dark matterinthe galactic dwarf satellites

Kohei Hayashi(Kavli IPMU)

2016/01/13

高エネルギーガンマ線でみる極限宇宙2015

Outlineu Properties of non-spherical dark halos in
the Galactic dwarf spheroidal (dSph)
galaxiesu Dark matter annihilation and decay from
non-spherical dark halos in dSphs
u Future prospects

2016/01/13

non-sphericaldark halo in dsphs

Galactic dSphs as a probe of DM
Mass to Light ratio (M/L) within stellar extent in dSphs(M/L)V ≈ 101〜103
dSphs arelargely dark matter dominated !

dSphs are ideal sites forstudying the properties
of Dark Matter!!
2016/01/13

McConnachie 2012

Deriving DM profiles from spherical mass models
Spherical mass models

not observed

DM halo proﬁle:Stellar proﬁle:

It is too simple, isn’t it?
2016/01/13

l-o-s velocity dispersion of stars [km/s]

observed“Spherical averaged”
l-o-s velocity dispersion profiles

Walker+ 2009

Major systematic uncertainty:
Spherical symmetry
ü Stellar distribuNons of dSphs are actually not spherical
typical projected axial ratio: 0.6 - 0.7

Sculptor

FornaxLeo I

Carinaü CDM models predict non-spherical virialized halos
MW-sized halo

2016/01/13

dSph-sized halo

Springel et al.2008

Major systematic uncertainty:
Spherical symmetry
ü Stellar distribuNons of dSphs are actually not spherical
typical projected axial ratio: 0.6 - 0.7

Construction of axisymmetric mass models for dSphs
Sculptor
FornaxLeo I
Carinato obtain plausible limits on
their density profiles and shapes of their DM halos
ü CDM models predict non-spherical virialized halos(KH & Chiba 2012, 2015a, b).
MW-sized halo

2016/01/13

dSph-sized halo

Springel et al.2008

!

※Assumptions※!
n Stellar components are in dynamical equilibrium."n Static gravitational potential is dominated by DM."n DSphs are considered as a collisionless system."n Axisymmetry in both stellar and DM components."
n Velocity anisotropy, βz , is constant.

・Axisymmetric Jeans equations: velocity anisotropy

・Luminous component

q : axial ratioq’ : projected q

・DM-halo component

Q : DM’s axial ratio!

※Assumptions※!
n Stellar components are in dynamical equilibrium."n Static gravitational potential is dominated by DM."n DSphs are considered as a collisionless system."n Axisymmetry in both stellar and DM components."
n Velocity anisotropy, βz , is constant.

・Axisymmetric Jeans equations: velocity anisotropy

・Luminous component

q : axial ratioq’ : projected q

Free parameters

・DM-halo component

Q : DM’s axial ratio

New constraint on shape of dark halo in dSphs
Hayashi & Chiba (2015b)

Line-of-sight velocity dispersion (km/s)
l-o-s
velocity dispersion (km/s)

DSph’s dark halos are not spherical but flattened.

Axial raNo ofMajor(Red),
DM halo:Q
Minor(Green),Intermediate(Blue)
10 Carina
864016 Fornax

Major axis
middle axis

Q=0.33

Minor axis

200

400

Our study was the first to show that dwarf spheroidal
14 Q=0.38
galaxies
have not spherical but flattened dark halos!
12
10
8
12
10
8
6
40Sculptor

200

400

600

800

1000

Q=0.450200
400
600(Projected)Major
Major
axis, middle
axis,axis,
Minor Minoraxis, Intermediateaxis (pc)axis (pc)1200

Major systematic uncertainty:
Spherical symmetry
Mass within a radius of 300 pc108Spherical model:
Strigari+ 2008, Nature
Draco

7

Sculptor

LeoI

FornaxSextans

M300(Msun)

10

CarinaCORE model (Non-spherical)
NFW model (Non-spherical)
Strigari+ 2008 (Spherical)

106

It is clear that our axisymmetric mass models provide a
Non-Sphericalmodelconstancy
different picture of this issue,
namely, the mass
KH & Chiba(2012) models is notwithin the inner 300 pc as arguedby sphericalnecessarily
the case.
105
105

2016/01/13

106
Luminosity (Lsun)

107

New universality for the DM halos
KH & Chiba(2015a,b) based on axisymmetric mass modelsü Maximum circular velocity
We suppose that a test particle perform
circular motion in a DM halo potential.

