arXiv subjects

R. Genzel

Publications and source records attributed to R. Genzel.

At least 181 records · Page 10Linked to original sources

arXiv2015

Obscuration in AGNs: near-infrared luminosity relations and dust colors

We combine two approaches to isolate the AGN luminosity at near-infrared wavelengths and relate the near-IR pure AGN luminosity to other tracers of the AGN. Using integral-field spectroscopic data of an archival sample of 51 local AGNs, we estimate the fraction of non-stellar light by comparing the nuclear equivalent width of the stellar 2.3 micron CO absorption feature with the intrinsic value for each galaxy. We compare this fraction to that derived from a spectral decomposition of the integrated light in the central arc second and find them to be consistent with each other. Using our estimates of the near-IR AGN light, we find a strong correlation with presumably isotropic AGN tracers. We show that a significant offset exists between type 1 and type 2 sources in the sense that type 1 sources are 7 (10) times brighter in the near-IR at log L_MIR = 42.5 (log L_X = 42.5). These offsets only becomes clear when treating infrared type 1 sources as type 1 AGNs. All AGNs have very red near-to-mid-IR dust colors. This, as well as the range of observed near-IR temperatures, can be explained with a simple model with only two free parameters: the obscuration to the hot dust and the ratio between the warm and hot dust areas. We find obscurations of A_V (hot) = 5 - 15 mag for infrared type 1 sources and A_V (hot) = 15 - 35 mag for type 2 sources. The ratio of hot dust to warm dust areas of about 1000 is nicely consistent with the ratio of radii of the respective regions as found by infrared interferometry.

astro-ph.GA↗

arXiv2015

High-J CO SLEDs in nearby infrared bright galaxies observed by Herschel-PACS

We report the detection of far-infrared (FIR) CO rotational emission from nearby active galactic nuclei (AGN) and starburst galaxies, as well as several merging systems and Ultra-Luminous Infrared Galaxies (ULIRGs). Using Herschel-PACS, we have detected transitions in the J$_{upp}$ = 14 - 20 range ($λ\sim$ 130 - 185 $μ$m, $ν\sim$ 1612 - 2300 GHz) with upper limits on (and in two cases, detections of) CO line fluxes up to J$_{upp}$ = 30. The PACS CO data obtained here provide the first well-sampled FIR extragalactic CO SLEDs for this range, and will be an essential reference for future high redshift studies. We find a large range in the overall SLED shape, even amongst galaxies of similar type, demonstrating the uncertainties in relying solely on high-J CO diagnostics to characterize the excitation source of a galaxy. Combining our data with low-J line intensities taken from the literature, we present a CO ratio-ratio diagram and discuss its potential diagnostic value in distinguishing excitation sources and physical properties of the molecular gas. The position of a galaxy on such a diagram is less a signature of its excitation mechanism, than an indicator of the presence (or absence) of warm, dense molecular gas. We then quantitatively analyze the CO emission from a subset of the detected sources with Large Velocity Gradient (LVG) radiative transfer models to fit the CO SLEDs. Using both single-component and two-component LVG models to fit the kinetic temperature, velocity gradient, number density and column density of the gas, we derive the molecular gas mass and the corresponding CO-to-H$_2$ conversion factor, $α_{CO}$, for each respective source. For the ULIRGs we find $α$ values in the canonical range 0.4 - 5 M$_\odot$/(K kms$^{-1}$pc$^2$), while for the other objects, $α$ varies between 0.2 and 14.} Finally, we compare our best-fit LVG model ..

astro-ph.GA↗

arXiv2015

The GRAVITY metrology system: narrow-angle astrometry via phase-shifting interferometry

