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Andrew Humphrey (2011)
We have analysed the spatially integrated kinematic properties of the ionized gas within the inner r ≲ few kpc in 13 optically selected SDSS type 2 quasars at z ∼ 0.3–0.6, using the [O 🇮🇮🇮]λλ4959,5007 lines. The line profiles show a significant asymmetry in 11 objects. There is a clear preference for blue asymmetries, which are found in 9/13 quasars at 10 per cent intensity level. In coherence with studies on other types of active and non active galaxies, we propose that the asymmetries are produced by outflows where differential dust extinction is at work. This scenario is favoured by other results we find: in addition to quiescent ambient gas, whose kinematic properties are consistent with gravitational motions, we have discovered highly perturbed gas in all objects. This gas emits very broad lines (R = FWHM[O 🇮🇮🇮]/FWHMstars ≳2).While the quiescent gas shows small or null velocity shifts relative to the systemic velocity, the highly perturbed gas trends to show larger shifts which, moreover, are blueshifts in general. Within a given object, the most perturbed gas trends to have the largest blueshift as well. All together support that the perturbed gas, which is responsible for the blue asymmetries of the line profiles, is outflowing. The outflowing gas is located within the quasar ionization cones, in the narrow line region. The relative contribution of the outflowing gas to the total [O 🇮🇮🇮] line flux varies from object to object in the range ∼10–70 per cent. An anticorrelation is found such that, the more perturbed the outflowing gas is, the lower its relative contribution is to the total [O 🇮🇮🇮] flux. This suggests that outflows with more perturbed kinematics involve a smaller fraction of the total mass of ionized gas. Although some bias affects the sample, we argue that ionized gas outflows are a common phenomenon in optically selected type 2 quasars at 0.3≲ z ≲ 0.6.
Ivanio Puerari (2010)
Power spectra of Large Magellanic Cloud (LMC) emission at 24, 70 and 160 μm observed with the Spitzer Space Telescope have a two-component power-law structure with a shallow slope of −1.6 at low wavenumber, 𝑘, and a steep slope of −2.9 at high 𝑘. The break occurs at 𝑘⁻¹~100− 200 pc, which is interpreted as the line-of-sight thickness of the LMC disk. The slopes are slightly steeper for longer wavelengths, suggesting the cooler dust emission is smoother than the hot emission. The power spectrum covers ~ 3.5 orders of magnitude and the break in the slope is in the middle of this range on a logarithmic scale. Large-scale driving from galactic and extragalactic processes, including disk self-gravity, spiral waves and bars, presumably cause the low- 𝑘 structure in what is effectively a two-dimensional geometry. Small-scale driving from stellar processes and shocks cause the high-k structure in a 3D geometry. This transition in dimensionality corresponds to the observed change in power spectrum slope. A companion paper models the observed power-law with a self-gravitating hydrodynamics simulation of a galaxy like the LMC.
IVANIO PUERARI (2009)
Fourier transform power spectra of azimuthal scans in 33 galaxies imaged with the Infrared Array Camera on the Spitzer Space Telescope show an approximate power-law structure over a wide range of wavenumbers with a gradual steepening from 3.6 or 4.5μm to 8.0 μm, in the order of an increasing contribution from gas and dust. At radii with active star formation, the average of the slopes of the 8μm power spectra at intermédiate spatial frequencies is about the same for all galaxies, independent of spiral arm morphology. These power spectra are reminiscent of turbulence, although the 8μm slopes, averaging −2.0, are slightly steeper tan expected (−1.7). Reconstructed images using only these intermediate spatial frequencies at 4.5 μm show aging star complexes distorted by shear. These sheared features illustrate the transition from a hierarchical structure during star formation into azimuthal star streams like the Pleiades moving group in the Solar neighborhood. This is the first time that young star streams have been observed in spiral galaxies other than the Milky Way.