Vcirc

Vcirc

Vmax

rmax indicates the radius of the maximum
value of circular velocity, Vmax.

rmaxrü DM surface density within rmax
for NEW proﬁles
2016/01/13

A common surface density scalefor dark halos
8dSphs (core) [This work]dSphs (cusp) [This work]
Spirals (THINGS)
Spirals (GHASP)
dIrrs
Spirals & Ellipticals

log (YVmax) [Msun pc-2]

6420-2

2016/01/13

50100

150

200250Vmax [km/s]

300350400450A common surface density scalefor dark halos
8dSphs (core) [This work]dSphs (cusp) [This work]
Spirals (THINGS)
Spirals (GHASP)
dIrrs
max
Spirals & Ellipticals

Dark matter surface density within r
issufficiently constant across a wide range of galaxies,
4 irrespective of dark halo density profiles.
log (YVmax) [Msun pc-2]

620-2

2016/01/13

50

100

150

200
250
Vmax [km/s]

300350400450Comparison with dark matter scenario
8ü At higher halo-mass range,this constancy for real galaxies
can be naturally reproducedby both CDM & WDM, eventhough do not perform any
ﬁbng to the data!
ü Mean surface density derived
from WDM largely deviatesfrom the observaNonal
constancy at dwarf-galaxy
mass scales.

dSphs (core) [This work]dSphs (cusp) [This work]
Spirals (THINGS)
Spirals (GHASP)
dIrrs
Spirals & Ellipticals

86

Warm dark matter scenario
is inconsistent with this constancy.
log (YVmax) [Msun pc-2]

62

CDM (WMAP7)
CDM (Planck)
WDM
2keV
3keV04-2

100

200

300

400

500

20-2

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4204060
Vmax [km/s]

80100

Comparison with dark matter scenario
866log (YVmax) [Msun pc-2]

ü At higher halo-mass range,
this constancy for real galaxies
can be naturally reproducedby both CDM & WDM, eventhough do not perform any
ﬁbng to the data!
ü Mean surface density derived
from WDM largely deviatesfrom the observaNonal
constancy at dwarf-galaxy
mass scales.

42CDM (WMAP7)
CDM (Planck)
WDM
2keV
3keV

04-2
100

200

300

40050020-2

2016/01/13

dSphs (core) [This work]dSphs (cusp) [This work]
Spirals (THINGS)
Spirals (GHASP)
dIrrs
Spirals & Ellipticals

8204060
Vmax [km/s]

80100

dark matterannihilation and decay from
non-spherical dark halo
KH, K. Ichikawa, S. Matsumoto, M. Ibe, M. N. Ishigaki & H. Sugai, 2016 (in preparation)

Indirect search for dark matter
Galactic dSphs are ideal sites for detecting a dark matter Signal !

Galactic dSphs:
ü largely dark matter
dominated systems(M/Ls ~ 10 to 1000)
ü locate close to the Sun(about 20 to 200 kpc)
ü lack of astrophysicalcontaminating gammaray sources (no gas &no current SF)
S. Okamoto PhD thesis

Upper limit on parNcle DM parameters
Observed
γ-ray ﬂux

TheoreNcal predicNons

Dark halo proﬁle (J-factor)

Bhattacherjee et al. 2014

To obtain further limits on properties of dark matter particle,
We need determine the dSph’s dark halo structure (J-factor) more precisely !

