molecular gas and star formation in nearby galaxies

12 October 2007 Space Telescope Science Institute

Molecular Gas and Star Formation in Nearby

Galaxies

Molecular Gas and Star Formation in Nearby

GalaxiesJean Turner

UCLA

with: David S. Meier, Lucian Crosthwaite, Chao-Wei Tsai, Sara Beck, Robert Hurt, Alaina Henry


Molecular gas and star formation in galaxies

present and future

I. CO, a tracer of star-forming gas in galaxies

II. Gas & star formation in spiral and dwarf

galaxies

III.Beyond CO: chemical diagnostics and feedback

IV. ALMA


present and future

I. CO, a tracer of star-forming gas in galaxies

II. Gas & star formation in spiral and dwarf

galaxies

III.Beyond CO: chemical diagnostics and feedback

IV. ALMA


CO is the tracer of molecular gas

Why not H2?

Excitation: first excited level is 510K above ground, but first quadrupole transition is J=2 rotational level…

You will see very warm (hundreds of K) gas, or fluorescent emission from H2

You will NOT see thermal emission from typical GMCs (4-30K), nor absorption (Av

> 3-5)


Why not H2?

Excitation: first excited level is 510K above ground, but first quadrupole transition is J=2 rotational level…

You will see very warm (hundreds of K) gas, or fluorescent emission from H2

You will NOT see thermal emission from typical GMCs (4-30K), nor absorption (Av

> 3-5)



Why CO?

Abundant, chemically stable, transitions accessible from the ground ( = 3mm, 1mm)

Easily excited: first excited rotational (J=1) level 5.5K

Easily thermalized: collisional excitation dominates at densities > a few hundred/cc

(low dipole moment and high opacity)


Why CO?

Abundant, chemically stable, transitions accessible from the ground ( = 3mm, 1mm)

Easily excited: first excited rotational (J=1) level 5.5K

Easily thermalized: collisional excitation dominates at densities > a few hundred/cc

(low dipole moment and high opacity)


CO is a tracer of molecular (HCO is a tracer of molecular (H22) mass) mass

Xco = ICO/NH2 = 2 x 1020 cm-2/K km/s, empirical

rays (CR+H) show Xco is good to x2 in Galaxy Bloemen et al. 1986, Strong et al. 1988

arises from observed size-linewidth relation for GMCs

Larson 1980, Solomon et al. 1987

can be understood in the context of virialized clouds

CO is a tracer of molecular (HCO is a tracer of molecular (H22) mass) mass

Xco = ICO/NH2 = 2 x 1020 cm-2/K km/s, empirical

rays (CR+H) show Xco is good to x2 in Galaxy Bloemen et al. 1986, Strong et al. 1988

arises from observed size-linewidth relation for GMCs

Larson 1980, Solomon et al. 1987

can be understood in the context of virialized clouds


Virialized clouds?

Column density at which H => H2 is the same as the column density of the critically-bound Bonner-Ebert sphere (i.e., “Jeans mass”) at inner disk pressures. Clouds in high P regions more likely to be H2.

Scoville & Sanders 1987, Elmegreen 1989, Elmegreen & Parravano 1996

Yet while clouds are bound they are not collapsing… otherwise SFR = 109 Msun/tff >200 Msun/yr, observed is 3-4 Msun/yr Zuckerman & Palmer 1974, Z & Evans 1974, Goldreich & Kwan 1979

GMCs appear to be turbulently supportedNorman & Silk 1980, McKee

Virialized clouds?

Column density at which H => H2 is the same as the column density of the critically-bound Bonner-Ebert sphere (i.e., “Jeans mass”) at inner disk pressures. Clouds in high P regions more likely to be H2.

Scoville & Sanders 1987, Elmegreen 1989, Elmegreen & Parravano 1996

Yet while clouds are bound they are not collapsing… otherwise SFR = 109 Msun/tff >200 Msun/yr, observed is 3-4 Msun/yr Zuckerman & Palmer 1974, Z & Evans 1974, Goldreich & Kwan 1979

GMCs appear to be turbulently supportedNorman & Silk 1980, McKee


CO is a tracer of molecular (HCO is a tracer of molecular (H22) ) massmass

Xco = ICO/NH2 = 2 x 1020 cm-2/K km/s

Ico = Tb dv ~ Tk v

Xco gives a dynamical mass like Tully-Fisher

relatively insensitive to metallicity (Maloney & Black 1988, Elmegreen

1989)

CO is a tracer of molecular (HCO is a tracer of molecular (H22) ) massmass

Xco = ICO/NH2 = 2 x 1020 cm-2/K km/s

Ico = Tb dv ~ Tk v

Xco gives a dynamical mass like Tully-Fisher

relatively insensitive to metallicity (Maloney & Black 1988, Elmegreen

1989)


