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Dust and Metal Column Densitiesin 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
Nu
mb
er o
f G
RB
s
< z >=2.2; Fynbo+09
Credit: Edo Berger
GR
B 0
9042
9B (
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
Metalsabsorption
High-z
Lyα absorption gives measure of neutral hydrogen column density, NHI
Optical vs. x-ray: the missing gas problem
(Watson et al., 2007)
NO,X
NHI
Soft X-ray absorption gives measure of total oxygen column density, NO,X
Starling+07
Schady+10
Lyα absorption gives measure of neutral hydrogen column density, NHI
Optical vs. x-ray: the missing gas problem
(Watson et al., 2007)
NO,X
NHI
Soft X-ray absorption gives measure of total oxygen column density, NO,X
Fynbo+09
Starling+07
Schady+10
QSO-DLAsGRBs
Fynbo+09
Optically brightOptically dark
NH,X
GRB Host: gas-rich
Watson+07
NH
I (cm
-2)
NH,X (cm-2)
TypicallyNH,X >> NHI
GRB host galaxies typically supersolar environments
and/or
X-ray observations probe larger column of gas than optical
GRB Host: gas-rich
Watson+07
NH
I (cm
-2)
NH,X (cm-2)
TypicallyNH,X >> NHI
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
NH
I (cm
-2)
NH,X (cm-2)
TypicallyNH,X >> NHI
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 NO,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 NH
(assuming solar abundances):NH,MII versus NH,X
Chen+11
GRB050820A
Neutral vs. Ionised Gas
Neutral gas = Total gas
20.0 20.5 21.0 21.5 22.0 22.5 Total Gas (Log NH,X)
Neutr
al G
as
(Log N
H,M
)
90% additional gasabsorbing soft x-ray
Schady+11
NH,FeII
NH,SiII NH,SII
NH,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
1
2
1
3
1
4
15
16
1
7
1
8
16.5 17.0 17.5 18.0 18.5 19.0
Log NCIV,X
SiIV
CIV
16.5 17.0 17.5 18.0 18.5 19.0
Log NSiIV,X
L
og N
SiIV
1
2
1
3
1
4
15
16
1
7
1
8
Only <10% of gas highly ionised(i.e. IP~140eV)
16.5 17.0 17.5 18.0 18.5 19.0
Log NNV,X
L
og N
NV
1
2
1
3
1
4
15
16
1
7
1
8
NV
Schady+11
Total NC (Log NC,X)
Total NSi (Log NSi,X)
Total NN (Log NN,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)
Flu
x D
ensi
ty (
mJy
)
Probing the ISM of GRB Hosts
SED for GRB 060729AV
3000 2000 1000Wavelength (Å)
Aλ/A
30
00
ÅSMCLMCMilky Way
Schady+10
Prochaska+09
CO
H2
Lyα
2175Å
GRB hosts: dust-poor?N
um
ber
of
Aft
erg
low
s
Afterglows AV [mag]Greiner+11
GRB070306(Jaunsen et al. 2009)
GRB080607(Perley et al. 2009)
3.2 5.5
Unbiased sampleOptically bright
NH/AV
Krühler+11
AV > 1
[NH,X/AV]sol 2x[NH,X/AV]sol 3x[NH,X/AV]sol
A
λ/A
30
00
Å
Wavelength (Å) 5500 3000 2000 1500 1215
2 3 4 5 6 7 8 Inverse Wavelength (μm-1)
Simultaneous SED analysis: Results
Low AV GRBsSMCLMCMilky WayGRB 070802GRB 080607
Schady+12
A v = 1.2
Av = 3.2
<A V> =
0.3
(Perley+11)
(Elíasdóttir+09)
Dust depletion vs. Dust Extinction
GRB070802
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 AV 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 (AV, extinction curve) dependent on global host galaxy properties? Older, more evolved galaxies have larger dust extinction and AV/NH,
flatter extinction curves, more pronounced 2175Å bump