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

All-sky 2MASS data

Cabrera-Lavers (2005)

Gas warp in the Milky Way

HI densities (Voskes 1999)

Gas warp maximum height:(Voskes 1999)

Φw=+5o

Northern warp

Southern warp

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!!

1) Warp: no vertical symmetry

López-Corredoira et al. (2007)

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

3) No conspiracy of two effects

Carraro et al. (2005)

Simply: Spiral armsdo also warp

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

Conn et al. (2008)

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.)Similarly with other regions

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

Cosmologists! My observationsshow that the galaxies are so… Go and build a model

which fits them.

Astronomer

INDUCTIVE METHOD