Dwarf Galaxies with Optical Signatures of Active Massive Black Holes
TL;DR: In this paper, a sample of 151 dwarf galaxies (10^8.5 < M_stellar < 10^9.5 Msun) that exhibit optical spectroscopic signatures of accreting massive black holes (BHs), increasing the number of known active AGN hosts by more than an order of magnitude.
Abstract: We present a sample of 151 dwarf galaxies (10^8.5 < M_stellar < 10^9.5 Msun) that exhibit optical spectroscopic signatures of accreting massive black holes (BHs), increasing the number of known active galaxies in this stellar mass range by more than an order of magnitude. Utilizing data from the Sloan Digital Sky Survey Data Release 8 and stellar masses from the NASA-Sloan Atlas, we have systematically searched for active BHs in ~25,000 emission-line galaxies with stellar masses comparable to the Magellanic Clouds and redshifts z<0.055. Using the narrow-line [OIII]/H-beta versus [NII]/H-alpha diagnostic diagram, we find photoionization signatures of BH accretion in 136 galaxies, a small fraction of which also exhibit broad H-alpha emission. For these broad-line AGN candidates, we estimate BH masses using standard virial techniques and find a range of 10^5 < M_BH < 10^6 Msun and a median of M_BH ~ 2 x 10^5 Msun. We also detect broad H-alpha in 15 galaxies that have narrow-line ratios consistent with star-forming galaxies. Follow-up observations are required to determine if these are true type 1 AGN or if the broad H-alpha is from stellar processes. The median absolute magnitude of the host galaxies in our active sample is Mg = -18.1 mag, which is ~1-2 magnitudes fainter than previous samples of AGN hosts with low-mass BHs. This work constrains the smallest galaxies that can form a massive BH, with implications for BH feedback in low-mass galaxies and the origin of the first supermassive BH seeds.
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TL;DR: In this paper, the precise localization of the repeating fast radio burst (FRB 121102) has provided the first unambiguous association (chance coincidence probability $p\lesssim3\times10^{-4}$) of an optical and persistent radio counterpart.
Abstract: The precise localization of the repeating fast radio burst (FRB 121102) has provided the first unambiguous association (chance coincidence probability $p\lesssim3\times10^{-4}$) of an FRB with an optical and persistent radio counterpart. We report on optical imaging and spectroscopy of the counterpart and find that it is an extended ($0.6^{\prime\prime}-0.8^{\prime\prime}$) object displaying prominent Balmer and [OIII] emission lines. Based on the spectrum and emission line ratios, we classify the counterpart as a low-metallicity, star-forming, $m_{r^\prime} = 25.1$ AB mag dwarf galaxy at a redshift of $z=0.19273(8)$, corresponding to a luminosity distance of 972 Mpc. From the angular size, the redshift, and luminosity, we estimate the host galaxy to have a diameter $\lesssim4$ kpc and a stellar mass of $M_*\sim4-7\times 10^{7}\,M_\odot$, assuming a mass-to-light ratio between 2 to 3$\,M_\odot\,L_\odot^{-1}$. Based on the H$\alpha$ flux, we estimate the star formation rate of the host to be $0.4\,M_\odot\,\mathrm{yr^{-1}}$ and a substantial host dispersion measure depth $\lesssim 324\,\mathrm{pc\,cm^{-3}}$. The net dispersion measure contribution of the host galaxy to FRB 121102 is likely to be lower than this value depending on geometrical factors. We show that the persistent radio source at FRB 121102's location reported by Marcote et al (2017) is offset from the galaxy's center of light by $\sim$200 mas and the host galaxy does not show optical signatures for AGN activity. If FRB 121102 is typical of the wider FRB population and if future interferometric localizations preferentially find them in dwarf galaxies with low metallicities and prominent emission lines, they would share such a preference with long gamma ray bursts and superluminous supernovae.
576 citations
Additional excerpts
...109.5M ) using BPT line diagnostics identified an AGN rate of ∼ 0.5 % (Reines et al. 2013), with an additional 0.05 % of dwarf galaxies searched exhibiting narrow emission lines consistent with star formation band broad Hα consistent with an AGN....
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TL;DR: In this paper, the relationship between BH mass and host galaxy total stellar mass was investigated using a sample of 262 broad-line active galactic nuclei (AGN) in the nearby Universe (z < 0.055), as well as 79 galaxies with dynamical BH masses.
