Feedback In Galaxy Evolution Research Articles

Galactic 26Al traces metal loss through hot chimneys

ABSTRACT Radioactive 26Al is an excellent tracer for metal ejection in the Milky Way, and can provide a direct constraint on the modelling of supernova feedback in galaxy evolution. Gamma-ray observations of the 26Al decay line have found high velocities and hence require a significant fraction of the Galactic 26Al in the hot component. At the same time, meteoritic data combined with simulation results suggest that a significant amount of 26Al makes its way into stars before decay. We investigated the distribution into hot and cold channels with a simulation of a Milky-Way-like galaxy with massive-star feedback in superbubbles and with ejecta traced by 26Al. About 30–40 per cent of the ejecta remain hot, with typical cooling times of the order Gyr. 26Al traces the footpoints of a chimney-fed outflow that mixes metals turbulently into the halo of the model galaxy on a scale of at least 50 kpc. The rest diffuses into cold gas ≲ 104 K, and may therefore be quickly available for star formation. We discuss the robustness of the result by comparison to a simulation with a different global flow pattern. The branching ratio into hot and cold components is comparable to that of longer term average results from chemical evolution modelling of galaxies, clusters, and the intracluster medium.

Do AGN triggering mechanisms vary with radio power? – I. Optical morphologies of radio-intermediate HERGs

ABSTRACT Active galactic nuclei (AGNs) with intermediate radio powers are capable of driving multiphase outflows in galaxy bulges, and are also more common than their high-radio-power counterparts. In-depth characterization of the typical host galaxies and likely triggering mechanisms for this population is therefore required in order to better understand the role of radio AGN feedback in galaxy evolution. Here, we use deep optical imaging data to study the detailed host morphologies of a complete sample of 30 local radio AGNs with high-excitation optical emission (HERG) spectra and intermediate radio powers [ z < 0.1; 22.5 < log($L_{\rm 1.4GHz}$) < 24.0 W Hz-1]. The fraction of hosts with morphological signatures of mergers and interactions is greatly reduced compared to the 2Jy radio-powerful galaxies [log($L_{\rm 1.4GHz}$) > 25.0 W Hz-1] with strong optical emission lines: 53 ± 9 per cent compared with 94 ± 4 per cent. In addition, the most radio-powerful half of the sample has a higher frequency of morphological disturbance than the least radio-powerful half (67 ± 12 per cent and 40 ± 13 per cent, respectively), including the eight most highly disturbed galaxies. This suggests that the importance of triggering nuclear activity in high-excitation radio galaxies (HERGs) through mergers and interactions reduces with radio power. Both visual inspection and detailed light profile modelling reveal a mixed population of early-type and late-type morphologies, contrary to the massive elliptical galaxy hosts of radio-powerful AGNs. The prevalence of late-type hosts could suggest that triggering via secular, disc-based processes has increased importance for HERGs with lower radio powers (e.g. disc instabilities and large-scale bars).

No evidence for quenching in quasars

AbstractThe role of quasar feedback in galaxy evolution remains poorly understood. Throughout this work, we explore the effects of negative feedback on star formation in quasar host galaxies, analysing two distinct populations of quasars. The first is a sample of high-redshift (z > 2) low-ionisation broad absorption line quasars (LoBALs) - a class of quasars hosting energetic mass outflows, in which we find evidence for prolific star formation (>750Mʘyr–1) exceeding that of non-BAL quasars at the same redshift. The second is a population of 207 low-redshift (z < 0.3) quasars, in which we find an enhancement in the SFRs of quasar hosts compared to the underlying galaxy population, with no quasars residing in quiescent hosts over the last 2Gyr. Overall, we find no evidence for galaxy-wide quenching in either population, rather we suggest that the dominant effect of quasar activity is to enhance star formation in the galaxy.

Feedback and Feeding in the Context of Galaxy Evolution withSPICA: Direct Characterisation of Molecular Outflows and Inflows

AbstractA far-infrared observatory such as theSPace Infrared telescope for Cosmology and Astrophysics, with its unprecedented spectroscopic sensitivity, would unveil the role of feedback in galaxy evolution during the last ~10 Gyr of the Universe (z= 1.5–2), through the use of far- and mid-infrared molecular and ionic fine structure lines that trace outflowing and infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni line shapes and absorption blueshifted wings in molecular lines with high dipolar moments, and through emission line wings of fine-structure lines of ionised gas. We quantify the detectability of galaxy-scale massive molecular and ionised outflows as a function of redshift in AGN-dominated, starburst-dominated, and main-sequence galaxies, explore the detectability of metal-rich inflows in the local Universe, and describe the most significant synergies with other current and future observatories that will measure feedback in galaxies via complementary tracers at other wavelengths.

