| 51. |
- Stanley, Flora, 1990, et al.
(författare)
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The mean star formation rates of unobscured QSOs: searching for evidence of suppressed or enhanced star formation
- 2017
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 472:2, s. 2221-2240
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the mean star formation rates (SFRs) in the host galaxies of similar to 3000 optically selected quasi-stellar objects (QSOs) from the Sloan Digital Sky Survey within the Herschel-ATLAS fields, and a radio-luminous subsample covering the redshift range of z = 0.2-2.5. Using Wide-field Infrared Survey Explorer (WISE) and Herschel photometry (12-500 mu m) we construct composite spectral energy distributions (SEDs) in bins of redshift and active galactic nucleus (AGN) luminosity. We perform SED fitting to measure the mean infrared luminosity due to star formation, removing the contamination from AGN emission. We find that the mean SFRs show a weak positive trend with increasing AGN luminosity. However, we demonstrate that the observed trend could be due to an increase in black hole (BH) mass (and a consequent increase of inferred stellar mass) with increasing AGN luminosity. We compare to a sample of X-ray selected AGN and find that the two populations have consistent mean SFRs when matched in AGN luminosity and redshift. On the basis of the available virial BH masses, and the evolving BH mass to stellar mass relationship, we find that the mean SFRs of our QSO sample are consistent with those of main sequence star-forming galaxies. Similarly the radio-luminous QSOs have mean SFRs that are consistent with both the overall QSO sample and with star-forming galaxies on the main sequence. In conclusion, on average QSOs reside on the main sequence of star-forming galaxies, and the observed positive trend between the mean SFRs and AGN luminosity can be attributed to BH mass and redshift dependencies.
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| 52. |
- Swinbank, A. M., et al.
(författare)
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An ALMA survey of sub-millimetre Galaxies in the Extended Chandra Deep Field South: the far-infrared properties of SMGs
- 2014
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 438:2, s. 1267-1287
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Tidskriftsartikel (refereegranskat)abstract
- We exploit Atacama Large Millimeter Array (ALMA) 870 mu m observations of sub-millimetre sources in the Extended Chandra Deep Field South to investigate the far-infrared properties of high-redshift sub-millimetre galaxies (SMGs). Using the precisely located 870 mu m ALMA positions of 99 SMGs, together with 24 mu m and radio imaging, we deblend the Herschel/SPIRE imaging to extract their far-infrared fluxes and colours. The median redshifts for ALMA LESS (ALESS) SMGs which are detected in at least two SPIRE bands increases with wavelength of the peak in their spectral energy distributions (SEDs), with z = 2.3 +/- 0.2, 2.5 +/- 0.3 and 3.5 +/- 0.5 for the 250, 350 and 500 mu m peakers, respectively. 34 ALESS SMGs do not have a >3 sigma counterpart at 250, 350 or 500 mu m. These galaxies have a median photometric redshift derived from the rest-frame UV-mid-infrared SEDs of z = 3.3 +/- 0.5, which is higher than the full ALESS SMG sample; z = 2.5 +/- 0.2. We estimate the far-infrared luminosities and characteristic dust temperature of each SMG, deriving L-IR = (3.0 +/- 0.3) x 10(12) L-circle dot (SFR = 300 +/- 30 M-circle dot yr(-1)) and T-d = 32 +/- 1 K. The characteristic dust temperature of these high-redshift SMGs is Delta T-d = 3-5K lower than comparably luminous galaxies at z = 0, reflecting the more extended star formation in these systems. We show that the contribution of S-870 mu m >= 1 mJy SMGs to the cosmic star formation budget is 20 per cent of the total over the redshift range z similar to 1-4. Adopting an appropriate gas-to-dust ratio, we estimate a typical molecular mass of the ALESS SMGs of M-H2 = (4.2 +/- 0.4) x 10(10) M-circle dot. Finally, we show that SMGs with S-870 mu m > 1 mJy (L-IR greater than or similar to 10(12) L-circle dot) contain similar to 10 per cent of the z similar to 2 volume-averaged H-2 mass density.
