Kalliopi M. Dasyra

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 subgroups, of weak FIR and strong FIR QSOs, and a third group of FIR nondetections. Assuming a starburst origin for the FIR, we obtain intrinsic active galactic nucleus (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 3 μm bump, which we interpret as the signature of the hottest AGN dust. They also display drops beyond ~20 μm that we interpret as the signature of the minimum temperature (~200 K) 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 in which 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 5100 A and two infrared starburst indicators: L(60 μm) and L(PAH 7.7 μm). The correlation of L(5100 A) with L(60 μm) can be used to measure the relative growth rates and lifetimes of the black hole and the new stars.

SPITZER MID-INFRARED SPECTROSCOPY OF INFRARED LUMINOUS GALAXIES AT z ∼ 2. III. FAR-IR TO RADIO PROPERTIES AND OPTICAL SPECTRAL DIAGNOSTICS

We present the mid-IR spectra taken with the Spitzer InfraRed Spectrograph (IRS) for a sample of 52 infrared luminous, high redshift galaxies selected in the Extragalactic First Look Survey (XFLS). The target sample is selected to have 24 μm flux densities brighter than 0.9mJy, and very red 24 μm– to–R and 24–to–8 μm colors. The color criteria were designed to pick out high redshift sources with either PAH emission and/or steep mid-IR continua. Based only on the mid-IR PAH emission and silicate absorption features, we are able to derive redshifts for 48 (48/52 = 92%) of the sources. The majority of these redshifts (36/48 = 75%) are beyond z = 1, in the range of 1.2 ≤ z ≤ 3.2. The Keck optical and near-IR spectroscopy of a subset has confirmed the mid-IR redshift identifications. The 52 spectra generally fall into three broad groups: (1) strong PAH emission, (2) heavily absorbed systems, and (3) mid-IR continuum dominated with weak PAH and/or silicate absorption features. Of the full sample, 35% have spectra with strong PAH emission (18/52, with 11 at z ≥ 1.6), 31% (16/52, at 1.77 ≤ z ≤ 3.2) are heavily absorbed systems with strong silicate absorption at 9.8 μm and also broad emission peak around 7.7 μm (likely distorted PAH emission). The remainder 34% of the sample are mid- IR continuum dominated systems, where 14 spectra have weak PAH emission and/or silicate absorption (thus yielding redshifts), and 4 sources are without any identifiable features. The detections of deep silicate absorption galaxies imply that our sample has a significant population (at least 31%) of extremely luminous and heavily absorbed systems at z ~ 2. Combining the spectra and broad band photometries at 8 μm and 70 μm, we fit the spectral continua and derived monochromatic, rest-frame 12 μm, continuum luminosities (νLν), ranging from 10^(11) − 10^(12.5)L_⊙. The monochromatic νL_(ν)(12 μm) is crudely 1/10th of L_(ir). Although our sample has a limited dynamic range in luminosity, we detect a weak trend that at the same redshift, sources with strong PAH emission tend to have lower luminosities than those of deeply embedded as well as continuum dominated systems.

A Deep Hubble Space Telescope H-Band Imaging Survey of Massive Gas-Rich Mergers. II. The QUEST QSOs

