arXiv subjects

Daeseong Park

Publications and source records attributed to Daeseong Park.

35 records · Page 2Linked to original sources

arXiv2015

The black hole mass - stellar velocity dispersion relation of narrow-line Seyfert 1 galaxies

Narrow-line Seyfert 1 galaxies (NLS1s) are arguably one of the key AGN subclasses in investigating the origin of the black hole mass - stellar velocity dispersion (M-sigma) relation because of their high accretion rate and significantly low black hole mass. Currently, it is under discussion whether present-day NLS1s offset from the M-sigma relation. Using the directly measured stellar velocity dispersion of 93 NLS1s at z<0.1, and black hole mass estimates based on the updated mass estimators, we investigate the M-sigma relation of NLS1s in comparison with broad-line AGNs. We find no strong evidence that the NLS1s deviates from the M-sigma relation, which is defined by reverberation-mapped type 1 AGNs and quiescent galaxies. However, there is a clear trend of the offset with the host galaxy morphology, i.e., more inclined galaxies toward the line-of-sight have higher stellar velocity dispersion, suggesting that the rotational broadening plays a role in measuring stellar velocity dispersion based on the single-aperture spectra from the Sloan Digital Sky Survey. In addition, we provide the virial factor log f = $0.05 \pm 0.12$ (f = 1.12), for black hole mass estimators based on the FWHM of H$β$, by jointly fitting the M-sigma relation using quiescent galaxies and reverberation-mapped AGNs.

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arXiv2014

Scaling relations between black holes and their host galaxies: comparing theoretical and observational measurements, and the impact of selection effects

We use the high-resolution simulation MassiveBlackII to examine scaling relations between black hole mass (MBH) and host galaxy properties (sigma, M*, and LV), finding good agreement with observational data, especially at the high-mass end. The simulations have less intrinsic scatter than observations, and the MBH-LV correlation has the largest scatter, suggesting it may the the least fundamental of the three relations. We find Gaussian scatter about all three relations, except among the highest mass galaxies, which host more massive black holes. Below z~2 the slopes for the full population remain roughly z-independent, and only steepen by 50% by z~4. The normalization of the sigma, LV relations evolve by 0.3, 0.43 dex, while the MBH correlation does not evolve to at least z~2. Testing for selection biases, we find samples selected by MBH or M* have steeper slopes than randomly selected samples. If unaccounted for, such a selection function would find faster evolution than inferred from a randomly selected sample, as objects at the highend of the relation tend to evolve more rapidly. We find a potential bias among high-LBH subsamples (tending to reside in higher mass galaxies), but these bright-AGN exhibit no intrinsic bias relative to fainter ones in equivalent-mass hosts, nor is there a significant difference between active- and inactive-samples. Finally we characterize the evolution of individual black holes along the scaling planes. Below the local relation, black holes grow faster than their host (72% of black holes 0.3 dex below the mean relation have a MBH-M* trajectory steeper than the local relation), while those above have shallower trajectories (only 14% are steeper than local). Black holes tend to grow faster than their hosts until surpassing the local relation, at which point their growth is suppressed while their hosts continue to grow, returning them to the mean relation.

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arXiv2014

Cosmic Evolution of Black Holes and Spheroids. V. The Relation Between Black Hole Mass and Host Galaxy Luminosity for a Sample of 79 Active Galaxies

We investigate the cosmic evolution of the black hole (BH) mass -- bulge luminosity relation using a sample of 52 active galaxies at $z \sim 0.36$ and $z \sim 0.57$ in the BH mass range of $10^{7.4-9.1} M_{\odot}$. By consistently applying multi-component spectral and structural decomposition to high-quality Keck spectra and high-resolution HST images, BH masses ($M_{\rm BH}$) are estimated using the H$β$ broad emission line combined with the 5100 Å nuclear luminosity, and bulge luminosities ($L_{\rm bul}$) are derived from surface photometry. Comparing the resulting $M_{\rm BH}-L_{\rm bul}$ relation to local active galaxies and taking into account selection effects, we find evolution of the form $M_{\rm BH} / L_{\rm bul} \propto (1+z)^γ$ with $γ=1.8\pm0.7$, consistent with BH growth preceding that of the host galaxies. Including an additional sample of 27 active galaxies with $0.5<z<1.9$ taken from the literature and measured in a consistent way, we obtain $γ=0.9\pm0.7$ for the $M_{\rm BH}-L_{\rm bul}$ relation and $γ=0.4\pm0.5$ for the $M_{\rm BH}$--total host galaxy luminosity ($L_{\rm host}$) relation. The results strengthen the findings from our previous studies and provide additional evidence for host-galaxy bulge growth being dominated by disk-to-bulge transformation via minor mergers and/or disk instabilities.

