| 1. |
- André, Ph., et al.
(author)
-
Probing the cold magnetised Universe with SPICA-POL (B-BOP)
- 2019
-
In: Publications Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 36
-
Research review (peer-reviewed)abstract
- Space Infrared Telescope for Cosmology and Astrophysics (SPICA), the cryogenic infrared space telescope recently pre-selected for a 'Phase A' concept study as one of the three remaining candidates for European Space Agency (ESA's) fifth medium class (M5) mission, is foreseen to include a far-infrared polarimetric imager [SPICA-POL, now called B-fields with BOlometers and Polarizers (B-BOP)], which would offer a unique opportunity to resolve major issues in our understanding of the nearby, cold magnetised Universe. This paper presents an overview of the main science drivers for B-BOP, including high dynamic range polarimetric imaging of the cold interstellar medium (ISM) in both our Milky Way and nearby galaxies. Thanks to a cooled telescope, B-BOP will deliver wide-field 100-350 mu m images of linearly polarised dust emission in Stokes Q and U with a resolution, signal-to-noise ratio, and both intensity and spatial dynamic ranges comparable to those achieved by Herschel images of the cold ISM in total intensity (Stokes I). The B-BOP 200 mu m images will also have a factor similar to 30 higher resolution than Planck polarisation data. This will make B-BOP a unique tool for characterising the statistical properties of the magnetised ISM and probing the role of magnetic fields in the formation and evolution of the interstellar web of dusty molecular filaments giving birth to most stars in our Galaxy. B-BOP will also be a powerful instrument for studying the magnetism of nearby galaxies and testing Galactic dynamo models, constraining the physics of dust grain alignment, informing the problem of the interaction of cosmic rays with molecular clouds, tracing magnetic fields in the inner layers of protoplanetary disks, and monitoring accretion bursts in embedded protostars.
|
|
| 2. |
- Grazian, A., et al.
(author)
-
Lyman continuum escape fraction of faint galaxies at z similar to 3.3 in the CANDELS/GOODS-North, EGS, and COSMOS fields with LBC
- 2017
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 602
-
Journal article (peer-reviewed)abstract
- Context. The reionization of the Universe is one of the most important topics of present-day astrophysical research. The most plausible candidates for the reionization process are star-forming galaxies, which according to the predictions of the majority of the theoretical and semi-analytical models should dominate the H I ionizing background at z greater than or similar to 3. Aims. We measure the Lyman continuum escape fraction, which is one of the key parameters used to compute the contribution of star-forming galaxies to the UV background. It provides the ratio between the photons produced at lambda <= 912 angstrom rest-frame and those that are able to reach the inter-galactic medium, i.e. that are not absorbed by the neutral hydrogen or by the dust of the galaxy's inter-stellar medium. Methods. We used ultra-deep U-band imaging (U = 30.2 mag at 1 sigma) from Large Binocular Camera at the Large Binocular Telescope (LBC/LBT) in the CANDELS/GOODS-North field and deep imaging in the COSMOS and EGS fields in order to estimate the Lyman continuum escape fraction of 69 star-forming galaxies with secure spectroscopic redshifts at 3.27 <= z <= 3.40 to faint magnitude limits (L = 0.2L*, or equivalently M-1500 similar to -19). The narrow redshift range implies that the LBC U-band filter exclusively samples the lambda <= 912 angstrom rest-frame wavelengths. Results. We measured through stacks a stringent upper limit (<1.7% at 1 sigma) for the relative escape fraction of H I ionizing photons from bright galaxies (L > L*), while for the faint population (L = 0.2L*) the limit to the escape fraction is less than or similar to 10%. We computed the contribution of star-forming galaxies to the observed UV background at z similar to 3 and find that it is not sufficient to keep the Universe ionized at these redshifts unless their escape fraction increases significantly (>= 10%) at low luminosities (M-1500 >= -19). Conclusions. We compare our results on the Lyman continuum escape fraction of high-z galaxies with recent estimates in the literature, and discuss future prospects to shed light on the end of the Dark Ages. In the future, strong gravitational lensing will be fundamental in order to measure the Lyman continuum escape fraction down to faint magnitudes (M-1500 similar to -16) that are inaccessible with the present instrumentation on blank fields. These results will be important in order to quantify the role of faint galaxies to the reionization budget.
|
|
| 3. |
- Cormier, D., et al.
