What drives the small-scale substructure of star formation in galaxies? an observational perspective
Margaret Meixner (Space Telescope Science Institute Johns Hopkins University
Omnarayani Nayak NASA/Goddard) (Isha)
Bram Ochsendorf, What drives Massive Star Formation?
• Massive stars are light beacons for all stars
• Massive stars ionize the gas H-alpha >8 M¤ • Heat the dust: IR luminosity or 24 micron flux l Massive star formation is difficult to observe • High mass stars are rare • High mass stars evolve very quickly • Most likely obscured by dust or found in dense clusters
7/5/18 Laws of SF: Meixner 2 Nearby Milky Way Massive star formation, we see “anectdotal” evidence for differences….
Orion
(1) Orion molecular cloud
2MASS extinction map Lada et al. 2010
(2) California molecular cloud
• Same in mass, size 2MASS extinction map • Different in SFR by factor of 10. Large scale effects? 7/5/18 Laws of SF: Meixner Lada et al. 2009 3 Massive Star Formation in the Large Magellanic Cloud • Thousands of Massive Star Formation Sites => Stastical samples • Lower Metallicity (0.5 solar) than Milky Way – peak star formation epoch l Known Distance: 50 kpc (Schaefer et al. 2008) l Gas Line-of-sight Thickness: 360 pc (Kim et al. 2003) l Rob Kennicutt studied star formation in the LMC (e.g. Kennicutt et al. 1995)
Meixner et al. (2006) 7/5/18 Laws of SF: Meixner R: MIPS 24, G: IRAC 8.0, B: IRAC 3.6 4 Star formation on Ochsendorf et al. (2017) Jameson et al. 2016 cloud scales: Methods (2) Dust continuum - (1) CO - MAGMA HERITAGE
1. Mass tracers
(1) 700 MYSOs (M > 8 Msun) (2) Hα + 24 micron
2. SFR tracers
7/5/18 Laws of SF: Meixner 5 SFR tracers agree => MYSO counting robust tracer
7/5/18 Laws of SF: Meixner Ochsendorf et al. (2017) 6 Multiple SFR tracers –> estimating SF history
Halpha
MYSOs
~5 Myr ~0.5 Myr 0 Myr
Star formation history
7/5/18 Laws of SF: Meixner 7 Global View: Star Formation Laws in LMC & SMC Self Regulating Star Formation Theory works reasonably well OML: Ostricker, McKee & Leroy 2010 KMT+: Krumholz 2013
Jameson et al. 2016
7/5/18 Laws of SF: Meixner 8 Kawamura (2009): Evolution of Giant Molecular Clouds in LMC 7/5/18 no massive starformation
Type 1
10-3 1 Laws of SF: Meixner only HIIregions Cloud ‘Type’ Type 2 2 3 HII regions +stellar clusters Type 3 9 Confirm that Type I clouds have little to no star formation activity Ochsendorf 7/5/18 no massive starformation
Type 1 et al. (2016)
10-3 1 Laws of SF: Meixner only HIIregions Cloud ‘Type’ Type 2 2 3 HII regions +stellar clusters Type 3 10 7/5/18 no massive starformation
Type 1
10-3 1 only HIIregions Cloud ‘Type’ Type 2 2 3 HII regions +stellar clusters Type 3 Ochsendorf et al. (2016) 11 Clustering of different generations of massive stars: within clouds and near each other
7/5/18 Laws of SF: Meixner Ochsendorf et al. (2016) 12 Take away points …
• Massive Young Stellar Objects (MYSOs) are robust tracers of star formation rate, esp. <0.5 Myr • Massive star formation occurs in ~48% of clouds. • Type I molecular clouds have no (little) massive star formation. • Massive stars do not typically form at the peak column density of molecular gas. • Massive star formation is correlated with the presence of a young stellar cluster. • This is independent on size and mass of the molecular cloud • Statistical evidence for propagating star formation over multiple generations extending to 10 Myr
7/5/18 Laws of SF: Meixner Ochsendorf et al. (2016) 13 SFR increases during GMC lifetime
-3 Ochsendorf et al. (2017) 10
1 2 3 Cloud ‘Type’
Kawamura et al. (2009)
Type 1 Type 2 Type 3 no massive star formation only HII regions HII regions + stellar clusters
7/5/18 TIME 14 More massive GMCs are less efficient in forming massive stars
)
- SFR does not scale linearly -1 with GMC mass Myr ( à Large GMCs have lower
SFR/Mcloud cloud M SFR/
Ochsendorf et al. (2017) CO cloud mass (Msun) More massive GMCs are less efficient in forming massive stars
) -1
- SFR does not scale linearly with GMC mass Myr ( à Large GMCs have lower
SFR/Mcloud cloud M - Consistent with results the SFR/ Milky Way (Lee et al. 2016 & Vutisalchavakul et al. 2016)
Ochsendorf et al. (2017) CO cloud mass (Msun) Star formation efficiency per free-fall time: observations versus theory
OBSERVATIONS
Scatter in εff = time-dependent SFR
Decrease in εff = SFR does not simply scale with cloud mass
7/5/18 Laws of SF: Meixner Ochsendorf et al. (2017) 17 Star formation efficiency per free-fall time: observations versus theory
OBSERVATIONS THEORY
Padoan & Nordlund 2011
Padoan & Nordlund 2011
7/5/18 Laws of SF: Meixner 18 Star formation efficiency per free-fall time: observations versus theory
OBSERVATIONS THEORY
Padoan & Nordlund 2011
Padoan & Nordlund 2011
7/5/18 Laws of SF: Meixner 19 Why would ‘efficiency’ decline?
