Presentation on theme: "The Serpens Star Forming Region in HCO +, HCN, and N 2 H + Michiel R. Hogerheijde Steward Observatory The University of Arizona."— Presentation transcript:
The Serpens Star Forming Region in HCO +, HCN, and N 2 H + Michiel R. Hogerheijde Steward Observatory The University of Arizona
Outline Molecular clouds and star formation The Serpens star-forming region Single-dish images Interferometer images Combination single-dish and interferometer Abundances A shock model for HCN and N 2 H + Conclusions
Molecular clouds and star formation Stars form in condensations in interstellar clouds Cloud structure determines stellar masses Jets, outflows affect cloud chemistry and structure
The Serpens star-forming region Dense cluster of pre– main-sequence stars Two condensations, NW and SE ~Dozen submm continuum peaks Many associated with YSOs, some starless cores SCUBA 850 µm on DSS image Davis et al. (1999)
JCMT/SCUBA images of Serpens Davis et al. (1999) SMM4 SMM11 SMM6 SMM2 SMM3 SMM1/ FIRS1 SMM8 SMM9/ S68N SMM10 SMM5
Many outflows ‘Tangle’ of outflows Intermediate velocities: ±7 km s -1 Extreme velocities: ±11 km s -1 Davis et al. (1999)
How do outflows affect structure and chemistry in Serpens? J=1–0 transitions ( ≈3 mm) of HCO +, HCN, N 2 H + Common tracers of dense [n(H 2 )≈10 5–6 cm -3 ] and cool (T kin ≈30 K) gas Morphology chemistry 4 Single-dish on-the-fly maps from Kitt Peak 12-meter telescope 4 Interferometer mosaics from the Berkeley- Illinois-Maryland array (SE region only)
Single-dish maps HCO + 1–0HCN 1–0N 2 H + 1–0 Resolution 1 = 0.12 pc = 21,000 AU
Single-dish maps N 2 H + equally strong in NE and SE –Follows submillimeter continuum HCO + and HCN peak in SE –Where most embedded YSOs and their outflows are E-W velocity gradient –Solid-body rotation, also noted by Olmi & Testi (2002)
Interferometer mosaics Higher resolution: 10–20 arcsec; 140 arcsecs primary field of view Filters out large-scale emission ~ 115 arcsec 13-point ‘mosaic’: overlapping pointings
Interferometer mosaics: N 2 H + Resolution 17 = pc = 7000 AU
Interferometer mosaics: N 2 H + Color: N 2 H + Contours: 850 µm
Interferometer mosaics: HCN Resolution 21 = pc = 8500 AU
Interferometer mosaics: HCO + Resolution 12 = pc = 4600 AU
Interferometer mosaics N 2 H + : –At continuum peaks –Ahead of SMM3’s jet –North of ‘shock position’ HCO + and HCN: –near YSOs, outflows Strong blue-shifted HCN west of SMM4: –‘shock position’
Combining single-dish and interferometer data Interferometers filter out emission on scales larger ~ shortest antenna spacing Missing ‘zero-spacing’ flux KP12m well matched to 6-m BIMA antennas Method: joint deconvolution
Combined BIMA and KP12m
Combined maps qualitatively look as expected High resolution of BIMA brings out velocity details on small scales ‘Washed out’ in KP12m map BIMA recovers ~30% of line flux
Abundances Are HCO + and HCN enhanced by outflow action? Throughout core, or only locally?
Abundances Olmi & Testi (2002) C 18 O 1–0 map FCRAO: 1 arcmin resolution T ex N(H 2 ) Use to derive abundances on 1 arcmin scales
Abundances HCO + HCNN2H+N2H+
Abundances Average Serpens Peak positions Dark cloud values a N2H+N2H+ 3.8x x (5–10)x HCO + 3.0x x (2–8)x10 -9 HCN 5.4x x (0.5–5)x10 -8 Factor 2 enhancement near YSOs (outflows) Abundances HCN, HCO + << dark clouds: depletion; T ex ? a) van Dishoeck et al. 1993; Ohishi et al. 1992; Turner 2000
Shock model for HCN and N 2 H + Offsets between HCN (color) and N 2 H + (contours) SMM3’s jetShock position
Shock model for HCN and N 2 H + C-type shock Magnetic precursor Ions accelerate, compress, and heat before neutrals N 2 H + emission up in precursor HCN abundance up in warm region: evaporation of ices Accompanying H 2 O destroys N 2 H + Draine & Katz (1986)
Two models for shock position: 1 Jet driven by SMM4, deflected by dense material. N 2 H + in magnetic precursor of C-type shock.
Two models for shock position: 2 Jet driven by SMM1, hitting dense matter. HCN at bow shock, N 2 H + along the sides where shock speeds are lower.
Conclusions HCN, HCO + locally enhanced by shocks Depleted in rest of cloud compared to dark- cloud values Unresolved observations would trace outflow- affected material preferrentially N 2 H + undepleted: traces condensations N 2 H + emission ahead of shocks: enhancement in magnetic precursor, destruction in warm region?
Future work C 18 O on 10–20 arcsec scales, fully sampled Higher-J lines: excitation HCN, HCO +, and N 2 H + High-resolution interferometry shock region; additional species Time-dependent shock-chemistry model
Many thanks to… Staff of the Kitt Peak 12 meter Radio Telescope Staff of the Berkeley-Illinois-Maryland Association millimeter array Chris Davis and Luca Olmi for making their data available electronically