess
component at 2-10 keV, using a power-law component with {alpha}_ph_ =
1.8. We used PSPC data to check the normalization of the reference
model. Including the spectral and flux level variation uncertainties, we
obtain a PDS 20-80 keV estimate of 0.9^+0.6^_-010^-2^ counts s^-1^, or
10% of the 20-80 keV HXR emission, consistent with Fusco-Femiano
et al. (1999). AGN 1E 1258+28.9, at 50' off-axis, is obscured by the PSPC
mirror support structure. The useful data still indicate a count rate
similar to that for X-Comae, indicating a significant contribution to
PDS. However, the nature of the source is not well known, and the
extrapolation toward higher energies is not justified. Seyfert 1
J125710.6+272418 is undetected, and thus its contribution is negligible
compared with that of X-Comae. The Coma field contains an unusually high
number, 26, of cataloged AGNs/QSOs, perhaps because the Coma field is
better studied than others. However, to make up all the HXR emission,
seven objects like X-Comae are needed, and this is ruled out for Coma on
the basis of the PSPC image.

3. 2002ApJ...576..688B
Re:COMA CLUSTER
Coma.-The Coma Cluster had its soft excess emission discovered
originally with EUVE (Lieu et al. 1996a), and this PSPC observation
confirms the excess emission with very large statistical significance.
The PSPC excess has an importance of ~20%-30% of the hot ICM
throughout the limits of our analysis (18' radius).

4. 2001A&A...369..441G
Re:ABELL 1656
3.2 Coma (Abell 1656)
The radio halo in Coma (Coma C) is the prototype and the best studied
example of cluster radio halos. It is located at the cluster center, shows
a rather regular shape and a large size.
Deiss et al. (1997) obtained a map at 1.4 GHz of the halo, after
subtraction of all discrete sources. They pointed out the similar extension
of the X-ray and the radio emission in E-W direction towards the NGC 4839
group. According to Burns et al. (1994) the X-ray morphology indicates that
the Coma cluster has undergone a collision with the NGC 4839 group about
2 Gyr ago. Moreover, recent works provide evidence for ongoing merging of
groups in the center of Coma (Colless & Dunn 1996; Vikhlinin et al. 1997;
Donnelly et al. 1999; Bravo-Alfaro et al. 2000).
We use here the radio map of Coma obtained with the Westerbork Synthesis
Radio Telescope at 90 cm at an angular resolution of 125" x 55" (Feretti &
Giovannini 1998) after subtraction of the discrete sources. In this radio
image the projected size of the halo is about 30'. The X-ray image was
obtained from Rosat PSPC observations (White et al. 1993) and was kindly
supplied by Dr. Briel.
In Fig. 5 we show the overlay between the radio (contours) and the X-ray
surface brightness (grey scale) images. For a better display (but not for
the data analysis) the radio map was smoothed, with a Gaussian of
125" x 125" (FWHM).
The grid cells have a size of 256" (166 kpc), while the concentric rings
have a thickness of 128". The shape of the two radial profiles are slightly
different and the point-to-point comparison of radio and X-ray brightness
shows a large scatter, which can also be seen in the radial profiles. It
might be worth to emphasize that the radio brightness emission in Coma is
lower than in the case of the other analyzed clusters: only a minority of
the data points are above the 3 sigma noise level (Fig. 6). This possibly
allows background noise to introduce additional scatter. However, the
error-weighting of the data should reduce the noise influence, although it
could introduce a bias towards flatter F_Radio_ - F_X_ relations (i.e.
smaller values of b). The fitted power-law relation (Eq. (1)) has the
normalization a = 0.03 +/- 0.01 and slope b = 0.64 +/- 0.07. We emphasize
that this sub-linear power law relation should be verified through a radio
map of higher sensitivity.
Figure 6 shows that a linear relation (b = 1) between grid values of the
radio and X-ray brightness may also be consistent with the data.

5. 1999MNRAS.306..857C
Re:ABELL 1656
This is the Coma cluster, and we have taken the spectrum only of the
more Western of the two dominant galaxies, NGC 4874.

6. 1998MNRAS.301..609B
Re:ABELL 1656
Abell 1656: Fig. 1j. The very rich Coma cluster has only one NAT
associated with it. The NAT is oriented in a direction similar to the
core elongation. It is believed that Coma has recently undergone a
cluster-subcluster merger (Burns et al. 1994b). This has been confirmed
by several optical studies (Baier 1984; Fitchett & Webster 1987;
Mellier et al. 1988; Caldwell et al. 1993; Zabludoff, Franx, & Geller
1993; Colless & Dunn 1996); however, the optical state of this cluster
is still poorly understood (e.g. Geller & Beers 1982; Dressler &
Schectman 1988; West & Bothun 1990). The merger hypothesis is supported
by filamentary X-ray emission in the East and SE detected through a
wavelet analysis (Vikhlinin, Forman & Jones 1997), and smaller X-ray
subclumps detected by the Einstein IPC (Davis & Mushotzky 1993). The
galaxy distribution in Coma is also peculiar, with the majority of
early-type galaxies lying along a filament to the NE/SW direction,
while the late-type galaxies are more symmetrically distributed
(Doi et al. 1995). The luminosity function in the core of Coma is well
fitted by a power law with slope -1.42 +/- 0.05 over the range
-19.4 < M_R_ < -11.4 (Bernstein et al. 1995). Caldwell et al. (1993)
detected a number of 'E+A' (Dressler & Gunn 1983) galaxies, which are
almost exclusively located to the SW of the cluster centre. This is a
surprising result, since most of these post-starburst galaxies are
detected in distant (z ~ 0.2) clusters (Butcher & Oemler 1978, 1984;
Dressler & Gunn 1983; Couch & Sharples 1987).

7. 1918PLicO..13....9C
Re:Coma Cluster
This region contains the most remarkable aggregation of closely packed small
nebulae known to me. About thirty are eatalogned in this area in the N. G. C.,
and some twenty-five more are given in N. G. C. II. In reality there are more
than three hundred small nebulae in an area about 50' x 40', a large proportion
of which are probably spirals. None of them are conspicuous objects. They are so
numerous that it is very difficult to locate those catalogued in the N. G. C.
with any certainty, except for a few of the brighter objects. See figure 3. 304
s.n.


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