Astron. Astrophys. Suppl. Ser. 136, 179-187

Spectroscopic observations of southern nearby galaxies

I. NGC 2442

E. Bajaja¹ - E. Agüero² - S. Paolantonio²

Send offprint request: E. Bajaja,
e-mail: bajaja@irma.iar.unlp.edu.ar

1 - Instituto Argentino de Radioastronomía, C.C. 5, 1894 Villa Elisa, Prov. de Bs.As., Argentina
2 - Observatorio Astronómico de Córdoba, Laprida 854, 5000 Córdoba, Argentina

Received August 31, 1998; accepted January 4, 1999

Abstract:

The galaxy NGC 2442 was observed with a REOSC spectrograph, installed in the 2.15 m CASLEO telescope, in order to derive galactic parameters from the observed optical lines and to compare them with the results of radioastronomical observations made in the continuum, at 843 MHz, with the MOST and in the CO lines with the SEST telescope. Recent publications allowed us to extend the comparison to results from interferometric observations of H$\alpha$ and H I 21 cm lines and of the continuum at 1415 MHz. The long slit observations were made placing the 5$\hbox{$.\mkern-4mu^\prime$}$8 slit at six different positions on the optical image of the galaxy. The emission line intensity ratios at the nuclear region indicate that NGC 2442 is a LINER. The electron temperature and volume density are $T_{\rm{e}} \approx$ 14 000 K and $N_{\rm{e}} \approx$ 530 cm^-3, respectively. In contrast, a spectrum of a region 87$\hbox{$^{\prime\prime}$}$ to the NE shows the typical characteristics of a H II region. In this case $T_{\rm{e}} \approx$ 6 500 K and $N_{\rm{e}} \approx$ 10 cm^-3. Good correlations between the distributions of intensities, velocity fields and rotation curves have been found for the optical and radio lines. It is shown that the three intensity peaks along the line at PA = 40$\hbox{$^\circ$}$ were not resolved by the observations at radio frequencies. The steep central rotation curve seen in CO has been confirmed and improved showing the existence of a disc or a ring, with a radius of 12$\hbox{$.\!\!^{\prime\prime}$}$5, rotating at 216/sin(i) $\rm \, km\, s^{-1}$. Two velocity components in three optical spectra obtained in the nuclear region, have been related to two small H$\alpha$ regions close to the nucleus and to the central ring. Asymmetries in the distributions of the emitting sources and irregularities in their velocity fields indicate the need of modelling the galaxy before any dynamical study is attempted.

Key words: galaxies: NGC 2442; kinematics and dynamics; nuclei; ISM