196 research outputs found
The Color Distributions of Globular Clusters in Virgo Elliptical Galaxies
This Letter presents the color distributions of the globular cluster (GC)
systems of 12 Virgo elliptical galaxies, measured using data from the Hubble
Space Telescope. Bright galaxies with large numbers of detected GC's show two
distinct cluster populations with mean V-I colors near 1.01 and 1.26. The GC
population of M86 is a clear exception; its color distribution shows a single
sharp peak near V-I=1.03. The absence of the red population in this galaxy, and
the consistency of the peak colors in the others, may be indications of the
origins of the two populations found in most bright elliptical galaxies.Comment: 5 pages, 1 figure, to be published in ApJ Letters Corrections to
introductio
Optimal multihump filter for photometric redshifts
We propose a novel type filter for multicolor imaging to improve on the
photometric redshift estimation of galaxies. An extra filter - specific to a
certain photometric system - may be utilized with high efficiency. We present a
case study of the Hubble Space Telescope's Advanced Camera for Surveys and show
that one extra exposure could cut down the mean square error on photometric
redshifts by 34% over the z<1.3 redshift range.Comment: 9 pages, 3 figures, LaTeX AASTeX, accepted to A
H-alpha imaging of the Local Volume galaxies I. The NGC 6946 galaxy group
We present new H-alpha imaging of all known dwarf irregular companions to NGC
6946: UGC 11583, KK 251, KK 252, KKR 55, KKR 56, Cepheus 1, KKR 59, and KKR 60.
The galaxies span a range of blue absolute magnitudes of [-13.6, -17.6],
relative gas content of [0.1, 2.5] M_sun/L_sun, current star formation activity
of [0.2, 5.2]10^-2 M_sun yr^-1, and timescale to exhaust the current gas supply
of [6, 86] Gyr.Comment: 4 pages, 1 figure. accepted to Research Note in Astronomy and
Astrophysic
Extreme Galactic-Winds and Starburst in IR Mergers and IR QSOs
We report -as a part of a long-term study of mergers and IR QSOs- detailed
spectroscopic evidences for outflow (OF) and/or Wolf Rayet features in: (i) low
velocity OF in the ongoing mergers NGC 4038/39 and IRAS 23128-5919; (ii)
extreme velocity OF (EVOF) in the QSOs IRAS 01003-2238 and IRAS 13218+0552;
(iii) OF and EVOF in a complete sample of ultra-luminous IR galaxies/QSOs ("The
IRAS 1 Jy MKO-KPNO Survey", of 118 objects). We found EVOF in IRAS 11119+3257,
14394+5332, 15130+1958 and 15462-0450. The OF components detected in these
objects were mainly associated to starburst processes: i.e., to galactic-winds
generated in multiple type II SN explosions and massive stars. The EVOF were
detected in objects with strong starburst plus obscured IR QSOs; which suggest
that interaction of both processes could generate EVOF. In addition, we analyze
the presence of Wolf Rayet features in the large sample of Bright PG-QSOs
(Boroson and Green 1992), and nearby mergers and galactic-wind galaxies. We
found clear WR features in the Fe II QSOs (type I): PG 1244+026, 1444+407,
1448+273, 1535+547; and in the IR merger Arp 220. HST archive images of IR+BAL
QSOs show in practically all of these objects "arc or shell" features probably
associated to galactic-winds (i.e., to multiple type II SN explosions) and/or
merger processes. Finally, we discuss the presence of extreme starburst and
galactic wind as a possible evolutive link between IR merger and IR QSOs; where
the relation between mergers and extreme starburst (with powerful
galactic-winds) plays in important role, in the evolution of galaxies.Comment: 14 pages, 6 figure
Physical Conditions in the Seyfert Galaxy NGC 2992
This paper presents long slit spectral maps of the bi-cone shaped extended
narrow line region (ENLR) in the Seyfert galaxy NGC 2992. We investigate the
physical properties of the ENLR via emission line diagnostics, and compare the
observations to shock and photoionization models for the excitation mechanism
of the gas. The line ratios vary as a function of position in the ENLR, and the
loci of the observed points on line ratio diagrams are shown to be most
consistent with shock+precursor model grids. We consider the energetics of a
nuclear ionizing source for the ENLR, and perform the q-test in which the rate
of ionizing photons from the nucleus is inferred from measurements of the
density and ionization parameter. The q-test is shown to be invalid in the case
of NGC 2992 because of the limitations of the [S II]6717/6731 density
diagnostic. The excitation of the gas is shown to be broadly consistent with
the kinematics, with higher [N II]6583/H-alpha present in the more dynamically
active region. We also show that the pressure associated with the X-ray
emitting plasma may provide a large fraction of the pressure required to power
the ENLR via shocks.Comment: 55 pages, 49 figures, ApJ accepted September 9, 1998. Figures 1a-f
are provided in jpeg forma
Spatially Resolved Far-Ultraviolet Spectroscopy of the Nuclear Region of NGC 1068
We carry out high-resolution FUSE spectroscopy of the nuclear region of NGC
1068. The first set of spectra was obtained with a 30" square aperture that
collects all emission from the narrow-line region. The data reveal a strong
broad OVI component of FWHM ~3500 kms-1 and two narrow OVI 1031/1037 components
of ~350 kms-1. The CIII 977 and NIII 991 emission lines in this spectrum can be
fitted with a narrow component of FWHM ~1000 kms-1 and a broad one of ~2500
kms-1. Another set of seven spatially resolved spectra were made using a long
slit of 1.25" X 20", at steps of ~1" along the axis of the emission-line cone.
