arXiv subjects

Ryan W. Pfeifle

Publications and source records attributed to Ryan W. Pfeifle.

23 records · Page 2Linked to original sources

arXiv2020

The Discovery of a Hidden Broad Line AGN in a Bulgeless Galaxy: Keck NIR Spectroscopic Observations of SDSS J085153.64+392611.76

We report the discovery of a buried, active supermassive black hole in SDSS J085153.64+392611.76, a bulgeless Seyfert 2 (Sy2) galaxy. Keck near-infrared observations reveal a hidden broad line region, allowing for the rare case where strong constraints can be placed on both the black hole mass and bulge component. Using virial mass estimators, we obtain a black hole mass of log($M_{\rm{BH}}/M_{\odot}$) = $6.78 \pm 0.50$. This is one of the only Sy2 AGN hosted in a bulgeless galaxy with a virial black hole mass estimate and could provide important constraints on the formation scenarios of the black hole seed population. The lack of a bulge component suggests that the SMBH has grown quiescently, likely caused by secular processes independent of major mergers. In the absence of a detectable bulge component, we find the $M_{\rm{BH}}$ - $M_{\rm{stellar}}$ relation to be more reliable than the $M_{\rm{BH}}$ - $M_{\rm{bulge}}$ relation. In addition, we detect extended narrow Pa$α$ emission that allows us to create a rotation curve where we see counter-rotating gas within the central kiloparsec (kpc). Possible causes of this counter-rotation include a galactic bar or disruption of the inner gas by a recent fly-by of a companion galaxy. This in turn could have triggered accretion onto the central SMBH in the current AGN phase.

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arXiv2020

Multi-wavelength observations of SDSS J105621.45+313822.1, a broad-line, low-metallicity AGN

In contrast to massive galaxies with Solar or super-Solar gas phase metallicities, very few Active Galactic Nuclei (AGN) are found in low-metallicity dwarf galaxies. Such a population could provide insight into the origins of supermassive black holes. Here we report near-infrared spectroscopic and X-ray observations of SDSS J105621.45+313822.1, a low-mass, low-metallicity galaxy with optical narrow line ratios consistent with star forming galaxies but a broad H$α$ line and mid-infrared colors consistent with an AGN. We detect the [Si VI] 1.96$μ$m coronal line and a broad Pa$α$ line with a FWHM of $850 \pm 25$~km~s$^{-1}$. Together with the optical broad lines and coronal lines seen in the SDSS spectrum, we confirm the presence of a highly accreting black hole with mass $(2.2 \pm 1.3) \times 10^{6}$~M$_{\odot}$, with a bolometric luminosity of $\approx10^{44}$~erg~s$^{-1}$ based on the coronal line luminosity, implying a highly accreting AGN. Chandra observations reveal a weak nuclear point source with $L_{\textrm{X,2-10 keV}} = (2.3 \pm 1.2) \times 10^{41}$~erg~s$^{-1}$, $\sim 2$ orders of magnitude lower than that predicted by the mid-infrared luminosity, suggesting that the AGN is highly obscured despite showing broad lines in the optical spectrum. The low X-ray luminosity and optical narrow line ratios of J1056+3138 highlight the limitations of commonly employed diagnostics in the hunt for AGNs in the low metallicity low mass regime.

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arXiv2019

Very long baseline interferometry observation of the triple AGN candidate J0849+1114

In the hierarchical structure formation model, galaxies grow through various merging events. Numerical simulations indicate that the mergers can enhance the activity of the central supermassive black holes in the galaxies. Pfeifle et al. (2019a) identified a system of three interacting galaxies, J0849$+$1114, and provided multiwavelength evidence of all three galaxies containing active galactic nuclei. The system has substantial radio emission, and with high-resolution radio interferometric observation we aimed to investigate its origin, whether it is related to star formation or to one or more of the active galactic nuclei in the system. We performed high-resolution continuum observation of J0849$+$1114 with the European Very Long Baseline Interferometry Network at $1.7$ GHz. We detected one compact radio emitting source at the position of the easternmost nucleus. Its high brightness temperature and radio power indicate that the radio emission originates from a radio-emitting active galactic nucleus. Additionally, we found that significant amount of flux density is contained in $\sim 100$ milliarcsec-scale feature related to the active nucleus.

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arXiv2019

A Triple AGN in a Mid-Infrared Selected Late Stage Galaxy Merger

The co-evolution of galaxies and the supermassive black holes (SMBHs) at their centers via hierarchical galaxy mergers is a key prediction of $Λ$CDM cosmology. As gas and dust are funneled to the SMBHs during the merger, the SMBHs light up as active galactic nuclei (AGNs). In some cases, a merger of two galaxies can encounter a third galaxy, leading to a triple merger, which would manifest as a triple AGN if all three SMBHs are simultaneously accreting. Using high-spatial resolution X-ray, near-IR, and optical spectroscopic diagnostics, we report here a compelling case of an AGN triplet with mutual separations < 10 kpc in the advanced merger SDSS J084905.51+111447.2 at z = 0.077. The system exhibits three nuclear X-ray sources, optical spectroscopic line ratios consistent with AGN in each nucleus, a high excitation near-IR coronal line in one nucleus, and broad Pa$α$ detections in two nuclei. Hard X-ray spectral fitting reveals a high column density along the line of sight, consistent with the picture of late-stage mergers hosting heavily absorbed AGNs. Our multiwavelength diagnostics support a triple AGN scenario, and we rule out alternative explanations such as star formation activity, shock-driven emission, and emission from fewer than three AGN. The dynamics of gravitationally bound triple SMBH systems can dramatically reduce binary SMBH inspiral timescales, providing a possible means to surmount the "Final Parsec Problem." AGN triplets in advanced mergers are the only observational forerunner to bound triple SMBH systems and thus offer a glimpse of the accretion activity and environments of the AGNs prior to the gravitationally-bound triple phase.

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arXiv2019

Buried Black Hole Growth in IR-selected Mergers: New Results from Chandra

Observations and theoretical simulations suggest that a significant fraction of merger-triggered accretion onto supermassive black holes is highly obscured, particularly in late-stage galaxy mergers, when the black hole is expected to grow most rapidly. Starting with the Wide-Field Infrared Survey Explorer all-sky survey, we identified a population of galaxies whose morphologies suggest ongoing interaction and which exhibit red mid-infrared colors often associated with powerful active galactic nuclei (AGNs). In a follow-up to our pilot study, we now present Chandra/ACIS and XMM-Newton X-ray observations for the full sample of the brightest 15 IR-preselected mergers. All mergers reveal at least one nuclear X-ray source, with 8 out of 15 systems exhibiting dual nuclear X-ray sources, highly suggestive of single and dual AGNs. Combining these X-ray results with optical line ratios and with near-IR coronal emission line diagnostics, obtained with the near-IR spectrographs on the Large Binocular Telescope, we confirm that 13 out of the 15 mergers host AGNs, two of which host dual AGNs. Several of these AGNs are not detected in the optical. All X-ray sources appear X-ray weak relative to their mid-infrared continuum, and of the nine X-ray sources with sufficient counts for spectral analysis, eight reveal strong evidence of high absorption with column densities of $N_\mathrm{H} \gtrsim 10^{23}$~cm$^{-2}$. These observations demonstrate that a significant population of single and dual AGNs are missed by optical studies, due to high absorption, adding to the growing body of evidence that the epoch of peak black hole growth in mergers occurs in a highly obscured phase.

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