Determining the dynamics of the ultracompact HII region (UCHII)

Monoceros R2

A. FuenteObservatorio Astronómico Nacional (OAN)

Why to study Monoceros R2?

Dynamically:

It is the closest UC HII region (d=830pc) and the best target to investigate this evolutionary stage in the formation of massive stars

From the chemical point of view:

Excellent target to investigate the chemistry of dense (n>105 cm-3) photon-dissociation regions with high UV fluxes (G0=5 105 Habing field). Pattern for Xgal and protostellar disks

Very simple geometry which allows detailed modeling

The latest stage in the formation of a massive star

Massive pre-stellar core → High mass protostellar object (HMPO) → Hot core → UC HII region

Figure adapted from van Dishoeck et al. (2011, PASP 123, 138)

*

Lifetime Paradox

Ultracompact HII regions are characterized for very small spatial scales (< 0.1 pc) and being embedded in the molecular cloud.

With densities of a few 105 cm-3, typical of giant molecular clouds the UCHII is expected to expand and its lifetime as UCHII is of around one thousand of years.

However the number of UCHII detected proves that the lifetime should be larger (“lifetime paradox”). Lifetime of UCHII should be around 105 yr.

Photodissociation Regions (PDRs)

Orion Bar 104 Draine Field cluster O stars 450pc edge-on

Mon R2: a prototypical UC HII region

13CO 2-1 C18O 2-1

FIRS 1 FIRS 1

Mol. bar Mol. bar

A small cluster of young stars (FIRS 1, 2, 3, 4, 5) is in the center of the HII region. The UC HII region is ionized by the more massive young B star FIRS 1

Observational study using the IRAM 30m telescope and Herschel (Mon R2 is one of the sources of the HSO Guarantee Time Key Project WADI (PI: Volker Ossenkopf)

CO+ and HOC+ in MonR2(Rizzo et al. 2003, ApJ 577, L153)

Detection of CO+ and HOC+ in the ionization front (IF)Abundance gradient between the IF and the Molecular Bar

C2H, c-C

3H

2, some dynamics

Rizzo et al. (2005, ApJ 634, 1133)

c-C3H

2

C1 C2

5 105 cm-3 >5 106 cm-3

Different excitation properties:C1 n(H

2) about 5 105 cm-3

C2 n(H2) always > 5 106 cm -3

Different chemical propertiesC2 only detected in PDR tracers

Probing the dense expanding layer around the UCHII region

C1 C2

Spitzer data (PAHs and H2)

Berné et al. (2009), ApJ 706, L160

Bright, extended emission of the PAHs bands and H2 rotational

linesLayered structure expected in a PDR

Different PDRs around UCHII region (different physical and chemical conditions)

G0 and n

H estimates from PAHs and H

2

H2 rotational lines are thermalized for n>104 cm-3

The I6.2

/I11.3

ratio is tracing the UV field allow to

determine the [PAH+]/[PAH0] ratio and the UV field(Galliano et al. 2008).

Mon R2: a prototypical UC HII region

13CO 2-1 C18O 2-1

FIRS 1 FIRS 1

Mol. bar Mol. bar

Cuts in CH (536 GHz, includes HCO+ 6-5), H2O (556GHz and 1113

GHz), CO 9-8, 13CO 10-9, CII, CH+

Pointed observations of OH+, H3O+, H

2O+, NH, 13CII, H

218O

Massive star forming region

Massive star forming region12CO 9-8 13CO 10-9

o-H2O 110-001

CII

p-H2O 111-00oo-NH3 10-00

Modeling water in Mon 2Pilleri et al. 2011 (in preparation)

D=830 pcCompact NeII emission= 24" (diameter)Hole of molecular emission= 40" (diameter) N(H2)= 2-- 6 1022 cm-2

Size of the core= 2' (diameter)

Our model:1st thin layer= 1mag with n=4 105 cm-3

2nd dense layer= 14 mag with n=6 106 cm-3

3rd low density layer= 50 mag with n= 5 104 cm-3

Vexpansion

=0.5 (R/Rout)-1 (from Fuente et al. 2010)

Non-local ALI model(Pilleri et al. 2011, in preparation)

Spherical modelNon local radiative transfer ( Cernicharo et al. 2006, ApJ 642, 940)

High velocity expanding layer

Tk >100 K

X(o-H2O) ≈10-7

Meudon PDR code v1.4.1 (Bourlot et al. 2006)

Modeling water in Mon 2Pilleri et al. 2011 (in preparation)

Low velocity molecular cloud

Tk <100 K

X(o-H2O)≈ 10-8

Absorption lines (OH+,H2O+)

OH+ absorption at redshifted and blueshifted velocities

The only way to explain the redshifted absorption is to assume the existence of a collapsing outer low density envelope.

Expansion Collapse

Absorption lines (OH+,H2O+)

[OH+]/[H2O+]=0.8

f(H2)=0.07

Similar to diffuse clouds(see Gerin et al. 2010)

Thin (1 mag) and dense (5 105 cm-3) expanding layer Traced by high-J CO rotational lines and water (Herschel data). Reasonably well explained by gas phase PDR chemical models

Thin (10mag) and dense (< 106 cm-3) molecular layerTraced by IRAM and Herschel data. Partially explained by gas phase PDR chemical models.

Thick (50mag) and low density collapsing layer (104 cm-3)OH+ absorption lines

Conclusions

3mm IRAM spectral surveyGinard et al. 2011 (in preparation)

Three targetted positions:(i) IF(ii) Molecular Bar(iii) PAH peak2 MHz -> 6 km/s

IF IF

IF

First detection of SO+ and C4H in

Mon R2

IF: 23 species (+ CO+ and HOC+)Mol Bar: about 30 species

Well known PDR tracers but also complex species common in warm star forming regions

Chemical differences among the 3 positions.

