Sang Chul Kim

Do Quiescent and Active Galaxies Have Different M_(BH)-σ* Relations?

To investigate the validity of the assumption that quiescent galaxies and active galaxies follow the same black hole mass (M_BH)-stellar velocity dispersion (σ*) relation, as required for the calibration of M_BH estimators for broad line active galactic nuclei (AGNs), we determine and compare the M_BH-σ* relations, respectively, for quiescent and active galaxies. For the quiescent galaxy sample, composed of 72 dynamical M_BH measurements, we update σ* 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 σ* measurement for two objects. Combining the two samples, we determine the virial factor f, first by scaling the active galaxy sample to the M_BH-σ* relation of quiescent galaxies, and second by simultaneously fitting the quiescent and active galaxy samples, as f=5.1^(+1.5)_(-1.1) and f=5.9^(+2.1)_(-1.5), respectively. The M_BH-σ* 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 σ*, 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_BH-σ* relation.

Deep Wide-Field BVI CCD Photometry of the Sextans Dwarf Spheroidal Galaxy*

We present deep wide-field VI CCD photometry of the Sextans dwarf spheroidal galaxy (dSph) in the Local Group, covering a field of 42 × 28 located at the center of the galaxy (supplemented by short B photometry). The limiting magnitudes with 50% completeness are V = 24.4 mag and I = 23.6 mag. Color-magnitude diagrams of the Sextans dSph show a well-defined red giant branch (RGB), blue horizontal branch (BHB), prominent red horizontal branch (RHB), and asymptotic giant branch (AGB), as well as ~120 variable star candidates including RR Lyrae stars and anomalous Cepheids, ~230 blue stragglers (BSs), and main-sequence (MS) stars. The main-sequence turnoff (MSTO) of the old population is found to be located at V ≈ 23.7 mag and V-I ≈ 0.56. The distance to the galaxy is derived using the I-band magnitude of the tip of the RGB at ITRGB = 15.95 ± 0.04: (m - M)0 = 19.90 ± 0.06, for an adopted reddening of E(B-V) = 0.01. This estimate agrees well with the distance estimate based on the mean V-band magnitude of the HB at V(HB) = 20.37 ± 0.04. The mean metallicity of the RGB is estimated from the V-I color: [Fe/H] = -2.1 ± 0.1 (statistical error) ±0.2 (standard calibration error) dex, with a dispersion of σ[Fe/H] = 0.2 dex. The age of the MSTO of the main old population is estimated to be similar to that of the metal-poor Galactic globular cluster M92, and some stellar populations with younger age are seen. There is found to be one RGB bump at V = 19.95 ± 0.05 mag (MV = 0.03 mag) and a weak brighter bump at V = 19.35 ± 0.05 mag (MV = -0.58 mag), which is probably an AGB bump. The V-band luminosity function of the RGB and MS stars is in general similar to that of the globular cluster M92, with a slight excess of stars in the magnitude range brighter than the MSTO with respect to that of M92. The bright BSs are more centrally concentrated than the faint BSs. The V-band luminosity function of the BSs in the inner region is found to extend to a brighter magnitude and to have a flatter slope compared with that of the BSs in the outer region. Significant radial gradients are seen for several kinds of populations: the RHB, the red RGB, the red subgiant branch (SGB), and the bright BSs are more centrally concentrated toward the center of the galaxy compared with the BHB, the blue RGB, the blue SGB, and the faint BSs, respectively.

THE GLOBULAR CLUSTER SYSTEM OF M60 (NGC 4649). II. KINEMATICS OF THE GLOBULAR CLUSTER SYSTEM

We present a kinematic analysis of the globular cluster (GC) system in the giant elliptical galaxy (gE) M60 in the Virgo Cluster, using a photometric and spectroscopic database of 121 GCs (83 blue and 38 red GCs). We have found that the M60 GC system shows a significant overall rotation. The rotation amplitude of the blue GCs is slightly smaller than or similar to that of the red GCs, and the position angles of their rotation axes are similar. The velocity dispersions about the mean velocity and about the best-fit rotation curve for the red GCs are marginally larger than those for the blue GCs. Comparison of observed stellar and GC velocity dispersion profiles with those calculated from the stellar mass profile shows that the mass-to-light ratio should increase as the galactocentric distance increases, indicating the existence of an extended dark matter halo. The sample of all the GCs in M60 is found to have a tangentially biased velocity ellipsoid, unlike the GC systems in other gEs. The two subsamples appear to have different velocity ellipsoids. The blue GC system has a modestly tangentially biased velocity ellipsoid, while the red GC system has a modestly radially biased or an isotropic velocity ellipsoid. We compare the kinematic properties of the M60 GC system to those of other gEs (M87, M49, NGC 1399, NGC 5128, and NGC 4636), and discuss the implication of these results for the formation models of the GC system in gEs.

