1. Surveys of nearby molecular clouds with Spitzer Lori Allen (NOAO) with much help from Mike Dunham (Yale), Neal Evans (Texas), Tom Megeath (Toledo), Rob Gutermuth (Smith), Dawn Peterson (SAO)

2. Spitzer Surveys of Nearby Clouds (large area imaging surveys within 1 kpc) c2d: Legacy Program (Evans et al. 2009) Gould Belt: Legacy Program (Allen et al. in prep.) Taurus: Legacy Program (Rebull et al. 2010) Orion: GTO program (Megeath et al. in prep.) Embedded Clusters: GTO program (Gutermuth et al. 2009) Cygnus-X: Cycle X Legacy Program (Hora et al. in prep.) CephOB3, NAN, Mon, S140 (Gutermuth in prep; Rebull et al. 2010) c2d/GB Survey Characteristics  3.6, 4.5, 5.8, 8.0, 24 and 70 micron (GB includes 160 micron)  Completeness: 90% to 0.05 Lsun; 50% to 0.01 Lsun (1-30 micron) Data Products  Available through SSC (Popular Data Products) and IRSA 

3. GB / Cepheus [Kirk et al.2009] 19.09.11mw20113

4. Spitzer Legacy data products Point source catalogues Spitzer and 2MASS fluxes, quality, characterization Image mosaics Ancillary data Extinction maps Re-sampled SWIRE catalogs  Documentation http://data.spitzer.caltech.edu/popular/ 19.09.11mw20114

5. c2d+GB : census of nearby YSO ~17 clouds, > 1600 YSO (Ser/Aql TBD) Large, uniform sample I: Flat: II: III: 19.09.11mw20115

6. [Gutermuth et al. 2008] Serpens South embedded cluster 0.5 pc 6 Protostar dominated cluster: 60% protostars (Class I + Flat) 70% protostars in core Core median density ~600 YSO/pc 2 19.09.11mw2011

7. Serpens South Spitzer and Herschel [Courtesy Vera Konyves] Spitzer 8  m Herschel rgb 350/160/100  m 19.09.11mw20117

8. 1.1mm continuum map (AzTEC/ASTE) Contours: 30 mJy / bm (x 2 per level) Central peak ~4 Jy / bm M(tot) > 1000 Msun [Gutermuth in prep.] [Also Maury et al. 2011] Serpens South

9. 1.1mm continuum map (AzTEC/ASTE) Contours: 30 mJy / bm (x 2 per level) Central peak ~4 Jy / bm Millimeter emission follows absorption feature Serpens South

10. Census Cloud IFlatIIIII*TotalIFlatIIIII* Perseus874222531385763523341 Ophiuch.354717634292284317150 Lup I,III,IV 510522794484933 Cham II61063786456215 Serpens362314028227331913045 Cor Aus13331754962217 Cepheus231165410318116113 Cham I,III71063786556218 Lup V,VI015738801978 Musca101111310111 Auriga3620811014736108121 Scorpius114391134 IC5146291287413228107915 Total2751819582461660242148918352 Number of YSO by Cloud and Class: c2d+GB c2d GB observed extinction corrected * Class III grossly incomplete 19.09.11mw201110

11. Timescales: previous work Previous estimates for timescales – t(I) ~ t(II) ~ 0.4 Myr In Ophiuchus (Wilking et al. 1989) – t(I) ~ t(flat) ~ 0.1 -- 0.2 Myr; Class II 1-2 Myr In Taurus (Kenyon and Hartmann 1995) Note t(II) ~ 10 t(I) – t(0) ~ 0.01 Myr (Andre, Oph) Rapid early accretion – Or t(0) ~ 0.1 Myr (Visser, larger sample) – Issues Small number statistics! Differences between clouds! 19.09.11mw201111

12. Clouds are all different Evans et al. 2008 Allen et al. in prep. Auriga 165 IC5146 132Perseus 385 Serpens 227Lupus I-III 94Ophiuchus 292 Large sample N > 1000 Average over several clouds

