arXiv subjects

Sylvain Veilleux

Publications and source records attributed to Sylvain Veilleux.

At least 181 records · Page 10Linked to original sources

arXiv2007

Uncovering the Active Galactic Nuclei in Low-Ionization Nuclear Emission-Line Regions with Spitzer

The impact of active galactic nuclei on low-ionization nuclear emission-line regions (LINERs) remains a vigorous field of study. We present preliminary results from a study of the mid-infrared atomic emission lines of LINERs with the Spitzer Space Telescope. We assess the ubiquity and properties of AGN in LINERs using this data. We discuss what powers the mid-infrared emission lines and conclude that the answer depends unsurprisingly on the emission line ionization state and, more interestingly, on the infrared luminosity.

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arXiv2007

The Oxygen Abundances of Luminous and Ultraluminous Infrared Galaxies

Luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) dominate the star formation rate budget of the universe at z > 1, yet no local measurements of their heavy element abundances exist. We measure nuclear or near-nuclear oxygen abundances in a sample of 100 star-forming LIRGs and ULIRGs using new, previously published, and archival spectroscopy of strong emission lines (including [O II] 3727, 3729 A) in galaxies with redshifts ~ 0.1. When compared to local emission-line galaxies of similar luminosity and mass (using the near-infrared luminosity-metallicity and mass-metallicity relations), we find that LIRGs and ULIRGs are under-abundant by a factor of two on average. As a corollary, LIRGs and ULIRGs also have smaller effective yields. We conclude that the observed under-abundance results from the combination of a decrease of abundance with increasing radius in the progenitor galaxies and strong, interaction- or merger-induced gas inflow into the galaxy nucleus. This conclusion demonstrates that local abundance scaling relations are not universal, a fact that must be accounted for when interpreting abundances earlier in the universe's history when merger-induced star formation was the dominant mode. We use our local sample to compare to high-redshift samples and assess abundance evolution in LIRGs and ULIRGs. We find that abundances in these systems increased by ~0.2 dex from z ~ 0.6 to z ~ 0.1. Evolution from z ~ 2 submillimeter galaxies to z ~ 0.1 ULIRGs also appears to be present, though uncertainty due to spectroscopic limitations is large.

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arXiv2007

Tracing PAHs and Warm Dust Emission in the Seyfert Galaxy NGC 1068

We present a study of the nearby Seyfert galaxy NGC 1068 using mid- and far- infrared data acquired with the IRAC, IRS, and MIPS instruments aboard the Spitzer Space Telescope. The images show extensive 8 um and 24 um emission coinciding with star formation in the inner spiral approximately 15" (1 kpc) from the nucleus, and a bright complex of star formation 47" (3 kpc) SW of the nucleus. The brightest 8 um PAH emission regions coincide remarkably well with knots observed in an Halpha image. Strong PAH features at 6.2, 7.7, 8.6, and 11.3 um are detected in IRS spectra measured at numerous locations inside, within, and outside the inner spiral. The IRAC colors and IRS spectra of these regions rule out dust heated by the AGN as the primary emission source; the SEDs are dominated by starlight and PAH emission. The equivalent widths and flux ratios of the PAH features in the inner spiral are generally consistent with conditions in a typical spiral galaxy ISM. Interior to the inner spiral, the influence of the AGN on the ISM is evident via PAH flux ratios indicative of a higher ionization parameter and a significantly smaller mean equivalent width than observed in the inner spiral. The brightest 8 and 24 um emission peaks in the disk of the galaxy, even at distances beyond the inner spiral, are located within the ionization cones traced by [O III]/Hbeta, and they are also remarkably well aligned with the axis of the radio jets. Although it is possible that radiation from the AGN may directly enhance PAH excitation or trigger the formation of OB stars that subsequently excite PAH emission at these locations in the inner spiral, the orientation of collimated radiation from the AGN and star formation knots in the inner spiral could be coincidental. (abridged)

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arXiv2007

Spitzer Quasar and ULIRG Evolution Study (QUEST): II. The Spectral Energy Distributions of Palomar-Green Quasars

