33 research outputs found
Dynamical evolution of local gas-rich galaxy mergers from NIR spectroscopy
This study aimed to trace how the stellar kinematics evolve when two gas-rich galaxies merge. To study the evolution of such mergers, Very-Large-Telescope observations were performed for the best-suited galaxy population in the local Universe, the Ultraluminous Infrared Galaxies (ULIRGs). The prodigious infrared emission in ULIRGs originates from the intense star formation that occurs when large amounts gas are driven to the center of the merging system. We acquired near-infrared H- and K-band spectroscopic data of 54 ULIRGs at various merger phases; approximately half of the sources in our sample have two distinct nuclei. For each source, we derived the stellar kinematics from the high-resolution spectra by studying the profile of the stellar CO absorption lines. The shape of the profile along various slit positions enables us to measure the rotational velocity, V_rot, and velocity dispersion, sigma, and to compute the stellar and black hole (BH) masses. We find that ULIRGs are mostly triggered by mergers of roughly equal-mass galaxies. Their mean velocity dispersion equals 150+- 33 km/s. A possible trend of dynamical heating of the galaxies as the merger evolves is observed at marginal statistical levels. The kinematic, structural, and photometric properties of ULIRGs indicate that they are dispersion-dominated systems and that they mainly result in the formation of 10^10-10^11 solar-mass elliptical galaxies (Es). Their locus on the fundamental plane of Es indicates that their end products are typically inconsistent with giant Es. The BH masses in ULIRGs are of the order 10^7- 10^8 solar. To investigate whether ULIRGs go through quasar (QSO) phases during their evolution, we have acquired similar data for 12 local Palomar-Green (PG) QSOs. The mean bulge dispersion of the PG QSOs in our sample equals 186 +-24 km/s. The measurement of the stellar dispersion in QSOs enables us to place them on significant observational diagrams, such as the local BH mass and host-galaxy bulge relation and the fundamental plane of Es. On the latter, PG QSOs are located between the regions occupied by moderate-mass and giant Es. Their bulge and BH masses are on the order of 10^11 and 5*10^7-10^8 solar masses respectively. PG QSOs seem to be triggered by gas-rich mergers, and therefore likely formed in an analogous manner to ULIRGs. However, other local QSOs with supermassive black holes of 5*10^8-10^9 solar masses that reside in massive spheroids have a different formation mechanism
Feeding and feedback in nuclei of galaxies
Our aim is to explore the close environment of Active Galactic Nuclei (AGN)
and its connection to the host galaxy through the morphology and dynamics of
the cold gas inside the central kpc in nearby AGN. We report Atacama Large
Millimeter/submillimeter Array (ALMA) observations of AGN feeding and feedback
caught in action in NGC613 and NGC1808 at high resolution (few pc), part of the
NUclei of GAlaxies (NUGA) project. We detected trailing spirals inside the
central 100pc, efficiently driving the molecular gas into the SMBH, and
molecular outflows driven by the AGN. We present preliminary results of the
impact of massive winds induced by radio jets on galaxy evolution, based on
observations of radio galaxies from the ALMA Radio-source Catalogue.Comment: 5 pages, 3 figures, to be published in Proceeding IAU Symposium No.
359, 2020, "Galaxy evolution and feedback across different environments",
Eds. T. Storchi-Bergmann, R. Overzier, W. Forman and R. Riffe
Spitzer- and Herschel-based Spectral Energy Distributions of 24 μm Bright z ~ 0.3-3.0 Starbursts and Obscured Quasars
In this paper, we characterize the infrared spectral energy distributions (SEDs) of mid-IR-selected z ∼ 0.3–3.0 and
LIR ∼ 10^(11)–10^(13) L_☉ galaxies, and study how their SEDs differ from those of local and high-z analogs. Infrared
SEDs depend both on the power source (AGN or star formation) and the dust distribution. Therefore, differences
in the SEDs of high-z and local galaxies provide clues as to differences in their physical conditions. Our mid-IR
flux-limited sample of 191 sources is unique in size, and spectral coverage, including Spitzer mid-IR spectroscopy.
