Download Importance of the bonus lines (depends on excitation)

Determining the dynamics of the
ultracompact HII region (UCHII)
Monoceros R2
A. Fuente
Observatorio 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
Mol. bar
FIRS 1
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-C3H2, some dynamics
Rizzo et al. (2005, ApJ 634, 1133)
c-C3H2
C1
5 105 cm-3
C2
>5 106 cm-3
Probing the dense expanding layer around the UCHII region
C1
C2
Different excitation properties:
C1 n(H2) about 5 105 cm-3
C2 n(H2) always > 5 106 cm -3
Different chemical properties
C2 only detected in PDR tracers
Spitzer data (PAHs and H2)
Berné et al. (2009), ApJ 706, L160
Bright, extended emission of the PAHs bands and H2 rotational lines
Layered structure expected in a PDR
Different PDRs around UCHII region (different physical and
chemical conditions)
G0 and nH estimates from PAHs and H2
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
Mol. bar
FIRS 1
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+, H2O+, NH, 13CII, H218O
Massive star forming region
Massive star forming region
12CO
9-8
o-NH3 10-00
13CO
10-9
o-H2O 110-001
CII
p-H2O 111-00o
Modeling water in Mon 2
Pilleri et al. 2011 (in preparation)
D=830 pc
Compact 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 model
Non local radiative transfer ( Cernicharo et al. 2006, ApJ 642, 940)
Modeling water in Mon 2
Pilleri et al. 2011 (in preparation)
Meudon PDR code v1.4.1 (Bourlot et al. 2006)
High velocity expanding layer
Tk >100 K
X(o-H2O) ≈10-7
Low velocity molecular cloud
Tk <100 K
X(o-H2O)≈ 10-8
Absorption lines (OH+,H2O+)
OH+ absorption at redshifted and
blueshifted velocities
Expansion
Collapse
The only way to explain the
redshifted absorption is to
assume the existence of a
collapsing outer low density
envelope.
Absorption lines (OH+,H2O+)
[OH+]/[H2O+]=0.8
f(H2)=0.07
Similar to diffuse clouds
(see Gerin et al. 2010)
Conclusions
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 layer
Traced 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
3mm IRAM spectral survey
Ginard et al. 2011 (in preparation)
Three targetted positions:
(i) IF
(ii) Molecular Bar
(iii) PAH peak
2 MHz -> 6 km/s
IF
IF
IF
List of detected species
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.
The fragmented ISM in the nucleus of M 82
A. Fuente
Observatorio 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 Lsun , 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
NH3 , CH3 OH, CH3 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 G0 =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)
M 82
(García-Burillo et al. 2002, ApJ 575, L55)
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.
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
M 51
Other Xgal PDRs (M51 and M83)
M 83
Tony & Daphne Hallas
Stephane Guisard & Robert Gendler
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 ∼G0 = 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. The
ratio of the two intensities lies at 4–5 at the
nuclei, indicating the presence of other
mechanisms heating the dust
Conclusion
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.