P. Ogle

The Nuclear Spectroscopic Telescope Array (NuSTAR) High-Energy X-Ray Mission

The Nuclear Spectroscopic Telescope Array (NuSTAR) is a National Aeronautics and Space Administration (NASA) Small Explorer mission that carried the first focusing hard X-ray (6-79 keV) telescope into orbit. It was launched on a Pegasus rocket into a low-inclination Earth orbit on June 13, 2012, from Reagan Test Site, Kwajalein Atoll. NuSTAR will carry out a two-year primary science mission. The NuSTAR observatory is composed of the X-ray instrument and the spacecraft. The NuSTAR spacecraft is three-axis stabilized with a single articulating solar array based on Orbital Sciences Corporations LEOStar-2 design. The NuSTAR science instrument consists of two co-aligned grazing incidence optics focusing on to two shielded solid state CdZnTe pixel detectors. The instrument was launched in a compact, stowed configuration, and after launch, a 10-meter mast was deployed to achieve a focal length of 10.15 m. The NuSTAR instrument provides sub-arcminute imaging with excellent spectral resolution over a 12-arcminute field of view. The NuSTAR observatory will be operated out of the Mission Operations Center (MOC) at UC Berkeley. Most science targets will be viewed for a week or more. The science data will be transferred from the UC Berkeley MOC to a Science Operations Center (SOC) located at the California Institute of Technology (Caltech). In this paper, we will describe the mission architecture, the technical challenges during the development phase, and the post-launch activities.

PAH Emission from Ultraluminous Infrared Galaxies

We explore the relationships between the polycyclic aromatic hydrocarbon (PAH) feature strengths, mid-infrared continuum luminosities, far-infrared spectral slopes, optical spectroscopic classifications, and silicate optical depths in a sample of 107 ULIRGs observed with the Infrared Spectrograph on the Spitzer Space Telescope. The detected 6.2 μm PAH equivalent widths (EWs) in the sample span more than 2 orders of magnitude (~0.006-0.8 μm), and ULIRGs with H II-like optical spectra or steep far-infrared spectral slopes (S_(25)/S_(60) 2.3) silicate optical depths. The far-infrared spectral slope is strongly correlated with PAH EW, but not with silicate optical depth. In addition, the PAH EW decreases with increasing rest-frame 24 μm luminosity. We argue that this trend results primarily from dilution of the PAH EW by continuum emission from dust heated by a compact central source, probably an AGN. High-luminosity, high-redshift sources studied with Spitzer appear to have a much larger range in PAH EW than seen in local ULIRGs, which is consistent with extremely luminous starburst systems being absent at low redshift, but present at early epochs.

When Is BL Lac Not a BL Lac

We have found broad Hα and Hβ line emission in spectra of BL Lacertae taken on 1995 May 21 and June 1: on those occasions BL Lac did not meet the defining criteria for the class named after it. The Hα line luminosity, ~2 × 1041 h-2 erg s-1 for H0 = 100 h km s-1 Mpc-1, is significantly above the detection threshold in older published spectra which do not show the line. Several possible explanations for the increase in broad line luminosity are discussed. The continuum was at the faint end of its commonly observed range: V ~ 16.0 on 1995 May 21. The polarization, measured on 1995 June 1, was also near the low end of the typical range in BL Lac: ~5.0% in PA ~ 22° near 7500 A, rising to ~6.1% in PA ~ 15° near 4900 A. Absorption features in the spectrum show the presence of the associated galaxy, but the light is still dominated by an underlying smooth continuum, the intrinsic shape of which is well approximated between 8000 and 4000 A by Fν ∝ ν-1.7, indicating a synchrotron origin. We confirm the narrow emission line redshift, z = 0.0686 ± 0.0004.

Aromatic Features in AGNs: Star-forming Infrared Luminosity Function of AGN Host Galaxies

We describe observations of aromatic features at 7.7 and 11.3 μm in AGNs of three types, including PG, 2MASS, and 3CR objects. The feature has been demonstrated to originate predominantly from star formation. Based on the aromatic-derived star-forming luminosity, we find that the far-IR emission of AGNs can be dominated by either star formation or nuclear emission; the average contribution from star formation is around 25% at 70 and 160 μm. The star-forming infrared luminosity functions of the three types of AGNs are flatter than those of field galaxies, implying that nuclear activity and star formation tend to be enhanced together. The star-forming luminosity function is also a function of the strength of nuclear activity from normal galaxies to the bright quasars, with luminosity functions becoming flatter for more intense nuclear activity. Different types of AGNs show different distributions in the level of star formation activity, with 2MASS > PG > 3CR star formation rates.

