Observations of DCO + : Tracing the abundance of CO and N 2 in prestellar. cores. Laurent Pagani LERMA, UMR8112 du CNRS, Observatoire de Paris

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1 Observations of DCO + : Laurent Pagani LERMA, UMR8112 du CNRS, Observatoire de Paris Tracing the abundance of CO and N 2 in prestellar L183 - Spitzer/IRAC4-8 µm cores with the contribution of A. Bourgoin & F. Lique

2 OVERVIEW (1)Deuteration & ortho-h 2 deuteration control (2)CO & N 2 : how to trace them? (3)Conclusions

3 OVERVIEW (1)Deuteration & ortho-h 2 deuteration control (2)CO & N 2 : how to trace them? (3)Conclusions 3

4 (1)Deuteration & ortho-h 2 deuteration control Deuteration in a nutshell (ζ,uv) + H H + + e - H + + D D + + H D + + H 2 HD + H +ΔE HD becomes the deuterium reservoir: HD/H 2 3 x 10-5 (ζ,uv) + H2 H2 + + e - H2 + + H2 H3 + + H H3 + is the starting point of the cold phase ion-neutral chemistry H HD H 2 D + + H K H CO HCO + + H 2 Deuteration is favored in the coldest environment H 2 D + + CO DCO + + H 2 HCO + + HD, X[H 2 D + ] = X[H 3 +] (Pagani et al. 1992) (while D/H , Linsky et al. 2007) H 2 D + + N2 N2D + + H 2 N2H + + HD, H 2 D + D 2 H + D 3 + 4

5 (1)Deuteration & ortho-h 2 deuteration control Detection of D 2 CO, ND 2 H, D 2 O, CD 2 OH, Detection of ND 3 and CD 3 OH : need for D 2 H + and D 3 + (Lis et al. 2002, Roberts et al. 2003) H HD H 2 D + + HD D 2 H + + HD H 2 D + + H K D 2 H + + H K D H K At low T kin, reactions only to the right! (Giles et al. 1992) But... 2 spin states per species (ortho & para), 3 spin states for D3 + o-h2 = p-h K o-h 2 D + = p-h 2 D K p-d 2 H + = o-d 2 H K etc.

6 (1)Deuteration & ortho-h 2 deuteration control H HD H 2 D + + H K??? p-h HD p-h 2 D + + p-h K p-h HD o-h 2 D + + p-h K p-h HD p-h 2 D + + o-h K p-h HD o-h 2 D + + o-h 2-25 K etc. p-h 2 D + + o-h 2 o-h 2 D + + p-h K o-h 2 controls the deuteration process! Pagani et al. 1992, 2009, Flower et al. 2006

7 (1)Deuteration & ortho-h 2 deuteration control ζ = s -1 ζ = s -1 ζ = s -1 X[e - ] X[CO] = 10-5 n(h 2 ) = cm -3 N 2 D + /N 2 H + ratio X[CO] = 10-6 n(h 2 ) = cm -3 o/p H 2 limited depletion ortho - H 2 > 1 % no H 2 D + Pagani et al. 2009

8 (1)Deuteration & ortho-h 2 deuteration control Ortho-H 2 : fabrication/destruction H 2 only fabricated on grains with o/p ratio = 3:1 ortho-h 2 destroyed via (Dalgarno et al. 1973, Le Bourlot 1991, Flower et al. 2006) : o-h 2 + H + p-h 2 + H + (Honvault et al. PRL 11+PCCP 11) o-h 2 + H + 3 p-h 2 + H + 3 (Hugo et al. 09, Crabtree et al. 11)

9 (1)Deuteration & ortho-h 2 deuteration control 1.5 My! Full chemical model OSU/Nahoon style + H 2 and H 3 + spin state chemistry Density = 10 4 cm -3 Pagani, Roueff & Lesaffre, 2012

10 (2)CO & N 2 : how to trace them? (1)Deuteration & ortho-h 2 deuteration control (2)CO & N 2 : how to trace them? (3)Conclusions

