Optical integral field spectroscopy of intermediate redshift infrared bright galaxies
Monthly Notices of the Royal Astronomical Societ Oxford University Press 486:4 (2019) 5621-5645
Abstract:
The extreme infrared (IR) luminosity of local luminous and ultraluminous IR galaxies (U/LIRGs; 11 < logLIR/L < 12 and logLIR/L > 12, respectively) is mainly powered by star formation processes triggered by mergers or interactions. While U/LIRGs are rare locally, at z > 1, they become more common, dominate the star formation rate (SFR) density, and a fraction of them are found to be normal disc galaxies. Therefore, there must be an evolution of the mechanism triggering these intense starbursts with redshift. To investigate this evolution, we present new optical SWIFT integral field spectroscopic H α + [N II] observations of a sample of nine intermediate-z (0.2Torus model properties of an ultra-hard X-ray selected sample of Seyfert galaxies
Monthly Notices of the Royal Astronomical Society Oxford University Press 486:4 (2019) 4917-4935
Abstract:
We characterize for the first time the torus properties of an ultra-hard X-ray (14–195 keV) volume-limited (DL < 40 Mpc) sample of 24 Seyfert (Sy) galaxies (BCS40 sample). The sample was selected from the Swift/BAT nine-month catalogue. We use high angular resolution nuclear infrared (IR) photometry and N-band spectroscopy, the CLUMPY torus models and a Bayesian tool to characterize the properties of the nuclear dust. In the case of the Sy1s, we estimate the accretion disc contribution to the subarcsecond resolution nuclear IR SEDs (∼0.4 arcsec) which is, on average, 46 ± 28, 23 ± 13, and 11 ± 5 per cent in the J, H, and K bands, respectively. This indicates that the accretion disc templates that assume a steep fall for longer wavelengths than 1 μm might underestimate its contribution to the near-IR emission. Using both optical (broad versus narrow lines) and X-ray (unabsorbed versus absorbed) classifications, we compare the global posterior distribution of the torus model parameters. We confirm that Sy2s have larger values of the torus covering factor (CT ∼ 0.95) than Sy1s (CT ∼ 0.65) in our volume-limited Seyfert sample. These findings are independent of whether we use an optical or X-ray classification. We find that the torus covering factor remains essentially constant within the errors in our luminosity range and there is no clear dependence with the Eddington ratio. Finally, we find tentative evidence that even an ultra-hard X-ray selection is missing a significant fraction of highly absorbed type 2 sources with very high covering factor tori.PAHs as tracers of the molecular gas in star-forming galaxies
Monthly Notices of the Royal Astronomical Society Oxford University Press 482:2 (2018) 1618-1633
Abstract:
We combine new CO(1–0) line observations of 24 intermediate redshift galaxies (0.03 < z < 0.28) along with literature data of galaxies at 0 < z < 4 to explore scaling relations between the dust and gas content using polycyclic aromatic hydrocarbon (PAH) 6.2 μm (L6.2), CO (L′CO), and infrared (LIR) luminosities for a wide range of redshifts and physical environments. Our analysis confirms the existence of a universal L6.2–L′CO correlation followed by normal star-forming galaxies (SFGs) and starbursts (SBs) at all redshifts. This relation is also followed by local ultraluminous infrared galaxies that appear as outliers in the L6.2–LIR and LIR–L′CO relations defined by normal SFGs. The emerging tight (σ ≈ 0.26 dex) and linear (α = 1.03) relation between L6.2 and L′CO indicates a L6.2 to molecular gas (MH2) conversion factor of α6.2 = MH2/L6.2 = (2.7 ± 1.3) × αCO, where αCO is the L′CO to MH2 conversion factor. We also find that on galaxy integrated scales, PAH emission is better correlated with cold rather than with warm dust emission, suggesting that PAHs are associated with the diffuse cold dust, which is another proxy for MH2. Focusing on normal SFGs among our sample, we employ the dust continuum emission to derive MH2 estimates and find a constant MH2/L6.2 ratio of α6.2 = 12.3 M⊙/L⊙(σ ≈ 0.3 dex). This ratio is in excellent agreement with the L′CO-based MH2/L6.2 values for αCO = 4.5 M⊙/(K km s−1 pc2) which is typical of normal SFGs. We propose that the presented L6.2–L′CO and L6.2–MH2 relations will serve as useful tools for the determination of the physical properties of high-z SFGs, for which PAH emission will be routinely detected by the James Webb Space Telescope.Spatially resolved cold molecular outflows in ULIRGs
Astronomy and Astrophysics Springer Nature (2018)
Abstract:
We present new CO(2-1) observations of 3 low-z (~350 Mpc) ULIRG systems (6 nuclei) observed with ALMA at high-spatial resolution (~500 pc). We detect massive cold molecular gas outflows in 5 out of 6 nuclei (0.3-5)x10^8 Msun. These outflows are spatially resolved with deprojected radii of 0.25-1 kpc although high-velocity molecular gas is detected up to ~0.5-1.8 kpc (1-6 kpc deprojected). The mass outflow rates are 12-400 Msun/yr and the inclination corrected average velocity of the outflowing gas 350-550 km/s (v_max = 500-900 km/s). The origin of these outflows can be explained by the nuclear starbursts although the contribution of an obscured AGN can not be completely ruled out. The position angle (PA) of the outflowing gas along the kinematic minor axis of the nuclear molecular disk suggests that the outflow axis is perpendicular to the disk for three of these outflows. Only in one case, the outflow PA is clearly not along the kinematic minor axis. The outflow depletion times are 15-80 Myr which are slightly shorter than the star-formation (SF) depletion times (30-80 Myr). However, we estimate that only 15-30% of the outflowing gas will escape the gravitational potential of the nucleus. The majority of the outflowing gas will return to the disk after 5-10 Myr and become available to form new stars. Therefore, these outflows will not likely quench the nuclear starbursts. These outflows would be consistent with being driven by radiation pressure (momentum-driven) only if the coupling between radiation and dust increases with increasing SF rates. This can be achieved if the dust optical depth is higher in objects with higher SF. The relatively small sizes (<1 kpc) and dynamical times (<3 Myr) of the cold molecular outflows suggests that molecular gas cannot survive longer in the outflow environment or that it cannot form efficiently beyond these distances or times. (Abridged)Resolving the Nuclear Obscuring Disk in the Compton-thick Seyfert Galaxy NGC 5643 with ALMA
ASTROPHYSICAL JOURNAL 859:2 (2018) ARTN 144