CO
                    <sup>+</sup>
                    in M82: A Consequence of Irradiation by X-Rays

Spaans, Marco; Meijerink, R.

doi:10.1086/520535

Cited by 24 publications

(14 citation statements)

References 18 publications

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“…In more extreme regions such as the photon dominated regions (PDRs) of the starburst galaxy M82 and near the nucleus of the Seyfert galaxy NGC1068, this ratio is found to range between 44 and 1 (Fuente et al 2008;Usero et al 2004). In no source has HOC + yet been found to be more abundant than HCO + and chemical models do not find this even in extreme X-ray dominated regions (Spaans & Meijerink 2007;Bayet et al 2011). We therefore conclude that HCO + is self-absorbed in Zw049.057 and in IC860.…”

Section: Appendix A: Self-absorbed Hcn and Hco + Linesmentioning

confidence: 65%

Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN

Aalto

Martín

Costagliola

et al. 2015

A&A

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We present high resolution (0. ′′ 4) IRAM PdBI and ALMA mm and submm observations of the (ultra) luminous infrared galaxies ((U)LIRGs) IRAS17208-0014, Arp220, IC860 and Zw049.057 that reveal intense line emission from vibrationally excited (ν 2 =1) J=3-2 and 4-3 HCN. The emission is emerging from buried, compact (r <17-70 pc) nuclei that have very high implied mid-infrared surface brightness >5 × 10 13 L ⊙ kpc −2 . These nuclei are likely powered by accreting supermassive black holes (SMBHs) and/or hot (>200 K) extreme starbursts. Vibrational, ν 2 =1, lines of HCN are excited by intense 14 µm mid-infrared emission and are excellent probes of the dynamics, masses, and physical conditions of (U)LIRG nuclei when H 2 column densities exceed 10 24 cm −2 . It is clear that these lines open up a new interesting avenue to gain access to the most obscured AGNs and starbursts. Vibrationally excited HCN acts as a proxy for the absorbed mid-infrared emission from the embedded nuclei, which allows for reconstruction of the intrinsic, hotter dust SED. In contrast, we show strong evidence that the ground vibrational state (ν=0), J=3-2 and 4-3 rotational lines of HCN and HCO + fail to probe the highly enshrouded, compact nuclear regions owing to strong self-and continuum absorption. The HCN and HCO + line profiles are double-peaked because of the absorption and show evidence of non-circular motions -possibly in the form of in-or outflows. Detections of vibrationally excited HCN in external galaxies are so far limited to ULIRGs and early-type spiral LIRGs, and we discuss possible causes for this. We tentatively suggest that the peak of vibrationally excited HCN emission is connected to a rapid stage of nuclear growth, before the phase of strong feedback.

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Section: Appendix A: Self-absorbed Hcn and Hco + Linesmentioning

confidence: 65%

Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN

Aalto

Martín

Costagliola

et al. 2015

A&A

Self Cite

112

183

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“…Is X-ray chemistry at work in M 82? Spaans & Meijerink (2007) proposed that the diffuse X-ray emission at 0.7 keV could contribute to produce the high abundances of reactive ions measured towards M 82. To obtain a deeper insight into the chemistry of these ions, we compared our high-angular resolution HOC + image with the spatial distribution of the X-ray emission.…”