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 active galactic nucleus (AGN) subclasses in investigating the origin of the black hole mass–stellar velocity dispersion () relation because of their high accretion rate and significantly low . Currently, it is under discussion whether present-day NLS1s offset from the relation. Using the directly measured stellar velocity dispersion of 93 NLS1s at z < 0.1, and estimates based on the updated mass estimators, we investigate the relation of NLS1s in comparison with broad-line AGNs. We find no strong evidence that the NLS1s deviates from the 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., galaxies that are more inclined toward the LOS have higher stellar velocity dispersions, 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 (f = 1.12), for estimators based on the FWHM of Hβ, by jointly fitting the relation using quiescent galaxies and reverberation-mapped AGNs.

Wide-Field Survey of Globular Clusters in M31. II. Kinematics of the Globular Cluster System*

We present a kinematic analysis of the globular cluster (GC) system in M31, using the velocity data for 504 GCs including those for 150 GCs in our wide-field survey. The all GC system shows strong rotation, with rotation amplitude of -->vrot ~ 190 km s−1, and weak rotation persists even for the outermost samples at -->| Y| ≥ 5 kpc, where Y represents the projected distance from the major axis. The rotation-corrected velocity dispersion for the GC system is estimated to be -->σp,r ~ 130 km s−1, and it increases from -->σp,r ~ 120 km s−1 at -->| Y| σp,r ~ 150 km s−1 at -->| Y| ≥ 5 kpc. These results are very similar to those for the metal-poor GCs. This shows that there is a dynamically hot halo in M31 that is rotating but primarily pressure-supported. We have identified 50 friendless GCs, and they appear to rotate around the major axis of M31. Both metal-rich GCs and metal-poor GCs show strong rotation in the inner region. The rotation for the faint GCs is stronger than that for the bright GCs. We have identified 56 GCs and GC candidates with X-ray detection including 39 GCs with measured velocities. The majority of X-ray-emitting GCs follow the disk rotation. We have derived a rotation curve of M31 using the GCs at -->| Y| ≤ 0.6 kpc. We have estimated the dynamical mass of M31 using Projected Mass Estimator (PME) and Tracer Mass Estimator (TME) as -->MPME = 5.5+ 0.4−0.3 × 1011 M☉ out to a radius of ~55 kpc and -->MTME = 19.2+ 1.4−1.3 × 1011 M☉ for a radius of ~100 kpc, respectively. We finally discuss the implication of these results and compare the kinematics of GCs with that of planetary nebulae in M31.

Wide-Field Survey of Globular Clusters in M31. I. A Catalog of New Clusters

We present the result of a wide-field survey of globular clusters (GCs) in M31 covering a 3° × 3° field centered on M31. We have searched for GCs on CCD images taken with Washington CMT1 filters at the KPNO 0.9 m telescope using the following steps: (1) inspection of morphological parameters given by the SExtractor package such as stellarity, full width at half-maximum, and ellipticity; (2) consulting the spectral types and radial velocities obtained from spectra taken with the Hydra spectrograph at the WIYN 3.5 m telescope; and (3) visual inspection of the images of each object. We have found 1164 GCs and GC candidates, of which 605 are newly found GCs and GC candidates and 559 are previously known GCs. Among the new objects there are 113 genuine GCs, 258 probable GCs, and 234 possible GCs, according to our classification criteria. Among the known objects there are 383 genuine GCs, 109 probable GCs, and 67 possible GCs. In total there are 496 genuine GCs, 367 probable GCs, and 301 possible GCs. Most of these newly found GCs have T1 magnitudes of 17.5-19.5 mag [17.9 < V < 19.9 mag assuming (C - T1) ≈ 1.5], and (C - T1) colors in the range 1-2.

The Star Formation History of LGS 3

We have determined the distance and star formation history of the Local Group dwarf galaxy LGS 3 from deep Hubble Space Telescope WFPC2 observations. LGS 3 is intriguing because ground-based observations showed that, while its stellar population is dominated by old, metal-poor stars, there is a handful of young, blue stars. Also, the presence of H I gas makes this a possible transition object between dwarf spheroidal and dwarf irregular galaxies. The HST data are deep enough to detect the horizontal branch and young main sequence for the first time. A new distance of D = 620 ± 20 kpc has been measured from the positions of the tip of the red giant branch, the red clump, and the horizontal branch. The mean metallicity of the stars older than 8 Gyr is [Fe/H] = -1.5 ± 0.3. The most recent generation of stars has [Fe/H] ≈ -1. For the first few Gyr the global star formation rate was several times higher than the historical average and has been fairly constant since then. However, we do see significant changes in stellar populations and star formation history with radial position in the galaxy. Most of the young stars are found in the central 63 pc (21), where the star formation rate has been relatively constant, while the outer parts have had a declining star formation rate.