II. Molecular gas and star formation in spirals and dwarfs

big galaxies and small galaxies appear to form stars differently

molecular observations: so far, anecdotal (small number

statistics)

galaxy colors & age-dependent features => SF depends on galaxy form

Kauffmann et al. 2006, SDSS

II. Molecular gas and star formation in spirals and dwarfs

big galaxies and small galaxies appear to form stars differently

molecular observations: so far, anecdotal (small number

statistics)

galaxy colors & age-dependent features => SF depends on galaxy form

Kauffmann et al. 2006, SDSS


IC 342IC 342 Red: HIGreen: COBlue: stars 1’ beam

VLA HI / NRAO 12m CO / DSS Crosthwaite et al. 2001

9 kpc




Interarm CO

CO arms become HI arms

HI & CO correlated Tilanus & Allen 1989-93


M83M83 Red: HIGreen: COBlue: stars 1’ beam

6 kpc

VLA HI / NRAO 12m CO / DSS Crosthwaite et al. 2002; HI: Tilanus & Allen 1993


M83M83

M83 has a sharp “edge”where both HI and H2

surface densities fall offat R ~ 6 kpc

Red: HIGreen: COBlue: stars 1’ beam

VLA HI / NRAO 12m CO / DSS Crosthwaite et al. 2002; HI: Tilanus & Allen 1993


M83 Gas “Edge”M83 Gas “Edge”

Fallsat gas = 15 Msun/pc2


NGC 6946NGC 6946

VLA HI / NRAO 12m CO / DSS

In NGC 6946 gas falls offgradually

SFR = gas

Schmidt law, n=1as opposed to Kennicutt law, n=1.4

Crosthwaite & Turner 2007

also seen by Crosthwaite et al. 2002, Wong & Blitz 2003

Red: HIGreen: COBlue: stars 1’ beam


Interferometric observations of CO: ~6” (200-400 pc)Interferometric observations of CO: ~6” (200-400 pc)

BIMA SONG: Regan et al. 2001, Helfer et al. 2003


Interferometric CO: Maffei 2 3” beamInterferometric CO: Maffei 2 3” beam



13 kpc 800 pc 320 pc

OVRO & BIMA: Meier & Turner 2007



320 pc


CO: contours greyscale: 3mm continuum, symbols: VLA subarcsec



320 pc


CO: contours greyscale: 3mm continuum, symbols: VLA subarcsec

Large star clusters forming here



320 pc


clouds tidally stretched along bar



320 pc



Xco too high by x2-4 - overpredicts cloud masses



320 pc





OVRO & BIMA, CO, 3” beam: Meier & Turner 2007

Big bar Little bar



OVRO & BIMA, CO, 3” beam: Meier & Turner 2007

“P-V” diagram: effective “slit” along major axis

Star formation occurs at the x1-x2 orbit intersections


Star formation and molecular gas in spirals

1. CO-emitting gas is star-forming gas; CO disk

same as optical disk, HI disk is much bigger

2. SF needs a trigger: spiral arms or, in

galactic centers, x1-x2 orbit intersections

3. Schmidt law dependence unclear, we find n=1

(SFR ~ gas) rather than Kennicutt law

(n= 1.4)

4. Xco overpredicts H2 mass in tidally supported

clouds in galactic centers

Star formation and molecular gas in spirals

1. CO-emitting gas is star-forming gas; CO disk

same as optical disk, HI disk is much bigger

2. SF needs a trigger: spiral arms or, in

galactic centers, x1-x2 orbit intersections

3. Schmidt law dependence unclear, we find n=1

(SFR ~ gas) rather than Kennicutt law

(n= 1.4)

4. Xco overpredicts H2 mass in tidally supported

clouds in galactic centers


dwarf galaxies: NGC 5253dwarf galaxies: NGC 5253

Calzetti et al. 1997Gorjian 1996

Looks like dE that has accreted gasNelson & Caldwell 1989

Numerous bright young clusters, ages3 to 50 Myr

More IR clusters than opticalSTIS: field stars lack O stars of the clusters, consistent with cluster dissolution on 10 Myr timescales or or bimodel SF

Calzetti et al. 1997, Tremonti et al. 2001Alonso-Herrero et al. 2004



Meier, Turner, & Beck 2002


SF efficiency=M/( M+ Mgas)=75%, on200 pc scales

In Galaxy,SFE~1-3% on GMC scales(SFE~30% on pc scales, ONC) Lada et al 1984

SFE 2 orders of magnitude higher than in Galaxy



Meier et al. 2002

E/VLA 7mm + NICMOS: Turner & Beck 2004


10 pc, 0.6”

embeddedIR clusteronly reallyvisible ~1.9-2 microns



Meier et al. 2002Rodriguez-Rico et al. 2007

E/VLA 7mm + NICMOS: Turner & Beck 2004

H53Calzetti et al. 1997Gorjian 1996

10 pc, 0.6”


image courtesy of NRAO/AUI HI: Yun, Ho, Lo 1994


Star formation and molecular gas in dwarf galaxies

1. Star formation in dwarf galaxies may be driven by accretion from outside — could explain “burstiness”

N5253: Meier et al. 2002, NGC 3077, Meier et al. 2003, Walter et al. 2004, He 2-

10? Kobulnicky et al. 2002 (rotation)

2. Is this mode of star formation fundamentally different wrt star formation efficiency (is it easier to form bound clusters in dwarfs?)3. Role of magnetic fields?