Section: Discussionmentioning

confidence: 99%

On the chemistry and distribution of HOC$\mathsf{^+}$ in M 82

Fuente¹,

García‐Burillo²,

Usero

et al. 2008

A&A

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Context. The molecular gas composition in the inner 1 kpc disk of the starburst galaxy M 82 resembles that of Galactic Photon Dominated Regions (PDRs). In particular, large abundances of the reactive ions HOC + and CO + have been measured in the nucleus of this galaxy. Two explanations have been proposed for such high abundances: the influence of intense UV fields from massive stars, or a significant role of X-Rays. Aims. Our aim is to investigate the origin of the high abundances of reactive ions in M 82. Methods. We have completed our previous 30 m HOC + J = 1 → 0 observations with the higher excitation HCO + and HOC + J = 4 → 3 and 3 → 2 rotational lines. In addition, we have obtained with the IRAM Plateau de Bure Interferometer (PdBI) a 4 resolution map of the HOC + emission in M 82, the first ever obtained in a Galactic or extragalactic source. Results. Our HOC + interferometric image shows that the emission of the HOC + 1 → 0 line is mainly restricted to the nuclear disk, with the maxima towards the E and W molecular peaks. In addition, line excitation calculations imply that the HOC + emission arises in dense gas (n ≥ 10 4 cm −3 ). Therefore, the HOC + emission is arising in the dense PDRs embedded in the M 82 nuclear disk, rather than in the intercloud phase and/or wind. Conclusions. We have improved our previous chemical model of M 82 by (i) using the new version of the Meudon PDR code; (ii) updating the chemical network; and (iii) considering two different types of clouds (with different thickness) irradiated by the intense interstellar UV field (G 0 = 10 4 in units of the Habing field) prevailing in the nucleus of M 82. Most molecular observations (HCO + , HOC + , CO + , CN, HCN, H 3 O + ) are well explained assuming that ∼87% of the mass of the molecular gas is forming small clouds (A v = 5 mag) while only ∼13% of the mass is in large molecular clouds (A v = 50 mag). Such a small number of large molecular clouds suggests that M 82 is an old starburst, where star formation has almost exhausted the molecular gas reservoir.

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“…The second is the value estimated by Suchkov et al (1993) to account for the physical conditions of the molecular gas in M 82. We are aware that X-rays are intense and could also play an important role in the chemistry (Fuente et al 2008;Spaans & Meijerink 2007). Our code does not include the X-rays in the chemical calculations.…”

Section: Chemical Modelmentioning

confidence: 99%

Chemical footprint of star formation feedback in M 82 on scales of ~100 pc

Ginard

Fuente

García‐Burillo

et al. 2015

A&A

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Context. M 82 is one of the nearest and brightest starburst galaxies. It has been extensively studied in the past decade and by now is considered the prototypical extragalactic photon-dominated region (PDR) and a reference for studying star formation feedback. Aims. Our aim is to characterize the molecular chemistry in M 82 at spatial scales of giant molecular clouds (GMCs), ∼100 pc, to investigate the feedback effects of the star formation activity. Methods. We present interferometric observations of the CN 1 → 0 (113.491 GHz), N 2 H + 1 → 0 (93.173 GHz), H (41) + ] ratio can be explained as the consequence of differences in the local intestellar UV field and in the average cloud sizes within the nucleus of the galaxy. Conclusions. Our high spatial resolution imaging of the starburst galaxy M 82 shows that the star formation activity has a strong impact on the chemistry of the molecular gas. In particular, the entire nucleus behaves as a giant PDR whose chemistry is determined by the local UV flux. The detection of N 2 H + shows the existence of a population of clouds with A v > 20 mag all across the galaxy plane. These clouds constitute the molecular gas reservoir for the formation of new stars and, although it is distributed throughout the nucleus, the highest concentration occurs in the outer x1 bar orbits (R ∼ 280 pc).

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CO ⁺ in M82: A Consequence of Irradiation by X-Rays

Cited by 24 publications

References 18 publications

Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN

Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN

On the chemistry and distribution of HOC$\mathsf{^+}$ in M 82

Chemical footprint of star formation feedback in M 82 on scales of ~100 pc

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CO + in M82: A Consequence of Irradiation by X-Rays

Cited by 24 publications

References 18 publications

Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN

Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN

On the chemistry and distribution of HOC$\mathsf{^+}$ in M 82

Chemical footprint of star formation feedback in M 82 on scales of ~100 pc

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CO ⁺ in M82: A Consequence of Irradiation by X-Rays