An Integral Field Study of Abundance Gradients in Nearby LIRGs

We present for the first time metallicity maps generated using data from the Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies (LIRGs) and discuss the abundance gradients and distribution of metals in these systems. We have carried out optical integral field spectroscopy (IFS) of several several LIRGs in various merger phases to investigate the merger process. In a major merger of two spiral galaxies with preexisting disk abundance gradients, the changing distribution of metals can be used as a tracer of gas flows in the merging system as low metallicity gas is transported from the outskirts of each galaxy to their nuclei. We employ this fact to probe merger properties by using the emission lines in our IFS data to calculate the gas-phase metallicity in each system. We create abundance maps and subsequently derive a metallicity gradient from each map. We compare our measured gradients to merger stage as well as several possible tracers of merger progress and observed nuclear abundances. We discuss our work in the context of previous abundance gradient observations and compare our results to new galaxy merger models which trace metallicity gradient. Our results agree with the observed flattening of metallicity gradients as a merger progresses. We compare our results with new theoretical predictions that include chemical enrichment. Our data show remarkable agreement with these simulations.Comment: Accepted for publication in ApJ. 26 pages, 18 figure

IC5063: AGN driven outflow of warm and cold gas

We present new ATCA 17- and 24-GHz radio images and ESO-NTT optical spectra of the radio-loud Seyfert galaxy IC5063, the first galaxy in which a fast (~ 600 km/s) outflow of neutral hydrogen was discovered. The new radio data confirm the triple radio structure with a central core and two resolved radio lobes. This implies that the previously detected fast outflow of neutral gas is occurring off-nucleus, near a radio lobe about 0.5 kpc from the core. The ionised gas shows complex kinematics in the region co-spatial with the radio emission. Broad and blueshifted (~ 500 km/s) emission is observed in the region of the radio lobe, at the same location as the blueshifted HI absorption. The velocity of the ionised outflow is similar to the one found in HI. The first order correspondence between the radio and optical properties suggests that the outflow is driven by the interaction between the radio jet and the ISM. Despite the high outflow velocities, no evidence is found for the ionisation of the gas being due to fast shocks in the region of the outflow, indicating that photoionisation from the AGN is likely to be the dominant ionisation mechanism. The outflow rate of the warm (ionised) gas is small compared to that of the cold gas. The mass outflow rate associated with the HI is in the same range as for ``mild'' starburst-driven superwinds in ULIRGs. However, in IC5063, the AGN-driven outflow appears to be limited to the inner kpc region of the galaxy. The kinetic power associated with the HI outflow is a small fraction (a few x 10^-4) of the Eddington luminosity of the galaxy but is a significant fraction (~ 0.1) of the nuclear bolometric luminosity. In IC5063, the outflows may have sufficient kinetic power to have a significant impact on the evolution of the ISM in the host galaxy.Comment: Accepted for publication in A&A, 11 pages, 8 figure

Galaxy-Wide Shocks in Late-Merger Stage Luminous Infrared Galaxies

We present an integral field spectroscopic study of two nearby Luminous Infrared Galaxies (LIRGs) that exhibit evidence of widespread shock excitation induced by ongoing merger activity, IC 1623 and NGC 3256. We show the importance of carefully separating excitation due to shocks vs. excitation by HII regions and the usefulness of IFU data in interpreting the complex processes in LIRGs. Our analysis focuses primarily on the emission line gas which is extensive in both systems and is a result of the abundant ongoing star formation as well as widespread LINER-like excitation from shocks. We use emission-line ratio maps, line kinematics, line-ratio diagnostics and new models as methods for distinguishing and analyzing shocked gas in these systems. We discuss how our results inform the merger sequence associated with local U/LIRGs and the impact that widespread shock excitation has on the interpretation of emission-line spectra and derived quantities of both local and high-redshift galaxies.Comment: 14 pages, 11 figures, Accepted to Ap

Quasar Feedback in the Ultraluminous Infrared Galaxy F11119+3257: Connecting the Accretion Disk Wind with the Large-Scale Molecular Outflow