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arXiv2014

Misclassified type 1 AGNs in the local universe

We search for misclassified type 1 AGNs among type 2 AGNs identified with emission line flux ratios, and investigate the properties of the sample. Using 4\,113 local type 2 AGNs at $0.02<z<0.05$ selected from Sloan Digital Sky Survey Data Release 7, we detected a broad component of the \Ha\ line with a Full-Width at Half-Maximum (FWHM) ranging from 1\,700 to 19\,090 \kms\ for 142 objects, based on the spectral decomposition and visual inspection. The fraction of the misclassified type 1 AGNs among type 2 AGN sample is $\sim$3.5%, implying that a large number of missing type 1 AGN population may exist. The misclassified type 1 AGNs have relatively low luminosity with a mean broad \Ha\ luminosity, log L$_{Hα} = 40.50\pm0.35$ \ergs, while black hole mass of the sample is comparable to that of the local black hole population, with a mean black hole mass, log M$_{\rm BH} = 6.94\pm0.51$ M$_{\odot}$. The mean Eddington ratio of the sample is log L$_{\rm bol}$/L$_{\rm Edd}$ = $-2.00\pm0.40$, indicating that black hole activity is relatively weak, hence, AGN continuum is too weak to change the host galaxy color. We find that the \OIII\ lines show significant velocity offsets, presumably due to outflows in the narrow-line region, while the velocity offset of the narrow component of the \Ha\ line is not prominent, consistent with the ionized gas kinematics of general type 1 AGN population.

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arXiv2014

A sub-kpc-scale binary AGN with double narrow-line regions

We present the kinematic properties of a type-2 QSO, SDSS J132323.33-015941.9 at z~0.35, based on the analysis of Very Large Telescope integral field spectroscopy and Hubble Space Telescope (HST) imaging, which suggest that the target is a binary active galactic nucleus (AGN) with double narrow-line regions. The QSO features double-peaked emission lines ([OIII] and Hb) which can be decomposed into two kinematic components. The flux-weighted centroids of the blue and red components are separated by ~0.2" (0.8 kpc in projection) and coincide with the location of the two stellar cores detected in the HST broad-band images, implying that both stellar cores host an active black hole. The line-of-sight velocity of the blue component is comparable to the luminosity-weighted velocity of stars in the host galaxy while the red component is redshifted by ~240 km/s, consistent with typical velocity offsets of two cores in a late stage of a galaxy merger. If confirmed, the target is one of the rare cases of sub-kpc scale binary AGNs, providing a test-bed for understanding the binary AGN population.

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arXiv2013

Calibrating CIV-based black hole mass estimators

We present the single-epoch black hole mass estimators based on the CIV (1549 A) broad emission line, using the updated sample of the reverberation-mapped AGNs and high-quality UV spectra. By performing multi-component spectral fitting analysis, we measure the CIV line widths (FWHM_CIV) and line dispersion (sigma_CIV) and the continuum luminosity at 1350 A (L_1350) to calibrate the CIV-based mass estimators. By comparing with the Hbeta reverberation-based masses, we provide new mass estimators with the best-fit relationships, i.e., M_BH \propto L_1350 ^ (0.50+-0.07) sigma_CIV ^2 and M_BH \propto L_1350 ^ (0.52+-0.09) FWHM_CIV ^ (0.56+-0.48). The new CIV-based mass estimators show significant mass-dependent systematic difference compared to the estimators commonly used in the literature. Using the published Sloan Digital Sky Survey QSO catalog, we show that the black hole mass of high-redshift QSOs decreases on average by ~0.25 dex if our recipe is adopted.

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arXiv2013

Do quiescent and active galaxies have different M_BH-sigma relations?

To investigate the validity of the assumption that quiescent galaxies and active galaxies follow the same black hole mass - stellar velocity dispersion relation, as required for the calibration of M_BH estimators for broad line AGNs, we determine and compare the M-sigma relations, respectively, for quiescent and active galaxies. For the quiescent galaxy sample, composed of 72 dynamical M_BH measurements, we update sigma for 28 galaxies using homogeneous H-band measurements that are corrected for galaxy rotation. For active galaxies, we collect 25 reverberation-mapped AGNs and improve sigma measurement for two objects . Combining the two samples, we determine the virial factor $f$, first by scaling the active galaxy sample to the M-sigma relation of quiescent galaxies, and second by simultaneously fitting the quiescent and active galaxy samples, as f=5.1_{-1.1}^{+1.5} and f=5.9_{-1.5}^{+2.1}, respectively. The M-sigma relation of active galaxies appears to be shallower than that of quiescent galaxies. However, the discrepancy is caused by a difference in the accessible M_BH distribution at given sigma, primarily due to the difficulty of measuring reliable stellar velocity dispersion for the host galaxies of luminous AGNs. Accounting for the selection effects, we find that active and quiescent galaxies are consistent with following intrinsically the same M-sigma relation.

