arXiv subjects

D. Lutz

Publications and source records attributed to D. Lutz.

At least 289 records · Page 16Linked to original sources

arXiv2007

Dust covering factor, silicate emission and star formation in luminous QSOs

We present Spitzer IRS low resolution, mid-IR spectra of a sample of 25 high luminosity QSOs at 2<z<3.5. When combined with archival IRS observations of local, low luminosity type-I AGNs, the sample spans five orders of magnitude in luminosity. We find that the continuum dust thermal emission at lambda(rest)=6.7um is correlated with the optical luminosity, following the non-linear relation L(6.7um) propto L(5100A)^0.82. We also find an anti correlation between the ratio L(6.7um)/L(5100A) and the [OIII]5007A line luminosity. These effects are interpreted as a decreasing covering factor of the circumnuclear dust as a function of luminosity. Such a result is in agreement with the decreasing fraction of absorbed AGNs as a function of luminosity recently found in various surveys. We clearly detect the silicate emission feature in the average spectrum, but also in four individual objects. These are the Silicate emission in the most luminous objects obtained so far. When combined with the silicate emission observed in local, low luminosity type-I AGNs, we find that the silicate emission strength is correlated with luminosity. The silicate strength of all type-I AGNs also follows a positive correlation with the black hole mass and with the accretion rate. The Polycyclic Aromatic Hydrocarbon (PAH) emission features, expected from starburst activity, are not detected in the average spectrum of luminous, high-z QSOs. The upper limit inferred from the average spectrum points to a ratio between PAH luminosity and QSO optical luminosity significantly lower than observed in lower luminosity AGNs, implying that the correlation between star formation rate and AGN power saturates at high luminosities.

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arXiv2007

PAH emission and star formation in the host of the z~2.56 Cloverleaf QSO

We report the first detection of the 6.2micron and 7.7micron infrared `PAH' emission features in the spectrum of a high redshift QSO, from the Spitzer-IRS spectrum of the Cloverleaf lensed QSO (H1413+117, z~2.56). The ratio of PAH features and rest frame far-infrared emission is the same as in lower luminosity star forming ultraluminous infrared galaxies and in local PG QSOs, supporting a predominantly starburst nature of the Cloverleaf's huge far-infrared luminosity (5.4E12 Lsun, corrected for lensing). The Cloverleaf's period of dominant QSO activity (Lbol ~ 7E13 Lsun) is coincident with an intense (star formation rate ~1000 Msun/yr) and short (gas exhaustion time ~3E7yr) star forming event.

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arXiv2007

A mid-infrared spectroscopic study of submillimeter galaxies: luminous starbursts at high redshift

We present rest frame mid-infrared spectroscopy of a sample of 13 submillimeter galaxies, obtained using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. The sample includes exclusively bright objects from blank fields and cluster lens assisted surveys that have accurate interferometric positions. We find that the majority of spectra are well fitted by a starburst template or by the superposition of PAH emission features and a weak mid-infrared continuum, the latter a tracer of Active Galactic Nuclei (including Compton-thick ones). We obtain mid-infrared spectroscopic redshifts for all nine sources detected with IRS. For three of them the redshifts were previously unknown. The median value of the redshift distribution is z~2.8 if we assume that the four IRS non-detections are at high redshift. The median for the IRS detections alone is z~2.7. Placing the IRS non-detections at similar redshift would require rest frame mid-IR obscuration larger than is seen in local ULIRGs. The rest frame mid-infrared spectra and mid- to far-infrared spectral energy distributions are consistent with those of local ultraluminous infrared galaxies, but scaled-up further in luminosity. The mid-infrared spectra support the scenario that submillimeter galaxies are sites of extreme star formation, rather than X-ray-obscured AGN, and represent a critical phase in the formation of massive galaxies.