In Tombesi et al. (2015), we reported the first direct evidence for a quasar accretion disk wind driving a massive molecular outflow. The target was F11119+3257, an ultraluminous infrared galaxy (ULIRG) with unambiguous type-1 quasar optical broad emission lines. The energetics of the accretion disk wind and molecular outflow were found to be consistent with the predictions of quasar feedback models where the molecular outflow is driven by a hot energy-conserving bubble inflated by the inner quasar accretion disk wind. However, this conclusion was uncertain because the energetics were estimated from the optically thick OH 119 um transition profile observed with Herschel. Here, we independently confirm the presence of the molecular outflow in F11119+3257, based on the detection of broad wings in the CO(1-0) profile derived from ALMA observations. The broad CO(1-0) line emission appears to be spatially extended on a scale of at least ~7 kpc from the center. Mass outflow rate, momentum flux, and mechanical power of (80-200) R_7^{-1} M_sun/yr, (1.5-3.0) R_7^{-1} L_AGN/c, and (0.15-0.40)% R_7^{-1} L_AGN are inferred from these data, assuming a CO-to-H_2 conversion factor appropriate for a ULIRG (R_7 is the radius of the outflow normalized to 7 kpc and L_AGN is the AGN luminosity). These rates are time-averaged over a flow time scale of 7x10^6 yrs. They are similar to the OH-based rates time-averaged over a flow time scale of 4x10^5 yrs, but about a factor 4 smaller than the local ("instantaneous"; <10^5 yrs) OH-based estimates cited in Tombesi et al. The implications of these new results are discussed in the context of time-variable quasar-mode feedback and galaxy evolution. The need for an energy-conserving bubble to explain the molecular outflow is also re-examined.Comment: 15 pages, 6 figures, 4 tables, accepted for publication in Ap

Outflows in Infrared-Luminous Starbursts at z < 0.5. I. Sample, NaI D Spectra, and Profile Fitting

We have conducted a spectroscopic survey of 78 starbursting infrared-luminous galaxies at redshifts up to z = 0.5. We use moderate-resolution spectroscopy of the NaI D interstellar absorption feature to directly probe the neutral phase of outflowing gas in these galaxies. Over half of our sample are ultraluminous infrared galaxies that are classified as starbursts; the rest have infrared luminosities in the range log(L_IR/L_sun) = 10.2 - 12.0. The sample selection, observations, and data reduction are described here. The absorption-line spectra of each galaxy are presented. We also discuss the theory behind absorption-line fitting in the case of a partially-covered, blended absorption doublet observed at moderate-to-high resolution, a topic neglected in the literature. A detailed analysis of these data is presented in a companion paper.Comment: 59 pages, 18 figures in AASTeX preprint style; to appear in September issue of ApJ

Metallicity gradients in local field star-forming galaxies: Insights on inflows, outflows, and the coevolution of gas, stars and metals

We present metallicity gradients in 49 local field star-forming galaxies. We derive gas-phase oxygen abundances using two widely adopted metallicity calibrations based on the [OIII]/Hbeta, [NII]/Halpha and [NII]/[OII] line ratios. The two derived metallicity gradients are usually in good agreement within +/-0.14 dex/R25 (R25 is the B-band iso-photoal radius), but the metallicity gradients can differ significantly when the ionisation parameters change systematically with radius. We investigate the metallicity gradients as a function of stellar mass (8<log(M*/Msun)<11) and absolute B-band luminosity (-16 > MB > -22). When the metallicity gradients are expressed in dex/kpc, we show that galaxies with lower mass and luminosity, on average, have steeper metallicity gradients. When the metallicity gradients are expressed in dex/R25, we find no correlation between the metallicity gradients, and stellar mass and luminosity. We provide a local benchmark metallicity gradient of field star-forming galaxies useful for comparison with studies at high redshifts. We investigate the origin of the local benchmark gradient using simple chemical evolution models and observed gas and stellar surface density profiles in nearby field spiral galaxies. Our models suggest that the local benchmark gradient is a direct result of the coevolution of gas and stellar disk under virtually closed-box chemical evolution when the stellar-to-gas mass ratio becomes high (>>0.3). These models imply low current mass accretion rates (<0.3xSFR), and low mass outflow rates (<3xSFR) in local field star-forming galaxies.Comment: 25 pages, 21 figures, accepted to MNRA

Spitzer Quasar and ULIRG Evolution Study (QUEST). IV. Comparison of 1-Jy Ultraluminous Infrared Galaxies with Palomar-Green Quasars

We report the results from a comprehensive study of 74 ultraluminous infrared galaxies (ULIRGs) and 34 Palomar-Green (PG) quasars within z ~ 0.3$ observed with the Spitzer Infrared Spectrograph (IRS). The contribution of nuclear activity to the bolometric luminosity in these systems is quantified using six independent methods that span a range in wavelength and give consistent results within ~ +/-10-15% on average. The average derived AGN contribution in ULIRGs is ~35-40%, ranging from ~15-35% among "cool" (f_25/f_60 =< 0.2) optically classified HII-like and LINER ULIRGs to ~50 and ~75% among warm Seyfert 2 and Seyfert 1 ULIRGs, respectively. This number exceeds ~80% in PG QSOs. ULIRGs fall in one of three distinct AGN classes: (1) objects with small extinctions and large PAH equivalent widths are highly starburst-dominated; (2) systems with large extinctions and modest PAH equivalent widths have larger AGN contributions, but still tend to be starburst-dominated; and (3) ULIRGs with both small extinctions and small PAH equivalent widths host AGN that are at least as powerful as the starbursts. The AGN contributions in class 2 ULIRGs are more uncertain than in the other objects, and we cannot formally rule out the possibility that these objects represent a physically distinct type of ULIRGs. A morphological trend is seen along the sequence (1)-(2)-(3), in general agreement with the standard ULIRG - QSO evolution scenario and suggestive of a broad peak in extinction during the intermediate stages of merger evolution. However, the scatter in this sequence, implies that black hole accretion, in addition to depending on the merger phase, also has a strong chaotic/random component, as in local AGN. (abridged)Comment: 61 pages, 39 figures, 16 tables, accepted for publication in ApJS, June 2009 issue. Unabbreviated version can be found at http://www.astro.umd.edu/~veilleux/pubs/quest4.pd

