New detections of Galactic molecular absorption systems toward ALMA calibrator sources

Ando, Ryo; Kohno, Kotaro; Tamura, Motohide; Izumi, Teruo; Umehata, Hideki; Nagai, Hiroshi

doi:10.1093/pasj/psv110

Cited by 16 publications

(28 citation statements)

References 36 publications

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“…Absorption from CS and H 13 CO + was not detected and will not be further discussed. H 2 column densities N(H 2 ) are derived from the absorption line profile of HCO + using N(HCO + ) = 1.10 × 10 12 cm −2 τ dv with the profile integral in units of km s −1 (Ando et al, 2016;Gerin & Liszt, 2017). N(HCO + ) is derived under the assumption that the rotational excitation temperature is that of the cosmic microwave background, which is justified by the weakness of HCO + emission in diffuse molecular gas, even when the absorption is quite optically thick (Liszt, 2012;Liszt & Pety, 2016).…”

Section: New Alma Absorption Measurements and H 2 Column Densitiesmentioning

confidence: 99%

Molecular gas and dark neutral medium in the outskirts of Chamaeleon

Liszt

Gérin

Grenier

2018

A&A

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Context. More gas is inferred to be present in molecular cloud complexes than can be accounted for by HI and CO emission, a phenomenon known as dark neutral medium (DNM) or CO-dark gas for the molecular part. Aims. To see if molecular gas can be detected in Chamaeleon where gas column densities in the DNM were inferred and CO emission was not detected. Methods. We took λ3mm absorption profiles of HCO + and other molecules toward thirteen background quasars across the Chamaeleon complex, only one of which had detectable CO emission. We derived the H 2 column density assuming N(HCO + )/N(H 2 )= 3 × 10 −9 as before.Results. With the possible exception of one weak continuum target, HCO + absorption was detected in all directions, C 2 H in 8 directions and HCN in 4 directions. The sightlines divide in two groups according to their DNM content with one group of eight directions having N(DNM) > ∼ 2×10 20 cm −2 and another group of five directions having N(DNM) < 0.5×10 20 cm −2 . The groups have comparable mean N(HI) associated with Chamaeleon 6 − 7 × 10 20 cm −2 and total hydrogen column density per unit reddening 6 − 7 × 10 21 cm −2 mag −1 . They differ, however, in having quite different mean reddening 0.33 vs 0.18 mag, mean N(DNM) 3.3 vs 0.14 ×10 20 cm −2 and mean molecular column density 2N(H 2 ) = 5.6 vs 0.8 ×10 20 cm −2 . The gas at more positive velocities is enriched in molecules and DNM.Conclusions. Overall the quantity of H 2 inferred from HCO + can fully account for the previously-inferred DNM along the sightlines studied here. H 2 is concentrated in the high-DNM group, where the molecular fraction is 46% vs. 13% otherwise and 38% overall. Thus, neutral gas in the outskirts of the complex is mostly atomic but the DNM is mostly molecular. Saturation of the HI emission line profile may occur along 3 of the 4 sightlines having the largest DNM column densities but there is no substantial reservoir of "dark" atomic or molecular gas that remains undetected as part of the inventory of dark neutral medium.

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Section: New Alma Absorption Measurements and H 2 Column Densitiesmentioning

confidence: 99%

Molecular gas and dark neutral medium in the outskirts of Chamaeleon

Liszt

Gérin

Grenier

2018

A&A

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“…Again we need to expand the sample of Galactic absorption systems with such rare species to obtain a comprehensive picture of the diffuse molecular media within the Galaxy, but a survey of new molecular absorption systems is always very time consuming and entails a significant risk of non-detection. Ando et al (2015) propose using the ALMA archive to search for new molecular absorption systems in mm/submm wavelengths, because the ALMA archive already offers a vast number of sensitive mm/submm spectra of extragalactic continuum sources, i.e., bandpass and/or visibility calibrators, which are essentially radio-loud quasars including BL-LAC objects. Because of the enormous improvement in sensitivity provided by ALMA, these calibrators in the ALMA archive are potentially ideal free lunch in the quest for molecular absorption systems from the Galaxy to the high-z universe without any new investment of observing time!…”