This is the second paper studying the QSOs in the spitzer QUEST sample. Previously we presented new PAH measurements and argued that most of the observed far infrared (FIR) radiation is due to star-forming activity. Here we present spectral energy distributions (SEDs) by supplementing our data with optical, NIR and FIR observations. We define two sub-groups of ``weak FIR'' and ``strong FIR'' QSOs, and a third group of FIR non-detections. Assuming a starburst origin for the FIR, we obtain ``intrinsic'' AGN SEDs by subtracting a starburst template from the mean SEDs. The resulting SEDs are remarkably similar for all groups. They show three distinct peaks corresponding to two silicate emission features and a 3mic bump that we interpret as the signature of the hottest AGN dust. They also display drops beyond 20mic that we interpret as the signature of the minimum temperature (about 200K) dust. This component must be optically thin to explain the silicate emission and the slope of the long wavelength continuum. We discuss the merits of an alternative model where most of the FIR emission is due to AGN heating. Such models are unlikely to explain the properties of our QSOs but they cannot be ruled out for more luminous objects. We also find correlations between the luminosity at 5100A and two infrared starburst indicators: L(60mic) and L(PAH 7.7mic). The correlation of L(5100A) with L(60mic) can be used to measure the relative growth rates and lifetimes of the black hole and the new stars.

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arXiv2006

Local Ultraluminous Infrared Galaxies and Quasars

This paper reviews the recent results from a comprehensive investigation of the most luminous mergers in the local universe, the ultraluminous infrared galaxies (ULIRGs) and the quasars. First, the frequency of occurrence and importance of black hole driven nuclear activity in ULIRGs are discussed using the latest sets of optical, near-infrared, mid-infrared, and X-ray spectra on these objects. Obvious trends with luminosity, infrared color, and morphology are pointed out. Next, the host galaxy properties of ULIRGs are described in detail and then compared with local quasar hosts and inactive spheroids. By and large, these data are consistent with the scenario where ULIRGs are intermediate-mass elliptical galaxies in formation and in the process of becoming moderate-luminosity optical quasars. The powerful galactic winds detected in many ULIRGs may help shed any excess gas during this transformation. However, this evolutionary scenario does not seem to apply to all ULIRGs and quasars: Ultraluminous infrared mergers do not always result in a quasar, and low-luminosity quasars near the boundary with Seyferts do not all show signs of a recent major merger.

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arXiv2005

Keck High-Resolution Spectroscopy of Outflows in Infrared Luminous Galaxies

Several recent studies have determined that large quantities of neutral gas are outflowing from the nuclei of almost all infrared-luminous galaxies. These measurements show that winds in infrared-luminous galaxies play a significant role in the evolution of galaxies and the intergalactic medium at redshifts z > 1, when infrared-luminous galaxies dominated the star formation rate of the universe. These conclusions rely on moderate resolution spectra (FWHM > 65 km/s) of the NaI D absorption line and the assumption that there are no unresolved, saturated velocity components. For the first time, we present high resolution spectra (FWHM = 13 km/s) of massive, infrared-luminous galaxies. The five galaxies in our sample are known to host outflows on the basis of previous observations. With the present observations, all NaI D velocity components are resolved with tau(NaI D1 5896 A) < 6. The column densities we measure are consistent within the errors with those measured from moderate-resolution observations. This confirms that the mass, momentum, and energy of outflowing gas in infrared-luminous galaxies have been measured correctly by previous studies.

