[en] We present observations at 1.2 mm with Max-Planck Millimetre Bolometer Array (MAMBO-II) of a sample of z ∼> 2 radio-intermediate obscured quasars, as well as CO observations of two sources with the Plateau de Bure Interferometer. The typical rms noise achieved by the MAMBO observations is 0.55 mJy beam^-1 and five out of 21 sources (24%) are detected at a significance of ≥3σ. Stacking all sources leads to a statistical detection of (S_1.2mm) = 0.96 ± 0.11 mJy and stacking only the non-detections also yields a statistical detection, with (S_1.2mm) = 0.51 ± 0.13 mJy. At the typical redshift of the sample, z = 2, 1 mJy corresponds to a far-infrared luminosity L_FIR∼4 x 10¹² L_sun. If the far-infrared luminosity is powered entirely by star formation, and not by active galactic nucleus heated dust, then the characteristic inferred star formation rate is ∼700 M_sun yr^-1. This far-infrared luminosity implies a dust mass of M_d∼3 x 10⁸ M_sun, which is expected to be distributed on ∼kpc scales. We estimate that such large dust masses on kpc scales can plausibly cause the obscuration of the quasars. Combining our observations at 1.2 mm with mid- and far-infrared data, and additional observations for two objects at 350 μm using SHARC-II, we present dust spectral energy distributions (SEDs) for our sample and derive a mean SED for our sample. This mean SED is not well fitted by clumpy torus models, unless additional extinction and far-infrared re-emission due to cool dust are included. This additional extinction can be consistently achieved by the mass of cool dust responsible for the far-infrared emission, provided the bulk of the dust is within a radius ∼2-3 kpc. Comparison of our sample to other samples of z ∼ 2 quasars suggests that obscured quasars have, on average, higher far-infrared luminosities than unobscured quasars. There is a hint that the host galaxies of obscured quasars must have higher cool-dust masses and are therefore often found at an earlier evolutionary phase than those of unobscured quasars. For one source at z = 2.767, we detect the CO(3-2) transition, with S_COΔν = 630 ± 50 mJy km s^-1, corresponding to L_CO(3-2) = 3.2 x10⁷ L_sun, or a brightness-temperature luminosity of L'_CO(3-2) = 2.4 x 10¹⁰ K km s^-1 pc². For another source at z = 4.17, the lack of detection of the CO(4-3) line suggests the line to have a brightness-temperature luminosity L'_CO(4-3) < 1 x 10¹⁰ K km s^-1 pc². Under the assumption that in these objects the high-J transitions are thermalized, we can estimate the molecular gas contents to be M_H2=1.9x10¹⁰ M _sun and <8 x 10⁹ M_sun, respectively. The estimated gas depletion timescales are τ_g = 4 Myr and <16 Myr, and low gas-to-dust mass ratios of M_g/M _d = 19 and <20 are inferred. These values are at the low end but consistent with those of other high-redshift galaxies.

[en] Using data from the Wide-field Infrared Survey Explorer mission, we have measured near infra-red (NIR) photometry of a diverse sample of dust-free stellar systems (globular clusters, dwarf and giant early-type galaxies) which have metallicities that span the range -2.2 < [Fe/H] (dex) < 0.3. This dramatically increases the sample size and broadens the metallicity regime over which the 3.4 (W1) and 4.6 μm (W2) photometry of stellar populations have been examined. We find that the W1 – W2 colors of intermediate and old (>2 Gyr) stellar populations are insensitive to the age of the stellar population, but that the W1 – W2 colors become bluer with increasing metallicity, a trend not well reproduced by most stellar population synthesis (SPS) models. In common with previous studies, we attribute this behavior to the increasing strength of the CO absorption feature located in the 4.6 μm bandpass with metallicity. Having used our sample to validate the efficacy of some of the SPS models, we use these models to derive stellar mass-to-light ratios in the W1 and W2 bands. Utilizing observational data from the SAURON and ATLAS3D surveys, we demonstrate that these bands provide extremely simple, yet robust stellar mass tracers for dust free older stellar populations that are freed from many of the uncertainties common among optical estimators.

[en] Astrochemistry is rapidly becoming one of the most powerful tools to study the structure and evolution of the central kiloparsec in spiral nuclei. Imagining the distribution of quiescent ion-molecule, photon-dominated region (PDR) and shock chemistry permits the triggers of nuclear starbursts to be identified and the bursts subsequent feedback to be constrained. Two new chemical methods for identifying the evolutionary phase of the starbursts in IC 342, NGC 6946 and Maffei 2 are discussed. The first method is to use the HCO⁺/N₂H⁺ ratio to constrain the degree of penetration of dense clumps by UV radiation. The second determines the evolutionary phase by mapping the amount and physical conditions of the densest molecular component via multi-transition HC₃N observations. With the full capabilities of radio facilities such as the VLA and ALMA, probing the changing gas chemistry on sub arcsecond scales in external galaxies will very soon be routine.

