Detections of water ice, hydrocarbons, and 3.3um PAH in z~2 ULIRGs

We present the first detections of the 3um water ice and 3.4um amorphous hydrocarbon (HAC) absorption features in z~2 ULIRGs. These are based on deep rest-frame 2-8um Spitzer IRS spectra of 11 sources selected for their appreciable silicate absorption. The HAC-to-silicate ratio for our z~2 sources is typically higher by a factor of 2-5 than that observed in the Milky Way. This HAC `excess' suggests compact nuclei with steep temperature gradients as opposed to predominantly host obscuration. Beside the above molecular absorption features, we detect the 3.3um PAH emission feature in one of our sources with three more individual spectra showing evidence for it. Stacking analysis suggests that water ice, hydrocarbons, and PAH are likely present in the bulk of this sample even when not individually detected. The most unexpected result of our study is the lack of clear detections of the 4.67um CO gas absorption feature. Only three of the sources show tentative signs of this feature and at significantly lower levels than has been observed in local ULIRGs. Overall, we find that the closest local analogs to our sources, in terms of 3-4um color, HAC-to-silicate and ice-to-silicate ratios, as well as low PAH equivalent widths are sources dominated by deeply obscured nuclei. Such sources form only a small fraction of ULIRGs locally and are commonly believed to be dominated by buried AGN. Our sample suggests that, in absolute number, such buried AGN are at least an order of magnitude more common at z~2 than today. The presence of PAH suggests that significant levels of star-formation are present even if the obscured AGN typically dominate the power budget.Comment: 39 pages, 14 figures, accepted for publication in Ap

Detections of CO Molecular Gas in 24um-Bright ULIRGs at z~2 in the Spitzer First Look Survey

We present CO observations of 9 ULIRGs at z~2 with S(24\mu m)>1mJy, 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 (PdBI) at IRAM, we detect CO J(3-2) [7 objects] or J(2-1) [1 object] line emission from 8 sources with integrated intensities Ic ~(5-9)sigma. The CO detected sources have a variety of mid-IR spectra, including strong PAH, deep silicate absorption and power-law continuum, implying that these molecular gas rich objects at z~2 could be either starbursts or dust obscured AGNs. The measured line luminosity L'[CO] is (1.28-3.77)e+10[K km/s pc^2]. The averaged molecular gas mass M(H2) is 1.7e+10Msun, assuming CO-to-H2 conversion factor of 0.8Msun/[K km/s pc^2]. Three sources (33%) -- MIPS506, MIPS16144 & MIPS8342 -- have double peak velocity profiles. The CO double peaks in MIPS506 and MIPS16144 show spatial separations of 45kpc and 10.9kpc, allowing the estimates of the dynamical masses of 3.2e+11*sin^(-2)(i)Msun and 5.4e+11*sin^{-2}(i)Msun respectively. The implied gas fraction, M(gas)/M(dyn), is 3% and 4%, assuming an average inclination angle. Finally, the analysis of the HST/NIC2 images, mid-IR spectra and IR SED revealed that most of our sources are mergers, containing dust obscured AGNs dominating the luminosities at (3-6)um. Together, these results provide some evidence suggesting SMGs, bright 24um 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.Comment: 15 pages, 8 figures, accepted for publication in ApJ

Mid-infrared selection of quasar-2s in Spitzer's First Look Survey

We present early results from the spectroscopic follow-up of a sample of candidate obscured AGN selected in the mid-infrared from the Spitzer First Look Survey. Our selection allows a direct comparison of the numbers of obscured and unobscured AGN at a given luminosity for the first time, and shows that the ratio of obscured to unobscured AGN at infrared luminosities corresponding to low luminosity quasars is ~1:1 at z~0.5. Most of our optically-faint candidate obscured AGN have the high-ionization, narrow-line spectra expected from type-2 AGN. A composite spectrum shows evidence for Balmer absorption lines, indicating recent star-formation activity in the host galaxies. There is tentative evidence for a decrease in the obscured AGN fraction with increasing AGN luminosity.Comment: To appear in the proceedings of the workshop "Multiband approach to AGN" Bonn October 2004 in Memorie della Societa Astronomica Italian

Large amounts of optically-obscured star formation in the host galaxies of some type-2 quasars