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arXiv2005

Outflows in Infrared-Luminous Starbursts at z < 0.5. II. Analysis and Discussion

We have performed an absorption-line survey of outflowing gas in 78 starburst-dominated, infrared-luminous galaxies. This is the largest study of superwinds at z < 3. Superwinds are found in almost all infrared-luminous galaxies, and changes in detection rate with SFR--winds are found twice as often in ultraluminous infrared galaxies (ULIRGs) as in less-luminous galaxies--reflect different wind geometries. The maximum velocities we measure are 600 km/s, though most of the outflowing gas has lower velocities (100-200 km/s). (One galaxy has velocities exceeding 1000 km/s.) Velocities in LINERs are higher than in HII galaxies, and outflowing ionized gas often has higher velocities than the neutral gas. Wind properties (velocity, mass, momentum, and energy) scale with galaxy properties (SFR, luminosity, and galaxy mass), consistent with ram-pressure driving of the wind. Wind properties increase strongly with increasing galactic mass, contrary to expectation. These correlations flatten at high SFR (> 10-100 M_sun/yr), luminosities, and masses. This saturation is due to a lack of gas remaining in the wind's path, a common neutral gas terminal velocity, and/or a decrease in the efficiency of thermalization of the supernovae energy. It means that mass entrainment efficiency, rather than remaining constant, declines in galaxies with SFR > 10 M_sun/yr and M_K < -24. Half of our sample consists of ULIRGs, which host as much as half of the star formation in the universe at z > 1. The powerful, ubiquitous winds we observe in these galaxies imply that superwinds in massive galaxies at redshifts above unity play an important role in the evolution of galaxies and the intergalactic medium.

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arXiv2005

Outflows in AGN/Starburst-Composite Ultraluminous Infrared Galaxies

Galactic superwinds occur in almost all infrared-luminous galaxies with star formation rates (SFRs) above 10 M_sun/yr, as shown by studies of the NaI D interstellar absorption line. We demonstrate that this result also applies to ultraluminous infrared galaxies (ULIRGs) which host an active galactic nucleus (AGN) embedded in a strong starburst (SFR > 100 M_sun/yr) by studying a sample of 26 Seyfert ULIRGs in NaI D. The infrared luminosity of these galaxies is powered jointly by the AGN and starburst. We find that there are hints of the influence of the AGN on outflows in Seyfert 2/starburst composites, but the evidence is not yet statistically conclusive. The evidence we find is lower wind detection rates (i.e., wind opening angles) in Seyfert 2 ULIRGs than in galaxies of comparable L_IR, higher velocities than in galaxies of comparable SFR, and correlations between the neutral gas and the ionized gas in the extended narrow-line region. Though the AGN probably contributes to the outflows in Seyfert 2 ULIRGs, its momentum and energy injection is equal to or less than that of the starburst. Similarly, the outflow mechanical luminosity (energy outflow rate) per unit radiative luminosity is the same for starburst and Seyfert 2 ULIRGs. In the nuclei of Seyfert 1s, we observe small-scale outflows that are powered solely by the AGN. However, in Mrk~231, we observe both a high-velocity, small-scale and low-velocity, extended outflow. The latter may be powered by a starburst or radio jet. These large-scale, lower-velocity outflows certainly exist in other Seyfert 1 ULIRGs, but they are washed out by the light of the nucleus.

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arXiv2005

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.

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arXiv2005

Extranuclear X-ray Emission in the Edge-on Seyfert Galaxy NGC 2992

We found several extranuclear (r >~ 3") X-ray nebulae within 40" (6.3 kpc at 32.5 Mpc) of the nucleus of the Seyfert galaxy NGC 2992. The net X-ray luminosity from the extranuclear sources is ~2-3 E39 erg/s (0.3-8.0 keV). The X-ray core itself (r <~ 1") is positioned at 9:45:41.95 -14:19:34.8 (J2000) and has a remarkably simple power-law spectrum with photon index Gamma=1.86 and Nh=7E21 /cm2. The near-nuclear (3" <~ r <~ 18") Chandra spectrum is best modelled by three components: (1) a direct AGN component with Gamma fixed at 1.86, (2) cold Compton reflection of the AGN component, and (3) a 0.5 keV low-abundance (Z < 0.03 Zsolar) "thermal plasma," with ~10% of the flux of either of the first two components. The X-ray luminosity of the 3rd component (the "soft excess") is ~1.4E40 erg/s, or ~5X that of all of the detected extranuclear X-ray sources. We suggest that most (~75-80%) of the soft excess emission originates from 1" < r < 3", which is not imaged in our observation due to severe CCD pile-up. We also require the cold reflector to be positioned at least 1" (158 pc) from the nucleus, since there is no reflection component in the X-ray core spectrum. Much of the extranuclear X-ray emission is coincident with radio structures (nuclear radio bubbles and large-scale radio features), and its soft X-ray luminosity is generally consistent with luminosities expected from a starburst-driven wind (with the starburst scaled from L_FIR). However, the AGN in NGC 2992 seems equally likely to power the galactic wind in that object. Furthermore, AGN photoionization and photoexcitation processes could dominate the soft excess, especially the \~75-80% which is not imaged by our observations.

