Peter Kamphuis

Kinematics of diffuse ionized gas in the disk halo interface of NGC 891 from Fabry-Pérot observations

Context. The properties of the gas in halos of galaxies constrain global models of the interstellar medium. Kinematical information is of particular interest since it is a clue to the origin of the gas. Aims. Here we report observations of the kinematics of the thick layer of the diffuse ionized gas in NGC 891 in order to determine the rotation curve of the halo gas. Methods. We have obtained a Fabry-Perot data cube in H alpha to measure the kinematics of the halo gas with angular resolution much higher than obtained from HI 21 cm observations. The data cube was obtained with the TAURUS II spectrograph at the WHT on La Palma. The velocity information of the diffuse ionized gas extracted from the data cube is compared to model distributions to constrain the distribution of the gas and in particular the halo rotation curve. Results. The best fit model has a central attenuation tau H alpha = 6, a dust scale length of 8.1 kpc, an ionized gas scale length of 5.0 kpc. Above the plane the rotation curve lags with a vertical gradient of -18.8 kms(-1) kpc(-1). We find that the scale length of the H alpha must be between 2.5 and 6.5 kpc. Furthermore we find evidence that the rotation curve above the plane rises less steeply than in the plane. This is all in agreement with the velocities measured in the HI.

Massive stars formed in atomic hydrogen reservoirs: H I observations of gamma-ray burst host galaxies

Long gamma-ray bursts (GRBs), among the most energetic events in the Universe, are explosions of massive and short-lived stars, so they pinpoint locations of recent star formation. However, several GRB host galaxies have recently been found to be deficient in molecular gas (H2), believed to be the fuel of star formation. Moreover, optical spectroscopy of GRB afterglows implies that the molecular phase constitutes only a small fraction of the gas along the GRB line of sight. Here we report the first ever 21 cm line observations of GRB host galaxies, using the AustraliaTelescope Compact Array, implying high levels of atomic hydrogen (Hu2009i), which suggests that the connection between atomic gas and star formation is stronger than previously thought. In this case, it is possible that star formation is directly fuelled by atomic gas (or that the Hu2009i-to-H2 conversion is very efficient, which rapidly exhaust molecular gas), as has been theoretically shown to be possible. This can happen in low-metallicity gas near the onset of star formation because cooling of gas (necessary for star formation) is faster than the Hu2009i-to-H2 conversion. Indeed, large atomic gas reservoirs, together with low molecular gas masses, stellar, and dust masses are consistent with GRB hosts being preferentially galaxies which have very recently started a star formation episode after accreting metal-poor gas from the intergalactic medium. This provides a natural route for forming GRBs in low-metallicity environments. The gas inflow scenario is also consistent with the existence of the companion Hu2009I object with no optical counterpart ~19 kpc from the GRBu2009060505 host, and with the fact that the Hu2009I centroids of the GRBu2009980425 and 060505 hosts do not coincide with optical centres of these galaxies, but are located close to the GRB positions.

HALOGAS observations of NGC 5023 and UGC 2082: modelling of non-cylindrically symmetric gas distributions in edge-on galaxies

In recent years, it has become clear that the vertical structure of disc galaxies is a key ingredient for understanding galaxy evolution. In particular, the presence and structure of extra-planar gas has been a focus of research. The Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey aims to provide a census on the rate of cold neutral gas accretion in nearby galaxies as well as a statistically significant set of galaxies that can be investigated for their extra-planar gas properties. In order to better understand the vertical structure of the neutral hydrogen in the two edge-on HALOGAS galaxies NGC 5023 and UGC 2082, we construct detailed tilted ring models. The addition of distortions resembling arcs or spiral arms significantly improves the fit of the models to these galaxies. In the case of UGC 2082, no vertical gradient in rotational velocity is required in either symmetric models nor non-symmetric models to match the observations. The best-fitting model features two arcs of large vertical extent that may be due to accretion. In the case of NGC 5023, a vertical gradient is required in symmetric models (dV/dz = -14.9 +/- 3.8 km s(-1) kpc(-1)) and its magnitude is significantly lowered when non-symmetric models are considered (dV/dz = -9.4 +/- 3.8 km s(-1) kpc(-1)). Additionally, it is shown that the underlying disc of NGC 5023 can be made symmetric, in all parameters except the warp, in non-symmetric models. In comparison to the classical modelling, these models fit the data significantly better with a limited addition of free parameters.

A dust component 2 kpc above the plane in NGC 891

Context. The halo of NGC 891 has been the subject of studies for more than a decade. One of its most striking features is the large asymmetry in Hα emission. In this letter, we will take a quantitative look at this asymmetry at different wavelengths for the first time. Aims. We suggest that NGC 891 is intrinsically almost symmetric and the large asymmetry in Hα emission is mostly due to dust attenuation. We will quantify the additional optical depth needed to cause the observed asymmetry in this model. Methods. By comparing large strips on the North East side of the galaxy with strips covering the same area in the South West we can quantify and analyze the asymmetry in the different wavelengths. Results. From the 24 µm emission we find that the intrinsic asymmetry in star formation in NGC 891 is small i.e., ∼30%. The additional asymmetry in Hα is modeled as additional symmetric dust attenuation which extends up to ∼40 �� (1.9 kpc) above the plane of the galaxy with a mid-plane value of τ = 0.8 and a scale height of 0.5 kpc

ASKAP HI imaging of the galaxy group IC 1459

We present HI imaging of the galaxy group IC 1459 carried out with six antennas of the Australian SKA Pathfinder equipped with phased-array feeds. We detect and resolve HI in eleven galaxies down to a column density of

Automated kinematic modelling of warped galaxy discs in large H i surveys: 3D tilted-ring fitting of H i emission cubes

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HALOGAS observations of NGC 4414: fountains, interaction, and ram pressure

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A tale of two galaxies: light and mass in NGC 891 and NGC 7814

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The second closest gamma-ray burst: sub-luminous GRB 111005A with no supernova in a super-solar metallicity environment

inside a ~6 deg

An H I view of galaxy conformity: H I-rich environment around H I-excess galaxies

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