Galaxy Zoo Talk

# Unique Core; is this an "X Center"

• 1st time seeing this type of ring where the edges flare out to points on either side; on closer examining is this also a "X Center"?

Posted

• by Budgieye moderator

Nice spot! jeffreyhrwtz 😃

#NGC 4128 NGC4128

77 references in NED

http://skyservice.pha.jhu.edu/DR9/ImgCutout/getjpeg.aspx?ra=182.13451413&dec=68.76760536&scale=0.09903175&width=800&height=512&opt=&query=

http://skyserver.sdss.org/dr9/en/tools/explore/obj.asp?ra=182.13451735313467&dec=68.76766426146177

1237658609833934885

https://talk.galaxyzoo.org/#/subjects/AGZ00022kn

Geometric shapes
Started 3 years ago by Alpha Aurigae https://talk.galaxyzoo.org/#/boards/BGZ0000001/discussions/DGZ00013ed but no analysis

Re: NGC catalogue LIST http://www.galaxyzooforum.org/index.php?topic=280028.msg596178#msg596178

HST observations of nuclear stellar disks http://adsabs.harvard.edu/abs/2004A%26A...428..877K

4.1 NGC 4128

The most distant galaxy in the sample is NGC 4128 (36 Mpc). It is an
S0 galaxy and it has not been detected in radio nor in IR. The
isophotal parameters show that it is disky between 35 and 530 pc. On 1
kpc scale it has boxy parameters and on larger scales it becomes disky
again.

The color image shows a red nucleus. The values for Fe5270 index
measured with an aperture bigger than the red nucleus are the smallest
in the sample of galaxies. This combination puts the points in Fig. 7
above the model grid.The difference in colors and line-strengths
between the two slit positions are small and within errors indicate
old stellar populations of $\sim$14 Gyr and metallicities between
[Fe/H]=-0.38 and solar.

It is probable that the difference in the color between the nucleus
and the rest of the galaxy, as well as the higher metallicity detected
in the nucleus is connected with the unusual spatially resolved
kinematic profiles (Fig. 8). The velocity dispersion is flat in the
center. The velocity curve also shows an unusual flattening in the
central 0 $.!!^{\prime\prime}$2, measurements being positive on the
both sides of the galaxy nucleus. Outside this radii the galaxy
rotates fast, as expected for a disk galaxy. Kinematics extracted
fitting to two different spectral regions are in a good agreement,
confirming the results. Having in mind the boxiness in the central
tens of arcseconds, the extracted kinematic indicates the existence of
a small ($\sim$35 pc in diameter) core, kinematically distinct from
the nuclear stellar disk.

The B-V color profile on the last panel of Fig. 8 shows a slightly
shifted ($\sim$17 pc from the center) peak of the red nucleus. This
supports the presence of a distinct component in the nucleus. On the
other hand, the spatially resolved line-strengths do not follow this
trend. The spectral observations of this galaxy have the smallest S/N
ratio, and the significance of this discovery is just above 1$\sigma$.
Deeper exposures of high spatial resolution, preferably with an
integral-field unit to cover the 2D structure, are needed to confirm
this result.

Considering the shape of the spatially resolved kinematic curves, the
four galaxies could be sorted in two groups: fast and kinematically
disturbed rotators. NGC 4570 and NGC 5308 belong to the first group.
Their rotation curves show clear signature of the stellar disks. The
rotation curves of NGC 4128 and NGC 4621 are much more complicated. In
the case of NGC 4621 the unusual mean velocity and velocity dispersion
curves are consistent with the known KDC (WEC02) in the nucleus.
Although based on a $1\sigma$ detection, we report the discovery of a
similar kinematically distinct core in the case of NGC 4128.

but also NGC 4128, which is additionally boxy and presents an interesting case. The time varying triaxial potential of the bars
offers exotic orbits that could explain the existence of kinematic and
photometric features. In this scenario, the KDCs are created from
enriched material transported inwards (perhaps even gas acquired
through a merger), which gets frozen on retrograde orbits tilted with
the respect to the equatorial plane.

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