We present Hubble Space Telescope images, and spectral energy distributions from optical to infrared wavelengths for a sample of six 0.3<z<0.8 type-2 quasars selected in the mid-infrared using data from the Spitzer Space Telescope. All the host galaxies show some signs of disturbance. Most seem to possess dusty, star-forming disks. The disk inclination, estimated from the axial ratio of the hosts, correlates with the depth of the silicate feature in the mid-infrared spectra, implying that at least some of the reddening towards the AGN arises in the host galaxy. The star formation rates in these objects, as inferred from the strengths of the PAH features and far-infrared continuum, range from 3-90 Msun/yr, but are mostly much larger than those inferred from the [OII]3727 emission line luminosity, due to obscuration. Taken together with studies of type-2 quasar hosts from samples selected in the optical and X-ray, this is consistent with previous suggestions that two types of extinction processes operate within the type-2 quasar population, namely a component due to the dusty torus in the immediate environment of the AGN, and a more extended component due to a dusty, star forming disk.Comment: 5 pages, 3 figures. Accepted by ApJ Letter

Spectral energy distributions of quasars selected in the mid-infrared

We present preliminary results on fitting of SEDs to 142 z>1 quasars selected in the mid-infrared. Our quasar selection finds objects ranging in extinction from highly obscured, type-2 quasars, through more lightly reddened type-1 quasars and normal type-1s. We find a weak tendency for the objects with the highest far-infrared emission to be obscured quasars, but no bulk systematic offset between the far-infrared properties of dusty and normal quasars as might be expected in the most naive evolutionary schemes. The hosts of the type-2 quasars have stellar masses comparable to those of radio galaxies at similar redshifts. Many of the type-1s, and possibly one of the type-2s require a very hot dust component in addition to the normal torus emission.Comment: 4 pages, 2 figures, to appear in the proceedings of The Spectral Energy Distribution of Galaxies, Preston, September 2011, eds R.J. Tuffs & C.C. Popesc

Rocuronium for intubation in parturients undergoing caesarean section

Background: Anaesthetic management of a parturient is a challenge because it involves simultaneous care of both mother and baby. Succinylcholine, a depolarizing muscle relaxant is most commonly used and considered “The Gold Standard’’ for tracheal intubation. Among currently available non-depolarizing neuromuscular blocking agent rocuronium bromide is the only agent that has rapid onset of action which is comparable to succinylcholine. Thus, rocuronium may provide alternative to succinylcholine for rapid sequence induction of anaesthesia wherever succinylcholine is contraindicated.Methods: In a control trial, 60 parturients of ASA grade I and II were randomly allocated in two groups of 30 patients each (group R and group S). After preoxygenation for a period of 5minutes rapid sequence induction done with thiopentone 5mg/kg for all patients. Muscle relaxant rocuronium (0.6mg/kg) was administered for group R. Succinylcholine was given in similar dosage (0.6mg/kg) for group S. The intubation was tried after 90 seconds in group R (rocuronium group) but after 60 seconds in group S (succinylcholie group). The intubating conditions were assessed and compared among the groups using criteria suggested by Cooper et al.Results: The mean intubation time was 98.3 seconds in group R and 67.9 seconds in group S. Rocuronium produced clinically acceptable intubating conditions in 28 out 30 patients (93.33%). Among these 28 patients 70% had excellent intubating conditions and 23.33% had good intubating conditions. Clinically acceptable intubating conditions were present in all 30 patients (100%-90% excellent and 10% good) who were administered succinylcholine. Succinylcholine produced excellent intubating conditions at 60 seconds (90 percent) compared to rocuronium (70 percent). However, this difference was statistically insignificant (p= 0.053). The mean Apgar score at 1 min and 5 min in group R was 8.1 and 8.83 as against 8.06 and 8.96 in babies born to mother in group S.Conclusions: Rocuronium (0.6mg/kg) provided acceptable intubation conditions after a waiting period of 90 seconds in 93.33% patients as against 100% patients in succinylcholine administered patients in equivalent dosage. So rocuronium is a promising alternative for rapid sequence induction in parturients in whom succinylcholine is not advisable or contraindicated

X-ray Constraints on the Active Galactic Nuclei Properties in Spitzer-Infrared Spectrograph Identified z ~ 2 Ultraluminous Infrared Galaxies

