Dust and Metal Column Densities in GRB Host Galaxies Patricia Schady (MPE) T.Dwelly, M.J.Page, J.Greiner, T.Krühler, S.Savaglio, S.R.Oates, A.Rau, M.Still + GROND and UVOT team

z Number of GRBs =2.2; Fynbo+09 Credit: Edo Berger GRB B (z=9.4) Fruchter+06 Probe young, star forming galaxies GRB hosts: probes to the distant Universe Blustin+06 Highly luminous synchrotron featureless spectra Dust extinction Metals absorption High-z

Lyα absorption gives measure of neutral hydrogen column density, N HI Optical vs. x-ray: the missing gas problem (Watson et al., 2007) N O,X N HI Soft X-ray absorption gives measure of total oxygen column density, N O,X Starling+07 Schady+10

Lyα absorption gives measure of neutral hydrogen column density, N HI Optical vs. x-ray: the missing gas problem (Watson et al., 2007) N O,X N HI Soft X-ray absorption gives measure of total oxygen column density, N O,X Fynbo+09 Starling+07 Schady+10 QSO-DLAs GRBs Fynbo+09 Optically bright Optically dark N H,X

GRB Host: gas-rich Watson+07 N HI (cm -2 ) N H,X (cm -2 ) Typically N H,X >> N HI  GRB host galaxies typically supersolar environments and/or  X-ray observations probe larger column of gas than optical

GRB Host: gas-rich Watson+07 N HI (cm -2 ) N H,X (cm -2 ) Typically N H,X >> N HI  GRB host galaxies typically supersolar environments and/or  X-ray observations probe larger column of gas than optical z Savaglio+09 Solar

GRB Host: gas-rich Watson+07 N HI (cm -2 ) N H,X (cm -2 ) Typically N H,X >> N HI  GRB host galaxies typically supersolar environments and/or  X-ray observations probe larger column of gas than optical

Metals vs. Metals More natural to compare N O,X to metals  Use weakly-ionised metal lines to trace neutral gas (Zn II, S II, Si II or Fe II )  Correct for dust-depletion  Convert metal column densities to N H (assuming solar abundances): N H,MII versus N H,X Chen+11 GRB050820A

Neutral vs. Ionised Gas Neutral gas = Total gas Total Gas (Log N H,X ) Neutral Gas (Log N H,M ) 90% additional gas absorbing soft x-ray Schady+11 N H,FeII N H,SiII N H,SII N H,ZnII

Highly Ionised Gas Component Chen+11 What is contribution to soft X-ray absorption from highly ionised gas?  CIV, SiIV, NV and OVI may trace gas closer GRB (Fox+08, Prochaska+08)

Fraction of Highly Ionised Gas Log N CIV Log N CIV,X SiIV CIV Log N SiIV,X Log N SiIV Only <10% of gas highly ionised (i.e. IP~140eV) Log N NV,X Log N NV NV Schady+11 Total N C (Log N C,X ) Total N Si (Log N Si,X ) Total N N (Log N N,X )

 Ionised gas is in highly ionised state i.e. not seen in optical  X-ray absorbed by intervening gas external to host galaxy  Intervening galaxies along line-of-sight (Campana+12)  A Warm Hot Intergalactic Medium within local Universe (Bahar+11)  Milky Way soft X-ray absorption is underestimated What is the origin of the soft X-ray excess?

Frequency (Hz) Flux Density (mJy) Probing the ISM of GRB Hosts SED for GRB AVAV Wavelength (Å) A λ /A 3000Å SMC LMC Milky Way Schady+10 Prochaska+09 CO H2H2 Lyα 2175Å

GRB hosts: dust-poor? Number of Afterglows Afterglows A V [mag] Greiner+11 GRB (Jaunsen et al. 2009) GRB (Perley et al. 2009) Unbiased sample Optically bright

N H /A V Krühler+11 A V > 1 [N H,X /A V ] sol 2x[N H,X /A V ] sol 3x[N H,X /A V ] sol

A λ /A 3000Å Wavelength (Å) Inverse Wavelength ( μ m -1 ) Simultaneous SED analysis: Results Low A V GRBs SMC LMC Milky Way GRB GRB Schady+12 A v = 1.2 A v = 3.2 = 0.3 (Perley+11) (Elíasdóttir+09)

Dust depletion vs. Dust Extinction GRB Schady+11

Conclusions  Rich sample of GRB optical and X-ray afterglow spectra  Can probe ionisation state and relative abundances of host galaxy gas  Can probe A V distribution and dust extinction law across cosmic time  Soft X-ray column densities typically an order of magnitude larger than neutral gas column densities  Majority of host gas is in a super ionised state ?  Soft X-rays absorbed by gas external to host; intervening galaxies, local WHIM, Milky Way?  Line-of-sight dust extinction properties (A V, extinction curve) dependent on global host galaxy properties?  Older, more evolved galaxies have larger dust extinction and A V /N H, flatter extinction curves, more pronounced 2175Å bump