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arXiv2006

Intense Star-formation and Feedback at High Redshift: Spatially-resolved Properties of the z=2.6 Submillimeter Galaxy SMMJ14011+0252

We present a detailed analysis of the spatially-resolved properties of the lensed submillimeter galaxy SMMJ14011+0252 at z=2.56, combining deep near-infrared integral-field data obtained with SPIFFI on the VLT with other multi-wavelength data sets. The broad characteristics of SMMJ14011+0252 are in agreement with what is expected for the early evolution of local massive spheroidal galaxies. From continuum and line flux, velocity, and dispersion maps, we measure the kinematics, star-formation rates, gas densities, and extinction for individual subcomponents. The star formation intensity is similar to low-redshift ``maximal starbursts'', while the line fluxes and the dynamics of the emission line gas provide direct evidence for a starburst-driven wind with physical properties very similar to local superwinds. We also find circumstantial evidence for "self-regulated" star formation within J1. The relative velocity of the bluer companion J2 yields a dynamical mass estimate for J1 within about 20 kpc, M_dyn \sim 1\times 10^{11} M_sun. The relative metallicity of J2 is 0.4 dex lower than in J1n/s, suggesting different star formation histories. SED fitting of the continuum peak J1c confirms and substantiates previous suggestions that this component is a z=0.25 interloper. When removing J1c, the stellar continuum and H-alpha line emission appear well aligned spatially in two individual components J1n and J1s, and coincide with two kinematically distinct regions in the velocity map, which might well indicate a merging system. This highlights the close similarity between SMGs and ULIRGs, which are often merger-driven maximal starbursts, and suggests that the intrinsic mechanisms of star-formation and related feedback are similar to low-redshift strongly star-forming systems.

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arXiv2006

Mid-Infrared Diagnostics of LINERs

We report results from the first mid-infrared spectroscopic study of a comprehensive sample of 33 LINERs, observed with the Spitzer Space Telescope. We compare the properties of two different LINER populations: infrared-faint LINERs, with LINER emission arising mostly in compact nuclear regions, and infrared-luminous LINERs, which often show spatially extended (non-AGN) LINER emission. We show that these two populations can be easily distinguished by their mid-infrared spectra in three different ways: (i) their mid-IR spectral energy distributions (SEDs), (ii) the emission features of polycyclic aromatic hydrocarbons (PAHs), and (iii) various combinations of IR fine-structure line ratios. IR-luminous LINERs show mid-IR SEDs typical of starburst galaxies, while the mid-IR SEDs of IR-faint LINERs are much bluer. PAH flux ratios are significantly different in the two groups. Fine structure emission lines from highly excited gas, such as [O IV], are detected in both populations, suggesting the presence of an additional AGN also in a large fraction of IR-bright LINERs, which contributes little to the combined mid-IR light. The two LINER groups occupy different regions of mid-infrared emission-line excitation diagrams. The positions of the various LINER types in our diagnostic diagrams provide important clues regarding the power source of each LINER type. Most of these mid-infrared diagnostics can be applied at low spectral resolution, making AGN- and starburst-excited LINERs distinguishable also at high redshifts.

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arXiv2006

Host dynamics and origin of Palomar-Green QSOs

We present host-galaxy velocity dispersions of 12 local (mainly Palomar-Green) quasi-stellar objects (QSOs) measured directly from the stellar CO absorption features in the H band. The mean bulge velocity dispersion of the QSOs in our sample is 186 km/s with a standard deviation of 24 km/s. The measurement of the stellar velocity dispersion in QSOs enables us to place them on observational diagrams such as the local black-hole mass to bulge-velocity-dispersion relation and the fundamental plane of early-type galaxies. Concerning the former relation, these QSOs have higher black hole masses than most Seyfert 1 AGNs with similar velocity dispersions. On the fundamental plane, PG QSOs are located between the regions occupied by moderate-mass and giant ellipticals. The QSO bulge and black hole masses, computed from the stellar velocity dispersions, are of order 10^11 M_sun and 10^8 M_sun respectively. The Eddington efficiency of their black holes is on average 0.25, assuming that all of the bolometric luminosity originates from the active nucleus. Our data are consistent with other lines of evidence that Palomar-Green QSOs are related to galaxy mergers with gas-rich components and that they are formed in a manner similar to the most massive Ultraluminous Infrared Galaxies, regardless of their far-infrared emission. However, PG QSOs seem to have smaller host dispersions and different formation mechanisms than QSOs with supermassive black holes of 5x10^8-10^9 M_sun that accrete at low rates and reside in massive spheroids.

