38 research outputs found
Does the Narrow [O III] 5007 Line Reflect the Stellar Velocity Dispersion in AGN?
It has been proposed that the width of the narrow [O III] 5007 emission line
can be used as a surrogate for the stellar velocity dispersion in active
galaxies. This proposition is tested using the SDSS EDR spectra of 107
low-redshift radio-quiet QSOs and Seyfert 1 galaxies by investigating the
correlation between black hole mass, as determined from H-beta FWHM and optical
luminosity, and [O III] FWHM. The correlation is real, but the scatter is
large. Without additional information or selection criteria, the [O III] width
can predict the black hole mass to a factor of 5.Comment: 15 pages including 2 figures, accepted for publication in Ap.
The ages of quasar host galaxies
We present the results of fitting deep off-nuclear optical spectroscopy of
radio-quiet quasars, radio-loud quasars and radio galaxies at z ~ 0.2 with
evolutionary synthesis models of galaxy evolution. Our aim was to determine the
age of the dynamically dominant stellar populations in the hos t galaxies of
these three classes of powerful AGN. Some of our spectra display residual
nuclear contamination at the shortest wavelengths, but the detailed quality of
the fits longward of the 4000A break provide unequivocal proof, if further
proof were needed, that quasars lie in massive galaxies with (at least at z ~
0.2) evolved stellar populations. By fitting a two-component model we have
separated the very blue (starburst and/or AGN contamination) from the redder
underlying spectral energy distribution, and find that the hosts of all three
classes of AGN are dominated by old stars of age 8 - 14 Gyr. If the blue
component is attributed to young stars, we find that, at most, 1% of the
baryonic mass of these galaxies is involved in star-formation activity at the
epoch of observation. These results strongly support the conclusion reached by
McLure et al. (1999) that the host galaxies of luminous quasars are massive
ellipticals which formed prior to the peak epoch of quasar activity at z ~ 2.5.Comment: 24 pages, LaTeX, uses MNRAS style file, incorporates 19 postscript
figures, final version, to be published in MNRA
A Candidate Sub-Parsec Supermassive Binary Black Hole System
We identify SDSS J153636.22+044127.0, a QSO discovered in the Sloan Digital
Sky Survey, as a promising candidate for a binary black hole system. This QSO
has two broad-line emission systems separated by 3500 km/sec. The redder system
at z=0.3889 also has a typical set of narrow forbidden lines. The bluer system
(z=0.3727) shows only broad Balmer lines and UV Fe II emission, making it
highly unusual in its lack of narrow lines. A third system, which includes only
unresolved absorption lines, is seen at a redshift, z=0.3878, intermediate
between the two emission-line systems. While the observational signatures of
binary nuclear black holes remain unclear, J1536+0441 is unique among all QSOs
known in having two broad-line regions, indicative of two separate black holes
presently accreting gas. The interpretation of this as a bound binary system of
two black holes having masses of 10^8.9 and 10^7.3 solar masses, yields a
separation of ~ 0.1 parsec and an orbital period of ~100 years. The separation
implies that the two black holes are orbiting within a single narrow-line
region, consistent with the characteristics of the spectrum. This object was
identified as an extreme outlier of a Karhunen-Loeve Transform of 17,500 z <
0.7 QSO spectra from the SDSS. The probability of the spectrum resulting from a
chance superposition of two QSOs with similar redshifts is estimated at
2X10^-7, leading to the expectation of 0.003 such objects in the sample
studied; however, even in this case, the spectrum of the lower redshift QSO
remains highly unusual.Comment: 8 pages, 2 figures, Nature in pres
HST Images and KPNO Spectroscopy of the Binary Black Hole Candidate SDSS J153636.22+044127.0
We present HST WFPC2/PC images and KPNO 4-m longslit spectroscopy of the QSO
SDSS J153636.22+044127.0, which we advanced as a candidate binary supermassive
black hole. The images reveal a close companion coincident with the radio
source identified by Wrobel & Laor (2009). It appears to be consistent with a
M_g ~ -21.4 elliptical galaxy, if it is at the QSO redshift. The spectroscopy,
however, shows no spatial offset of the red or blue Balmer line subcomponents.