11 (2)CO & N 2 : how to trace them? 1) Atoms and grains condensate 2) H2 forms on grains 3a) UV is stopped 3b) Temperature drops 4) Molecules form 5) Water freezes on grains 6) Cores form & depletion appears Prediction : Herbst & Klemperer st Observation : Lemme et al B68 C 18 O N 2 H AND C 18 ODEPLETIONINCOLDDARKCLOUD N2H + Vol.570 C 18 O Bergin et al (a) ComparisonofC 18 O J p 1 0 integrated emission (contours) in B68 superposed on a map of visual extinction derived by ALL01 and convolved AM resolution. The C Ocontoursbeginat0.2Kkms andstepinunitsof0.1kkms.thea V imageisscaledfrom0to27mag.(b) Comparison 1 1 J p 1 0 integrated emission (contours) and the visual extinction image. The N 2 H contours begin at 0.3 K km s and step in units of 0.2 K km s. aps were referenced to a p 17 h 22 m 38 ṣ 2 and d p (J2000). The peak is located 6 east and 12 south of this position. A V AV Pagani et al with the visual extinction data using the techniques first edjeudi in Lada 11 etjuillet al. (1994). 13 For C 18 O, there is little scatter, thin C 17 O emission ( t 0.4), shown as an inset in the lower right-hand corner of Figure 1b, displays similar behavior and

12 (2)CO & N2: how to trace them? + N2H traces the dense gas Coreshine Pagani et al Steinacker et al (3.6 µm Spitzer/IRAC) 12

13 12 Problem : core CO emission masked by envelope emission & N2 is not measurable! L. Pagani et al.: L1506 : a prestellar core in the making 3 ig. 2. Left: lowresolution 13 CO (J:1 0) integrated intensity map of the L1506 Taurus cloud filament(originaldatafromnercessianetal.1988). ontour levels are 0.5 to 4.5 K km s 1 by steps of 1 K km s 1.ThePOM-12.5-mdishhasa4.5 resolution as shown in the bottom right corner. he square indicates the surface mapped in C 18 O(J:2 1).Theoffsets are with respect to L1506C coordinates (see text). Right:thesmoothedC 18 O :2 1) integrated intensity map. Superposed to the map is the strip path observed with PRONAOS (Stepnik et al. 2003) along which we observed CO, C 18 O, and N 2 H + with a good signal to noise ratio (see Fig. 3). The crosses indicate the observed points and the 3 white boxes (superposed 3 crosses) the points observed also in C 17 O(seeFig.5).Thedegraded30-mbeamsizeisrepresented.Levels are from 0.1 to 0.7 K km s 1 by eps of 0.1 K km s 1.The(0,0)positioncorrespondstoα 2000 = 4 h 18 m 50 s δ 2000 = see Figure 13. Blue diamonds represent the location of the lowest χr 2, note they are in averaged since it is focused only on the central region of each core. (2)CO & N 2 : how to trace them? one of these cores is significantly depleted holds even taking into account reasonable variances in outer radius, temperature, and canonical abundance. In no case did we find varying any of these parameters substantially affected the results. This work is unique in that we have tested a more complete parameter space of r d, f d,andc 18 Ocanonicalabundancethanpreviously published work. While outer radius does not impact our results, choices of temperature Brady-Ford profile& and Shirley, canonical 2011 abundance : can. Even fixing these parameters, we cannot, however, robustly distinguish between a factor of 10 depletion and a factor of 1000 in f d,astheχr 2 are very similar (e.g., Figures 15, 10, and 11). In contrast, the depletion radius, r d,forsomeofourcoresis more strongly constrained than f d ;however,r d values for many of these cores are separated by little more than a beam width, and four of the cores have the same value for r d.workbylee et al. (2003) alsofoundf d hard to constrain. At the distance of Taurus, information in the HHT maps contains information on scales larger than θ mb /2 = 2100 AU. Greater spatial resolution would better constrain r d.improved resolution may even help constrain f d.forinstance,futureobservations with the 50 m Large Millimeter Telescope operating at 1.3 mm would increase our resolution by a factor of five. The difficulty in determining the absolute value of f d limits our Fig. 3. Spectra taken along the PRONAOS cut (see Fig. 2). The upper row shows the 13 CO (J:1 0) spectra. The middle L1506C row shows the C 18 O(J:1 0)spectra.Thelowerrow shows the N 2 H + (J:1 0) spectra. The velocity scale is 6.5 to 8 km s 1 for 13 CO and C 18 O, and 5.5 to 9 km s 1 Pagani et al for N 2 H +. Offsets increase from 13

