A zoom into the nuclei of IC1459 and NGC7582

Team responsible: H. Dejonghe (University of Ghent)
Team members: H. Kuntschner, M. Baes, S. De Rijcke

Finding chart: IC1459NGC7582

We propose to use SINFONI to take K-band spectra of the circumnuclear (3.2 arcsec)2 region of the nearby galaxies IC1459 and NGC7582. Both have prototypical Seyfert 2 nuclei, which can serve to guide the AO module, such that we can achieve a resolution of 0.1 arcsec, corresponding to a linear distance of the order of 5 pc. We will map the distribution and kinematics of the molecular and ionized hydrogen with the H2 S(1-0) and Brγ lines over the entire field of view. This will allow us to constrain the size and orientation of the putative molecular torus. Moreover, since the nuclei have relatively strong stellar absorption features, we can study the kinematics of the nuclear stellar population with the CO(2-1) bandhead, well within the sphere of influence of the central black hole. The combination of gas and stellar kinematics will be used to determine the black hole mass. As the number of spiral galaxies with a dynamically central black hole mass is small, the proposed program will in a critical way probe the generality of the M(BH)-sigma relation in the low-mass regime.

Target list
NameRA(2000)DEC(2000)Plate-Scale(s)Bands(s)Exp.time(on source)
IC145922:57:10.60-36:27:44.0100K2.5 h
NGC758223:18:23.78-42:22:16.64100K2.5 h

Scientific rationale:
One of the major breakthroughs in our quest towards the understanding of galaxies has been the discovery that most of them harbour a black hole (BH) in their center. Though suspected for some time already, the strong evidence for this is relatively recent. This has mainly to do with the fact that, though the BH mass is very large to solar standards (at least 1 million, up to one billion solar masses), the dynamical impact is significant only over relatively small regions of the order of tens of parsecs. Any kinematical signature therefore is detectable only with very high angular resolution, and state-of-the art spectral resolution. The problem is compounded by the environment around the center, which is mostly dusty and therefore difficult to observe in the optical.

Somewhat surprisingly, the masses obtained so far correlate strongly with the large scale properties of the host galaxies, which in all likelyhood means that the BH plays a major role in the formation and the evolution of galaxies. This correlation is based on some thirty secure mass determinations for mostly early type systems. For spirals however, which form the lower mass end of the galaxy population, the BH masses are consequently smaller and mass determinations are more difficult and fewer (only a handful secure determinations).

SINFONI offers a unique possibility to increase the number statistics for BH mass determinations in spirals, due to its high angular resolution and the near-infrared integral field spectroscopy. This latter capability is crucial, since spirals often contain a nuclear disk of unknown orientation, so that long-slit spectroscopy is generally insufficient. With this program we want to explore the possible impact of SINFONI in this area of galaxy research.

We propose to observe IC1459 and NGC7582. These galaxies are nearby Seyferts, which are well-known prototypical members of their class, and therefore also of great interest by themselves. Moreover, the pointlike bright nucleus should be appropriate to guide the AO. With the proposed resolution of 0.1 arcseconds, we obtain a spatial resolution of the order of 5 parsecs, which should be more than sufficient to probe the BH mass.

Observing strategy
The nucleus of IC1459 is relatively bright in the K-band, such that a total exposure time of 2.5h on source is sufficient to obtain a SNR of 15 per resolution element. This integration should be split in short exposures of 240 sec each, dithered over 1 pixel in the usual way. Separate sky exposures are required, with a significant fraction of the on-source exposure time (1h). At least two velocity standard stars (late-type stars, typical of a circumnuclear environment) with a high SNR (at least 75) should be measured. Dwarfs should be observed as telluric template stars.