Star formation in the Local Group Guido De Marchi (ESA), Nino - - PowerPoint PPT Presentation

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Star formation in the Local Group Guido De Marchi (ESA), Nino - - PowerPoint PPT Presentation

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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

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!1

Star formation
 in the Local Group

Guido De Marchi (ESA), Nino Panagia (STScI)
 
 Elena Sabbi (STScI), Giacomo Beccari (ESO) and NIRSpec GTO team

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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

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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

PMS stars: How to find them?

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Spectroscopic search

signs of
 accretion

!4

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Until JWST only feasible in the Milky Way


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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

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  • In massive young clusters in the local group thousands PMS stars continue 


to accrete much longer than the few Myr typical of nearby associations

De Marchi et al. 2011b, 2011c, 2013

gives L(Hα)

30 Dor (LMC) NGC 346 (SMC) De Marchi et al. 2011a, 2017

  • 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

Actively accreting PMS stars

!7

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5000 10000 15000 20000 25000 30000 5000 10000 15000 20000 X Y

1 2 3 4 5 6 7 8 9

Accretion rate and metallicity

~ 200 pc HTTP (Sabbi et al. 2014, 2016) Hodge 301 NGC 2060 R 136

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Hα photometry

De Marchi, Panagia & Beccari 2017

R136 Cluster within r < 20 pc ~1,000 stars

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Hα photometry

Tarantula
 Nebula within r < 120 pc ~14,000 stars

De Marchi, Panagia, Sabbi, et al. (in prep) !10

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Tarantula

De Marchi, Panagia, Sabbi, et al. (in prep) !11

PMS stars in the Tarantula

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AV=1

2 Myr 4 8 16 32

De Marchi, Panagia, Sabbi, et al. (in prep) !12

14,000 and counting…

Tarantula

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UV U V J I H De Marchi et al. 2016

Reddening vector in all bands

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  • 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

Extinction law at optical and infrared

!14

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AV=1

2 Myr 4 8 16 32

De Marchi, Panagia, Sabbi, et al. (in prep) !15

14,000 and counting…

Tarantula

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> 16 Myr < 8 Myr

De Marchi, Panagia, Sabbi, et al. (in prep) !16

Tarantula

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14,000 and counting…

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H301 R136 NGC 2060

N E

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< 8 Myr

N E

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> 16 Myr

N E

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Multiple generations ubiquitous

  • Multi-generation pattern always seen, Δt ~ 10 Myr
  • Younger PMS stars always more concentrated
  • Older PMS stars always more widely distributed

De Marchi et al. 2013 De Marchi et al. 2011b

NGC602 in SMC NGC346 in SMC

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Accretion evolution with time

De Marchi, Panagia, Beccari 2017 R 136

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Accretion evolution with time

Hartmann et al. 1998

Sicilia-Aguilar et al. 2006; 2010

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Accretion evolution with time

De Marchi, Panagia, Beccari 2017 R 136

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Accretion evolution with time

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De Marchi, Panagia, Beccari 2017 R 136

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Accretion evolution with time

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De Marchi, Panagia, Beccari 2017 R 136

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SMC LMC MW

De Marchi, Panagia & Beccari 2017

Accretion rate and metallicity

!23

LH 95

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N E

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10 σV

NE field NW field

Hα variability

SE field SW field

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!26 De Marchi, Panagia, Sabbi (in prep)

Hα variability


 Stars with 5 
 Hα epochs

  • < 8 Myr
  • 8–16 Myr
  • > 16 Myr


bright faint

Hα fluctuation [mag] Hα brightness [mag]

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< 8 Myr > 16 Myr

Hα variability

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Richert, Lyra & Kuchner 2017

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  • < 8 Myr
  • 8–16 Myr
  • > 16 Myr


!29 De Marchi, Panagia, Sabbi (in prep)

Hα variability: a Poisson toy-model

Hα fluctuation [mag] Hα brightness [mag]

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  • < 8 Myr
  • 8–16 Myr
  • > 16 Myr


Average accretion in Mirandas per week

!29 De Marchi, Panagia, Sabbi (in prep)

20 4 64 1

Miranda: ~ 5 x 10 –11 M◉

Hα variability: a Poisson toy-model

Hα fluctuation [mag] Hα brightness [mag]

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6

Looking ahead with JWST

N E

NGC 3603 (MW) 30 Dor (LMC) NGC 346 (SMC)

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 Rich sample of younger and older PMS stars

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N E

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7

Fitting targets in microshutters

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7

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Pa α

G235M (R~1000) for line luminosity G235H (R~2700) for gas kinematics

KAB~22 Br γ Br β

Observations: spectral features

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NIRCam will cover fields about 7.5 arcmin from NIRSpec, still plenty 


  • f 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.

Coordinated parallels

Pa α Br α F150W F182M F277W F430M

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  • 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) 


Summary

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www.starformation.eu