We report the results from a deep Hubble Space Telescope (HST) NICMOS H-band imaging survey of 28 z < 0.3 QSOs from the Palomar-Green (PG) sample. This program is part of QUEST (Quasar/ULIRG Evolution Study) and complements a similar set of data on 26 highly nucleated ULIRGs presented in Paper I. Our analysis indicates that the fraction of QSOs with elliptical hosts is higher among QSOs with undetected far-infrared (FIR) emission, small infrared excess (L_IR/L_B < 10), and luminous hosts. The hosts of FIR-faint QSOs show a tendency to have less pronounced merger-induced morphological anomalies and larger QSO-to-host luminosity ratios on average than the hosts of FIR-bright QSOs, consistent with late-merger evolution from FIR-bright to FIR-faint QSOs. The spheroid sizes (~ 0.3-5.5 kpc) and total host luminosities (~ 0.6-7.2 L*_H ) of the radio-quiet PG QSOs in our sample are statistically indistinguishable from the ULIRG hosts presented in Paper I, while those of radio-loud PG QSOs are systematically larger and more luminous. ULIRGs and PG QSOs with elliptical hosts fall near, but not exactly on, the fundamental plane of inactive spheroids. We confirm the systematic trend noted in Paper I for objects with small (~<2 kpc) spheroids to be up to ~ 1 mag brighter than inactive spheroids. The host colors and wavelength dependence of their sizes support the idea that these deviations are at least in part due to non-nuclear star formation. However, the amplitudes of these deviations depend mainly on host sizes, and possibly on infrared excess, but not on merger phase, QSO-to-host luminosity ratio, optical spectral type, active galactic nucleus fractional contribution to the bolometric luminosity, or host R – H color. Taken at face value (i.e., no correction for extinction or the presence of a young stellar population), the H-band spheroid-host luminosities imply black hole masses ~ (5-200) × 10^7 M and sub-Eddington mass accretion rates for both QSOs and ULIRGs. These results are compared with published black hole mass estimates derived from other methods.

HST NICMOS Imaging of z ~ 2, 24 μm-selected Ultraluminous Infrared Galaxies

We present Hubble Space Telescope NICMOSH-band imaging of 33 ultraluminous infrared galaxies (ULIRGs) at z ~ 2 that were selected from the 24 µm catalog of the Spitzer Extragalactic First Look Survey. The images reveal that at least 17 of the 33 objects are associated with interactions. Up to one-fifth of the sources in our sample could be minor mergers, whereas only two systems are merging binaries with luminosity ratio ≤ 3 : 1, which is characteristic of local ULIRGs. The rest-frame optical luminosities of the sources are of the order 10^(10)-10^(11) L⊙ and their effective radii range from 1.4 to 4.9 kpc. The most compact sources are either those with a strong active nucleus continuum or those with a heavy obscuration in the mid-infrared regime, as determined from Spitzer Infrared Spectrograph data. The luminosity of the 7.7 µm feature produced by polycyclic aromatic hydrocarbon molecules varies significantly among compact systems, whereas it is typically large for extended systems. A bulge-to-disk decomposition performed for the six brightest (m_H < 20) sources in our sample indicates that they are best fit by disklike profiles with small or negligible bulges, unlike the bulge-dominated remnants of local ULIRGs. Our results provide evidence that the interactions associated with ultraluminous infrared activity at z ~ 2 can differ from those at z ~ 0.

Infrared luminosities and aromatic features in the 24 μm flux-limited sample of 5muses

We study a 24 μm selected sample of 330 galaxies observed with the infrared spectrograph for the 5 mJy Unbiased nSpitzer Extragalactic Survey. We estimate accurate total infrared luminosities by combining mid-IR spectroscopy nand mid-to-far infrared photometry, and by utilizing newempirical spectral templates from Spitzer data. The infrared luminosities of this sample range mostly from 10^9 L_⊙ to 10^(13.5) L_⊙,with 83% in the range 10^(10) L_⊙ < L_(IR) < 10^(12) L_⊙. The redshifts range from 0.008 to 4.27, with a median of 0.144. The equivalent widths of the 6.2 μm aromatic feature have a bimodal distribution, probably related to selection effects. We use the 6.2μm polycyclic aromatic hydrocarbon equivalent width (PAH EW) to classify our objects as starburst (SB)-dominated (44%), SB-AGN composite (22%), and active galactic nucleus (AGN)-dominated (34%). The high EW objects (SB-dominated) tend to have steeper mid-IR to far-IR spectral slopes and lower L_(IR) and redshifts. The low EW objects (AGN-dominated) tend to have less steep spectral slopes and higher L_(IR) and redshifts. This dichotomy leads to a gross correlation between EW and slope, which does not hold within either group. AGN-dominated sources tend to have lower log(L_(PAH7.7 μm)/L_(PAH11.3 μm)) ratios than star-forming galaxies, possibly due to preferential destruction of the smaller aromatics by the AGN. The log(L_(PAH7.7 μm)/L_(PAH11.3 μm)) ratios for star-forming galaxies are lower in our sample than the ratios measured from the nuclear spectra of nearby normal galaxies, most probably indicating a difference in the ionization state or grain size distribution between the nuclear regions and the entire galaxy. Finally, we provide a calibration relating the monochromatic continuum or aromatic feature luminosity to L_(IR) for different types of objects.

