Astro-Ph: The scatter about the "Universal" dwarf spheroidal mass profile

PhD student, Michelle L. M. Collins, working with Scott Chapman (IoA, Cambridge) and members of the Pan-Andromeda Archaeological Survey (PAndAS) (including me), has had her paper on the study of the size of dwarf galaxies accepted for publication in MNRAS. This paper shows further evidence that the dwarf galaxies around the Milky Way are different from those around its sister, the Andromeda Galaxy, and suggests that there must have been some difference in the way these two similar galaxies formed and evolved. Well done Michelle!!!

The scatter about the "Universal" dwarf spheroidal mass profile: A kinematic study of the M31 satellites, And V and And VI

M. L. M. Collins, S. C. Chapman, R. M. Rich, R. A. Ibata, M. J. Irwin, J. Peñarrubia, N. Arimoto, A. M. Brooks, G. F. Lewis, A. W. McConnachie, K. Venn

While the satellites of the Milky Way (MW) have been shown to be largely consistent in terms of their mass contained within one half--light radius (M_{half}) with a "Universal" mass profile, a number of M31 satellites are found to be inconsistent with such relations, and seem kinematically colder in their central regions than their MW cousins. In this work, we present new kinematic and updated structural properties for two M31 dSphs, And V and And VI using data from the Keck Low Resolution Imaging Spectrograph (LRIS) and the DEep Imaging Multi-Object Spectrograph (DEIMOS) instruments and the Subaru Suprime-Cam imager. We measure systemic velocities of v_r=-393.1+/-4.2km/s and -344.8+/-2.5km/s, and dispersions of sigma_v=11.5{+5.3}{-4.4}km/s and sigma_v=9.4{+3.2}{-2.4}km/s for And V and And VI respectively, meaning these two objects are consistent with the trends in sigma_v and r_{half} set by their MW counterparts. We also investigate the nature of this scatter about the MW dSph mass profiles for the "Classical" (i.e. M_V<-8) MW and M31 dSphs. When comparing both the "classical" MW and M31 dSphs to the best--fit mass profiles in the size--velocity dispersion plane, we find general scatter in both the positive (i.e. hotter) and negative (i.e. colder) directions from these profiles. However, barring one exception (CVnI) only the M31 dSphs are found to scatter towards a colder regime, and, excepting the And I dSph, only MW objects scatter to hotter dispersions. We also note that the scatter for the combined population is greater than expected from measurement errors alone. We assess this divide in the context of the differing disc-to-halo mass (i.e. stars and baryons to total virial mass) ratios of the two hosts and argue that the underlying mass profiles for dSphs differ from galaxy to galaxy, and are modified by the baryonic component of the host. 

Comments

Post a Comment

Popular posts from this blog

Falling into a black hole: Just what do you see?

Image
Everyone loves black holes. Immense gravity, a one-way space-time membrane, the possibility of links to other universes. All lovely stuff. A little trawl of the internets reveals an awful lot of web pages discussing black holes, and discussions about spaghettification, firewalls, lost information, and many other things. Actually, a lot of the stuff out there on the web is nonsense, hand-waving, partly informed guesswork. And one of the questions that gets asked is "What would you see looking out into the universe?" Some (incorrectly) say that you would never cross the event horizon, a significant mis-understanding of the coordinates of relativity. Other (incorrectly) conclude from this that you actually see the entire future history of the universe play out in front of your eyes. What we have to remember, of course, is that relativity is a mathematical theory, and instead of hand waving, we can use mathematics to work out what we will see. And that's what I did. ...
Read more

Journey to the Far-Side of the Sun

Image
There was a movie, in the old days, Journey to the Far-Side of the Sun  (also known as Doppleganger) which (spoiler alert) posits that there is a mirror version of the Earth hidden on the other side of the Sun, sharing the orbit with our Earth. The idea is that this planet would always be hidden behind the Sun, and so we would not know it there there. This idea comes up a lot, over and over again. In fact, it came up again last week on twitter. But there's a problem. It assumes the Earth is on a circular orbit. I won't go into the details here, but one of the greatest insights in astronomy was the discovery of Kepler's laws of planetary motion , telling us that planets move on elliptical orbits. With this, there was the realisation that planets can't move at uniform speeds, but travel quickly when closer to the Sun, while slowing down as their orbits carry them to larger distance.  There has been a lot of work examining orbits in the Solar System, and you can  s...
Read more

Moving Charges and Magnetic Fields

Image
Still struggling with grant writing season, so another post which has resulted in my random musings about the Universe (which actually happens quite a lot). In second semester, I am teaching  electricity and magnetism to our First Year Advanced Class . I really enjoy teaching this class as the kids are on the ball and can ask some deep and meaningful questions. But the course is not ideal. Why? Because we teach from a textbook and the problem is that virtually all modern text books are almost the same. Science is trotted out in an almost historical progression. But it does not have to be taught that way. In fact, it would be great if we could start with  Hamiltonian and Lagrangian  approaches, and derive physics from a top down approach. We're told that it's mathematically too challenging, but it really isn't. In fact, I would start with a book like  The Theoretical Minimum , not some multicoloured compendium of physics. We have to work with what we have! ...
Read more