Canis Major overdensity and Monoceros Ring explained in terms of
Transcript of Canis Major overdensity and Monoceros Ring explained in terms of
Canis Major overdensity andMonoceros Ring explained in
terms of pure Milky Waystructure
Martín López-CorredoiraInstituto de Astrofísica de Canarias (Tenerife, Spain)
Leiden; July 14th, 2009
Colaborators: P. L. Hammersley, Y. Momany, S. Zaggia, A. Cabrera-Lavers
Canis Major and its stream?
Martin & Ibata (2003)
Monoceros Stream
A new streamdiscovered:
(e.g., Newberg et al. 2002, Rocha-Pinto et al. 2003,
Conn et al. 2005)
Canis Major: a galaxy covering
~50º of sky and at only ~8 kpc from
the Sun, fromwhich we had notrealized before?
A new galaxy discovered! (e.g., Martin et al. 2004, Martínez-Delgado et al. 2005,
Bellazzini et al. 2006)
Or just the warpof our Galaxy?
Stellar warp(+flare) in the Milky Way
López-Corredoira et al. (2002):zw=Cw Rεw sin (Φ-Φw) – (15 pc)
(valid for R<13 kpc)zw: height of disc over plane b=0
Cw: amplitude of the warp=1.2e-3 pcεw: exponent of the warp=5.25±0.50Φw: galactocentric azimuth of warp
line of nodes=-5o ± 5o
R: galactocentric distance (kpc)Φ: galactocentric azimuth
2MASS data
Canis Major: BumpBellazzini et al. (2006)
López-Corredoira (2006)
Extrapolation of southernwarp for 13<R<16 kpc:
constant height
Canis Major: Overdensity of red clump stars
Model from López-Corredoira et al. (2002)Φw=-5o lmax=270o
Φw=+5o lmax=248o
lmax=244oBellazzini et al. (2006): 5o<|b|<15o
López-Corredoira (2006)
Canis Major: Blue plume
Carraro et al. (2005): open squares open clustersfilled triangles BP population
Moitinho et al. (2006): open cluster NGC 2362, l=238.2o, b=-5.5o
Blue Plume: B5-A5 stars with <100 Myr in the Norma-Cygnus or Perseus spiral arms
Canis Major: Metallicity
-0.4<[Fe/H]<-0.7 (Bellazzini et al. 2006)
(as expected in the outer disc, at R=13 kpc)
Canis Major: velocity of stars- Radial velocities: distribution explained in terms
of the Galactic rotation (Momany et al. 2006).- Tangential velocities perpendicular to the disc:
* The selected stars might be contamination notassociated with CMa (Momany et al. 2006) [blue plume].* The expected warp signature is compatible with the negative vertical velocity (Momany et al. 2006) [7σ came from errors in distancedetermination of Hipparcos OB stars in Drimmel et al. (2000)].
- Unknown warp velocities:* They depend on the model of warp formation.* Asymmetries in the warp. Dinescu et al. (2005)
Canis Major (2nd. round): discovering flaws in 2007 papers withinterpretations different to a Galactic warp
López-Corredoira et al. (2007)
Butler et al. (B07), Conn et al. (C07), de Jong et al. 2007 (d07) claims against the warp:
1) The warp should give similar star counts and CM diagrams at l=2400, b=-30±Δb and we seedifferences (B07,C07)
2) The warp produces a maximum of the counts at(m-M)~10.5 [d=1.3 kpc] instead of the obs. 7 kpcand it is a wider structure than Canis Major (B07)
3) There is a blue plume population in our CM diagrams typical of dwarf galaxies…Young pop. in spiral arm in our Galaxy? hummm, maybe…! But this would be a conspiracy of two effects (warps and spiral arms) (B07, d07)
4) [Fe/H] down to -1.0±0.2 at some fields (d07)
Reply:
1) The mid plane of the warp at b=-30
is not a plane of symmetry
2) B07 calculations are wrong.Possible source of error: maybe theyhave used dN/dm α ρr instead of
dN/dm α ρr3
3) There is no conspiracy, but just oneeffect: the warp which includes the oldand the young populations of the disc(spiral arms)
4) The thick disc has metallicity in theouter Galaxy around -1.0 while thethin disc around -0.5 with r.m.s. of0.4-0.5 mag. NO PROBLEM!!
2) Differential star counts:For a given direction (l,b), without extinction a population
with absolute magnitude M gives total star counts up to m:
N(<m)=ω∫0r(m) dx x2 ρ(x)
r(m)=10(m-M+5)/5
Thus, the differential star counts (counts per unit magnitude)
A(m) ≡ dN(m)/dm = ω ρ[r(m)] r(m)3 ln(10)/5
4) No population older than MW thick disc/halo
- No stars with lowermetallicity than expected(López-Corredoira et al.
2007)- No excess of RR Lyrae
(Mateu et al. 2009) - No excess of Open
Clusters (Piatti & Clariá2008)
Monoceros ring
SDSS data
Galactic models with cut-off at R=14 kpc (Besançon) or without flaredo not reproduce the CM diagram
Monoceros ring
A thin+thick disc witheach component:
ρ(R,z)= ρsun hz,sun/hz(R)e((-R+Rsun)/hR) e-|z|/hz(R)
flared at R>16 kpc:
hz(R)= hz(Rsun) e(R-16 kpc)/hrf
Hammersley & López-Corredoira (in prep.)
Monoceros ring
Hammersley & López-Corredoira (in prep.)
A flared thick+thindisc which extendsup to R>20 kpc do
reproduce Monoceros
Monoceros: metallicity
Monoceros:[Fe/H]=-0.96, rms=0.15
(Ivezik et al. 2008)
typical of the thick disc
Conclusions:
Warped+flared disc can explain the excess of starsand CM diagrams in Canis Major and Monoceros.
Metallicities, velocities,… are also compatible withour knowledges about the Galaxy
MORAL 1: a model of the Galaxy ≠ Galaxy, so features not included in a model are not
necessarily extragalactic
MORAL 2: Cosmological models ≠ Universe, so do notuse them as guides of what should be observed
Astronomers! My modelpredicts there should be
plenty of streams andsatellites around galaxies. Go
and look for them!
ΛCDM
Cosmologist
DEDUCTIVEMETHOD