139 research outputs found
Defying jet-gas alignment in two radio galaxies at z~2 with extended light profiles: Similarities to brightest cluster galaxies
We report the detection of extended warm ionized gas in two powerful
high-redshift radio galaxies, NVSS J210626-314003 at z=2.10 and TXS 2353-003 at
z=1.49, that does not appear to be associated with the radio jets. This is
contrary to what would be expected from the alignment effect, a characteristic
feature of distant, powerful radio galaxies at z> 0.6. The gas also has smaller
velocity gradients and line widths than most other high-z radio galaxies with
similar data. Both galaxies are part of a systematic study of 50 high-redshift
radio galaxies with SINFONI, and are the only two that are characterized by the
presence of high surface-brightness gas not associated with the jet axis and by
the absence of such gas aligned with the jet. Both galaxies are spatially
resolved with ISAAC broadband imaging covering the rest-frame R band, and have
extended wings that cannot be attributed to line contamination. We argue that
the gas and stellar properties of these galaxies are more akin to gas-rich
brightest cluster galaxies in cool-core clusters than the general population of
high-redshift radio galaxies at z>2. In support of this interpretation, one of
our sources, TXS 2353-003, for which we have H\alpha\ narrowband imaging, is
associated with an overdensity of candidate H\alpha\ emitters by a factor of 8
relative to the field at z=1.5. We discuss possible scenarios of the
evolutionary state of these galaxies and the nature of their emission line gas
within the context of cyclical AGN feedback.Comment: A&A in pres
Are we seeing accretion flows in a 250kpc-sized Ly-alpha halo at z=3?
Using MUSE on the ESO-VLT, we obtained a 4 hour exposure of the z=3.12 radio
galaxy MRC0316-257. We detect features down to ~10^-19 erg/s/cm^2/arcsec^2 with
the highest surface brightness regions reaching more than a factor of 100
higher. We find Ly-alpha emission out to ~250 kpc in projection from the active
galactic nucleus (AGN). The emission shows arc-like morphologies arising at
150-250 kpc from the nucleus in projection with the connected filamentary
structures reaching down into the circum-nuclear region. The most distant arc
is offset by 700 km/s relative to circum-nuclear HeII 1640 emission, which we
assume to be at the systemic velocity. As we probe emission closer to the
nucleus, the filamentary emission narrows in projection on the sky, the
relative velocity decreases to ~250 km/s, and line full-width at half maximum
range from 300-700 km/s. From UV line ratios, the emission on scales of 10s of
kpc from the nucleus along a wide angle in the direction of the radio jets is
clearly excited by the radio jets and ionizing radiation of the AGN. Assuming
ionization equilibrium, the more extended emission outside of the axis of the
jet direction would require 100% or more illumination to explain the observed
surface brightness. High speed (>300 km/s) shocks into rare gas would provide
sufficiently high surface brightness. We discuss the possibility that the arcs
of Ly-alpha emission represent accretion shocks and the filamentary emission
represent gas flows into the halo, and compare our results with gas accretion
simulations.Comment: 4 pages, 2 figures, 1 table, A&A letters accepte
The Herschel view of the environment of the radio galaxy 4C+41.17 at z = 3.8
We present Herschel observations at 70, 160, 250, 350 and 500 ÎŒm of the environment of the radio galaxy 4C+41.17 at z = 3.792. About 65 per cent of the extracted sources are securely identified with mid-infrared sources observed with the Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 ÎŒm. We derive simple photometric redshifts, also including existing 850 and 1200 ÎŒm data, using templates of active galactic nuclei, starburst-dominated systems and evolved stellar populations. We find that most of the Herschel sources are foreground to the radio galaxy and therefore do not belong to a structure associated with 4C+41.17. We do, however, find that the spectral energy distribution (SED) of the closest (âŒ25 arcsec offset) source to the radio galaxy is fully consistent with being at the same redshift as 4C+41.17. We show that finding such a bright source that close to the radio galaxy at the same redshift is a very unlikely event, making the environment of 4C+41.17 a special case. We demonstrate that multiwavelength data, in particular on the RayleighâJeans side of the SED, allow us to confirm or rule out the presence of protocluster candidates that were previously selected by single wavelength data setsPeer reviewe
The first 62 AGN observed with SDSS-IV MaNGA -- III: stellar and gas kinematics
We investigate the effects of Active Galactic Nuclei (AGN) on the gas
kinematics of their host galaxies, using MaNGA data for a sample of 62 AGN
hosts and 109 control galaxies (inactive galaxies). We compare orientation of
the line of nodes (kinematic Position Angle - PA) measured from the gas and
stellar velocity fields for the two samples. We found that AGN hosts and
control galaxies display similar kinematic PA offsets between gas and stars.