The VLTI instrument GRAVITY will provide very powerful astrometry by combining the light from four telescopes for two objects simultaneously. It will measure the angular separation between the two astronomical objects to a precision of 10 microarcseconds. This corresponds to a differential optical path difference (dOPD) between the targets of few nanometers and the paths within the interferometer have to be maintained stable to that level. For this purpose, the novel metrology system of GRAVITY will monitor the internal dOPDs by means of phase-shifting interferometry. We present the four-step phase-shifting concept of the metrology with emphasis on the method used for calibrating the phase shifts. The latter is based on a phase-step insensitive algorithm which unambiguously extracts phases in contrast to other methods that are strongly limited by non-linearities of the phase-shifting device. The main constraint of this algorithm is to introduce a robust ellipse fitting routine. Via this approach we are able to measure phase shifts in the laboratory with a typical accuracy of lambda/2000 or 1 nanometer of the metrology wavelength.

astro-ph.IM↗

arXiv2014

High-lying OH absorption, [C II] deficits, and extreme $L_{\mathrm{FIR}}/M_{\mathrm{H2}}$ ratios in galaxies

Herschel/PACS observations of 29 local (Ultra-)Luminous Infrared Galaxies, including both starburst and AGN-dominated sources as diagnosed in the mid-infrared/optical, show that the equivalent width of the absorbing OH 65 um Pi_{3/2} J=9/2-7/2 line (W_{eq}(OH65)) with lower level energy E_{low}~300 K, is anticorrelated with the [C ii]158 um line to far-infrared luminosity ratio, and correlated with the far-infrared luminosity per unit gas mass and with the 60-to-100 um far-infrared color. While all sources are in the active L_{IR}/M_{H2}>50 Lsun/Msun mode as derived from previous CO line studies, the OH65 absorption shows a bimodal distribution with a discontinuity at L_{FIR}/M_{H2}~100 Lsun/Msun. In the most buried sources, OH65 probes material partially responsible for the silicate 9.7 um absorption. Combined with observations of the OH 71 um Pi_{1/2} J=7/2-5/2 doublet (E_{low}~415 K), radiative transfer models characterized by the equivalent dust temperature, Tdust, and the continuum optical depth at 100 um, tau_{100}, indicate that strong [C ii]158 um deficits are associated with far-IR thick (tau_{100}>~0.7, N_{H}>~10^{24} cm^{-2}), warm (Tdust>~60 K) structures where the OH 65 um absorption is produced, most likely in circumnuclear disks/tori/cocoons. With their high L_{FIR}/M_{H2} ratios and columns, the presence of these structures is expected to give rise to strong [C ii] deficits. W_{eq}(OH65) probes the fraction of infrared luminosity arising from these compact/warm environments, which is >~30-50% in sources with high W_{eq}({OH65}). Sources with high W_{eq}({OH65}) have surface densities of both L_{IR} and M_{H2} higher than inferred from the half-light (CO or UV/optical) radius, tracing coherent structures that represent the most buried/active stage of (circum)nuclear starburst-AGN co-evolution.

astro-ph.GA↗

arXiv2014

The KMOS^3D Survey: design, first results, and the evolution of galaxy kinematics from 0.7<z<2.7

We present the KMOS^3D survey, a new integral field survey of over 600 galaxies at 0.7 1$, implying that the star-forming 'main sequence' (MS) is primarily composed of rotating galaxies at both redshift regimes. When considering additional stricter criteria, the Halpha kinematic maps indicate at least ~70% of the resolved galaxies are disk-like systems. Our high-quality KMOS data confirm the elevated velocity dispersions reported in previous IFS studies at z>0.7. For rotation-dominated disks, the average intrinsic velocity dispersion decreases by a factor of two from 50 km/s at z~2.3 to 25 km/s at z~0.9 while the rotational velocities at the two redshifts are comparable. Combined with existing results spanning z~0-3, disk velocity dispersions follow an approximate (1+z) evolution that is consistent with the dependence of velocity dispersion on gas fractions predicted by marginally-stable disk theory.

