Detection of the H92<i>α</i>recombination line from the starbursts in the Circinus galaxy and NGC 1808

Roy, A. L.; Goss, W. M.; Anantharamaiah, K. R.

doi:10.1051/0004-6361:20077405

Cited by 17 publications

(17 citation statements)

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“…Our observation of NGC 4945 reported here was the third detection made in our ATCA survey for H92α emission. The other two detections from this survey (NGC 3256 and the Circinus galaxy) were reported by Roy et al (2005, and2008). NGC 4945 has proven to be the strongest known extragalactic RRL emitter on the sky.…”

Section: Introductionsupporting

confidence: 51%

“…There are now 15 known extragalactic RRL detections (including NGC 4945), all in bright starburst galaxies, which are listed by Roy et al (2008). Most of those detections resulted from improving the search sensitivity by a factor of ten during the 1990s and by making surveys of promising bright candidates using the Very Large Array (VLA) and ATCA.…”

Section: Introductionmentioning

confidence: 99%

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Detection of the H92αrecombination line from NGC 4945

Roy

Oosterloo

Goss³

et al. 2010

A&A

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Context. Hydrogen ionized by young, high-mass stars in starburst galaxies radiates radio recombination lines (RRLs), whose strength can be used as a diagnostic of the ionization rate, conditions and gas dynamics in the starburst region, without problems of dust obscuration. However, the lines are weak and only few extragalactic starburst systems have been detected. Aims. We aimed to increase the number of known starburst systems with detectable RRLs for detailed studies, and we used the line properties to study the gas properties and dynamics. Methods. We searched for the RRLs H91α and H92α with rest frequencies of 8.6 GHz and 8.3 GHz in the nearby southern Seyfert galaxy NGC 4945 using the Australia Telescope Compact Array with resolution of 3 . This yielded a detection from which we derived conditions in the starburst regions. Results. We detected RRLs from the nucleus of NGC 4945 with a peak line strength integrated over the source of 17.8 mJy, making it the strongest extragalactic RRL emitter known at this frequency. The line and continuum emission from NGC 4945 can be matched by a model consisting of a collection of 10 to 300 H II regions with temperatures of 5000 K, densities of 10 3 cm −3 to 10 4 cm −3 and a total effective diameter of 2 pc to 100 pc. The Lyman continuum production rate required to maintain the ionization is 6 × 10 52 s −1 to 3 × 10 53 s −1 , which requires 2000 to 10 000 O5 stars to be produced in the starburst, inferring a star formation rate of 2 M yr −1 to 8 M yr −1 . We resolved the rotation curve within the central 70 pc region and this is well described by a set of rotating rings that were coplanar and edge on. We found no reason to depart from a simple flat rotation curve. The rotation speed of 120 km s −1 within the central 1 (19 pc) radius infers an enclosed mass of 3 × 10 7 M , and an average surface density with the central 19 pc of 25 000 pc −2 , which exceeds the threshold gas surface density for star formation. Conclusions. We discovered RRLs from NGC 4945. It is the strongest known extragalactic RRL emitter and is suited to high-quality spectroscopic study. We resolved the dynamics of the ionized gas in the central 70 pc and derived conditions and star formation rates in the ionized gas.

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Section: Introductionsupporting

confidence: 51%

Section: Introductionmentioning

confidence: 99%

Detection of the H92αrecombination line from NGC 4945

Roy

Oosterloo

Goss³

et al. 2010

A&A

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“…The ionized gas mass is obtained from the integrated Hα flux of the ionization cone within the central 30 × 30 arcsec 2 (Elmouttie et al 1998a). Since most of the ionized gas appears to reside in the ionization cone and starburst ring, within a radius of ≈ 300 pc (Marconi et al 1994), we do not envision the total ionized gas mass competing with that of the neutral gas (recently, Roy, Goss & Anantharamaiah 2008 estimate an ionized gas mass of between 3 × 10 3 and 1 × 10 6 M ⊙ within a radius of 0.7 kpc). For the stellar mass content we have simply used the value typical for a large spiral and the dust mass is estimated from the gas‐to‐dust ratio given by Schmidt & Boller (1993).…”