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| 53. |
- Swinbank, A. M., et al.
(författare)
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An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field-South: detection of C II at z=4.4
- 2012
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 427:2, s. 1066-1074
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Tidskriftsartikel (refereegranskat)abstract
- We present Atacama Large Millimeter Array (ALMA) 870-mu m (345-GHz) observations of two submillimetre galaxies (SMGs) drawn from an ALMA study of the 126 submillimetre sources from the LABOCA Extended Chandra Deep Field-South Survey (LESS). The ALMA data identify the counterparts to these previously unidentified submillimetre sources and serendipitously detect bright emission lines in their spectra which we show are most likely to be [CII] 157.74 mu m emission yielding redshifts of z = 4.42 and 4.44. This blind detection rate within the 7.5-GHz bandpass of ALMA is consistent with the previously derived photometric redshift distribution of SMGs and suggests a modest, but not dominant (less than or similar to 25 per cent), tail of 870-mu m selected SMGs at z greater than or similar to 4. We find that the ratio of L-[CII]/L-FIR in these SMGs is much higher than seen for similarly far-infrared-luminous galaxies at z similar to 0, which is attributed to the more extended gas reservoirs in these high-redshift ultraluminous infrared galaxies (ULIRGs). Indeed, in one system we show that the [C II] emission shows hints of extended emission on greater than or similar to 3 kpc scales. Finally, we use the volume probed by our ALMA survey to show that the bright end of the [CII] luminosity function evolves strongly between z = 0 and similar to 4.4, reflecting the increased interstellar medium cooling in galaxies as a result of their higher star formation rates. These observations demonstrate that even with short integrations, ALMA is able to detect the dominant fine-structure cooling lines from high-redshift ULIRGs, measure their energetics and spatially resolved properties and trace their evolution with redshift.
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| 54. |
- Umehata, Hideki, et al.
(författare)
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ALMA Observations of Ly alpha Blob 1 : Multiple Major Mergers and Widely Distributed Interstellar Media
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 918:2
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of a giant Lyα blob (LAB) in the SSA22 protocluster at z = 3.1, SSA22-LAB1, taken with the Atacama Large Millimeter/submillimeter Array. Dust continuum, along with [C ii] 158 μm and CO(4–3) line emission have been detected in LAB1, showing complex morphology and kinematics across a ∼100 kpc central region. Seven galaxies at z = 3.0987–3.1016 in the surroundings are identified in [C ii] and dust continuum emission, with two of them potential companions or tidal structures associated with the most massive galaxies. Spatially resolved [C ii] and infrared luminosity ratios for the widely distributed media (L[Cɪɪ]/LIR ≈ 10−2−10−3) suggest that the observed extended interstellar media are likely to have originated from star formation activity and the contribution from shocked gas is probably not dominant. LAB1 is found to harbor a total molecular gas mass Mmol = (8.7 ± 2.0) × 1010 M⊙, concentrated in the core region of the Lyα-emitting area. While (primarily obscured) star formation activity in the LAB1 core is one of the most plausible power sources for the Lyα emission, multiple major mergers found in the core may also play a role in making LAB1 exceptionally bright and extended in Lyα as a result of cooling radiation induced by gravitational interactions.
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| 55. |
- Umehata, Hideki, et al.
(författare)
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ALMA Reveals Strong [C II] Emission in a Galaxy Embedded in a Giant Ly alpha Blob at z=3.1
- 2017
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 834:2
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Tidskriftsartikel (refereegranskat)abstract
- We report the result from observations conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) to detect [C II] 158 mu m fine structure line emission from galaxies embedded in one of the most spectacular Ly alpha blobs (LABs) at z = 3.1, SSA22-LAB1. Of three dusty star-forming galaxies previously discovered by ALMA 860 mu m dust continuum survey toward SSA22-LAB1, we detected the [C II] line from one, LAB1-ALMA3 at z = 3.0993 +/- 0.0004. No line emission was detected, associated with the other ALMA continuum sources or from three rest-frame UV/optical selected z(spec) similar or equal to 3.1 galaxies within the field of view. For LAB1-ALMA3, we find relatively bright [C II] emission compared to the infrared luminosity (L-[C II]/LIR approximate to 0.01) and an extremely high [C II] 158 mu m and [N II] 205 mu m emission line ratio (L[C II]/L[N II] > 55). The relatively strong [C II] emission may be caused by abundant photodissociation regions and sub-solar metallicity, or by shock heating. The origin of the unusually strong [C II] emission could be causally related to the location within the giant LAB, although the relationship between extended Ly alpha emission and interstellar medium conditions of associated galaxies is yet to be understand.