We report Chandra X-ray constraints for 20 of the 52 high-redshift ultraluminous infrared galaxies (ULIRGs) identified in the Spitzer Extragalactic First Look Survey with f_ν(24 μm) > 0.9 mJy, log[(νf_ν(24μm)/(νf_ν(R)] > 1, and log[(νf_ν(24μm)/(νf_ν(8μm)] > 0.5. Notably, decomposition of Spitzer mid-infrared IRS spectra for the entire sample indicates that they are comprised predominantly of weak polycyclic aromatic hydrocarbon ULIRGs dominated by hot-dust continua, characteristic of active galactic nuclei (AGNs) activity. Given their redshifts, they have AGN bolometric luminosities of ≈10^(45)-10^(47) erg s^(–1) comparable to powerful quasi-stellar objects (QSOs). This, coupled with their high IR-to-optical ratios and often significant silicate absorption, strongly argues in favor of these mid-IR objects being heavily obscured QSOs. Here we use Chandra observations to further constrain their obscuration. At X-ray energies, we marginally detect two ULIRGs, while the rest have only upper limits. Using the IRS-derived 5.8 μm AGN continuum luminosity as a proxy for the expected X-ray luminosities, we find that all of the observed sources must individually be highly obscured, while X-ray stacking limits on the undetected sources suggest that the majority, if not all, are likely to be at least mildly Compton-thick (N_H ≳ 10^(24) cm^(–2)). With a space density of ≈1.4 × 10^(–7) Mpc^(–3) at z ~ 2, such objects imply an obscured AGN fraction (i.e., the ratio of AGNs above and below N_H = 10^(22) cm^(–2)) of ≳ 1.7:1 even among luminous QSOs. Given that we do not correct for mid-IR extinction effects and that our ULIRG selection is by no means complete for obscured AGNs, we regard our constraints as a lower limit to the true obscured fraction among QSOs at this epoch. Our findings, which are based on extensive multi-wavelength constraints including Spitzer IRS spectra, should aid in the interpretation of similar objects from larger or deeper mid-IR surveys, where considerable uncertainty about the source properties remains and comparable follow-up is not yet feasible

Mid-Infrared Spectra of High Redshift (z>2) Radio Galaxies

We present the first mid-infrared Spitzer/Infrared Spectrograph (IRS) observations of powerful radio galaxies at z>2. These radio galaxies, 4C +23.56 (z=2.48) and 6C J1908+7220 (z=3.53), both show strong mid-infrared continua, but with 6C J1908+7220 also showing strong PAH emission at rest-frame 6.2 and 7.7um. In 4C+23.56 we see no obvious PAH features above the continuum. The PAH emission in 6C J1908+7220 is the amongst the most distant observed to date and implies that there is a large instantaneous star formation rate (SFR). This is consistent with the strong detection of 6C J1908+7220 at far-IR and sub-mm wavelengths, indicative of large amounts of cold dust, ~10^9Msun. Powerful radio galaxies at lower redshifts tend to have weak or undetectable PAH features and typically have lower far-IR luminosities. In addition, 4C 23.56 shows moderate silicate absorption as seen in less luminous radio galaxies, indicating tau_{9.7um}=0.3+/-0.05. This feature is shifted out of the observed wavelength range for 6C J1908+7220. The correlation of strong PAH features with large amounts of cold dust, despite the presence of a powerful AGN, is in agreement with other recent results and implies that star formation at high redshift is, in some cases at least, associated with powerful, obscured AGN.Comment: 6 pages, 3 figures, includes emulateapj.cls, in press ApJ

VLA/JVLA monitoring of bright northern radio sources

We report multiple epoch VLA/JVLA observations of 89 northern hemisphere sources, most with 37 GHz flux density >1 Jy, observed at 4.8, 8.5, 33.5, and 43.3 GHz. The high frequency selection leads to a predominantly flat spectrum sample, with 85% of our sources being in the Planck Early Release Compact Source Catalog (ERCSC). These observations allow us to: 1) validate Planck’s 30 and 44 GHz flux density scale; 2) extend the radio spectral energy distributions of Planck sources to lower frequencies allowing for the full 5−857 GHz regime to be studied; and 3) characterize the variability of these sources. At 30 GHz and 44 GHz, the JVLA and Planck flux densities agree to within ~3%. On timescales of less than two months the median variability of our sources is 2%. On timescales of about a year the median variability increases to 14%. Using the WMAP 7-year data, the 30 GHz median variability on a 1−6 years timescale is 16%