Was 49b: An Overmassive AGN in a Merging Dwarf Galaxy?

Secrest, Nathan J.; Schmitt, Henrique R.; Blecha, Laura; Rothberg, Barry; Fischer, J.

doi:10.3847/1538-4357/836/2/183

Cited by 28 publications

(38 citation statements)

References 104 publications

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“…The velocities of the optical emission lines from the two nuclei differ by ∼70 km s −1 . The extreme luminosity of Was 49b is unusual for an AGN in the smaller galaxy of a minor-merger system (Secrest et al 2017). Was 49b is also radio-loud, and its radio emission is resolved in our GMRT 1.4 GHz continuum map.…”

Section: J1214+2931mentioning

confidence: 74%

Prevalence of neutral gas in centres of merging galaxies

Dutta

Srianand

Gupta

2018

Monthly Notices of the Royal Astronomical Society

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We present Giant Metrewave Radio Telescope and Very Large Array observations of H i 21-cm absorption in ten z 0.2 galaxy mergers that host strong radio sources. Seven of these mergers show strong absorption [with N (H i) ∼ 10 21−22 cm −2 , for spin temperature of 100 K and unit covering factor], leading to a total detection rate of 83 ± 17% in low-z radio-loud galaxy mergers. This is ∼ 3 − 4 times higher than that found for intrinsic H i 21-cm absorption in low-z radio sources in general. The fraction of intrinsic absorbers that are associated with mergers increases with increasing N (H i) threshold, i.e. ∼40% and 100% of the absorbers with N (H i) > 10 21 cm −2 and > 10 22 cm −2 arise from mergers, respectively. The distribution of N (H i) among the mergers is significantly different from that found in isolated systems, with mergers giving rise to six times stronger absorption on average. The fraction of redshifted absorption components (with respect to the systemic velocity of the radio source obtained from optical emission lines) among mergers is found to be higher by two to three times compared to that found for non-interacting systems. Follow-up spatially-resolved multi-wavelength spectroscopy is essential to understand the exact connection between the presence of circumnuclear neutral gas and the AGN activity in these mergers.

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Section: J1214+2931mentioning

confidence: 74%

Prevalence of neutral gas in centres of merging galaxies

Dutta

Srianand

Gupta

2018

Monthly Notices of the Royal Astronomical Society

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“…Indeed, only 0.1% of quasars are found in pairs with projected separations of tens to hundreds of kiloparsecs (e.g., Foreman et al 2009;Hennawi et al 2010), and until recently only a handful of confirmed dual AGNs with projected separations less than 10 kpc were known in the universe (e.g., NGC 6240: Komossa et al 2003;Mrk 463: Bianchi et al 2008;Arp 299: Ballo et al 2004;3C 75: Owen et al 1985; Radio Galaxy 0402+379: Rodriguez et al 2006;Was49: Moran et al 1992;Secrest et al 2017), all of which were discovered serendipitously. In the past few years, with the advent of large-scale optical spectroscopic surveys, more systematic surveys of dual AGNs have been possible.…”

Section: The Rarity Of Dual Agnsmentioning

confidence: 99%

“…We demonstrated in our previous study of interacting galaxies (Satyapal et al 2014) that both -> W W 1 2 0.5 and -> W W 1 2 0.8 color cuts produce qualitatively similar results. We note that hydrodynamic merger simulations that include radiative transfer predict that the -W W 1 2 color rises above 0.5 just before the stage of peak black hole growth, where star formation rates (SFRs) are high and where dual AGNs are expected to be found (L. Blecha et al 2017, in preparation; see also Snyder et al 2013;Roebuck et al 2016, for simulations of the mid-infrared spectral energy distribution with varying contributions of AGN and star formation activity), and that a color cut of -> W W 1 2 0.5 is actually more effective at finding dual AGN candidates than is the Blecha et al 2017, in preparation). We emphasize that the adopted color cut of -> W W 1 2 0.5 is optimized to provide the most inclusive sample of merger AGN candidates.…”

