71 research outputs found
STIS spectroscopy of the emission line gas in the nuclei of nearby FR-I galaxies
We present the results of the analysis of a set of medium resolution spectra,
obtained by the Space Telescope Imaging Spectrograph on board the Hubble Space
Telescope, of the emission line gas present in the nuclei of a complete sample
of 21 nearby, early-type galaxies with radio jets (the UGC FR-I Sample). For
each galaxy nucleus we present spectroscopic data in the region of H-alpha and
the dervived kinematics.
We find that in 67% of the nuclei the gas appears to be rotating and, with
one exception, the cases where rotation is not seen are either face on or have
complex central morphologies. We find that in 62% of the nuclei the fit to the
central spectrum is improved by the inclusion of a broad component. The broad
components have a mean velocity dispersion of 1349 +/- 345 km\s and are
redshifted from the narrow line components (assuming an origin in H-alpha) by
486 +/- 443 km\s.Comment: 119 pages, 26 figures, ApJS Accepted, version with full figures
available at http://www.astro.columbia.edu/~jake/pub/fr1datapaper.pd
Infrared Emission from the Nearby Cool Core Cluster Abell 2597
We observed the brightest central galaxy (BCG) in the nearby (z=0.0821) cool
core galaxy cluster Abell 2597 with the IRAC and MIPS instruments on board the
Spitzer Space Telescope. The BCG was clearly detected in all Spitzer
bandpasses, including the 70 and 160 micron wavebands. We report aperture
photometry of the BCG. The spectral energy distribution exhibits a clear excess
in the FIR over a Rayleigh-Jeans stellar tail, indicating a star formation rate
of ~4-5 solar masses per year, consistent with the estimates from the UV and
its H-alpha luminosity. This large FIR luminosity is consistent with that of a
starburst or a Luminous Infrared Galaxy (LIRG), but together with a very
massive and old population of stars that dominate the energy output of the
galaxy. If the dust is at one temperature, the ratio of 70 to 160 micron fluxes
indicate that the dust emitting mid-IR in this source is somewhat hotter than
the dust emitting mid-IR in two BCGs at higher-redshift (z~0.2-0.3) and higher
FIR luminosities observed earlier by Spitzer, in clusters Abell 1835 and Zwicky
3146.Comment: Accepted at Ap
An optical-IR jet in 3C133
We report the discovery of a new optical-IR synchrotron jet in the radio
galaxy 3C133 from our HST/NICMOS snapshot survey. The jet and eastern hotspot
are well resolved, and visible at both optical and IR wavelengths. The IR jet
follows the morphology of the inner part of the radio jet, with three distinct
knots identified with features in the radio. The radio-IR SED's of the knots
are examined, along with those of two more distant hotspots at the eastern
extreme of the radio feature. The detected emission appears to be synchrotron,
with peaks in the NIR for all except one case, which exhibits a power-law
spectrum throughout.Comment: ApJ accepted. 14 pages, 6 figure
Dominant Nuclear Outflow Driving Mechanisms in Powerful Radio Galaxies
In order to identify the dominant nuclear outflow mechanisms in Active
Galactic Nuclei, we have undertaken deep, high resolution observations of two
compact radio sources (PKS 1549-79 and PKS 1345+12) with the Advanced Camera
for Surveys (ACS) aboard the Hubble Space Telescope. Not only are these targets
known to have powerful emission line outflows, but they also contain all the
potential drivers for the outflows: relativistic jets, quasar nuclei and
starbursts. ACS allows the compact nature (<0.15") of these radio sources to be
optically resolved for the first time. Through comparison with existing radio
maps we have seen consistency in the nuclear position angles of both the
optical emission line and radio data. There is no evidence for bi-conical
emission line features on the large-scale and there is a divergance in the
relative position angles of the optical and radio structure. This enables us to
exclude starburst driven outflows. However, we are unable to clearly
distinguish between radiative AGN wind driven outflows and outflows powered by
relativistic radio jets. The small scale bi-conical features, indicative of
such mechanisms could be below the resolution limit of ACS, especially if
aligned close to the line of sight. In addition, there may be offsets between
the radio and optical nuclei induced by heavy dust obscuration, nebular
continuum or scattered light from the AGN.Comment: 9 pages, 8 figures, emulateapj, ApJ Accepte
