76 research outputs found
Integral-Field Spectroscopy of High-Redshift Galaxies: Implications for Early Galaxy Evolution
Several lines of evidence suggest that the most active phase of galaxy
evolution, especially in the most massive systems, was largely
completed by . This results, e.g., from the observation that
the most massive galaxies at low redshift have very old stellar
populations ( Gyr) and very little gas to fuel subsequent
star formation. Similarly, active galactic nuclei (AGN) were more
numerous and brighter in the early universe. Ultimately, the direct
observation of high-redshift galaxies will be the only way to
understand which processes shaped the universe we see today, in
spite of the rich ``fossil'' data sets we have of the Milky Way and
neighboring galaxies. Thanks to the new m telescope class and
novel instrumentation, including SPIFFI/SINFONI on the VLT, individual
galaxies at redshifts ( Gyr after the Big Bang)
are now within the reach of astronomical spectrographs.
Methodologically, this thesis focuses on the analysis of spectrally
and spatially resolved optical emission lines, first of all \ha\ and
[OIII]\lam5007, which are shifted into the near-infrared. {\sc Spiffi
/ Sinfoni}
is very suited to such a programme, because it records the spectra of
a contiguous field of view of up to 8\arcsec8\arcsec. The
internal kinematic and chemical gradients within a galaxy can thus be
measured in a single observation. Galaxies in the early universe had
particularly high star-formation rates, so that many targets are
bright optical line emitters. Internal kinematics are measured
through the Doppler effect, line profiles and widths indicate the
presence of an AGN, galactic ``superwinds'' and the relationship of
chaotic to ordered motion. Star-formation rates are measured from the
luminosity of the Balmer lines, especially \ha. Characteristic line
ratios indicate the presence of an AGN, chemical composition, and
electron densities in the ISM, and they allow to distinguish shocks
and photoionization.
This thesis is a pilot study: It comprises 9
galaxies that fulfill a variety of selection criteria: they are
either bright UV or submillimeter emitters, or they are radio-loud.
Perhaps the most fundamental result is that gravity (dominated by dark
matter) is the main driver of early galaxy evolution, but it
is not the only important process. Star formation and AGN cause
hydrodynamical feedback processes, which might be a sign of
self-regulated galaxy evolution. It is found that star-formation
related feedback had similar properties at low and high redshift, but
that AGN-driven gas expulsion might have played a major role in the
high-redshift evolution of galaxies, that is without low-redshift
equivalent. Another important result is the rotation curve we find in
the central kiloparsec of a gravitationally lensed UV-selected
galaxy. Velocity gradients of \kms\ have been observed in
many high-redshift galaxies, but the interpretation as rotation curves
is generally not unique. Given the relatively coarse spatial
resolution of high-redshift galaxy data, two nearby galaxies, maybe
interacting or undergoing a merger, might blend into one smooth
velocity gradient. Galaxy mergers are an important ingredient of the
``hierarchical model'', the current paradigm of structure formation,
and therefore nearby galaxy pairs were likely more common at high
redshift than they are today. The large similarity of the lensed
rotation curve with those of nearby galaxies might be a first sign
that galaxies evolved inside-out
ALMA Observations of a Candidate Molecular Outflow in an Obscured Quasar
We present Atacama Large Millimeter/Submillimeter Array (ALMA) CO (1-0) and
CO (3-2) observations of SDSS J135646.10+102609.0, an obscured quasar and
ultra-luminous infrared galaxy (ULIRG) with two merging nuclei and a known
20-kpc-scale ionized outflow. The total molecular gas mass is M_{mol} ~
9^{+19}_{-6} x 10^8 Msun, mostly distributed in a compact rotating disk at the
primary nucleus (M_{mol} ~ 3 x 10^8 Msun) and an extended tidal arm (M_{mol} ~
5 x 10^8 Msun). The tidal arm is one of the most massive molecular tidal
features known; we suggest that it is due to the lower chance of shock
dissociation in this elliptical/disk galaxy merger. In the spatially resolved
CO (3-2) data, we find a compact (r ~ 0.3 kpc) high velocity (v ~ 500 km/s)
red-shifted feature in addition to the rotation at the N nucleus. We propose a
molecular outflow as the most likely explanation for the high velocity gas. The
outflowing mass of M_{mol} ~ 7 x 10^7 Msun and the short dynamical time of
t_{dyn} ~ 0.6 Myr yield a very high outflow rate of \dot{M}_{mol} ~ 350 Msun/yr
and can deplete the gas in a million years. We find a low star formation rate
(< 16 Msun/yr from the molecular content and < 21 Msun/yr from the far-infrared
spectral energy distribution decomposition) that is inadequate to supply the
kinetic luminosity of the outflow (\dot{E} ~ 3 x 10^43 erg/s). Therefore, the
active galactic nucleus, with a bolometric luminosity of 10^46 erg/s, likely
powers the outflow. The momentum boost rate of the outflow (\dot{p}/(Lbol/c) ~
3) is lower than typical molecular outflows associated with AGN, which may be
related to its compactness. The molecular and ionized outflows are likely two
distinct bursts induced by episodic AGN activity that varies on a time scale of
10^7 yr.Comment: 16 pages, 7 figures, ApJ accepte
Observations of Feedback from Radio-Quiet Quasars: I. Extents and Morphologies of Ionized Gas Nebulae
Black hole feedback -- the strong interaction between the energy output of
supermassive black holes and their surrounding environments -- is routinely
invoked to explain the absence of overly luminous galaxies, the black hole vs.
