HALOGAS: HI Observations and Modeling of the Nearby Edge-on Spiral Galaxy NGC 4565

Gianfranco Gentile

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40 Citations (Scopus)


We present 21 cm observations and models of the neutral hydrogen in NGC 4565, a nearby, edge-on spiral galaxy, as part of the Westerbork Hydrogen Accretion in LOcal GAlaxieS survey. These models provide insight concerning both the morphology and kinematics of H I above, as well as within, the disk. NGC 4565 exhibits a distinctly warped and asymmetric disk with a flaring layer. Our modeling provides no evidence for a massive, extended H I halo. We see evidence for a bar and associated radial motions. Additionally, there are indications of radial motions within the disk, possibly associated with a ring of higher density. We see a substantial decrease in rotational velocity with height above the plane of the disk (a lag) of -40+5 - 20 km s-1 kpc-1 and -30+5 - 30 km s-1 kpc-1 in the approaching and receding halves, respectively. This lag is only seen within the inner ~4farcm75 (14.9 kpc) on the approaching half and ~4farcm25 (13.4 kpc) on the receding half, making this a radially shallowing lag, which is now seen in the H I layers of several galaxies. When comparing results for NGC 4565 and those for other galaxies, there are tentative indications of high star formation rate per unit area being associated with the presence of a halo. Finally, H I is found in two companion galaxies, one of which is clearly interacting with NGC 4565.
Original languageEnglish
Article number37
Number of pages17
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 31 Oct 2012


  • galaxies : halos
  • galaxies : indi
  • galaxies : kinematics and dynamics
  • galaxies : spiral
  • galacties : structure


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