Star formation and molecular gas in dwarf galaxies

1. Star formation in dwarf galaxies may be driven by accretion from outside — could explain “burstiness”

N5253: Meier et al. 2002, NGC 3077, Meier et al. 2003, Walter et al. 2004, He 2-

10? Kobulnicky et al. 2002 (rotation)

2. Is this mode of star formation fundamentally different wrt star formation efficiency (is it easier to form bound clusters in dwarfs?)3. Role of magnetic fields?


III. Beyond CO: chemical diagnostics & feedback

III. Beyond CO: chemical diagnostics & feedback


NGC 253 2mm survey IRAM 30 mNGC 253 2mm survey IRAM 30 mNGC 253 SURVEY

(Martin et al.,2006)First unbiased line survey in a galaxy IRAM: 129.1 - 175.2 GHz @ dv ~ 9 km/s

IRAM

2MASS - Jarrett

CSCCH


Imaging Chemistry in Galaxies: IC 342 Owens Valley mm ArrayImaging Chemistry in Galaxies: IC 342 Owens Valley mm Array

N2H+ HNC HC3N C2H C34S HNCO CH3OH

central 300 pc

3mm lines: molecules have similar excitation

differences are chemical

contours: 13CO, color = molecules Meier & Turner 2005



PC Axis 1:

Density-weightedmean column density

Meier & Turner 2005




PC Axis 1:


PC Axis 2:

Shock tracers vs PDR molecules

Meier & Turner 2005




PC Axis 1:


PC Axis 2:

Shock tracers vs PDR molecules

CO, N2H+, HNC, HCN; gas tracersC2H, C34S: PDR Methanol, HCNO:

shocks

Meier & Turner 2005



Beyond CO: chemical diagnostics & feedback

1. High resolution imaging (ALMA) reduces chemical complexity by isolating regions of common chemistry in galaxies

2. Studies of nearby galaxies suggest that there are classes of molecules, such as:

Gas tracers: CO, N2H+, HCN, HNC

Grain chemistry (shocks?) tracers: methanol, HNCO (spiral arms)

PDR tracers: C2H (B stars rather than O?)

Beyond CO: chemical diagnostics & feedback

1. High resolution imaging (ALMA) reduces chemical complexity by isolating regions of common chemistry in galaxies

2. Studies of nearby galaxies suggest that there are classes of molecules, such as:

Gas tracers: CO, N2H+, HCN, HNC

Grain chemistry (shocks?) tracers: methanol, HNCO (spiral arms)

PDR tracers: C2H (B stars rather than O?)


IV. ALMAIV. ALMA

“up to 64” (currently 50) x 12m antennas

12 x 7m antennas (ACA)

EU (ESO), NA (NRAO, Canada), J (Japan, Taiwan)

in the Atacama desert of Northern Chile, 16,400 ft

heterodyne receivers from 0.3 to 9.6mm (v < .05km/s)

spatial resolution to 5 mas sensitivity: 7 Jy in 1 hr, continuum brightness 0.8mK


ALMA Science DriversALMA Science Drivers

1. Detect CO in an L galaxy at z = 3.

2. Resolve gas kinematics in protoplanetary disks at 150 AU.

3. Imaging comparable to HST.


ALMA SiteALMA Site


ALMA is near San Pedro de AtacamaALMA is near San Pedro de Atacama


San Pedro de AtacamaSan Pedro de Atacama


San Pedro de Atacama

San Pedro de Atacama


ALMA siteALMA site


QuickTime™ and aH.264 decompressor

are needed to see this picture.


ALMA buildingsALMA buildings


ALMA antennas - five in Chile already! 3 can bowALMA antennas - five in Chile already! 3 can bow

Melco/Mitsubishi antennas, ALMA-J


ALMA transporter: “Otto”ALMA transporter: “Otto”


ALMA timescalesALMA timescales

First interferometric observations 2008

Call for proposals 2009

Early science 2010

Full operations 2012



Current understanding

CO gas is star-forming gasXco may give reliable masses in absence of other

dynamical effectsStar formation needs a trigger, not just gas:

Spirals: related to spiral structure and bar orbits

Dwarfs: accretion of intergalactic gas

Bright futures (ALMA, CARMA, PdBI):

CO and gas across the universe (z=10?)Modes & triggers of star formation (clusters, field stars)Gas-dominated galaxies? (gas ages)Extragalactic chemistry: chemical diagnostics of galaxy evolution


Current understanding

CO gas is star-forming gasXco may give reliable masses in absence of other

dynamical effectsStar formation needs a trigger, not just gas:

Spirals: related to spiral structure and bar orbits

Dwarfs: accretion of intergalactic gas

Bright futures (ALMA, CARMA, PdBI):

CO and gas across the universe (z=10?)Modes & triggers of star formation (clusters, field stars)Gas-dominated galaxies? (gas ages)Extragalactic chemistry: chemical diagnostics of galaxy evolution

molecular gas and star formation in nearby galaxies

Documents

beamvla hi nrao

dss crosthwaite

hi armshi

tracer of star

tracer of molecular

tracer of molecular

beam6 kpcvla hi nrao

lucian crosthwaite