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arXiv2013

Calibrating stellar velocity dispersions based on spatially-resolved h-band spectra for improving the m-sigma relation

To calibrate stellar velocity dispersion measurements from optical and near-IR stellar lines, and to improve the black hole mass (MBH)- stellar velocity dispersion (sigma) relation, we measure stellar velocity dispersions based on high quality H-band spectra for a sample of 31 nearby galaxies, for which dynamical MBH is available in the literature. By comparing velocity dispersions measured from stellar lines in the H-band with those measured from optical stellar lines, we find no significant difference, suggesting that optical and near-IR stellar lines represent the same kinematics and that dust effect is negligible for early-type galaxies. Based on the spatially-resolved rotation and velocity dispersion measurements along the major axis of each galaxy, we find that a rotating stellar disk is present for 80% of galaxies in the sample. For galaxies with a rotation component, velocity dispersions measured from a single aperture spectrum can vary by up to ~20%, depending on the size of the adopted extraction aperture. To correct for the rotational broadening, we derive luminosity-weighted velocity dispersion within the effective radius of each galaxy, providing uniformly measured velocity dispersions to improve the MBH-sigma relation.

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arXiv2012

Recalibration of the virial factor and M-sigma relation for local active galaxies

Determining the virial factor of the broad-line region (BLR) gas is crucial for calibrating AGN black hole mass estimators, since the measured line-of-sight velocity needs to be converted into the intrinsic virial velocity. The average virial factor has been empirically calibrated based on the M-sigma relation of quiescent galaxies, but the claimed values differ by a factor of two in recent studies. We investigate the origin of the difference by measuring the M-sigma relation using an updated galaxy sample from the literature, and explore the dependence of the virial factor on various fitting methods. We find that the discrepancy is primarily caused by the sample selection, while the difference stemming from the various regression methods is marginal. However, we generally prefer the FITEXY and Bayesian estimators based on Monte Carlo simulations for the M-sigma relation. In addition, the choice of independent variable in the regression leads to ~0.2 dex variation in the virial factor inferred from the calibration process. Based on the determined virial factor, we present the updated M-sigma relation of local active galaxies.

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arXiv2012

Accretion Properties of High- and Low-Excitation Young Radio Galaxies

Young radio galaxies (YRGs) provide an ideal laboratory to explore the connection between accretion disk and radio jet thanks to their recent jet formation. We investigate the relationship between the emission-line properties, the black hole accretion rate, and the radio properties using a sample of 34 low-redshift (z < 0.4) YRGs. We classify YRGs as high-excitation galaxies (HEGs) and low-excitation galaxies (LEGs) based on the flux ratio of high-ionization to low-ionization emission lines. Using the Hα luminosities as a proxy of accretion rate, we find that HEGs in YRGs have \sim1 dex higher Eddington ratios than LEGs in YRGs, suggesting that HEGs have higher mass accretion rate or higher radiative efficiency than LEGs. In agreement with previous studies, we find that the luminosities of emission lines, in particular Hα, are correlated with radio core luminosity, suggesting that accretion and young radio activities are fundamentally connected.

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arXiv2011

The Lick AGN Monitoring Project: Recalibrating Single-Epoch Virial Black Hole Mass Estimates

We investigate the calibration and uncertainties of black hole mass estimates based on the single-epoch (SE) method, using homogeneous and high-quality multi-epoch spectra obtained by the Lick Active Galactic Nucleus (AGN) Monitoring Project for 9 local Seyfert 1 galaxies with black hole masses < 10^8 M_sun. By decomposing the spectra into their AGN and stellar components, we study the variability of the single-epoch Hbeta line width (full width at half-maximum intensity, FWHM_Hbeta; or dispersion, sigma_Hbeta) and of the AGN continuum luminosity at 5100A (L_5100). From the distribution of the "virial products" (~ FWHM_Hbeta^2 L_5100^0.5 or sigma_Hbeta^2 L_5100^0.5) measured from SE spectra, we estimate the uncertainty due to the combined variability as ~ 0.05 dex (12%). This is subdominant with respect to the total uncertainty in SE mass estimates, which is dominated by uncertainties in the size-luminosity relation and virial coefficient, and is estimated to be ~ 0.46 dex (factor of ~ 3). By comparing the Hbeta line profile of the SE, mean, and root-mean-square (rms) spectra, we find that the Hbeta line is broader in the mean (and SE) spectra than in the rms spectra by ~ 0.1 dex (25%) for our sample with FWHM_Hbeta < 3000 km/s. This result is at variance with larger mass black holes where the difference is typically found to be much less than 0.1 dex. To correct for this systematic difference of the Hbeta line profile, we introduce a line-width dependent virial factor, resulting in a recalibration of SE black hole mass estimators for low-mass AGNs.