Abstract: Scaling relations between central black hole (BH) mass and host galaxy properties are of fundamental importance to studies of BH and galaxy evolution throughout cosmic time. Here we investigate the relationship between BH mass and host galaxy total stellar mass using a sample of 262 broad-line active galactic nuclei (AGN) in the nearby Universe (z < 0.055), as well as 79 galaxies with dynamical BH masses. The vast majority of our AGN sample is constructed using Sloan Digital Sky Survey spectroscopy and searching for Seyfert-like narrow-line ratios and broad H-alpha emission. BH masses are estimated using standard virial techniques. We also include a small number of dwarf galaxies with total stellar masses M_stellar < 10^9.5 Msun and a sub-sample of the reverberation-mapped AGNs. Total stellar masses of all 341 galaxies are calculated in the most consistent manner feasible using color-dependent mass-to-light ratios. We find a clear correlation between BH mass and total stellar mass for the AGN host galaxies, with M_BH proportional to M_stellar, similar to that of early-type galaxies with dynamically-detected BHs. However, the relation defined by the AGNs has a normalization that is lower by more than an order of magnitude, with a BH-to-total stellar mass fraction of M_BH/M_stellar ~ 0.025% across the stellar mass range 10^8 < M_stellar/Msun < 10^12. This result has significant implications for studies at high redshift and cosmological simulations in which stellar bulges cannot be resolved.
400 citations
TL;DR: The GW190521 signal is consistent with a binary black hole (BBH) merger source at redshift 0.13-0.30 Gpc-3 yr-1.8 as discussed by the authors.
Abstract: The gravitational-wave signal GW190521 is consistent with a binary black hole (BBH) merger source at redshift 0.8 with unusually high component masses, 85-14+21 M o˙ and 66-18+17 M o˙, compared to previously reported events, and shows mild evidence for spin-induced orbital precession. The primary falls in the mass gap predicted by (pulsational) pair-instability supernova theory, in the approximate range 65-120 M o˙. The probability that at least one of the black holes in GW190521 is in that range is 99.0%. The final mass of the merger (142-16+28 M o˙) classifies it as an intermediate-mass black hole. Under the assumption of a quasi-circular BBH coalescence, we detail the physical properties of GW190521's source binary and its post-merger remnant, including component masses and spin vectors. Three different waveform models, as well as direct comparison to numerical solutions of general relativity, yield consistent estimates of these properties. Tests of strong-field general relativity targeting the merger-ringdown stages of the coalescence indicate consistency of the observed signal with theoretical predictions. We estimate the merger rate of similar systems to be 0.13-0.11+0.30 Gpc-3 yr-1. We discuss the astrophysical implications of GW190521 for stellar collapse and for the possible formation of black holes in the pair-instability mass gap through various channels: via (multiple) stellar coalescences, or via hierarchical mergers of lower-mass black holes in star clusters or in active galactic nuclei. We find it to be unlikely that GW190521 is a strongly lensed signal of a lower-mass black hole binary merger. We also discuss more exotic possible sources for GW190521, including a highly eccentric black hole binary, or a primordial black hole binary.
347 citations
Cites background from "Dwarf Galaxies with Optical Signatu..."
...…associated with low-luminosity active galactic nuclei (AGNs; Filippenko & Sargent 1989; Filippenko & Ho 2003; Barth et al. 2004, 2005; Greene & Ho 2004, 2007; Seth et al. 2010; Dong et al. 2012; Reines et al. 2013; Baldassare et al. 2015, 2016, 2017; den Brok et al. 2015; Mezcua et al. 2016, 2018)....
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University of Utah1, Max Planck Society2, European Southern Observatory3, University of Queensland4, Michigan State University5, Sternberg Astronomical Institute6, Smithsonian Astrophysical Observatory7, Macquarie University8, Australian Astronomical Observatory9, University of California, Santa Cruz10, Heidelberg University11, University of Texas at Austin12
TL;DR: Adaptive optics kinematic data of the ultra-compact dwarf galaxy M60-UCD1 that show a central velocity dispersion peak exceeding 100 kilometres per second and modest rotation are reported, implying a large population of previously unrecognized supermassive black holes in other ultra-Compact dwarf galaxies.
