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Notes for object Virgo Cluster

7 note(s) found in NED.

1. 2006A&A...453..447E
Virgo cluster
The Virgo cluster was observed with XMM-Newton by Matsushita et al. (2002). The
gas parameters are taken from their analysis. However the total luminosity of
David et al. (1993) is used for our calculations. The large difference between
the cool core luminosity and the luminosity within the (larger) cooling radius
is due to the extremely shallow density profile ({beta} ~ 0.5) of Virgo.
However, this should not affect our RM estimates too much, since only a
~{beta} 0.25 should lead to problems, as was argued in Sect. 3.7.

2. 2004ApJ...608..166N
Virgo. Virgo has an active nucleus, M87, and a jet in the
center. XMM-Newton data yield power-law slopes of 2.2+-0.2 and
2.5 +- +-0.4 for the nucleus and the bright knot in the jet
Bohringer et al. 2001) at 90% confidence, and no indication of
excess absorption. The 2' MECS data do not provide good constraint
on the slope of the nonthermal component. We thus fit the 2' MECS
data with a model consisting of MEKAL and a power law, both absorbed
by the galactic N_H_, fixing the photon index to 2.3, based on the
XMM-Newton observations (Bohringer et al. 2001), thus obtaining the
normalization and its uncertainty for the power-law component. We
determined the thermal component of Virgo by using the above-determined
central power-law model together with MEKAL when fitting the 0-8' keV
MECS data. The best-fit parameters T = 2.35+-0.04 keV and abundance
0.49+-0.04 solar are consistent with XMM-Newton results. Letting only
the thermal model normalization be a free parameter, we then normalized
this model to the PDS FOV using 12-20 keV PDS data. According to this
model, M87 contributes 17%+-3% of the nonthermal emission in the 20-80 keV
band. Allowing spectral variability for M87, we repeated the above
exercise keeping {alpha}_ph_ at 2.0 and 1.7. The resulting M87 contribution
to the HXR emission is 20%-30% and 30%-50%, respectively. Unless the
spectrum of M87 has a strong hard excess, the nonthermal PDS signal of
Virgo cannot be explained entirely by M87. We keep the {alpha}_ph_ = 2.3
results, i.e., an M87 contribution of 4.5+-0.7 x 10^-2^ counts s^-1^ and
the thermal model prediction of 0.3+-0.210^-2^ counts s^-1^ to the PDS
20-80 keV band.

3. 2002ApJ...576..688B
Virgo.-Along with Coma, it was one of the two clusters where the soft
excess emission was initially discovered, in a deep EUVE observation
(Lieu et al. 1996b). The PSPC excess emission, already reported also
in Bonamente et al. (2001b), is strongly detected with {eta}~ 0.3-0.4
throughout the limits of this investigation (18' radius). This cluster
is at very low redshift (z = 0.0043), similar to that of the Fornax
Cluster; it shows a rather flat radial trend of the soft excess,
completely different from that of Fornax over the same interval of
radii (~0-100 kpc).

4. 2001ApJS..137..139S
The Virgo Cluster. - Given the evidence for substantial depth to the
Virgo Cluster (e.g., Yasuda, Fukugita, & Okamura 1997), we adopt individual
distance estimates to Virgo members as follows. For NGC 4321 (M100) we
adopt the Cepheid distance from Freedman et al. (1994). For NGC 4536 we
adopt the Cepheid distance from Saha et al. (1996). For NGC 4571 we adopt
the bright star distance of Pierce, McClure, & Racine (1992). For NGC 4579
we adopt the SN II expanding photosphere distance from Eastman et al.
(1996). For NGC 4639 we adopt the Cepheid distance from Sandage et al.
(1996). Schoniger & Sofue (1997) derive distances for NGC 4303, NGC 4438,
and NGC 4647, based on combined CO and H I Tully-Fisher. For NGC 4429 we
adopt the fundamental plane distance of Gavazzi et al. (1999). For NGC 4527
we adopt the SN Ia distance from Shanks (1997). Teerikorpi et al. (1992)
give Tully-Fisher distances for NGC 4567 and NGC 4845. Yasuda et al. (1997)
give B-band Tully-Fisher distances for a large sample of Virgo galaxies.
The Yasuda et al. (1997) distances match the available Cepheid distances
within the errors. We adopt the Yasuda et al. (1997) distances for the
following galaxies: NGC 4178, NGC 4192, NGC 4206, NGC 4212, NGC 4216,
NGC 4235, NGC 4254, NGC 4298, NGC 4351, NGC 4388, NGC 4394, NGC 4424,
NGC 4450, NGC 4501, NGC 4522, NGC 4535, NGC 4548, NGC 4569, NGC 4651,
NGC 4654, NGC 4689, and NGC 4698. We adopt the Yasuda et al. (1997) mean
Virgo distance of 16.0 Mpc for NGC 4643 and NGC 4665. We adopt the
Gavazzi et al. (1999) distances for NGC 4461, NGC 4464, NGC 4477, and
NGC 4503.