astro-ph.GA↗

arXiv2014

Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass

We combine molecular gas masses inferred from CO emission in 500 star forming galaxies (SFGs) between z=0 and 3, from the IRAM-COLDGASS, PHIBSS1/2 and other surveys, with gas masses derived from Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. We constrain the scaling relations of molecular gas depletion time scale (tdepl) and gas to stellar mass ratio (Mmolgas/M*) of SFGs near the star formation main-sequence with redshift, specific star formation rate (sSFR) and stellar mass (M*). The CO- and dust-based scaling relations agree remarkably well. This suggests that the CO-H2 mass conversion factor varies little within 0.6dex of the main sequence (sSFR(ms,z,M*)), and less than 0.3dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that tdepl scales as (1+z)^-0.3 *(sSFR/sSFR(ms,z,M*))^-0.5, with little dependence on M*. The resulting steep redshift dependence of Mmolgas/M* ~(1+z)^3 mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high M* are driven by the flattening of the SFR-M* relation. Throughout the redshift range probed a larger sSFR at constant M* is due to a combination of an increasing gas fraction and a decreasing depletion time scale. As a result galaxy integrated samples of the Mmolgas-SFR rate relation exhibit a super-linear slope, which increases with the range of sSFR. With these new relations it is now possible to determine Mmolgas with an accuracy of 0.1dex in relative terms, and 0.2dex including systematic uncertainties.

astro-ph.GA↗

arXiv2014

The host galaxies of X-ray selected Active Galactic Nuclei to z=2.5: Structure, star-formation and their relationships from CANDELS and Herschel/PACS

We study the relationship between the structure and star-formation rate (SFR) of X-ray selected low and moderate luminosity active galactic nuclei (AGNs) in the two Chandra Deep Fields, using Hubble Space Telescope imaging from the Cosmic Assembly Near Infrared Extragalactic Legacy Survey (CANDELS) and deep far-infrared maps from the PEP+GOODS-Herschel survey. We derive detailed distributions of structural parameters and FIR luminosities from carefully constructed control samples of galaxies, which we then compare to those of the AGNs. At z~1, AGNs show slightly diskier light profiles than massive inactive (non-AGN) galaxies, as well as modestly higher levels of gross galaxy disturbance (as measured by visual signatures of interactions and clumpy structure). In contrast, at z~2, AGNs show similar levels of galaxy disturbance as inactive galaxies, but display a red central light enhancement, which may arise due to a more pronounced bulge in AGN hosts or due to extinguished nuclear light. We undertake a number of tests of these alternatives, but our results do not strongly favour one interpretation over the other. The mean SFR and its distribution among AGNs and inactive galaxies are similar at z>1.5. At z<1, however, clear and significant enhancements are seen in the SFRs of AGNs with bulge-dominated light profiles. These trends suggest an evolution in the relation between nuclear activity and host properties with redshift, towards a minor role for mergers and interactions at z>1.5.

astro-ph.GA↗

arXiv2014

Evidence for Wide-Spread AGN Driven Outflows in the Most Massive z~1-2 Star Forming Galaxies

In this paper we follow up on our previous detection of nuclear ionized outflows in the most massive (log(M*/Msun) >= 10.9) z~1-3 star-forming galaxies (Forster Schreiber et al.), by increasing the sample size by a factor of six (to 44 galaxies above log(M*/Msun) >= 10.9) from a combination of the SINS/zC-SINF, LUCI, GNIRS, and KMOS^3D spectroscopic surveys. We find a fairly sharp onset of the incidence of broad nuclear emission (FWHM in the Ha, [NII], and [SII] lines ~ 450-5300 km/s), with large [NII]/Ha ratios, above log(M*/Msun) ~ 10.9, with about two thirds of the galaxies in this mass range exhibiting this component. Broad nuclear components near and above the Schechter mass are similarly prevalent above and below the main sequence of star-forming galaxies, and at z~1 and ~2. The line ratios of the nuclear component are fit by excitation from active galactic nuclei (AGN), or by a combination of shocks and photoionization. The incidence of the most massive galaxies with broad nuclear components is at least as large as that of AGNs identified by X-ray, optical, infrared or radio indicators. The mass loading of the nuclear outflows is near unity. Our findings provide compelling evidence for powerful, high-duty cycle, AGN-driven outflows near the Schechter mass, and acting across the peak of cosmic galaxy formation.

