arXiv subjects

Christian Henkel

Publications and source records attributed to Christian Henkel.

111 records · Page 7Linked to original sources

arXiv1999

HST and VLA Observations of the H2O Gigamaser Galaxy TXS2226-184

We present HST/WFPC2 images in Halpha+[NII]6548,6583 lines and continuum radiation and a VLA map at 8 GHz of the H2O gigamaser galaxy TXS2226-184. This galaxy has the most luminous H2O maser emission known to date. Our red continuum images reveal a highly elongated galaxy with a dust lane crossing the nucleus. The surface brightness profile is best fitted by a bulge plus exponential disk model, favoring classification as a highly inclined spiral galaxy (i=70 degree). The color map confirms the dust lane aligned with the galaxy major axis and crossing the putative nucleus. The Halpha+[NII] map exhibits a gaseous, jet-like structure perpendicular to the nuclear dust lane and the galaxy major axis. The radio map shows compact, steep spectrum emission which is elongated in the same direction as the Halpha+[NII] emission. By analogy with Seyfert galaxies, we therefore suspect this alignment reflects an interaction between the radio jet and the ISM. The axes of the nuclear dust disk, the radio emission, and the optical line emission apparently define the axis of the AGN. The observations suggest that in this galaxy the nuclear accretion disk, obscuring torus, and large scale molecular gas layer are roughly coplanar. Our classification of the host galaxy strengthens the trend for megamasers to be found preferentially in highly inclined spiral galaxies.

astro-ph↗

arXiv1998

The detection of extragalactic $^{15}$N: Consequences for nitrogen nucleosynthesis and chemical evolution

Detections of extragalactic $^{15}$N are reported from observations of the rare hydrogen cyanide isotope HC$^{15}$N toward the Large Magellanic Cloud (LMC) and the core of the (post-) starburst galaxy NGC 4945. Accounting for optical depth effects, the LMC data from the massive star-forming region N113 infer a $^{14}N/^{15}$N ratio of 111 $\pm$ 17, about twice the $^{12}C/^{13}$C value. For the LMC star-forming region N159HW and for the central region of NGC 4945, $^{14}N/^{15}$N ratios are also $\approx$ 100. The $^{14}N/^{15}$N ratios are smaller than all interstellar nitrogen isotope ratios measured in the disk and center of the Milky Way, strongly supporting the idea that $^{15}$N is predominantly of `primary' nature, with massive stars being its dominant source. Although this appears to be in contradiction with standard stellar evolution and nucleosynthesis calculations, it supports recent findings of abundant $^{15}$N production due to rotationally induced mixing of protons into the helium-burning shells of massive stars.

astro-ph↗

arXiv1997

Molecular gas in the elliptical galaxy NGC759. Interferometric CO observations

Interferometric observations of the CO(1-0) line in the elliptical galaxy NGC759 shows that it contains 2 10^9 Mo of molecular gas, confined to a circumnuclear ring with an average radius of only 650pc. The maximum gas surface density is 750 Mo/pc^2, which is comparable to the critical gas surface density for large scale gravitational instabilities. The low CO(2-1)/CO(1-0) ratio of 0.4 is consistent with a two-component molecular gas, consisting of a cold and dense phase, containing most of the mass, and a warm and diffuse component dominating the CO emission. We use a mass model for the underlying galaxy which is applicable to spherical galaxies with an r^1/4 luminosity profile. This leads to more modest estimates of the molecular gas fraction and gas surface density then would have been derived using simpler models, suggesting that many of the spectacular molecular gas properties of ultraluminous FIR galaxies, which could be described by similar mass models, may have to be revised. We discuss the possibility that NGC759 is in a late stage of a merging between two gas-rich disk galaxies.

astro-ph↗