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arXiv2003

Multiwavelength Observations of Galactic Winds: Near and Far

This paper provides a critical discussion of the observational evidence for winds in our own Galaxy, in nearby star-forming and active galaxies, and in the high-redshift universe. The implications of galactic winds on the formation and evolution of galaxies and the intergalactic medium are briefly discussed. A number of observational challenges are mentioned to inspire future research directions.

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arXiv2003

Galactic Winds: Near and Far

Multiwavelength data on star-forming galaxies provide strong evidence for large-scale galactic winds in both nearby and distant objects. The results from recent ground-based and space-borne programs are reviewed. The impact of these winds on the host galaxies and the surrounding environment is discussed in the context of galaxy evolution.

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arXiv2003

The AGN Content of Ultraluminous IR Galaxies: High Resolution VLA Imaging of the IRAS 1Jy ULIRG Sample

This paper presents the results of a high resolution radio imaging survey of 83 of the 118 ultraluminous infrared galaxies (ULIRGs) in the IRAS 1 Jy ULIRG sample. We have observed these ULIRGs at 15GHz with the Very Large Array (VLA). We find that ~75% of Seyferts (both type 1 and 2) and LINERs have radio nuclei which are compact at our 150mas resolution. The detection rate of HII nuclei is significantly lower (32%); the detections among these are preferentially HII + LINER/Seyfert composite nuclei. Among ULIRGs with multiple optical or near-IR nuclei our observations detected only one (or no) nucleus; in these the radio detection is typically towards the brightest near-IR nucleus. The compactness of the radio sources, the higher detection rates in AGN-type nuclei than HII nuclei, the preferential detection of nuclei with unresolved point sources in the near-IR, the low soft X-ray to nuclear radio luminosity ratio (arguing against thermal emission powering the radio nuclei), and the lack of correlation between radio power and Halpha luminosity, all support an origin of the detected radio nuclei in AGN related activity. This result is especially interesting for LINER ULIRGs for which signatures of AGNs have often been ambiguous in other wavebands. Such a high incidence of AGN would provide, for the first time, a large sample in which to study the interplay between AGN, starbursts, and galaxy mergers.

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arXiv2003

Extraplanar Emission-Line Gas in Edge-On Spiral Galaxies. I. Deep Emission-Line Imaging

The extraplanar diffuse ionized gas (eDIG) in 17 nearby, edge-on disk galaxies is studied using deep Taurus Tunable Filter Halpha and [N II] lambda 6583 images and conventional interference filter Halpha + [N II] lambda 6548, 6583 images which reach flux levels generally below about 1 x 10^{-17} erg s^{-1} cm^{-2} arcsec^{-2}. [N II] lambda 6583/Halpha excitation maps are available for 10 of these objects. All but one galaxy in the sample exhibit eDIG. The contribution of the eDIG to the total Halpha luminosity is relatively constant, of order 12 +/- 4%. The Halpha scale height of the eDIG derived from a two-exponential fit to the vertical emission profile ranges from 0.4 kpc to 17.9 kpc, with an average of 4.3 kpc. This average value is noticeably larger than the eDIG scale height measured in our Galaxy and other galaxies. This difference in scale height is probably due in part to the lower flux limits of our observations. A quantitative analysis of the topology of the eDIG confirms that several galaxies in the sample have a highly structured eDIG morphology. The distribution of the eDIG emission is often correlated with the locations of the H II regions in the disk. A strong correlation is found between the star formation rate (IR luminosity) per unit disk area and the extraplanar ionized mass, providing further support for a strong connection between the disk and eDIG components in these galaxies. The excitation maps confirm that the [N II]/Halpha ratios are systematically higher in the eDIG than in the disk. More detail is given in Paper II. (abridged)

