Maite Beltrán

Osservatorio Astrofisico di Arcetri

The intringuing hot molecular core G31.41+0.31

The HMC G31.41+0.31

• G31.41 is a hot core (without UCHII) at a distance of 7.9 kpc

• G31.41 luminosity, 3 105 L⨀, suggests that it harbors O-type (proto)stars

Clump

UC HII

HMC

G31.41 is located at a distance of 7.9 kpc,

LIRAS = 3x105 L consistent with an embedded star of 25➔ M

Glycolaldehyde in G31.41+0.31

Glycolaldehyde, the simplest of the monosaccharide sugars that reacts with propenal to form ribose was detected for the first time towards a HMC OUTSIDE the Galactic Center in G31.41+0.31.

Beltrán et al. (2009)

1.4 mm

2.1 mm

2.9 mm

Very compact emission (~1.3”, ~10,000 AU) unlike in Sgr B2.

Estimated abundance of the order of 10-8. Only small amounts of CO need to be processed on grains to reproduce the observed column densities with the HMC model of Viti et al. (2004).

Plateau de Bure

Glycolaldehyde in HMCs

Beltrán et al. (in preparation)

contours: CH3CN

greyscale: glyco

A rotating toroid in G31.41+0.31

G31.41 is a rotating toroid with R ~ 8000 AU, Mcore = 490 M, Mdyn = 87 M, and Vrot = 2.10 km/s (Beltrán et al. 2004, 2005; Girart, MTB et al. 2009; Cesaroni, MTB et al. 2011)

Mcore 6 x Mdyn core unstable and undergoing ➔collapse.

The two white dots denote the free-free continuum sources (radio jets) detected by Cesaroni et al. (2010).

Cesaroni, Beltrán et al. (2011)

CH3OH

Girart, Beltrán et al. (2009)

Magnetic field in G31.41+0.31

Hot core elongated in NE-SW direction

Dust polarization observations have revealed dust linearly polarized emission mainly along the major axis of the HMC: B lines perpendicular to the major axis of the HMC, in the direction of rotation or accretion, with a clear ‘’pinched’’ morphology (Girart, Beltrán et al. 2009).

The dust polarization pattern suggests an hourglass shape morphology, similar to the one found in low-mass regions (e.g NGC1333 IRAS4A: Girart et al. 2006) but the scale and mass involved are much larger.

dust polarized emission velocity gradient

Girart, Beltrán et al. (2009)

870 m

G31.41+0.31

CH3OH

B-field strength ~10 mG; =0.35±0.29/0.20 ➝ Emagnetic > Eturbulent Mass-to-flux ratio (wrt critical value): 2.7 (supercritical)

Magnetic field in G31.41+0.31

Girart, Beltrán et al. (2009)

The more compact transitions show a shorter velocity range, that is a smaller rotation velocity

Rotation and radius have been measured from the Half Maximum contour of different methanol transitions in the zero and first order maps of the integrated emission.

The measured spin velocity of the hot core decreases with decreasing radius

Therefore the angular momentum is not conserved: Magnetic braking. Theoretical models of magnetic braking predict a spin down (Basu & Mouschovias 1994; Mellon & Li 2008)

Magnetic fields might play an important role in the formation of massive stars and could control the dynamical evolution (gravitational collapse) of the cores.

Inverse P-Cygni profiles in G31.41+0.31

There is a clear inverse P-Cygni in C34S (7-6), H2CO (31,2-21,1), and CN (2-1) profiles that

suggests infalling gas.

Red-shifted absorption observed against the bright continuum emission of a very hot compact dust component.

Vinf=|VLSR-Vred|~3.1 km/s

Accretion rate =/4 [3x10-3 – 3x10-2] M/yr

for (4080-12640 AU)

C34S (7-6)

Frau et al. (in preparation)

CN (2-1)

Girart, Beltrán et al. (2009)

absorption

emission

Outflows in G31.41+0.31

Cesaroni, Beltrán et al. (2011)

CO observations reveal a complex outflow emission (Cesaroni, Beltrán et al. 2011):

at high velocities E-W outflow at systemic velocities: 2 outflows? NE-SW wide-angle outflow? (CH3OH: Araya et al. 2008)

Can CH3CN (and CO) trace a NE-SW bipolar ouflow?

☺if CH3CN indicates rotation, where is the perpendicular outflow?