• Larger clouds have larger diffuse envelopes
à contaminated by addition of ‘diffuse’ (non-SF) gas?
continuum
dust CO/
cloud mass 7/5/18 Laws of SF: Meixner Ochsendorf et al. (2016) 20 Take Aways…
• Models assume SFR as stationary à observed to be dynamic (scatter) • Models predict increase SFE with cloud mass à observed to be decreasing
• Global cloud properties irrelevant to the massive star formation properties of GMCs
= SF efficiency
Total mass
7/5/18 Laws of SF: Meixner 21 Current Theories on How Massive Stars Form
Monolithic Collapse Competitive Accretion Filamentary Collision Tan et al. (2004), Zinnecker et al. (2007) Bonnell et al. (2004 Fukui et al. (2015)
7/5/18 Laws of SF: Meixner 22 Detailed Studies: 30 Doradus, N159, H72.97-69.39 (N79)
30 Doradus
N159
H72.97-69.39 (N79)
Nayak et al. (2016), Nayak et al. (2018), 7/5/18 Laws of SF: Meixner Nayak et al. (submitted) 23 Relating YSOs and Molecular Gas Where are YSOs Located in Relation to the Molecular Gas?
N159W Gresycale: 13 CO Contour: CS
N159E
30Dor Gresycale: HST Contour: 12 CO Nayak et al. (2016), Nayak et al. (2018) 7/5/18 24 Relating YSOs and Molecular Gas: N159W Where are YSOs Located in Relation to the Molecular Gas?
N159W Gresycale: 13 CO Contour: CS
7/5/18 Laws of SF: Meixner Nayak et al. (2016), Nayak et al.25 (2018) Relating YSOs and Molecular Gas Where are YSOs Located in Relation to the Molecular Gas?
N159W Gresycale: 13 CO Contour: CS All YSOs >23 M¤ are associated with molecular gas
7/5/18 Laws of SF: Meixner Nayak et al. (2016), Nayak et al.26 (2018) Relating YSOs and Molecular Gas Where are YSOs Located in Relation to the Molecular Gas?
N159W Gresycale: 13 CO Contour: CS All YSOs >23 M¤ are associated with molecular gas Not all YSOs have associated molecular gas
7/5/18 Laws of SF: Meixner Nayak et al. (2016), Nayak et al.27 (2018) Relating YSOs and Molecular Gas Where are YSOs Located in Relation to the Molecular Gas?
N159W Gresycale: 13 CO Contour: CS All YSOs >23 Msun are associated with dense molecular gas Not all YSOs have associated molecular gas
Not all clumps are associated with YSOs
7/5/18 Laws of SF: Meixner Nayak et al. (2016), Nayak et al.28 (2018) Relating YSOs and Molecular Gas: N159W Differences Between Clumps With and Without YSOs Mass Density
-2 log(mass) [Msun ] log(mass density) [Msun pc ]
-2 log(mass) [Msun ] log(mass density) [Msun pc ]
7/5/18 Laws of SF: Meixner 29 Nayak et al. (2018) Relating YSOs and Molecular Gas: N159W Differences Between Clumps With and Without YSOs Mass Density
-2 log(mass) [Msun ] log(mass density) [Msun pc ]
Threshold -2 500 M¤ pc
-2 log(mass) [Msun ] log(mass density) [Msun pc ] Massive star formation occurs in clumps Massive star formation occurs in clumps with higher mass with higher mass density Nayak et al. (2018) Relating YSOs and Molecular Gas Size-Linewidth Relation Can Be Used to Quantify Turbulence
7/5/18 Laws of SF: Meixner Nayak et al. (2018) 31 Relating YSOs and Molecular Gas Using Virial Parameter to Predict YSO Formation Mechanism
Ekinetic = Egravitational
log (clump mass) [Msun] Krumholz et al. (2005), Nayak et al. (2018) 7/5/18 Laws of SF: Meixner 32 Relating YSOs and Molecular Gas Using Virial Parameter to Predict YSO Formation Mechanism
Monolithic Collapse
Ekinetic = Egravitational
Competitive Accretion
log (clump mass) [Mlog (clump mass) [Msunsun] ] Krumholz et al. (2005), Nayak et al. (2018) 7/5/18 Laws of SF: Meixner 33 Take Aways - Relating YSOs and Molecular Gas
l The highest mass YSOs are located i molecular gas clouds.
