492 research outputs found
The Spectral Energy Distribution of Normal, Starburst and Active Galaxies
We present the results of an extensive literature search of multiwavelength
data for a sample of 59 galaxies, consisting of 26 Starbursts, 15 Seyfert 2's,
5 LINER's, 6 normal spirals and 7 normal elliptical galaxies. The data include
soft X-ray fluxes, ultraviolet and optical spectra, near, mid/far infrared
photometry and radio measurements, selected to match as closely as possible the
IUE aperture (10" X 20"). The galaxies are separated into 6 groups with similar
characteristics, namely, Ellipticals, Spirals, LINER's, Seyfert 2's, Starbursts
of Low and High reddening, for which we create average spectral energy
distributions (SED). The individual groups SED's are normalized to the
7000\AA flux and compared, looking for similarities and differences
among them.The bolometric fluxes of different types of galaxies were calculated
integrating their SED's. These values are compared with individual waveband
flux densities, in order to determine the wavebands which contribute most to
the bolometric flux. Linear regressions were performed between the bolometric
and individual band fluxes for each kind of galaxy. These fits can be used in
the calculation of the bolometric flux for other objects of similar activity
type, but with reduced waveband information. We have also collected
multiwavelength data for 4 HII regions, a thermal supernova remnant, and a
non-thermal supernova remnant (SNR), which are compared with the Starburst
SED's.Comment: 29 pages, 13 postscript figures and 10 tables. To appear in The
Astronomical Journa
The Temperature of Extended Gas in Active Galaxies -- Evidence for Matter-Bounded Clouds
We report measurements of the electron temperature at about a dozen locations
in the extended emission-line regions of five active (Seyfert and radio)
galaxies. Temperatures (T_{[OIII]} and T_{[NII]}) have been determined from
both the I([OIII]\lambda4363)/I([OIII]\lambda5007) and
I([NII]\lambda5755)/I[NII]\lambda6583) ratios. T_{[OIII]} lies in the range
(1.0 -- 1.7) \times 10^{4}K. We find a strong trend for T_{[OIII]} to be higher
than T_{[NII]}, with the difference typically being \approx 5,000K. Because the
critical density for collisional de-excitation of the ^{1}D{_2} level in NII is
lower than that of the same level in OIII, the deviations of the measured
intensity ratios from those expected for T_{[OIII]} = T_{[NII]} in the low
density limit are unlikely to result from collisional de-excitation. The
measured values of T_{[OIII]} and the differences between T_{[OIII]} and
T_{[NII]} are very similar to those found in Galactic planetary nebulae. It is
argued that the dominant form of energy input to the clouds is photoionization,
but detailed modelling indicates that the temperature difference is too large
to be accounted for in terms of photoionization of ionization-bounded clouds.
We propose instead that both matter- and ionization-bounded clouds are present
in the extended emission-line regions, with most of the [OIII] emission
originating from a hot zone in the matter-bounded clouds and essentially all of
the [NII] from the ionization-bounded clouds.Comment: 14 pages, Latex, 3 postscript figures Astrophysical Journal
(Letters), in press for June 20 1997 issue, Volume 48
A New Superwind Wolf-Rayet Galaxy Mrk 1259
We report the discovery of a starburst-driven wind (superwind) from the
starburst nucleus galaxy Mrk 1259. The estimated number ratio of Wolf-Rayet
(WR) to O stars amounts to ~0.09. While the nuclear emission-line region is due
to usual photoionization by massive stars, the circumnuclear emission-line
regions show anomalous line ratios that can be due to cooling shocks. Since the
host galaxy seems to be a face-on disk galaxy and the excitation conditions of
the circumnuclear emission-line regions show the spatial symmetry, we consider
that we are seeing the superwind nearly from a pole-on view. Cooling shock
models may explain the observed emission line ratios of the circumnuclear
regions although a factor of 2 overabundance of nitrogen is necessary. All
these suggest that the high-mass enhanced starburst occurred ~5X10^6 years ago
in the nuclear region of Mrk 1259.Comment: To be published in the Astrophysical Journal Letters, 15 pages, 4
figure
Ages and metallicities of circumnuclear star formation regions from Gemini IFU observations
Aims: We derive the age and metallicity of circumnuclear star formation
regions (CNSFRs) located in the spiral galaxies NGC6951 and NGC1097, and
investigate the cause of the very low equivalent widths of emission lines found
for these regions.
