Importance of the bonus lines (depends on excitation) - IRAM

36 Pages·2013·3.27 MB·English

7th IRAM 30m Summer School
Photon Dominated Regions
III. Chemistry
A. Fuente
Observatorio Astronómico Nacional (OAN, Spain)
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 , it has been
sun
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 , CH OH, CH CN, HNCO, and SiO (Mauesberger & Henkel 1989,
3 3 3
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 estimated a UV field of G =104 in units of the Habing field
0
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
M 82: XDR or PDR?
(Spaans & Meijerink 2007, ApJ 664, L23)
Detection of H O+
3
(van der Tak et al. 2008, ApJ 492, L675)
Van der Tak et al. (2008) detected H O+ using the JCMT. They
3
concluded in agreement with our results, that the H O+ abundance is
3
consistent with that expected in a PDR with enhanced cosmic ray
flux.
Interferometric observations of M 82
(Fuente et al. 2008, ApJ 492, L675)
The HOC+ emission comes 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.