13. Assumptions: Time is the only variable (all masses co-eval) Star formation continuous Class II lasts 2 Myr (half-life) THEN t(Class I) = 0.47 Myr t(Flat) = 0.38 Myr (bit longer than most previous estimates) Caveats: Depends on how  is calculated Class 0 mixed with Class I 17 clouds, 1660 YSO c2d + GB surveys I: Flat: II: III: 14% 9% 55% 21% II III I F 21% 55%

14. Timescales for YSO evolution SED class may not map directly to evolutionary stage For example, are all Class I’s embedded? 19.09.11mw201114

15. MISidentified YSOs from SED FITS (MISFITS; Heiderman et al.) Checking Class I sources in c2d and GB surveys HCO + J=3-2 line, CSO and applied to APEX So far, 7% Flat and 42% Class I detected from sample of ~100 (northern clouds). Clouds: Aur, Cep, IC5146, Lup, Oph, Per, Sco, Ser, Ser-Aqu, Musca 1519.09.11mw2011

16. Protostellar Evolution: the “Luminosity Problem” Many Class I sources are under-luminous for predicted infall rates (10 -6 M o /yr) Suggests episodic accretion in early stages. (See Kenyon et al. 1990 &1994; Kenyon & Hartmann 1995; Dunham et al. 2009; Evans et al. 2009; Enoch et al. 2009)

17. Many are under-luminous Predicted L = GM(dM/dt)/R= 1.6 L sun for standard (Shu) accretion onto M = 0.08 M sun, R = 3 R sun. Most (59%) are below this. [ Dunham et al. 2010a] 19.09.11mw201117

18. With 2D, Outflows, Episodic Accretion [Dunham et al. 2010a] 19.09.11mw201118

19. All(?) surveys out to 1 kpc Cloud(s)IFlatIIIII*TotalReference c2d1691326561271084Evans et al. 2009 GB10958336108>619Allen et al. 2011 Taurus47 (23)33 (16)139 (38)141 (70)360 (147)Rebull et al. 2010 Orion42828823310Megeath et al. 2011 N. Am.22419410872371742Rebull et al. 2009 Cep OB32617018351412172Gutermuth &Pipher S140144243436526Gutermuth&Pipher Cygnus-X1143162712445612121336Hora et al. 2011 Total>31,000 No corrections for extinction or completeness 19.09.11mw201119

20. SFR –  gas relations [Gutermuth et al. 2011; Heiderman et al. 2010; Evans et al. 2009] See talks by Heiderman (later today), Megeath (Thursday), Lada (Thursday) 19.09.11mw201120

21. log (YSO per sq. pc) YSO Surface densities for nearby clouds (ordered by total number of YSO)

22. Census within 1 kpc: YSO 10k 14 cloud complexes, 20 clouds > 10,000 YSO Fraction in clusters (N>10) = 67% (N>100) = 10% But varies greatly from cloud to cloud: Fewer than half the nearby clouds contain clusters of N>100 Statistics less complete than for c2d+GB

23. For cloud complexes within 1 kpc, the fraction of young stars in clusters as a function of cluster size (3363) (10) 2319.09.11mw2011

24. Distribution of surface densities [Bressert et al. 2010] See talk by Bressert (Thursday) Smooth distribution of YSO surface densities 19.09.11mw201124

25. Summary There’s a lot of Spitzer data out there.  3.6-160  m complements Herschel Lifetimes of Class I, Flat stages longer Based on N>1600, highly complete sample More evidence for episodic accretion early Observed protostar luminosities low  SFR ~ 10 x exgal relations Variations from cloud to cloud factor of 100 19.09.11mw201125

26. How “Efficient” is Star Formation? Not very for the cloud as a whole – 2% to 5% of mass with A V > 2 is in dense cores (Enoch et al. 2007) – 3% to 6% is in stars Large variations in SF rate – Serpens is 360 times more productive than Cha III – Normalized to area, Serpens is 100 times Cha III Quite efficient in dense gas – Current TOTAL M * similar to M dense – Depletion time is 0.6 to 2.9 Myr 19.09.11mw201126

