Science objectives and limitations of interferometric high resolution FIR observations

Transcription

1 Science objectives and limitations of interferometric high resolution FIR observations Luigi Spinoglio, Stefano Pezzuto, John Scige Liu - IAPS-INAF Daniele Schito - AGI Given the results of the FISICA project, we discuss the scientific capabilities of the baseline interferometer, showing, besides the power to reach important science goals, also the implicit limitations of the instrument. These limitations include the low sensitivity as well as the relatively long observing times, as compared to other ground-based or space facilities. 1

2 The need of high spakal resolukon in the FIR is clear, because this is the only spectral range from the visible to the radio where high spakal resolukon is not (or will not be) covered by exiskng or planned facilikes. (courtesy of Th. de Graaw) 2

3 Spa$al resolu$on and assump$ons for the minimum detectable flux To roughly simulate the observakons that the FIR interferometer will be able to perform we have made the following assumpkons: 1. given a maximum and minimum baseline for a parkcular observakon that saksfy the need to explore some spakal scales, the total number of uv points has been computed using tangent mirror coverage, to give the best uv coverage. we used: number of uv points= int( {π*[(baseline_max^2)-(baseline_min^2)]}/2*(diameter_dish^2)) 2. the sensikvity has been assumed to be 1E-19 W/m^2 (1sigma, 1 hour) which is roughly equal to the eskmated sensikvity of the SAFARI FTS spectrometer planned (Kll 2014) to be onboard of SPICA, based on the current consolidated TES detector technologies. 3. to compute the sensikvity of an interferometric observakon, we use the similarity to the queskon on the integrakon Kme of an FTS (Felgec advantage*) in spakal mulkplexing instead of spectral. Therefore the S/N rako is proporkonal to the square root of the number of samples, which in our case is converted in the number of uv points. 4. the Kme to perform a spectroscopic FTS scan is set to 12.6 sec. * The Fellgec advantage, also known as the mulkplex principle, states that when obtaining a spectrum when measurement noise is dominated by detector noise (which is independent of the power of radiakon incident on the detector), a mulkplex spectrometer such as a Fourier transform spectrometer will produce a relakve improvement in signal-to-noise rako, compared to an equivalent scanning monochromator, of the order of the square root of m, where m is the number of sample points comprising in the spectrum. 3

4 Science cases: Star and planet forma$on The evolukon from a protostellar core into a low-mass star follows a sequence of spectral energy distribukons where the peak emission moves from submm to far-ir. The star shines in the opkcal only when the circumstellar envelope and most of its disk are removed. The spakal scales decrease from a typical dense core radius of 0.005pc (~1000AU) (e.g. Simpson et al. 2011) in the prestellar phase, down to a disk radius of ~100 AU (e.g. DG Tau, Simon et al. 2000), in the premain sequence phase, corresponding to an angular size of 0.75 arcsec at the distance of the closest star forming regions in the Milky Way (D=140pc, Ophiucus and Taurus). The spa$al scale of 100AU indicates the transi$on between the op$cally thin prestellar envelope and the op$cally thick protostellar source. This scale corresponds to an angular size of 0.4 at the distance of Perseus and 0.25 at the distance of Orion, among the most representakve star forming regions in the Milky Way. To study protostellar evolukon, leading to the formakon of planets out of the circumstellar disks, subarcsecond resolu$on at the peak emission wavelengths (50-200µm) is therefore needed. Luigi Spinoglio - 3rd FISICA Workshop - London December 2015

5 Science case 1: Star Formation: Protostars è protostar with a linear dimension of 100AU in the Perseus star forming region at a distance of 250pc. The needed resolukon is 0.4 at 100µm. To reach this resolukon, the max baseline is 62.5m, and, assuming the scan Kme of 12.6 sec., the total Kme needed to cover all spakal scales from 0.4 to 10 on-source is ~5.3 hours, corresponding to 1530 u-v points with 2 scans per pair of u-v points. The eskmated flux of H 2 O lines come from predickons of the First HydrostaKc Cores models of Omukai (2007) is 5.4E-20 W/m2. Assuming a sensikvity of 10^-19 W/m2 (1 sigma, 1 hour), a deteckon of these lines will be reached at 3 sigma in about 30 hours, therefore 5 scans per uv point will be needed. This observakon is at the limit of the instrument. 5

