167 research outputs found
The black holes of radio galaxies during the "Quasar Era": Masses, accretion rates, and evolutionary stage
We present an analysis of the AGN broad-line regions of 6 powerful radio
galaxies at z>~2 (HzRGs) with rest-frame optical imaging spectroscopy obtained
at the VLT. All galaxies have luminous (L(H-alpha)=few x 10^44 erg s^-1),
spatially unresolved H-alpha line emission with FWHM>= 10,000 km s^-1 at the
position of the nucleus, suggesting their AGN are powered by supermassive black
holes with masses of few x 10^9 M_sun and accretion luminosities of a few
percent of the Eddington luminosity. In two galaxies we also detect the BLRs in
H-beta, suggesting relatively low extinction of A_V~1 mag, which agrees with
constraints from X-ray observations. By relating black hole and bulge mass, we
find a possible offset towards higher black-hole masses of at most ~0.6 dex
relative to nearby galaxies at a given host mass, although each individual
galaxy is within the scatter of the local relationship. If not entirely from
systematic effects, this would then suggest that the masses of the host
galaxies have increased by at most a factor ~4 since z~2 relative to the
black-hole masses, perhaps through accretion of satellite galaxies or because
of a time lag between star formation in the host galaxy and AGN fueling. We
also compare the radiative and mechanical energy output (from jets) of our
targets with predictions of recent models of "synthesis" or "grand unified" AGN
feedback, which postulate that AGN with similar radiative and mechanical energy
output rates to those found in our HzRGs may be nearing the end of their period
of active growth. We discuss evidence that they may reach this stage at the
same time as their host galaxies.Comment: A&A in pres
Energetics of the molecular gas in the H_2 luminous radio galaxy 3C 326: Evidence for negative AGN feedback
We present a detailed analysis of the gas conditions in the H_2 luminous radio galaxy 3C 326 N at z ~ 0.1, which has a low star-formation
rate (SFR ~ 0.07 M_⊙ yr^(−1)) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency
is likely a factor ~ 10−50 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry
with existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H_2 line emission is factors
10−100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of
3C 326 N in the optical suggests an outflow with a terminal velocity of ~−1800 km s^(−1) and a mass outflow rate of 30−40 M_⊙ yr^(−1),
which cannot be explained by star formation. The mechanical power implied by the wind, of order 10^(43) erg s^(−1), is comparable to the
bolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where
a small fraction of the mechanical energy of the radio jet is deposited in the interstellar medium of 3C 326 N, which powers the outflow,
and the line emission through a mass, momentum and energy exchange between the different gas phases of the ISM. Dissipation times
are of order 10^(7−8) yrs, similar or greater than the typical jet lifetime. Small ratios of CO and PAH surface brightnesses in another 7 H_2
luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies
in a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of
≥ 10^(11) M_⊙ could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback
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
The dynamics of the ionized and molecular ISM in powerful obscured quasars at z>=3.5
We present an analysis of the kinematics and excitation of the warm ionized
gas in two obscured, powerful quasars at z>=3.5 from the SWIRE survey, SWIRE
J022513.90-043419.9 and SWIRE J022550.67-042142, based on imaging spectroscopy
on the VLT. Line ratios in both targets are consistent with luminous
narrow-line regions of AGN. SWIRE J022550.67-042142 has very broad (FWHM=2000
km/s), spatially compact [OIII] line emission. SWIRE J022513.90-043419.9 is
spatially resolved, has complex line profiles of H-beta and [OIII], including
broad wings with blueshifts of up to -1500 km/s relative to the narrow
[OIII]5007 component, and widths of up to FWHM=5000 km/s. Estimating the
systemic redshift from the narrow H-beta line, as is standard for AGN host
galaxies, implies that a significant fraction of the molecular gas is
blueshifted by up to ~ -1000 km/s relative to the systemic velocity. Thus the
molecular gas could be participating in the outflow. Significant fractions of
the ionized and molecular gas reach velocities greater than the escape
velocity. We compare empirical and modeling constraints for different energy
injection mechanisms, such as merging, star formation, and momentum-driven AGN
winds. We argue that the radio source is the most likely culprit, in spite of
the sources rather modest radio power of 10^25 W/Hz. Such a radio power is not
uncommon for intense starburst galaxies at z~2. We discuss these results in
light of the co-evolution of AGN and their host galaxy.Comment: Accepted by MNRA
The Average Optical Spectra of Intense Starbursts at z~2: Outflows and the Pressurization of the ISM
An important property of star-forming galaxies at z~1-2 is the high local
star-formation intensities they maintain over tens of kiloparsecs at levels
that are only observed in the nearby Universe in the most powerful nuclear
starbursts. To investigate how these high star-formation intensities affect the
warm ionized medium, we present an analysis of the average spectra of about 50
such galaxies at z~1.2-2.6 and of subsamples selected according to their local
and global star-formation intensity. Stacking allows us to probe relatively
weak lines like [SII]\lambda \lambda 6716,6731 and [OI]\lambda 6300, which are
tracers of the conditions of the ISM and are undetectable in most individual
targets. We find higher gas densities (hence pressures) in intensely
star-forming regions compared to fainter diffuse gas and, overall, values that