27. Similar Relation in Regions forming High Mass Stars Green line is  (YSOs) ~  2 (gas) Red points are Class I (more likely to be in formation region) Gutermuth 19.09.11mw201127

28. Lessons from Nearby Clouds  SFR ~ 10 times prediction of relations for galaxies on average Variations from cloud to cloud factor of 100 These regions are forming only low mass stars – Would not even be seen in most exgal SFR tracers On scales where SF actually happens… – Dependence on S mol may be very strong SFR determined on sub-pc scales << exgal resolution 19.09.11mw201128

29. Summary Stars form mostly in clustered environments – Regions of high extinction, dense gas – About half in large (N>100) clusters Mass function may trace IMF of stars Timescales for Class 0 and I longer Shu inside-out collapse consistent, except – Luminosities imply accretion is episodic Efficiencies in clouds are low (3-6%) – Efficiencies in dense cores are high (>25%) Exgal prescriptions do not work locally 19.09.11mw201129

30. YSO per sq. pc Number of clouds Median density of young stars for 15 molecular clouds Median density not a strong function of total number of YSO

31. YSO per sq. pc Number of clouds Median density of young stars for 15 molecular clouds Median density not a strong function of cloud mass

32. YSO per sq. pc Number of clouds Peak density of young stars for 15 molecular clouds Peak density a weak function of number of YSO

33. Fraction of young stars in clusters (> 10 per sq pc) Fraction in clusters not strongly correlated with total number of YSO. Fraction in clusters

34. Fraction of young stars in clusters (> 10 per sq pc) …nor with cloud mass Fraction in clusters

35. Conclusions We used Spitzer to identify >7000 YSO in 15 molecular clouds within 500 pc  Molecular clouds form stars with a wide range of surface densities.  The median surface density does not correlate with the total number of YSO nor with the cloud mass.  The fraction of YSO in clusters (N >10 pc -2 ) does not depend strongly on the total number of YSO, nor on the total cloud mass.  The clouds divide into low and high fraction of clustering (e.g. Taurus-like and Orion-like).  Peak surface densities are highest in the two most massive clouds.

36. Fraction of young stars in groups of > 10 per sq pc > 100 per sq pc Fraction in “clusters” weakly correlated with global average gas density Fraction in “clusters”

37. Rates and efficiencies Star formation rates range from cloud to cloud, from 5 Msun/Myr to 1000 Msun/Myr SF efficiencies from 0.6% to 8% (cloud-wide) Taken together, for all 10k YSO within 1 kpc: SFR = 2700 Msun/Myr SFE = 2%

38. Timescales for earlier stages For 3 clouds with millimeter maps (Enoch08) – Use T bol to separate Class 0 from I – Absence of IR source to say starless – Largest sample to date: 200 cores – N(0) = 0.44N(I), so t(0) = 0.16 Myr Not consistent with fast, early infall (Andre et al.) Except Oph: 0.04 Myr, Oph was basis of low t(0) – Oph has faster evolution or not continuous – N(SL) = 0.8 N(0+I), so t(SL) ~ 0.46 Myr After > 2 x 10 4 cm –3 t(SL) ~ 3 t ff ; between predictions of fast and slow 19.09.11mw201138

39. Starless Core Lifetimes Enoch et al. 2008 19.09.11mw201139

40. Comparison to Shu model Assume inside-out collapse at 0.19 km/s – Sound speed at 10 K In 0.57/2 Myr, r inf = 0.057 pc – Consistent with some sizes – Mean separation in clusters 0.072 pc (Gutermuth) At dM/dt = 1.6 x 10 –6 M sun /yr, M * ~ f 0.90 M sun – If f ~ 0.3, get 0.27 M sun ~ modal mass Consistent with assumptions, most data Picture holds together, except… 19.09.11mw201140

41. Class and Tbol in nearby clouds Alternative “classification” 19.09.11mw201141

42. Star formation efficiency  In dense cores SFE is high, 15-30% (Note filamentary structure)  Cloud-wide SFE is low, 3-6% Perseus: Bolocam 1.3 mm [Enoch et al. 2007]