Missing baryons and missing metals in galaxies: clues from the Milky Way Smita Mathur The Ohio State University With Anjali Gupta, Yair Krongold, Fabrizio Nicastro, M. Galeazzi

In the low-redshift Universe, baryons are missing on all scales Galaxies Clusters Universe

Where are the Galactic missing baryons? Circum-Galactic Medium: extending up to the virial radius (~250kpc) Local Group Medium scale length of ~ 1 Mpc Local WHIM filament scale length > 1 Mpc 10 5 K < T < 10 7 K

Simulations of the CGM Stinson et al. 2011

Diffuse Warm-hot CGM

First detection of warm-hot gas at redshift zero. PKS Nicastro et al. 2002

Z=0 X-ray absorption toward Mrk 421

z = 0 X-ray Absorption In several high S/N Chandra spectra: –Mkn 421 (Williams et al. 2005) –Mkn 279 (Williams et al. 2006) –PKS (Nicastro et al. 2002) –3C 273 (Fang et al. 2003) –Other sightlines with lower significance (McKernan et al 2004) Always OVII, sometimes other species At Chandra gratings resolution lines are unresolved

Origin Hot Galactic Halo/Corona… –From galaxy formation / feedback processes … or Local Warm-Hot IGM? –Predicted by simulations (Kravtsov et al. 2002)

Our Chandra Survey of O VII and O VIII Chandra sight lines Previous OVII detection 29 sight lines with good S/N near OVII z=0 region O VII detection in 21 sight lines O VII detection in 21 sight lines O VIII detection in 8 sight lines O VIII detection in 8 sight lines

OVII OVIII OVII and OVIII z=0 Absorption Log T = K

Column Density Measurement Optically thin line N(ion) = 1.3 × (EW/f λ 2 ) cm -2 For OVII EW(Kβ)/EW(Kα) = Most of OVII Kα are saturated

log(N OVII ) and b contour

Average Log N OVII = ± 0.08 cm -2Average Log N OVII = ± 0.08 cm -2 ….2-3 times higher than previous estimates

Absorption line studies measure: Column density N H = n e L Column density N H = n e L Emission studies measure: Emission Measure EM = n e 2 L Emission Measure EM = n e 2 L

Galactic Halo Emission Measure Henley et al. (2010) and Yoshino et al. (2009) Galactic Halo temperature is fairly constant T = ( ) × 10 6 K ….same as what we found for the absorbing gas. EM = (Z/Z Θ ) cm -6 pc

Combining Absorption and Emission Measurement n e = (2.0 ± 0.6 )× 10 −4 (0.5/f OVII ) −1 cm −3 (0.5/f OVII ) 2 (Z Θ /Z) kpc L = (71.8 ± 30.2) (8.51 × /(A O /A H ))(0.5/f OVII ) 2 (Z Θ /Z) kpc L > 41.6 kpc n e < 2.6 × 10 −4 cm −3

Mass Probed by OVII and OVIII X-ray Absorbing/Emitting Gas Phase M total > 1.7 × 10 9 M Θ M total > 1.7 × 10 9 (fc/0.72) (8.51 × /(A O /A H )) 3 (0.5/f OVII ) 5 (Z Θ /Z) 3 M Θ For Z = 0.3Z Θ L > 138 kpc M total > 6.1 × M Θ Gupta, Mathur , 2014

Courtesy: Chandra presss office

Fang, Bullock R 100kpc

Future directions Probing the anisotropy: emission and absorption along the same sightline. -- New Suzaku observations -- New XMM-Newton Observations. Different density and temperature profiles: e.g. Maller-Bullock profile in NFW halo. Probing the multi-phase medium: other ions dominant at different temperatures.

Missing metals Peeples+ 2013

Adding halo contribution

Conclusion X-rays provides evidence for hot (T>10 6 K) gas in and around the Milky Way. X-ray OVII and O VIII absorption lines at z=0 probe the hot gas extending over a large region around the Milky Way, with a radius of over 100 kpc. The mass content of this phase is over M Θ. A large fraction of Galactic missing baryons are in this hot phase. Appears to be a robust result supported by theoretical models.

Input to galaxy-formation and evolution models Flat profiles such as Maller & Bullock profile are preferred over NFW Strong feedback on galactic scale important Metals preferentially expelled?

Next 15 years Focus on Grating observations ( c.f. UV focus on HST ) CGM/WHIM science enabled by Chandra ( c.f. COS halo project ) Athena path-finder With enough time, Yes, We Can!

This is a robust result! Is the z=0 absorption mostly from the Galactic disk? No. What about the uniform density profile? No problem: gives a lower limit on mass. Are the emission and absorption at different temperatures? No.

….. no anticorrelation between EW and sin(b)

OVII EW Distribution ___ O VII detection O VII upper limit

The X-ray Advantage Similarly for C V, C VI, N VI, N VII, Ne IX, Ne X, Fe XVII, Si XIII