THE ∼0.9 mJy SAMPLE: A MID-INFRARED SPECTROSCOPIC CATALOG OF 150 INFRARED-LUMINOUS, 24 μm SELECTED GALAXIES AT 0.3 ⩽ z ⩽ 3.5

We present a catalog of mid-infrared (MIR) spectra of 150 infrared (IR) luminous galaxies in the Spitzer extragalactic first look survey obtained with the IR spectrograph on board the Spitzer Space Telescope. The sample is selected to be brighter than ~0.9 mJy at 24 μm and it has a redshift distribution in the range [0.3, 3.5], with a peak at z = 1. It primarily comprises ultraluminous IR galaxies (ULIRGs) at z ≳ 1 and luminous IR galaxies at z < 1, as estimated from their monochromatic rest-frame 14 μm luminosities. The number of sources with spectra that are dominated by an active galactic nucleus (AGN) continuum is 49, while 39 sources have strong, star formation related features. For this classification, we used the equivalent width (EW) of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature. Several intermediate and high z starbursts have higher PAH EW than local ULIRGs, which could be indicative of an elevated star formation activity. Moreover, an increase in the AGN activity is observed with increasing z and luminosity, based on the decreasing EW of PAHs and the increasing [Ne III]/ [Ne II] ratio. Spectral stacking leads to the detection of weak features such as the 3.3 μm PAH, the H_2 0-0 S(1) and S(3) lines, and the [Ne V] line. We observe differences in the flux ratios of PAHs in the stacked spectra of IR-luminous galaxies with redshift or luminosity, which cannot be attributed to extinction effects since both the depth and the profile of the silicate absorption feature at 9.7 μm remain the same at z < 1 and z ≥ 1. When placing the observed galaxies on IR color-color diagrams, we find that the wedge defining AGNs comprises most sources with continuum-dominated spectra, but also contains many starbursts and sources with strong silicate absorption at 9.7 μm. The comparison of the 11.3 μm PAH EW and the H-band effective radius, measured from Hubble Space Telescope data, indicates that sources with EWs ≥ 2 μm, are typically more extended than ~3 kpc. However, there is no strong correlation between the MIR spectral type and the near-IR extent of the sources.

Detections of CO molecular gas in 24 μm bright ULIRGs at z ~ 2 in the Spitzer first look survey

We present CO observations of nine ultra-luminous infrared galaxies (ULIRGs) at z ~ 2 with f_(ν)(24 μm) ≳ 1 mJy, previously confirmed with the mid-IR spectra in the Spitzer First Look Survey. All targets are required to have accurate redshifts from Keck/GEMINI near-IR spectra. Using the Plateau de Bure millimeter-wave Interferometer at the Institute for Radioastronomy at Millimeter Wavelengths, we detect CO J(3-2) (seven objects) or J(2-1) (one object) line emission from eight sources with integrated intensities I_c ~ 5σ-9σ. The CO-detected sources have a variety of mid-IR spectra, including strong polycyclic aromatic hydrocarbon, deep silicate absorption, and power-law continuum, implying that these molecular gas-rich objects at z ~ 2 could be either starbursts or dust-obscured active galactic nuclei (AGNs). The measured line luminosity L_(CO) is (1.28-3.77) × 10^(10) K km/s pc^2. The averaged molecular gas mass is 1.7 × 10^(10) M_☉, assuming CO-to-H_2 conversion factor of 0.8 M (K km/s pc^2)^(–1). Three sources (33%)—MIPS506, MIPS16144, and MIPS8342—have double peak velocity profiles. The CO double peaks in MIPS506 and MIPS16144 show spatial separations of 45 kpc and 10.9 kpc, allowing the estimates of the dynamical masses of 3.2 × 10^(11) sin^(–2)(i) M_☉ and 5.4 × 10^(11) sin^(–2)(i) M, respectively. The implied gas fraction, M_(gas)/M_(dyn), is 3% and 4%, assuming an average inclination angle. Finally, the analysis of the Hubble Space Telescope/NIC2 images, mid-IR spectra, and IR spectral energy distribution revealed that most of our sources are mergers, containing dust-obscured AGNs dominating the luminosities at (3-6) μm. Together, these results provide some evidence suggesting submillimeter galaxies, bright 24 μm, z ~ 2 ULIRGs, and QSOs could represent three different stages of a single evolutionary sequence, however, a complete physical model would require much more data, especially high spatial resolution spectroscopy.