We present wide-field 1.1mm continuum imaging of the nearby spiral galaxy M 33, conducted with the AzTEC bolometer camera on ASTE.We show that the 1.1mm flux traces the distribution of dust with T ~ 20K. Combined with far-infrared imaging at 160µm, we derived the dust temperature distribution out to a galactic radius of ~7 kpc with a spatial resolution of ~150 pc. Although the 1.1mm flux was observed predominantly near star-forming regions, we found a smooth radial temperature gradient declining from ~20K to ~13K consistent with recent results from the Herschel satellite. Further comparisons of individual regions show a strong correlation between the cold dust temperature and the KS band brightness, but not with the ionizing flux. The observed results imply that the dominant heating source of cold dust at few hundred parsec scales is due to non-OB stars, even when associated with star-forming regions.
David Hughes (2012)
The James Clerk Maxwell Telescope Nearby Galaxies Legacy Survey (NGLS) comprises an Hi-selected sample of 155 galaxies spanning all morphological types with distances less than 25 Mpc. We describe the scientific goals of the survey, the sample selection, and the observing strategy. We also present an atlas and analysis of the CO J=3-2 maps for the 47 galaxies in the NGLS which are also part of the Spitzer Infrared Nearby Galaxies Survey.We find a wide range of molecular gas mass fractions in the galaxies in this sample and explore the correlation of the far-infrared luminosity, which traces star formation, with the CO luminosity, which traces the molecular gas mass. By comparing the NGLS data with merging galaxies at low and high redshift which have also been observed in the CO J=3-2 line, we show that the correlation of far-infrared and CO luminosity shows a significant trend with luminosity. This trend is consistent with a molecular gas depletion time which is more than an order of mag- nitude faster in the merger galaxies than in nearby normal galaxies. We also find a strong correlation of the LFIR/LCO(3-2) ratio with the atomic to molecular gas mass ratio. This correlation suggests that some of the far-infrared emission originates from dust associated with atomic gas and that its contribution is particularly important in galaxies where most of the gas is in the atomic phase.
Galaxies: ISM Galaxies: kinematics and dynamics Galaxies: spiral ISM: molecules Stars: formation CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA MEDIO INTERPLANETARIO SATÉLITES SATÉLITES
We report on the detection of an extremely bright (∼37 mJy at 1100 μm and ∼91 mJy at 880 μm) submillimetre galaxy (SMG), AzTEC-ASTE-SXDF1100.001 (hereafter referred to as SXDF1100.001 or Orochi), discovered in the 1100 μm observations of the Subaru/XMM–Newton Deep Field using AzTEC on ASTE. Subsequent CARMA 1300-μm and SMA 880-μm observations successfully pinpoint the location of Orochi and suggest that it has two components, one extended [full width at half-maximum (FWHM) of ∼4 arcsec] and one compact (unresolved). Z-Spec on CSO has also been used to obtain a wide-band spectrum from 190 to 308 GHz, although no significant emission/absorption lines were found. The derived upper limit to the line-to-continuum flux ratio is 0.1–0.3 (2σ) across the Z-Spec band.
Based on the analysis of the derived spectral energy distribution from optical to radio wavelengths of possible counterparts near the SMA/CARMA peak position, we suggest that Orochi is a lensed, optically dark SMG lying at z ∼ 3.4 behind a foreground, optically visible
(but red) galaxy at z ∼ 1.4. The deduced apparent (i.e., no correction for magnification) infrared luminosity (LIR) and star formation rate (SFR) are 6 × 10¹³ Lꙩ and 11 000Mꙩ yr⁻¹, respectively, assuming that the LIR is dominated by star formation. These values suggest that
Orochi will consume its gas reservoir within a short time-scale (3 × 10⁷ yr), which is indeed comparable to those in extreme starbursts like the centres of local ultraluminous infrared galaxies (ULIRGs).