However, we note that AGN have larger fractional velocity dispersion
differences between gas and stars [] when compared to their controls, as
obtained from the velocity dispersion values of the central (nuclear) pixel
(2.5" diameter). The AGN have a median value of of
, while the the median value for the control
galaxies is . 75% of the AGN show
, while 75% of the normal galaxies show , thus we suggest that the parameter can be
used as an indicative of AGN activity. We find a correlation between the
[OIII]5007 luminosity and for our sample. Our main
conclusion is that the AGN already observed with MaNGA are not powerful enough
to produce important outflows at galactic scales, but at 1-2 kpc scales, AGN
feedback signatures are always present on their host galaxies.Comment: 19 pages, 8 figures, published in MNRA
Star formation in the dwarf Seyfert galaxy NGC 4395: Evidence for both AGN and SNe feedback?
We present a detailed multi-wavelength study of star formation in the dwarf
galaxy NGC 4395 which hosts an active galactic nucleus (AGN). From our
observations with the Ultra-Violet Imaging Telescope, we have compiled a
catalogue of 284 star forming (SF) regions, out of which we could detect 120 SF
regions in H observations. Across the entire galaxy, we found the
extinction corrected star formation rate (SFR) in the far ultra-violet (FUV) to
range from 2.0 10 Myr to 1.5 10
Myr with a median of 3.0 10 Myr
and age to lie in the range of 1 to 98 Myr with a median of 14 Myr. In
H we found the SFR to range from 7.2 10
Myr to 2.7 10 Myr with a median
of 1.7 10 Myr and age to lie between 3 to 6 Myr
with a median of 5 Myr. The stellar ages derived from H show a gradual
decline with galactocentric distance. We found three SF regions close to the
center of NGC~4395 with high SFR both from H and UV which could be
attributed to feedback effects from the AGN. We also found six other SF regions
in one of the spiral arms having higher SFR. These are very close to supernovae
remnants which could have enhanced the SFR locally. We obtained a specific SFR
(SFR per unit mass) for the whole galaxy 4.64 10 yr.Comment: 10 pages, 11 figures, Accepted for publication in Ap
Mildly suppressed star formation in central regions of MaNGA Seyfert galaxies
Negative feedback from accretion onto super-massive black holes (SMBHs), that
is to remove gas and suppress star formation in galaxies, has been widely
suggested. However, for Seyfert galaxies which harbor less active, moderately
accreting SMBHs in the local universe, the feedback capability of their black
hole activity is elusive. We present spatially-resolved H measurements
to trace ongoing star formation in Seyfert galaxies and compare their specific
star formation rate with a sample of star-forming galaxies whose global galaxy
properties are controlled to be the same as the Seyferts. From the comparison
we find that the star formation rates within central kpc of Seyfert galaxies
are mildly suppressed as compared to the matched normal star forming galaxies.