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arXiv2009

The Bridge Effect of Void Filaments

Cosmic filaments play a role of bridges along which matter and gas accrete onto galaxies to trigger star formation and feed central black holes. Here we explore the correlations between the intrinsic properties of void galaxies and the linearity R_L of void filaments (degree of filament's straightness). We focus on void regions since the bridge effect of filaments should be most conspicuous in the pristine underdense regions like voids. Analyzing the Millennium-Run semi-analytic galaxy catalogue, we identify void filaments consisting of more than four galaxies (three edges) and calculate the means of central black hole mass, star formation rate, and stellar mass as a function of R_L. It is shown that the void galaxies constituting more straight filaments tend to have higher luminosity, more massive central black holes and higher star formation rate. Among the three properties, the central black hole mass is most strongly correlated with R_L. It is also shown that the dark halos constituting straight filaments tend to have similar masses. Our results suggest that the fuel-supply for central black holes and star formation of void galaxies occurs most efficiently along straight void filaments whose potential wells are generated by similar-mass dark halos.

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arXiv2009

The Size Distribution of Void Filaments in a LCDM Cosmology

The size distribution of mini-filaments in voids has been derived from the Millennium Run halo catalogs at redshifts z=0,0.5,1 and 2. It is assumed that the primordial tidal field originated the presence of filamentary substructures in voids and that the void filaments have evolved only little, keeping the initial memory of the primordial tidal field. Applying the filament-finding algorithm based on the minimal spanning tree (MST) technique to the Millennium voids, we identify the mini-filaments running through voids and measure their sizes at each redshift. Then, we calculate the comoving number density of void filaments as a function of their sizes in the logarithmic interval and determine an analytic fitting function for it. It is found that the size distribution of void mini-filaments in the logarithmic interval has an almost universal shape, insensitive to the redshift: In the short-size section it is well approximated as a power-law, while in the long-size section it decreases exponentially. We expect that the universal size distribution of void filaments may provide a useful cosmological probe without resorting to the rms density fluctuations.

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arXiv2009

Constraining the Dark Energy Equation of State with Cosmic Voids

Our universe is observed to be accelerating due to the dominant dark energy with negative pressure. The dark energy equation of state (w) holds a key to understanding the ultimate fate of the universe. The cosmic voids behave like bubbles in the universe so that their shapes must be quite sensitive to the background cosmology. Assuming a flat universe and using the priors on the matter density parameter (Omega_m) and the dimensionless Hubble parameter (h), we demonstrate analytically that the ellipticity evolution of cosmic voids may be a sensitive probe of the dark energy equation of state. We also discuss the parameter degeneracy between w and Omega_m.

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arXiv2007

Void-Supercluster Alignments

We investigate alignments between the spin axes of cosmic voids and the principal axes of nearby superclusters using the Millennium Run simulation of a LCDM cosmology. The concept of void spin was first introduced by Lee and Park in 2006 to quantify the tidal effect on voids from the surrounding matter distribution. Our numerical analysis reveals that the void spin axes are strongly aligned with the supercluster minor axes, but anti-aligned with the major axes, and have no correlations with the intermediate axes. We provide physical explanations to this numerical results on the basis of tidally induced correlations. It is expected that our work will provide a new insight into the characterization of the cosmic web on the largest scale.

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arXiv2007

Void Ellipticity Distribution as a Probe of Cosmology

Cosmic voids refer to the large empty regions in the universe with a very low number density of galaxies. Voids are likely to be severely disturbed by the tidal effect from the surrounding dark matter. We derive a completely analytic model for the void ellipticity distribution from physical principles. We use the spatial distribution of galaxies in a void as a measure of its shape, tracking the trajectory of the void galaxies under the influence of the tidal field using the Lagrangian perturbation theory. Our model implies that the void ellipticity distribution depends sensitively on the cosmological parameters. Testing our model against the high-resolution Millennium Run simulation, we find excellent quantitative agreement of the analytic predictions with the numerical results.

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arXiv2006

Rotation of Cosmic Voids and Void-Spin Statistics

We present a theoretical study of void spins and their correlation properties. The concept of the spin angular momentum for an unbound void is introduced to quantify the effect of the tidal field on the distribution of matter that make up the void. Both the analytical and numerical approaches are used for our study. Analytically, we adopt the linear tidal torque model to evaluate the void spin-spin and spin-density correlations, assuming that a void forms in the initial region where the inertia momentum and the tidal shear tensors are maximally uncorrelated with each other. Numerically, we use the Millennium run galaxy catalog to find voids and calculate their spin statistics. The numerical results turn out to be in excellent agreement with the analytic predictions, both of which consistently show that there are strong spatial alignments between the spin axes of neighbor voids and strong anti-alignments between the void spin axes and the directions to the nearest voids. We expect that our work will provide a deeper insight into the origin and properties of voids and the large scale structure.

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