6 Star forma$on: Protoplanetary disks: Forma$on of planetary systems Besides the far-ir conknuum, due to dust emission, of the various phases, from the prestellar cores, through Class 0 and I, to the Class II, where the disk is skll energekcally important, a wealth of atomic and molecular transikons are crucial to study the physics and the chemistry of the whole evolukonary sequence, from prestellar cores to protoplanetary disks. Examples include the H 2 O lines from the envelope, the OH and CO lines from the accrekng gas disk, the molecular hydrogen at 28μm and the lines from ouplows and shocks: such as [SiII]35µm and [OI]63µm, as well as the strong molecular lines from OH and H 2 O. The figure shows the structure and the spakal scale of a protoplanetary disk: the FIRI resolukon of 0.1 will allow the observakons of outer disk regions at the distance of the closest star forming regions (140pc). Luigi Spinoglio - 3rd FISICA Workshop - London December 2015

7 Science case 2: Star forma$on: Protoplanetary disks/forma$on of planetary systems è protoplanetary disk with a linear dimension to be explored from ~30AU to ~100AU in the Taurus star forming region at a distance of 140pc. The needed resolukon ranges from 0.25 to 0.75, corresponding to baselines of 100m and 33m. The number of uv points is ~3500, and the total Kme needed on-source is 12.2 hours. PredicKons of protoplanetary disks models (Kamp et al. 2010, model B: R in =30- R out =100AU) at 131pc and 45 incl. (in agreement with Herschel, Pinte et al. 2010) give [OI]63µm: 3.7E-16 and [OI]145µm: 3.1E-17. Bergin et al. (2013) detected in TW Hya the HD λ112.0µm (J=1-0, T ex =128 K) line with a flux of F=(6.3±0.7)x10-18 W/m2. Assuming a sensikvity of 10^-19 W/m2 (1 sigma, 1 hour), the total Kme of 12.2 hours of this observakon will allow 3 sigma deteckons of lines ~20 Kmes fainter than the HD112µm line (and ~90 Kmes fainter that the [OI]145µm line). 7

8 Star formakon: Binary and mulkple systems One of the queskons that can directly be answered by FIR interferometric imaging is the following: Do massive clumps form only one massive star or do they break up? High angular resolukon is the key observakonal technique. We take as an example the lowmass protostellar source L1448 at a distance of 250pc: the separakon between the two components observed with the IRAM PdB Interferometer at 1.3mm is about 2.4 arcsec, which corresponds to 600AU. The resolukon of 0.1 arcsec provided by FIRI allows to separate 100AU at the distance of 1kpc and 300AU at the distance of 3kpc, this lacer encloses most high mass star forming regions in our galaxy. Imaging interferometry in the FIR is able to study the fragmentakon of molecular clouds cores into fragments, bringing to the formakon of binary or mulkple stellar systems. Luigi Spinoglio 8-3rd FISICA Workshop - London 15-17

9 Science case 3: Star forma$on: Binary and mul$ple systems è binary protostellar system with a linear dimension to be explored of 100AU in the Orion star forming region at a distance of 400pc. The needed resolukon is 0.25 corresponding to ~2500 u-v points with 2 scans per pair of u-v points and the total Kme needed on-source is 8.8 hours. The fluxes scaled to an area of x of the proto-binary system NGC1333- IRAS4, assuming an emission region of 1000AU (Karska et al. 2013) (1/100 of the observed flux and scaled at a distance D=400pc) are: [OI]63µm: 9E-19; H 2 O: in the range 8E-19-4E-18 and CO: in the range 2E-19-4E-18W/m2. The integrated flux observed in IRAS4A at HDO@893GHz with HIFI (Coutens et al 2013), scaled at D=400pc is HDO: 4E-18W/m2. Assuming a sensikvity of 10^-19 W/m2 (1 sigma, 1 hour), the total Kme of 8.8 hours will allow deteckons at 3 sigma of ~1E-19W/m2, therefore all lines will be detected at S/N>3 sigma. 9

