Massive Star-Formation in G studied by means of Maser VLBI and Thermal Interferometric Observations Luca Moscadelli INAF – Osservatorio Astrofisico di Arcetri

MAIN COLLABORATORS: Goddi C. Harvard-Smithsonian Center for Astrophysics Cesaroni R., Codella C. INAF – Osservatorio Astrofisico di Arcetri Sanna A. Universitá di Cagliari Beltrán M.T. Departament d’Astronomia i Meteorologia, Universitat de Barcelona Furuya R. Subaru Telescope, National Astronomical Observatory of Japan

Source Target SFR G D ≈ 7.7 kpc L bol ≤ L ʘ Scientific Aim Addressing open problems of massive star formation as: 1)Mass Accretion Process (Disk-mediated ? Coalescence ?). 2)Acceleration and Collimation of (proto-)Stellar Outflows. 3)Determining the Evolutionary Phase: HMPO → UCHII → HII Talk Obiective Synergy of Maser VLBI and Thermal Interferometry allows to study the physical conditions and the gas kinematics on scales of 10 – AU from the massive YSO.

Most Intense Maser Emissions in Massive Star-forming Regions 22 GHz Water Masers: observed with VLBA at four epochs 6.7 GHz Methanol Masers: observed with EVN at two epochs (by now) Very Long Baseline Array Phase-reference observations ⇒ maser absolute positions determined with mas accuracy

Maser Excitation Conditions { 22 GHz Water Masers: collisional pumping ( pre-shock n H2 ~10 7 cm - 3 ) n H2 ~ 10 9 cm -3, T K ≥ 400 K { 6.7 GHz Methanol Masers: radiative pumping by 50  m photons n H2 ~ cm -3, T K ~ K Physical conditions of masing gas are known within one order of magnitude

Do CH 3 OH and H 2 O masers trace specific (and distinct) environments / phases of massive star formation ? Towards several YSOs VLBI shows ordered structures in either maser type. 1 arcsec resolution radio to near-infrared observations → Complexity. Masers of each type likely trace several environments / phases. No evidence of spatial correlation between the two maser types. (Beuther et al. 2002; De Buizer et al. 2002; Walsh et al. 1998)

Multi-epoch water maser VLBI towards high-mass YSOs Torrelles et al : 3 epoch water maser VLBA towards W75N-VLA1 and VLA2 + Apr * May × Jun cm VLA-A continuum VLA2 VLA1 ▲ VLA-A H 2 O maser

IRAS map : 1.3mm PdBI ____ : CH 3 1.2mm Minier et al Δ V r / Δ S = 2 km s -1 / 95 AU M c = 0.04 M ⊙ ( Beuther et al ; Leurini et al )

Study of CH 3 OH and H 2 O maser associations can help identifying the maser environments by comparing the spatial and velocity distribution of the two maser types. VLBI of CH 3 OH and H 2 O associations are missing in literature A convenient start is observing the few known candidate massive YSOs (already well studied with interferometers in thermal emissions) showing maser emission in both molecules.

VLBI Observations of Maser Associations towards Massive YSOs : observed : partially reduced : analysed : observed

(Furuya et al. 2002) (Codella et al. 1997) B C D A (Walsh et al. 1998) (Forster & Caswell 1989) T d = 90 K M c = 550 M ⊙ T d < 30 K M c > 100 M ⊙ T d = 30 K M c = 250 M ⊙ T d = 90 K M c < 40 M ⊙

●: BIMA CH 3 OH 95 GHz ▲ :VLA CH 3 OH 44 GHz — : PdBI 12 CO image: NMA CS(3-2)

Beltran et al : PdBI 1.3 mm continuum image : VLA 1.3 cm continuum ●: EVN CH 3 OH 6.7 GHz A1A1 A2A2

A2A2 A1A1 A1

UCHII REGION SPECTRUM; ZAMS SPECTRAL TYPE O9.5, M ≈ 20 M ⊙ Beltran et al. 2007

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz A 1 A 1 - North A 1 - South

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz A 1 - North A 1 - South A 1

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz A 1 - North

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz A 1 - North

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz A 1 - North R mean = 540 AU

Water Maser Shell Kinematic Status: R 0 ≈ 500 AU, V 0 ≈ 40 km s -1 Maser Action → pre-shock n H > 10 6 cm -3 Wind-driven shell For a ZAMS O9.5 type: M w ~10 -6 M ⊙ yr -1, V w ~2000 km s -1, L w ~ erg s -1 Analytic model (Shull 1980) t 0 (the shell age) Two unknowns: t 0 (the shell age) n H (H particle ambient density) n H (H particle ambient density)

