Hot baryons around Milky Way-like galaxies

Hot baryons around Milky Way-like galaxies

Hot baryons around Milky Way-like galaxies
Constraints from XMM and forecasts for ALMA
Jesper Rasmussen
Dark Cosmology Centre, Univ. of Copenhagen
Hot X-ray gas around (“quiescent”) spirals
Itʼs there −
at least around the monsters,
vc ≳ 400 km/s
(Anderson+11, Dai+12)
Talk outline
(1) New results: Detection of X-ray gas around a vc ~ 300 km/s spiral (preliminary)
(2) Alternative results: Can we probe this gas using spin-flip emission?
Simulations: Hot baryons in disk galaxy halos
JR+ 09:
NGC 5170
Extraplanar gas in
cosmological SPH simulations
of spiral galaxies
NGC 5746
New deep X-ray observations of NGC 5746
SBb spiral, MB = −21.8
vc = 318 ± 10 km/s
( ~ 3 times MW mass)
D = 27 Mpc
SFR = 0.9 ± 0.2 M⊙/yr:
− 10% of MW per disk area
− insufficient to drive SN outflow
(Strickland+04)
XMM 200 ks: Very deep X-ray view of a nearby spiral
Chandra, 36 ks, over Hα :
XMM: pn + 2MOS, 160/225 ks:
60 × 60 kpc 100 kpc
Rasmussen+ 09
XMM: Hot gas detected out to R ≈ 20 kpc
kpc: 5
20
pn only,
0.3-1 keV diffuse,
extraplanar emission
40
~ 700 net cts !
LX ≈ 8 × 1038 erg/s
Matches sims.
But need verification from
• MOS1/2
• Other backg.sub. methods
Extracting disk galaxies form cosmological SPH simulations
6 disks, vc ≈ 180 − 320 km/s. Used in Rasmussen+ 09.
Original sims:
Sommer-Larsen+ 05, Romeo+ 06
− Star formation + SN (AGN) feedback
− Radiative cooling
− Chemical evolution (10 elements)
− Cosmic UV field
− Thermal conduction
Remarkable agreement with simulation predictions
Assuming T ≈ Tvir (and Z = 0.2 Z⊙):
LX, disk excluded, within R = 30/50 kpc:
ROSAT stacking
of spirals, diffuse
emission only
(Anderson+ 12)
Hot gas mass and cooling rate also consistent with sims
Hot gas mass within R = 30/50 kpc:
ROSAT stacking
of spirals
(Anderson+ 12)
⦁
Cooling rate M = Mgas/tcool:
Hot gas halo in NGC 5746 is dynamically unimportant
Baryon inventory of NGC 5746
Mhot / Mdyn (R ≲ 30 kpc) ~ 0.002
(Rand & Benjamin 08)
Mhot / M★ ~ 0.006
Mhot / MHI ~ 0.1
Cooling/accretion vs. SF
⦁
Mhot / SFR ~ 0.1
Classical cooling flow cannot maintain SF
Hot accreted halos of L ≲ L* galaxies beyond reach?
Detection in emission would generally require either
(1) Stacking (Anderson+ 12)
(2) Next-gen. X-ray observatories
(3) Alternative approaches
Spin-flip emission from hot gas
at mm-wavelengths
(Sunyaev + Churazov 84)
Detectable with ALMA?
Spin-flip emission: Hyperfine structure transitions
H in ground state:
Magnetic moment of e− must interact
with that of nucleus.
But this doesnʼt just happen in H.
Most common ones:
1H: H I line at 1.4 GHz
14N: H-like N VII at 53.0 GHz
Most important lines probe hot gas in mm-region
> 1% of element in
relevant ionization stage
λ = 6.68 mm
λ = 1.21 mm
Spin-flip emissivity: Strong temperature dependence
Emissivity: Function of T, ngas, Z, z
Model predictions: Total spin-flip luminosities
Clusters
Groups
E
Spirals:
JR+ 09
Spirals
Early-type
(Kawata &
Gibson 05)
ALMA brightness temperatures: Mostly very low...
Within R = 30 kpc:
Within R = 30 kpc
Clusters
Groups
Early-type
Spirals
Preliminary results
Clusters
Groups
With the online ALMA sensitivity calculator at
http://almascience.eso.org,
Early-type
Spirals
requiring 3-σ detection with full array:
(1)
Lines from cluster cores detectable in < 5 hrs
even when not incorporating velocity information
(2)
But galaxy halos and typical groups beyond reach (texp > 1 month)
ALMA: Galactic hot halos undetectable in emission.
Summary
(1) Deep XMM observations of NGC 5746 (~ 3 times MW mass)
− M ≈ 1 × 109 M⊙ extraplanar X-ray gas, with LX ≈ 1 × 1039 erg/s
⦁
⦁
− Mhot ≈ 0.08 M⊙/yr → Mhot / SFR ~ 0.1
(2) Probing hot galactic halos with hyperfine structure lines
− Not feasible in emission with ALMA
− But potentially complementary probe of dense ICM