10 The Galac$c Center Results from Herschel (Goicoechea et al. 2013) indicakng the richness of the far-ir spectra of the SgrA* source and of the CND. Ley: the [OI]63µm map. Right: the complete µm PACS spectrum of SgrA* and the CND Luigi Spinoglio - 3rd FISICA 10 Workshop - London At 8kpc, the GalacKc Center distance, 0.25 corresponds to 0.01 pc, i.e. ~2000 AU. We can see (from NACO and SINFONI observakons at the VLT, ESO) the spakal distribukon of early and late-type stars, colored in blue and red, respeckvely, showing a steep increase in the density (and brightness) of bright early-type stars (Genzel et al. 2010). A similar resolukon in mid- to far-ir imaging spectroscopy would be able to overcome the obscurakon that might affect the field and see through the innermost region of the GalacKc Center.

11 Science case 5: The galactic Center è map a region of about 1 arcmin squared around the GalacKc Center at a resolukon of 2000AU at a distance of ~8kpc. The needed resolukon is The total number of u-v points is ~1900 and the Kme needed on-source is 6.6 hours. The flux scaled to an area of 0. 25x0. 25 from Herschel observakons (Goicoechea et al 2013) is [OI]63µm: 2.4E-17, CO(14-13)@186µm: 1.9E-19, CO(24-23)@108µm: 2.0E-20W/m2. Assuming a sensikvity of 10^-19 W/m2 (1 sigma, 1 hour), the total Kme of 6.6 hours will allow 3 sigma deteckons of lines of 1.2E-19W/m2, i.e. 200 Kmes fainter than [OI]63µm and of the order of the CO(14-13). The CO(24-23) would remain undetected. 11

12 considerakons about compektors SPICA will be a valuable compektor for this kind of observakons (Science cases 1-5), because of the very high sensikvity of its grakng spectrometers of the order of 1E-20W/m2 (1σ, 1 hour) in the low resolukon mode (R~300), which is one order of magnitude becer than the interferometer. SPICA will however fail to spakally separate the emission region(s) because of its large diffrackon limit due to its mirror size of 2.5m, therefore the interferometer would be superior where there is the superposikon in a field of 5-10 arcsec of different emission components. For science case 1-2, we expect that the emission from a protostellar core or a protoplanetary disk is masked by that one from its envelope and surrounding material, therefore there is the need for both high spakal and spectral resolukon to be able to disentangle either spakally (interferometer) or spectroscopically (R>10000) the different emission components. Binary and mulkple stellar systems, as well as the GalacKc Center are crowded fields, therefore a single dish measurement will not be able to disentangle the individual sources. In order to beat our compektors, it is therefore recommended to improve both the spectroscopic sensikvity and spectroscopic resolukon of the baseline interferometer. ALMA will of course play a role here, because it has the two above qualikes in a complementary spectral range, in molecular lines at lower excitakon. 12

13 AGNs in the Local Universe AcKve GalacKc Nuclei (AGN) are important not only by themselves, but also because of their role in galaxy evolukon. Since the discovery of the relakon in the Local Universe (Magorrian et al. 1998) between mass of the black hole (BH) and the velocity dispersion of the galackc bulge stars, it was realized that the black hole growth is connected with the building of the stellar populakon. It is crucial to study in the Local Universe the physical properkes of AGNs, such as the accrekon geometry and the line and conknuum emission regions, the Narrow, Coronal and Broad Line regions as well as the molecular tori, but also the AGN feeding and the feedback from the AGN to the galaxy, in forms of winds, jets and atomic and molecular ouplows. Recent Herschel spectroscopy (Fischer et al 2010, Sturm et al 2011, Spoon et al 2013) and millimeter interferometry (Feruglio et al 2010, Aalto et al 2012, Cicone et al 2012, Maiolino et al 2012) indicate that AGN ouplow can have enough energy to quench star formakon on a galaxy wide scale. 13

