52 research outputs found
NICMOS Observations of Low-Redshift Quasar Host Galaxies
We have obtained Near-Infrared Camera and Multi-Object Spectrometer images of
16 radio quiet quasars observed as part of a project to investigate the
``luminosity/host-mass limit.'' The limit results were presented in McLeod,
Rieke, & Storrie-Lombardi (1999). In this paper, we present the images
themselves, along with 1- and 2-dimensional analyses of the host galaxy
properties. We find that our model-independent 1D technique is reliable for use
on ground-based data at low redshifts; that many radio-quiet quasars live in
deVaucouleurs-law hosts, although some of the techniques used to determine host
type are questionable; that complex structure is found in many of the hosts,
but that there are some hosts that are very smooth and symmetric; and that the
nuclei radiate at ~2-20% of the Eddington rate based on the assumption that all
galaxies have central black holes with a constant mass fraction of 0.6%.
Despite targeting hard-to-resolve hosts, we have failed to find any that imply
super-Eddington accretion rates.Comment: To appear in ApJ, 28 pages including degraded figures. Download the
paper with full-resolutio figures from
http://www.astro.wellesley.edu/kmcleod/mm.p
An Exploration of the Tully-Fisher Relation for Extreme Late-Type Spiral Galaxies
This paper explores the adherence of 47 extreme late-type galaxies to the B-
and V-band Tully-Fisher relations defined by a sample of local calibrators. In
both bands we find the mean luminosity at a given line width for extreme
late-type spirals to lie below that predicted by standard Tully-Fisher
relations. While many of the extreme late-type spirals do follow the
Tully-Fisher relation to within our observational uncertainties, most of these
galaxies lie below the normal, linear Tully-Fisher relation, and some are
underluminous by more than 2 sigma (i.e. >1.16 magnitudes in V). This suggests
a possible downward curvature of the Tully-Fisher relation for some of the
smallest and faintest rotationally supported disk galaxies. This may be a
consequence of the increasing prevalence of dark matter in these systems. We
find the deviation from the Tully-Fisher relation to increase with decreasing
luminosity and decreasing optical linear size in our sample, implying that the
physically smallest and faintest spirals may be a structurally and
kinematically distinct class of objects.Comment: 32 pages, 13 figures; to appear in the November A
Quasars and Ultraluminous Infrared Galaxies: At the Limit?
We have detected the host galaxies of 16 nearby, radio-quiet quasars using
images obtained with the Near-Infrared Camera and Multi-Object Spectrometer
(NICMOS). We confirm that these luminous quasars tend to live in luminous,
early-type host galaxies, and we use the host-galaxy magnitudes to refine the
luminosity/host-mass limit inferred from ground-based studies. If quasars obey
the relation found for massive dark
objects in nonactive galaxies, then our analysis implies that they radiate at
up to of the Eddington rate. An analogous analysis for ultraluminous
infrared galaxies shows them to accrete at up to similar Eddington fractions,
consistent with the hypothesis that some of them are powered by embedded
quasars.Comment: 9 pages, includes 2 eps figs, accepted to ApJLet
The Extended Line Region of 3C 299
We present results of HST observations of the radio galaxy 3C 299. The
broad-band F702W (R) and F555W (V) images (WFPC2/PC) show an elliptical galaxy,
with a comet-like structure extending to the NE in the radio jet direction. The
[OIII]5007 emission line map, shows a bi-conical structure centered on
the nucleus, that overlaps the structure found in the broad-band filters. The
radio core coincides with the center of the bi-conical structure and the radio
axes are aligned with the direction of the cones. These data show clear
evidence of a strong interaction between the radio jet and the NE morphology of
the galaxy. We show evidence that this NE region is an ENLR; the line-ratio
diagnostics show that models involving gas shocked by the radio-jet plus
ionization from a precursor HII region, produced itself by the ionizing photons
of the postshocked gas on the preshocked gas provide a good match to the
observations. We investigate the spatial behavior of the ionizing parameter
, by determining the [OIII]/[OII] line ratio which is sensitive to the
change of the ionization parameter, and trace its behavior over the ENLR along
the radio jet direction. We find that [OIII]/[OII] does not follow a simple
dilution model, but rather that it is approximately constant over a large range
of distance from the nucleus thus requiring a local source of ionization which
seems to be compatible with the shock models driven by the radio jet.Comment: 17 pages, 9 Postscript figures, ApJ accepted, uses aaspp.st
Type II Quasars from the Sloan Digital Sky Survey: V. Imaging host galaxies with the Hubble Space Telescope
Type II quasars are luminous Active Galactic Nuclei whose centers are
obscured by large amounts of gas and dust. In this paper we present 3-band HST
images of nine type II quasars with redshifts 0.2 < z < 0.4 selected from the
Sloan Digital Sky Survey based on their emission line properties. The intrinsic
luminosities of these AGN are estimated to be -24 > M_B > -26, but optical
obscuration allows their host galaxies to be studied unencumbered by bright
nuclei. Each object has been imaged in three continuum filters (`UV', `blue'
and `yellow') placed between the strong emission lines. The spectacular, high
quality images reveal a wealth of details about the structure of the host
galaxies and their environments. Six of the nine galaxies in the sample are
ellipticals with de Vaucouleurs light profiles, one object has a well-defined
disk component and the remaining two have marginal disks. Stellar populations
of type II quasar hosts are more luminous (by a median of 0.3-0.7 mag,
depending on the wavelength) and bluer (by about 0.4 mag) than are M* galaxies
at the same redshift. When smooth fits to stellar light are subtracted from the
images, we find both positive and negative residuals that become more prominent
toward shorter wavelengths. We argue that the negative residuals are due to
kpc-scale dust obscuration, while most positive residuals are due to the light
from the nucleus scattered off interstellar material in the host galaxy.
