View
217
Download
1
Category
Tags:
Preview:
Citation preview
X-ray Study of the Local Hot Gas
Taotao Fang
UCB
WithClaude Canizares, Chris Mckee and Mark Wolfire
Z = 0 X-ray Absorber
Where are the local X-ray absorbers?
• Typically these lines are unresolved, which implies an upper limit of line width of ~ 0.025 Å, or ~ 350 km s-1 at 21.6 Å. This means a upper limit of distance of ~ 5 Mpc if the Hubble constant is 70 km s-1 Mpc-1.
• The typical column density of O VII absorbers is ~ 1016 cm-2.
300 kpc
Local Group
R=1 Mpc
MS 0737+7441 PG 1211+143NGC 3227 Mkn 509NGC 4258 Ton S180MCG 6-30-15 NGC 7469NGC 4593 Mkn 766H 1426+428 Ton 1388PKS 0558-504 Mkn 501NGC 3783 1H 1219+301H 1821+643 3C 273NGC 5548 NGC 4051PKS 2155-304 Mkn 421
Target:
ALL SKY MAP, O VI AND O VII
O VI data from Sembach et al. (2003)
X-ray Absorption in the Intervening Systems:(z > 0)
• PKS 2155-304 (Fang et al. 2002)– 4 x 1015 cm-2
• H 1821+643 (Mathur et al. 2003)– 2-3
• Mkn 421 (Nicastro et al. 2004)– (0.7 - 1) x 1015 cm-2
• 3C 120 (Mckernan et al. 2004)– Based on very low counts (<10 counts per bin)
• Why we see so many local (z = 0) absorbers with high column densities, but so little intervening absorbers with small column densities?
• One solution: these X-ray absorbers are associated with our Milky Way, in stead of the Local Group.– Expected number of absorber along LOS;– Soft X-ray background emission measurement; – Some diagnostic observations;
Expected Number of Absorbers:• Basic assumption: X-ray absorbers are associated with halos, either MW type,
or LG type.
• Model A: halo distribution (PS) + gas distribution (NFW) + metal distribution
– TOO MANY UNCERTAINTIES, CAN FIT ANY DATA!
• Model B: start from observations
– Covering factor: C
– Uniformly distributed within the halo
R R
€
N ∝C × R2 × nhalo × L
ROSAT ALL SKY MAP
• Three components:– Extragalactic X-ray background from point sources (and WHIM?), power
law spectrum.– Local hot bubble, producing thermal emission around 106K, within a bubble
with radius of ~ a few hundred pc around the Sun.– Halo component, producing thermal emission around 106.3 K. X-ray data
showed (Garmire et al. 1992) the emission measure from this component is:
• Combining with X-ray absorption measure, we found:
• CAUTION: the temperature of this hot halo component is extremely uncertain, varying from 106 to 106.5 K.
Soft X-ray Background
€
ne2L = 2.5 ×10−3ZO
−1 cm−6 pc
€
ne ≈ 5 ×10−4 cm−3; L ≈ 20ZO−1 kpc
Diagnostic Observations
• 4U 1820 (LMXB)• D < 7.6 kpc• Futamoto et al (2004)
• GX 339 (LMXB)• D < 4.0 kpc• Miller et al (2004)• Caution: high column density of O VIII!
Total Baryon Mass and Fraction
Summary• Observation:
– In a total of 22 los, Chandra & XMM detected 9 los show z = 0 X-ray absorption lines with high column density;
– All los with more than 60 counts per bin showed z = 0 lines;– Very few intervening absorption systems were reported, with
very low ion column densities.• We argue that these local X-ray absorbers are possibly associated
with MW halo, instead of intragroup medium in LG– Expected number of the absorbers– Soft X-ray background emission measurement;– Diagnostic observations of nearby targets
• From SXB and X-ray absorption measurement, we constrain the the properties of the X-ray absorbers as
€
ne ≈ 5 ×10−4 cm−3; L ≈ 20ZO−1 kpc
Total Baryon Mass and Fraction
• Given a covering factor C, total number of X-ray “cloud” with a radius of r and within a halo of radius R, are:
• Since the total mass within these X-ray “cloud” must be smaller than the total baryon mass of the halo, we have:
€
Ncl =4
3
R
r
⎛
⎝ ⎜
⎞
⎠ ⎟2
C
€
R ≤ 0.5 MpcZO1
⎛
⎝ ⎜
⎞
⎠ ⎟
1
2 C
0.5
⎛
⎝ ⎜
⎞
⎠ ⎟−
1
2 Ωb
0.044
⎛
⎝ ⎜
⎞
⎠ ⎟
1
2 Mhalo
1012 M
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
1
2
Ionization fraction for O VI, O VII, and O VIII
McCammon et al. (2002)
Chandra Moon Observation
Chandra Moon Spectrum
Wergerlin et al.(2004)
X-ray Emission Line Measurement
• In most case, the line intensity of O VII triplet is:
• At the temperature where O VII ionization peaks, the collisional excitation rate
We then have:€
IOVII ≤ (5 −10) photons cm-2s-1sr -1
€
S ≥10−12 cm3s−1
€
ne ≤ 9 ×10−3 cm−3; r ≥ 0.2ZO−1 kpc
X-ray Study of the Local Hot Gas
Recommended