VLBA Observations of Sub-Parsec Structure in Mrk 231: Interaction between a Relativistic Jet and a BAL Wind
We report on the first high frequency VLBI observations of the nearby broad
absorption line quasar (BALQSO), Mrk 231. Three epochs of observations were
achieved at 15 GHz and 22 GHz, two of these included 43 GHz observations as
well. The nuclear radio source is resolved as a compact double. The core
component experienced a strong flare in which the flux density at 22 GHz
increased by (45 mJy) in three months. Theoretical models of the flare
imply that the emission is likely enhanced by very strong Doppler boosting of a
highly relativistic ejecta with a kinetic energy flux, . Combining our data with two previous epochs of 15 GHz data,
shows marginal evidence for the slow advance of the secondary component
(located pc from the core) over a 9.4 year span. We estimate
that the long term time averaged kinetic energy flux of the secondary at
. Low frequency VLBA observations
indicate that the secondary is seen through a shroud of free-free absorbing gas
with an emission measure of . The
steep spectrum secondary component appears to be a compact radio lobe that is
associated with a working surface between the ram-pressure confined jet, and a
dense medium that is likely to be the source of the free-free absorption. The
properties of the dense gas are consistent with the temperatures, displacement
from the nucleus and the column density of total hydrogen commonly associated
with the BAL wind.Comment: To appear in Ap
3C236: Radio Source, Interrupted?
We present new HST STIS/MAMA near-UV images and archival WFPC2 V and R band
images which reveal the presence of four star forming regions in an arc along
the edge of the dust lane in the giant (4 Mpc) radio galaxy 3C236. Two of the
star forming regions are relatively young with ages of order 1E7 yr, while the
other two are older with ages of order 1E8 - 1E9 yr which is comparable to the
estimated age of the giant radio source. Based on dynamical and spectral aging
arguments, we suggest that the fuel supply to the AGN was interrupted for 1E7
yr and has now been restored, resulting in the formation of the inner 2 kpc
scale radio source. This time scale is similar to that of the age of the
youngest of the star forming regions. We suggest that the transport of gas in
the disk is non-steady and that this produces both the multiple episodes of
star formation in the disk as well as the multiple epochs of radio source
activity. If the inner radio source and the youngest star forming region are
related by the same event of gas transport, the gas must be transported from
the hundreds of pc scale to the sub-parsec scale on a time scale of 1E7 yr,
which is similar to the dynamical time scale of the gas on the hundreds of pc
scales
BIMA Millimeter-Wave Observations of the Core-Jet and Molecular Gas in the FR I Radio Galaxy NGC 3801
We present BIMA 3 mm observations of the radio continuum source and the molecular gas disk in the radio loud Fanaroff & Riley Type I (FR I) galaxy NGC 3801. We have detected a continuum source in the nucleus and determined that it has a flat millimeter-wave spectrum, suggesting that the emission is non-thermal and due to an AGN; the radio core is not evident in existing VLA observations. We also map the extended 3 mm emission from the previously known radio jets. In addition, we detect CO (1â0) emission associated with the dust disk observed in previous HST images. A velocity gradient is observed, indicating a two kpc radius rotating gas ring or disk oriented roughly perpendicular to the radio jets. The inferred molecular gas mass of the disk is M(H2) = 3Ă108Mâ, about 1% of the dynamical mass. We also find a 108 Mâ molecular gas clump not associated with the gas disk. There is evidence that this gas is associated with a merger and is infalling. This suggests that FR I type activity is related to merger activity, as is thought to be the case for FR II type radio galaxies. We also find indications that one of the radio jets is entraining gas from the infalling molecular gas
An infrared survey of brightest cluster galaxies: Paper I
We report on an imaging survey with the Spitzer Space Telescope of 62
brightest cluster galaxies with optical line emission. These galaxies are
located in the cores of X-ray luminous clusters selected from the ROSAT All-Sky
Survey. We find that about half of these sources have a sign of excess infrared
emission; 22 objects out of 62 are detected at 70 microns, 18 have 8 to 5.8
micron flux ratios above 1.0 and 28 have 24 to 8 micron flux ratios above 1.0.