3D Integral Field Observations of Ten Galactic Winds - I. Extended phase (>10 Myr) of mass/energy injection before the wind blows

We present 3D spectroscopic observations of a sample of 10 nearby galaxies with the AAOmega-SPIRAL integral field spectrograph on the 3.9m AAT, the largest survey of its kind to date. The double-beam spectrograph provides spatial maps in a range of spectral diagnostics: [OIII] 5007, H-beta, Mg-b, NaD, [OI] 6300, H-alpha, [NII] 6583, [SII] 6717, 6731. All of the objects in our survey show extensive wind-driven filamentation along the minor axis, in addition to large-scale disk rotation. Our sample can be divided into either starburst galaxies or active galactic nuclei (AGN), although some objects appear to be a combination of these. The total ionizing photon budget available to both classes of galaxies is sufficient to ionise all of the wind-blown filamentation out to large radius. We find however that while AGN photoionisation always dominates in the wind filaments, this is not the case in starburst galaxies where shock ionisation dominates. This clearly indicates that after the onset of star formation, there is a substantial delay (> 10 Myr) before a starburst wind develops. We show why this behavior is expected by deriving ``ionisation'' and dynamical timescales for both AGNs and starbursts. We establish a sequence of events that lead to the onset of a galactic wind. The clear signature provided by the ionisation timescale is arguably the strongest evidence yet that the starburst phenomenon is an impulsive event. A well-defined ionisation timescale is not expected in galaxies with a protracted history of circumnuclear star formation. Our 3D data provide important templates for comparisons with high redshift galaxies.[Abridged]Comment: 43 pages, 30 figures, Accepted for publication in ApJ Jan-2010, Full resolution figures available from: http://www.aao.gov.au/AAO/local/www/rgs/work/winds/public/papers/SPIRAL_WINDS_hi-res.htm

Gas-Phase Oxygen Gradients in Strongly Interacting Galaxies: I. Early-Stage Interactions

A consensus is emerging that interacting galaxies show depressed nuclear gas metallicities compared to isolated star-forming galaxies. Simulations suggest that this nuclear underabundance is caused by interaction-induced inflow of metal-poor gas, and that this inflow concurrently flattens the radial metallicity gradients in strongly interacting galaxies. We present metallicities of over 300 HII regions in a sample of 16 spirals that are members of strongly interacting galaxy pairs with mass ratio near unity. The deprojected radial gradients in these galaxies are about half of those in a control sample of isolated, late-type spirals. Detailed comparison of the gradients with simulations show remarkable agreement in gradient distributions, the relationship between gradients and nuclear underabundances, and the shape of profile deviations from a straight line. Taken together, this evidence conclusively demonstrates that strongly interacting galaxies at the present day undergo nuclear metal dilution due to gas inflow, as well as significant flattening of their gas-phase metallicity gradients, and that current simulations can robustly reproduce this behavior at a statistical level.Comment: Accepted for publication in Ap

Exploring the Dust Content of Galactic Winds with Herschel. I. NGC 4631

We present a detailed analysis of deep far-infrared observations of the nearby edge-on star-forming galaxy NGC 4631 obtained with the Herschel Space Observatory. Our PACS images at 70 and 160 um show a rich complex of filaments and chimney-like features that extends up to a projected distance of 6 kpc above the plane of the galaxy. The PACS features often match extraplanar Halpha, radio-continuum, and soft X-ray features observed in this galaxy, pointing to a tight disk-halo connection regulated by star formation. On the other hand, the morphology of the colder dust component detected on larger scale in the SPIRE 250, 350, and 500 um data matches the extraplanar H~I streams previously reported in NGC 4631 and suggests a tidal origin. The PACS 70/160 ratios are elevated in the central ~3.0 kpc region above the nucleus of this galaxy (the "superbubble"). A pixel-by-pixel analysis shows that dust in this region has a higher temperature and/or an emissivity with a steeper spectral index (beta > 2) than the dust in the disk, possibly the result of the harsher environment in the superbubble. Star formation in the disk seems energetically insufficient to lift the material out of the disk, unless it was more active in the past or the dust-to-gas ratio in the superbubble region is higher than the Galactic value. Some of the dust in the halo may also have been tidally stripped from nearby companions or lifted from the disk by galaxy interactions.Comment: Accepted for publication in The Astrophysical Journa