Scattered light makes a significant contribution to the broad band continuum
emission and can be the dominant component of the extended emission in the UV
in extreme cases.Comment: 51 pages, including 12 grey scale figures, 4 color figures, 5 tables.
In press in AJ. Version with higher-resolution images available at
http://www.astro.princeton.edu/~nadia/qso2.html. (Minor changes in response
to the referee report
Spectroscopy of Low Surface Brightness Galaxies with the Hobby-Eberly Telescope
We have obtained low resolution spectra of nineteen red and blue low surface
brightness galaxies, using the Marcario Low Resolution Spectrograph on the 9.2m
Hobby-Eberly Telescope. These galaxies form a very heterogeneous class, whose
spectra qualitatively resemble those of high surface brightness galaxies
covering the full range of spectra seen in galaxies of Hubble types from E to
Irr. We use a combination of emission line (EW(Halpha), NII/Halpha) and
absorption line (Mgb, Hbeta, ) based diagnostics to investigate the
star-formation and chemical enrichment histories of these galaxies. These are
diverse, with some galaxies having low metallicity and very young mean stellar
ages, and other galaxies showing old, super-solar metallicity stellar
populations. In contrast with some previous studies which found a strong trend
of decreasing metallicity with decreasing central surface brightness, we find a
population of galaxies with low surface brightness and near-solar metallicity.
Correlations between several of the gas phase and stellar population age and
metallicity indicators are used to place contraints on plausible evolutionary
scenarios for LSB galaxies. The redshift range spanned by these galaxies is
broad, with radial velocities from 3400 km/s to more than 65000 km/s. A subset
of the sample galaxies have published HI redshifts and gas masses based on
observations with the Arecibo 305m single-dish radio telescope, which place
these galaxies far off of the mean Tully-Fisher relation. Our new optical
redshifts do not agree with the published HI redshifts for these galaxies. Most
of the discrepancies can be explained by beam confusion in the Arecibo
observations, causing erroneous HI detections for some of the galaxies.Comment: 31 pages, 12 figures, 7 tables. Uses emulateapj5.sty and
onecolfloat5.sty, which are included. Accepted for publication in the
Astronomical Journa
Oxygen and Nitrogen in Leo A and GR 8
We present elemental abundances for multiple HII regions in Leo A and GR 8
obtained from long slit optical spectroscopy of these two nearby low luminosity
dwarf irregular galaxies. As expected from their luminosities, and in agreement
with previous observations, the derived oxygen abundances are extremely low in
both galaxies. High signal-to-noise ratio observations of a planetary nebula in
Leo A yield 12 + log(O/H) = 7.30 +/- 0.05; "semi-empirical" calculations of the
oxygen abundance in four HII regions in Leo A indicate 12 + log(O/H) = 7.38 +/-
0.10. These results confirm that Leo A has one of the lowest ISM metal
abundances of known nearby galaxies. Based on results from two HII regions with
high signal-to-noise measurements of the weak [O III] 4363 line, the mean
oxygen abundance of GR 8 is 12 + log(O/H) = 7.65 +/- 0.06; using "empirical"
and "semi-empirical" methods, similar abundances are derived for 6 other GR 8
HII regions. Similar to previous results in other low metallicity galaxies, the
mean log(N/O) = -1.53 +/- 0.09 for Leo A and -1.51 +/- 0.07 for GR 8. There is
no evidence of significant variations in either O/H or N/O in the HII regions.
