Transcript niriss_PMOs

NIRISS GTO
Planemos in star-forming regions
David Lafrenière and the NIRISS team
October 20, 2015
JWST NIRCam GTO meeting
8-10 June 2014, Zurich
Substellar IMF in SFRs
• Shape of IMF at lowest masses can inform BD/planet formation
• Turbulent fragmentation, dynamical ejection from multiple systems, disk
fragmentation and ejection, all of the above
Scholz et al. 2012a,b
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IMF well characterised down to ~10 Jupiter masses in several regions
dN/dM ~consistent with a single power law from 0.5 Msun to ~12-15 Mjup
Possible turnover below this mass regime
Star-to-BD ratio is typically in the range 2-5
NIRISS team meeting
20-21October 2015, Montreal
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Going below ~5-10 Mjup
• In the field, microlensing surveys indicate there could be ~2 PMOs
per star (Sumi et al. 2011), but result is highly debated
• Stark contrast to scarcity seen at 5-12 Mjup in SFRs
• If true, a large population of 1-5 Mjup PMOs must exist in SFRs
• ~100 such objects in each nearby SFRs
• Different origin than the more massive BD, formed as planets?
• In SFRs, little/no robust statistics <10 Mjup
• Need to establish firmly whether there is a turnover at ~10 Mjup
• Fragmentation limit, bottom of star formation
• Need to quantify the population of PMOs, especially <5 Mjup.
• Rogue planets, regime of planet formation
• We propose to do a survey using NIRISS WFSS to find isolated
planetary mass objects (PMOs) down to 2 Mjup in nearby SFRs
NIRISS team meeting
20-21October 2015, Montreal
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A NIRISS search for rogue planets in SFRs
• A survey ~75 sq. arcmin sensitive down to 2 Mjup in
each of 3 nearby (relatively dispersed, low AV) SFRs:
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r Oph, ~1 Myr, ~140 pc
Cha I, ~2 Myr, ~160 pc
NGC 1333, 1-3 Myr, ~230 pc
15 fields (2.2’x2.2’) per region
• Using Wide-Field Slit-less Spectroscopy (WFSS) mode:
• Spectroscopy of every source in the 2.2’x2.2’ FOV at resolving
power of ~150, in F150W and F200W
• Complemented by imaging in F115W
(and F150W/F200W)
• A. Scholz, R. Jayawardhana et al.
NIRISS team meeting
20-21October 2015, Montreal
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WFSS sensitivities, F150W
Corresponding Mjup at 3 Myr & 200 pc:
NIRISS team meeting
20-21October 2015, Montreal
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~3
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~1.5
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A NIRISS search for rogue planets in SFRs
• Goal of 2 Mjup at a minimum S/N of 10 per resolution
element for all regions observed (1-3 Myr, Av<5-10)
• At ~150 pc, corresponds to AB mag of ~22.2 in H and K
(~150 s and ~240 s per field, resp.)
• ~6 hr for Cha I & r Oph
• At ~250 pc, corresponds to AB mag of ~23.3 in H and K
(~400 s and ~600 s per field, resp.)
• ~8 hr for NGC 1333.
• Including overheads, amounts to grand total of ~20 hr.
• We have deep ground-based imaging (H~21-22) of all
regions to be targeted (from SONYC) and we can select
fields to avoid avoid bright stars, high extinction regions
and reflection nebulas
NIRISS team meeting
20-21October 2015, Montreal
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A NIRISS search for rogue planets in SFRs
• The R150 H & K spectroscopy resolution is
sufficient to unambiguously identify planetary
mass objects and provide a first estimate of
temperature and thus mass.
Scholz et al. 2012
• Imaging is further useful (and low cost) to
estimate luminosities, and verify extinction.
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Estimates of luminosity, temperature and mass can
be used to check consistency of models.
NIRISS team meeting
20-21October 2015, Montreal
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Outcomes
• Most optimistic scenario (Sumi et al. field microlensing result is true)
• ~2-5 detections per NIRISS field observed (0.5-1 per sq.arcmin)
• About 100 objects in total (of ~2-5 Mjup)
• Perhaps half of this is more reasonable
• Most pessimistic scenario (microlensing result is false)
• Based solely on extrapolation of known IMF: 5-6 in total for program
(0.1-0.3 per field).
• But this is uncharted territory! Could be more?
• In all cases, every object found is brighter than HVega~21 and easily
doable with high resolution spectroscopy
• NIRSpec R~2700 at S/N~20: 60 min at H and ~10 min at K
• E.g. measure C/O ratio to trace formation mechanism
NIRISS team meeting
20-21October 2015, Montreal
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Possible follow-up/collaborations
• NIRSpec spectroscopy
• need broad spectral coverage from 1-5 um to improve Teff/mass
estimates
• need higher resolution
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to constrain shape of the H-band better
to see atomic features
to measure abundances
to test for accretion
• Coverage & resolution for testing atmosphere models
• models are not great in this Teff regime (1000-2000 K), testing
models and improving fundamental parameters (and building the
mass function) will go hand in hand.
• MIRI photometry
• would be interesting to test for disks
NIRISS team meeting
20-21October 2015, Montreal
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NIRCAM PMOs in SFRs program
• Similar but based on a different strategy
• Target denser SFRs whose core is well-matched to
NIRCam FOV
• One pointing per SFRs (in the core) & multi-color
imaging:
• F070W, F115W, F277W, F444 W +4 intermediate band filters,
F140, F182, F300, F335
• ~8 hours total per field (8 filters), reach <2 Mjup at Av>20
• Gives initial selection, about 1/3 are expected to be
contaminants
• Follow-up of every candidate with NIRSPec R=100
spectroscopy for confirmation/characterization
• I don’t know how long this will take…
• M. Meyer et al.
NIRISS team meeting
20-21October 2015, Montreal
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NIRCAM
• Outcome:
• ~50-100 PMOs per field, based on extrapolation of known IMF
and some reasonable assumptions.
• Fainter objects than NIRISS
• >10-20 additional mag of AV vs the NIRISS program, so >2-4 mag
fainter
• Detailed characterization at high resolution, wider spectral coverage
more difficult.
NIRISS team meeting
20-21October 2015, Montreal
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NIRISS and NIRCam programs
• Are the NIRISS/NIRCam programs competing? Is one
better? Are they complementary?
• My view is that both programs are complementary and
should both be done (and well coordinated)
• Shared by Aleks Scholz and others.
• NIRISS: bright objects for follow-ups, access to dispersed
regions/outer parts of cluster/regions with low AV
• NIRCam: more but fainter objects, better for statistics, access to
dense regions/core
• IMF measurement is difficult, going at it with multiple approaches
is best.
• Could do one region in common with both instruments.
NIRISS team meeting
20-21October 2015, Montreal
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