JET-POWERED MOLECULAR HYDROGEN EMISSION FROM RADIO GALAXIES

H2 pure-rotational emission lines are detected from warm (100–1500 K) molecular gas in 17/55 (31% of) radio galaxies at redshift z< 0.22 observed with the Spitzer IR Spectrograph. The summed H2 0–0 S(0)–S(3) line luminosities are L(H2) = 7 × 10 38 –2 × 10 42 erg s −1 , yielding warm H2 masses up to 2 × 10 10 M� . These radio galaxies, of both FR radio morphological types, help to firmly establish the new class of radio-selected molecular hydrogen emission galaxies (radio MOHEGs). MOHEGs have extremely large H2 to 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission ratios: L(H2)/L(PAH7.7) = 0.04–4, up to a factor 300 greater than the median value for normal star-forming galaxies. In spite of large H2 masses, MOHEGs appear to be inefficient at forming stars, perhaps because the molecular gas is kinematically unsettled and turbulent. Low-luminosity mid-IR continuum emission together with low-ionization emission line spectra indicates low-luminosity active galactic nuclei (AGNs) in all but three radio MOHEGs. The AGN X-ray emission measured with Chandra is not luminous enough to power the H2 emission from MOHEGs. Nearly all radio MOHEGs belong to clusters or close pairs, including four cool-core clusters (Perseus, Hydra, A2052, and A2199). We suggest that the H2 in radio MOHEGs is delivered in galaxy collisions or cooling flows, then heated by radio-jet feedback in the form of kinetic energy dissipation by shocks or cosmic rays.

Chandra Observations of the X-Ray Narrow-Line Region in NGC 4151

We present the first high-resolution X-ray spectrum of the Seyfert 1.5 galaxy NGC 4151. Observations with the Chandra High-Energy Transmission Grating Spectrometer reveal a spectrum dominated by narrow emission lines from a spatially resolved (1.6 kpc), highly ionized nebula. The X-ray narrow-line region is composite, consisting of both photoionized and collisionally ionized components. The X-ray emission lines have similar velocities, widths, and spatial extent to the optical emission lines, showing that they arise in the same region. The clouds in the narrow-line region must contain a large range of ionization states in order to explain both the optical and X-ray photoionized emission. Chandra data give the first direct evidence of X-ray line emission from a hot plasma (T ~ 107 K) that may provide pressure confinement for the cooler (T = 3 × 104 K) photoionized clouds.

Energetics of the molecular gas in the H_2 luminous radio galaxy 3C 326: Evidence for negative AGN feedback

We present a detailed analysis of the gas conditions in the H_2 luminous radio galaxy 3C 326 N at z ~ 0.1, which has a low star-formation rate (SFR ~ 0.07 M_⊙ yr^(−1)) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency is likely a factor ~ 10−50 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry with existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H_2 line emission is factors 10−100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of 3C 326 N in the optical suggests an outflow with a terminal velocity of ~−1800 km s^(−1) and a mass outflow rate of 30−40 M_⊙ yr^(−1), which cannot be explained by star formation. The mechanical power implied by the wind, of order 10^(43) erg s^(−1), is comparable to the bolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where a small fraction of the mechanical energy of the radio jet is deposited in the interstellar medium of 3C 326 N, which powers the outflow, and the line emission through a mass, momentum and energy exchange between the different gas phases of the ISM. Dissipation times are of order 10^(7−8) yrs, similar or greater than the typical jet lifetime. Small ratios of CO and PAH surface brightnesses in another 7 H_2 luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies in a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of ≥ 10^(11) M_⊙ could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback.

