OBSERVATIONS OF THE OCULAR GALAXY NGC-2535 AND ITS STARBURST COMPANION NGC-2536

Citation
M. Kaufman et al., OBSERVATIONS OF THE OCULAR GALAXY NGC-2535 AND ITS STARBURST COMPANION NGC-2536, The Astronomical journal, 114(6), 1997, pp. 2323
Citations number
41
Journal title
ISSN journal
00046256
Volume
114
Issue
6
Year of publication
1997
Database
ISI
SICI code
0004-6256(1997)114:6<2323:OOTOGN>2.0.ZU;2-N
Abstract
H I, radio continuum, and (CO)-C-12 J = 1 --> 0 observations at resolu tions of 12 '' to 33 '' (= 2.9-8 kpc), and B, I, J, and K-band images, are presented of the galaxy NGC 2535 and its small starburst companio n NGC2536. NGC 2535 has an ocular (eye-shaped) structure with two long tidal arms indicative of a recent, close, nonmerging encounter. Our o bservations reveal widespread high velocity dispersions (30 km s(-1)) in the H I gas and five clouds with masses of similar to 10(8) M. in t he tidal arms of NGC 2535. These clouds do not correspond to the most luminous blue knots or to major clumps in the old stellar population, Similar phenomena were found previously in other pairs (IC 2163/NGC 22 07 and NGC 5774/5), suggesting that enhanced turbulence and massive ga s clouds may be a general feature of interacting spiral galaxies durin g an early phase of post-encounter evolution. A search for (CO)-C-12 J =1-->0 emission at 11 positions in NGC 2535 and one position in NGC 25 36 yielded two clear detections, one at the center of NGC 2535 and the other on its tidal tail but close to the center of NGC 2535. Most of the massive H I clouds in NGC 2535 are not detected in CO emission, Th e virial masses of these clouds are significantly greater than their m easured masses in gas, presumably because of the presence of old disk stars in the clouds. A form of the virial theorem that includes gas an d stars is presented. NGC 2535 shows several unusual features, includi ng an intrinsically oval shape to the disk, that are similar to those in the ocular galaxy IC 2163 studied previously. NGC 2535 also contain s structures that are not seen in IC 2163. For example, there is an ex tended (R = 48 kpc) H I envelope and a long, outer, elliptically-shape d H I are in NGC 2535 that may be a gravitational wake produced by the passage of the companion within or close to the envelope. In the radi o continuum, NGC 2535 exhibits a bar-like feature that leads the small stellar bar by 50 degrees. The starburst companion, NGC 2536, lies in a 2x10(9) M. clump of H I gas at the outer end of the tidal bridge fr om NGC 2535. Most of the gas in this clump is associated with the brid ge, The H I emission on the anticompanion side of NGC 2536 has the sam e line-of-sight velocity and projected position as some of the bridge gas there, This observation is consistent with a previous model by Kla ric in which NGC 2536 accretes gas from NGC 2535; we even find an H I feature that may represent bridge gas streaming towards NGC 2536. The Failure to detect (CO)-C-12 emission in NGC 2536 places an upper limit of 6 x 10(8) M. on its H-2 mass if the standard value of the conversi on factor between I-CO and N(H-2) applies. (C) 1997 American Astronomi cal Society. [S0004-6256(97)01412-X].