Prof Chris Lintott

Abstract:

The very high rates of second generation star formation detected and inferred in high redshift objects should be accompanied by intense millimetre-wave emission from hot core molecules. We calculate the molecular abundances likely to arise in hot cores associated with massive star formation at high redshift, using several independent models of metallicity in the early Universe. If the number of hot cores exceeds that in the Milky Way Galaxy by a factor of at least one thousand, then a wide range of molecules in high redshift hot cores should have detectable emission. It should be possible to distinguish between independent models for the production of metals and hence hot core molecules should be useful probes of star formation at high redshift.

Abstract:

The very high rates of second generation star formation detected and inferred in high-redshift objects should be accompanied by intense millimetre-wave emission from hot core molecules. We calculate the molecular abundances likely to arise in hot cores associated with massive star formation at high redshift, using several different models of metallicity in the early Universe. If the number of hot cores exceeds that in the Milky Way Galaxy by a factor of at least 1000, then a wide range of molecules in high-redshift hot cores should have detectable emission. It should be possible to distinguish between different models for the production of metals and hence hot core molecules should be useful probes of star formation at high redshift. © 2005 RAS.

Abstract:

Recent observations suggest that the behavior of tracer species such as N2H+ and CS is significantly different in regions of high- and low-mass star formation. In the latter, N2H+ is a good tracer of mass, while CS is not. Observations show the reverse to be true in high-mass star formation regions. We use a computational chemical model to show that the abundances of these and other species may be significantly altered by a period of accelerated collapse in high-mass star-forming regions. We suggest that these results provide a potential explanation of the observations, and make predictions for the behavior of other species. © 2005. The American Astronomical Society. All rights reserved.

Abstract:

Recent observations suggest that the behaviour of tracer species such as N_2H+ and CS is significantly different in regions of high and low mass star formation. In the latter, N_2H+ is a good tracer of mass, while CS is not. Observations show the reverse to be true in high-mass star formation regions. We use a computational chemical model to show that the abundances of these and other species may be significantly altered by a period of accelerated collapse in high mass star forming regions. We suggest these results provide a potential explanation of the observations, and make predictions for the behaviour of other species.

Abstract:

Understanding the processes that drive the formation of black holes (BHs) is a key topic in observational cosmology. While the observed $M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ correlation in bulge-dominated galaxies is thought to be produced by major mergers, the existence of a $M_{\mathrm{BH}}$--$M_{\star}$ relation, across all galaxy morphological types, suggests that BHs may be largely built by secular processes. Recent evidence that bulge-less galaxies, which are unlikely to have had significant mergers, are offset from the $M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ relation, but lie on the $M_{\mathrm{BH}}$--$M_{\star}$ relation, has strengthened this hypothesis. Nevertheless, the small size and heterogeneity of current datasets, coupled with the difficulty in measuring precise BH masses, makes it challenging to address this issue using empirical studies alone. Here, we use Horizon-AGN, a cosmological hydrodynamical simulation to probe the role of mergers in BH growth over cosmic time. We show that (1) as suggested by observations, simulated bulge-less galaxies lie offset from the main $M_{\mathrm{BH}}$--$M_{\mathrm{Bulge}}$ relation, but on the $M_{\mathrm{BH}}$--$M_{\star}$ relation, (2) the positions of galaxies on the $M_{\mathrm{BH}}$--$M_{\star}$ relation are not affected by their merger histories and (3) only $\sim$35 per cent of the BH mass in today's massive galaxies is directly attributable to merging -- the majority ($\sim$65 per cent) of BH growth, therefore, takes place gradually, via secular processes, over cosmic time.