Jet-shocked H₂ and CO in the Anomalous Arms of Molecular Hydrogen Emission Galaxy NGC 4258

June 2014 • 2014ApJ...788L..33O

Authors • Ogle, P. M. • Lanz, L. • Appleton, P. N.

Abstract • We present a Spitzer Infrared Spectrograph map of H₂ emission from the nearby galaxy NGC 4258 (Messier 106). The H₂ emission comes from 9.4 ± 0.4 × 10⁶ M _⊙ of warm molecular hydrogen heated to 240-1040 K in the inner anomalous arms, a signature of jet interaction with the galaxy disk. The spectrum is that of a molecular hydrogen emission galaxy (MOHEG), with a large ratio of H₂ over 7.7 μm polycyclic aromatic hydrocarbon emission (0.37), characteristic of shocked molecular gas. We find close spatial correspondence between the H₂ and CO emission from the anomalous arms. Our estimate of cold molecular gas mass based on CO emission is 10 times greater than our estimate of 1.0 × 10⁸ M _⊙ based on dust emission. We suggest that the X _CO value is 10 times lower than the Milky Way value because of high kinetic temperature and enhanced turbulence. The H₂ disk has been overrun and is being shocked by the jet cocoon, and much of the gas originally in the disk has been ejected into the galaxy halo in an X-ray hot outflow. We measure a modest star formation rate of 0.08 M _⊙ yr^-1 in the central 3.4 kpc² that is consistent with the remaining gas surface density.

Links

• PREPRINT http://arxiv.org/abs/1405.2040
• NED https://ned.ipac.caltech.edu/uri/NED::InRefcode/2014ApJ...788L..33O
• ELECTR https://doi.org/10.1088%2F2041-8205%2F788%2F2%2FL33
• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2014ApJ...788L..33O
• PDF https://iopscience.iop.org/article/10.1088/2041-8205/788/2/L33/pdf
• PDF https://stacks.iop.org/2041-8205/788/L33/pdf
• DATA https://archive.stsci.edu/mastbibref.php?bibcode=2014ApJ...788L..33O
• DATA https://cda.harvard.edu/chaser?obsid=350,1618,2340
• DATA https://irsa.ipac.caltech.edu/bibdata/2014/O/2014ApJ...788L..33O.html