Elliptical Galaxies Spiral Galaxies Barred Spiral Lenticular Irregular L arge M agellanic C loud Dwarf Spheroidal Galaxy Isochrone 25x10 8 yrs Isochrone 4x10 9 yrs IMF in the ρ Oph Association ID: 543700
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Slide1
14-The Evolution of Stars and Gas in GalaxiesSlide2
Elliptical GalaxiesSlide3
Spiral GalaxiesSlide4
Barred Spiral
Lenticular
Irregular (
L
arge
M
agellanic
C
loud)
Dwarf Spheroidal GalaxySlide5Slide6Slide7
Isochrone - 2.5x10
8
yrs
Isochrone - 4x10
9
yrsSlide8Slide9Slide10Slide11Slide12Slide13
IMF in the ρ Oph AssociationSlide14Slide15
Ivan Baldry (2008)
www.astro.ljmu.ac.uk/~ikb/research/imf-use-in-cosmology.htmlSlide16
“The observations are consistent with a single underlying IMF, although the scatter at and below the stellar/sub-stellar boundary clearly calls for further study
.”Bastian et al, 2010, ARAA, 48, 339Slide17
Is the IMF Universal in Space and Time?
The situation is complicated!Doesn’
t seem to be tremendously different within the Milky Way Galaxy, although some obvious differences existM/L in other galaxies - tricky - L is dominated by late-type giants, while M is dominated by dwarf stars
and dark matterHowever, the presence of metals in high-z systems might require a flatter IMF with more massive stars than local IMFSlide18
What about the Star-Formation Rate?
Stars more massive than 2 Msun evolve so quickly they are a good indicator of
current SFR. The past SFR needs to include lower-mass stars - much harder to do (don
’t know ages!)Oort Limit (kinematic) - stars are 70-95 M
sun
pc
-2
. Guessing the time dependence gives 1.5 < SFR < 25
M
sun
pc
-2
Gyr
-1
(but we don’t really know if SFR is currently decreasing or increasing!)Star counts give 43-144
Msun pc-2 and 3 < SFR < 7
M
sun
pc
-2
Gyr
-1
Rough mean of these 2 methods: SFR ~ 10 (+10/-5)
M
sun
pc
-2
Gyr
-1
Slide19
The SFR Depends on Location in the MWG!
Current MWG star formation is dominated by 2 regions:Innermost 1 kpc
Ring between 5-8 kpc of center
And the actual rate is probably dominated by a wide variety of (often) little understood processes: gas density, shock conditions (local sound speed, shock frequency & strength), global and local gas rotation and shear, magnetic field strength, gas metal abundance (cooling!) and the background star density.May need to depend on more general ideas based on relevant factors - a complete analytic description is probably beyond hope at this point.Slide20
Nucleosynthesis & Chemical Enrichment
Main SequenceM<1.1Msun
- pp chain makes He from HM>1.1Msun - CNO makes He from H, while N builds up at expense of CO (Note that this requires pre-existing C)
Post-MSLow-mass stars: Red Giant Tip through Horizontal Branch to Asymptotic Giant Branch - He converted to C and O - winds & PN
High-mass stars: He converted to C and O heavy metals produced through Fe - winds & SN II
Some WD stars in binaries also return heavies - SN ISlide21Slide22Slide23
“G-DwarfProblem”
(There is a deficit of metal poor G stars)Solar neighborhood can be modeled as a closed system
It started as 100% metal-free gasThe IMF is constantThe gas is chemically homogeneous with time
Infall - most stars formed after significant enrichment
Pregalactic
burst of massive stars
Variable IMF
ISM chemically inhomogeneousSlide24Slide25Slide26Slide27
Clouds Above the Galactic Plane
Galactic Fountains?Primordial Local Group Mini-Clouds
Tail-End of MWG FormationTidally-Stripped Gas from Passing Small GalaxySlide28
Magellanic StreamSlide29Slide30Slide31
Abundance Gradients in the Galaxy??Slide32
Korotin et al. 2014, arXiv:1408.6103v1Slide33
Rosolowsky & Simon (2007)