This page describes Millimetron Science Cases and can be edited by registered users
Interstellar Medium
Protoplanetary discs
- Heterodyne spectroscopy of disks:
- low-resolution spectroscopy of disks:
- Case 2
CMB
- Case 1
- Case 2
High Redshift Quasars
Summary: The energetics and kinematics of highly obscured quasars can be traced with fine-structure and CO line emission. For z>4, the [OI] 63 um line and very high J CO lines are particularly well suited to find growing black holes with Millimetron.
After the first detection of supermassive black holes at z~6, there has been a strong effort to find more sources at high redshift and to study their properties. Further high-z quasi-stellar objects (QSOs) have been found in surveys like the Sloan Digital Sky Survey (SDSS), the Canada-France high-redshift quasar survey, the UKIDSS Large Area Survey and the Palomar-QUEST survey. They have been studied by follow-up observations with Chandra, the Subaru Telescope, with IR spectroscopy, near-IR spectroscopy, mid-IR observations, Swift observations, VLBA observations, the Very Large Array as well as the Very Long Baseline Array. Some of their host galaxies have also been detected in CO and submm emission.
These observations furthermore inferred a number of relations between the mass of the central black hole and the properties of their host galaxy. The Magorrian relation connects the velocity dispersion and the mass of the galactic bulge with the black hole mass. Quasars with black hole masses of the order 10^9 Mo are observed with supersolar metallicities even at z~6. In the nearby universe, correlations have been found between black hole mass and metallicity, with a mild slope of 0.38+-0.07. This is plausible, as it is generally recognized that the overall mass of a galaxy is correlated with its metallicity.
In the local universe, active galactic nuclei (AGN) can be studied in much more detail and with higher resolution. An example that has been studied particularly well, in different wavelengths and with high resolution is the AGN NGC 1068. Its direct X-ray emission is shielded through absorption along the line of sight, but there is evidence for reflected X-ray photons that are scattered into the line of sight. Its molecular disk has been studied through emission from different species, in particular molecular CO and fine-structure lines. The continuum emission and the distribution of dust has been measured as well. NGC 1068 provides an excellent test case for the inner structure of active galaxies.
The formation of quasars and their supermassive black holes is still one of the unresolved riddles of structure formation and cosmology. The simplest scenarios assume that they have grown from the remnants of the first stars, which are believed to be very massive \citep{Abel02, Bromm04, Glover05}, and whose black hole remnants could grow further by accretion. Such a scenario however has problems, as the remnants of the first stars typically do not end up in the most massive quasars at redshift z~6 \citep{Trenti08}, and radiative feedback from the stellar progenitor can delay accretion as well \citep{Johnson07, Alvarez08, Milosavljevic08}. In case of Eddington accretion, seed black holes of $\sim10^5\,M_\odot$ are required in order to grow to the observed supermassive black holes at $z\sim6$ \citep{Shapiro05}.
Recently, it has also been discussed whether the first stars in the early universe were powered by dark matter annihilation rather than nuclear fusion \citep{Spolyar08, Iocco08}. Such stars could reach masses of the order $1000\ M_\odot$ \citep{FreeseBodenheimer08, IoccoBressan08} and were considered as possible progenitors for the first supermassive black holes. The evolution of such stars on the main sequence has been calculated by \citet{Taoso08} and \citet{Yoon08}. However, it was shown that such stellar models are highly constrained by the observed reionization optical depth \citep{SchleicherBanerjee08a, SchleicherBanerjee08c}. Also, we note that such seeds would still require super-Eddington accretion to grow to the observed supermassive black holes at $z\sim6$.
Therefore, alternative scenarios have been considered that lead to the formation of massive seed black holes by direct collapse \citep{Eisenstein95, Koushiappas04, Begelman06, Spaans06, Dijkstra08}. However, for such scenarios, the situation is also not entirely clear. For instance, \citet{Lodato06} argue that the gas in such halos should fragment if \HzI cooling is efficient, and \citet{Omukai08} and \citet{Jappsen08} suggest that a non-zero metallicity will lead to fragmentation as well. Simulations by \citet{Clark08} support these conjectures.
The black hole population at high redshift is further constrained by observations of the soft X-ray background. These constraints indicate that the population of high-redshift quasars was not sufficient to reionize the universe \citep{Dijkstra04}, and suggest an upper limit to the black hole density of $\sim 4\times104 Mo Mpc{-3}$ \citep{Salvaterra05}. The latter depends in particular on the adopted spectra and luminosity of the black hole, as well as their duty cycles, and it has been argued that larger black hole populations are conceivable as well \citep{Zaroubi07}. It is therefore important to probe the number density of black holes and AGN activity as a function of redshift by direct observations.
Constraints from the X-ray background, with particular focus on black hole luminosities below the Eddington limit as observed in many local AGN, indicate that up to 20% of high-redshift black holes can be active quasars. Counting dark matter halos, and adopting the Magorrian relationship, one finds from figure 
that almost one black hole of 1E5 Mo is present in 1 Mpc at z=6. With NGC 1068 as a reference system, line fluxes observable with Millimetron can be found. Between 1-10 sources should be detectable with Millimetron for a field of view of $\sim(1')^2$. (TO BE CONTINUED)
etc
Massive Star Formation
Summary : water and its isotopologues (HDO, H2170, H218O) plays a important role in the physical and chemical evolution of the enveloppe of High-Mass protostellar objects. These objects have a very short lifetime and, through their high activity forming massive protostars, they can enrich the interstellar medium during two phases: (i) the proto-stellar phase with an enhanced gas-grain chemistry induced by high turbulences, shocks and products depletion on icy grains, (ii) disruption of the external enveloppe during the HII bubble extension, leading to a second star formation generation in which dusty chemically enriched enveloppes remains for the formation of planetary systems. Water, that our atmosphere does not permit to observe from the ground, gets high-frequency rotational transitions (from 183 to more than 2000 GHz) that the millimetron should be able to observe.
- Water line emissions (high-resolution spectroscopy and high-resolution maps)
- Dust opacity measurements (medium resolution)
- Large scale dynamics (high-resolution spectroscopy)
- Rotational diagrams surveys (multi-wavelength studies of J from ground-state to very high-J transitions lines)