astro-ph.GA↗

arXiv2014

The SINS/zC-SINF survey of z~2 galaxy kinematics: Evidence for powerful AGN-driven nuclear outflows in massive star-forming galaxies

We report the detection of ubiquitous powerful nuclear outflows in massive (> 10^11 Msun) z~2 star-forming galaxies (SFGs), which are plausibly driven by an Active Galactic Nucleus (AGN). The sample consists of the eight most massive SFGs from our SINS/zC-SINF survey of galaxy kinematics with the imaging spectrometer SINFONI, six of which have sensitive high-resolution adaptive optics (AO) assisted observations. All of the objects are disks hosting a significant stellar bulge. The spectra in their central regions exhibit a broad component in Halpha and forbidden [NII] and [SII] line emission, with typical velocity FWHM ~ 1500 km/s, [NII]/Halpha ratio ~ 0.6, and intrinsic extent of 2 - 3 kpc. These properties are consistent with warm ionized gas outflows associated with Type 2 AGN, the presence of which is confirmed via independent diagnostics in half the galaxies. The data imply a median ionized gas mass outflow rate of ~ 60 Msun/yr and mass loading of ~ 3. At larger radii, a weaker broad component is detected but with lower FWHM ~ 485 km/s and [NII]/Halpha ~ 0.35, characteristic for star formation-driven outflows as found in the lower-mass SINS/zC-SINF galaxies. The high inferred mass outflow rates and frequent occurrence suggest the nuclear outflows efficiently expel gas out of the centers of the galaxies with high duty cycles, and may thus contribute to the process of star formation quenching in massive galaxies. Larger samples at high masses will be crucial to confirm the importance and energetics of the nuclear outflow phenomenon, and its connection to AGN activity and bulge growth.

astro-ph.CO↗

arXiv2013

Hydrodynamical simulations of a compact source scenario for G2

The origin of the dense gas cloud G2 discovered in the Galactic Center (Gillessen et al. 2012) is still a debated puzzle. G2 might be a diffuse cloud or the result of an outflow from an invisible star embedded in it. We present here detailed simulations of the evolution of winds on G2's orbit. We find that the hydrodynamic interaction with the hot atmosphere present in the Galactic Center and the extreme gravitational field of the supermassive black hole must be taken in account when modeling such a source scenario. We find that the hydrodynamic interaction with the hot atmosphere present in the Galactic Center and the extreme gravitational field of the supermassive black hole must be taken in account when modeling such a source scenario. We also find that in this scenario most of the Brγ luminosity is expected to come from the highly filamentary densest shocked wind material. G2's observational properties can be used to constrain the properties of the outflow and our best model has a mass outflow rate of Mdot,w=8.8 x 10^{-8} Msun/yr and a wind velocity of vw = 50 km/s. These values are compatible with those of a young TTauri star wind, as already suggested by Scoville & Burkert (2013).

astro-ph.GA↗

arXiv2013

The evolution of the dust and gas content in galaxies

We use deep Herschel PACS and SPIRE observations in GOODSS, GOODSN and COSMOS to estimate the average dust mass (Mdust) of galaxies on a redshift-stellar mass (Mstar)-SFR grid. We study the scaling relations between Mdust, Mstar and SFR at z<=2.5. No clear evolution of Mdust is observed at fixed SFR and Mstar. We find a tight correlation between SFR and Mdust, likely a consequence of the Schmidt-Kennicutt (S-K) law. The Mstar-Mdust correlation observed by previous works flattens or sometimes disappears when fixing the SFR. Most of it likely derives from the combination of the Mdust-SFR and Mstar-SFR correlations. We then investigate the gas content as inferred by converting Mdust by assuming that the dust/gas ratio scales linearly with the gas metallicity. All galaxies in the sample follow, within uncertainties, the same SFR-Mgas relation (integrated S-K law), which broadly agrees with CO-based results for the bulk of the population, despite the completely different approaches. The majority of galaxies at z~2 form stars with an efficiency (SFE=SFR/Mgas) ~5 times higher than at z~0. It is not clear what fraction of such variation is an intrinsic redshift evolution and what fraction arises from selection effects. The gas fraction (fgas) decreases with Mstar and increases with SFR, and does not evolve with z at fixed Mstar and SFR. We explain these trends by introducing a universal relation between fgas, Mstar and SFR, non-evolving out to z~2.5. Galaxies move across this relation as their gas content evolves in time. We use the 3D fundamental fgas-Mstar-SFR relation and the redshift evolution of the Main Sequence to estimate the evolution of fgas in the average population of galaxies as a function of z and Mstar, and we find evidence a downsizing scenario.