We find that (1) Major emission lines in the FUSE wavelength range consist of a
broad and a narrow component; (2) There is a gradient in the velocity field for
the narrow OVI component of ~200 kms-1 from ~2" southwest of the nucleus to ~4"
northeast. A similar pattern is also observed with the broad OVI component,
with a gradient of ~3000 kms-1. These are consistent with the HST/STIS findings
and suggest a biconical structure in which the velocity field is mainly radial
outflow; (3) A major portion of the CIII and NIII line flux is produced in the
compact core. They are therefore not effective temperature diagnostics for the
conical region; and (4) The best-fitted UV continuum suggests virtually no
reddening, and the HeII 1085/1640 ratio suggests a consistently low extinction
factor across the cone.Comment: To appear in the Astrophysical Journal. 37 pages with 12 figure
ASCA Observations of the Composite Warm Absorber in NGC 3516
We obtained X-ray spectra of the Seyfert 1 galaxy NGC~3516 in March 1995
using ASCA. Simultaneous far-UV observations were obtained with HUT on the
Astro-2 shuttle mission. The ASCA spectrum shows a lightly absorbed power law
of energy index 0.78. The low energy absorbing column is significantly less
than previously seen. Prominent O~vii and O~viii absorption edges are visible,
but, consistent with the much lower total absorbing column, no Fe K absorption
edge is detectable. A weak, narrow Fe~K emission line from cold
material is present as well as a broad Fe~K line. These features are
similar to those reported in other Seyfert 1 galaxies. A single warm absorber
model provides only an imperfect description of the low energy absorption. In
addition to a highly ionized absorber with ionization parameter and
a total column density of , adding a lower
ionization absorber with and a total column of significantly improves the fit. The contribution of
resonant line scattering to our warm absorber models limits the Doppler
parameter to at 90\% confidence. Turbulence at the sound
speed of the photoionized gas provides the best fit. None of the warm absorber
models fit to the X-ray spectrum can match the observed equivalent widths of
all the UV absorption lines. Accounting for the X-ray and UV absorption
simultaneously requires an absorbing region with a broad range of ionization
parameters and column densities.Comment: 14 pages, 4 Postscript figures, uses aaspp4.sty To appear in the
August 20, 1996, issue of The Astrophysical Journa
Large-Scale Outflows in Edge-on Seyfert Galaxies. I. Optical Emission- Line Imaging and Optical Spectroscopy
We have launched a search for large-scale (\gapprox1 kpc) minor-axis
outflows in edge-on Seyfert galaxies in order to assess their frequency of
occurrence and study their properties. Here we present optical continuum and
\han2 line images and/or minor-axis long-slit spectra of 22 edge-on Seyfert
galaxies. Six of these galaxies show at least one of the following: (i)
bi-symmetric H halos extending along the minor axis, (ii) bright
emission-line complexes at distances \gapprox4 kpc (in projection) out of the
disk, and (iii) double-peaked emission-line profiles from the gas along the
minor-axis, suggesting that a wind-blown bubble is present. Our results
indicate that \gapprox of Seyferts have good evidence for
minor-axis galactic outflows. Kinetic luminosities of the galactic outflows in
our sample Seyferts are 1010 erg~s, assuming all
of the observed minor-axis emission is produced by the outflow. These values
are, in general, 0.1 as large as those for well-studied cases of
superwinds in starburst galaxies (Heckman, Armus \& Miley 1990). However,
far-infrared luminosities of our sample Seyferts are also 0.1 as large.
Both starburst-driven superwinds and wide-angled outflows from the active
galactic nucleus are possible explanations for the observed large-scale
outflows.Comment: 34 pages (text and tables) AASTEX, figures available from
[email protected], ApJ Supp., June 199
A Radio Study of the Seyfert Galaxy IC 5063: Evidence for Fast Gas Outflow
New radio continuum (8 GHz and 1.4 GHz) and HI 21 cm line observations of the
Seyfert 2 galaxy IC 5063 (PKS 2048-572) were obtained with the Australia
Telescope Compact Array (ATCA). The 8 GHz image reveals a linear triple
structure (~4'', 1.5 kpc) oriented perpendicular to the optical polarization
position angle. It is aligned with the inner dust lane and shows strong
morphological association with the narrow emission line region (NLR). At 21 cm,
very broad (~700 km/s) HI absorption is observed against the strong continuum
source. This absorption is almost entirely blueshifted, indicating a fast net
outflow, but a faint and narrow redshifted component is also present. In IC
5063 we see clear evidence for strong shocks resulting from the radio
plasma-ISM interaction in the central few kpc. However, the energy flux in the
radio plasma is an order of magnitude smaller than the energy emitted in
emission lines. Thus, shocks are unlikely to account solely for the global
ionization of the emission line region, particularly at large distances.
The HI emission outlines a warped disk associated with the system of dust
lanes some ~2' (~38 kpc) in radius. The lack of kinematically disturbed gas
outside the central few kpc, coupled with the disk warp and close morphological
connection of the inner dust lanes and the large-scale ionized gas, support the
idea that the gas at large radii is photoionized by the central region, while
shadowing effects are important in defining its X-shaped morphology. The
kinematics of the ionized and of the neutral gas suggests the existence of a
dark halo.Comment: 18 pages, 8 Postscript figures, 3 jpeg figures, Postscript preprint
is available from http://jhufos.pha.jhu.edu/~zlatan/papers.htm
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