NGC 4449: Atomic and molecular gas in an interacting system
Oskar Karczewski CEA Saclay, France
in collaboration with Suzanne Madden, Vianney Lebouteiller, Frédéric Galliano, Deidre Hunter (Lowell), Serena Viti (UCL)
Molecular Gas in Galactic Environments ∙ 7 April 2016 NGC 4449
● dwarf irregular galaxy at 3.8 Mpc
● SFR ~ 0.5 M⊙/yr
● Z ~ 1/3 Z⊙
● one of Herschel Dwarf Galaxy Survey targets (Madden+2013)
NGC 4449
● dwarf irregular galaxy at 3.8 Mpc
● SFR ~ 0.5 M⊙/yr
● Z ~ 1/3 Z⊙
● one of Herschel Dwarf Galaxy Survey targets (Madden+2013)
9 L∗ ~ 6 × 10 L⊙ 9 M∗ ~ 10 M⊙ 6 Mdust ~ 3 × 10 M⊙
Karczewski+2013
Spectroscopic data from Herschel and Spitzer
[O I]63 [C II]158 Herschel
Spectroscopic data from Herschel and Spitzer
[O I]63 [C II]158 Herschel
PAHs [Ne III]15.5 [S III]18.7 [Si II]34.5 Modified PAHfit (Smith+2007) Spitzer Dust emission
Total IR emission at a 7.7 arcsec resolution from PACS/100. Also see TIR calibrations by Galametz+2013.
Dust emission
Total IR emission at a 7.7 arcsec Improved fits at low S/N resolution from PACS/100. Also see TIR calibrations by Galametz+2013.
Deriving physical properties of the ISM
Diagnostic lines observable by Spitzer and Herschel (Kennicutt+2011)
Deriving physical properties of the ISM
3 Diagnostic lines observable Strength of the interstellar Atomic gas density n0 [cm ] by Spitzer and Herschel radiation field G0 (Kennicutt+2011) PDR models of Kaufman+1999, Kaufman+2006
Companion galaxy
Rich+2012
Companion galaxy
80 km/s +15 km/s
VLA H I observations (Hunter+1999) Companion galaxy
80 km/s +15 km/s
Reconstructed path of close encounter Properties of gas in NGC 4449
H II regions along the tidal tail
Properties of gas in NGC 4449
H II regions along the tidal tail O I is an important coolant near prominent H II regions
Properties of gas in NGC 4449
H II regions along the tidal tail O I is an important coolant near prominent H II regions C II is an important coolant away from prominent H II regions
Properties of gas in NGC 4449
H II regions along the tidal tail O I is an important coolant near prominent H II regions C II is an important coolant away from prominent H II regions Si II cooling enhanced locally
Gas heating and cooling in NGC 4449
NGC 4449 LMC (Karczewski et al. in prep) (Lebouteiller+2012)
Properties of gas in NGC 4449
H II regions along the tidal tail O I is an important coolant near prominent H II regions C II is an important coolant away from prominent H II regions Si II cooling enhanced locally Heating and cooling processes on scales of 300 pc similar to those in the LMC
Atomic and molecular gas
H II regions along the tidal tail O I is an important coolant near prominent H II regions C II is an important coolant away from prominent H II regions Si II cooling enhanced locally Heating and cooling processes on scales of 300 pc similar to those in the LMC
CO(10) data from Kohle 1999, Böttner+2003
Atomic and molecular gas
Preliminary – awaiting new CO data
Atomic and molecular gas
H II regions along the tidal tail O I is an important coolant near prominent H II regions C II is an important coolant away from prominent H II regions Si II cooling enhanced locally Heating and cooling processes on scales of 300 pc similar to those in the LMC C II and Si II cooling enhanced towards regions of low CO CO(10) data from Kohle 1999, Böttner+2003
Star formation in a perturbed ISM
CO emission west of the optical body confirmed by new IRAM 30m and JCMT observations
Ongoing JCMT observations of CO(32)
Star formation in a perturbed ISM
CO emission west of the optical body confirmed by new IRAM 30m and JCMT observations 3 Young cluster (~ 6 Myr, 10 M⊙; Annibali+2011) associated with molecular gas
Ongoing JCMT observations of CO(32)
Star formation in a perturbed ISM
CO emission west of the optical body confirmed by new IRAM 30m and JCMT observations 3 Young cluster (~ 6 Myr, 10 M⊙; Annibali+2011) associated with molecular gas … and with filaments of atomic gas
Ongoing JCMT observations of CO(32)
Star formation triggered by gas compression?
Star formation triggered by gas compression?
Profiles along the path
Conclusions
● the faceon orientation and the geometry of interaction make NGC 4449 an interesting system to study ● [Si II] is likely to be excited in the neutral medium ● observations of atomic and molecular gas suggest compression of gas into filaments ● our multiwavelength data suggest a sequence of events in the ISM where cooling by [Si II], [C II] and CO leads to the formation of new stars