astro-ph.CO↗

arXiv2013

The evolution of the dust temperatures of galaxies in the SFR$-M_{\ast}$ plane up to $z$$\,\thicksim\,$$2$

[Abridged] We study the evolution of the dust temperatures of galaxies in the SFR-M* plane up to z~2 using observations from the Herschel Space Observatory. Starting from a sample of galaxies with reliable star-formation rates (SFRs), stellar masses (M*) and redshift estimates, we grid the SFR-M* parameter space in several redshift ranges and estimate the mean Tdust of each SFR-M*-z bin. Dust temperatures are inferred using the stacked far-infrared flux densities of our SFR-M*-z bins. At all redshifts, Tdust increases with infrared luminosities (LIR), specific SFRs (SSFR; i.e., SFR/M*) and distances with respect to the main sequence (MS) of the SFR-M* plane (i.e., D_SSFR_MS=log[SSFR(galaxy)/SSFR_MS(M*,z)]). The Tdust-SSFR and Tdust-D_SSFR_MS correlations are statistically more significant than the Tdust-LIR one. While the slopes of these three correlations are redshift-independent, their normalizations evolve from z=0 and z~2. We convert these results into a recipe to derive Tdust from SFR, M* and z. The existence of a strong Tdust-D_SSFR_MS correlation provides us with information on the dust and gas content of galaxies. (i) The slope of the Tdust-D__SSFR_MS correlation can be explained by the increase of the star-formation efficiency (SFE; SFR/Mgas) with D_SSFR_MS as found locally by molecular gas studies. (ii) At fixed D_SSFR_MS, the constant Tdust observed in galaxies probing large ranges in SFR and M* can be explained by an increase or decrease of the number of star-forming regions with comparable SFE enclosed in them. (iii) At high redshift, the normalization towards hotter temperature of the Tdust-D_SSFR_MS correlation can be explained by the decrease of the metallicities of galaxies or by the increase of the SFE of MS galaxies. All these results support the hypothesis that the conditions prevailing in the star-forming regions of MS and far-above-MS galaxies are different.

astro-ph.CO↗

arXiv2013

The SINS/zC-SINF survey of z~2 galaxy kinematics: evidence for gravitational quenching

As part of the SINS/zC-SINF surveys of high-z galaxy kinematics, we derive the radial distributions of H-alpha surface brightness, stellar mass surface density, and dynamical mass at ~2 kpc resolution in 19 z~2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. From these data we infer the radial distribution of the Toomre Q-parameter for these main-sequence star forming galaxies (SFGs), covering almost two decades of stellar mass (10^9.6 to 10^11.5 solar masses). In more than half of our SFGs, the H-alpha distributions cannot be fit by a centrally peaked distribution, such as an exponential, but are better described by a ring, or the combination of a ring and an exponential. At the same time the kinematic data indicate the presence of a mass distribution more centrally concentrated than a single exponential distribution for 5 of the 19 galaxies. The resulting Q-distributions are centrally peaked for all, and significantly exceed unity there for three quarters of the SFGs. The occurrence of H-alpha rings and of large nuclear Q-values is strongly correlated, and is more common for the more massive SFGs. While our sample is small and there remain substantial uncertainties and caveats, our observations are consistent with a scenario in which cloud fragmentation and global star formation are secularly suppressed in gas rich high-z disks from the inside out, as the central stellar mass density of the disks grows.

