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In this paper we derive a possible mass profile for the low surface brightness galaxy, Malin 1, based upon previously published space-based and ground-based photometric properties and kinematics. We use properties of the bulge, normal disk, outer extended disk, and H imass as inputs into mass profile models. We find that the dark matter halo model of Malin 1 is best described by a halo profile that has undergone adiabatic contraction, inconsistent with the findings for most disk galaxies to date, yet consistent with rotation curve studies of M31. More importantly, we find that Malin 1 is baryon dominated in its central regions out to a radius of (in the bulge region). Low surface brightness galaxies are often referred to as being dark matter dominated at all radii. If this is the case, then Malin 1 would seem to have characteristics similar to those of normal barred disk galaxies, as suggested by other recent work. We also find that Malin 1 falls on the rotation curve shear versus spiral arm pitch angle relation for normal galaxies, although more LSB galaxies need to be studied to determine if this is typical.

We report the discovery of a galaxy cluster serendipitously detected as an extended X-ray source in an offset observation of the group NGC 5044. The cluster redshift, z = 0.281, determined from the optical spectrum of the brightest cluster galaxy, agrees with that inferred from the X-ray spectrum using the Fe Ka complex of the hot ICM (z = 0.27 +- 0.01). Based on the 50 ks XMM-Newton observation, we find that within a radius of 383 kpc the cluster has an unabsorbed X-ray flux fX(0.5-2 keV) = (3.34img1.gif) x 10-13 ergs cm-2 s-1, a bolometric X-ray luminosity LX = (2.21img2.gif) x 1044 ergs s-1, kT = 3.57 +- 0.12 keV, and metallicity 0.60 +- 0.09 Z. The cluster obeys the scaling relations for LX and T observed at intermediate redshift. The mass derived from an isothermal NFW model fit is Mvir = 3.89 +- 0.35 x 1014 M, with a concentration parameter, c = 6.7 +- 0.4, consistent with the range of values expected in the concordance cosmological model for relaxed clusters. The optical properties suggest this could be a "fossil cluster."

We investigate the use of spiral arm pitch angles as a probe of disk galaxy mass profiles. We confirm our previous result that spiral arm pitch angles (P) are well correlated with the rate of shear (S) in disk galaxy rotation curves by using a much larger sample (51 galaxies) than used previously (17 galaxies). We use this correlation to argue that imaging data alone can provide a powerful probe of galactic mass distributions out to large look-back times. In contrast to previous work, we show that observed spiral arm pitch angles are similar when measured in the optical (at 0.4 mm) and the near-infrared (at 2.1 mm) with a mean difference of 2.deg3 +- 2.deg7. This is then used to strengthen the known correlation between P and S using B-band images. We then use two example galaxies to demonstrate how an inferred shear rate coupled with a bulge-disk decomposition model and a Tully-Fisher-derived velocity normalization can be used to place constraints on a galaxy's baryon fraction and dark matter halo profile. We show that ESO 582-G12, a galaxy with a high shear rate (slightly declining rotation curve) at ~10 kpc, favors an adiabatically contracted halo, with high initial NFW concentration (cvir > 16) and a high fraction of halo baryons in the form of stars (~15%-40%). In contrast, IC 2522 has a low shear rate (rising rotation curve) at ~10 kpc and favors nonadiabatically contracted models with low NFW concentrations (cvir [?] 2-8) and a low stellar baryon fraction <10%.