Methods: We used optical two-dimensional spectroscopic data obtained with
Gemini GMOS-IFUs and a grid of photoionization models to derive the the
metallicities and ages of CNSFRs.
Results: We find star formation rates in the range 0.002-0.14 Msun/yr and
oxygen abundance of 12+log(O/H)~8.8 dex, similar to those of most metal-rich
nebulae located in the inner region of galactic disks.
Conclusions: We conclude that the very low emission-line equivalent widths
observed in CNSFRs are caused by the ``contamination'' of the continuum by (1)
contribution of the underlying bulge continuum combined with (2) contribution
from previous episodes of star formation at the CNSFRs.Comment: Accepted for publication in Astronomy and Astrophysic
An atlas of Calcium triplet spectra of active galaxies
We present a spectroscopic atlas of active galactic nuclei covering the
region around the 8498, 8542, 8662 Calcium triplet (CaT) lines. The sample
comprises 78 objects, divided into 43 Seyfert 2s, 26 Seyfert 1s, 3 Starburst
and 6 normal galaxies. The spectra pertain to the inner ~300 pc in radius, and
thus sample the central kinematics and stellar populations of active galaxies.
The data are used to measure stellar velocity dispersions (sigma_star) both
with cross-correlation and direct fitting methods. These measurements are found
to be in good agreement with each-other and with those in previous studies for
objects in common. The CaT equivalent width is also measured. We find average
values and sample dispersions of W_CaT of 4.6+/-2.0, 7.0 and 7.7+/-1.0
angstrons for Seyfert 1s, Seyfert 2s and normal galaxies, respectively. We
further present an atlas of [SIII]\lambda 9069 emission line profiles for a
subset of 40 galaxies. These data are analyzed in a companion paper which
addresses the connection between stellar and Narrow Line Region kinematics, the
behaviour of the CaT equivalent width as a function of sigma_star, activity
type and stellar population properties.Comment: 18 pages, 10 figures, accepted for publication in MNRA
Contribution of a Disk Component to Single Peaked Broad Lines of Active Galactic Nuclei
We study the disk emission component hidden in the single-peaked Broad
Emission Lines (BELs) of Active Galactic Nuclei (AGN). We compare the observed
broad lines from a sample of 90 Seyfert 1 spectra taken from the Sloan Digital
Sky Survey with simulated line profiles. We consider a two-component Broad Line
Region (BLR) model where an accretion disk and a surrounding non-disk region
with isotropic cloud velocities generate the simulated BEL profiles. The
analysis is mainly based in measurements of the full widths (at 10%, 20% and
30% of the maximum intensity) and of the asymmetries of the line profiles.