are comparable to starburst regions and the diffuse ISM in nearby galaxies. By
modeling the H\alpha\ surface brightnesses and [SII]/H\alpha\ line ratios with
the Cloudy photoionization code, we find that our galaxies continue trends
observed in local galaxies, where gas pressures scale with star-formation
intensity. We discuss these results in the context of models of self-regulated
star formation, where star formation determines the average thermal and
turbulent pressure in the ISM, which in turn determines the rate at which stars
can form, finding good agreement with our data. We also confirm the detection
of broad, faint lines underlying H\alpha\ and [NII], which have previously been
considered evidence of either outflows or active galactic nuclei. Finding that
the broad component is only significantly detected in stacks with the highest
average local and global star-formation intensities strongly supports the
outflow interpretation, and further emphasizes the importance of star-formation
feedback and self-regulation in the early Universe.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
CO line emission in the halo of a radio galaxy at z=2.6
We report the detection of luminous CO(3-2) line emission in the halo of the
z=2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at
optical to mid-infrared wavelengths implying a stellar mass < few x10^9 M_sun
and relatively low star-formation rates. With the IRAM PdBI we find two CO
emission line components at the same position at ~80 kpc distance from the HzRG
along the axis of the radio jet, with different blueshifts of few 100 km s^-1
relative to the HzRG and a total luminosity of ~2x10^10 K km s^-1 pc^2 detected
at 8 sigma significance. HzRGs have significant galaxy overdensities and
extended halos of metal-enriched gas often with embedded clouds or filaments of
denser material, and likely trace very massive dark-matter halos. The CO
emission may be associated with a gas-rich, low-mass satellite galaxy with
little on-going star formation, in contrast to all previous CO detections of
galaxies at similar redshifts. Alternatively, the CO may be related to a gas
cloud or filament and perhaps jet-induced gas cooling in the outer halo,
somewhat in analogy with extended CO emission found in low-redshift galaxy
clusters.Comment: MNRAS Letters, accepte
On the self-regulation of intense star-formation in galaxies at z=1-3
(abridged) We have analyzed the properties of the rest-frame optical emission
lines of a sample of 53 intensely star forming galaxies at z=1.3 to 2.7
observed with SINFONI on the ESO-VLT. We find large velocity dispersions in the
lines, sigma=30-250 km/s. Our data agree well with simulations where we applied
beam-smearing and assumed a scaling relation of the form: velocity dispersion
is proportional to the square root of the star-formation intensity
(star-formation rate per unit area). We conclude that the dispersions are
primarily driven by star formation. To explain the high surface brightness and
optical line ratios, high thermal pressures in the warm ionized medium, WIM,
are required (log P/k (K/cm^3)>~6-7). Such thermal pressures in the WIM are
similar to those observed in nearby starburst galaxies, but occur over much
larger physical scales. Moreover, the relatively low ionization parameters
necessary to fit the high surface brightnesses and optical line ratios suggest
that the gas is not only directly associated with regions of star formation,
but is wide spread throughout the general ISM. Thus the optical emission line
gas is a tracer of the large scale dynamics of the bulk of the ISM. We present
a simple model for the energy input from young stars in an accreting galaxy, to
argue that the intense star-formation is supporting high turbulent pressure,
which roughly balances the gravitational pressure and thus enables distant gas
accreting disks to maintain a Toomre disk instability parameter Q~1. For a star
formation efficiency of 3%, only 5-15% of the mechanical energy from young
stars that is deposited in the ISM is needed to support the level of turbulence
required for maintaining this balance. Since this balance is maintained by
energy injected into the ISM by the young stars themselves, this suggests that
star formation in high redshift galaxies is self-regulating.Comment: A&A in press; 15 figure
Dense gas without star formation: the kpc-sized turbulent molecular disk in 3C 326 N
We report the discovery of a 3 kpc disk of few 10^9 M_⊙ of dense, warm H_2 in the nearby radio galaxy 3C 326 N, which shows no signs of ongoing or recent star formation and falls a factor of 60 below the Schmidt-Kennicutt law. Our VLT/SINFONI imaging spectroscopy shows broad (FWHM ~ 500 km s^(-1)) ro-vibrational H_2 lines across the entire disk, with irregular profiles and line ratios consistent with shocks. The ratio of turbulent to gravitational energy suggests that the gas is highly turbulent and not gravitationally bound. In the absence of the driving by the jet, the short turbulent dissipation times indicate that the gas should collapse rapidly and form stars, at odds with the recent star-formation history. Motivated by hydrodynamic models of rapid H_2 formation boosted by turbulent compression, we propose that the molecules formed from diffuse atomic gas in the turbulent jet cocoon. Since the gas is not self-gravitating, it cannot form molecular clouds or stars while the jet is active, and is likely to disperse and become atomic again after the nuclear activity ceases. We speculate that very low star-formation rates are to be expected under such conditions, provided that the large-scale turbulence controls the gas dynamics in molecular clouds. Our results illustrate that jets may create large molecular reservoirs as expected in “positive feedback” scenarios of AGN-triggered star formation, but that this alone is insufficient to trigger star formation
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