[en] We present the Chandra discovery of soft diffuse X-ray emission in NGC 4151 (L_0.5-2keV ∼ 10³⁹ erg s^-1), extending ∼2 kpc from the active nucleus and filling in the cavity of the H I material. The best fit to the X-ray spectrum requires either a kT ∼ 0.25 keV thermal plasma or a photoionized component. In the thermal scenario, hot gas heated by the nuclear outflow would be confined by the thermal pressure of the H I gas and the dynamic pressure of inflowing neutral material in the galactic disk. In the case of photoionization, the nucleus must have experienced an Eddington limit outburst. For both scenarios, the active galactic nucleus (AGN)-host interaction in NGC 4151 must have occurred relatively recently (some 10⁴ yr ago). This very short timescale to the last episode of high activity phase may imply such outbursts occupy ∼>1% of AGN lifetime.

[en] This paper is the third in a series in which we present deep Chandra ACIS-S imaging spectroscopy of the Seyfert 1 galaxy NGC 4151, devoted to study its complex circumnuclear X-ray emission. Emission features in the soft X-ray spectrum of the bright extended emission (L_0.3-2keV ∼ 10⁴⁰ erg s^–1) at r > 130 pc (2'') are consistent with blended brighter O VII, O VIII, and Ne IX lines seen in the Chandra HETGS and XMM-Newton RGS spectra below 2 keV. We construct emission line images of these features and find good morphological correlations with the narrow-line region clouds mapped in [O III] λ5007. Self-consistent photoionization models provide good descriptions of the spectra of the large-scale emission, as well as resolved structures, supporting the dominant role of nuclear photoionization, although displacement of optical and X-ray features implies a more complex medium. Collisionally ionized emission is estimated to be ∼<12% of the extended emission. Presence of both low- and high-ionization spectral components and extended emission in the X-ray image perpendicular to the bicone indicates leakage of nuclear ionization, likely filtered through warm absorbers, instead of being blocked by a continuous obscuring torus. The ratios of [O III]/soft X-ray flux are approximately constant (∼15) for the 1.5 kpc radius spanned by these measurements, indicating similar relative contributions from the low- and high-ionization gas phases at different radial distances from the nucleus. If the [O III] and X-ray emission arise from a single photoionized medium, this further implies an outflow with a wind-like density profile. Using spatially resolved X-ray features, we estimate that the mass outflow rate in NGC 4151 is ∼2 M_☉ yr^–1 at 130 pc and the kinematic power of the ionized outflow is 1.7 × 10⁴¹ erg s^–1, approximately 0.3% of the bolometric luminosity of the active nucleus in NGC 4151.

[en] We present the first images of the J = 5-4 and J = 16-15 lines of the dense gas tracer, cyanoacetylene, HC₃N, in an external galaxy. The central 200 pc of the nearby star-forming spiral galaxy, IC 342, was mapped using the Very Large Array and the Plateau de Bure Interferometer. HC₃N(5-4) line emission is found across the nuclear mini-spiral, but is very weak toward the starburst site, the location of the strongest mid-IR and radio emission. The J = 16-15 and 10-9 lines are also faint near the large H II region complex, but are brighter relative to the 5-4 line, consistent with higher excitation. The brightest HC₃N emission is located in the northern arm of the nuclear mini-spiral, 100 pc away from the radio/IR source to the southwest of the nucleus. This location appears less affected by ultraviolet radiation and may represent a more embedded, earlier stage of star formation. HC₃N excitation temperatures are consistent with those determined from C¹⁸O; the gas is dense 10⁴ - 10⁵ cm^-3 and cool, T_k < 40 K. So as to not violate limits on the total H₂ mass determined from C¹⁸O, at least two dense components are required to model IC 342's giant molecular clouds. These observations suggest that HC₃N(5-4) is an excellent probe of the dense, quiescent gas in galaxies. The high excitation combined with faint emission toward the dense molecular gas at the starburst indicates that it currently lacks large masses of very dense gas. We propose a scenario where the starburst is being caught in the act of dispersing or destroying its dense gas in the presence of the large H II region. This explains the high star formation efficiency seen in the dense component. The little remaining dense gas appears to be in pressure equilibrium with the starburst H II region.

