Molecular Gas at GMC Scale -- from CARMA to ALMA – Fumi ...overlaid on CARMA+45m image. Velocity...
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2. Target: M51 CARMA Observations Nearby D = 8.4±0.6 Mpc (Feldmeier et al. 1997) Face-on i = 15° (Regan et al. 2001) Grand-design Spiral Structure Arm Class = 12 (Elmegreen & Elmegreen 1987) ISM evolution: dust lanes (molecular gas) -> star forming regions Density wave enhanced by the interaction with the companion Giant Molecular Clouds (GMCs) 40 pc, 10 5-6 Msun found in both arm and interarm regions Giant Molecular Associations (GMAs) > 100 pc, > 10 7 Msun found in spiral arms only Gas Evolution across Spiral Arms GMCs -> GMA -> star formation + GMCs GMAs seem to be single structure (as surface density of GMAs and GMCs are consistent) 1. Molecular Gas in Spiral Galaxy The resolution of CO data (4” or 150pc) is not small enough to resolve GMAs. Introduction HST Molecular gas distribution from NRO45m+CARMA CO(1-0) data (Koda et al. 2009) White square = Field of view (1’x1’) of CARMA B-array obs. Purpose To resolve GMAs and detect GMC-scale structures in external galaxies To understand molecular gas evolution across spiral arms Observations detail Single pointing toward the brightest GMA in M51 • Field of view = the white box in the HST image 12CO(1-0) in USB & 13CO(1-0) in LSB Hybrid correlator setting: 62MHz x 3 for source & 500MHz x 3 for calibrator CARMA B-configuration (Nov-Dec 2008) • Beamsize = 0.8” x 0.7” ~ 30pc • Shortest baseline = 25kλ ~ 8” ~ 340pc 5 tracks (34 hours in total) of observations Sensitivity = 14mJy/beam (dV=5.1km/s) • Corresponds to 1.5x10 5 Msun • 3σ ~ typical GMC mass B CDE UV coverage for B- and CDE-configurations 23 CARMA antennas Results (from 12CO data; only marginal detection in 13CO) 1. Internal structure of GMAs • Only a few detections in each GMA • Missing flux ~ 90% • GMAs are not ensemble of GMCs but are discrete and smooth structures. 2. Effect of spiral arms on gas evolution • Among the detections, more massive clumps (～ 10 6 Msun) are detected in downstream of the spiral arm (spatially as well as kinematically). • Most of them have nearby star-forming regions. • These clumps are at a later stage of molecular gas evolution across the arm (and probably cores of GMAs). Basic Features of CARMA Location: California, USA Altitude: 2000m Inhomogeneous Array: 10m x 6 + 6m x 9 antennas (+ 3.5m x 8) The best target to study the gas evolution across spiral arms! Caltech Location of CARMA & Caltech Integrated intensity of CARMA B-array data. Contour levels are 0.432 Jy/beam km/s times 1, 3, 5. Synthesized beam is shown at the bottom left. Clumps defined by the clump find algorithm shown as green circles. Contours from B-array data overlaid on CARMA+45m image. Velocity field map from CARMA+45m data. Contour step is 10km/s. Examples of spectra for clumps. Note the difference in flux. Most of the flux (~90%) is resolved out! Resolving GMC-scale structures in galactic disk are important on understanding 1. Internal structure of GMAs 2. Molecular gas evolution under the influence of spiral structures Data Analysis 1. clump find 2. comparison with CARMA+45m data 3. comparison with Hα & Paα data Molecular gas evolution! Offset between the peak velocity. V ofs = V peak (B) - V peak (45m+CARMA) From the spatial positions, larger clumps are on downstream of the spiral arm. Blueshifted = downstream! (Galactic rotation is counter clock wise.) Upstream Downstream From the velocity difference, massive clumps are on downstream of the spiral arm. Clump1 (&7): accompanied by a nearby star forming region Clump4: on-site star formation. Extinction in Ha is very high! Hα Paα Hα Paα Massive clumps = later stage of evolution
Transcript of Molecular Gas at GMC Scale -- from CARMA to ALMA – Fumi ...overlaid on CARMA+45m image. Velocity...
