High density tracers of molecular gas in earlytype galaxies Alison Crocker (UMass Amherst) and Melanie Krips, Martin Bureau, Katey Alatalo, Leo Blitz, Timothy Davis, Lisa Young and the Atlas3D team, Estelle Bayet
Introduction Stereotypical early-type galaxy (E or S) = red and dead : no star formation, no cold gas But now lots of evidence that this picture does not hold: HI: ½ of all field ETG (Grossi+ 9, ( Oosterloo+ CO: ¼ of ETG UV blue: 3% of ETG Optically blue: 6% of ETG (Combes+ 7, ( 5 (Yi+ ( 9 (Schawinski+ ( Young+
Introduction Stereotypical early-type galaxy (E or S) = red and dead : no star formation, no cold gas But now lots of evidence that this picture does not hold: HI: ½ of all field ETG (Grossi+ 9, ( Oosterloo+ CO: ¼ of ETG UV blue: 3% of ETG Optically blue: 6% of ETG (Combes+ 7, ( 5 (Yi+ ( 9 (Schawinski+ ( Young+ Atlas3D project- a multi-wavelength volume-selected survey of 6 early-type galaxies (IFU spectroscopy, optical photometry, CO (single-dish + interferometry), HI, FIR)
Introduction As part of Atlas3D, a CO(-) and (-) survey was conducted at the IRAM 3m detected 56/6 (=%), no trend with mass or environment (see Davis poster, Young+ ) no slow rotators with CO (the new true ellipticals)
Introduction As part of Atlas3D, a CO(-) and (-) survey was conducted at the IRAM 3m detected 56/6 (=%), no trend with mass or environment (see Davis poster, Young+ ) no slow rotators with CO (the new true ellipticals) NEXT STEP: What is the state of the molecular gas in early-type galaxies? Unique, relevant properties:. Very central CO distributions shear important?. Significant hot gas strong confinement by hydrostatic pressure? 3. Gas not being replenished (some very low H -to-hi ratios)
Observations and Sample Observed ~/3 brightest (=8) CO detections in: 3 CO(-), 3 CO(-), HCN(-), HCO+(-) at IRAM 3m Sample - H masses: 8-9 M - Avg. H surface densities: ~- M pc - - Stellar masses: ~ - M - Mix of cluster, field, group
Hope that: Plan CO/ 3 CO indicates average optical depth of CO HCN/ 3 CO indicates dense gas fraction Of course, complications- Abundance issues: C/ 3 C decreases with chemical enrichment, HCN influenced by AGN(?) Fractionation towards 3 CO at cold gas temps (lower CO/ 3 CO) Selective photodissociation of 3 CO in PDRs (higher CO/ 3 CO)
NGC33 NGC764 UGC959 NGC5866 T mb (mk) 8 CO(-) 6 4-8 CO(-) 6 4-8 3 CO(-) 6 4 - -4 3 CO(-) 5 6 CO(-) 4-8 CO(-) 6 4 - -4 6 3 CO(-) 4 - -4 3 CO(-) 5 8 CO(-) 6 4-8 CO(-) 6 4-4 3 CO(-) - -4 3 CO(-) 5-5 4 CO(-) 3-4 CO(-) 3-8 3 CO(-) 6 4 - -4 5 3 CO(-) 5-5 3 - - 4 - HCN(-) HCO + (-) X -4-6 5 5 V LSR (km/s) -5 - - 3 - - -3 HCN(-) HCO + (-) 5 3 35 V LSR (km/s) - - - -3 3 - - HCN(-) X HCO + (-) 5 5 V LSR (km/s) -5 3 - - -3 3 - - HCN(-) HCO + (-) 5 5 V LSR (km/s)
T mb (mk) 4 NGC33 8 CO(-) 6-8 CO(-) 6 4-8 3 CO(-) 6 4 - -4 3 CO(-) 5-5 3 - - 4 - HCN(-) HCO + (-) -4-6 5 5 V LSR (km/s) 4 NGC764 6 CO(-) 5 5 5 8/8 detected in -5 HCO + (-) -5 - - 3 - - -3 HCN(-) HCO + (-) 5 3 35 V LSR (km/s) 4 UGC959 8 CO(-) 6 - - - 8 8 CO(-) 4 CO(-) 6 3 CO(-) 6 4 4 - -4 - - 6 3 4 CO(-) 8 CO(-) CO(-) 4 6 4 8/8 detected in 3 CO(-) - - and (-) - -4-4 -4 3 CO(-) 5 CO(-) CO(-) X /8 detected in HCN(-) - - - -3 3 - - 5 5 V LSR (km/s) -5 3 HCN(-) - - X -3 HCO + 3 (-) NGC5866 4 CO(-) 3 - - HCN(-) HCO + (-) 5 5 V LSR (km/s)
CO/ 3 CO Optically thick Optically thin NGC66 Order-of-magnitude range (3-3) CO/ 3 CO(-) NGC456 NGC4459 NGC3665 (-) and (-) ratios well correlated no huge differences in excitation or beam filling CO/ 3 CO(-)
CO/ 3 CO Optically thick Optically thin CO/ 3 CO(-) NGC456 NGC4459 NGC3665 NGC66 E/S Spiral Starburst Seyfert E and Ss mostly seen in same range as spirals, Seyferts and starbursts But 3 galaxies have extremely low ratios, similar to what is observed for MW GMCs! (No diffuse molecular gas?) CO/ 3 CO(-) Compilation of Seyferts and starbursts from Krips et al. ; spiral range from Paglione et al.