High-ionization mid-infrared lines as black hole mass and bolometric luminosity indicators in active galactic nuclei

We present relations of the black hole mass and the optical luminosity with the velocity dispersion and the luminosity of the [Ne v] and the [O iv] high-ionization lines in the mid-infrared (MIR) for 28 reverberation-mapped active galactic nuclei. We used high-resolution Spitzer Infrared Spectrograph and Infrared Space Observatory nShort Wavelength Spectrometer data to fit the profiles of these MIR emission lines that originate from the narrow-line region of the nucleus. We find that the lines are often resolved and that the velocity dispersion of [Ne v] and [O iv] follows a relation similar to that between the black hole mass and the bulge stellar velocity dispersion found for local galaxies. The luminosity of the [Ne v] and the [O iv] lines in these sources is correlated nwith that of the optical 5100 continuum and with the black hole mass. Our results provide a means to derive °A black hole properties in various types of active galactic nuclei, including highly obscured systems.

FIRST STELLAR VELOCITY DISPERSION MEASUREMENT OF A LUMINOUS QUASAR HOST WITH GEMINI NORTH LASER GUIDE STAR ADAPTIVE OPTICS

We present the first use of the Gemini North laser guide star adaptive optics (LGS AO) system and an integral field unit (IFU) to measure the stellar velocity dispersion of the host of a luminous quasar. The quasar PG 1426+015 (z =0.086) was observed with the Near-Infrared Integral Field Spectrometer (NIFS) on the 8 m Gemini North telescope in the H band as part of the Science Verification phase of the new ALTAIR LGS AO system. The NIFS IFU and LGS AO are well suited for host studies of luminous quasars because one can achieve a large ratio of host to quasar light. We have measured the stellar velocity dispersion of PG 1426+015 from 0.1 to 1 (0.16 to 1.6 kpc) to be 217 ± 15 km s^(-1) based on high signal-to-noise ratio measurements of Si i, Mg i, and several CO band heads. This new measurement is a factor of 4 more precise than a previous measurement obtained with long-slit spectroscopy and good, natural seeing, yet was obtained with a shorter net integration time. We find that PG 1426+015 has a velocity dispersion that places it significantly above the M_(BH)^(-σ) relation of quiescent galaxies and lower luminosity active galactic nuclei with black hole masses estimated from reverberation mapping. We discuss several possible explanations for this discrepancy that could be addressed with similar observations of a larger sample of luminous quasars.

HST/NICMOS IMAGING OF BRIGHT HIGH-REDSHIFT 24 μm SELECTED GALAXIES: MERGING PROPERTIES

We present new results on the physical nature of infrared-luminous sources at 0.5 0.9 mJy. We find many (~60%) of our sources to possess an important bulge and/or central point source component, most of which reveal additional underlying structures after subtraction of a best-fit Sersic (or Sersic+PSF) profile. Based on visual inspection of the NIC2 images and their residuals, we estimate that ~80% of all our sources are mergers. We calculate lower and upper limits on the merger fraction to be 62% and 91%, respectively. At z 3.36) quasars to live in faint and compact hosts and show that these are likely high-redshift analogs of local dense-core mergers. We find late-stage mergers to possess predominantly unobscured AGN spectra, but do not observe other morphological classes to carry any specific combination of τ_(9.7) μm and polycyclic aromatic hydrocarbon (PAH) equivalent width. This suggests a high degree of variation in the PAH emission and silicate absorption properties of these mergers, and possibly throughout the merging process itself.