☺ the PV plot of the 12CO emission in the direction of the CH3CN velocity gradient is consistent with the Hubble-law expansion observed in molecular outflows

☹ CH313CN “outflow parameters” too high (Mout=290 M,

P = 1200 Mkm/s, F=0.3 Mkm/s/yr, Lbol= 6 × 106 L)

☹ the velocity gradient would involve the whole core not only gas emitting in the wings. Most CH3CN affected by the velocity gradient

☹ dynamical timescale (4x103 yr) too short to form hot core species (Charnley et al. 2002)

☹ not compatible with the hourglass-shaped morphology of the magnetic field

Outflows in G31.41+0.31

Cesaroni, Beltrán et al. (2011)

Can CH3CN (and CO) trace a NE-SW bipolar ouflow?

☺if CH3CN indicates rotation, where is the perpendicular outflow?

☺ the PV plot of the 12CO emission in the direction of the CH3CN velocity gradient is consistent with the Hubble-law expansion observed in molecular outflows

☹ CH313CN “outflow parameters” too high (Mout=290 M,

P = 1200 Mkm/s, F=0.3 Mkm/s/yr, Lbol= 6 × 106 L)

☹ the velocity gradient would involve the whole core not only gas emitting in the wings. Most CH3CN affected by the velocity gradient

☹ dynamical timescale (4x103 yr) too short to form hot core species (Charnley et al. 2002)

☹ not compatible with the hourglass-shaped morphology of the magnetic field

Maser jet in G31.41+0.31

H2O and CH3OH maser VLBI observations have revealed an extremely compact and highly collimated jet (Moscadelli et al. 2012)

the spots outline an elliptical pattern with major axis oriented roughly N-S and centered in one of the two cm sources detected towards the center (Cesaroni et al. 2010)

Major and minor axes are 1.4” and 0.24” (11000 and 1900 AU) with PA = 8°, and maser average expansion velocity 20 km/s.

Jet dynamical timescale is 1300 yr

Jet momentum rate is 0.1M/yr consistent with a powering source of L > 104 L

Moscadelli et al. (2011)

H2O

CH3OHH2O

CH3CN

Maser jet in G31.41+0.31

Moscadelli et al. (2011)

H2O

CH3OHH2O

Where is the large-scale bipolar outflow?

CH3CN

H2O and CH3OH maser VLBI observations have revealed an extremely compact and highly collimated jet (Moscadelli et al. 2012)

the spots outline an elliptical pattern with major axis oriented roughly N-S and centered in one of the two cm sources detected towards the center (Cesaroni et al. 2010)

Major and minor axes are 1.4” and 0.24” (11000 and 1900 AU) with PA = 8°, and maser average expansion velocity 20 km/s.

Jet dynamical timescale is 1300 yr

Jet momentum rate is 0.1M/yr consistent with a powering source of L > 104 L

Molecular jet in G31.41+0.31

SMA observations at 345 GHz and 0.8” reveal two possible jets (outflows):

E-W (PA=90o) south of the HMC center

N-S (PA=15o) associated with maser jet

Alternative explanation: NE-SW wide-angle jet (PA=68o) less convincing

ALMA and G31.41+0.31(and HMCs)

1. Keplerian circumstellar disk in G31.41+0.31

ALMA should be sensitive enough to detect a disk up to distances of 20 kpc (Cesaroni 2008)

Angular resolution of 0.1” (790 AU) should detect an embedded disk in G31 (if it exists)

2. Jets and outflows in G31.41+0.31

ALMA SiO observations at 0.1”-0.2” resolution (separation of the two cm sources and minor axis of maser distribution) ➔ information on the jet ejection process on scales < 1000 AU and on the interaction between the ejected material and the surrounding entrained gas in G31

3. Distribution and abundance of glycolaldehyde in G31.41+0.31

ALMA will resolve G31 and map the distribution of glycolaldehyde on scales smaller than 1000 AU.

ALMA (8 GHz BW) will allow simultaneous observations of several transitions of glycolaldehyde with different line strengths and energies (excitation conditions) ➔ temperature, column density and abundance to further constrain the formation routes (e.g. Woods et al. 2012).

4. Magnetic field in G31.41+0.31

ALMA polarization capabilities will allow to study the morphology of the magnetic field at a scale similar to the separation of the cm sources (0.2”)

OPEN QUESTIONS: