Lighting the dark molecular gas using the MIR H 2 rotational lines Aditya Togi Advisor: JD Smith University of Toledo 19 th June

GalaxyISM Curry Spices 2

H 2 important for star formation Bigiel et al., 2008, AJ, 136,

H 2 not observed due to cold ISM No dipole moment Need high temperature to excite H 2 4

Need indirect tracer to detect H 2 - CO, dust, SFR, γ-rays α CO, gal = 4.35 M ʘ (pc 2 K km/s) -1 5 Solomon et al; 1987, ApJ, 319, 730

Dark Molecular Gas – not traced by CO Wolfire et al; 2010, ApJ, 716,

MIR-H 2 rotational lines by - IRS Spitzer 7 5μm – 38μm S(0) to S(7)

H 2 rotational lines in MIR spectral region Smith et al; 2007, ApJ, 656, 770 8

= 85= 50= Power law distribution of H 2

Discrete temperature fit T 1 = 156K T 2 = 408K Roussel et al., 2007, ApJ, 669, 959 Model fit using continuous power law distribution 50 to 2000K with power law index

Molecular gas traced by H 2 rotational lines 11

Model predicts H 2 gas in low metallicity system 12

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Expectation from JWST - MIRI H 2 MIR lines S(1)/S(2) and higher till z = 0.65/1.30 At z = 0.5 (3 Gpc) detecting S(1) needs 70min for S/N = 10 ALMA – Good check JWST(MIRI) - Good help 14

Model benefits and cost to astronomers Continuous temperature distribution of molecules Recover total H 2 gas MIRI instrument of JWST Solve for α CO factor problem Cost Assumes LTE approximation Need 3 rotational lines of H 2  A new method to calculate H 2 gas mass - useful in low metallicity systems and at high redshifts 15 Benefits

Thank You Questions, Discussions, Suggestions 16