We combine new ASTE/AzTEC 1.1 mm maps of the galaxy pair NGC 1512/1510 with archival Spitzer IRAC and MIPS images covering the wavelength range 3.6–160 μm from the SINGS project. The availability of the 1.1 mm map enables us to measure the long–wavelength tail of the dust emission in each galaxy, and in sub–galactic regions in NGC 1512, and to derive accurate dust masses. The two galaxies form a pair consisting of a large, high–metallicity spiral (NGC 1512) and a low metallicity, blue compact dwarf (NGC 1510), which we use to compare similarities and contrast differences. Using the models of Draine & Li (2007), the derived total dust masses are (2.4±0.6)×10⁷ M⊙ and (1.7±3.6)×10⁵ M⊙ for NGC 1512 and NGC 1510, respectively. The derived ratio of dust mass to H 🇮 gas mass for the galaxy pair, Md/MH🇭🇮 ∼0.0034, is much lower (by at least a factor of 3) than expected, as previously found by Draine et al. (2007). In contrast, regions within NGC 1512, specifically the central region and the arms, do not show such unusually low Md/M🇭🇮 ratios; furthermore, the dust– to–gas ratio is within expectations for NGC 1510. These results suggest that a fraction of the H 🇮 included in the determination of the Md/M🇭🇮 ratio of the NGC 1512/NGC 1510 pair is not associated with the star forming disks/regions of either galaxy. Using the dust masses derived from the models of Draine & Li (2007) as reference, we perform simple two–temperature modified–blackbody fits to the far–infrared/mm data of the two galaxies and the sub–regions of NGC 1512, in order to derive and compare the dust masses associated with warm and cool dust temperature components. As generally expected, the warm dust temperature of the low–metallicity, low–mass NGC 1510 (T w⁓36 K) is substantially higher than the corresponding warm temperature of the high–metallicity spiral NGC 1512 (Tw⁓24 K). In both galaxies (albeit with a large uncertainty for NGC 1510), our fits indicate that a substantial fraction (>93%) of the total dust mass is in a cool dust component, with temperatures ⁓14–16 K for NGC 1512 and ⁓15–24 K for NGC 1510. This result is similar to what is determined for a few other nearby galaxies.
Galaxies: individual (NGC 1510, NGC 1512) Galaxies: ISM Galaxies: starburst (ISM:) dust, extinction CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA
OLGA MERCEDES VEGA CASANOVA (2011)
Context. A large fraction of early-type galaxies (ETGs) shows emission lines in their optical spectra, mostly with LINER characteristics. Despite the number of studies, the nature of the ionization mechanisms is still debated. Many ETGs also show several signs of rejuvenation episodes. Aims. We aim to investigate the ionization mechanisms and the physical processes of a sample of ETGs using mid-infrared spectra. Methods. We present here low resolution Spitzer-IRS spectra of 40 ETGs, 18 of which from our proposed Cycle 3 observations, selected from a sample of 65 ETGs showing emission lines in their optical spectra. We homogeneously extract the mid-infrared (MIR) spectra, and after the proper subtraction of a “passive” ETG template, we derive the intensity of the ionic and molecular lines and of the polycyclic aromatic hydrocarbon (PAH) emission features. We use MIR diagnostic diagrams to investigate the powering mechanisms of the ionized gas. Results. The mid-infrared spectra of early-type galaxies show a variety of spectral characteristics. We empirically sub-divide the sample into five classes of spectra with common characteristics. Class-0, accounting for 20% of the sample, are purely passive ETGs with neither emission lines nor PAH features. Class-1 show emission lines but no PAH features, and account for 17.5% of the sample. Class-2, in which 50% of the ETGs are found, as well as having emission lines, show PAH features with unusual ratios, e.g. 7.7 μm/11.3 μm ≤ 2.3. Class-3 objects (7.5% of the sample) have emission lines and PAH features with ratios typical of star-forming galaxies. Class-4, containing only 5% of the ETGs, is dominated by a hot dust continuum. The diagnostic diagram [Ne 🇮🇮🇮]15.55 μm/[Ne 🇮🇮]12.8 μm vs. [S🇮🇮🇮]33.48 μm/[Si 🇮🇮]34.82 μm, is used to investigate the different mechanisms ionizing the gas. According to the above diagram most of our ETGs contain gas ionized via either AGN-like or shock phenomena, or both. Conclusions. Most of the spectra in the present sample are classified as LINERs in the optical window. The proposed MIR spectral classes show unambiguously the manifold of the physical processes and ionization mechanisms, from star formation, low level AGN activity, to shocks (H₂), present in LINER nuclei.