5. 2000ApJS..128..431F
The structural complexity of the Virgo Cluster has been recognized
and studied for more than 30 yr (e.g., de Vaucouleurs & de Vaucouleurs
1973). We limit our analysis to the regions where galaxies with Cepheid
distances are found. For these regions, Table 6 summarizes the spatial
and kinematical structures identified by different authors within the
cluster. In spite of the complication introduced by the fact that a
succession of authors have used different criteria and different
nomenclature to describe the structure within the cluster, all agree in
identifying two prominent substructures, defined by the projected
density of galaxies. These structures are associated with, but not
centered on, the two brightest Virgo galaxies, M87 and NGC 4472. We
follow Huchra (1985) and refer to these as the M87 subcluster and the
NGC 4472 subcluster, respectively. Table 6 shows that the mean
velocities of the two subclusters, measured within a 2^deg^ radius, are
the same. When higher velocity spirals located at larger radii from the
center are included, the mean velocity for the NGC 4472 subcluster
increases, while the mean velocity for the M87 subcluster remains
approximately constant. The two subclusters also differ in their ratio
of spirals to ellipticals, which is smaller in the M87 than in the
NGC 4472 subcluster.
The physical reality of the two subclusters is confirmed by X-ray
data. The ROSAT observations of the Virgo Cluster (Bohringer et al.
1994) show in beautiful detail the distribution of X-ray-emitting gas
first detected by the Einstein and EXOSAT satellites. These
observations show that the Virgo Cluster core is filled with hot gas,
and that the M87 subcluster corresponds to the deepest potential well.
In contrast to the fact that neither M87 nor NGC 4472 are at the
geometrical center of the galaxies isopleths, to first order each galaxy
is at the center of the X-ray-emitting corona, and consequently of the
dark mass that dominates the cluster, with M87 having the lion's share.
Based on velocities and Tully-Fisher and fundamental-plane distances to
59 early-type and 75 late-type galaxies, Gavazzi et al. (1999) conclude
that the M87 and NGC 4472 subclusters are at the same distance (a
conclusion also supported by the SBF observations presented in
Ajhar et al. 2000).

6. 2000ApJS..128..431F
Of the galaxies with Cepheid distances, NGC 4321, NGC 4548, and
NGC 4571 are located in the M87 subcluster, while NGC 4535 is located in
the NGC 4472 subcluster. The association of NGC 4536 and NGC 4496A is
more problematic, since the galaxies are found over 5^deg^ south of
NGC 4472. According to Gavazzi et al. (1999), the two galaxies are
within the NGC 4472 subcluster, which they extend farther south than
previous authors, and beyond the region dominated by the X-ray emission
associated with NGC 4472 (even if NGC 4496A is not included in the
Gavazzi et al. survey, its location and its systemic velocity place it
within the subcluster). Therefore, we include all three galaxies in the
NGC 4472 subcluster; in practice, this decision is of little
consequence, since the three galaxies have very similar Cepheid
In addition to the two subclusters described above, Gavazzi et al.
(1999) identify several other clumps, one of which, named the "E cloud,"
is located to the east of the M87 subcluster and contains our last
Cepheid galaxy, NGC 4639. Cloud E is found to have the same recessional
velocity as the M87 subcluster, but is ~ 0.4 +/- 0.2 mag in the
background. In keeping with Huchra's nomenclature, we rename this region
the NGC 4649 (M60) subcluster, from the most prominent galaxy found
here. We would like to stress that while the physical association of
galaxies in the M87 and NGC 4472 subclumps is well established, this is
not the case for the NGC 4649 subclump, and in fact SBF distances in
this region (Ajhar et al. 2000; Ferrarese et al. 2000a) are very
heterogeneous and point to a more complex structure than that envisioned
by Gavazzi et al. (1999).

7. 2000ApJS..128..431F
We would like to spend a few extra words regarding the confinement
of NGC 4639 to a different region of the Virgo Cluster than M87 and
NGC 4472, which, as described above, are likely to define the cluster's
center. The issue is particularly important because the Cepheid distance
modulus to NGC 4639 is ~ 31.9 mag, while the remaining five Cepheid
galaxies have a distance modulus of ~ 31.0 mag, with very small
dispersion. The reasonable doubt here is that M100, NGC 4494A, NGC 4535,
NGC 4536, and NGC 4548 might be at the near side of the cluster, while
NGC 4639 might be at the far side, and therefore the "true" distance to
the Virgo Cluster would be better defined by the mean of all six Cepheid
distances, rather than by the mean of the five "nearby" galaxies. In
addition to the (admittedly not very strong) evidence reported above
that NGC 4639 lies in a clump that seems to be at slightly larger
distances than the region around M87 and NGC 4472, there are two strong
reasons to reject NGC 4639 in determining the distance to the Virgo
Cluster. The first is based on simple geometrical arguments: NGC 4639 is
located 3^deg^ east of M87, which is also the radius of the cluster's
core as defined by Huchra (1985). If the cluster is approximatively
spherical, then the back-to-front depth of the core corresponds to
0.2 mag in distance modulus. NGC 4639 is ~ 0.8 mag more distant than the
other Cepheid galaxies, implying that it is in the background to the
cluster. The question remains whether the remaining five Cepheid
galaxies are indeed representative of the Virgo Cluster mean distance.
The strongest argument in support of this hypothesis is from Bohringer
et al. (1997) and Vollmer et al. (1999), who found that NGC 4548 shows
clear signs of its interstellar medium being stripped and distorted as
a consequence of the galaxy passing close to the center of the potential
well of the cluster.
Galaxies with PNLF, TRGB, GCLF, and SBF distances are placed in one
of the three subclusters in the Virgo Cluster (M87, NGC 4472, and
NGC 4649); for those galaxies that are not included in the Gavazzi
study, the classification was based on redshift and position, and it was
unambiguous in all cases.
Figure 2 shows the ROSAT X-ray map of the Virgo Cluster (from
Bohringer et al. 1994). The straight lines define the regions into which
Gavazzi et al. (1999) divide the cluster. The circles, triangles, and
squares show the location of the galaxies with Cepheid, SBF, GCLF, and
PNLF distances presented in this paper.

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