Here, we add Herschel photometry at 250μm, 350μm, and 500μm, which allows us, through fitting an empirical
SED model, to obtain accurate total IR luminosities, as well as constrain the relative contributions of AGNs and
starbursts to those luminosities. Our sample includes three broad categories of SEDs: ∼23% of the sources are
AGNs (i.e., where the AGN contributes >50% of L_(IR)), ∼30% are starbursts where an AGN contributes <20%
of LIR, and the mid-IR spectra are starburst-like (i.e., strong polycyclic aromatic hydrocarbon features); and the
largest group (∼47%) are composites which show both significant AGN and starburst activity. The AGN-dominated
sources divide into ones that show a strong silicate 9.7μm absorption feature, implying highly obscured systems,
and ones that do not. The high-Ï„_(9.7) sources are half of our z > 1.2 AGNs, but show SEDs that are extremely
rare among local AGNs. The 30% of the sample that are starbursts, even the z ∼ 2, L_(IR) ∼ 10^(13) L_☉ ones, have
lower far-IR to mid-IR continuum ratios than local Ultra Luminous Infrared Galaxies (ULIRGs) or the z ∼ 2 submm
galaxies—effectively the SEDs of our z ∼ 2 starburst-dominated ULIRGs are much closer to those of local
Luminous Infrared Galaxies than ULIRGs. This is consistent with our earlier finding that, unlike local ULIRGs,
our high-z starbursts are typically only in the early stages of a merger. The SEDs of the composite sources are most similar to the local archetypal warm ULIRG, Mrk231, which supports the interpretation of their consisting of both AGN and starburst components. In summary, our results show that there is strong evolution in the SEDs between
local and z ∼ 2 IR-luminous galaxies, as well as that there is a wide range of SEDs among high redshift IR-luminous sources. The publicly available SED templates we derive from our sample will be particularly useful for infrared population synthesis models, as well as in the interpretation of other mid-IR high-z galaxies, in particular those detected by the recent all sky Wide-field Infrared Survey Explorer
HST NICMOS imaging of z~2, 24 micron-selected Ultraluminous Infrared Galaxies
We present Hubble Space Telescope NICMOS H-band imaging of 33 Ultraluminous
Infrared Galaxies (ULIRGs) at z~2 that were selected from the 24 micron catalog
of the Spitzer Extragalactic First Look Survey. The images reveal that at least
17 of the 33 objects are associated with interactions. Up to one fifth of the
sources in our sample could be minor mergers whereas only 2 systems are merging
binaries with luminosity ratio <=3:1, which is characteristic of local ULIRGs.
The rest-frame optical luminosities of the sources are of the order 10^10-10^11
L_sun and their effective radii range from 1.4 to 4.9 kpc. The most compact
sources are either those with a strong active nucleus continuum or those with a
heavy obscuration in the mid-infrared regime, as determined from Spitzer
Infra-Red Spectrograph data. The luminosity of the 7.7 micron feature produced
by polycyclic aromatic hydrocarbon molecules varies significantly among compact
systems whereas it is typically large for extended systems. A bulge-to-disk
decomposition performed for the 6 brightest (m_H<20) sources in our sample
indicates that they are best fit by disk-like profiles with small or negligible
bulges, unlike the bulge-dominated remnants of local ULIRGs. Our results
provide evidence that the interactions associated with ultraluminous infrared
activity at z~2 can differ from those at z~0.Comment: ApJ, in press. Document revised to match the journal versio
HST NICMOS imaging of z ~ 2, 24 µm-selected ultraluminous infrared galaxies
We present Hubble Space Telescope NICMOSH-band imaging of 33 ultraluminous infrared galaxies (ULIRGs) at z ~ 2 that were selected from the 24 µm catalog of the Spitzer Extragalactic First Look Survey. The images reveal that at least 17 of the 33 objects are associated with interactions. Up to one-fifth of the sources in our sample could be minor mergers, whereas only two systems are merging binaries with luminosity ratio ≤ 3 : 1, which is characteristic of local ULIRGs. The rest-frame optical luminosities of the sources are of the order 10^(10)-10^(11) L⊙ and their effective radii range from 1.4 to 4.9 kpc. The most compact sources are either those with a strong active nucleus continuum or those with a heavy obscuration in the mid-infrared regime, as determined from Spitzer Infrared Spectrograph data. The luminosity of the 7.7 µm feature produced by polycyclic aromatic hydrocarbon molecules varies significantly among compact systems, whereas it is typically large for extended systems. A bulge-to-disk decomposition performed for the six brightest (m_H < 20) sources in our sample indicates that they are best fit by disklike profiles with small or negligible bulges, unlike the bulge-dominated remnants of local ULIRGs. Our results provide evidence that the interactions associated with ultraluminous infrared activity at z ~ 2 can differ from those at z ~ 0
Far-infrared line spectra of Seyfert galaxies from the Herschel-PACS Spectrometer
We present spectroscopic observations of FIR fine-structure lines of 26
Seyfert galaxies obtained with the Herschel-PACS spectrometer. These
observations are complemented by spectroscopy with Spitzer-IRS and
Herschel-SPIRE. The ratios of the OIII, NII, SIII and NeV lines have been used
to determine electron densities in the ionised gas regions. The CI lines,
observed with SPIRE, have been used to measure the densities in the neutral
gas, while the OI lines provide a measure of the gas temperature, at densities
below 10000 cm-3. Using the OI145/63um and SIII33/18um line ratios we find an
anti-correlation of the temperature with the gas density. Using various
fine-structure line ratios, we find that density stratification is common in
