The Baryonic Contents of the Universe: mission requirements

1
The Baryonic Contents of the Universe mission
requirements

• Takaya OhashiTokyo Metropolitan University

2
Science of the baryon survey

• WHIM warm-hot intergalactic medium
• Identification of the major form of baryons in
  the present universe dark baryon or missing
  baryon problem
• Direct view of the 3-dimensional structure of the
  universe
• Evolution of the hot phase of the universe
  different view of the evolution against collapsed
  cold-phase objects (stars, galaxies)
• Metal enrichment history

Dark Matter
Baryons 4
Dark Energy
Dark baryon (60-80)
Hot gas
Stars, Galaxies
3
WHIM major form of baryons

• Half of the baryons at z0 are in the form of
  WHIM
• 71 of metals in the universe are contained in
  WHIM
• Median metallicity of Oxygen is 0.18 solar in WHIM

Cen and Ostriker astro-ph/0601008
4
Cosmic web Millenium simulation
125 Mpc/h
z0
z1.4
z5.7
Virgo consortium http//www.virgo.dur.ac.uk/

• WHIM is the major baryonic form after z 0.5
• Necessary survey area to see structures 100200
  Mpc
• 100 Mpc corresponds to 28.8? (z0.05),
  15.2?(z0.1), 6.3? (z0.3)
• Therefore, the survey area should be at least
  10? about 100 pointings with 1? field of view

5
Tracer of LSS
Galaxies (104K)
Darkmatter
WHIM (105-107 K) is the best tool to trace the
cosmic large-scale structure
Yoshikawa et al. 2001, ApJ, 558, 520
size 30 h-1 Mpc
Cluster gas (107K)
IGM (105K)
6
Thermal history of the universe
WHIM will tell us the evolution of the hot-phase
material in the universe
7
Scientific requirements concerning the WHIM survey

• Clear detection of missing baryons separation
  from the Galactic oxygen lines which are 100
  times more intense DE, S, W
• Observation of the cosmic web structure in a
  reasonable mission time (lt 3 yrs) DE, S, W, sun
  angle constraint
• Detection of helium like oxygen triplet lines
  temperature and abundance of the cloud are
  constrained DE, S, W
• Bulk motion or turbulence of the filament 1000
  km s-1 DE, S, W

8
OVII OVIII Emission Lines

• High resolution and high sensitivity (SW and DE)
  observations will detect WHIM oxygen emission
  lines
• Intensity ratios of the lines can tell us the
  temperature and ionization condition

9
Simulated OVII OVIII lines
1000 photons
100 photons
With gt 100 (nearly 1000) photons, we can utilize
triplet line from oxygen ? unambiguous line
identification ? determination of redshift and
temperature
10
He-like Oxygen K line
DE2eV
DE1eV
DE5eV
DE10eV
DE lt 5 eV is necessary to resolve line
components which enables us temperature
determination unambiguously
11
He-like Iron K lines
DE2eV
DE1eV
DE5eV
DE10eV
DE 10 eV can still resolve line components
12
Spectrum of a 3 keV plasma
DE lt 5 eV seems necessary for clear line
separation
13
Detectable photons
Yoshikawa et al. (2003) Pub.Astron.Soc.Japan 55
879
0.88 deg2 texp300 ks

• DIOS spec is assumed area 110 cm2
• Number of detected line photons typically 200
  cts/line
• Factor of several better statistics (? 1000
  cts/line) is desirable
• With 500 cm2 area, 1000 counts are obtained in
  300 ksec (4-5 days)

14
Fraction of baryons detectable via oxygen emission
OVII
OVIII
DIOS detection limit (Texp105s S/N10)
DIOS detection limit (Texp105s S/N10)
15
Observable sky
13x 13 accessible 1 yr
1 year
10x 10100 day x 2
7x 750 day x 2
Allowed sun angle 90 deg 25 deg (DIOS)
FOV direction perpendicular to the sun enables us
very deep exposure of the pole regions
16
Summary of mission requirements

• Energy resolution lt 5 eV is necessary to
  separate oxygen line triplets. Goal is 2 eV.
• Area gt100 cm2 to survey 10? x 10? sky in 1-2
  yrs. 500 cm2 as the goal is reasonable.
• Field of view should be close to 1? to observe
  the large-scale structure. This should be kept as
  the basic requirement.
• Sun angle constraint preferable to have the
  field direction perpendicular to the sun
  direction, but not absolute.
• Life at least 3 yrs, goal is 5 yrs or more
• Imaging instrument desirable to have a
  wide-field fine imaging detector on board.
  Otherwise, we observe the XMM or Chandra survey
  fields. This is necessary to know contaminating
  oxygen sources (starbursts, AGN, groups, )