Abstract: Dynamical modelling of the ultra-compact dwarf galaxy M60-UCD1 reveals the presence of a supermassive black hole; this suggests the object is a stripped galaxy nucleus and implies the existence of supermassive black holes in many other ultra-compact dwarf galaxies. The object M60-UCD1 is the brightest ultracompact dwarf galaxy (UCD) currently known and — at about 200 million solar masses — one of the most massive. Anil Seth et al. have used adaptive optics spectra to resolve the kinematics of M60-UCD1. They detect a supermassive black hole of 21 million solar masses at its centre. M60-UCD1 is thus the lowest-mass system known to host a supermassive black hole. The authors suggest that it may once have been at the centre of a larger galaxy that was later tidally torn apart by a massive neighbour. Their analysis also shows that M60-UCD1's stellar mass is consistent with its luminosity, implying that many other ultra-compact dwarf galaxies may contain previously unrecognized supermassive black holes. Ultra-compact dwarf galaxies are among the densest stellar systems in the Universe. These systems have masses of up to 2 × 108 solar masses, but half-light radii of just 3–50 parsecs1. Dynamical mass estimates show that many such dwarfs are more massive than expected from their luminosity2. It remains unclear whether these high dynamical mass estimates arise because of the presence of supermassive black holes or result from a non-standard stellar initial mass function that causes the average stellar mass to be higher than expected3,4. Here we report adaptive optics kinematic data of the ultra-compact dwarf galaxy M60-UCD1 that show a central velocity dispersion peak exceeding 100 kilometres per second and modest rotation. Dynamical modelling of these data reveals the presence of a supermassive black hole with a mass of 2.1 × 107 solar masses. This is 15 per cent of the object’s total mass. The high black hole mass and mass fraction suggest that M60-UCD1 is the stripped nucleus of a galaxy. Our analysis also shows that M60-UCD1’s stellar mass is consistent with its luminosity, implying a large population of previously unrecognized supermassive black holes in other ultra-compact dwarf galaxies2.
269 citations
TL;DR: In this article, the authors presented optical and X-ray observations of the dwarf galaxy RGG 118 taken with the Magellan Echellette Spectrograph on the 6.5 m Clay Telescope and Chandra Xray Observatory.
Abstract: Scaling relations between black hole (BH) masses and their host galaxy properties have been studied extensively over the last two decades, and point toward co-evolution of central massive BHs and their hosts. However, these relations remain poorly constrained for BH masses below . Here we present optical and X-ray observations of the dwarf galaxy RGG 118 taken with the Magellan Echellette Spectrograph on the 6.5 m Clay Telescope and Chandra X-ray Observatory. Based on Sloan Digital Sky Survey spectroscopy, RGG 118 was identified as possessing narrow emission line ratios indicative of photoionization partly due to an active galactic nucleus. Our higher resolution spectroscopy clearly reveals broad H? emission in the spectrum of RGG 118. Using virial BH mass estimate techniques, we calculate a BH mass of ?50,000 . We detect a nuclear X-ray point source in RGG 118, suggesting a total accretion powered luminosity of , and an Eddington fraction of ?1%. The BH in RGG 118 is the smallest ever reported in a galaxy nucleus and we find that it lies on the extrapolation of the relation to the lowest masses yet.
231 citations
Cites background or methods from "Dwarf Galaxies with Optical Signatu..."
...The final equation used to estimate BH mass is given in Reines et al. (2013); we also adopt a scale factor of = 1....
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...We analyzed the spectrum of RGG 118 using custom emission line fitting software developed in Python and broadly following the procedure laid out in Reines et al. (2013)....
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...More recently, Reines et al. (2013) increased the number of known AGN in dwarf galaxies by an order of magnitude by searching for narrow and broad emission line AGN signatures in a sample of nearby (z ....
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...We are in the process of measuring BH masses and velocity dispersions for additional targets identified by Reines et al. (2013)....
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...G A ] 2 4 Ju n 20 15 (14 May 2007) shows evidence for broad Hα emission (see top right of Figure 2), but it was not identified by Reines et al. (2013) because it falls below their broad Hα detection limit of ∼ 2 × 1039 erg s−1 (at their sample median redshift of z∼0.03)....
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References
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TL;DR: In this article, the average extinction law over the 3.5 micron to 0.125 wavelength range was derived for both diffuse and dense regions of the interstellar medium. And the validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature.
Abstract: The parameterized extinction data of Fitzpatrick and Massa (1986, 1988) for the ultraviolet and various sources for the optical and near-infrared are used to derive a meaningful average extinction law over the 3.5 micron to 0.125 wavelength range which is applicable to both diffuse and dense regions of the interstellar medium. The law depends on only one parameter R(V) = A(V)/E(B-V). An analytic formula is given for the mean extinction law which can be used to calculate color excesses or to deredden observations. The validity of the law over a large wavelength interval suggests that the processes which modify the sizes and compositions of grains are stochastic in nature and very efficient.
