Raghvendra Sahai Jet Propulsion Laboratory

SHOCKED & SCORCHED Free-Floating Evaporating Gas Globules

and Star Formation

Mark R. Morris, UCLA

Mark J. Claussen, National Radio Astronomy Observatory

RS acknowledges financial support from (i) NASA Long Term Space Astrophysics award, (ii) STScI HST/GO award, (iii) JPL RTD awards

Background • Massive stars have a profound effect on stars that

subsequently form in their vicinity (significantly affecting the IMF, the star formation efficiency, and the total extent and mass of star clusters).

Ionizing radiation can produce compact structures in

Massive Star-Forming Regions (MSFRs):

• Proplyds (Orion, e.g., O'Dell, Wen, and Hu 1993; Ricci, Robberto, and Soderblom 2008).

• EGGs (M16, Hester et al. 1996).

We report here on a study of a class of objects we first identified in the Cygnus MSFR that we have named “free-floating EGGs” (frEGGs).

• Exciting new “clean-cut” probes of the effect of massive stars on subsequent star formation.

Discovery of Prototype: The Tadpole (Sahai, Morris, Claussen 2012, ApJ 751, 69)

line flux

Slit 2 Slit 1

N

E

(a)

(b)

(c)Found in HST optical imaging survey for a subclass of dying stars Tadpole shape, bow-shock structure at head and extended wiggly tail • H2 S(1) 2.1 mm emission

from hot, shocked gas near central star (also from PDR at periphery of tadpole)

• Pa b from ionized gas in outflow or disk emission, centered on star (also from PDR)

Luminous young star in the interior of the head

• Wiggles on periphery: Kelvin-Helmholtz instabilities

(a) HST (ACS) image (red: 0.8 mm, green: 0.6 mm) (b) Spitzer (IRAC) 8 mm image (c) Palomar 200-in (TripleSpec) – (slit 1) red: Pa b, green H2 S(1), (slit 2 ) black H2 S(1)

IRAS20324+4057 (Cyg OB2 cluster located 10 pc to the NW)

Hierarchical Star-Formation in IRAS20324

b

b

a

cometaryknot

c

a

SED modeling of luminous star (online 2-D dust radiative transfer tool, Robitaille et al. 2007)

L* ~ 500 L⊙

M* ~ 4.5-6.5 M⊙ Teff ~ 4150K

Outflow cavity inclined ~20° to line-of-sight (consistent with HST image).

Cometary knot structure shows outflow cavity around a luminous YSO

Molecular-line Observations

A

B

13CO J=2−1 (X 2)

HCO+ J=3−2 (X 5)

CS J=2−1 (X 10)

CO J=2−1

Vlsr (km/s)

TR

(K

)

Strong emission from IRAS20324=Tadpole (A) and the Goldfish (B), at Vlsr ~ 8-12 km/s (panel size: 5.5’ x 5’) Molecular Mass ~ 1-3 M⊙

High-density tracers in IRAS20234

CS J=2-1, HCO+ J=3-2 (as well as HNC, HCN, N2H+ 3-2 lines, not shown) imply the presence of dense cores (~105-6 cm-3) in the Tadpole and Goldfish

Channels Maps of CO 2-1 emission (using SMT 10m, Arizona Radio Observatory)

VLA Imaging

Object C

Object A(Tadpole)

Object B

(Goldfish)

N

E

Objects ionized on their peripheries by external UV radiation Tadpole detected at both 8.5 & 22.5 GHz F(22.5 GHz) ~ 0.55 x F(8.5 GHz)

i.e., negative spectral index: Non-thermal emission?

EVLA (C-array) map of 8.5 GHz emission towards Tadpole and Goldfish (insets show IRAC 8 mm images for two of these).