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arXiv2003

Extraplanar Emission-Line Gas in Edge-On Spiral Galaxies. II. Optical Spectroscopy

The results from deep long-slit spectroscopy of nine edge-on spiral galaxies with known extraplanar line emission are reported. Emission from Halpha, [N II] lambda 6548, 6583, and [S II] lambda 6716, 6731 is detected out to heights of a few kpc in all of these galaxies. Several other fainter diagnostic lines such as [O I] lambda 6300, [O III] lambda 4959, 5007, and He I lambda 5876 are also detected over a smaller scale. The relative strengths, centroids and widths of the various emission lines provide constraints on the electron density, temperature, reddening, source(s) of ionization, and kinematics of the extraplanar gas. In all but one galaxy, photoionization by massive OB stars alone has difficulties explaining all of the line ratios in the extraplanar gas. Hybrid models that combine photoionization by OB stars and another source of ionization such as photoionization by turbulent mixing layers or shocks provide a better fit to the data. The (upper limits on the) velocity gradients measured in these galaxies are consistent with the predictions of the galactic fountain model to within the accuracy of the measurements.

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arXiv2002

The AGN Paradigm: Radio-Quiet Objects

The current paradigm for radio-quiet AGNs is reviewed, taking into account new results from recent large-scale surveys carried out from the ground and from space. Topics include structure of the central engine, AGN demography, fueling/triggering processes, and connection between the supermassive black hole, host galaxy, circumnuclear starburst and AGN. Dependences on AGN power and lookback time are pointed out in the discussion. Suggestions for future avenues of research are mentioned in the last section.

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arXiv2002

Fabry-Perot Survey of Emission-Line Galaxies

The recent results from a deep Fabry-Perot survey of nearby active and star-forming galaxies are presented. Line-emitting material is detected over two orders of magnitude in galactocentric radius, from the 100-pc scale of the active or starbursting nucleus out to several 10s of kpc, sometimes well beyond the optical confines of the host galaxies. The excitation and dynamical properties of the nuclear gas are studied to constrain the impact of galactic winds on the host galaxies and their environment. The properties of the warm ionized material on the outskirts of galaxies provide important clues for understanding galaxy formation and evolution. A new technique to search for starburst-driven wind galaxy candidates is discussed. The next generation of Fabry-Perot instruments on large telescopes promises to improve the sensitivity of emission-line galaxy surveys at least tenfold.

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arXiv2002

Keck Absorption-Line Spectroscopy of Galactic Winds in Ultraluminous Infrared Galaxies

In this paper, we present moderately-high resolution (~65 km/s) spectroscopy, acquired with ESI on Keck II, of 11 ultraluminous infrared galaxies at z < 0.3 from the IRAS 1 Jy sample. The targets were chosen as good candidates to host galaxy-scale outflows, and most have infrared luminosities dominated by star formation. We use a chi-squared minimization to fit one- to three-component profiles to the NaI D interstellar absorption doublet in each object. Assuming that gas blueshifted by more than 70 km/s relative to the systemic velocity of the host is outflowing, we detect outflows in 73% of these objects. We adopt a simple model of a mass-conserving free wind to infer mass outflow rates in the range (dM/dt)_tot(H) = 13-133 M_sun/yr for galaxies hosting a wind. These values of (dM/dt)_tot, normalized to the corresponding global star formation rates inferred from infrared luminosities, are in the range eta = (dM/dt)_tot / SFR = 0.1-0.7. This is on average a factor of only 10 less than eta from recent measurements of nearby dwarfs, edge-on spirals, and lower-luminosity infrared galaxies. Within our sample, we conclude that eta has no dependence on the mass of the host (parameterized by host galaxy kinematics and absolute R- and K'-band magnitudes). We also attempt to estimate the average escape fraction = Sum(dM/dt_esc^i) / Sum(dM/dt_tot^i) and ``ejection efficiency'' = Sum(dM/dt_esc^i) / Sum(SFR^i) for our sample, which we find to be \~0.4-0.5 and ~0.1, respectively. The complex absorption-line properties of Mrk 231, an ultraluminous infrared galaxy which is optically classified as a Seyfert 1, are discussed separately in an appendix.

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