CO/ 3 CO CO/ 3 CO(-) -5-4 -3 - M K..4.6.8. -3 - - - 3 f 6 /f th nearest gal. (Mpc -3 ) log(h /HI) Galaxies with the lowest CO/ 3 CO ratios are in the most luminous (massive) galaxies Some relation with dust (double branch: starburst and not) No clear dependence on environment or H /HI ratio
CO/ 3 CO CO/ 3 CO(-) -5-4 -3 - M K..4.6.8. -3 - - - 3 f 6 /f th nearest gal. (Mpc -3 ) log(h /HI) Galaxies with the lowest CO/ 3 CO ratios are in the most luminous (massive) galaxies Some relation with dust (double branch: starburst and not) No clear dependence on environment or H /HI ratio
CO/ 3 CO CO/ 3 CO(-) -5-4 -3 - M K Why? Some options:..4.6.8. -3 - - - 3 f 6 /f th nearest gal. (Mpc -3 ) log(h /HI) low in coldest-dust galaxies -> fractionation low in most massive/highest metallicity -> abundance low in most massive/lowest turbulence gas -> optical depth
CO/ 3 CO CO/ 3 CO(-) -5-4 -3 - M K..4.6.8. -3 - - - 3 f 6 /f th nearest gal. (Mpc -3 ) log(h /HI) Comparison to spirals (Paglione+) Overlap with dust temp, not with mass (if fractionation partly to blame, also working similarly in spirals)
Low dense gas fraction HCN/CO High dense gas fraction HCN/ CO(-)... NGC456 NGC367 NGC4459.. HCN/ 3 CO(-) NGC66 Consider HCN/ 3 CO as tracing the fraction of dense molecular gas Smallish range.-.5 Also the unusual NGC66 (molecular outflow galaxy, see Alatalo poster!)
Low dense gas fraction HCN/CO High dense gas fraction HCN/ CO(-).. E/S Spiral Starburst Seyfert NGC456 NGC367 NGC4459 NGC66 E and Ss are to the low side- lower than starbursts, Seyferts, possibly spirals Thus inefficient at making densest gas.... HCN/ 3 CO(-) 3 optically thick galaxies again short on CO Compilation of Seyferts and starbursts from Krips et al.
CO/HCN CO/HCN(-) -5-4 -3 - M K..4.6.8. -3 - - - 3 f 6 /f th nearest gal. (Mpc -3 ) log(h /HI) Again, massive galaxies low in CO- not just a C vs 3 C effect! Most likely culprit: high optical depth in CO on a global scale for these galaxies. Same basic pattern with dust temp (except 66)
CO/HCN CO/HCN(-) -5-4 -3 - M K..4.6.8. -3 - - - 3 f 6 /f th nearest gal. (Mpc -3 ) log(h /HI) Again, massive galaxies low in CO- not just a C vs 3 C effect! Most likely culprit: high optical depth in CO on a global scale Is correlation with mass or dust temp more fundamental, or all related to lower turbulence/increased self-absorption?
HCN/ CO CO/HCN(-) -5-4 -3 - M K..4.6.8. -3 - - - 3 f 6 /f th nearest gal. (Mpc -3 ) log(h /HI) Add normal spirals from Gao & Solomon 4 (< L sun in FIR)
HCN/ 3 CO less dense 3 CO/HCN(-) more dense -5-4 -3 - M K..4.6.8. -3 - - - 3 f 6 /f th nearest gal. (Mpc -3 ) log(h /HI) No clear correlation with luminosity, dust temp, environment or H /HI ratio for HCN/ 3 CO No uniform spiral comparison sample
HCN/HCO + HCN/HCO + (-).. HCN/ 3 CO(-) E/S Starburst Seyfert Wider spread in HCN/ HCO+ than seen in local GMCs (pink range), but big error bars Effect of AGN for some, but not all have an AGN... Some other chemical effect?
Conclusions Most early-type galaxies broadly resemble spirals in terms of CO/ 3 CO, HCN/ 3 CO and HCN/ CO ratios More luminous (massive) early-types have more optically thick CO (possible effect of lower turbulence) Dust temp also correlates with diffuse molecular content (cold dust, less diffuse), but double-branched Some interesting HCN/HCO+ ratios, but need to be better understood
Other work and ALMA LVG modeling by Bayet (see poster for first results!) Herschel line studies of these galaxies (SPIRE FTS + PACS spectroscopy) ALMA will enable resolved studies of these highdensity tracers in ETG ALMA s increased sensitivity will also allow us to probe below these brightest (and most peculiar) ETG to normal star forming ETG Of course, need sample readjustment to South...
HCO + Atlas3D E/Ss Gao & Solomon 4 L FIR (L O ) 9 Slope =.3 Slope =. 7 8 9 L CO(-) (K km s - pc - ) 6 7 8 9 L HCN(-) (K km s - pc - )