Post on 27-Dec-2015
The Baryon Induced Transformation of CDM Halos
Mario G. Abadi
Universidad Nacional de Córdoba, CONICETArgentina
In collaboration with Julio Navarro and the Canadian Computational
Cosmology Collaboration (C4), University of Victoria, Canada
LENAC Latin-american WorkshopOctober 29 to November 1
Guaruja Brazil
How dark matter halos are transformed by baryons?
Profile (Theory vs Simulations)
Shape (Sphericity vs Triaxiality)
Orientation (Halo vs Disk)
Profile: Theory Blumenthal et al. (1986)
Contraction of a dark matter halo in response to condensation
of baryons in its center.
The cooling of gas in the centers of dark matter halos is
expected to lead to a more concentrated dark matter
distribution.
The response of dark matter to the condensation of baryons is
usually calculated using the standard model of adiabatic
contraction
Adiabatic contraction
Spherically simetric dark matter halo with circular orbits
Conservation of the adiabatic invariant M(r)r
I=Integral of q dp = Integral of p dq
If p is the circular velocity, then dq=r dtheta
I=Integral of v r dtheta using v^2=GM/r
I=Int(GM/r)^(1/2) r dtheta = (GM/r)^(1/2)
Int(dtheta)/2pi=(GM/r)^(1/2)
I=GMr=r^2 v^2
Profile: Simulations Gnedin et al (2004)
High-resolution cosmological simulations which include gas
dynamics, radiative cooling, and star formation
Particle orbits in the halos are highly eccentric
Dissipation of gas indeed increases the density of dark matter
and steepens its radial profile in the inner regions of halos
compared to the case without cooling Simple modification of the assumed invariant from M(r)r to
M(r_av)r, where r and r_av are the current and orbit-
averaged particle positions
Profile: Simulations Abadi et al. (2006)
The adiabatic contraction model
C4 Numerical simulations
Simulations of 13 galactic dark matter halos
With and without gas
High and low resolution
One halo also at super high and super low resolution
Profile: Simulations Abadi et al. (2006)
The abadiatic contraction model
C4 Numerical simulations
Simulations of 13 galactic dark matter halos
With and without gas
High and low resolution
One halo also at super high and super low resolution
Circular Velocity Profile
Circular velocity and density profiles are increased by the presence of the baryons
Different models give different dark matter profiles in the inner parts
Contracted dark matter halos
Polinomial fit to infer contracted dark matter profiles from non-contracted dark matter + gas profiles
Inverse model
● Total mass of the disk Mdisk
● Contribution of the exponential disk to the total velocity
● Vdisk^2(r)=2 G Mdisk/Rdisk x^2 (I0(x) K0(x)-I1(x) K1(x))
● where x=r/2/Rdisk
● Contribution of the (contracted) dark matter halo to the total velocity
Vdark^2=Vrot^2-Vdisk^2
● Invert the model in order to obtain the circular velocity of the non-
contracted (i.e. without gas) dark matter (only) halo at r=2.2Rdisk
● Assuming the shape of the dark matter halo (i.e. a concentration
parameter “c” for the NFW fit), you have the non-contracted dark
matter halo density profile and its Vvirial and Vmaximum
Application to the Milky Way
Mdisk=6.0x10^10 solar masses
Rdisk=3.5 kpc
Vrot(2.2Rdisk)=220 km/sec
Mvir=1.9, 1.0 and 0.3 10^12 solar masses
Mvir > Mdisk/f_b=0.4 10^12 solar masses
Ours: Vmax=188, Vvir=156 km/s
Gnedin: Vmax=155, Vvir=129 km/s
Standard: Vmax=107, Vvir= 89 km/s
Application to other galaxies
● Main observables for galaxies: x-band surface brightness
profile (photometry) and rotation curve (kinematic)● Obtain x-band scalelength Rdisk of and exponential disk,
rotational velocity Vrot(r=2.2Rdisk) and also x-band total
luminosity L● Assume a stellar mass-to-light ratio M/L (REM: depends on the
color index)● It is possible to obtain the disk total mass Mdisk ● Go back 3 slides: “Inverse model”● Compare Vrot vs Vmax
Luminosities and Scalelenghts
● Courteau (1996, 1997) 306 galaxies with luminosities and scalelengths in
Kent-Thuan-Gunn system r-band. Also luminosities in Johnson B-band
from RC3 taken from NED
● r=R+0.94 (Jorgensen 1994)
● Courteau et al (2000) only 36 galaxies with absolute magnitudes and
scalelenghts in "Landolt" (is interchangeable
with Johnson) I-band and SDSS colors (g-r)
and (g-i)
● i=I+0.62 and g=V+0.49 (Courteau et al 2006)
● M-Msun=-2.5Log(L/Lsun)
Mass-to-light ratio guesstimation from Bell & de Jong (2001)
● Compute R=r-0.354 (Jorgensen 1994), then compute B-R, thenM/LR=aR+bR(B-R)
● Compute i=I+0.62, then g=i+(g-i), then V=g-0.49, then (V-I), then M/LI=aI+bI (V-I)
Application to UGC 5794
Mdisk=7.4x10^9 solar masses
Rdisk=2.5 kpc
Vrot(2.2Rdisk)=128 km/sec
Mvir=1.9, 1.8 and 1.6 10^12 solar masses
Mvir > Mdisk/f_b=5.4 10^10 solar masses
Vrot vs Vmax: Galaxies “with” disk
● Vrot = Vmax corresponds to
semianalytic models that
simultaneously reproduce
both the Tully-Fisher and the
luminosity function● There are differences
between the 3 models
Vrot vs Vmax: Galaxies “without” disk
● Vrot = Vmax corresponds to
semianalytic models that
simultaneously reproduce
both the Tully-Fisher and the
luminosity function● There are no differences
between the 3 models
Conclusions
● A new model for the contraction of dark matter halos● Previous models (probably?) overestimate the amount of
contraction (Bower & Benson: reason for small disk in semianalytic models?)
● Nice rotation curve for the Milky Way● Agreement with semianalytic models● Pending: application to other galaxies with more or less
reliable M/L ratios