Major systematic uncertainties on J• Non-spherical dark halo
Most previous works estimated J values by assuming spherical massmodels, even though dark halos in dSphs are not spherical but elongated(Hayashi & Chiba 2012, 2015b).

• Foreground contaminations
These have largely impact on determining dark halo profiles, especiallyultra faint dwarfs (Bonnivard et al. 2015).

• Data volume
The constraints on dark halo structures in dSphs are aﬀected largely by the lackof kinemaNc sample and distribuNon of member stars (Hayashi & Chiba 2015b).

2016/01/13

Our targets

17 UFDs

7 classicals

Axisymmetric Jeans equations

J-factor values for axisymmetric mass models

The highest J-value !
v It is found that there are differences
between the values of J-factors
estimated from spherical and nonspherical models, especially forUFDs.
v Errors of our work are larger thanprevious one because axisymmetricmass models pretty good fit to thedata compared with spherical ones.
v Segue 2, Leo IV & Draco 2 haveextremely low J-values because
these galaxies have very smallvalues of ρs and rs due to low
velocity dispersions.
v Triangulum 2 has the highest
J-value, log10(J)=21.29+1.62-2.05 !!

Classical dwarfs

futureprospects

subaruprimefocusspectrograph

第4回観測的宇宙論ワークショップ

Major systematic uncertainties on J• Non-spherical dark halo
Most previous works estimated J values by assuming spherical massmodels, even though dark halos in dSphs are not spherical but elongated(Hayashi & Chiba 2012, 2015b).

• Foreground contaminations
These have largely impact on determining dark halo profiles, especiallyultra faint dwarfs (Bonnivard et al. 2015).

• Data volume
The constraints on dark halo structures in dSphs are aﬀected largely by the lackof kinemaNc sample and distribuNon of member stars (Hayashi & Chiba 2015b).

2016/01/13

Wide & deep survey of MW dwarf galaxies
w. Subaru/PFS
Blue dots: spectroscopic targets
in previous work (Walker+ 2009)

FoV for pervious survey

Sculptornominal boundary (rt ~ 76’), but more memberstars actually exist inside/beyond this limit.

CumulaNve number of observable stars(previous work by Walker+ 2009)

Wide & deep survey of MW dwarf galaxies
w. Subaru/PFS
Blue dots: spectroscopic targets
in previous work (Walker+ 2009)PFS FOVFoV for pervious survey

CumulaNve number of observable stars
w. Subaru/PFS>800 stars observable
Subaru/PFSSculptor
nominal boundary (rt ~ 76’), but more member
stars actually exist inside/beyond this limit.

Subaru/PFS enables us to measurea large number of stellar spectra overunprecedentedly wide outer areas,
where DM largely dominates!
⇒ Best for studying the nature of DM

PFS Survey
Precise measurement of DM Halo Profiles K. Ichikawa
Stellar Velocity Data
DM Halo:Fit

DM GravitaNonal PotenNal
J-factor =(number of stars)

Velocity data of>~ 800 stars enable
to determine DM halo
proﬁles very precisely!

J-factor is determined very precisely!
⇒ nature of DMsubaruprimefocusspectrograph

第4回観測的宇宙論ワークショップ

Summary & Future works
1.
2.

3.

4.
5.

We have constructed axisymmetric mass models for dSphs in theMW to obtain plausible limits on the structure of their dark halos.
We find that the total mass of the dSphs enclosed within 300 pc
varies from 106 M¤ to 107 M¤. This is quit different from theconclusion based on spherical models.
It is found that dark matter surface density within a radius of Vmax isnearly constant across a wide range of galaxies, and this universality
is enable us to obtain the limits on particle masses of WDM scenario.
J-factor values are changed by assuming dark halo mass models.
We will investigate how much Subaru-PFS can reduce the J-factor
uncertainties of non-spherical dark halos.

2016/01/13