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arXiv2006

The rapid formation a large rotating disk galaxy three billion years after the Big Bang

[Abridged] Over the past two decades observations and theoretical simulations have established a global frame-work of galaxy formation and evolution in the young Universe. Galaxies formed as baryonic gas cooled at the centres of collapsing dark matter halos. Mergers of halos led to the build up of galaxy mass. A major step forward in understanding these issues requires well resolved physical information on individual galaxies at high redshift. Here we report adaptive optics, spectroscopic observations of a representative luminous star forming galaxy when the Universe was only twenty percent of its age. The superior angular resolution of these data reveals the physical and dynamical properties of a high redshift galaxy in unprecedented detail. A large and massive rotating proto-disk is channelling gas towards a growing central stellar bulge hosting an accreting massive black hole.

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arXiv2006

Dynamical properties of Ultraluminous Infrared Galaxies. II. Traces of dynamical evolution and end products of local ultraluminous mergers

We present results from our Very Large Telescope large program to study the dynamical evolution of local Ultraluminous Infrared Galaxies (ULIRGs) and QSOs. This paper is the second in a series presenting the stellar kinematics of 54 ULIRGs, derived from high resolution, long-slit H- and K-band spectroscopy. The data presented here, including observations of 17 new targets, are mainly focused on sources that have coalesced into a single nucleus. The stellar kinematics, extracted from the CO ro-vibrational bandheads in our spectra, indicate that ULIRG remnants are dynamically heated systems with a mean dispersion of 161 km/s. The combination of kinematic, structural, and photometric properties of the remnants indicate that they mostly originate from major mergers and that they result in the formation of systems supported by random motions, therefore, elliptical galaxies. The peak of the velocity dispersion distribution and the locus of ULIRGs on the fundamental plane of early-type galaxies indicate that the end products of ultraluminous mergers are typically moderate-mass ellipticals (of stellar mass ~10^10 - 10^11 M_sun). Converting the host dispersion into black hole mass with the aid of the M_BH-sigma relation yields black hole mass estimates of the order 10^7 - 10^8 M_sun and high accretion rates with Eddington efficiencies often >0.5.

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arXiv2006

Lyman Break Galaxies Under a Microscope: The Small Scale Dynamics and Mass of an Arc in the Cluster 1E0657-56

Using the near-infrared integral-field spectrograph SPIFFI on the VLT, we have studied the spatially-resolved dynamics in the z=3.2 strongly lensed galaxy 1E0657-56 ``arc+core''. The lensing configuration suggests that the high surface brightness ``core'' is the M=20 magnified central 1 kpc of the galaxy (seen at a spatial resolution of about 200 pc in the source plane), whereas the fainter ``arc'' is a more strongly magnified peripheral region of the same galaxy at about a half-light radius, which otherwise appears to be a typical z=3 Lyman break galaxy. The overall shape of the position-velocity diagram resembles the ``rotation curves'' of the inner few kpcs of nearby L* spiral galaxies. The projected velocities rise rapidly to 75 km/s within the core. This implies a dynamical mass of M_dyn = 10^9.3 M_sun within the central kpc, and suggests that in this system the equivalent of the mass of a present-day L* bulge at the same radius was already in place by z>=3. Approximating the circular velocity of the halo by the measured asymptotic velocity of the rotation curve, we estimate a dark matter halo mass of M_halo = 10^11.7 +/- 0.3, in good agreement with large-scale clustering studies of Lyman break galaxies. The baryonic collapse fraction is low compared to actively star-forming ``BX'' and low-redshift galaxies around z=2, perhaps implying comparatively less gas infall to small radii or efficient feedback. Even more speculatively, the high central mass density might indicate highly dissipative gas collapse in very early stages of galaxy evolution, in approximate agreement with what is expected for ``inside-out'' galaxy formation models.