STRONG MOLECULAR HYDROGEN EMISSION AND KINEMATICS OF THE MULTIPHASE GAS IN RADIO GALAXIES WITH FAST JET-DRIVEN OUTFLOWS

Observations of ionized and neutral gas outflows in radio galaxies (RGs) suggest that active galactic nucleus (AGN) radio jet feedback has a galaxy-scale impact on the host interstellar medium, but it is still unclear how the molecular gas is affected. Thus, it is crucial to determine the physical conditions of the molecular gas in powerful RGs to understandhowradiosourcesmayregulatethestarformationintheirhostgalaxies.WepresentdeepSpitzerInfrared Spectrograph (IRS) high-resolution spectroscopy of eight nearby RGs that show fast Hi outflows. Strikingly, all of these Hi-outflow RGs have bright H2 mid-IR lines that cannot be accounted for by UV or X-ray heating. This strongly suggests that the radio jet, which drives the Hi outflow, is also responsible for the shock excitation of the warm H2 gas. In addition, the warm H2 gas does not share the kinematics of the ionized/neutral gas. The mid-IR-ionized gas lines (with FWHM up to 1250 km s −1 for [Neii]12.8 μm) are systematically broader than the H2 lines, which are resolved by the IRS in ≈60% of the detected lines (with FWHM up to 900 km s −1 ). In five sources, 3C 236, 3C 293, 3C 459, 4C 12.50, and PKS 1549-79, the [Neii]12.8 μm line, and to a lesser extent the [Neiii]15.5 μm and [Nev]14.3 μm lines, clearly exhibits blueshifted wings (up to −900 km s −1 with respect to the systemic velocity) that match well the kinematics of the outflowing Hi or ionized gas. The H2 lines do not show these broad wings, except tentative detections in 4C 12.50, 3C 459, and PKS 1549-79. This shows that, contrary to the Hi gas, the H2 gas is inefficiently coupled to the AGN jet-driven outflow of ionized gas. While the dissipation of a small fraction (<10%) of the jet kinetic power can explain the turbulent heating of the molecular gas, our data show that the bulk of the warm molecular gas is not expelled from these galaxies.

Spectropolarimetry of Two Broad Absorption Line Quasars with the W. M. Keck Telescope

We have observed the broad absorption line quasars PHL 5200 and 01052265 with spectropolarimetry at the Keck telescope. In PHL 5200 the continuum is consistent with a power law with constant polarization,p 55.1%. A drop in polarization in the red is explained with dilution by unpolarized Fe II emission. In both objects the permitted emission lines are unpolarized. In PHL 5200 the semiforbidden line C III] l1909 is weakly polarized; weattributethistoresonancescattering.Thepolarizationrisesinthebroadabsorptiontroughs,toapeakof12% in both objects. The high values ofpare restricted to a narrow velocity range that is well inside the absorption troughs. In each object, the polarization position angle is constant, except that in PHL 5200 there are marginally significant rotations in the C IVtrough and in the C III] emission line. We describe two simple geometries that can explain some of these features. In thefirst, there are scattered and direct rays; in the troughs the direct ray (unpolarized) is largely absorbed, and we mainly see the highly polarized scattered ray. In the other, the high trough polarization is caused by resonance scattering. Subject headings: polarization—quasars: absorption lines—quasars: emission lines— quasars: individual (PHL 5200, 01052265)

Powerful H

We present results from the mid-infrared spectral mapping of Stephans Quintet using the Spitzer Space Telescope. A 1000 km s^(-1) collision (t_(col) = 5 × 10^6 yr) has produced a group-wide shock, and for the first time the large-scale distribution of warm molecular hydrogen emission is revealed, as well as its close association with known shock structures. In the main shock region alone we find 5.0 × 10^8 M_☉ of warm H_2 spread over ~480 kpc^2 and additionally report the discovery of a second major shock-excited H_2 feature, likely a remnant of previous tidal interactions. This brings the total H2 line luminosity of the group in excess of 10^(42) erg s^(-1). In the main shock, the H_2 line luminosity exceeds, by a factor of 3, the X-ray luminosity from the hot shocked gas, confirming that the H_2-cooling pathway dominates over the X-ray. [Si II]34.82 μm emission, detected at a luminosity of 1/10th of that of the H_2, appears to trace the group-wide shock closely, and in addition, we detect weak [Fe II]25.99 μm emission from the most X-ray luminous part of the shock. Comparison with shock models reveals that this emission is consistent with regions of fast shocks (100 km s^(-1) < V_s < 300 km s^(-1)) experiencing depletion of iron and silicon onto dust grains. Star formation in the shock (as traced via ionic lines, polycyclic aromatic hydrocarbon and dust emission) appears in the intruder galaxy, but most strikingly at either end of the radio shock. The shock ridge itself shows little star formation, consistent with a model in which the tremendous H_2 power is driven by turbulent energy transfer from motions in a post-shocked layer which suppresses star formation. The significance of the molecular hydrogen lines over other measured sources of cooling in fast galaxy-scale shocks may have crucial implications for the cooling of gas in the assembly of the first galaxies.