Comparing these parameters for the simulated and observed H broad
lines, we {found} that the hidden disk emission {may} be present in BELs even
if the characteristic {of two peaked line profiles is} absent. For the
available sample of objects (Seyfert 1 galaxies with single-peaked BELs), our
study indicates that, {in the case of the hidden disk emission in single peaked
broad line profiles}, the disk inclination tends to be small (mostly
) and that the contribution of the disk emission to the total flux
should be smaller than the contribution of the surrounding region.Comment: 18 Figures, 1 Table, MNRAS-accepted. MNRAS-accepte
Ionized and hot molecular outflows in the inner 500 pc of NGC1275
The role of feedback from Active Galactic Nuclei (AGN) in the evolution of
galaxies is still not not fully understood, mostly due to the lack of
observational constraints in the multi-phase gas kinematics on the ten to
hundred parsec scales. We have used the Gemini Near-infrared Integral Field
Spectrograph (NIFS) to map the molecular and ionized gas kinematics in the
inner 900900 pc of the Seyfert galaxy NGC1275 at a spatial
resolution of 70 pc. From the fitting of the CO absorption bandheads in
the K-band, we derive a stellar velocity dispersion of km s,
which implies a black hole mass of
M. We find hot ( K) molecular and ionized outflows with
velocities of up to 2 000 km s and mass outflow rates of
yr and yr,
respectively, in each of these gas phases. The kinetic power of the ionized
outflows corresponds to only 0.05 per cent of the luminosity of the AGN of NGC
1275, indicating that they are not powerful enough to provide significant AGN
feedback, but may be effective in redistributing the gas in the central region
of the galaxy. The AGN driven outflows seem to be responsible for the shocks
necessary to produce the observed H and [Fe II] line emission.Comment: Accepted for publication in MNRA
The Nature of the Optical Light in Seyfert 2 Galaxies with Polarized Continuum
We investigate the nature of the optical continuum and stellar population in
the central kpc of the Seyfert 2s Mrk 348, Mrk 573, NGC 1358 and Mrk 1210 using
long-slit spectra obtained along the radio or extended emission axis. These
galaxies are known to have polarized continuum-including polarized broad lines
in Mrk 348 and Mrk 1210--and previous studies indicate featureless continuum
(FC) contributions in the 20-50% range at 5500 A. Nevertheless, our
measurements of the equivalent widths of absorption lines and continuum ratios
as a function of distance from the nuclei show no dilution of the lines nor
bluening of the spectrum, as expected if a blue FC was present at the nucleus
in the above proportions. We investigate one possibility to account for this
effect: that the stellar population at the nucleus is the same as that from the
surrounding bulge and dominates the nuclear light. A spectral analysis confirms
that this hypothesis works for Mrk 348, NGC 1358 and Mrk 1210, for which we
find stellar contributions at the nucleus larger than 90% at all wavelengths.
We find that a larger stellar population contribution to the nuclear spectra
can play the role of the ``second FC'' source inferred from previous studies.
Stellar population synthesis shows that the nuclear regions of Mrk 348 and Mrk
1210 have important contributions of young to intermediate age stars (0--100
Myr), not present in templates of elliptical galaxies. In the case of Mrk 1210,
this is further confirmed by the detection of a ``Wolf-Rayet feature'' in the
nuclear emission-line spectrum.Comment: ApJ, accepted. Uses aaspp4.sty. [22 pages
Nuclear spirals as feeding channels to the Supermassive Black Hole: the case of the galaxy NGC 6951
We report the discovery of gas streaming motions along nuclear spiral arms
towards the LINER nucleus of the galaxy NGC 6951. The observations, obtained
using the GMOS integral field spectrograph on the Gemini North telescope,
yielded maps of the flux distributions and gas kinematics in the Halpha,
[NII]6584 and [SII]6717,31 emission lines of the inner 7x5 arcsec^2 of the
galaxy. This region includes a circumnuclear star-forming ring with radius
500pc, a nuclear spiral inside the ring and the LINER nucleus. The kinematics
of the ionized gas is dominated by rotation, but subtraction of a kinematic
model of a rotating exponential disk reveals deviations from circular rotation
within the nuclear ring which can be attributed to (1) streaming motions along
the nuclear spiral arms and (2) a bipolar outflow which seems to be associated
to a nuclear jet. On the basis of the observed streaming velocities and
geometry of the spiral arms we estimate a mass inflow rate of ionized gas of
3x10^(-4) Msun/yr, which is of the order of the accretion rate necessary to
power the LINER nucleus of NGC 6951. Similar streaming motions towards the
nucleus of another galaxy with LINER nucleus -- NGC 1097 -- have been reported
by our group in a previous paper. Taken together, these results support a
scenario in which nuclear spirals are channels through which matter is
transferred from galactic scales to the nuclear region to feed the supermassive
black hole.Comment: 25 pages, 6 eps figures, accepted for publication in Ap
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