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| 56. |
- Van de Steene, G. C., et al.
(författare)
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Herschel imaging of the dust in the Helix nebula (NGC 7293)
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 574
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Tidskriftsartikel (refereegranskat)abstract
- Aims. In our series of papers presenting the Herschel imaging of evolved planetary nebulae, we present images of the dust distribution in the Helix nebula (NGC 7293). Methods. Images at 70, 160, 250, 350, and 500 mu m were obtained with the PACS and SPIRE instruments on board the Herschel satellite. Results. The broadband maps show the dust distribution over the main Helix nebula to be u npy and predominantly present in the barrel wall. We determined the spectral energy distribution of the main nebula in a consistent way using Herschel. IRAS. and Planck flux values, The emissivity index of beta = 0.99 +/- 0.09, in combination with the carbon rich molecular chemistry of the nebula, indicates that the dust consists mainly of amorphous carbon. The dust excess emission from the central star disk is detected at 70 pm and the flux measurement agrees with previous measurement. We present the temperature and dust column density maps. The total dust mass across the Helix nebula (without its halo) is determined to be 3.5 x 10(-3) M-circle dot at a distance of 216 pc. The temperature map shows dust temperatures between 22 K and 42 K, which is similar to the kinetic temperature of the molecular gas, confirming that the dust and gas co exist in high density clumps. Archived images are used to compare the location of the dust emission in the far infrared (Herschel) with the ionized (GALEX and H-beta) and molecular (H-2) component. The different emission components are consistent with the Helix consisting of a thick walled barrel-like structure inclined to the line of sight. The radiation field decreases rapidly through the barrel wall.
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| 57. |
- van der Wiel, M. H. D., et al.
(författare)
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Signatures of warm carbon monoxide in protoplanetary discs observed with Herschel SPIRE
- 2014
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 444:4, s. 3911-3925
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Tidskriftsartikel (refereegranskat)abstract
- Molecular gas constitutes the dominant mass component of protoplanetary discs. To date, these sources have not been studied comprehensively at the longest far-infrared and shortest submillimetre wavelengths. This paper presents Herschel SPIRE FTS spectroscopic observations towards 18 protoplanetary discs, covering the entire 450-1540 GHz (666-195 mu m) range at upsilon/Delta upsilon approximate to 400-1300. The spectra reveal clear detections of the dust continuum and, in six targets, a significant amount of spectral line emission primarily attributable to (CO)-C-12 rotational lines. Other targets exhibit little to no detectable spectral lines. Low signal-to-noise detections also include signatures from (CO)-C-13, [C I] and HCN. For completeness, we present upper limits of non-detected lines in all targets, including low-energy transitions of H2O and CH+ molecules. The 10 (CO)-C-12 lines that fall within the SPIRE FTS bands trace energy levels of similar to 50-500 K. Combined with lower and higher energy lines from the literature, we compare the CO rotational line energy distribution with detailed physical-chemical models, for sources where these are available and published. Our (CO)-C-13 line detections in the disc around Herbig Be star HD 100546 exceed, by factors of similar to 10-30, the values predicted by a model that matches a wealth of other observational constraints, including the SPIRE (CO)-C-12 ladder. To explain the observed (CO)-C-12/(CO)-C-13 ratio, it may be necessary to consider the combined effects of optical depth and isotope selective (photo) chemical processes. Considering the full sample of 18 objects, we find that the strongest line emission is observed in discs around Herbig Ae/Be stars, although not all show line emission. In addition, two of the six T Tauri objects exhibit detectable (CO)-C-12 lines in the SPIRE range.
