Fraternali, F., Binney, J.J., 2006, MNRAS 366, 449.

1
APO
Deep optical imaging over the past 15 years
has shown that several spiral galaxies possess
thick ionized gas disks and, in some cases,
halos. The extent and brightness of this gas is
generally correlated with the level of star
formation in the disk, suggesting a "galactic
fountain" origin for the gas. However,
preliminary kinematic studies do not always agree
with a fountain model (e.g. Heald et al., 2006,
Fraternali Binney 2006) and some of the gas may
stem from continuing infall. The ionization would
still be provided by star formation in the disk,
but the gas itself might have a different origin.
One way to address this is to determine in more
detail the velocities of the gas for a larger
sample of galaxies. We present initial results
of observations of the edge-on galaxies NGC891
and NGC4244 using a multi-long-slit setup on the
DIS spectrograph on the ARC 3.5m telescope. In
combination with a 25Å Ha filter, 16 slits of 2"
by 4.5' spaced 15" apart were observed
simultaneously over a 4' by 4.5' field of view.
In the case of NGC891, we obtained a medium-deep
spectrum of the Northern half of the halo. We
tested the accuracy of our velocity measurements
by comparing them with previous observations, and
we expanded on the spatial coverage of velocity
measurements of ionized gas in the halo. For
NGC4244, deep optical imaging has not shown a
very extended diffuse ionized gas halo. For this
galaxy, our principal goal is to use our
spectroscopic data to improve upon the
sensitivity limits set in the imaging studies and
to see if there is ionized gas above the
mid-plane.
Fig. 1
Summary
Fig. 5
Radial Velocities of the ionized gas measured
in the disk-halo interface of NGC4244. Slit 8 was
centered on the nucleus. The distance between
slits is 15 or 225 pc. The trend towards
lagging rotation for the halo gas is expected to
be most prominent for slits farthest away from
the center. We see the signature in slits 1, 13,
15, and 16 where the gas at higher distance above
the plane is closer to the systemic radial
velocity of NGC4244.
We present initial results of
multi-long-slit spectroscopy of two edge-on
galaxies. We demonstrate that we can measure
velocities of ionized gas in the halo out to 4
kpc in the case of NGC 891. From the velocity
fields, it appears that the halo gas lags disk
rotation, but this effect is only clearly present
2 kpc or more above the disk. This is in
agreement with other measurements (Heald et.al.,
2006 Kamphuis et.al., 2007) and with the
velocities of the HI halo gas (Oosterloo et.al.,
2007). For NGC 4244, which has a very faint
DIG halo, we detect ionized gas to higher
distances above the plane than seen before. We
have selected a sample of 12 edge-on galaxies for
further study, which will be done in
collaboration with R. Rand and B. Benjamin.
Through longer exposure times, a higher
resolution grating, on-chip binning, and new
filters, our future data will be 2.5 to 4 times
more sensitive than shown here. This provides a
new avenue for studying the origin and dynamics
of gas in thick disks and halos, and it may help
in unravelling the origin of ionization of the
gas.
References
Acknowledgements
Fraternali, F., Binney, J.J., 2006, MNRAS 366,
449. Heald, G.H., etal., 2006, ApJ 647,
1018. Hoopes, C.G., Walterbos, R.A.M., Rand,
R.J., 1999, ApJ 522, 669. Kamphuis, P. etal.,
2007, AA 498, 951. Oosterloo, T., Fraternali,
F., Sancisi, R., 2007, AJ 134, 1019.
This research was supported by an award from
Research Corporation. We acknowledge early
discussions about this mode of spectroscopy with
Robert Braun and the late Michael Ledlow.