tracing molecular gas mass in extreme environments

Ming Zhu (JAC/NRC)

P. P. Papadopoulos (Argelander Institute for Astronomy, Germany)Yu Gao (Purple Mountain Observatory, China)

Ernie R. Seaquist (U. of Toronto, Canada)Manolis Xilouris (National Observatory of Athens, Greece)

Nario Kuno (Nobeyama Radio Observatory, Japan)Loretta Dunne (Nottingham University, UK)Ute Lisenfeld (University of Granada, Spain)

Tracing molecular gas Tracing molecular gas mass in extreme mass in extreme

environmentsenvironments

IntroductionCO(1-0) as a M(H2) tracer

Introduction

• Conventional way to derive molecular gas mass using the empirical relation

N (H2) =X Ico or M(H2)=X Lco– X is the CO-to-H2 conversion factor – X depends on metallicity (Wilson 1995)– X is 5 times smaller in the nuclear regions of IR-

luminous galaxies (Downes & Solomon 1998)– How different is the X factor in different types of

galaxies?

• Derive M(H2) from dust mass – Can we use the Galactic gas-to-dust ratio in external

galaxies? How big is the variation?

Dust mass Gas mass

• Derive M(H2) from dust mass – Our Galaxy gas/dust ~ 150

– Can we use the Galactic gas-to-dust ratio in external galaxies? Is it a constant? How much does it variate?

Sample: 1. Antennae Galaxies

Arp299

Taffy Galaxies

NGC3310

NGC157

Single dish data for NGC4038/39

High quality data:

wavelength telescope resolution cover-region12CO(1-0) Nobeyama 45-m 15” 60”x100”12CO(2-1) JCMT 20” 50”x50”12CO(3-2) JCMT 14” 60”x90”13CO(2-1) JCMT 20” 5 points13CO(3-2) JCMT 14” 2 points

N4038: CO(1-0) on K band

CO10 and CO32

NGC3310

NGC157

Taffy: CO(3-2) profiles on CO(1-0)

R31 on Antenne

Excitation --CO(3-2)/(1-0) on ISO image

Excitation Analysis: LVG modeling

r21=Ico(2-1)/Ico(1-0) r31=Ico(3-2)/Ico(1-0) R10= I_13co(1-0)/I_12co(1-0) R21=I_12co(2-1)/I_13co(2-1)

Tk, n(H2), Nco/dV, Zco X = Nco/dV / Trad

Excitation analysis: r31 ratio

LVG model fitting

Preliminary Results

X factor (as a factor 1/f of the galactic value Xo)

UGC 12915 3-6UGC12914 2-7Taffy Bridge 6-13N4038C 4-6N4039C 3-7Overlap Region 5-10N3310 2-3 (excitation effect offset by metallicity

eff)N157C 4-8N157S 1-2(the uncertainty could be a factor of 2 or 3)

Non-viralized clouds

LVG model results dV/dr = (10- 100) km/s/pc

(if [12CO/H2] = 10 ^-4)

but Virialized dV/dr < 3 km/s/pc

Nco/dV = (1.5 -1.9) x 10^15 cm{-2}

X = Nco/Ico =(5.1-6.4) x 10^19 cm^-2/(K km/s)

11- 13 times smaller than the Galactic value !!

==> True M(H2) < M(H2*) = X Lco

Summary I

• The X factor can vary by a factor of 10 from galaxy to galaxy and also within one galaxy.

• In starburst galaxies and interacting galaxies, the X factor is smaller than the galactic value by a factor of 5.

• In the spiral arm of quiet galaxies the X factor is close to that of the Milky Way.

• In extreme environment, the X factor is within 1 order of magnitude of Xo

Dust mass Gas mass

• Derive M(H2) from dust mass – Our Galaxy gas/dust ~ 150

– Can we use the Galactic gas-to-dust ratio in external galaxies? Is it a constant? How much does it variate?

Scuba 850 on Ant

NGC3310: 850 on HI

NGC157: SCUBA 850 on HI

NGC4038/39

SED of NGC3310

SED of NGC1569

NGC3310 radiation field

NGC157 radiation field

NGC3310 –enhanced VSG

NGC3310 M(HI)/M(dust)

Gas-to-dust ratio in NGC4038/39

Zhu et al. (2003)

Gas-to-dust ratio in Taffy galaxies

N157 and N3310

Summary II

• Large variation in the gas-to-dust ratio in interacting systems

• NGC 3310 shows excess 850 emission which could be explained by a large fraction of very small dust grains due to a strong radiation field in this galaxy.

Hubble Deep Field

(Hughes et al. 1998, Nature)

Next Step

• JCMT local universe survey of nearby galaxies with SCUBA-2 and HARP

JCMT nearby galaxy survey(Wilson et al.)

• JCMT local universe survey of nearby galaxies with SCUBA-2 and HARP

• 200 galaxies (HI fluxes selected)

• 32 galaxies in SINGS

• CO1-0 data from BIMA or NRO 45m

Nearby Galaxy Survey

Goals:1.Physical properties of dust in Galaxies

2.Molecular gas mass and gas-to-dust ratio

3.Effect of galaxy morphology

4.Luminosity and dust mass function

Ophiuchus

• Most mass is in diffuse region– Ophiuchus, d=160pc, 4 deg^2 region

– 2000 Msun from extinction

– 50 Msun in submm dust core , less than 2.5%

Av > 15

• So most mass in not detectable in submm• Can be observed in CO

Perseus

• Most mass is in diffuse region– Perseus (d=300pc) for example 3 deg^2 region– 17000 Msun from visual extinction Av=2,

less than 10% from Av> 5 (Bachiller & Cernicharo 1986),

– 2600 Msun in dust core , less than 20%– 6000 Msun by C18O (Hatchell et al. 2000) .