Section: Masses In Circinusmentioning

confidence: 99%

The large-scale atomic and molecular gas in the Circinus galaxy

Curran¹,

Koribalski²,

Bains³

2008

Monthly Notices of the Royal Astronomical Society

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We have used the Australia Telescope Compact Array (ATCA) and the Swedish–ESO Submillimetre Telescope (SEST) to map the large‐scale atomic and molecular gas in the nearby (4 Mpc) Circinus galaxy. The ATCA H i mosaic of Circinus exhibits the warps in position angle and inclination revealed in the single‐pointing image of Jones et al., both of which appear to settle beyond the inner 30 kpc which was previously imaged. The molecular gas has been mapped in both the CO J= 1 → 0 and J= 2 → 1 transitions down to a column density of (3σ), where we derive a total molecular gas mass of . Within a radius of 3 kpc, i.e. where CO was clearly detected, the molecular fraction climbs steeply from ≈ 0.7 to unity (where , cf. NH i= 1021 cm−2) with proximity to the nucleus. Our H i mosaic gives an atomic gas mass of MH i≈ 6 × 109 M⊙, which is 70 per cent of the fully mapped single dish value. Combining the atomic and molecular gas masses gives a total gas mass of , cf. the total dynamical mass of ≈ 3 × 1011 M⊙ within the inner 50 kpc of our mosaiced image. The total neutral gas mass to dynamical mass ratio is therefore 3 per cent, consistent with the SAS3 (Third Small Astronomy Satellite) classification of Circinus. The high (molecular) gas mass fraction of per cent found by Curran et al., only occurs close to the central ≈ 0.5 kpc and falls to ≲10 per cent within and outwith this region, allaying previous concerns regarding the validity of applying the Galactic conversion ratio to Circinus. The rotation curve, as traced by both the H i and CO, exhibits a steep dip at ≈ 1 kpc, the edge of the atomic/molecular ring, within which the starburst is occurring. We find the atomic and molecular gases to trace different kinematical features and believe that the fastest part (≳130 km s−1) of the subkpc ring consists overwhelmingly of molecular gas. Beyond the inner kpc, the velocity climbs to settle into a solid body rotation of ≈ 150 km s−1 at ≳10 kpc. Most of the starlight emanates from within this radius and so much of the dynamical mass, which remains climbing to the limit of our data (≳50 kpc), must be due to the dark matter halo.

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“…Work by Anantharamaiah and collaborators established the Very Large Array (VLA) as a powerful instrument for extragalactic RRL observations (e.g., Anantharamaiah et al 1993;Zhao et al 1996;Zhao et al 1997;Phookun et al 1998;Anantharamaiah et al 2000;Das et al 2001;Mohan et al 2001Mohan et al , 2002Roy et al 2005;Mohan et al 2005;Roy et al 2008). 1 Most of these observations were at frequencies 8.3 GHz; this was the highest frequency for which the VLA correlator had a large enough velocity coverage to observe the entire line using a single correlator tuning.…”

Section: Introductionmentioning

confidence: 99%

Unveiling Extragalactic Star Formation Using Radio Recombination Lines: An Expanded Very Large Array Pilot Study With NGC 253

Kepley

Chomiuk

Johnson

et al. 2011

ApJ

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Radio recombination lines (RRLs) are powerful, extinction-free diagnostics of the ionized gas in young, star-forming regions. Unfortunately, these lines are difficult to detect in external galaxies. We present the results of EVLA observations of the RRL and radio continuum emission at 33 GHz from NGC 253, a nearby nuclear starburst galaxy. We detect the previously unobserved H58α and H59α RRLs and make simultaneous sensitive measurements of the continuum. We measure integrated line fluxes of 44.3 ± 0.7 W m −2 and 39.9 ± 0.8 W m −2 for the H58α and H59α lines, respectively. The thermal gas in NGC 253 is kinematically complex with multiple velocity components. We constrain the density of the thermal gas to 1.4 − 4 × 10 4 cm −3 and estimate an ionizing photon flux of 1 × 10 53 s −1 . We use the RRL kinematics and the derived ionizing photon flux to show that the nuclear region of NGC 253 is not gravitationally bound, which is consistent with the outflow of gas inferred from the X-ray and Hα measurements. The line profiles, fluxes, and kinematics of the H58α and H59α lines agree with those of RRLs at different frequencies confirming the accuracy of the previous, more difficult, high frequency observations. We find that the EVLA is an order of magnitude more efficient for extragalactic RRL observations than the VLA. These observations demonstrate both the power of the EVLA and the future potential of extragalactic RRL studies with the EVLA.

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Detection of the H92αrecombination line from the starbursts in the Circinus galaxy and NGC 1808

Cited by 17 publications

References 50 publications

Detection of the H92αrecombination line from NGC 4945

Detection of the H92αrecombination line from NGC 4945

The large-scale atomic and molecular gas in the Circinus galaxy

Unveiling Extragalactic Star Formation Using Radio Recombination Lines: An Expanded Very Large Array Pilot Study With NGC 253

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