2. Target: M51
CARMA Observations
Nearby D = 8.4±0.6 Mpc (Feldmeier et al.
1997) Face-on i = 15° (Regan et al. 2001)
Grand-design Spiral Structure Arm Class = 12 (Elmegreen &
Elmegreen 1987) ISM evolution: dust lanes (molecular
gas) -> star forming regions Density wave enhanced by the
interaction with the companion
Giant Molecular Clouds (GMCs) 40 pc, 105-6 Msun found in both arm and interarm regions Giant Molecular Associations (GMAs) > 100 pc, > 107 Msun found in spiral arms only
Gas Evolution across Spiral Arms GMCs -> GMA -> star formation + GMCs GMAs seem to be single structure (as surface
density of GMAs and GMCs are consistent)
1. Molecular Gas in Spiral Galaxy
The resolution of CO data (4” or 150pc) is not small enough to resolve GMAs.
Introduction
HST
Molecular gas distribution from NRO45m+CARMA CO(1-0) data (Koda et al. 2009)
White square = Field of view (1’x1’) of CARMA B-array obs.
Purpose To resolve GMAs and detect GMC-scale structures
in external galaxies To understand molecular gas evolution across
spiral arms
Observations detail Single pointing toward the brightest GMA in M51
• Field of view = the white box in the HST image 12CO(1-0) in USB & 13CO(1-0) in LSB Hybrid correlator setting: 62MHz x 3 for source &
500MHz x 3 for calibrator CARMA B-configuration (Nov-Dec 2008)
• Beamsize = 0.8” x 0.7” ~ 30pc• Shortest baseline = 25kλ ~ 8” ~ 340pc
5 tracks (34 hours in total) of observations Sensitivity = 14mJy/beam (dV=5.1km/s)
• Corresponds to 1.5x105 Msun• 3σ ~ typical GMC mass
B CDE
UV coverage for B- and CDE-configurations
23 CARMA antennas
Results (from 12CO data; only marginal detection in 13CO)
1. Internal structure of GMAs• Only a few detections in each GMA• Missing flux ~ 90%• GMAs are not ensemble of GMCs but are discrete
and smooth structures.2. Effect of spiral arms on gas evolution
• Among the detections, more massive clumps (～106 Msun) are detected in downstream of the spiral arm (spatially as well as kinematically).
• Most of them have nearby star-forming regions.• These clumps are at a later stage of molecular gas
evolution across the arm (and probably cores of GMAs).
Basic Features of CARMA Location: California, USA Altitude: 2000m Inhomogeneous Array: 10m x 6
+ 6m x 9 antennas (+ 3.5m x 8)
The best target to study the gas evolution across spiral arms!
Caltech
Location of CARMA & Caltech
Integrated intensity of CARMA B-array data. Contour levels are 0.432 Jy/beam km/s times 1, 3, 5. Synthesized beam is shown at the bottom left.
Clumps defined by the clump find algorithm shown as green circles.
Contours from B-array data overlaid on CARMA+45m image.
Velocity field map from CARMA+45m data. Contour step is 10km/s.
Examples of spectra for clumps. Note the difference in flux. Most of the flux (~90%) is resolved out!
Resolving GMC-scale structures in galactic disk are important on understanding
1. Internal structure of GMAs2. Molecular gas evolution under the influence
of spiral structures
Data Analysis1. clump find 2. comparison with CARMA+45m data
3. comparison with Hα & Paα dataMolecular gas evolution!
Offset between the peak velocity.Vofs = Vpeak(B) - Vpeak(45m+CARMA)
From the spatial positions, larger clumps are on downstream of the spiral arm.
Blueshifted = downstream!(Galactic rotation is counter clock wise.)
Upstream
Downstream
From the velocity difference, massive clumps are on downstream of the spiral arm.
Clump1 (&7): accompanied by a nearby star forming region
Clump4: on-site star formation. Extinction in Ha is very high!
Hα Paα Hα Paα
Massive clumps = later stage of evolution