these active galaxies. On average, the electron densities increase with the
ionisation potential of the ions producing the NII, SIII and NeV emission. The
infrared emission lines arise partly in the Narrow Line Region (NLR)
photoionised by the AGN central engine, partly in HII regions photo ionised by
hot stars and partly in neutral gas in photo-dissociated regions (PDRs). We
attempt to separate the contributions to the line emission produced in these
different regions by comparing our emission line ratios to empirical and
theoretical values. In particular, we tried to separate the contribution of AGN
and star formation by using a combination of Spitzer and Herschel lines, and we
found that, besides the well known mid-IR line ratios, the mixed mid-IR/far-IR
line ratio of OIII88um/OIV26um can reliably discriminate the two emission
regimes, while the far-IR line ratio of CII157um/OI63um is only able to mildly
separate the two regimes. By comparing the observed CII157um/NII205um ratio
with photoionisation models, we also found that most of the CII emission in the
galaxies we examined is due to PDRs.Comment: Accepted for publication in ApJ Main Journal on the 5th November
2014, 25 pages, 16 figure
Infrared luminosities and aromatic features in the 24 μm flux-limited sample of 5muses
We study a 24 μm selected sample of 330 galaxies observed with the infrared spectrograph for the 5 mJy Unbiased
Spitzer Extragalactic Survey. We estimate accurate total infrared luminosities by combining mid-IR spectroscopy
and mid-to-far infrared photometry, and by utilizing newempirical spectral templates from Spitzer data. The infrared luminosities of this sample range mostly from 10^9 L_⊙ to 10^(13.5) L_⊙,with 83% in the range 10^(10) L_⊙ < L_(IR) < 10^(12) L_⊙. The redshifts range from 0.008 to 4.27, with a median of 0.144. The equivalent widths of the 6.2 μm aromatic feature have a bimodal distribution, probably related to selection effects. We use the 6.2μm polycyclic aromatic hydrocarbon equivalent width (PAH EW) to classify our objects as starburst (SB)-dominated (44%), SB-AGN composite (22%), and active galactic nucleus (AGN)-dominated (34%). The high EW objects (SB-dominated) tend to have steeper mid-IR to far-IR spectral slopes and lower L_(IR) and redshifts. The low EW objects (AGN-dominated) tend to have less steep spectral slopes and higher L_(IR) and redshifts. This dichotomy leads to a gross correlation between EW and slope, which does not hold within either group. AGN-dominated sources tend to have lower log(L_(PAH7.7 μm)/L_(PAH11.3 μm)) ratios than star-forming galaxies, possibly due to preferential destruction of the smaller aromatics by the AGN. The log(L_(PAH7.7 μm)/L_(PAH11.3 μm)) ratios for star-forming galaxies are lower in our sample than the ratios measured from the nuclear spectra of nearby normal galaxies, most probably indicating a difference in the ionization state or grain size distribution between the nuclear regions and the entire galaxy. Finally, we provide a calibration relating the monochromatic continuum or aromatic feature luminosity to L_(IR) for different types of objects
First Stellar Velocity Dispersion Measurement of a Luminous Quasar Host with Gemini North Laser Guide Star Adaptive Optics
We present the first use of the Gemini North laser guide star adaptive optics
(LGS AO) system and an integral field unit (IFU) to measure the stellar
velocity dispersion of the host of a luminous quasar. The quasar PG1426+015
(z=0.086) was observed with the Near-Infrared Integral Field Spectrometer
(NIFS) on the 8m Gemini North telescope in the H-band as part of the Science
Verification phase of the new ALTAIR LGS AO system. The NIFS IFU and LGS AO are
well suited for host studies of luminous quasars because one can achieve a
large ratio of host to quasar light. We have measured the stellar velocity
dispersion of PG1426+015 from 0.1'' to 1'' (0.16 kpc to 1.6 kpc) to be 217+/-15
km/s based on high signal-to-noise ratio measurements of Si I, Mg I, and
several CO bandheads. This new measurement is a factor of four more precise
than a previous measurement obtained with long-slit spectroscopy and good,
natural seeing, yet was obtained with a shorter net integration time. We find
that PG1426+015 has a velocity dispersion that places it significantly above
the M-sigma relation of quiescent galaxies and lower-luminosity active galactic
nuclei with black hole masses estimated from reverberation mapping. We discuss
several possible explanations for this discrepancy that could be addressed with
similar observations of a larger sample of luminous quasars.Comment: 5 pages, 2 figures; accepted by ApJ Letter
A plausible link between dynamically unsettled molecular gas and the radio jet in NGC 6328
We report the detection of outflowing molecular gas at the center of the
nearby radio galaxy NGC6328 (z=0.014), which has a gigahertz-peaked spectrum
radio core and a compact (2 pc) young double radio lobe tracing jet. Utilizing
Atacama Large Millimeter/submillimeter Array (ALMA) CO(2-1) and CO(3-2)
observations, as well as a novel code developed to fit the 3D gas distribution
and kinematics, to study the molecular gas kinematics, we find that the bulk of
the gas is situated within a highly warped disk structure, most likely the
result of a past merger event. Our analysis further uncovers, within the inner
regions of the gas distribution (R<300 pc) and at a position angle aligning
with that of the radio jet (150 degrees), the existence of two anti-diametric
molecular gas structures kinematically detached from the main disk. These
structures most likely trace a jet-induced cold gas outflow with a total lower
limit mass of mass, corresponding to an
outflow rate of and a kinetic power of
. The energy required to maintain such
a molecular outflow is aligned with the mechanical power of the jet.Comment: 19 pages, 13 figures, Accepted for publication in A