(author)
-
The molecular gas reservoir of 6 low-metallicity galaxies from the Herschel Dwarf Galaxy Survey A ground-based follow-up survey of CO(1-0), CO(2-1), and CO(3-2)
- 2014
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 564
-
Journal article (peer-reviewed)abstract
- Context. Observations of nearby starburst and spiral galaxies have revealed that molecular gas is the driver of star formation. However, some nearby low-metallicity dwarf galaxies are actively forming stars, but CO, the most common tracer of this reservoir, is faint, leaving us with a puzzle about how star formation proceeds in these environments. Aims. We aim to quantify the molecular gas reservoir in a subset of 6 galaxies from the Herschel Dwarf Galaxy Survey with newly acquired CO data and to link this reservoir to the observed star formation activity. Methods. We present CO(1-0), CO(2-1), and CO(3-2) observations obtained at the ATNE Mopra 22-m, APEX, and IRAM 30-m telescopes, as well as [CII] 157 mu m and [OI] 63 mu m observations obtained with the Herschel/PACS spectrometer in the 6 low-metallicity dwarf galaxies: Haro 11, Mrk 1089, Mrk 930, NGC 4861, NGC 625, and UM 311. We derived their molecular gas masses from several methods, including using the CO-to-H-2 conversion factor X-CO (both Galactic and metallicity-scaled values) and dust measurements. The molecular and atomic gas reservoirs were compared to the star formation activity. We also constrained the physical conditions of the molecular clouds using the non-LTE code RADEX and the spectral synthesis code Cloudy. Results. We detect CO in 5 of the 6 galaxies, including first detections in Haro 11 (Z similar to 0.4 Z(circle dot)), Mrk 930 (0.2 Z(circle dot)), and UM 311 (0.5 Z(circle dot)), but CO remains undetected in NGC 4861 (0.2 Z(circle dot)). The CO luminosities are low, while [CII] is bright in these galaxies, resulting in [CII]/CO(1-0) >= 10 000. Our dwarf galaxies are in relatively good agreement with the Schmidt-Kennicutt relation for total gas. They show short molecular depletion timescales, even when considering metallicity-scaled X-CO factors. Those galaxies are dominated by their HI gas, except Haro 11, which has high star formation efficiency and is dominated by ionized and molecular gas. We determine the mass of each ISM phase in Haro 11 using Cloudy and estimate an equivalent X-CO factor that is 10 times higher than the Galactic value. Overall, our results confirm the emerging picture that CO suffers from significant selective photodissociation in low-metallicity dwarf galaxies.
|
|
| 4. |
- Drouart, Guillaume, 1987, et al.
(author)
-
Rapidly growing black holes and host galaxies in the distant Universe from the Herschel Radio Galaxy Evolution Project
- 2014
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 566
-
Journal article (peer-reviewed)abstract
- We present results from a comprehensive survey of 70 radio galaxies at redshifts 1 10(12) L-circle dot) or hyper-luminous (L-tot(IR) > 10(13) L-circle dot) infrared galaxies. We fit the infrared SEDs with a set of empirical templates which represent dust heated by a variety of starbursts (SB) and by an active galactic nucleus (AGN). We find that the SEDs of radio galaxies require the dust to be heated by both AGN and SB, but the luminosities of these two components are not strongly correlated. Assuming empirical relations and simple physical assumptions, we calculate the star formation rate (SFR), the black hole mass accretion rate ((M) over dot(BH)), and the black hole mass (M-BH) for each radio galaxy. We find that the host galaxies and their black holes are growing extremely rapidly, having SFR approximate to 100-5000 M-circle dot yr(-1) and. (M) over dot(BH) approximate to 1-100 M(circle dot)yr(-1). The mean specific SFRs (sSFR) of radio galaxies at z > 2 : 5 are higher than the sSFR of typical star forming galaxies over the same redshift range, but are similar or perhaps lower than the galaxy population for radio galaxies at z
|
|
| 5. |
- Galametz, M., et al.