Pereira & Miranda (2007) identified these (A,B,C) as emission-line objects (Ha, [NII]) in ground-based spectroscopic study (of post-AGB candidates)

Non-thermal Emission from IRAS20324

1. Confirm non-thermal emission

2. Find strong variability FERMI data show a large reservoir of freshly accelerated cosmic rays towards Cygnus (Ackerman et al 2011)

Radio SED of the Tadpole

Aug 2009 Apr 2013 (data fit using model with

optically-thin synchrotron-emission, power-law exponent d=3 of electron energy distribution)

(detailed modelling needed)

Interaction of a pulse of relativistic particles with a compressed magnetic layer in the Tadpole head?

Interaction of a pulse of relativistic particles with a compressed magnetic layer in the Tadpole head?

New D-array data

Ground-based narrow-band optical imaging showed objects as dark silhouettes (some with bright rims) against a bright nebular background , classified as proplyd candidates(Smith, Bally & Morse 2003; HST data from Smith, Bally & Walborn 2010)

Proplyd frEGG in Carina (Sahai, Guesten, Morris, ApJ Letters, 2012)

Carina-frEGG1: one of 12 “proplyd” candidates in Carina MSFR

(a) Spitzer 8 mm (b) HST/ACS F658N (Ha+[NII]) (c) VLT Ks (AO) (panel size 14.6” x 24.4”)

CO J=6-5 Map

Carina-frEGG 1: Molecular-line Observations APEX 12-m (Chile) observations: 1. Map CO J=3-2, 4-3, 6-5, 7-6 2. On-source observations 13CO, HCN & HCO+ 3-2 3. Continuum source 350 mm (upper limit, 870 mm) 4. Weak high-velocity wings: outflow from YSO

Model: source-size 11.7 arcsec2 (HST image) (use RADEX non-LTE online tool to model CO, 13CO) Tk~ 40K (cool component, t[12CO] >>1) (red circles) 150K (hot component, t[12CO] <<1) (blue circles) Density ~ 105-6 cm-3

Mass: 0.35 M⊙ proplyd (frEGG)

The Central Star of Carina-frEGG 1 SED Modelling

• L*(star, disk-accretion): 6-10 L⊙

• M*~0.1-0.65 M⊙

• Teff~2600-3800K

• inclination (outflow axis to line-of-sight) ~18° [strong asymmetry in lobes in Ks]

• very high extinction to central star (Av > 100) [star not seen even at 8 mm]

• dust mass ~ 0.001 M⊙

Observed and model SED fits from online 2-D dust radiative transfer tool (as for IRAS20324)

Proplyds or frEGGs?

Wright et al. (2012, Cygnus MSFR): unlikely to be EGGs because about 70% of these appear to contain young stars, compared to 15% for M16 EGGs

Smith et al. (2003, Carina MSFR): proplyd candidates much larger (>15,000 AU) than in Orion (~few x 100 AU) because perhaps disks larger/more massive, or FUV/EUV ratio higher in Carina

arguments not compelling

Mm-wave data imply large molecular masses towards these objects rule out proplyd hypothesis • frEGG CO, 13CO line-intensities rule out

small, i.e., disk-sized sources • no dense molecular medium found

towards any known proplyd • Orion proplyd disk masses, 0.003-0.07

M⊙ (Mann and Williams 2010) imply relatively small masses for the circumstellar material being evaporated from them.

(we labelled these objects as free-floating EGGs or frEGGs, since they appear as isolated objects in HII regions of MSFRs, to distinguish them from the “attached” EGGs in M16)

Our studies suggest that most large proplyds may have been misclassified (we are carrying out molecular-line observations of objects classified as proplyds in other MSFRs to confirm this hypothesis).