This suggests that the feedback of moderate SMBH accretion could, to some
extent, regulate the ongoing star formation in these intermediate to late type
galaxies under secular evolution.STFC
ER
Faint [CI](1-0) emission in z 3.5 radio galaxies
We present Atacama Large Millimeter/sub-millimeter Array (ALMA) neutral
carbon, [C I](1-0), line observations that probe molecular hydrogen gas (H)
within seven radio galaxies at surrounded by extended
( kpc) Ly- nebulae. We extract [C I](1-0) emission from the
radio-active galactic nuclei (AGN) host galaxies whose positions are set by
near-infrared detections and radio detections of the cores. Additionally, we
place constraints on the galaxies' systemic redshifts via He II 1640
lines seen with the Multi-Unit Spectroscopic Explorer (MUSE). We detect faint
[C I] emission in four out of seven sources. In two of these galaxies, we
discover narrow line emission of full width at half maximum km
s which may trace emission from bright kpc-scale gas clouds within the
ISM. In the other two [C I]-detected galaxies, line dispersions range from
km s and may be tracing the rotational component of the
cold gas. Overall, the [C I] line luminosities correspond to H masses of
M for the detections
and M for the [C I] non-detections
in three out of seven galaxies within the sample. The molecular gas masses in
our sample are relatively low in comparison to previously reported measures for
similar galaxies which are M Our
results imply that the observed faintness in carbon emission is representative
of a decline in molecular gas supply from previous star-formation epochs and/or
a displacement of molecular gas from the ISM due to jet-powered outflows.Comment: 16 pages, 4 figures and 5 tables. Accepted for publication in MNRA
Starburst and old stellar populations in the z -~ 3.8 radio galaxies 4c 41.17 and TN J2007-1316
Using the new evolutionary code PĂ©gase.3, we undertook an evolutionary spectral synthesis of the opticalâIRâsubmm spectral energy distribution of two distant (z = 3.8) radio galaxies, 4C 41.17 and TN J2007â1316. These two radio galaxies were selected from the HeRGĂ (Herschel Radio Galaxies Evolution) Project in particular for their faint active galactic nucleus contribution and because they show evidence of a large stellar contribution to their bolometric luminosity. PĂ©gase.3 coherently models the reprocessing of the stellar luminosity to dust emission, allowing us to build UV to IRâsubmm spectral energy distribution libraries that can then be used to fit spectral energy distributions in the observer's frame. Our principal conclusion is that a single stellar population is insufficient to fit the spectral energy distribution of either radio galaxy. Our best fits are a sum of two evolving stellar populations â a recent starburst plus an old population â plus the thermal emission from an active galactic nucleus (which provides a good fit to the mid-IR emission). The two stellar components are: (i) a massive -~ 1011â Mâ) starburst -~30 Myr after formation, which is required simultaneously to fit the far-IR Herschel to submm data and the optical data; and (ii) an older massive (-~ 1011â12â Mâ) early-type galaxy population,-~1.0âGyr old, which is required principally to fit the mid-IR Spitzer/IRAC data.A young population alone is insufficient because an evolved giant star population produces a 1-ÎŒm rest-frame peak that is observed in the IRAC photometry. This discovery confirms that many of the stellar populations in high-redshift radio galaxies were formed by massive starbursts in the early Universe. Gas-rich mergers and/or jetâcloud interactions are favoured for triggering the intense star formation necessary to explain the properties of the spectral energy distributions. The discovery of similar characteristics in two distant radio galaxies suggests that multiple stellar populations, one old and one young, may be a generic feature of the luminous infrared radio galaxy population
3C 220.3: a radio galaxy lensing a submillimeter galaxy
Herschel Space Observatory photometry and extensive multiwavelength followup
have revealed that the powerful radio galaxy 3C 220.3 at z=0.685 acts as a
gravitational lens for a background submillimeter galaxy (SMG) at z=2.221. At
an observed wavelength of 1mm, the SMG is lensed into three distinct images. In
the observed near infrared, these images are connected by an arc of 1.8" radius
forming an Einstein half-ring centered near the radio galaxy. In visible light,
only the arc is apparent. 3C 220.3 is the only known instance of strong
galaxy-scale lensing by a powerful radio galaxy not located in a galaxy cluster
and therefore it offers the potential to probe the dark matter content of the
radio galaxy host. Lens modeling rejects a single lens, but two lenses centered
on the radio galaxy host A and a companion B, separated by 1.5", provide a fit
consistent with all data and reveal faint candidates for the predicted fourth
and fifth images. The model does not require an extended common dark matter
halo, consistent with the absence of extended bright X-ray emission on our
Chandra image. The projected dark matter fractions within the Einstein radii of
A (1.02") and B (0.61") are about 0.4 +/- 0.3 and 0.55 +/- 0.3. The mass to
i-band light ratios of A and B, M/L ~ 8 +/- 4 Msun/Lsun, appear comparable to
those of radio-quiet lensing galaxies at the same redshift in the CASTLES, LSD,
and SL2S samples. The lensed SMG is extremely bright with observed f(250um) =
440mJy owing to a magnification factor mu~10. The SMG spectrum shows luminous,
narrow CIV 154.9nm emission, revealing that the SMG houses a hidden quasar in
addition to a violent starburst. Multicolor image reconstruction of the SMG
indicates a bipolar morphology of the emitted ultraviolet (UV) light suggestive
of cones through which UV light escapes a dust-enshrouded nucleus.Comment: 17 pages, 14 Figures, accepted for publication in Ap
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