astro-ph.CO↗

arXiv2013

Reversal or no reversal: the evolution of the star formation rate-density relation up to z~1.6

We investigate the evolution of the star formation rate (SFR)-density relation in the Extended Chandra Deep Field South (ECDFS) and the Great Observatories Origin Deep Survey (GOODS) fields up to z~1.6. In addition to the "traditional method", in which the environment is defined according to a statistical measurement of the local galaxy density, we use a "dynamical" approach, where galaxies are classified according to three different environment regimes: group, "filament-like", and field. Both methods show no evidence of a SFR-density reversal. Moreover, group galaxies show a mean SFR lower than other environments up to z~1, while at earlier epochs group and field galaxies exhibit consistent levels of star formation (SF) activity. We find that processes related to a massive dark matter halo must be dominant in the suppression of the SF below z~1, with respect to purely density-related processes. We confirm this finding by studying the distribution of galaxies in different environments with respect to the so-called Main Sequence (MS) of star-forming galaxies. Galaxies in both group and "filament-like" environments preferentially lie below the MS up to z~1, with group galaxies exhibiting lower levels of star-forming activity at a given mass. At z>1, the star-forming galaxies in groups reside on the MS. Groups exhibit the highest fraction of quiescent galaxies up to z~1, after which group, "filament-like", and field environments have a similar mix of galaxy types. We conclude that groups are the most efficient locus for star-formation quenching. Thus, a fundamental difference exists between bound and unbound objects, or between dark matter haloes of different masses.

astro-ph.CO↗

arXiv2013

The Mean Star-Forming Properties of QSO Host Galaxies

Quasi-stellar objects (QSOs) occur in galaxies in which supermassive black holes (SMBHs) are growing substantially through rapid accretion of gas. Many popular models of the co-evolutionary growth of galaxies and SMBHs predict that QSOs are also sites of substantial recent star formation, mediated by important processes, such as major mergers, which rapidly transform the nature of galaxies. A detailed study of the star-forming properties of QSOs is a critical test of such models. We present a far-infrared Herschel/PACS study of the mean star formation rate (SFR) of a sample of spectroscopically observed QSOs to z~2 from the COSMOS extragalactic survey. This is the largest sample to date of moderately luminous AGNs studied using uniform, deep far-infrared photometry. We study trends of the mean SFR with redshift, black hole mass, nuclear bolometric luminosity and specific accretion rate (Eddington ratio). To minimize systematics, we have undertaken a uniform determination of SMBH properties, as well as an analysis of important selection effects within spectroscopic QSO samples that influence the interpretation of SFR trends. We find that the mean SFRs of these QSOs are consistent with those of normal massive star-forming galaxies with a fixed scaling between SMBH and galaxy mass at all redshifts. No strong enhancement in SFR is found even among the most rapidly accreting systems, at odds with several co-evolutionary models. Finally, we consider the qualitative effects on mean SFR trends from different assumptions about the star-forming properties of QSO hosts and redshift evolution of the SMBH-galaxy relationship. While limited currently by uncertainties, valuable constraints on AGN-galaxy co-evolution can emerge from our approach.

astro-ph.CO↗

arXiv2013

Hydrodynamical simulations of a compact source scenario for the Galactic Center cloud G2

The origin of the dense gas cloud G2 discovered in the Galactic Center (Gillessen et al. 2012) is still a debated puzzle. G2 might be a diffuse cloud or the result of an outflow from an invisible star embedded in it. We present hydrodynamical simulations of the evolution of different spherically symmetric winds of a stellar object embedded in G2. We find that the interaction with the ambient medium and with the extreme gravitational field of the supermassive black hole in the Galactic Center must be taken into account for such a source scenario. The thermal pressure of the hot and dense atmosphere confines the wind, while its ram pressure shapes it via stripping along the orbit, with the details depending on the wind parameters. Tidal forces squeeze the wind near pericenter, reducing it to a thin and elongated filament. We also find that in this scenario most of the Brγ luminosity is expected to come from the densest part of the wind, which has a highly filamentary structure with low filling factor. The observations can be best matched by a mass outflow rate of Mdot,w=8.8 x 10^{-8} Msun/yr and a wind velocity of vw = 50 km/s. These values are compatible with those of a young T Tauri star wind, as already suggested by (Scoville & Burkert 2013).