14 (2)CO & N 2 : how to trace them? DCO + peaks in the cores! 1995ApJ B - CO disappears - DCO + appears - DCO + daughter of CO trouble? No! Solution! (Butner et al. 1995) 14

15 (2)CO & N 2 : how to trace them? Ø [CO] = & [HD] = Ø H HD H 2 D + + H 2 ( 20 %) Ø H CO HCO + + H 2 ( 80 %) Ø H 2 D + + CO HCO +, DCO + + HD, H 2 [H 2 D + ][CO] cst [DCO + ] cst So, we can have DCO + in a CO-depleted core

16 (2)CO & N 2 : how to trace them? Steady-state model Pagani, Roueff & Lesaffre, 2012

17 (2)CO & N 2 : how to trace them? A full chemical model to relate CO & DCO + and N2 & N2D +? Initial conditions? Sensitivity to parameters? Measurable Balance H CO HCO + + H 2 (100%) H 2 D + + CO DCO + + H 2 (33%) HCO + + HD (66%) D 2 H + + CO HCO + + D 2 (33%) DCO + + HD (66%) D CO DCO + + D 2 (100%) H N2 N2H + + H 2 (100%) H 2 D + + N2 N2D + + H 2 (33%) N2H + + HD (66%) D 2 H + + N2 N2H + + D 2 (33%) N2D + + HD (66%) D N2 N2D + + D 2 (100%) DCO + HCO + N2D + N2H + N2D +, N2H + + CO N2 + DCO +, HCO + 17

18 (2)CO & N 2 : how to trace them? N 2 H +, N 2 D +, and H 2 D + cut and fit CORE N 2 H + CORE N 2 D + H 2 D +

19 (2)CO & N 2 : how to trace them? Low gas temperature and N2D + /N2H + profile, ratio and depletion Pagani et al

20 (2)CO & N 2 : how to trace them? DCO + L183 Observations N2D + 20

21 (2)CO & N 2 : how to trace them? DCO + L183 Observations N2D + Relative abundances 21

22 (2)CO & N 2 : how to trace them? L183 : CO and N 2 abundances GBT CO depletion : 400 inside the core, 2000 from undepleted envelope? N2 depletion : 20 inside the core A possible explanation : CN not depleted in L183 (Hily-Blant, 2008, 2010) CN + N N2 + C could compensate for N2 depletion! Pagani et al

23 (2)CO & N 2 : how to trace them? L183 : CO and N 2 abundances GBT CO depletion : 400 inside the core, 2000 from undepleted envelope? N2 depletion : 20 inside the core A possible explanation : CN not depleted in L183 (Hily-Blant, 2008, 2010) CN + N N2 + C could compensate for N2 depletion! Pagani et al

24 (1)Deuteration & ortho-h 2 deuteration control (2)CO & N 2 : how to trace them? (3)Conclusions

25 D Chemistry is very sensitive to conditions: it can help to trace them and trace the history of star formation (Pagani, Roueff & Lesaffre, 2012; Pagani et al. 2013) D Chemistry must treat all spin states separately + state-to-state chem. (Pagani et al. 1992, Flower et al., 2006, Pagani et al. 2009, Hugo et al. 2009) Ortho-H 2 is the key species in H 3 +-carried Deuterium chemistry Ortho-H 2 is abundant outside prestellar cores (> 10%) and drops inside (< 1%) (Pagani et al. 2009) Steady-state is normally not possible : too much deuteration (DCO + everywhere, N2D + /N2H + >> 1,...) Deuterium chemistry helps to trace CO and N2 detailled depletion profiles CO depletion over 2000? (3)Conclusions N2 depletion compensated by in-situ formation? (Pagani, Bourgoin, Lique, 2012, A&A, 548, L4) Thank you for your attention

The Chemical Composition of a Molecular Cloud at the Outer Edge of the Galaxy

The Chemical Composition of a Molecular Cloud at the Outer Edge of the Galaxy Carnegie Observatories Astrophysics Series, Vol. 4: Origin and Evolution of the Elements, 2003 ed. A. McWilliam and M. Rauch (Pasadena: Carnegie Observatories, http://www.ociw.edu/ociw/symposia/series/symposium4/proceedings.html)