bulge correlations and the similarity of black hole accretion and star
formation histories. Yet direct probes of this process in action are scarce and
limited to small samples of active nuclei. We present Gemini IFU observations
of the distribution of ionized gas around luminous, obscured, radio-quiet (RQ)
quasars at z~0.5. We detect extended ionized gas nebulae via [O III]5007
emission in every case, with a mean diameter of 28 kpc. These nebulae are
nearly perfectly round. The regular morphologies of nebulae around RQ quasars
are in striking contrast with lumpy or elongated nebulae seen around radio
galaxies at low and high redshifts. We present the uniformly measured
size-luminosity relationship of [O III] nebulae around Seyfert 2 galaxies and
type 2 quasars spanning 6 orders of magnitude in luminosity and confirm the
flat slope of the correlation (R ~ L^{0.25+/-0.02}). We find a universal
behavior of the [O III]/H-beta ratio in our entire RQ quasar sample: it
persists at a constant value (~10) in the central regions, until reaching a
"break" isophotal radius ranging from 4 to 11 kpc where it starts to decrease.
We propose a model of clumpy nebulae in which clouds that produce line emission
transition from being ionization-bounded at small distances from the quasar to
being matter-bounded in the outer parts of the nebula, which qualitatively
explains the observed line ratio and surface brightness profiles. It is
striking that we see such smooth and round large-scale gas nebulosities in this
sample, which are inconsistent with illuminated merger debris and which we
suggest may be the signature of accretion energy from the nucleus reaching gas
at large scales.Comment: 44 pages, 11 figures, 3 tables. Accepted for publication in MNRA
Observations of Feedback from Radio-Quiet Quasars - II. Kinematics of Ionized Gas Nebulae
The prevalence and energetics of quasar feedback is a major unresolved
problem in galaxy formation theory. In this paper, we present Gemini Integral
Field Unit observations of ionized gas around eleven luminous, obscured,
radio-quiet quasars at z~0.5 out to ~15 kpc from the quasar; specifically, we
measure the kinematics and morphology of [O III]5007 emission. The round
morphologies of the nebulae and the large line-of-sight velocity widths (with
velocities containing 80% of the emission as high as 1000 km/s combined with
relatively small velocity difference across them (from 90 to 520 km/s) point
toward wide-angle quasi-spherical outflows. We use the observed velocity widths
to estimate a median outflow velocity of 760 km/s, similar to or above the
escape velocities from the host galaxies. The line-of-sight velocity dispersion
declines slightly toward outer parts of the nebulae (by 3% per kpc on average).
The majority of nebulae show blueshifted excesses in their line profiles across
most of their extents, signifying gas outflows. For the median outflow
velocity, we find a kinetic energy flow between 4x10^{44} and 3x10^{45} erg/s
and mass outflow rate between 2000 and 20000 Msun/yr. These values are large
enough for the observed quasar winds to have a significant impact on their host
galaxies. The median rate of converting bolometric luminosity to kinetic energy
of ionized gas clouds is ~2%. We report four new candidates for "super-bubbles"
-- outflows that may have broken out of the denser regions of the host galaxy.Comment: 23 pages, 10 figures, 2 tables, accepted for publication in MNRA
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
Dense gas without star formation: The kpc-sized molecular disk in 3C326 N
We report the discovery of a 3 kpc disk of few 10^9 Ms of dense, warm H_2 in
the nearby radio galaxy 3C326 N, which shows no signs of on-going or recent
star formation and falls a factor 60 below the Schmidt-Kennicutt law.