astro-ph.GA↗

arXiv2013

The Mid-infrared Emission of Narrow-Line Active Galactic Nuclei: Star-Formation, Nuclear Activity and two populations revealed by WISE

We explore the nature of the long-wavelength mid-infrared (MIR) emission of a sample of 13000 local Type II (narrow-line) Active Galactic Nuclei (AGNs) from the Sloan Digital Sky Survey (SDSS) using 12 and 22 micron photometry from the WISE all-sky survey. In combination with FIRST 1.4 GHz measurements, we show that AGNs divide into two relatively distinct populations or "branches" in the plane of MIR and radio luminosity. Seyfert galaxies lie almost exclusively on a MIR-bright branch (Branch A), while low-ionization nuclear emission line galaxies (LINERs) are split evenly into Branch A and the MIR-faint Branch B. We devise various tests to constrain the processes that define the branches, including a comparison to the properties of pure star-forming (SF) inactive galaxies on the MIR-Radio plane. We demonstrate that the total MIR emission of objects on Branch A, including most Seyfert galaxies, is governed primarily by host star-formation, with about 15% of the 22 micron luminosity coming from AGN-heated dust. This implies that on-going dusty star-formation is a general property of Seyfert host galaxies. We show that the 12 micron broad-band luminosity of AGNs on Branch A is suppressed with respect to star-forming galaxies, possibly due to the destruction of PAHs or deeper 10 microns Si absorption in AGNs. We uncover a correlation between the MIR luminosity and [O III] luminosity in AGNs. This suggests a relationship between the SFR and nuclear luminosity in the AGN population, but we caution on the importance of selection effects inherent to such AGN-dominated emission-line galaxies in driving such a correlation. We highlight the MIR-radio plane as a useful tool in comparative studies of SF and nuclear activity in AGN.

astro-ph.CO↗

arXiv2013

Fast Molecular Outflows in Luminous Galaxy Mergers: Evidence for Quasar Feedback from Herschel

We report the results from a systematic search for molecular (OH-119 um) outflows with Herschel-PACS in a sample of 43 nearby (z < 0.3) galaxy mergers, mostly ultraluminous infrared galaxies (ULIRGs) and QSOs. We find that the character of the OH feature (strength of the absorption relative to the emission) correlates with that of the 9.7-um silicate feature, a measure of obscuration in ULIRGs. Unambiguous evidence for molecular outflows, based on the detection of OH absorption profiles with median velocities more blueshifted than -50 km/sec, is seen in 26 (70%) of the 37 OH-detected targets, suggesting a wide-angle (~145 degrees) outflow geometry. Conversely, unambiguous evidence for molecular inflows, based on the detection of OH absorption profiles with median velocities more redshifted than +50 km/sec, is seen in only 4 objects, suggesting a planar or filamentary geometry for the inflowing gas. Terminal outflow velocities of ~-1000 km/sec are measured in several objects, but median outflow velocities are typically ~-200 km s^{-1}. While the outflow velocities show no statistically significant dependence on the star formation rate, they are distinctly more blueshifted among systems with large AGN fractions and luminosities [log (L_AGN / L_sun) > 11.8 +/- 0.3]. The quasars in these systems play a dominant role in driving the molecular outflows. In contrast, the most AGN dominated systems, where OH is seen purely in emission, show relatively modest OH line widths, despite their large AGN luminosities, perhaps indicating that molecular outflows subside once the quasar has cleared a path through the obscuring material.

astro-ph.CO↗