Kavli Affiliate: Jing Wang
| First 5 Authors: Jiang-Tao Li, Li-Yuan Lu, Zhijie Qu, Robert A. Benjamin, Joel N. Bregman
| Summary:
The extraplanar diffuse ionized gas (eDIG) represents ionized gases traced by
optical/UV lines beyond the stellar extent of galaxies. We herein introduce a
novel multi-slit narrow-band spectroscopy method to conduct spatially resolved
spectroscopy of the eDIG around a sample of nearby edge-on disk galaxies
(eDIG-CHANGES). In this paper, we introduce the project design and major
scientific goals, as well as a pilot study of NGC 3556 (M108). The eDIG is
detected to a vertical extent of a few kpc above the disk, comparable to the
X-ray and radio images. We do not see significant vertical variation of the [N
II]/H$alpha$ line ratio. A rough examination of the pressure balance between
different circum-galactic medium (CGM) phases indicates the magnetic field is
in a rough pressure balance with the X-ray emitting hot gas, and may play an
important role in the global motion of both the eDIG and the hot gas in the
lower halo. At the location of an HST/COS observed UV bright background AGN
$sim29rm~kpc$ from the center of NGC 3556, the magnetic pressure is much
lower than that of the hot gas and the ionized gas traced by UV absorption
lines, although the extrapolation of the pressure profiles may cause some
biases in this comparison. By comparing the position-velocity diagrams of the
optical and CO lines, we also find the dynamics of the two gas phases are
consistent with each other, with no evidence of a global inflow/outflow and a
maximum rotation velocity of $sim150rm~km~s^{-1}$.
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