Free flowin g wind Shocked wind bubble shocked ionized shell 22 GHz H 2 O masers 6.7 GHz CH 3 OH masers Ambient Medium n H ~ 10 7 cm -3, T ~ 150 K Shocked Molecular Shell n H ~ 10 9 cm -3, T > 400 K V s = 40 km s -1

Water Maser Shell Kinematic Status: R 0 ≈ 500 AU, V 0 ≈ 40 km s -1 Maser Action → pre-shock n H > 10 6 cm -3 pressure and momentum-driven solutions require: t 0 ≈ 40 yr, n H ~ 10 7 cm -3 t 0 ≈ 40 yr, n H ~ 10 7 cm -3 radio appearance similar to an UCHII region radio appearance similar to an UCHII region Wind-driven shell For a ZAMS O9.5 type: M w ~10 -6 M ⊙ yr -1, V w ~2000 km s -1, L w ~ erg s -1

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz A 1 - North

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz A 1 - North : EVN CH 3 OH barycent. ●: EVN CH 3 OH 6.7 GHz

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz R mean = 540 AU A 1 - North

Radiation Pressure driving the expanding CH 3 OH maser shell L bol /(c 4 π R 2 ch3oh ) = ρ v 2 L bol = 7 x 10 4 L ⊙, R ch3oh = 600 AU ⇒ 9 x erg cm -3 ρ = 10 7 n H2 cm -3, v = 5 km s -1 ⇒ 8 x erg cm -3

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz A 1 - North A 1 - South A 1

A 1 - South ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz

A 1 - South ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz : EVN CH 3 OH barycent.

● : VLA H 2 O 22.2 GHz image:VLA-B 1.3cm continuum A1A1 A2A2 B C

: VLA-B 1.3cm peak ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz : PdBI 1.3 mm continuum A 2

●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz : PdBI 1.3 mm continuum : VLA-B 1.3cm peak A 2

● : VLA H 2 O 22.2 GHz image:VLA-B 1.3cm continuum A1A1 A2A2 B C

▲: VLBA H 2 O 22.2 GHz C 800 AU

▲: VLBA H 2 O 22.2 GHz C 800 AU

▲: VLBA H 2 O 22.2 GHz C

C

C

CONCLUSION S We have determined absolute positions and velocities for the 22.2 GHz water and 6.7 GHz methanol masers towards the massive SFR G Main results are: 1) CH 3 OH 6.7 GHz and H 2 O 22.2GHz masers serve (help) identifying the location of YSOs (Ex.: A1N, A2, cluster of YSOs in C) 2) CH 3 OH 6.7 GHz and H 2 O 22.2GHz masers can co-exist during the same phase of massive star-formation, BUT they likely originate from different environments (Ex.: A1N, A2, A1S (?) )

3) Strong CH 3 OH 6.7 GHz emission needs T d ~ 100 K. The earliest phases of massive star-formation are probably NOT traced by this maser type (Ex.: C). 6.7 GHz masers emerge around UCHII regions (Ex.: A1N, A2(?)), but they are also seen in absence of radio continuum (Ex.: A1S) 4) Water masers trace (collimated or wide-angle) outflows from the earliest (C) to the UCHII phases (A1N). In A1N, the fast expansion of the UCHII region seen in the H 2 O masers might be a characteristic feature of the evolution of an O type ZAMS star. The latest phases are probably NOT traced by H 2 O masers.

●: EVN CH 3 OH 6.7 GHz A2A2 A1A1 KEPLERIAN MASS = 19 M ⊙ KEPLERIAN MASS = 55 M ⊙ SPIN-UP SIGNATURE: across 0.02 pc ΔV = 9(A1)and 6(A2)km s -1 A2A2 A1A1

image:VLA 7mm continuum ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz : VLBA H 2 O barycent. A 1 - North

●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz : PdBI 1.3 mm continuum : VLA-B 1.3cm peak : EVN CH 3 OH barycent. A 2

: VLA-B 1.3cm peak ●: EVN CH 3 OH 6.7 GHz ▲: VLBA H 2 O 22.2 GHz : PdBI 1.3 mm continuum A 2

▲: VLBA H 2 O 22.2 GHz C