Cygnus

W5

Many frEGGs in Cygnus and W5

We have already identified about 20 frEGGs in each of these star forming regions from IRAC 8 mm images (sizes ~ 15,000-100,000 AU), searching for more (ADAP proposal)

Some objects show bright point sources signifying embedded YSOs

Cygnus frEGGs: Molecular Line Survey

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

-5 0 5 10 15 20 25

Antenna Temp (K)

LSR VEL (km/s)

HCO+ 3−2SMT 10Mtadpole 10

tadpole 11

tadpole 10

tadpole 11

Single-dish molecular-line survey:

(i) CO & 13CO 2-1 mapping (ii) High-density tracer molecular lines J=3-2 Lines of HCO+, N2H+, HNC, HCN

In all cases, we find isolated molecular globules • Masses ~ few M⊙ or more (depending on size) • Dense gas (105-6 cm-3)

Spitzer IRAC images from Cygnus X

Legacy Survey program (PI: J. Hora)

-5 0 5 10 15 20 25 Vlsr (km/s)

1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

TA*

(K)

3-2

Single-dish molecular-line survey observations

• Derive masses, temperatures, densities, and lifetimes (106 yr) of these frEGGs (Sahai, Morris, Claussen 2014)

Mm-wave interferometric observations needed

• Probe the dense dusty cores in frEGGs, search for YSO outflows/ disks, which may or may not be visible at optical or infrared wavelengths (S. Schnee talk, this meeting).

W5 frEGGs: Molecular Line Survey W5(W)-frEGG02, one of ~20 frEGGs in W5

Unbound Bound Numerical simulations of turbulent clouds (Dale+2012,2013): (a) Bound Ekin/Egrav=0.7 (b) Unbound

Ekin/Egrav=2.3 Unbound clouds make large bubbles & frEGG-like structures more efficiently

frEGGs can constrain models of MSFRs

RV[frEGG] offset from RV[parent]! • predicted in numerical simulations of

MSFRs, when R = (turbulent pressure, parent cloud) /(ionized-gas pressure, HII region) is high (Tremblin+2012)

When R high, simulations also produce frEGG-like globules in abundance!

Tremblin+2012 : such globules are dynamically ejected into HII region.

• Caveat: “rocket effect” on frEGGs is alternate possibility, although current simulations (Dale+2013) indicate that the same effect on parent cloud reduces the magnitude of the offset.

Radial Velocities of frEGGs (RV[frEGG]) and parent cloud structures (RV[parent]) in the W5(E) MSFR, from molecular-line observations.

Radial Velocities of frEGGs

Searching for Young Stellar Objects in frEGG Cores

Keck (AO, NGS & LGS) near-infrared (H, K’, L’ bands) observations of frEGGS (Cygnus, W5) • 2/9 frEGGS show stellar sources

and (one-sided) outflow cavities in scattered light at 1.65 & 2 mm.

• Compact luminous sources in Spitzer IRAC images (3.6-8 mm) at same location as stellar sources

direct evidence for the presence of very young stars forming in the dense dusty, molecular cores of frEGGs.

High-angular resolution (0.1”) optical imaging required to observe outflow cavities/ jets to confirm the presence of YSOs in frEGG cores

(top) Keck (AO) K-band , (bottom) IRAC 8 mm

Summary 1. Large (> 10,000 AU) isolated tadpole-shaped structures are not proplyds, but free-

floating Evaporating Gas Globules (frEGGs); found in several MSFRs.

2. They are being shaped and compressed by the harsh ionizing radiation and winds from massive stars in the neighborhood.

3. A significant fraction of these are obviously forming stars (and at least one of these shows hierarchical star-formation). (corollary: some proplyds evolve from frEGGs)

4. Potential probes of triggered star formation in action (e.g., compression due to high ambient pressure triggers or enhances star formation in frEGGs).

5. Offer a diagnostic window on initial conditions in MSFRs (e.g., turbulent to ionized gas pressure; unbound or bound cloud).

Future Work 1. Collect statistical samples of frEGGs in a variety of MSFRs (ADAP 2014 proposal).

2. Carry out observations with HST, mm-wave interferometers such as ALMA (outflows/ disks/ jets associated with YSOs), SOFIA/GREAT (mass in PDR, photoevaporative outflow [cycle 3 proposal]), and Jansky VLA (thermal/non-thermal radio continuum: mass in photoionized region).

3. Compare results with, and motivate new simulations of turbulent molecular clouds irradiated by nearby OB stars.

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