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arXiv2006

Spitzer Quasar and ULIRG evolution study (QUEST): I. The origin of the far infrared continuum of QSOs

This paper addresses the origin of the far-infrared (FIR) continuum of QSOs, based on the Quasar and ULIRG Evolution Study (QUEST) of nearby QSOs and ULIRGs using observations with the Spitzer Space Telescope. For 27 Palomar-Green QSOs at z <~ 0.3, we derive luminosities of diagnostic lines ([NeII]12.8um, [NeV]14.3um, [OIV]25.9um) and emission features (PAH7.7um emission which is related to star formation), as well as continuum luminosities over a range of mid- to far-infrared wavelengths between 6 and 60um. We detect star-formation related PAH emission in 11/26 QSOs and fine-structure line emission in all of them, often in multiple lines. The detection of PAHs in the average spectrum of sources which lack individual PAH detections provides further evidence for the widespread presence of PAHs in QSOs. Similar PAH/FIR and [NeII]/FIR ratios are found in QSOs and in starburst-dominated ULIRGs and lower luminosity starbursts. We conclude that the typical QSO in our sample has at least 30% but likely most of the far-infrared luminosity (~ 10^(10...12)Lsun) arising from star formation, with a tendency for larger star formation contribution at the largest FIR luminosities. In the QSO sample, we find correlations between most of the quantities studied including combinations of AGN tracers and starburst tracers. The common scaling of AGN and starburst luminosities (and fluxes) is evidence for a starburst-AGN connection in luminous AGN. Strong correlations of far-infrared continuum and starburst related quantities (PAH, low excitation [NeII]) offer additional support for the starburst origin of far-infrared emission.

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arXiv2006

SINFONI Integral Field Spectroscopy of z~2 UV-selected Galaxies: Rotation Curves and Dynamical Evolution

We present 0.5" resolution near-IR integral field spectroscopy of the Ha line emission of 14 z~2 UV-selected BM/BX galaxies obtained with SINFONI at ESO/VLT. The mean Ha half-light radius r_1/2 is about 4kpc and line emission is detected over > ~20kpc in several sources. In 9 sources, we detect spatially-resolved velocity gradients, from 40 to 410 km/s over ~10kpc. The observed kinematics of the larger systems are consistent with orbital motions. Four galaxies are well described by rotating disks with clumpy morphologies and we extract rotation curves out to radii > ~10kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities v_c of 180+-90 km/s and dynamical masses of (0.5-25)x10^10 Msun within r_1/2. On average, the dynamical masses are consistent with photometric stellar masses assuming a Chabrier/Kroupa IMF but too small for a 0.1-100 Msun Salpeter IMF. The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. The specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average v_c at 10kpc, the virial mass of the typical halo of a galaxy in our sample is 10^(11.7+-0.5) Msun. Kinematic modeling of the 3 best cases implies a ratio of v_c to local velocity dispersion of order 2-4 and accordingly a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ~500Myr. We also argue that if our BM/BX galaxies were initially gas rich, their clumpy disks will subsequently lose their angular momentum and form compact bulges on a timescale of ~1 Gyr. [ABRIDGED]

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arXiv2006

Hubble Space Telescope H-Band Imaging Survey of Massive Gas-Rich Mergers

We report the results from a deep HST NICMOS H-band imaging survey of a carefully selected sample of 33 luminous, late-stage galactic mergers at z < 0.3. Signs of a recent galactic interaction are seen in all of the objects in the HST sample, including all 7 IR-excess Palomar-Green (PG) QSOs in the sample. Unsuspected double nuclei are detected in 5 ULIRGs. A detailed two-dimensional analysis of the surface brightness distributions in these objects indicates that the great majority (81%) of the single-nucleus systems show a prominent early-type morphology. However, low-surface-brightness exponential disks are detected on large scale in at least 4 of these sources. The hosts of 'warm' AGN-like systems are of early type and have less pronounced merger-induced morphological anomalies than the hosts of cool systems with LINER or HII region-like nuclear optical spectral types. The host sizes and luminosities of the 7 PG~QSOs in our sample are statistically indistinguishable from those of the ULIRG hosts. In comparison, highly luminous quasars, such as those studied by Dunlop et al. (2003), have hosts which are larger and more luminous. The hosts of ULIRGs and PG QSOs lie close to the locations of intermediate-size (about 1 -- 2 L*) spheroids in the photometric projection of the fundamental plane of ellipticals, although there is a tendency in our sample for the ULIRGs with small hosts to be brighter than normal spheroids. Excess emission from a young stellar population in the ULIRG/QSO hosts may be at the origin of this difference. Our results provide support for a possible merger-driven evolutionary connection between cool ULIRGs, warm ULIRGs, and PG~QSOs although this sequence may break down at low luminosity. (abridged)

