Spectral Line Surveys with the CSOSusanna L. Widicus Weaver, Department of Chemistry, Emory University

Matthew Sumner, Frank Rice, Jonas Zmuidzinas, Department of Physics, Caltech

Geoffrey Blake, Department of Geological & Planetary Sciences, Department of Chemistry, Caltech

The Widicus Weaver Group

Mary RadhuberJay KrollBrandon CarrollJake LaasThomas Anderson

New Receiver Technology at the CSO

• “Z-Rex” receiver designed for external galaxy searches at high-z

• Broad frequency coverage

• High S/N

• Double sideband (DSB) receiver

Facility CSO Receivers Z-Rex

Tsys (K, SSB) 120 100

Spectral (IF) Bandwidth (GHz) 1 4

Z-Rex is an ideal receiver for spectral line surveys!

What is a Line Survey?Typical Observations Individual, narrow frequency windows

targeting only a handful of transitions.

Line SurveyA series of spectral windows pieced together to provide spectral coverage across a

large frequency range.

Why Line Surveys?• More lines observed

more detection certainty

• Uniform coverage under similar instrument conditions

minimizes calibration inconsistencies

• Comprehensive intensity information

reliable model of physical conditions

• Broadband spectral coverage

large amounts of info, and fast

Why New Molecular Line Surveys?

Our Goals:• Conduct surveys for many different types of sources• Achieve high spectral sensitivity (for new molecule

ID)• Obtain full picture of chemical, physical conditions

for each source• Compare results to astrochemical models

• New astrochemical models explain formation of complex organics

• Models require complete chemical, physical picture for input/comparison

• Physical parameters, abundances often educated guesses

• Few surveys access differing chemical, physical environments

Garrod, Widicus Weaver, & Herbst, ApJ 682, 2008

The Orion KL Region

http://oobleck.ifa.hawaii.edu:8080/where/images/orion.jpg

Orion KL star forming region

http://www.mpg.de/bilderBerichteDokumente/multimedial/bilderWissenschaft/2009/02/Walter0902/Web_Zoom.jpeg

From Liu, S.-Y. et al. (ApJ 576, 2002)

CSO Beam Size at = 1 mm

Previous Orion KL Surveys>50 radio frequency Orion spectral line surveys

reported in the literature!

OVRO survey at = 1.3 mm215 – 263 GHzRMS~ 150 mK

800 resolved spectral features29 molecular species IDed

The Challenge: DSB Spectra

+ =

Image sideband

Observed Double Sideband Spectrum

Frequency sideband

desired line position

desired line position

Spectra from Nummelin et al. (ApJ Supp. Series 117, 1998)

Lower Sideband Upper Sideband

-IF +IF

LO

Spectral Coverage on Orion

Initial Deconvolution of Orion Spectra

Blake et al. OVRO survey: RMS = 150 mK, integration time ~ weeks (months?)Our survey: RMS = 30 mK, time ~ 4 nights

Line Identification Progress

Total Lines >3 5548

Assigned Lines (to date) 662 (11.9%)

Unidentified Lines 4886 (88.1%)

Lines Assigned in Previous Surveys 400

New Lines Assigned (to date) 262

Line Identification ProgressMolecule Lines Previously Observed New Lines Observed

CO 2 0DNC 1 0C17O 1 0H2CO 1 0

CH3CCH 5 0CH3

13CN 2 0HNCO 3 0C33S 1 0HDO 2 1CN 11 1

CH3CN 20 113CS 1 1C34S 1 1H2CS 7 2

13CH3CN 7 3CH2CO 4 5

HCOOH 7 6C2H5CN 60 22CH3OH 55 42

13CH3OH 11 42CH3CHO 4 46CH3OCH3 20 61

Line Identification

Next Steps?Orion Survey Analysis• Finalize spectral deconvolution

incorporate baseline subtraction, test for “ghosts”

• Analyze spectral informationdetermine lineshapes, intensities

• Identify more lines from previously detected molecules

include weak lines, isotopologues, vibrational states

• Rotational diagram analysis for each moleculeaccount for multiple sources,

velocities, temperatures

Beyond the Orion Survey• Line surveys of other sources

completed: Sgr B2(N-LMH), NGC 1333-IRAS 4, L1157

upcoming: W51 e1/e2, G34.3+0.2, W3(H2O) & W3(OH)

• Laboratory spectroscopic studies • Comparison to astrochemical models• ID of new molecules

only after complete simulation of known molecules is achieved

1 – 50 GHzFrequencySynthesizer

VDI Multiplier chain50 GHz – 1.2 THz Detector

Gas Flow Cell

To Computer

Sample Input To Vacuum Pump

Laboratory Spectral Cataloging

Methanol Broadband Scan Dimethyl Carbonate (CH3OCOOCH3)

First light April 1, 2009!

AcknowledgementsThe Widicus Weaver Group:

Mary RadhuberJay KrollBrandon CarrollJake LaasThomas Anderson

John Pearson & Brian Drouin @ JPL

CSO Local Staff