(author)
-
Water, methanol and dense gas tracers in the local ULIRG Arp 220: results from the new SEPIA Band 5 Science Verification campaign
- 2016
-
In: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 462:1, s. L36-L40
-
Journal article (peer-reviewed)abstract
- We present a line survey of the ultraluminous infrared galaxy Arp 220, taken with the newly installed SEPIA (Swedish-European Southern Observatory PI receiver for APEX) Band 5 instrument on APEX (Atacama Pathfinder Experiment). We illustrate the capacity of SEPIA to detect the 183.3 GHz H(2)O3(1,3)-2(2,0) line against the atmospheric H2O absorption feature. We confirm the previous detection of the HCN(2-1) line, and detect new transitions of standard dense gas tracers such as HNC(2-1), HCO+(2-1), CS(4-3), (CS)-S-34(4-3) and HC3N(20-19). We also detect HCN(2-1) v(2) = 1 and the 193.5 GHz methanol (4-3) group for the first time. The absence of time variations in the megamaser water line compared to previous observations seems to rule out an AGN nuclear origin for the line. It could, on the contrary, favour a thermal origin instead, but also possibly be a sign that the megamaser emission is associated with star-forming cores washed out in the beam. We finally discuss how the new transitions of HCN, HNC and HCO+ refine our knowledge of the interstellar medium physical conditions in Arp 220.
|
|
| 6. |
- Gullberg, B., et al.
(author)
-
The mysterious morphology of MRC0943-242 as revealed by ALMA and MUSE
- 2016
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 586
-
Journal article (peer-reviewed)abstract
- © 2016 ESO. We present a pilot study of the z = 2.923 radio galaxy MRC0943-242, where we combine information from ALMA and MUSE data cubes for the first time. Even with modest integration times, we disentangle the AGN and starburst dominated components. These data reveal a highly complex morphology as the AGN, starburst, and molecular gas components show up as widely separated sources in dust continuum, optical continuum, and CO line emission observations. CO(1-0) and CO(8-7) line emission suggest that there is a molecular gas reservoir offset from both the dust and the optical continuum that is located ∼90 kpc from the AGN. The UV line emission has a complex structure in emission and absorption. The line emission is mostly due to a large scale ionisation cone energised by the AGN, and a Lyα emitting bridge of gas between the radio galaxy and a heavily star-forming set of components. Strangely, the ionisation cone has no Lyα emission. We find this is due to an optically thick layer of neutral gas with unity covering fraction spread out over a region of at least ∼100 kpc from the AGN. Other less thick absorption components are associated with Lyα emitting gas within a few tens of kpc from the radio galaxy and are connected by a bridge of emission. We speculate that this linear structure of dust, Lyα and CO emission, and the redshifted absorption seen in the circum nuclear region may represent an accretion flow feeding gas into this massive AGN host galaxy.
|
|
| 7. |
- König, Sabine, 1983, et al.
(author)
-
Subarcsecond imaging of the water emission in Arp 220
- 2017
-
In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 602, s. 42-
-
Journal article (peer-reviewed)abstract
- Aims. Extragalactic observations of water emission can provide valuable insight into the excitation of the interstellar medium. In particular they allow us to investigate the excitation mechanisms in obscured nuclei, that is, whether an active galactic nucleus or a starburst dominates.Methods. We use subarcsecond resolution observations to tackle the nature of the water emission in Arp 220. ALMA Band 5 science verification observations of the 183 GHz H2O 313 − 220 line, in conjunction with new ALMA Band 7 H2O 515 − 422 data at 325 GHz, and supplementary 22 GHz H2O 616 − 523 VLA observations, are used to better constrain the parameter space in the excitation modeling of the water lines.Results. We detect 183 GHz H2O and 325 GHz water emission toward the two compact nuclei at the center of Arp 220, being brighter in Arp 220 West. The emission at these two frequencies is compared to previous single-dish data and does not show evidence of variability. The 183 and 325 GHz lines show similar spectra and kinematics, but the 22 GHz profile is significantly different in both nuclei due to a blend with an NH3 absorption line.Conclusions. Our findings suggest that the most likely scenario to cause the observed water emission in Arp 220 is a large number of independent masers originating from numerous star-forming regions.
|
|