Section: Sample Selectionmentioning

confidence: 99%

Buried AGNs in Advanced Mergers: Mid-infrared Color Selection as a Dual AGN Candidate Finder

Satyapal

Secrest

Ricci

et al. 2017

ApJ

Self Cite

132

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A direct consequence of hierarchical galaxy formation is the existence of dual supermassive black holes, which may be preferentially triggered as active galactic nuclei (AGNs) during galaxy mergers. Despite decades of searching, however, dual AGNs are extremely rare, and most have been discovered serendipitously. Using the all-sky WISE survey, we identified a population of over 100 morphologically identified interacting galaxies or mergers that display red mid-infrared colors often associated in extragalactic sources with powerful AGNs. The vast majority of these advanced mergers are optically classified as star-forming galaxies, which suggests that they may represent an obscured population of AGNs that cannot be found through optical studies. In this work, we present Chandra/ACIS observations and near-infrared spectra with the Large Binocular Telescope of six advanced mergers with projected pair separations less than ∼10 kpc. The combined X-ray, near-infrared, and mid-infrared properties of these mergers provide confirmation that four out of the six mergers host at least one AGN, with four of the mergers possibly hosting dual AGNs with projected separations less than ∼10 kpc, despite showing no firm evidence for AGNs based on optical spectroscopic studies. Our results demonstrate that (1) optical studies miss a significant fraction of single and dual AGNs in advanced mergers, and (2) mid-infrared pre-selection is extremely effective in identifying dual AGN candidates in late-stage mergers. Our multi-wavelength observations suggest that the buried AGNs in these mergers are highly absorbed, with intrinsic column densities in excess of~> N 10 H 24 cm −2, consistent with hydrodynamic simulations.

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“…NuS-TAR data allows us to uncover the reflection component of Was 49, that is not constrained with Chandra and Swift-BAT data alone. Was 49 NuSTAR spectrum has been analyzed also by Secrest et al (2017), finding bestfit photon index (Γ=1.6±0.1) and intrinsic absorption (N H =2.3…”

Section: +079mentioning

confidence: 99%

Chandra and NuSTAR Follow-up Observations of Swift-BAT-selected AGNs

Marchesi¹,

Tremblay²,

Ajello³

et al. 2017

ApJ

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Based on current models of the Cosmic X-ray Background (CXB), heavily obscured Active Galactic Nuclei (AGN) are expected to make up ∼ 10% of the peak emission of the CXB and ∼ 20% of the total population of AGN, yet few of these sources have been recorded and characterized in current surveys. Here we present the Chandra follow-up observation of 14 AGN detected by Swift-BAT. For five sources in the sample, NuSTAR observations in the 3-80 keV band are also available. The X-ray spectral fitting over the 0.3-150 keV energy range allows us to determine the main X-ray spectral parameters, such as the photon index and the intrinsic absorption, of these objects, and to make hypotheses on the physical structures responsible for the observed spectra. We find that 13 of the 14 objects are absorbed AGN, and one is a candidate Compton thick AGN, having intrinsic absorption N H > 10 24 cm −2 . Finally, we verified that the use of NuSTAR observations is strategic to strongly constrain the properties of obscured AGN, since the best-fit values we obtained for parameters such as the power-law photon index Γ and the intrinsic absorption N H changed sometimes significantly fitting the spectra with and without the use of NuSTAR data.

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Was 49b: An Overmassive AGN in a Merging Dwarf Galaxy?

Cited by 28 publications

References 104 publications

Prevalence of neutral gas in centres of merging galaxies

Prevalence of neutral gas in centres of merging galaxies

Buried AGNs in Advanced Mergers: Mid-infrared Color Selection as a Dual AGN Candidate Finder

Chandra and NuSTAR Follow-up Observations of Swift-BAT-selected AGNs

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