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arXiv2006

Mid-infrared Spitzer spectra of X-ray selected Type 2 QSOs: QSO2s are not ULIRGs

We have performed a spectroscopic study of 7 Type 2 QSOs using the mid-infrared spectrometer IRS on board the Spitzer Space Telescope. These are (to our knowledge) the first mid-IR spectra of X-ray selected QSO2s taken. The objects have been selected according to their high intrinsic luminosities and column densities in the X-rays. Their spectra strongly differ from template spectra of Type 2 AGN at lower luminosities. They do not exhibit strong PAH dust emission features from circum-nuclear star forming regions, typical for lower luminosity Type 2 Seyfert galaxies or other previously used QSO2 templates, such as the (Ultra)luminous Infrared Galaxy ((U)LIRG) NGC 6240. They also do not show the ice and silicate absorption features of highly luminous but deeply embedded compact nuclei seen in some ULIRGs. Instead they reveal a relatively featureless, rising continuum similar to luminous Type 1 AGN. We also find evidence for a 10 micron silicate feature in emission. Models of dusty tori in the AGN unification scenario predict this only for Type 1 AGN. The ratio of the AGN continuum luminosity at 6 micron to the absorption corrected 2-10keV X-ray AGN luminosity is very similar to that found in Seyfert galaxies. X-ray selected QSO2s are thus characterized by powerful AGN in hosts with a luminosity due to star formation < 1e11 L_sol. The dominance of the AGN light in the mid-IR spectra of QSO2s together with their flatter spectral energy distributions (SEDs) places important constraints on models of the cosmic infrared background and of the star formation history of the universe.

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arXiv2005

Probing for evolutionary links between local ULIRGs and QSOs from NIR spectroscopy

We present a study of the dynamical evolution of Ultraluminous Infrared Galaxies (ULIRGs), merging galaxies of infrared luminosity >10^12 L_sun. During our Very Large Telescope large program, we have obtained ISAAC near-infrared, high-resolution spectra of 54 ULIRGs (at several merger phases) and 12 local Palomar-Green QSOs to investigate whether ULIRGs go through a QSO phase during their evolution. One possible evolutionary scenario is that after nuclear coalescence, the black hole radiates close to Eddington to produce QSO luminosities. The mean stellar velocity dispersion that we measure from our spectra is similar (~160 km/s) for 30 post-coalescence ULIRGs and 7 IR-bright QSOs. The black holes in both populations have masses of order 10^7-10^8 M_sun (calculated from the relation to the host dispersion) and accrete at rates >0.5 Eddington. Placing ULIRGs and IR-bright QSOs on the fundamental plane of early-type galaxies shows that they are located on a similar region (that of moderate-mass ellipticals), in contrast to giant ellipticals and radio-loud QSOs. While this preliminary comparison of the ULIRG and QSO host kinematical properties indicates that (some) ULIRGs may undergo a QSO phase in their evolutionary history before they settle down as ellipticals, further data on non-IR excess QSOs are necessary to test this scenario.

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arXiv2005

Dynamical properties of Ultraluminous Infrared Galaxies I: Mass ratio conditions for ULIRG activity in interacting pairs

We present first results from our Very Large Telescope large program to study the dynamical evolution of Ultraluminous Infrared Galaxies (ULIRGs), which are the products of mergers of gas-rich galaxies. The full data set consists of high resolution, long-slit, H- and K-band spectra of 38 ULIRGs and 12 QSOs (between 0.042 3:1 typically do not force enough gas into the center to generate ULIRG luminosities.

