Luminous Infrared Galaxies with the Submillimeter Array: Probing the Extremes of Star Formation Chris Wilson (McMaster), Glen Petitpas, Alison Peck, Melanie Krips (CfA), Brad Warren (McMaster), Mrk273 UGC5101 Daisuke Iono (NAOJ), Andrew Baker (Rutgers), Paul Ho, Satoki Matsushita (ASIAA), T.J. Cox (CfA), Lee Armus (IPAC), Mika Juvela (Helsinki), Chris Mihos (Case Western), Ylva Pihlstrom (UNM), Min Yun (U.Mass), A. Atkinson, J. Golding (McMaster)

Luminous Infrared Galaxies with the Submillimeter Array 1.What are Luminous Infrared Galaxies? 2.An SMA Legacy Project: Gas Morphology and Dynamics in U/LIRGs 3.First results 1.gas-to-dust ratio 2.star formation versus gas concentration 3.comparison to high-redshift submillimeter galaxies

ULIRGS are galaxy mergers All galaxies with L FIR > 5x10 11 L o are interacting or close pairs (Sanders et al. 1987) Figure from Galliano 2004 Scoville et al. 2000

Luminosity Source: Starbursts and AGN 70-80% predominantly starbursts 20-30% predominantly AGN Genzel et al. 1998

Dusty galaxies at high redshift: ULIRGs on steroids? Cosmologically significant population of very luminous dusty galaxies discovered at submm wavelengths For z>0.5, 5 mJy at 850  m implies L > 8x10 12 L o Tacconi et al Ivison et al. 2000

Gas Morphology and Dynamics in Luminous Infrared Galaxies: An SMA Legacy Project Determine the distributions, kinematics, and physical conditions of dense molecular gas in U/LIRGs Determine the spatial distribution of dust in U/LIRGs Constrain the origin of nuclear OH megamasers Determine how the gas properties change as the interaction progresses Compare the properties of the dense gas in local ULIRGs with the high-redshift submillimeter sources

The Submillimeter Array 8 x 6m antennas, maximum baseline 500 m Dual frequency operation at 230, 345, 690 GHz 2 GHz bandwidth = 2600 km/s at 230 GHz Angular resolution of our survey is 1-4” (CO 3-2 and 880 micron continuum)

Gas Morphology and Dynamics in Luminous Infrared Galaxies: Sample Selection Representative sample of 14 luminous and ultraluminous infrared galaxies D L < 200 Mpc (resolution 1” ~ 1 kpc) log(L FIR ) > 11.4 All with previous interferometric observations in the CO J=1-0 line

The Nearby Luminous Infrared Galaxy Sample

Centrally compact CO 3-2 emission (HST images of Arp55 and I from Evans, Vavilkin, et al., 2007, in prep.) Mrk231Mrk273 I UGC5101Arp55

But some systems are very extended CO emission in VV114 shows three peaks spaced over 4 kpc (10”) 5 out of 14 galaxies in our sample show two or more components

880  m continuum overlaid on CO3-2 Contours are 2,3,4 … X 5 mJy/beam Field of view 4”x4”. All sources detected at 4 sigma or better. Mrk231 Mrk273I UGC5101Arp55(NE)

The Gas to Dust Mass Ratio M dust assumes  = 0.9 cm 2 /g and T dust from modified blackbody fit to global data from 60 to 800  m (cf. Klaas et al. 2001) M(H 2 ) = 0.8 L(CO1-0) (Downes & Solomon 1998); assume CO3-2/1-0=0.5 (our data) Calculate gas to dust ratio in central beam only (CO much more sensitive than continuum per unit mass) Average gas/dust ratio = 120 +/- 30 Standard deviation 109: significant scatter

Peak H 2 surface density correlates with L FIR /M H 2 (Scoville et al. 1991)

With more uniform spatial resolution, correlation disappears Log(L FIR /M H 2 ) (L o /M o ) Log(  H 2 ) (M o pc -2 )

Do see a correlation of peak H 2 surface density with L FIR Log(L FIR ) Log(  H 2 )

Implications for star formation No obvious correlation of star formation efficiency (L FIR /M H 2 ) with peak H 2 surface density Possible correlation of star formation rate with peak H 2 surface density Suggests increased star formation rate/AGN activity in U/LIRGs is due to increased availability of fuel in central kiloparsec

Extremely high central gas surface densities Peak gas surface densities range from 10 3 to 10 4 M o /pc 2 inside kpc 2 area –A V = mag Average volume density at peak range from n H = 20 to 300 cm -3 –Estimated as (gas surface density) / (beam radius) Average density is comparable to a GMC, but volume is times larger –1 kpc versus pc

ULIRGs at low and high redshift Compare fourteen local galaxies with eight high- redshift galaxies; all in CO 3-2 (Tacconi et al. 2006, Downes & Solomon 2003, Genzel et al. 2003, Weiss et al. 2003) Compared to local galaxies, high-redshift galaxies are at least an order of magnitude more luminous in CO 3-2 –L CO = 3.5x10 10 versus 2.6x10 9 K km/s pc 2 May have much larger FWHM diameters –5 kpc versus 900 pc for nine galaxies 5 local galaxies have two nuclei separated by 4-32 kpc These galaxies are at faint luminosity end of our sample

Conclusions A large survey of warm dense molecular gas in nearby luminous infrared galaxies shows –Gas to dust mass ratio very similar to Galaxy –Very high central gas surface densities and volume densities –Star formation rate (not efficiency) correlates with central gas surface density Direct comparison of CO3-2 shows high-redshift submillimeter galaxies are more luminous and (perhaps) less centrally concentrated than local ULIRGs UGC5101 The Submillimeter Array is a joint project between the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academia Sinica.

The end

Velocity Fields within R<1 kpc Mrk231I Mrk273 UGC5101Arp55(NE)Arp55(SW)

The Nearby Luminous Infrared Galaxy Sample (IRAS , NGC6240 not shown)

Further analysis: an example Combine CO 3-2, 2-1, and 1-0, and 13 CO 2-1, to determine the physical properties of the molecular gas SMA data: Petitpas et al Spitzer image: Wang et al. 2004

Further analysis (cont.) Compare morphology and kinematics to numerical simulations to constrain merger age and establish a merger sequence –Correlate changes in gas physical properties with merger stage –Feed results on physical properties back into models to improve gas physics Narayanan et al. 2006

ALMA: Mass Function of Super- Giant Molecular Complexes Wilson et al ALMA will let us study molecular clouds and complexes in galaxies out to 200 Mpc - can reach masses as small as 5x10 6 M o at 200 Mpc in just one hour (3 sigma) SGMC mass function in the Antennae