A Search For Fragmentation in Starless Cores with ALMA

Scott Schnee (NRAO)Hector Arce, Tyler Bourke,

Xuepeng Chen, James Di Francesco, Michael Dunham, Doug Johnstone,

Stella Offner, Jaime Pineda,Daniel Price, Sarah Sadavoy

28-July-2014

Turbulence Scales With Size

(Larson 1981)

Log size of cloud (pc)

Log

line

wid

th (k

m/s

)

Line Width is Constant on Small Scales

(Pineda et al. 2011)

Core propertiesd ≈ 0.1 pcn ≈ 104-6 cm-3

T ≈ 10 KM ≈ 1-10 M

cs ≈ 0.2 km/sσ ≈ 0.1-0.2 km/s

Does fragmentation continue down to smaller scales?

Project Idea

• Choose a promising sample of starless cores• Look for evidence for fragmentation– Yes: support for turbulent fragmentation– No: support for disk fragmentation?

• Observe cores with mm interferometers– Provides high spatial resolution– Dust continuum provides unambiguous mass tracer

CARMA – Big Pine, CaliforniaAntenna numbers, sizes

6 x 10.4m, 9 x 6.1m, 8 x 3.5m

Sample 1

• 3mm continuum survey of 11 starless cores• Chosen from Enoch et al. (2006; 2008)

Bolocam 1.1mm survey of Perseus• Starless status based on Spitzer NIR-MIR data• Peak fluxes >200 mJy beam-1 in Bolocam data• Median mass of 1.47 M⊙ • Median density of 3.2×105 cm−3

• Observed with CARMA • 3mm continuum– 5” resolution– 40” largest angular scale

• Follow-up observations with – CARMA (3mm spectral lines)– SMA (1.3mm continuum, CO J=2-1)– Spitzer (70 μm continuum)

Sample 1

CARMA & SZA 3mm Continuum

(Schnee et al. 2010)

0.01 pc

Perbo58 and Perbo 45 as Protostars

Greyscale and Green contours: 1.3mm continuum emission

Red and blue contours:Red and blue-shifted CO (2-1) emission

(0.3-7.3 & 7.3-14.3 km/s)

(Dunham, Chen, Arce, Bourke, Schnee, & Enoch

2011)

(also: Schnee, Di Francesco, Enoch, Friesen, Johnstone, & Sadavoy 2012)

SMA – Mauna Kea, HawaiiAntenna numbers, sizes

8 x 6m

Sample 2• 1.3mm continuum and CO (2-1) survey of 5

starless cores• Chosen from Sadavoy et al. (2010) SCUBA 850

μm survey of nearby molecular clouds• Starless status based on Spitzer NIR-MIR data• Observed with SMA in compact configuration– 1.3mm continuum– 12CO (2-1), 13CO (2-1), C18O (2-1), N2D+ (3-2)– 3” resolution– 8” largest angular scale

Per 8 as a Protostar

Black: 1.3mm continuum (0.1 – 0.5 Jy/beam)Red: 12CO (2-1) Tint 9 km/s ≤ v ≤ 18 km/sBlue: 12CO (2-1) Tint -2 km/s ≤ v ≤ 5 km/sColor contours at 3, 6, …, 21 K km/s

Black: C18O Tint in intervals of 2 K km/sColor: C18O VLSR

(Schnee, Sadavoy, Di Francesco, Johnstone & Wei 2012)

12CO and continuum C18O and continuum

ALMA – Atacama Desert, Chile

Antenna numbers, sizes32 x 12m, 9 x 7m (Cycle 1)

54 x 12m, 12 x 7m (Full Science)

Sample 3• 3mm continuum and CO (1-0) survey of 72

starless and protostellar cores• Chosen from Belloche et al. (2011) LABOCA 1mm

survey of Chamaeleon I• Starless / protostellar status based on NIR data• Observed with ALMA in Cycle 1– 3” resolution– 25” largest angular scale

CARMA, SMA, and ALMA Projects

Array Resolution Frequency(GHz)

rms(mJy)

rms (M)

# sources Time per source

CARMA 5” 100 1 0.2 11 10 hours

SMA 3” 230 1 0.02 5 3 hours

ALMA 3” 115 0.1 0.01 72 1.2 minutes

ALMA 3mm Continuum

0.01 pc

Every Starless Core

(Schnee et al. in prep.)

ALMA 3mm Continuum

0.01 pc

Double source Single source

(Schnee et al. in prep.)

ALMA Results• Starless Cores– No continuum detection

• FHSC candidate Chamaeleon-MMS1– Extended 3mm continuum detected

• Protostars– 19 cores with 3mm continuum (point-like)– 25 total protostellar candidates detected– new YSO candidates • 7 not found in Dunham et al. (2013)• 2 not found in Winston et al. (2012)

(Schnee et al. in prep.)

Simulations of Turbulent Fragmentation in Starless Cores

(Offner, Capodilupo, Schnee, & Goodman 2011)

Simulated ALMA Full Science + ACA observations

Summary• Observational evidence for fragmentation in

starless cores? – Not yet.– Low levels of turbulence in starless cores leads to

low levels of fragmentation– Multiplicity set at protostellar stage? Disk

fragmentation?– More sensitive observations needed?

• Interferometric observations in the millimeter or submillimeter can find hidden protostars– Up to 20% of “starless” cores are actually

protostars

L1451-mm: Another Hidden Protostar

(Pineda, Arce, Schnee et al. 2011)

L1451-mm: Another Hidden Protostar

Black Contours:SMA 1.3mm continuum

Blue Contours:Blue-shifted CO (2-1)1.9-3.7 km/s

Red Contours:Red-shifted CO (2-1)5.3 – 6.9 km/s

(Pineda, Arce, Schnee et al. 2011)

Starless Cores Are Not Detected by CARMA

1. Offset from (0,0) position given in Enoch et al. (2006)2. Derived from Gaussian fit to flux distribution3. Deconvolved using the synthesized beam4. For non-detections, 3σ upper limits to a point source are given5. Does not include SZA data, so some 3mm emission is resolved out

(Schnee et al. 2010)

Sample 2

• 3.2 M⊙ ≤ M ≤ 8.1 M⊙

• 2.1 ≤ M/MJ ≤ 4.9

Starless Cores Are Not Detected by SMA

• 3σ upper limits for non-detections < 0.02 M⊙

(Schnee, Sadavoy, Di Francesco, Johnstone & Wei 2012)