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arXiv2005

Evolution of local Ultraluminous mergers from NIR spectroscopy

We present results from our VLT Large Program to study the dynamical evolution of Ultraluminous Infrared Galaxies (ULIRGs). We have so far obtained near-infrared high-resolution ISAAC spectra of 53 local ULIRGs at several merger timescales and 12 Palomar-Green QSOs (more than half of which are IR-bright sources). We have extracted the stellar velocity dispersion and rotational velocity along our slits to derive the kinematics of the merging galaxies. These quantities enable us to answer the following questions about the evolution of ULIRGs: 1) What are the progenitor mass ratios?, 2) How do the stellar kinematics evolve?, and, 3) Is there a connection between ULIRGs and QSOs? We find that the Ultraluminous phase is mainly triggered by mergers of approximately equal mass galaxies, however, less violent minor mergers (of progenitor mass ratio ~3:1) also exist in our sample. Dynamical heating of the merging hosts is observed as the stellar systematic rotation decreases with time in favour of the increase of random motions. The merger remnants, being dispersion-dominated systems with non-negligible rotation, resemble elliptical galaxies. Placing ULIRGs on the fundamental plane of early-type galaxies shows that they resemble intermediate-mass ellipticals. After the nuclear coalescence, the black hole masses of ULIRGs, calculated from their relation to the host dispersions, are of the order 10^7-10^8 M_sun. To investigate whether ULIRGs go through a QSO phase during their evolution, we perform a similar (preliminary) analysis of the IR-bright-QSO kinematics. We find that the average dispersion of the IR-bright QSOs is similar to that of the ULIRG remnants, indicating that evolutionary links between the two populations may exist.

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arXiv2005

Millimeter observations of obscured Spitzer 24 micron sources

We present MAMBO 1.2mm observations of 40 extragalactic sources from the Spitzer First Look Survey that are bright in the mid-infrared (S_24um>1mJy) but optically obscured (log_10 (nu F_nu (24um))/(nu F_nu (0.7um))>1). We use these observations to search for cold dust emission, probing the similarity of their spectral energy distributions to star forming infrared galaxies or obscured AGN. The sample as a whole is well detected at mean S_1.2mm=0.74+-0.09mJy and S_1.2mm/S_24um=0.15+-0.03. Seven (three) of the sources are individually detected at >3sigma (>5sigma) levels. Mean millimeter fluxes are higher for sources with the reddest mid-infrared/optical colors. Optically faint but with relatively low mm to mid-infrared ratio, the typical SEDs are inconsistent with redshifted SED shapes of local star-forming infrared galaxies. They also differ from SEDs of typical submillimeter selected galaxies, with the 24um sources that are individually detected by MAMBO possibly representing intermediate objects. Compared to star-forming galaxies, a stronger but optically obscured mid-infrared component without associated strong far-infrared emission has to be included. This component may be due to luminous optically obscured AGN, which would represent a significant part of the high redshift AGN population.

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arXiv2005

Follow-Up Near-infrared Spectroscopy of Ultraluminous Infrared Galaxies observed by ISO

We present low resolution near-infrared spectroscopy of an unbiased sample of 24 ultraluminous infrared galaxies (ULIRGs), selected from samples previously observed spectroscopically in the mid-infrared with the Infrared Space Observatory (ISO). Qualitatively, the near-infrared spectra resemble those of starbursts. Only in one ULIRG, IRAS 04114-5117E, do we find spectroscopic evidence for AGN activity. The spectroscopic classification in the near-infrared is in very good agreement with the mid-infrared one. For a subset of our sample for which extinction corrections can be derived from Pa-alpha and Br-gamma, we find rather high Pa-alpha luminosities, in accordance with the powering source of these galaxies being star formation.[Fe] emission is strong in ULIRGs and may be linked to starburst and superwind activity. Additionally, our sample includes two unusual objects. The first, IRAS F00183-7111, exhibits extreme [Fe] emission and the second, IRAS F23578-5307, is according to our knowledge one of the most luminous infrared galaxies in H2 rotation-vibration emission.

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