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Understanding the Nearby Star-Forming Universe with JWST

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Understanding the Nearby Star-Forming Universe with JWST Star formation in the Local Group Guido De Marchi (ESA), Nino Panagia (STScI) Elena Sabbi (STScI), Giacomo Beccari (ESO) and NIRSpec GTO team !1 Motivation • Solar mass stars account for most of the star formation in galaxies • Low mass stars can form in small clouds as well as in big ones, and form on longer timescale than massive stars • Need to probe diverse environments, Magellanic Clouds crucial for metallicity • At redshift z~2, environment was similar to Magellanic Clouds !2 PMS stars: How to find them? Low-mass stars grow in mass over time through accretion of matter from a circumstellar disc (e.g. Lynden-Bell & Pringle 1974; Bertout 1989) Typical signature: UV, IR and Hα excess emission How to measure it? Need spectroscopy Well calibrated relationship between L(Hα) and Lacc Spectroscopic search signs of accretion !4 Until JWST only feasible in the Milky Way In the meanwhile… Powerful method combines HST broad- (V, I ) and narrow- band (Hα) photometry and allows us to: • identify all objects with Hα excess emission • derive accretion luminosity and mass accretion rates • for hundreds of stars simultaneously De Marchi, Panagia & Romaniello 2010, ApJ, 715, 1 Beccari, Spezzi, De Marchi et al. 2010, ApJ, 720, 1108 De Marchi, Panagia & Sabbi 2011, ApJ, 740, 10 De Marchi, Panagia, Romaniello et al. 2011, ApJ, 740, 11 Spezzi, De Marchi, Panagia et al. 2012, MNRAS, 421, 78 De Marchi, Beccari & Panagia 2013, ApJ, 775, 68 Beccari, De Marchi, Panagia et al. 2015, A&A, 574, A44 De Marchi, Panagia & Beccari 2017, ApJ, 846, 110 Biazzo, Beccari, De Marchi, Panagia 2019, ApJ, 875, 51 !6 Actively accreting PMS stars • These PMS stars are discovered from broad-band (V, I) and narrow-band (Hα) photometry and show strong Hα excess emission due to ongoing accretion De Marchi et al. 2011a, 2017 De Marchi et al. 2011b, 2011c, 2013 gives L(Hα) 30 Dor (LMC) NGC 346 (SMC) • In massive young clusters in the local group thousands PMS stars continue to accrete much longer than the few Myr typical of nearby associations !7 Hodge 301 HTTP (Sabbi et al. 2014, 2016) Accretion rate and metallicity 1 2 3 20000 NGC 2060 4 5 6 Y 10000 15000 7 R 136 8 9 5000 ~ 200 pc 5000 10000 15000 20000 25000 30000 X Hα photometry De Marchi, Panagia & Beccari 2017 R136 Cluster within r < 20 pc ~1,000 stars !9 Hα photometry De Marchi, Panagia, Sabbi, et al. (in prep) Tarantula Nebula within r < 120 pc ~14,000 stars !10 PMS stars in the Tarantula De Marchi, Panagia, Sabbi, et al. (in prep) Tarantula !11 11 14,000 and counting… De Marchi, Panagia, Sabbi, et al. (in prep) Tarantula 2 Myr 4 8 AV=1 16 32 !12 Reddening vector in all bands De Marchi et al. 2016 UV U V I J H !13 Extinction law at optical and infrared • Not just a few lines of sight, but thousands! • Additional grey component, excess of big grains De Marchi & Panagia 2019, 2014; De Marchi et al. 2016 Galactic ISM !14 11 14,000 and counting… De Marchi, Panagia, Sabbi, et al. (in prep) Tarantula 2 Myr 4 8 AV=1 16 32 !15 12 14,000 and counting… De Marchi, Panagia, Sabbi, et al. (in prep) Tarantula < 8 Myr > 16 Myr !16 N E H301 R136 NGC 2060 N E < 8 Myr N E > 16 Myr Multiple generations ubiquitous De Marchi et al. 2013 De Marchi et al. 2011b NGC602 in SMC NGC346 in SMC • Multi-generation pattern always seen, Δt ~ 10 Myr • Younger PMS stars always more concentrated • Older PMS stars always more widely distributed !18 Accretion evolution with time De Marchi, Panagia, Beccari 2017 R 136 !19 Accretion evolution with time Sicilia-Aguilar et al. 2006; 2010 Hartmann et al. 1998 !20 Accretion evolution with time De Marchi, Panagia, Beccari 2017 R 136 !21 Accretion evolution with time R 136 De Marchi, Panagia, Beccari 2017 !22 Accretion evolution with time R 136 De Marchi, Panagia, Beccari 2017 !22 Accretion rate and metallicity De Marchi, Panagia & Beccari 2017 SMC LMC MW LH 95 !23 N E !25 Hα variability NE field NW field 10 σ V SE field SW field Hα variability De Marchi, Panagia, Sabbi (in prep) Stars with 5 Hα epochs • < 8 Myr • 8–16 Myr • > 16 Myr fluctuation [mag] α H bright faint Hα brightness [mag] !26 Hα variability < 8 Myr > 16 Myr !27 Richert, Lyra & Kuchner 2017 Hα variability: a Poisson toy-model De Marchi, Panagia, Sabbi (in prep) • < 8 Myr • 8–16 Myr • > 16 Myr fluctuation [mag] α H Hα brightness [mag] !29 Hα variability: a Poisson toy-model De Marchi, Panagia, Sabbi (in prep) Average accretion in Mirandas per week • < 8 Myr • 8–16 Myr • > 16 Myr 1 fluctuation [mag] α H 4 20 64 –11 Miranda: ~ 5 x 10 M◉ Hα brightness [mag] !29 6 Looking ahead with JWST NGC 3603 (MW) 30 Dor (LMC) NGC 346 (SMC) N N E E Spectra of ~100 stars per field, easy with NIRSpec: R~1000–2700, 1.7 – 3.0 μm, include Paα, Brβ, Brγ Photometry of thousands of stars in Paα, Brα with NIRCam!30 Rich sample of younger and older PMS stars 7 Fitting targets in microshutters 7 13 Observations: spectral features Pa α KAB~22 Br γ Br β G235M (R~1000) for line luminosity G235H (R~2700) for gas kinematics !32 Coordinated parallels NIRCam will cover fields about 7.5 arcmin from NIRSpec, still plenty of star formation going on in those regions! Broad- and narrow-band (Pa α, Br α) imaging to identify PMS stars that are accreting. Same as we did with HST Hα photometry. Pa α Br α F277W F150W F182M F430M !33 Summary • Multi-generation patterns common in all regions, Δt ~ 10 Myr, younger generations are always more concentrated • Extinction in starburst cluster is temporarily altered by SNe-II for Δt ~ 50 – 100 Myr after star formation episode • Mass accretion rate depends on metallicity, at low metallicity stars accrete more and longer, sizeable fraction of stellar mass accreted during PMS phase • Accretion process is discrete and made up of a number of clumps all with a similar mass (~ Miranda) !34 www.starformation.eu.
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