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

L1157 (Spitzer)

Bow-shockB1

protostar

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,

Deuterated fractions in L1157-B1

WALL

ARCH

HEAD

TOTAL

Dfrac(H2CO) = Dfrac(CH3OH) within the errors

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