List of detected species

The fragmented ISM in the nucleus of M 82

A. FuenteObservatorio Astronómico Nacional (OAN)

M 82

M82 is one of the nearest and brightest starburst galaxies. Located at a distance of 3.9 Mpc, and with a luminosity of 3.7x 1010 L

sun , it has been

extensively studied at all wavelengths.

M 82

1.- Compared to other prototypical nearby starburst galaxies like NGC 253 and IC 342, M82 presents systematically low abundances of the molecules NH

3 , CH

3 OH, CH

3 CN, HNCO, and SiO (Mauesberger & Henkel 1989,

A&A 223, 79; Weiss et al. 2001, ApJ 554, L143).

2.- Wolfire et al. (1990, ApJ 358, 116) modeled the C II , Si II , and O I emission and estimateda UV field of G

0 =104 in units of the Habing field

and a density of n >104 cm-3 for the atomic component.

3.- Suchkov et al. (1993, ApJ 413, 542) estimates a cosmic ray flux of 4 10-15 s-1, 100 times higher than the Galactic value.

M 82(García-Burillo et al. 2002, ApJ 575, L55)

Izqda: Emisión de SiO (García-Burillo et al. 2001, ApJ 563, L27) superpuesta a la imagen de continuo a 4.8 GHz (Wills et al. 1999, MNRAS 309, 395). Dcha: Emisión de HCO superpuesta a la emisión de H13CO+ (A) y CO (García-Burillo et al., 2002, ApJ 575, L55; Mao et al. 2000, A&A 358,433)

A high N(HCO)/N(H13CO+) ratio is an evidence for PDR. N (HCO)/N (H13CO+) abundance ratios range from ∼ 50 (Horesehead), ∼ 30 (in the Orion bar) to ∼ 3 (in NGC 7023).

N (HCO)/N (H13CO+) 3.6 in M82, ∼ the nuclear disk of M82 can be viewed as a giant PDR of 650 pc.

M 82(García-Burillo et al. 2002, ApJ 575, L55)

CN/HCN ratio in M 82(Fuente et al. 2005, ApJ 619, L155)

The [CN]/[HCN] and [HCO+]/[HOC+] ratios in all the disk of M82 (650pc) similar to the Orion Bar. This comfirms that the nucleus of M82 is a giant PDR.

CO+ and HOC+ in M82(Fuente et al. 2006, ApJ 641, L105)

[CO+]/[HCO+] >0.04 are measured across the inner 650 pc of the nuclear disk of M82.

[HCO+]/[HOC+] 40∼

Preliminary model(Fuente et al. 2005, ApJ 619, L155)

The low [HCO+]/[HOC+] ratio can only be explained if the nucleus of M82 is formed by small (r ~0.02–0.2 pc) and dense (n a few ∼times 104 –105 cm-3 ) clouds immersed in an intense UV field of 104 ( in units of the Habing field) and with an enhanced cosmic ray flux.

Detection of H3O+

(van der Tak et al. 2008, ApJ 492, L675)

Van der Tak et al. (2008) detected H3O+ using the JCMT. They

concluded in agreement with our results, that the H3O+ abundance is

consistent with that expected in a PDR with enhanced cosmic ray flux.

M 82: XDR or PDR?(Spaans & Meijerink 2007, ApJ 664, L23)

Interferometric observations of M 82(Fuente et al. 2008, ApJ 492, L675)

The HOC+ emission comex from the galaxy disk like most molecular species.There is no spatial correlation between the HOC+ abundance and the[HOC+]/[HCO+] ratio with the X ray flux.

Interferometric observations of M 82(Fuente et al. 2008, ApJ 492, L675)

We model our clouds using the updated Meudon code and plane clouds illuminated from the both sides.

Interferometric observations of M 82(Fuente et al. 2008, ApJ 492, L675)

We cannot fit the [CO+]/[HCO+] and [CN]/[HCN] ratios with a single cloud type.

We can better fit the observations if we consider two types of clouds: (i) most of the mass(87%) is in small clouds of Av=5mag; (ii) a small percentage of the mass (13%) is in very large molecular clouds (50 mag) .

Starburst evolution

The differences between the chemistry of NGC 253, IC 342 and M82 can be understood as an indicator of different phases of starburst evolution, being NGC 253 in an earlier phase and M82, the more evolved one (García-Burillo et al., 2002, ApJ 575, L55, Aladro et al. 2011, A&A 525, 89).

Aladro et al. 2011, A&A 525, 89

Other Xgal PDRs (M51 and M83)

Stephane Guisard & Robert Gendler

M 83

M 51

Tony & Daphne Hallas

Other Xgal PDRs(Kramer et al., 2005, A&A 441, 961)

They compare the emission of the CI and CO rotational lines with the FIR lines of CII (157 µm), OI(63 μm) and NII (122μm) (ISO data) in terms of PDRs.

Other Xgal PDRs(Kramer et al., 2005, A&A 441, 961)

The best fits to the latter ratios yield densities of 104 cm−3 and FUV fields of G∼ 0 = 20–30 times the average interstellar field. At the outer positions, the observed total infrared intensities are in agreement with the derived best fitting FUV intensities. Theratio of the two intensities lies at 4–5 at the nuclei, indicating the presence of other mechanisms heating the dust

The study of the physics and chemistry of PDRs is useful, even necessary, for the comprehension of the evolution of the ISM in our Galaxy and external galaxies.

Conclusion