[en] We report on the imaging analysis of ∼200 ks sub-arcsecond resolution Chandra Advanced CCD Imaging Spectrometer (ACIS-S) observations of the nearby Seyfert 1 galaxy NGC 4151. Bright, structured soft X-ray emission is observed to extend from 30 pc to 1.3 kpc in the southwest from the nucleus, much farther than seen in earlier X-ray studies. The terminus of the northeastern X-ray emission is spatially coincident with a CO gas lane, where the outflow likely encounters dense gas in the host galactic disk. X-ray emission is also detected outside the boundaries of the ionization cone, which indicates that the gas there is not completely shielded from the nuclear continuum, as would be the case for a molecular torus collimating the bicone. In the central r < 200 pc region, the subpixel processing of the ACIS data recovers the morphological details on scales of <30 pc (<0.''5) first discovered in Chandra High Resolution Camera images. The X-ray emission is more absorbed toward the boundaries of the ionization cone, as well as perpendicular to the bicone along the direction of a putative torus in NGC 4151. The innermost region where X-ray emission shows the highest hardness ratio is spatially coincident with the near-infrared-resolved H₂ emission and dusty spirals we find in an Hubble Space Telescope V - H color image. The agreement between the observed H₂ line flux and the value predicted from X-ray-irradiated molecular cloud models supports photo-excitation by X-rays from the active nucleus as the origin of the H₂ line, although contribution from UV fluorescence or collisional excitation cannot be ruled out with current data. The discrepancy between the mass of cold molecular gas inferred from recent CO and near-infrared H₂ observations may be explained by the anomalous CO abundance in this X-ray-dominated region. The total H₂ mass derived from the X-ray observation agrees with the recent measurement by Storchi-Bergmann et al.

[en] We study the neutral hydrogen properties of a sample of 20 bulgeless disk galaxies (Sd-Sdm Hubble types), an interesting class that can be used to constrain galaxy formation and evolution, especially the role of mergers versus internal processes. Our sample is composed of nearby (within 32 Mpc), moderately inclined galaxies that bracket the circular velocity of 120 km s^-1, which has been found to be associated with a transition in dust scale heights in edge-on, late-type disks. Here, we present H I channel maps, line profiles, and integrated intensity maps. We also derive kinematic parameters, including the circular velocity, from rotation curve analyses and calculate the integrated H I flux and H I mass for each galaxy in the sample. Three of the 20 galaxies in our sample have kinematically distinct outer components with major axes that differ by 30⁰-90⁰ from the main disk. These distinct outer components may be due to a recent interaction, which would be somewhat surprising because the disks do not contain bulges. We will use the data products and derived properties in subsequent investigations into star formation and secular evolution in bulgeless disks with circular velocities above and below 120 km s^-1.

[en] We study the relation between the surface density of gas and star formation rate in 20 moderately inclined, bulgeless disk galaxies (Sd-Sdm Hubble types) using CO(1-0) data from the IRAM 30 m telescope, H I emission line data from the VLA/EVLA, Hα data from the MDM Observatory, and polycyclic aromatic hydrocarbon emission data derived from Spitzer IRAC observations. We specifically investigate the efficiency of star formation as a function of circular velocity (v_circ). Previous work found that the vertical dust structure and disk stability of edge-on, bulgeless disk galaxies transition from diffuse dust lanes with large scale heights and gravitationally stable disks at v_circ < 120 km s^–1 (M_* ∼< 10¹⁰ M_☉) to narrow dust lanes with small scale heights and gravitationally unstable disks at v_circ > 120 km s^–1. We find no transition in star formation efficiency (Σ_SFR/Σ_Hi+H2) at v_circ = 120 km s^–1 or at any other circular velocity probed by our sample (v_circ = 46-190 km s^–1). Contrary to previous work, we find no transition in disk stability at any circular velocity in our sample. Assuming our sample has the same dust structure transition as the edge-on sample, our results demonstrate that scale height differences in the cold interstellar medium of bulgeless disk galaxies do not significantly affect the molecular fraction or star formation efficiency. This may indicate that star formation is primarily affected by physical processes that act on smaller scales than the dust scale height, which lends support to local star formation models.

[en] We present Karl G. Jansky Very Large Array molecular line observations of the nearby starburst galaxy NGC 253, from SWAN, the Survey of Water and Ammonia in Nearby galaxies. SWAN is a molecular line survey at centimeter wavelengths designed to reveal the physical conditions of star-forming gas over a range of star-forming galaxies. NGC 253 has been observed in four 1 GHz bands from 21 to 36 GHz at 6″ ∼ 100 pc) spatial and 3.5 km s⁻¹ spectral resolution. In total we detect 19 transitions from 7 molecular and atomic species. We have targeted the metastable inversion transitions of ammonia (NH₃) from (1, 1) to (5, 5) and the (9, 9) line, the 22.2 GHz water (H₂O) ($6_{16}\text{--}{5}_{23}$) maser, and the 36.1 GHz methanol (CH₃OH) ($4_{-<!--\; ???\; -->1}\text{--}{3}_0$) maser. Using NH₃ as a thermometer, we present evidence for uniform heating over the central kpc of NGC 253. The molecular gas is best described by a two kinetic temperature model with a warm 130 K and a cooler 57 K component. A comparison of these observations with previous ALMA results suggests that the molecular gas is not heated in photon-dominated regions or shocks. It is possible that the gas is heated by turbulence or cosmic rays. In the galaxy center we find evidence for NH₃(3, 3) masers. Furthermore, we present velocities and luminosities of three water maser features related to the nuclear starburst. We partially resolve CH₃OH masers seen at the edges of the bright molecular emission, which coincides with expanding molecular superbubbles. This suggests that the masers are pumped by weak shocks in the bubble surfaces.