Near-infrared imaging and spectroscopy of the nuclear region of the disturbed Virgo cluster spiral NGC4438
Abstract
We present near-infrared (NIR) Very Large Telescope (VLT) Infrared Spectrometer and Array Camera (ISAAC) imaging and spectroscopy of the peculiar Virgo galaxy NGC4438, whose nucleus has been classified as a low-ionization nuclear emission-line region (LINER). The data are supplemented by mid-infrared imaging, and compared to previous HST broad-band images. Images and position-velocity maps of the [FeII] and H2 line emissions are presented and compared with the distribution of the optical narrow-line region and radio features. Our results show that shocks (possibly driven by a radio jet) contribute to an important fraction of the excitation of [FeII], while X-ray heating from a central active galactic nucleus (AGN) may be responsible for the H2 excitation. We address the question whether the outflow has an AGN or a starburst origin by providing new estimates of the central star formation rate and the kinetic energy associated with the gas. By fitting a Sérsic bulge, an exponential disc and a compact nuclear source to the light distribution, we decomposed NGC4438's light distribution and found an unresolved nuclear source at 0.8arcsec resolution with MK = -18.7 and J - H = 0.69. Our measured bulge velocity dispersion, 142 kms-1, together with the standard relation, suggests a central black hole mass of . The stellar kinematics measured from the NIR CO lines show a strong peak in the velocity dispersion of σ0 ~ 178 kms-1 in the central 0.5arcsec, which is possible kinematic evidence of a central black hole. We calculated a general expression for the integrated Sérsic profile flux density in elliptical geometry, including the case of `discy' isophotes.
Based on VLT service mode observations (Programme 69.B-0411) and TIMMI2 (run 68.D-0432) gathered at the European Southern Observatory, Chile. E-mail: s.perez2@physics.ox.ac.uk- Publication:
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Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 2009
- DOI:
- 10.1111/j.1365-2966.2009.15603.x
- arXiv:
- arXiv:0908.3477
- Bibcode:
- 2009MNRAS.400.2098P
- Keywords:
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- galaxies: active;
- galaxies: individual: NGC4438;
- galaxies: starburst;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 13 pages, 12 figures. Affiliation added. Higher resolution images