26 research outputs found
The Black Hole Mass - Galaxy Bulge Relationship for QSOs in the SDSS DR3
We investigate the relationship between black hole mass and host galaxy
velocity dispersion for QSOs in Data Release 3 of the Sloan Digital Sky Survey.
We derive black hole mass from the broad Hbeta line width and continuum
luminosity, and the bulge stellar velocity dispersion from the [OIII] narrow
line width. At higher redshifts, we use MgII and [OII] in place of Hbeta and
[OIII]. For redshifts z < 0.5, our results agree with the black hole mass -
bulge velocity dispersion relationship for nearby galaxies. For 0.5 < z < 1.2,
this relationship appears to show evolution with redshift in the sense that the
bulges are too small for their black holes. However, we find that part of this
apparent trend can be attributed to observational biases, including a Malmquist
bias involving the QSO luminosity. Accounting for these biases, we find ~0.2
dex evolution in the black hole mass-bulge velocity dispersion relationship
between now and redshift z ~ 1.Comment: Accepted by ApJ, 15 pages, 9 figure
A variability study of the Seyfert 2 galaxy NGC 6300 with XMM-Newton
We present the results of timing analysis of the XMM-Newton observation of
the Seyfert 2 galaxy NGC 6300. The hard X-ray spectrum above 2 keV consists of
a Compton-thin-absorbed power law, as is often seen in Seyfert 2 galaxies. We
clearly detected rapid time variability on a time scale of about 1000 s from
the light curve above 2 keV. The excess variance of the time variability
(sigma2_RMS) is calculated to be ~0.12, and the periodogram of the light curve
is well represented by a power law function with a slope of 1.75. In contrast
with previous results from Seyfert 2 nuclei, these variability characteristics
are consistent with those of Seyfert 1 galaxies. This consistency suggests that
NGC 6300 has a similar black hole mass and accretion properties as Seyfert 1
galaxies. Using the relation between time variability and central black hole
mass by Hayashida et al. (1998), the black hole mass of NGC 6300 is estimated
to be ~2.8x10^5 Mo. Taking uncertainty of this method into account, the black
hole mass is less than 10^7 Mo. Taking the bolometric luminosity of 3.3x10^43
erg/s into consideration, this yields an accretion rate of > 0.03 of the
Eddington value, and comparable with estimates from Seyfert 1 galaxies using
this method. The time variability analysis suggests that NGC 6300 actually has
a Seyfert 1 nucleus obscured by a thick matter, and more generally provides a
new pillar of support for the unified model of Seyfert galaxies based on
obscuration.Comment: 11 pages, 6 figures, accepted for publication in Ap
Deep CCD Surface Photometry of Galaxy Clusters I: Methods and Initial Studies of Intracluster Starlight
We report the initial results of a deep imaging survey of galaxy clusters.
The primary goals of this survey are to quantify the amount of intracluster
light as a function of cluster properties, and to quantify the frequency of
tidal debris. We outline the techniques needed to perform such a survey, and we
report findings for the first two galaxy clusters in the survey: Abell 1413,
and MKW 7 . These clusters vary greatly in richness and structure. We show that
our surface photometry reliably reaches to a surface brightness of \mu_v = 26.5
mags per arcsec. We find that both clusters show clear excesses over a
best-fitting r^{1/4} profile: this was expected for Abell 1413, but not for MKW
7. Both clusters also show evidence of tidal debris in the form of plumes and
arc-like structures, but no long tidal arcs were detected. We also find that
the central cD galaxy in Abell 1413 is flattened at large radii, with an
ellipticity of , the largest measured ellipticity of any cD galaxy
to date.Comment: 58 pages, 24 figures, accepted for publication in the Astrophysical
Journal. Version has extremely low resolution figures to comply with 650k
limit. High resolution version is available at
http://burro.astr.cwru.edu/johnf/icl1.ps.gz Obtaining high resolution version
is strongly reccomende
Statistical Properties of Radio Emission from the Palomar Seyfert Galaxies
We have carried out an analysis of the radio and optical properties of a
statistical sample of 45 Seyfert galaxies from the Palomar spectroscopic survey
of nearby galaxies. We find that the space density of bright galaxies (-22 mag
