Colloquia

2019 HotSci at STScI

Wed 14 Aug 2019
Location:

Space Telescope Science Institute (STScI)
3700 San Martin Drive
Baltimore, MD 21218

Time:

2:45 PM - 4:00 PM

Contact Information:

Have questions? Please contact Martha Devaud.

Description:

Featuring Patrick Ogle on A Break in the Tully-Fisher Relation and Cosmic Mass Limit for Spiral Galaxies and Annalisa Calamida on A Stellar Halo Surrounding Omega Cen.

Notes:

All talks are held on Wednesdays in the STScI John N. Bahcall Auditorium at 3:00 p.m. preceded by refreshments at 2:45 p.m.

Name: Patrick Ogle 
Title: A Break in the Tully-Fisher Relation and Cosmic Mass Limit for Spiral Galaxies
Abstract: Super spiral galaxies are the most massive, giant spiral galaxies in the local universe, at redshift z<0.3. I measured H-alpha rotation curves for 16 super spiral galaxies with SALT and found unprecedented rotation velocities up to 570 km/s, indicating very massive dark matter halos. Super spirals break from the baryonic Tully-Fisher relation established for less massive galaxies, with baryonic masses that are much smaller than what that relation predicts. They appear to obey a stellar mass limit of 6E11 Msun, set by the critical mass for shocks at the virial radius of their dark matter halos. Once they hit that limit, they can no longer efficiently accrete cold gas. The existence of a cosmic mass limit for galaxies also has important implications for the formation and evolution of giant elliptical galaxies at the centers of massive galaxy clusters, and puts the final nail in the coffin of the Modified Newtonian Gravity (MOND) theory. 

Name: Annalisa Calamida
Title: A Stellar Halo Surrounding Omega Cen
Abstract: I will present results from a catalog of ~1.8 million Omega Cen member stars derived from DECam photometry covering a field of view of ~5x5 degrees across the cluster and HST data for the innermost regions.  The unprecedented accuracy of DECam photometry, the depth and field coverage, combined with HST data for the cluster core, allowed me for the first time to derive the global stellar density profile of Omega Cen based on star counts of red-giant and main-sequence stars from 1 to ~140 arcminutes. The King and Wilson models fail to reproduce the outermost shape of Omega Cen density profile suggesting that the interaction with the Galactic tidal field and the presence of potential escaper (extra-tidal) stars need to be taken into account to explain the observations. The best fit of Omega Cen density profile is found with the SPES models which include potential escaper stars, confirming the presence of a stellar halo around the cluster.