Altogether 35 of 62 objects in our survey exhibit at least one of these signs
of infrared excess. Four galaxies with infrared excesses have a 4.5/3.6 micron
flux ratio indicating the presence of hot dust, and/or an unresolved nucleus at
8 microns. Three of these have high measured [OIII](5007A)/Hbeta flux ratios
suggesting that these four, Abell 1068, Abell 2146, and Zwicky 2089, and
R0821+07, host dusty active galactic nuclei (AGNs). 9 objects (including the
four hosting dusty AGNs) have infrared luminosities greater than 10^11 L_sol
and so can be classified as luminous infrared galaxies (LIRGs). Excluding the
four systems hosting dusty AGNs, the excess mid-infrared emission in the
remaining brightest cluster galaxies is likely related to star formation.Comment: accepted for publication in ApJ
Hubble Space Telescope Imaging of Brightest Cluster Galaxies
We used the HST WFPC2 to obtain I-band images of the centers of 81 brightest
cluster galaxies (BCGs), drawn from a volume-limited sample of nearby BCGs. The
images show a rich variety of morphological features, including multiple or
double nuclei, dust, stellar disks, point source nuclei, and central surface
brightness depressions. High resolution surface brightness profiles could be
inferred for 60 galaxies. Of those, 88% have well-resolved cores. Twelve
percent of the BCG sample lacks a well-resolved core; all but one of these BCGs
have ``power-law'' profiles. Some of these galaxies have higher luminosities
than any power-law galaxy identified by Faber et al. (1997), and have physical
upper limits on the break radius well below the values observed for core
galaxies of the same luminosity. These results support the idea that the
central structure of early-type galaxies is bimodal in its physical properties,
but also suggest that there exist high luminosity galaxies with power-law
profiles (or unusually small cores). The BCGs in the latter category tend to
fall at the low end of the BCG luminosity function and tend to have low values
of the quantity alpha (the logarithmic slope of the metric luminosity as a
function of radius, at 10 kpc). Since theoretical calculations have shown that
the luminosities and alpha values of BCGs grow with time as a result of
accretion, this suggests a scenario in which elliptical galaxies evolve from
power-law profiles to core profiles through accretion and merging. This is
consistent with theoretical scenarios that invoke the formation of massive
black hole binaries during merger events (Abridged).Comment: Accepted for publication in AJ. Postscript file with high resolution
figures (1 and 3) is available at
http://spider.ipac.caltech.edu/staff/seppo/bcgfig
HST/STIS Spectroscopy of the Lyman-Alpha Emission Line in the Central Dominant Galaxies in A426, A1795, and A2597: Constraints on Clouds in the Intracluster Medium
We report on HST/STIS spectra of the Lyman-alpha emission in the central
dominant galaxies in three rich clusters of galaxies. We find evidence for a
population of clouds in the intracluster medium.We detect 10 Ly-alpha
absorption systems towards the nucleus of NGC1275 with columns of N(HI)
1E12-1E14 cm-2. The detected absorption features are most consistent with
associated nuclear absorption systems. There is very little nuclear absorption
at the systemic velocity in NGC1275. This implies that the large columns
detected in the 21 cm line towards the parsec scale radio source avoid the line
of sight to the nucleus. This gas may be located in a circumnuclear disk or
torus. We detect at least one and possibly two absorption features towards the
extended Ly-alpha in A426. We do not detect absorption towards the extended
Ly-alpha emission in A1795, and A2597 with upper limits N(HI) 1E13 cm-2 for
optically thin absorbers. Our data constrain the covering factor of any high
column density gas in the ICM to be less than 25%. Our results suggest that the
lack of observed intermediate temperature gas is not explained by obscuration.
In addition, the low columns of gas on the 100 kpc scales in the ICM suggests
that (1) the rate at which cold gas accumulates in the ICM on these scales is
very low, and (2) the dense nebulae in the central 10 kpc must have cooled or
been deposited in situ.Comment: 6 figure
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