l There are massive YSOs with no associated molecular gas.
l Clumps with massive YSOs have higher mass and density in comparison to clumps without massive YSOs
-2 l Threshold for Massive Star formation ≥ 500 M¤ pc
l The size-linewidth relation is indication of turbulence
l Massive YSOs in the LMC are undergoing monolithic collapse
7/5/18 Laws of SF: Meixner 34 A Potential Embedded Super Star Cluster (SSC) H72.97-69.39
10 -7 LIR= 2.2e+06 Lsolar 10 -8
10 -9 !!!
10 -10
chart -11 10
-12 the 10 1 10 100 1000 off
MYSOs C-HII
Mottram et al. 2011 7/5/18 Laws of SF: Meixner 35 Ochsendorf et al. (2017, Nature Astronomy) H72.97-69.39 ALMA Hydrogen Recombination Line
H30α
Nayak et al. (submitted)
Object log(Ncontinuum) [1/s] Type
N79 SSC H72.79-69.39 51.35 > O3
N159E Papillon YSO 50.04 > O3 N159W YSO-N 50.18 Laws of SF: Meixner > O3 36 H72.97-69.39 Filaments on Large and Small Scales (also seen in N159 E & W)
Nayak et al. (submitted) 7/5/18 Laws of SF: Meixner 37 Studying Potential Embedded SSC Bipolar Outflow and Rotating Toroid
ALMA ALMA SO2 13CO (2-1) Direction of Direction of Outflow Outflow
250 km/ s 240 km/ s 230 km/ s 220 km/ 7/5/18 s -0.4 pc -0.2 pc 0.0 pc 0.2 pc 0.4 pc 38 Nayak et al. (submitted) Studying Potential Embedded SSC Complex Dynamic of H72.97-69.39
7/5/18 Laws of SF: Meixner 39 6.6' 100 pc
H72.97-69.39
Ochsendorf et al. (2017, Nature Astronomy) 7/5/18 Laws of SF: Meixner 40 N79 is a younger, embedded version of 30 Doradus
Mirrored positions of H72.97-69.39 and R136 on tidal arms suggest common formation pathway for SSCs
30 Dor HI image
30 Dor
N79
7/5/18 Ochsendorf et al. 2017, Nature Astronomy 41 JWST Cycle 1 GTO program PI M. Meixner cores/flaments/YSOs clumps/clusters GMCs/HII regions Milky Way LMC N79 SMC NGC6822
0 N66 Z / Z I Zw 18
JWST GTO star formation
Pety et al. 2013 Spatial resolution (pc)
Are there substantial differences in SF with environment?
7/5/18 Laws of SF: Meixner 42
Origins Space Telescope: Wavelengths: 5-620 μm JWST area~25 m2 Cold optics ~4 K Fast motion: 100” s-1
NASA Large Mission Study For 2020 Decadal
To learn more: origins.ipac.caltech.edu
Best Wishes Rob! Herschel Users Group (HUG)
7/5/18 Laws of SF: Meixner 44 Summary points
• Massive star formation is correlated with the presence of a young stellar cluster. • Observed Star Formation Efficiency Declines with Cloud mass and does not match theory (increases) -2 l Threshold for Massive Star formation ≥ 500 M¤ pc l The size-linewidth relation is indication of turbulence l Massive YSOs in the LMC are more likely undergoing monolithic collapse l Discovery of a potential embedded and forming SSC, H72.97-69.39 - future R136? • Highest mass objects, e.g. H72.97-69.39, located at collision of 2+ filaments and highest density gas.
7/5/18 Laws of SF: Meixner 45 7/5/18 Laws of SF: Meixner 46 Is H72.97-69.39 a SSC?
Star Formation Rate (SFR) ★ = H α SFR = MYSO SFR
Ochsendor & Nayak et al. (2017, Nature Astronomy) 7/5/18 Laws of SF: Meixner 47 Is H72.97-69.39 a SSC?
Star Formation Rate (SFR)
SFR has decreased
SFR has increased
Ochsendor & Nayak et al. (2017, Nature Astronomy) 7/5/18 Laws of SF: Meixner 48 Increase in linewidth also seen in Milky Way Massive Star Formation Regions
7/5/18 Laws of SF: Meixner Ballesteros-Paredes et al. (2011) 49
Star formation efficiency per free-fall time: observations vs theory
OBSERVATIONS THEORY
PadoanKrumholz & & NordlundMcKee 2005 2011
7/5/18 Laws of SF: Meixner 50 OST Gains in Sensitivity Because it is Cold (4 K)
Equivalent difference for an optical telescope to achieve 1000 times higher sensitivity
Meixner et al. in prep, SPIE 7/5/18 Laws of SF: Meixner 51