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| 58. |
- van Hoof, P. A. M., et al.
(författare)
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A Herschel study of NGC 650
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 560, s. A7-
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Tidskriftsartikel (refereegranskat)abstract
- As part of the Herschel guaranteed time key project Mass loss of Evolved StarS (MESS) we have imaged a sample of planetary nebulae. In this paper we present the Photodetector Array Camera and Spectrometer (PACS) and Spectral and Photometric Imaging Receiver (SPIRE) images of the classical bipolar planetary nebula NGC 650. We used these images to derive a temperature map of the dust. We also constructed a photoionization and dust radiative transfer model using the spectral synthesis code Cloudy. To constrain this model, we used the PACS and SPIRE fluxes and combined them with hitherto unpublished International Ultraviolet Explorer (IUE) and Spitzer InfraRed Spectrograph (IRS) spectra as well as various other data from the literature. A temperature map combined with a photoionization model were used to study various aspects of the central star, the nebula, and in particular the dust grains in the nebula. The central star parameters are determined to be T-eff = 208 kK and L = 261 L-circle dot assuming a distance of 1200 pc. The stellar temperature is much higher than previously published values. We confirm that the nebula is carbon-rich with a C/O ratio of 2.1. The nebular abundances are typical for a type IIa planetary nebula. With the photoionization model we determined that the grains in the ionized nebula are large (assuming single-sized grains, they would have a radius of 0.15 mu m). Most likely these large grains were inherited from the asymptotic giant branch phase. The PACS 70/160 mu m temperature map shows evidence of two radiation components heating the grains. The first component is direct emission from the central star, while the second component is diffuse emission from the ionized gas (mainly Ly alpha). We show that previous suggestions of a photo-dissociation region surrounding the ionized region are incorrect. The neutral material resides in dense clumps inside the ionized region. These may also harbor stochastically heated very small grains in addition to the large grains.
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| 59. |
- van Hoof, P. A. M., et al.
(författare)
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Herschel images of NGC 6720 : H-2 formation on dust grains
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518, s. L137-
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Tidskriftsartikel (refereegranskat)abstract
- Herschel PACS and SPIRE images have been obtained of NGC 6720 (the Ring nebula). This is an evolved planetary nebula with a central star that is currently on the cooling track, due to which the outer parts of the nebula are recombining. From the PACS and SPIRE images we conclude that there is a striking resemblance between the dust distribution and the H-2 emission, which appears to be observational evidence that H-2 forms on grain surfaces. We have developed a photoionization model of the nebula with the Cloudy code which we used to determine the physical conditions of the dust and investigate possible formation scenarios for the H-2. We conclude that the most plausible scenario is that the H-2 resides in high density knots which were formed after the recombination of the gas started when the central star entered the cooling track. Hydrodynamical instabilities due to the unusually low temperature of the recombining gas are proposed as a mechanism for forming the knots. H-2 formation in the knots is expected to be substantial after the central star underwent a strong drop in luminosity about one to two thousand years ago, and may still be ongoing at this moment, depending on the density of the knots and the properties of the grains in the knots.
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| 60. |
- Vandenbussche, B., et al.
(författare)
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The beta Pictoris disk imaged by Herschel PACS and SPIRE
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 518:Article Number: L133
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Tidskriftsartikel (refereegranskat)abstract
- We obtained Herschel PACS and SPIRE images of the thermal emission of the debris disk around the A5V star beta Pic. The disk is well resolved in the PACS filters at 70, 100, and 160 mu m. The surface brightness profiles between 70 and 160 mu m show no significant asymmetries along the disk, and are compatible with 90% of the emission between 70 and 160 mu m originating in a region closer than 200 AU to the star. Although only marginally resolving the debris disk, the maps obtained in the SPIRE 250-500 mu m filters provide full-disk photometry, completing the SED over a few octaves in wavelength that had been previously inaccessible. The small far-infrared spectral index (beta = 0.34) indicates that the grain size distribution in the inner disk (
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