14 Infrared fine structure lines density ionizakon 14

15 Science case 6: AGNs in the Local Universe è map the emission line regions in local AGNs at an average distance of 50 Mpc. The maximum resolukon of 0.10 is needed for this project, because we want to resolve the Narrow Line Region. This will be reached at wavelengths of < 50 µm, where many of the important AGN mid- IR fine structure lines lie, such as [OIV]26µm and [NeV]24µm. The total number of u-v points is ~3900 and the total Kme needed on-source is 13.7 hours. The scaled line flux values, assuming a NLR extension of 500pc, from local (D~50Mpc) Seyfert galaxies (Tommasin et al. 2010; Spinoglio et al. 2015) )(1/400 of the observed flux) are: min, ave, max [OIV]26µm:1E-19, 1E-18, 3E-18W/ m2; [NeV]24µm:3E-20, 2.8E-19, 9E-19W/m2; [OI]63µm: 6E-19, 2.6E-18, 7.6E-18W/m2. In the Kme of 13.7 hours a 3 sigma sensikvity of ~1.2E-19W/m2 will be reached, allowing to detect most lines above, except the minimum expected value for the [NeV]24µm, far below deteckon. 15

16 considerakons about compektors Also in this case SPICA will be a valuable compektor for this kind of observakons. SPICA will however fail to spakally separate the emission region(s). JWST-MIRI up to the wavelength of 28µm, will be able to map (at its diffrackon limit of ~0.2 comparable to FIRI at 5µm and ~1 at 25µm) the emission of high ionizakon AGN lines, eg.[nevi]7.6µm [NeV]14-24µm and [OIV]26µm. ALMA will of course play a role here, however no high-ionizakon line from the AGN is within the ALMA atmospheric windows. Therefore ALMA can study the low temperature gas excited in the star formakon processes within local galaxies. In order to beat our compektors, it is therefore recommended to improve both the spectroscopic sensikvity and spectroscopic resolukon of the baseline interferometer. 16

17 Cosmology: AGN vs Starburst evolukon along cosmic Kmes The far-ir spectral domain is the most adequate to study galaxy evolukon at the maximum of its ackvity - both AGN and SF - by overcoming dust obscurakon and observing the peak conknuum emission. The starburst emission regions in galaxies has a linear size of 1-2 kpc and can be resolved at any redshiy using FIR interferometry reaching an angular resolukon of 0.1 arcsec. In fact, as shown in the figure, beyond the redshiy z=2, due to the standard cosmology, the apparent size of astrophysical objects starts to decrease as a funckon of redshiy. We will therefore be able with FIRI to study both photometrically and specroscopically how the starburst components evolve in cosmic Kmes. Whilst the AGN Narrow line Regions will not be resolved beyond z=0.1, spectroscopy will skll allow to disentangle starburst and AGN components through bright fine structure lines. 17 ANGULAR SIZES OF THE RELEVANT FIR EMITTING COMPONENTS OF GALAXIES AS A FUNCTION OF REDSHIFT, FOLLOWING THE STANDARD COSMOLOGICAL MODEL (SPERGEL ET AL. 2007). Luigi Spinoglio - 3rd FISICA Workshop - London December 2015

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19 Science case 7: Galaxy Formation and Evolution: Resolving Starburst structures at high redshift For this science case we need to map the starburst and the galaxy disk of distant galaxies at a redshiy of, e.g. z=2, corresponding to an average distance of ~16 Gpc. The maximum resolukon of 0.10 is needed for this project, because we want to resolve the starburst structures. The total Kme needed on-source is 13.6 hours, corresponding to ~3900 u-v points with 2 scans per pair of u-v points. EsKmated fluxes should range between: 1E-20 < F < 5E-20W/m2. Therefore the es$mated 3 sigma sensikvity of ~1.2E-19W/m2 will not be adequate. Observing Kmes of about 5-6 Kmes longer (~80 hours) will allow deteckng lines of the order of 5E-20W/m2 19

20 considerakons about compektors ObservaKons of the intermediate redshiy starburst component in galaxies is a goal that cannot be reached with the baseline interferometer. SPICA will be a valuable compektor for this kind of observakons. ALMA will of course play a role here, through deteckon of the low temperature gas excited in the star formakon processes in distant galaxies. Many examples are already available in the literature 20