deuterated molecules: a chemical filter for recently evaporated gas francesco fontani (inaf-oaa) c....
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Deuterated molecules: a chemical filter for recently
evaporated gas
Francesco Fontani (INAF-OAA)
C. Codella, C. Ceccarelli, B. Lefloch, M.E. Palumbo … et al.
Formation of D-molecules
H3+ + HD H2D+ + H2 + 230K1. If T ≤ 20 K
H2D+/H3+ increases in cold gas
(>> D/H cosmic abundance ~10-5)
CH3+ + HD CH2D+ + H2 + 390K
C2H2+ + HD C2HD+ + H2 + 550K
H3+ + CO HCO+ + H2
H2D+ + CO DCO+ + H2
2. If CO freezes-out (i.e. n≥105 cm-3)
H3+ and H2D+ combine with other neutrals, X,
Increasing [XD+]/[XH+] ratios (e.g., X=N2 N2D+/N2H+ ~0.1)
Roberts & Millar 89; Gerlich+02; Asvany+04; Gerlich & Schlemmer 02; Flower+06
3. If o-/p-H2 is low H2D+/H3
+ is high H3
+ + HD H2D+ + o-H2 Internal energy of o-H2
170K higher than p-H2
H2D+ + CN DCN+ + H2 HCND+ + e- DNC + H
H2D+ + N2 N2D+ + H2
H2D+ + NH3 NH3D+ + H2 ; NH3D+ + e- NH2D + H
Gas: Ion-molecule reactions
Grains: hydrogenation forms saturated species…and their deuterated forms!
Watson & Salpeter 1972; Hasegawa et al. 1992; Caselli et al. 1993; Turner 2001; Roueff et al. 2007; Caselli & Ceccarelli 2012; Ceccarelli et al. 2012, PPVI
O OH H2O / HDO
C CH CH2 CH3 CH4 / CH3D N NH NH2 NH3 / NH2D CO HCO H2CO / HDCO H3CO CH3OH / CH2DOH
H2D+ + H2CO H2DCO+ + H2 ; H2DCO+ + e- HDCO + H
Formation of D-molecules: gas vs grain
B1 shock
B2
Gueth et al. (1998), Benedettini et al. (2007), Codella et al. (2009)
all highest velocity tracers converge here !
The L1157-B1 chemically rich bow-shock
Powered by a Class 0 source (d = 250 pc) Most chemically rich outflow known so far: SiO, SO,NH3, CH3OH, H2O, and many other molecules!
Precessing molecular outflow associated with bow shocks seen in CO (Gueth et al. 1996) and H2 (Neufeld et al. 2009): B1 is the brightest shocked region.
Deuterated molecules in L1157-B1!Codella+12, ApJ, 757, L9
L1157-B1 surveyed as part of the Herschel/CHESS and IRAM-30m/ASAI Large Programmes (Ceccarelli+10, http://www.oan.es/asai) in: 78 – 350 GHz (IRAM-30m) 500 – 2000 GHz (Herschel)
12 lines of deuterated molecules detected
Column densities of HDO, HDCO and CH2DOH consistent with “multi-layer” ices formed before the passage of the shock, and released into the gas by grain sputtering!
PdBI angular resolution ~ 2.4”
HDCO emission delineates V-like region: the interface between shock and ambient material !!!
Similar to CH3CN (Codella+09)
Fontani, Codella, Ceccarelli, LeFloch, Viti & Benedettini 2014, ApJL, 788, 43
….and CH3CHO (Codella+15)
First clear evidence of HDCO as shock tracer
PdBI angular resolution ~ 2.4”
CH2DOH emission faint and clumpy
….likewise CH3OH (Benedettini+12)…
BUT DIFFICULT TO DEFINE AN EMITTING REGION!
CH2DOH in L1157-B1:SHOCK TRACER?
Fontani+2014, ApJL, 788, 43
ARCH and HEAD cover similar areas, and have similar temperatures (Codella+09);
H2CO formed in the gas similar:
Ngasarch ≈ Ngas
head ≈ Ntothead
H2CO released from the grains different:
Ngrainarch >> Ngrain
head ~ 0
Ntotarch – Ntot
head ≈ Ngrainarch
deuterated fraction on grains is:
Ntot(HDCO)arch/Ngrain(H2CO)arch ≅ 0.1
“clean” estimate of HDCO/H2CO on grain mantles!
HH 212: HDCO in a rotating cavity!
ALMA cycle-1 (PI: Codella); Fontani et al. , in prep.
HDCO (red and blue)
Codella et al. (2014)
3200
A.U
.
220 A.U.
H2CO/CH3OH in L1157-B1: laboratory vs observations
Palumbo et al., in prep.
DOSE = ice age * CR fluxAssuming ζ = 3x10-16 s-1 (Podio et al. 2014), the age is ~ 106 years
Deuterated molecules in shocks:summary and conclusions
(1) The cavities of protostellar shocks are rich in HDCO. HDCO and CH2DOH emission associated with the interface between shock and ambient gas in L1157-B1 and HH 212 associated with grain sputtering – shock tracers
(2) “clean” measurement of HDCO/H2CO on GRAIN MANTLES (~0.1)
(3) “age” of grain processing from HDCO/CH3OH? To be confirmed
Deuterated molecules are “chemical filters” for material formed on grain mantles and recently evaporated/desorbed
IRAC 8 m (grey) CO(2-1) (contours)(Looney et al. 2007, Bachiller et al. 2001)
B1 shock
B2
Powered by a Class 0 source (d = 250 pc) Most chemically rich outflow known so far: SiO, SO,NH3, CH3OH, H2O, and many other molecules!
PdBI CO(1-0)+ SiO(2-1)+CS(2-1) (Gueth et al. 1996, 1998, Benedettini et al. 2007)
Herschel-PACS H2O@179 m (Nisini et al. 2010)
Precessing molecular outflow associated with bow shocks seen in CO (Gueth et al. 1996) and H2 (Neufeld et al. 2009): B1 is the brightest shocked region.
The L1157-B1 chemically rich bow-shock