Section: Alma Detections Of New Galactic Molecular Absorption Systemsmentioning

confidence: 99%

“…Elevated HCN/HCO + ratios in massive (and presumably shocked) molecular outflows driven by the powerful AGN in Mrk 231 would be consistent with this view Figure 3. Column density ratios of HCO to H 13 CO + as a function of the column density of H 13 CO + , including two new detections of HCO absorption (J1717-337 and NRAO530; Ando et al 2015). Molecular absorption systems toward J1717-337, NRAO530, 3C111, and BL-LAC show elevated HCO/H 13 CO + column density ratios similar to the value in the Horsehead Nebula (Gerin et al 2009), indicating that the diffuse media in the Galaxy seen toward these radio sources are exposed in the intense UV field.…”

Section: Unveiling the Nature Of Obscured Galaxiesmentioning

confidence: 99%

“…Molecular absorption systems toward J1717-337, NRAO530, 3C111, and BL-LAC show elevated HCO/H 13 CO + column density ratios similar to the value in the Horsehead Nebula (Gerin et al 2009), indicating that the diffuse media in the Galaxy seen toward these radio sources are exposed in the intense UV field. Figure modified from Ando et al (2015).…”

Section: Unveiling the Nature Of Obscured Galaxiesmentioning

confidence: 99%

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High resolution ALMA observations of dense molecular medium in the central regions of active galaxies

et al. 2015

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Abstract. In the central regions of active galaxies, dense molecular medium are exposed to various types of radiation and energy injections, such as UV, X-ray, cosmic ray, and shock dissipation. With the rapid progress of chemical models and implementation of new-generation mm/submm interferometry, we are now able to use molecules as powerful diagnostics of the physical and chemical processes in galaxies. Here we give a brief overview on the recent ALMA results to demonstrate how molecules can reveal underlying physical and chemical processes in galaxies. First, new detections of Galactic molecular absorption systems with elevated HCO/H 13 CO + column density ratios are reported, indicating that these molecular media are irradiated by intense UV fields. Second, we discuss the spatial distributions of various types of shock tracers including HNCO, CH3OH and SiO in NGC 253 and NGC 1068. Lastly, we provide an overview of proposed diagnostic methods of nuclear energy sources using ALMA, with an emphasis on the synergy with sensitive mid-infrared spectroscopy, which will be implemented by JWST and SPICA to disentangle the complex nature of heavily obscured galaxies across the cosmic time.

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“…extragalactic sources lying in front of background quasars (squares), Sagittarius B2 (crosses), and the Milky Way (pentagons). The original data are taken fromWiklind & Combes (1997a, 1996b,a, 1997b;Muller et al (2011);Greaves & Nyman (1996);Lucas & Liszt (1994, 1996;Liszt & Lucas (2001);Godard et al (2010);Ando et al (2016);Riquelme et al (2018).…”

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confidence: 99%

A molecular absorption line survey toward the AGN of Hydra-A

Rose,

Edge,

Combes

et al. 2020

Preprint

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We present Atacama Large Millimeter/submillimeter Array observations of the brightest cluster galaxy Hydra-A, a nearby (z = 0.054) giant elliptical galaxy with powerful and extended radio jets. The observations reveal CO(1-0), CO(2-1), 13 CO(2-1), CN(2-1), SiO(5-4), HCO + (1-0), HCO + (2-1), HCN(1-0), HCN(2-1), HNC(1-0) and H 2 CO(3-2) absorption lines against the galaxy's bright and compact active galactic nucleus. These absorption features are due to at least 12 individual molecular clouds which lie close to the centre of the galaxy and have velocities of approximately −50 to +10 km s −1 relative to its recession velocity, where positive values correspond to inward motion. The absorption profiles are evidence of a clumpy interstellar medium within brightest cluster galaxies composed of clouds with similar column densities, velocity dispersions and excitation temperatures to those found at radii of several kpc in the Milky Way. We also show potential variation in a ∼ 10 km s −1 wide section of the absorption profile over a two year timescale, most likely caused by relativistic motions in the hot spots of the continuum source which change the background illumination of the absorbing clouds.

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New detections of Galactic molecular absorption systems toward ALMA calibrator sources

Cited by 16 publications

References 36 publications

Molecular gas and dark neutral medium in the outskirts of Chamaeleon

Molecular gas and dark neutral medium in the outskirts of Chamaeleon

High resolution ALMA observations of dense molecular medium in the central regions of active galaxies

A molecular absorption line survey toward the AGN of Hydra-A

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