11,704 citations
"Dwarf Galaxies with Optical Signatu..." refers methods in this paper
...In the fitting process, we allow for reddening from dust using the Galactic extinction curve of Cardelli et al. (1989) and Gaussian smoothing to match the absorption line widths....
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TL;DR: In this article, the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities.
Abstract: We present a new model for computing the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities. These predictions are based on a newly available library of observed stellar spectra. We also compute the spectral evolution across a larger wavelength range, from 91 A to 160 micron, at lower resolution. The model incorporates recent progress in stellar evolution theory and an observationally motivated prescription for thermally-pulsing stars on the asymptotic giant branch. The latter is supported by observations of surface brightness fluctuations in nearby stellar populations. We show that this model reproduces well the observed optical and near-infrared colour-magnitude diagrams of Galactic star clusters of various ages and metallicities. Stochastic fluctuations in the numbers of stars in different evolutionary phases can account for the full range of observed integrated colours of star clusters in the Magellanic Clouds. The model reproduces in detail typical galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We exemplify how this type of spectral fit can constrain physical parameters such as the star formation history, metallicity and dust content of galaxies. Our model is the first to enable accurate studies of absorption-line strengths in galaxies containing stars over the full range of ages. Using the highest-quality spectra of the SDSS EDR, we show that this model can reproduce simultaneously the observed strengths of those Lick indices that do not depend strongly on element abundance ratios [abridged].
10,384 citations
TL;DR: The Sloan Digital Sky Survey (SDSS) as mentioned in this paper provides the data to support detailed investigations of the distribution of luminous and non-luminous matter in the Universe: a photometrically and astrometrically calibrated digital imaging survey of pi steradians above about Galactic latitude 30 degrees in five broad optical bands.
Abstract: The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and non- luminous matter in the Universe: a photometrically and astrometrically calibrated digital imaging survey of pi steradians above about Galactic latitude 30 degrees in five broad optical bands to a depth of g' about 23 magnitudes, and a spectroscopic survey of the approximately one million brightest galaxies and 10^5 brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS, and serves as an introduction to extensive technical on-line documentation.
10,039 citations
TL;DR: In this paper, the merits of various emission-line intensity ratios for classifying the spectra of extragalactic objects were investigated and it was shown empirically that several combinations of easily-measured lines can be used to separate objects into one of four categories according to the principal excitation mechanism: normal H II regions, planetary nebulae, objects photoionized by a power-law continuum, and objects excited by shock-wave heating.
Abstract: An investigation is made of the merits of various emission-line intensity ratios for classifying the spectra of extragalactic objects. It is shown empirically that several combinations of easily-measured lines can be used to separate objects into one of four categories according to the principal excitation mechanism: normal H II regions, planetary nebulae, objects photoionized by a power-law continuum, and objects excited by shock-wave heating. A two-dimensional quantitative classification scheme is suggested.
4,734 citations
"Dwarf Galaxies with Optical Signatu..." refers background in this paper
...AGNs and H II regions separate cleanly in two-dimensional strong line diagnostic diagrams that take pairs of lines close together in frequency to mitigate the effects of reddening (Baldwin et al. 1981; Veilleux & Osterbrock 1987; Kewley et al. 2001; Kauffmann et al. 2003b; Kewley et al. 2006)....
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TL;DR: The mass of supermassive black holes correlate almost perfectly with the velocity dispersions of their host bulges, Mbh ∝ σα, where α = 48 ± 05.
Abstract: The masses of supermassive black holes correlate almost perfectly with the velocity dispersions of their host bulges, Mbh ∝ σα, where α = 48 ± 05 The relation is much tighter than the relation between Mbh and bulge luminosity, with a scatter no larger than expected on the basis of measurement error alone Black hole masses recently estimated by Magorrian et al lie systematically above the Mbh-σ relation defined by more accurate mass estimates, some by as much as 2 orders of magnitude The tightness of the Mbh-σ relation implies a strong link between black hole formation and the properties of the stellar bulge
4,557 citations
"Dwarf Galaxies with Optical Signatu..." refers background in this paper
...The growth of supermassive BHs appears to be linked to the evolution of their hosts, with more massive galaxies generally harboring more massive BHs (e.g., Gebhardt et al. 2000a; Ferrarese & Merritt 2000; Marconi & Hunt 2003; Gültekin et al. 2009; McConnell & Ma 2013)....
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