The metallicity-luminosity relation for nearby (D < 5 Mpc) dwarf irregular
galaxies with measured oxygen abundances has a mean correlation of 12 +
log(O/H) = 5.67 - 0.151 M_B with a dispersion in oxygen about the relationship
of 0.21. These observations confirm that gas-rich low luminosity galaxies have
extremely low elemental abundances in the ionized gas-phase of their
interstellar media. Although Leo A has one of the lowest metal abundances of
known nearby galaxies, detection of tracers of an older stellar population
indicate that it is not a newly formed galaxy as has been proposed for some
other similarly low metallicity star forming galaxies.Comment: 36 pages, 7 figures. Accepted to Ap
An Unusual Radio Galaxy in Abell 428: A Large, Powerful FR I Source in a Disk-Dominated Host
We report the discovery of a powerful (~10^{24} Watts/Hz) FR I radio source
in a highly flattened disk-dominated galaxy. Half of the radio flux from this
source is concentrated within the host galaxy, with the remainder in a pair of
nearly symmetrical lobes with total extent ~200kpc nearly perpendicular to the
disk. The traditional wisdom maintains that powerful, extended radio sources
are found only in ellipticals or recent merger events. We report B,R,J, and K
imaging, optical spectroscopy, a rotation curve, an IRAS detection, and a VLA
20cm image for this galaxy, 0313-192. The optical and NIR images clearly show a
disk. We detect apparent spiral arms and a dust-lane from B band imaging. The
reddened nucleus is consistent with extinction by a similar dust-lane. The
optical spectrum suggests a central AGN and some evidence of a starburst, with
both the AGN and central starlight appearing substantially reddened. From
analysis of the extended line emission in [OIII] and H-alpha we derive a
rotation curve consistent with an early- type, dusty spiral seen edge-on. From
the IRAS detection at 60 and 100 microns, we find that the ratio of Far IR to
radio flux places this object firmly as a radio galaxy (i.e. the radio emission
is not powered by star formation). The radio structure suggests that the radio
source in this galaxy is related to the same physical mechanisms present in
jet-fed powerful radio sources, and that such powerful, extended sources can
(albeit extremely rarely) occur in a disk-dominated host.Comment: 30 pages LaTeX, 1 table, 8 postscript figures. Accepted for
publication in the Astrophysical Journa
Modelling the Interstellar Medium of Low Surface Brightness Galaxies: Constraining Internal Extinction, Disk Color Gradients, and Intrinsic Rotation Curve Shapes
We use a combination of three-dimensional Monte Carlo radiative transfer
techniques and multi-wavelength (BRHK,H alpha) imaging data to investigate the
nature of the interstellar medium (ISM) in the edge-on, low surface brightness
(LSB) galaxy UGC7321. Using realistic models that incorporate multiple
scattering effects and clumping of the stars and the interstellar material, we
explore the distribution and opacity of the interstellar material (gas+dust),
and its effects on the observed stellar disk luminosity profiles, color
gradients, and rotation curve shape. We find that UGC7321 contains a small but
non-negligible dusty component to its ISM, yielding a B-band optical depth
tau_e,B~4.0 from disk edge to center. A significant fraction (~50+/-10%) of the
interstellar material in the innermost regions of UGC7321 appears to be
contained in a clumpy medium, indicating that LSB galaxies can support a
modest, multi-phase ISM structure. In spite of the clear presence of dust, we
conclude that the large radial optical color gradients observed in UGC7321 and
other similar LSB spiral galaxies cannot be accounted for by dust and must
result primarily from significant stellar population and/or metallicity
gradients. We show that realistic optical depth effects will have little impact
on the observed rotation curves of edge-on disk galaxies and cannot explain the
linear, slowly rising rotation curves seen in some edge-on LSB spirals.
Projection effects create a far larger uncertainty in recovering the true
underlying rotation curve shape of galaxies viewed at inclinations i>85
degrees.Comment: accepted to ApJ; 16 pages, 2 tables, and 18 figures; uses
emulateapj.st
The Relationship Between Gas, Stars, and Star Formation in Irregular Galaxies: A Test of Simple Models
We explore various instability models for the onset of star formation in
irregular galaxies. Critical gas densities are calculated for gravitational
instabilities with a thin, pure-gas disk, and with a thick disk composed of gas
and a star-like fluid. We also calculated the stability properties of three
dimensional systems including dark matter, considered the thermal state of the
gas, and used a modified threshold column density written in terms of the local
rate of shear instead of the epicyclic frequency. The model predictions were
compared to the azimuthally-averaged present day star formation activity traced
by the Halpha surface brightness, and to the 1 Gyr-integrated star formation
activity represented by the stellar surface brightness.
The ratio of the observed gas density to the critical gas density is lower by
a factor of 2 in most of the Im galaxies than it is in spiral galaxies. Star
formation ends before this ratio drops significantly in the outer regions, and
it remains high in the inner regions where the ratio is often low. These
results suggest that the critical gas density does not trace star formation
with the same detail in irregular galaxies as it appears to trace it in giant
spiral galaxies. The only azimuthally-averaged quantity that correlates with
the current star formation activity in irregulars is the stellar surface
density. Theoretical implications are discussed.Comment: 39 pages, 7 figures, to appear in Astrophysical Journal, Vol. 493,
Feb 1, 199
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