Extended Star Clusters in the Remote Halo of the Intriguing Dwarf Galaxy NGC?6822

We present a study on four new star clusters discovered in the halo of the intriguing dwarf irregular galaxy NGC 6822 from a wide-field survey covering 3{sup 0} x 3{sup 0} area carried out with MegaCam at the Canada-France-Hawaii Telescope. The star clusters have extended structures with half-light radii R{sub h} {approx} 7.5-14.0 pc, larger than typical Galactic globular clusters and other known globular clusters in NGC 6822. The integrated colors and color-magnitude diagrams of resolved stars suggest that the new star clusters are 2-10 Gyr old and relatively metal poor with Z = 0.0001-0.004 based on the comparison with theoretical models. The projected distance of each star cluster from the galaxy center ranges from 10.7 ({approx}1.5 kpc) to 77 ({approx}11 kpc), far beyond the optical body of the galaxy. Interestingly, the new star clusters are aligned along the elongated old stellar halo of NGC 6822, which is almost perpendicular to the H I gas distribution where young stellar populations exist. We also find that the colors and half-light radii of the new clusters are correlated with the galactocentric distance: clusters farther from the galaxy center are larger and bluer than those closer to the galaxy center. We discuss themorexa0» stellar structure and evolution of NGC 6822 implied by these new extended star clusters in the halo. We also discuss the current status of observational and theoretical understandings regarding the origin of extended star clusters in NGC 6822 and other galaxies.«xa0less

Washington CCD Photometry of the Globular Cluster System of the Giant Elliptical Galaxy M60 in Virgo

We present a photometric study of the GCs in the giant elliptical galaxy M60 in the Virgo Cluster, based on deep, relatively wide field Washington -->CT1 CCD images. The CMD reveals a significant population of GCs in M60 and a large number of young luminous clusters in NGC 4647, a small companion spiral northwest of M60. The color distribution of the GCs in M60 is clearly bimodal, with a blue peak at -->(C − T1) = 1.37 and a red peak at -->(C − T1) = 1.87. We derive two new transformation relations between the -->(C − T1)0 color and [Fe/H] using the data for the GCs in our Galaxy and M49. Using these relations, we derive the metallicity distribution of the GCs in M60, which is also bimodal: a dominant metal-poor component with center at -->[ Fe/H ] = − 1.2, and a weaker metal-rich component with center at -->[ Fe/H ] = − 0.2. The radial number density profile of the GCs is more extended than that of the stellar halo, and the radial number density profile of the blue GCs is more extended than that of the red GCs. The number density maps of the GCs show that the spatial distribution of the blue GCs is roughly circular, while that of the red GCs is elongated similarly to that of the stellar halo. We estimate the total number of the GCs in M60 to be -->3600 ± 500 and the specific frequency to be -->SN = 3.8 ± 0.4. The mean color of the bright blue GCs gets redder as they get brighter in both the inner and outer region of M60. This blue tilt is seen also in the outer region of M49, the brightest Virgo galaxy. Implications of these results are discussed.

The Globular Cluster System of M60 (NGC 4649). I. Canada-France-Hawaii Telescope MOS Spectroscopy and Database*

We present radial velocity measurements for globular clusters in M60, a giant elliptical galaxy in the Virgo Cluster. Target globular cluster candidates were selected using Washington photometry based on deep 16 --> × 16 --> images taken at the KPNO 4 m telescope and using VI photometry derived from Hubble Space Telescope WFPC2 archival images. The spectra of the target objects were obtained with the Multi-Object Spectrograph at the Canada-France-Hawaii Telescope. We have measured the radial velocities of 111 objects in the field of M60: 93 globular clusters (72 blue globular clusters with 1.0 ≤ C– -->T1 T1 + 27−25 km s−1, which is in good agreement with the velocity of the nucleus of M60 ( -->vgal = 1056 km s−1). Combining our results with data from the literature, we present a master catalog of radial velocities for 121 globular clusters in M60. The velocity dispersion of the clusters in the master catalog is found to be 234 -->+ 13−14 km s−1 for the entire sample, 223 -->+ 13−16 km s−1 for 83 blue globular clusters, and 258 -->+ 21−31 km s−1 for 38 red globular clusters.