Galaxies: elliptical and lenticular, cD Galaxies: fundamental parameters Galaxies: evolution Galaxies: ISM CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA
GUILLERMO TENORIO TAGLE (2009)
We present Integral Field Unit GMOS-IFU data of the compact HII Galaxy UM 408, obtained at Gemini South telescope, in order to derive the spatial distribution of emission lines and line ratios, kinematics, plasma parameters, and oxygen abundances as well the integrated properties over an area of 3′′×4′′.4 equivalent with ∼750 × 1100 pc located in the central part of the galaxy. The starburst in this area is resolved into two giant regions of about 1′′.5 and 1′′ (∼375 and ∼250 pc) diameter, respectively and separated 1.5-2′′ (∼500 pc). The extinction distribution concentrate its highest values close but not coincident with the maxima of Hα emission around each one of the detected regions. This indicates that the dust has been displaced from the exciting clusters by the action of their stellar winds. The ages of these two regions, estimated using Hβ equivalent widths, suggest that they are coeval events of ∼5 Myr with stellar masses of ∼10⁴M⊙. We have also used [OIII]/Hβ and [SII]/Hα ratio maps to explore the excitation mechanisms in this galaxy. Comparing the data points with theoretical diagnostic models, we found that all of them are consistent with excitation by photoionization by massive stars. The Hα emission line was used to measure the radial velocity and velocity dispersion. The heliocentric radial velocity shows an apparent systemic motion where the east part of the galaxy is blueshifted, while the west part is redshifted, with a relative motion of ∼ 10 km s⁻¹. The velocity dispersion map shows supersonic values typical for extragalactic HII regions. Oxygen abundances were calculated from the [OIII]λλ4959,5007/[OIII]λ4363 ratios. We derived an integrated oxygen abundance of 12+log(O/H)=7.87 summing over all spaxels in our field of view. An average value of 12+log(O/H)=7.77 and a difference of Δ(O/H)=0.47 between the minimum and maximum values (7.58±0.06-8.05±0.04) were found, considering all data points where the oxygen abundance was measured. The spatial distribution of oxygen abundance does not show any significant gradient across the galaxy. On the other hand, the bulk of data points are lying in a region of ±2σ dispersion (with σ=0.1 dex) around the average value, confirming that this compact HII galaxy as other previously studied dwarf irregular galaxies is chemically homogeneous.
ROBERTO GIOVANNI TERLEVICH (2012)
We use the self-consistent model technique developed by Martín-Manjón et al. That combines the chemical evolution with stellar population synthesis and photoionization codes, to study the star formation scenarios capable of reproducing the observed properties of star-forming galaxies. The comparison of our model results with a data base of HII galaxies shows that the observed spectra and colours of the present burst and the older underlying population are reproduced by models in a bursting scenario with star formation efficiency involving close to 20 per cent of the total mass of gas, and interburst times longer than 100 Myr, and more probably around 1 Gyr. Other modes like gasping and continuous star formation are not favoured.
HII regions Galaxies: dwarf Galaxies: evolution Galaxies: ISM Galaxies: starburst Galaxies: star formation CIENCIAS FÍSICO MATEMÁTICAS Y CIENCIAS DE LA TIERRA ASTRONOMÍA Y ASTROFÍSICA ASTRONOMÍA Y ASTROFÍSICA