Galaxies that shine: radiation-hydrodynamical simulations of disc galaxies

Radiation feedback is typically implemented using subgrid recipes in hydrodynamical simulations of galaxies. Very little work has so far been performed using radiation-hydrodynamics (RHD), and there is no consensus on the importance of radiation feedback in galaxy evolution. We present RHD simulations of isolated galaxy disks of different masses with a resolution of 18 pc. Besides accounting for supernova feedback, our simulations are the first galaxy-scale simulations to include RHD treatments of photo-ionisation heating and radiation pressure, from both direct optical/UV radiation and multi-scattered, re-processed infrared (IR) radiation. Photo-heating smooths and thickens the disks and suppresses star formation about as much as the inclusion of ("thermal dump") supernova feedback does. These effects decrease with galaxy mass and are mainly due to the prevention of the formation of dense clouds, as opposed to their destruction. Radiation pressure, whether from direct or IR radiation, has little effect, but for the IR radiation we show that its impact is limited by our inability to resolve the high optical depths for which multi-scattering becomes important. While artificially boosting the IR optical depths does reduce the star formation, it does so by smoothing the gas rather than by generating stronger outflows. We conclude that although higher-resolution simulations, and potentially also different supernova implementations, are needed for confirmation, our findings suggest that radiation feedback is more gentle and less effective than is often assumed in subgrid prescriptions.

Radio-AGN feedback: when the little ones were monsters

We present a study of the evolution of the fraction of radio-loud active galactic nuclei (AGN) as a function of their host stellar mass. We make use of two samples of radio galaxies: one in the local universe, $0.01 < z < 0.3$, using a combined SDSS-NVSS sample and one at higher redshifts, $0.5 < z < 2$, constructed from the VLA-COSMOS_DEEP Radio Survey at 1.4 GHz and a K$_s$-selected catalogue of the COSMOS/UltraVISTA field. We observe an increase of more than an order of magnitude in the fraction of lower mass galaxies ($M_* < 10^{10.75}$ M$_{\odot}$) which host Radio-Loud AGN with radio powers $P_{1.4GHz} > 10^{24}$ W/Hz at z ~ 1-2 while the radio-loud fraction for higher mass galaxies ($M_* > 10^{11.25}$ M$_{\odot}$) remains the same. We argue that this increase is driven largely by the increase in cold or radiative mode accretion with increasing cold gas supply at earlier epochs. The increasing population of low mass Radio-Loud AGN can thus explain the upturn in the Radio Luminosity Function (RLF) at high redshift which is important for understanding the impact of AGN feedback in galaxy evolution.

FeLoBAL Outflow Variability Constraints from Multi-Year Observations

AbstractThe physical properties and dynamical behavior of Broad Absorption Line (BAL) outflows are crucial themes in understanding the connections between galactic centers and their hosts. FeLoBALs (identified with the presence of low-ionization Fe II BALs) are a peculiar class of quasar outflows that constitute ~ 1% of the BAL population. With their large column densities and apparent outflow kinetic luminosities, FeLoBALs appear to be exceptionally powerful and are strong candidates for feedback in galaxy evolution. We conducted variability studies of 12 FeLoBAL quasars with emission redshifts 0.69 ≤ z ≤ 1.93, spanning both weekly and multi-year timescales in the quasar's rest frame. We detected absorption-line variability from low-ionization species (Fe II, Mg II) in four of our objects, with which we established a representative upper limit for the distance of the absorber from the supermassive black hole (SMBH) to be ~20 parsecs. Our goals are to understand the mechanisms producing the variability (e.g. ionization changes or gas traversing our line of sight) and place new constraints on the locations, structure, and kinetic energies of the outflows.

Large-scale environments ofz &lt; 0.4 active galaxies

Properties of galaxies depend on their large-scale environment. As the influence of active galactic nuclei (AGN) in galaxy evolution is becoming more evident, their large scale environments may help us understand the evolutionary processes leading to activity. The effect of activity can be seen particularly by showing if different types of active galaxies are formed by similar mechanisms. Our aim is to study the supercluster-scale environments of active galaxies up to redshift 0.4. Our data includes quasars, BL Lac objects, Seyfert and radio galaxies. We use a three-dimensional low-resolution luminosity-density field constructed of a sample of luminous red galaxies in the seventh data release of the Sloan Digital Sky Survey. We calculate the average density of this field in a volume of a 3\,$h^{-1}$Mpc sphere around each AGN for estimating the environmental density levels of different types of AGN. This analysis gives us the distribution of AGN in the global environment of superclusters, filaments, and voids. Our results show that while radio-quiet quasars and Seyfert galaxies are mostly located in low-density regions, radio galaxies have higher environmental densities. BL Lac objects usually have low-density environments, but some of them are also in very high density regions. Our results give support to the theory of galaxy evolution where galaxies are affected by two modes of AGN feedback: quasar mode that turns a blue star-forming galaxy into a red and dead one, and radio mode that regulates the growth of massive elliptical galaxies. We conclude that quasars are in lower density environments than radio galaxies most likely because the galaxies in rich environments have evolved to a state suitable for radio-loud activity earlier. Galaxies in poor environment have evolved slower, and are still going through the earlier quasar mode feedback in galaxy evolution.

Massive galaxies with very young AGN

AbstractGigahertz Peaked Spectrum (GPS) radio galaxies are generally thought to be the young counterparts of classical extended radio sources and live in massive ellipticals. GPS sources are vital for studying the early evolution of radio-loud AGN, the trigger of their nuclear activity, and the importance of feedback in galaxy evolution. We study the Parkes half-Jansky sample of GPS radio galaxies of which now all host galaxies have been identified and 80% has their redshifts determined (0.122 &lt; z &lt; 1.539). Analysis of the absolute magnitudes of the GPS host galaxies show that at z &gt; 1 they are on average a magnitude fainter than classical 3C radio galaxies. This suggests that the AGN in young radio galaxies have not yet much influenced the overall properties of the host galaxy. However their restframe UV luminosities indicate that there is a low level of excess as compared to passive evolution models.