Mario Klaric

Dust Spirals and Acoustic Noise in the Nucleus of the Galaxy NGC 2207

Observations with the Hubble Space Telescope reveal an irregular network of dust spiral arms in the nuclear region of the interacting disk galaxy NGC 2207. The spirals extend from ~50 to ~300 pc in galactocentric radius, with a projected width of ~20 pc. Radiative transfer calculations determine the gas properties of the spirals and the inner disk and imply a factor of ~4 local gas compression in the spirals. The gas is not strongly self-gravitating, nor is there a nuclear bar, so the spirals could not have formed by the usual mechanisms applied to main galaxy disks. Instead, they may result from acoustic instabilities that amplify at small galactic radii. Such instabilities may promote gas accretion into the nucleus.

Hubble Space Telescope Observations of Dust and Star-forming Regions in the Ocular Galaxy IC 2163 and Its Spiral Companion NGC 2207

Hubble Space Telescope observations in U, B, V, and I passbands of the interacting spiral galaxies IC 2163 and NGC 2207 are used to measure extinctions in the cloud and intercloud regions and ages and luminosities of the star-forming regions. The extinction in the part of NGC 2207 seen in projection against IC 2163 was determined by using the method of White & Keel. The extinctions there and elsewhere were also determined from radiative transfer models of the magnitude differences between clouds and their surroundings. The intercloud extinction in V band ranges from 0.5 to 1 mag on the line of sight, and the cloud extinction ranges from 1 to 2 mag. The measured star-forming regions in these galaxies have a power-law relation between size and luminosity and a power-law luminosity distribution function. These power laws are consistent with a fractal dimension for the star formation that is the same as that for interstellar gas, D ~ 2.2, extending over scales ranging from 20 to 1000 pc. Fifteen compact massive star clusters that are analogous to super–star clusters found in starburst regions are in the spiral arms of NGC 2207. Nothing is peculiar about these regions except for a high H I velocity dispersion (~50 km s-1). Two more super–star clusters are in the tidally compressed oval of IC 2163. These clusters have masses ranging from ~10^4 to 2 × 10^5 M⊙ and ages of a few times 10^6 yr.

Hubble Space Telescope Observations of the Interacting Galaxies NGC 2207 and IC 2163

Original article can be found at: http://www.journals.uchicago.edu/AJ/--Copyright American Astronomical Society

HST observations of the interacting galaxies NGC 2207 and IC 2163

Original article can be found at: http://www.journals.uchicago.edu/AJ/--Copyright American Astronomical Society

The spiral-compact galaxy pair AM 2208-251: Computer simulations versus observations

An attempt is made to explain the observations of the spiral compact-companion system AM 2208 - 251 using a self-gravitating computer simulation of tidal effects of the companion on the spirals disk. The companion swings past the disk in an initially zero energy orbit and pulls out particles forming a bridge and tail spiral arms. The gas particles in the disk are allowed to collide. As a result of collisions, clumps of gas particles are obtained, which are considered to be star-formation sites. To find the best agreement between the observations and the model, mass of companion, distance of approach, azimuthal viewing angle, and viewing time are changed. The model agrees best with the observations for the companion mass equal to 0.2 galaxy mass at 144 million yr after perigalactic point, azimuthal viewing angle 90 deg to the bridge arm, and distance of approaches 24 kpc, or 1.36 disk radii. 12 refs.

Ocular Galaxies: NGC 2535 and its Starburst Companion NGC 2536

We obtained HI, radio continuum, and 12CO J = 1 → 0observations at resolutions of 12″ to 33″ (= 2.9 – 8 kpc), and B, I, J, and K-band images, of the galaxy NGC 2535 and its small starburst companion NGC 2536. NGC 2535 has an ocular (eye-shaped) structure indicative of a recent, close, nonmerging encounter. Our observations reveal widespread high velocity dispersions (30 kms-1) in the HI gas and five clouds with masses of ∼ 108 M⨀ in the tidal arms of NGC 2535. CO emission was detected at the center and on the tidal tail, but close to the center, of NGC 2535; no CO emission was detected from the companion. NGC 2535 has an intrinsically oval shape to the disk, an extended (R = 48 kpc) HI envelope and an outer elliptically-shaped HI arc that may be a gravitational wake produced by the passage of the companion within or close to the extended HI envelope. The starburst companion, NGC 2536, lies in a 2 x 109 M⨀ clump of HI gas at the outer end of the tidal bridge from NGC 2535. A full account our results appears in Kaufman et al. (1997, AJ, 114, 2323).