VLT/SINFONI imaging spectroscopy shows broad (FWHM \sim 500 km/s)
ro-vibrational H_2 lines across all of the disk, with irregular profiles and
line ratios consistent with shocks. The ratio of turbulent and gravitational
energy suggests that the gas is highly turbulent and not gravitationally bound.
In absence of the driving by the jet, short turbulent dissipation times suggest
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 sets
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 not sufficient to
trigger star formation.Comment: A&A accepte
Using ALMA to resolve the nature of the early star-forming large-scale structure PLCK G073.4-57.5
Galaxy clusters at high redshift are key targets for understanding matter
assembly in the early Universe, yet they are challenging to locate. A sample of
>2000 high-z candidate structures has been found using Planck's all-sky submm
maps, and a sub-set of 234 have been followed up with Herschel-SPIRE, which
showed that the emission can be attributed to large overdensities of dusty
star-forming galaxies. In order to resolve and characterise the individual
galaxies we targeted the eight brightest SPIRE sources in the centre of the
Planck peak PLCK G073.4-57.5 using ALMA at 1.3 mm, and complemented these
observations with data from IRAC, WIRCam J,K, and SCUBA-2. We detected a total
of 18 millimetre galaxies brighter than 0.3 mJy in 2.4 arcmin^2. The ALMA
source density is 8-30 times higher than average background estimates and
larger than seen in typical 'proto-cluster' fields. We were able to match all
but one of the ALMA sources to a NIR counterpart. The most significant (four)
SCUBA-2 sources are not included in the ALMA pointings, but we find an 8sigma
stacking detection of the ALMA sources in the SCUBA-2 map at 850 um. We derive
photo-z, L_IR, SFR, stellar mass, T_dust, M_dust for all of the ALMA galaxies;
the photo-zs identify two groups each of five sources, at z~1.5 and 2.4. The
two groups show two 'red sequences' (i.e. similar NIR [3.6]-[4.5] colours and
different J-K colours). The majority of the ALMA-detected galaxies are on the
SFR versus stellar mass main sequence, and half of the sample is more massive
than the characteristic stellar mass at the corresponding redshift.
Serendipitous CO line detections in two of the galaxies appear to match their
photometric redshifts at z~1.54. We performed an analysis of star-formation
efficiencies and CO- and mm-continuum-derived gas fractions of our ALMA
sources, combined with a sample of 1<z<3 cluster and proto-cluster members.Comment: 26 pages, revised version, Astronomy & Astrophysics accepte
Herschel Extreme Lensing Line Observations: Dynamics of two strongly lensed star forming galaxies near redshift z = 2
We report on two regularly rotating galaxies at redshift z=2, using high
resolution spectra of the bright [CII] 158 micron emission line from the HIFI
instrument on the Herschel Space Observatory. Both SDSS090122.37+181432.3
("S0901") and SDSS J120602.09+514229.5 ("the Clone") are strongly lensed and
show the double-horned line profile that is typical of rotating gas disks.
Using a parametric disk model to fit the emission line profiles, we find that
S0901 has a rotation speed v sin(i) = 120 +/- 7 km/s and gas velocity
dispersion sigma < 23 km/s. The best fitting model for the Clone is a
rotationally supported disk having v sin(i) = 79 +/- 11 km/s and sigma < 4km/s.
However the Clone is also consistent with a family of dispersion-dominated
models having sigma = 92 +/- 20 km/s. Our results showcase the potential of the
[CII] line as a kinematic probe of high redshift galaxy dynamics: [CII] is
bright; accessible to heterodyne receivers with exquisite velocity resolution;
and traces dense star-forming interstellar gas. Future [CII] line observations
with ALMA would offer the further advantage of spatial resolution, allowing a
clearer separation between rotation and velocity dispersion.Comment: 20 pages, 4 figures; in press at The Astrophysical Journa
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