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Register a new userA Low-Mass Black Hole in the Nearby Seyfert Galaxy UGC 06728
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We present the results of a recent reverberation mapping campaign for UGC 06728, a nearby low-luminosity Seyfert 1 in a late-type galaxy. Nightly monitoring in the spring of 2015 allowed us to determine an H$beta$ time delay of $tau = 1.4 pm 0.8$ days. Combined with the width of the variable H$beta$ line profile, we determine a black hole mass of $M_{rm BH} = (7.1 pm 4.0) times 10^5$ M$_{odot}$. We also constrain the bulge stellar velocity dispersion from higher-resolution long slit spectroscopy along the galaxy minor axis and find $sigma_{star} = 51.6 pm 4.9$ km s$^{-1}$. The measurements presented here are in good agreement with both the $R_{rm BLR} - L$ relationship and the $M_{rm BH}-sigma_{star}$ relationship for AGNs. Combined with a previously published spin measurement, our mass determination for UGC 06728 makes it the lowest-mass black hole that has been fully characterized, and thus an important object to help anchor the low-mass end of black hole evolutionary models.
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Intermediate mass black holes (IMBHs) have masses between the $10^2!-!10^6$ M$_odot$ and are key to our understanding of the formation of massive black holes. The known population of IMBH remains small, with a few hundred candidates and only a handful of them confirmed as bona-fide IMBHs. Until now, the most widely used selection method is based on spectral analysis. Here we present a methodology to select IMBH candidates via optical variability analysis of the nuclear region of local galaxies ($z leqslant 0.35$). Active IMBH accreting at low rates show small amplitude variability with time scales of hours, as it is seen in one of the known IMBH NGC4395. We found a sample of $sim !500$ galaxies evidencing fast and small amplitude variation in their weekly based light curves. We estimate an average occupancy fraction of 4% and a surface density of $sim !3$ deg$^{-2}$, which represent an increase by a factor of $sim!40$ compared to previous searches. A large fraction ($78%$) of the candidates are in spiral galaxies. We preliminary confirm the AGN nature of 22 sources via BPT diagrams using SDSS legacy spectra. Further confirmation of these candidates will require multiwavelength observations, especially in X-ray and radio bands.
We present 0farcs{14}-resolution Atacama Large Millimeter/submillimeter Array (ALMA) CO(2$-$1) observations of the circumnuclear gas disk in UGC 2698, a local compact galaxy. The disk exhibits regular rotation with projected velocities rising to 450 km s$^{-1}$ near the galaxy center. We fit gas-dynamical models to the ALMA data cube, assuming the CO emission originates from a dynamically cold, thin disk, and measured the mass of the supermassive black hole (BH) in UGC 2698 to be $M_{mathrm{BH}} = (2.46 pm{0.07}$ [$1sigma$ stat] $^{+0.70}_{-0.78}$ [sys])$times 10^9$ $M_odot$. UGC 2698 is part of a sample of nearby early-type galaxies that are plausible $zsim2$ red nugget relics. Previous stellar-dynamical modeling for three galaxies in the sample found BH masses consistent with the BH mass$-$stellar velocity dispersion ($M_{mathrm{BH}}-sigma_star$) relation but over-massive relative to the BH mass$-$bulge luminosity ($M_{mathrm{BH}}-L_{mathrm{bul}}$) correlation, suggesting that BHs may gain the majority of their mass before their host galaxies. However, UGC 2698 is consistent with both $M_{mathrm{BH}}-sigma_star$ and $M_{mathrm{BH}}-L_{mathrm{bul}}$. As UGC 2698 has the largest stellar mass and effective radius in the local compact galaxy sample, it may have undergone more recent mergers that brought it in line with the BH scaling relations. Alternatively, given that the three previously-measured compact galaxies are outliers from $M_{mathrm{BH}}-L_{mathrm{bul}}$, while UGC 2698 is not, there may be significant scatter at the poorly sampled high-mass end of the relation. Additional gas-dynamical $M_{mathrm{BH}}$ measurements for the compact galaxy sample will improve our understanding of BH$-$galaxy co-evolution.
The existence of binary supermassive black holes (SBHs) is predicted by models of hierarchical galaxy formation. To date, only a single binary SBH has been imaged, at a projected separation of 7.3 parsecs. Here we report the detection of a candidate dual SBH with projected separation of 0.35 pc in the gas-rich interacting spiral galaxy NGC 7674 (Mrk 533). This peculiar Seyfert galaxy possesses a $sim$0.7 kpc Z-shaped radio jet; the leading model for the formation of such sources postulates the presence of an uncoalesced binary SBH created during the infall of a satellite galaxy. Using very long baseline interferometry (VLBI), we imaged the central region of Mrk 533 at radio frequencies of 2, 5, 8 and 15 GHz. Two, possibly inverted-spectrum radio cores were detected at 15 GHz only; the 8-15 GHz spectral indices of the two cores are $ge-0.33$ and $ge-0.38$ ($pm 30%$), consistent with accreting SBHs. We derive a jet speed $sim0.28c$ from multi-epoch parsec-scale data of the hotspot region, and a source age $ge8.2times10^3$ yrs.
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We report results of the first reverberation mapping campaign of I Zwicky 1 during $2014$-$2016$, which showed unambiguous reverberations of the broad H$beta$ line emission to the varying optical continuum. From analysis using several methods, we obtain a reverberation lag of $tau_{rm Hbeta}=37.2^{+4.5}_{-4.9},$ days. Taking a virial factor of $f_{_{rm BLR}}=1$, we find a black hole mass of $M_{bullet}=9.30_{-1.38}^{+1.26}times 10^6 M_{odot}$ from the mean spectra. The accretion rate is estimated to be $203.9_{-65.8}^{+61.0},L_{rm Edd}c^{-2}$, suggesting a super-Eddington accretor, where $L_{rm Edd}$ is the Eddington luminosity and $c$ is the speed of light. By decomposing {it Hubble Space Telescope} images, we find that the stellar mass of the bulge of its host galaxy is $log (M_{rm bulge}/M_{odot}) = rm 10.92pm 0.07$. This leads to a black hole to bulge mass ratio of $sim 10^{-4}$, which is significantly smaller than that of classical bulges and elliptical galaxies. After subtracting the host contamination from the observed luminosity, we find that I Zw 1 follows the empirical $R_{rm BLR}propto L_{5100}^{1/2}$ relation.
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