The companion is thus not the source of either the red or blue broad line
systems; SDSS J153636.22+044127.0 cannot be explained as a chance superposition
of objects, or as an ejected black hole. Over the Delta T=0.75 yr difference
between the rest frame epochs of the present and SDSS spectroscopy, we find no
velocity shift to within 40 km/s, nor any amplitude change in either broad line
system. The lack of a shift can be admitted under the binary hypothesis if the
implied radial velocity is a larger component of the full orbital velocity than
was assumed in our earlier work. A strong test of the binary hypothesis
requires yet longer temporal baselines. The lack of amplitude variations is
unusual for the alternative explanation of this object as a "double-peaked"
emitter; we further argue that SDSS J153636.22+044127.0 has unique spectral
features that have no obvious analogue with other members of this class.Comment: 19 pages, 7 figures, revised and accepted for publication in Ap
Exploring the Spectral Space of Low Redshift QSOs
The Karhunen-Loeve (KL) transform can compactly represent the information
contained in large, complex datasets, cleanly eliminating noise from the data
and identifying elements of the dataset with extreme or inconsistent
characteristics. We develop techniques to apply the KL transform to the
4000-5700A region of 9,800 QSO spectra with z < 0.619 from the SDSS archive. Up
to 200 eigenspectra are needed to fully reconstruct the spectra in this sample
to the limit of their signal/noise. We propose a simple formula for selecting
the optimum number of eigenspectra to use to reconstruct any given spectrum,
based on the signal/noise of the spectrum, but validated by formal
cross-validation tests. We show that such reconstructions can boost the
effective signal/noise of the observations by a factor of 6 as well as fill in
gaps in the data. The improved signal/noise of the resulting set will allow for
better measurement and analysis of these spectra. The distribution of the QSO
spectra within the eigenspace identifies regions of enhanced density of
interesting subclasses, such as Narrow Line Seyfert 1s (NLS1s). The weightings,
as well as the inability of the eigenspectra to fit some of the objects, also
identifies "outliers," which may be objects that are not valid members of the
sample or objects with rare or unique properties. We identify 48 spectra from
the sample that show no broad emission lines, 21 objects with unusual [O III]
emission line properties, and 9 objects with peculiar H-beta emission line
profiles. We also use this technique to identify a binary supermassive black
hole candidate. We provide the eigenspectra and the reconstructed spectra of
the QSO sample.Comment: 34 pages, 14 figures, revised version resubmitted to the Astronomical
Journa
The UV Properties of the Narrow Line Quasar I Zwicky 1
I Zw 1 is the prototype narrow line quasar. We report here the results of our
study of the UV emission of I Zw 1 using a high S/N (50-120) spectrum obtained
with the HST FOS. The following main new results are obtained: 1. The Mg II and
Al III doublets are partially/fully resolved. The measured doublet ratios
verify theoretical predictions that the lines are thermalized in the BLR. 2. A
weak associated UV absorption system is detected in N~V, and possibly also in C
IV and Lya, suggesting an outflow with a velocity of 1870 km/s and velocity
dispersion <300 km/s. 3. Lines from ions of increasing ionization level show
increasing excess blue wing flux, and an increasing line peak velocity shift,
reaching a maximum blueshift of about 2000 km/s for He II 1640. This may
indicate an out-flowing component in the BLR, where the ionization level
increases with velocity, and which is visible only in the approaching
direction. The highest velocity part of this outflow may produce the associated
UV absorption system. 4. The small C III] 1909 EW, and the small C III]
1909/Lya and C III] 1909/Si III] 1892 flux ratios indicate a typical BLR
density of 10^11, i.e. about an order of magnitude larger than implied by C
III] 1909 in most quasars. A BLR component of a higher density is implied by
the EW and doublet ratio of the Al III 1857 doublet. 5. Prominent Fe II UV 191
emission is seen, together with weaker line emission at 1294 and 1871 A. These
three features have been proposed as evidence for significant Lya pumping of
the 8-10 eV levels of Fe II. 6. Significant Fe III emission is present. The Fe
III UV 34 and UV 48 multiplets are clearly resolved, and Fe III UV 1, UV 47, UV
50, and UV 68 may also be present. (Shortened version)Comment: 28 pages, 1 table and 7 figures included. Uses aas2pp4.sty. Scheduled
for the Astrophysical Journal November 10, 1997 issue, Vol. 48
Deep CCD Surface Photometry of the Edge-On Spiral NGC 4244
We have obtained deep surface photometry of the edge-on spiral galaxy NGC
4244. Our data reliably reach 27.5 R magnitude arcsec^{-2}, a significant
improvement on our earlier deep CCD surface photometry of other galaxies. NGC
4244 is a nearby Scd galaxy whose total luminosity is approximately one
magnitude fainter than the peak of the Sc luminosity function. We find that it
has a simple structure: a single exponential disk, with a scale height h_Z =
246 +/- 2 pc, a scale length h_R = 1.84 +/- 0.02 kpc and a disk cutoff at a
radius R(max) = 10.0 kpc (5.4 scale lengths). We confirm a strong cutoff in the
stellar disk at R(max), which happens over only 1 kpc. We do not see any
statistically significant evidence for disk flaring with radius. Unlike the
more luminous Sc galaxies NGC 5907 and M 33, NGC 4244 does not show any
evidence for a second component, such as a thick disk or halo, at mu(R) < 27.5
magnitude arcsec^{-2}.Comment: 36 pages, including 12 figures; accepted for publication in Sept 99
A
The KPNO International Spectroscopic Survey. V. H-alpha-selected Survey List 3
The KPNO International Spectroscopic Survey (KISS) is an objective-prism
survey designed to detect extragalactic emission-line objects. It combines many
of the features of previous slitless spectroscopic surveys with the advantages
of modern CCD detectors, and is the first purely digital objective-prism survey
for emission-line galaxies (ELGs). Here we present the third list of ELG
candidates selected from our red spectral data, which cover the wavelength
range 6400 to 7200 A. In most cases, the detected emission line is H-alpha. The
current survey list covers the region of the NOAO Deep Wide-Field Survey
(NDWFS). This survey covers two fields; the first is 3 x 3 degrees square and
located at RA = 14h 30m, DEC = 34.5 deg (B1950), the second is 2.3 x 4.0
degrees and centered at RA = 2h 7.5m, DEC = -4.75 deg. A total area of 19.65
deg^2 is covered by the KISS data. A total of 261 candidate emission-line
objects have been selected for inclusion in the survey list (13.3 per deg^2).
We tabulate accurate coordinates and photometry for each source, as well as
estimates of the redshift, emission-line flux and line equivalent width based
on measurements of the digital objective-prism spectra. The properties of the
KISS ELGs are examined using the available observational data. When combined
with the wealth of multi-wavelength data already available for the NDWFS
fields, the current list of KISS ELGs should provide a valuable tool for
studying star-formation and nuclear activity in galaxies in the local universe.Comment: 18 pages, including 10 figures and 4 tables. Accepted for publication
in the December, 2005 A