<= M_{B_T} <= -18 mag) showing Seyfert activity is (1.25 +/- 0.38) X 10^{-3}
Mpc^{-3}, considerably higher than found in other Seyfert samples. Host galaxy
types, radio spectra, and radio source sizes are uncorrelated with Seyfert
type, as predicted by the unified schemes for active galaxies. Approximately
half of the detected galaxies have flat or inverted radio spectra, more than
expected based on previous samples. Surprisingly, Seyfert 1 galaxies are found
to have somewhat stronger radio sources than Seyfert 2 galaxies at 6 and 20 cm,
particularly among the galaxies with the weakest nuclear activity. We suggest
that this difference can be accommodated in the unified schemes if a minimum
level of Seyfert activity is required for a radio source to emerge from the
vicinity of the active nucleus. Below this level, Seyfert radio sources might
be suppressed by free-free absorption associated with the nuclear torus or a
compact narrow-line region, thus accounting for both the weakness of the radio
emission and the preponderance of flat spectra. Alternatively, the flat spectra
and weak radio sources might indicate that the weak active nuclei are fed by
advection-dominated accretion disks.Comment: 18 pages using emulateapj5, 13 embedded figures, accepted by Ap
Remnant of a "Wet" Merger: NGC 34 and Its Young Massive Clusters, Young Stellar Disk, and Strong Gaseous Outflow
This paper presents new images and spectroscopy of NGC 34 (Mrk 938) obtained with the du Pont 2.5-m and Baade 6.5-m telescopes at Las Campanas, plus photometry of an HST archival V image. This Mv = -21.6 galaxy has often been classified as a Seyfert 2, yet recently published infrared spectra suggest a dominant central starburst. We find that the galaxy features a single nucleus, a main spheroid containing a blue central disk, and tidal tails indicative of two former disk galaxies. These galaxies appear to have completed merging. The remnant shows three clear optical signs that the merger was gas-rich ("wet") and accompanied by a starburst: (1) It sports a rich system of young star clusters, of which 87 have absolute magnitudes -10.0 > Mv > -15.4. Five clusters with available spectra have ages in the range 0.1-1.0 Gyr, photometric masses between 2x10^6 and 2x10^7 Msun, and are gravitationally bound young globulars. (2) The blue central disk appears to be young. It is exponential, can be traced to >10 kpc radius, and has a smooth structure and colors suggest- ing a dominant, ~400 Myr old poststarburst population. And (3), the center of NGC 34 drives a strong outflow of cool, neutral gas, as revealed by broad blueshifted Na I D lines. The mean outflow velocity of this gas is -620 km/s, while the maximum velocity reaches -1050 km/s. We suggest that NGC 34 stems from two recently merged gas-rich disk galaxies with an estimated mass ratio between 1/3 and 2/3. The remnant seems to have first experienced a galaxy-wide starburst that then shrank to its current central and obscured state. The strong gaseous outflow came last. (Abridged
Stochastic Relaxation as a Tool for Bayesian Modeling of Astronomical Images
. Sampling techniques are used to explore the Bayesian posterior density in imaging problems. Besides the familiar MAP estimators, such techniques can easily provide more detailed information on the posterior, such as moments and marginal densities. From these, error bars and confidence levels can be assessed, and hypothesis testing performed. The algorithms are implemented in IRAF, and are being tested on both simulated and actual ROSAT images. 1. Introduction The image formation process introduces uncertainties in pixel values, due to both deterministic (Point Response Function, PRF) and random (noise) effects. The traditional approach to this problem involves some sort of inversion technique, and these are usually unable to use optimally all of the information available both a priori and in the data. An alternative approach is to adopt a data modeling perspective of the imaging problem. The work reported here aims at developing Bayesian-inference signal modeling methods based on sa..
Bragg stacks enhancing upconversion for photovoltaics: A theoretical and experimental analysis
To enhance upconversion, we optimize Bragg stacks considering changes of local field, density of states and dynamics of β-NaYF4:Er3+. We experimentally characterize the impact on upconversion luminescence, spectrally resolved and power-dependent